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MANUALMONITOR AND CONTROL THE FORMING AND PRESSING OF PAPER, BOARD OR

TISSUE

This Monitor & Control manual must be used in conjunction

with the SOP / Operating Instructions manual

Unit Standard 256282NQF Level 4Credits: 15

Compiled by:Marick Hornsveld

Rev.1 – January 09

Moderated by: Lorato Mokgosi & Piet Putter

Learner Name:

Learner Number:

Sparrow Consulting © January 2009 Rev.1 – Jan 09

Table of Contents

UNIT 1: INTRODUCTION TO THE FORMING AND PRESSING PROCESS10

1.1 Instructions10

1.2 Introduction 13

1.3 The approach flow system 15

1.3.1 Functioning of the approach flow system 16

1.3.2 Design of the approach flow system 16

1.3.3 Manifold distributor (flow spreader)18

1.4 The headbox 20

1.4.1 Pressurised headbox 21

1.4.2 Headbox showers 24

1.4.3 Total head control 24

1.4.4 Air flow control systems 26

1.4.5 Liquid flow control 27

1.4.6 Stock flow control systems 29

1.4.7 Hydraulic headboxes 30

1.4.8 Headbox design 32

1.4.9 Stationary headbox elements 34

1.4.10 Slice 36

1.4.11 Headbox operation 36

1.4.12 Headbox problems 37

1.4.13 Headbox operational parameters 40

1.4.14 Headbox efficiency 40

1.4.15 Cross-machine basis weight profile 41

1.4.16 The dilution headbox 42

1.5 The forming section 43

1.6 The Fourdrinier 44

1.6.1 Drainage principles of the Fourdrinier 44

1.7 Drainage profiles 46

1.7.1 Consistency 47

1.7.2 Vacuum 48

1.8 Fourdrinier table equipment 48

1.8.1 Forming board 48

1.8.2 Foil blades 49

1.8.3 Wet and dry suction boxes 50

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1.8.4 Suction couch 52

1.8.5 Couch operation 52

1.8.6 Suction couch - open draw 52

1.9 The twin wire former 53

1.9.1 Layering 53

1.10 Principles of modern twin wire drainage formation 54

1.10.1 Hybrid formers 54

1.10.2 Roll formers 55

1.10.3 Blade formers 56

1.10.4 Twin wire formers, practical problems 57

1.11 The press section 58

1.11.1 Water removal and paper consolidation in a wet press 59

1.11.2 Pressing action 59

1.12 Water removal in a transversal flow press nip 60

1.12.2 Factors influencing press water removal performance 64

1.12.3 Primary variables65

1.12.4 Press loading 65

1.12.5 Effect on paper and the paper machine 69

1.12.6 Sheet transfer and wet web strength development 69

1.12.7 Rolls of the press section 70

1.12.8 Shoe with belt type press 72

1.12.9 Shoe with elastomeric sleeve roll 73

1.12.10 Roll crowning 73

1.13 Press nips 73

UNIT 2: MONITOR AND CONTROL ANCILLARY SYSTEMS 752.1 Instructions75

2.2 Introduction 79

2.3 Mechanical equipment 79

2.3.1 Bulk handling equipment 79

2.3.2 Conveying equipment 82

2.3.3 Weighing equipment 88

2.3.4 Solids storage methods 88

2.4 Electrical equipment 96

2.4.1 Electrical motors 96

2.4.2 Switchgear 97

2.4.3 Drive equipment 98

2.4.4 Electrical safety 100

Manual 3 US 256282


2.4.5 Isolation of electrical, hydraulic and air driven machines or equipment 101

2.5 Instrumentation 101

2.5.1 Key functions of instrumentation 102

2.5.2 Methods of display 103

2.5.3 How to read a gauge 104

2.5.4 Control valves 106

2.5.5 Controllers 106

2.6 Utilities 107

2.6.1 Compressed air supply108

2.6.2 Steam systems 110

2.6.3 Steam generation 110

2.6.4 Steam applications 111

2.7 Mill cooling water112

2.8 Electrical power 113

2.9 Monitor the ancillary systems 114

2.9.1 What is a parameter? 114

2.9.2 What is a variable? 115

2.9.3 What is a deviation? 115

UNIT 3: PROCESS MATERIALS 1173.1 Instructions117

3.2 Introduction 122

3.3 What is a Quality Management System? 122

3.3.1 Quality control 122

3.3.2 Quality assurance 124

3.3.3 Quality management 124

3.4 The quality standards of process materials 124

3.4.1 Quality of raw materials and ingredients 125

3.4.2 Quantities of raw materials and ingredients 125

3.4.3 Contamination 125

3.4.4 Raw material problems125

3.5 Consequences of poor quality control 126

3.5.1 Consequences for the customers 126

3.5.2 Consequences for the organisation 127

3.5.3 Consequences for the individual and colleagues 128

3.5.4 Consequences for the community 128

UNIT 4: MONITOR AND CONTROL THE FORMING AND PRESSING PROCESS 129

Manual 4 US 256282


4.1 Instructions129

4.2 Introduction 133

4.3 Normal operating conditions 133

4.4 Maintaining process variables 133

4.5 Deviations from normal conditions 134

4.5.1 Detecting problems in a process 134

4.6 Abnormal conditions 134

4.7 A problem solving strategy 135

ANNEXURE 1: RESOURCES 137

ANNEXURE 2: US 256282 138

Figures and tablesFigure 1: Wet end processes............................................................................................14

Figure 2: An approach flow system...................................................................................16

Figure 3: Stock addition and mixing..................................................................................17

Figure 4: Manifold distribution...........................................................................................19

Figure 5: Long tube bank..................................................................................................20

Figure 6: Side view of a pressurised headbox..................................................................22

Figure 7: Hornbostel control system.................................................................................25

Figure 8: Head control by air and level control by stock flow............................................25

Figure 9: Total head control by stock flow and level control by air....................................26

Figure 10: Constant flow airflow pump and automatically adjusted bleed valve...............26

Figure 11: Constant pressure air fan driven by a variable speed motor...........................27

Figure 12: Constant volume air pump and twin valve system...........................................27

Figure 13: Main control valve............................................................................................28

Figure 14: Variable speed fan pump.................................................................................28

Figure 15: Main control valve located in recirculation line.................................................29

Figure 16: Total head and level control.............................................................................30

Figure 17: Hydraulic headbox (Escher-Wyss)...................................................................31

Figure 18: Pulsation attenuators.......................................................................................32

Figure 19: MD basis weight profile, time domain..............................................................32

Figure 20: Tapered flow header........................................................................................33

Figure 21: Stationary flow stilling devices.........................................................................34

Figure 22: Step diffuser.....................................................................................................35

Figure 23: Dilution headbox..............................................................................................43

Manual 5 US 256282


Figure 24: Diagram of Fourdrinier section.........................................................................44

Figure 25: Table layout – sheet formation.........................................................................45

Figure 26: Acceptable drainage profile.............................................................................46

Figure 27: Unacceptable drainage profile.........................................................................47

Figure 28: Layered structure.............................................................................................54

Figure 29: Water removal cost in the former, press- and dryer sections..........................59

Figure 30: Transversal flow nip.........................................................................................61

Figure 31: Spiral chute......................................................................................................79

Figure 32: Examples of other chutes................................................................................80

Figure 33: A centrifugal discharge bucket elevator...........................................................80

Figure 34: Positive discharge bucket conveyor..................................................................81

Figure 35: Continuous bucket elevator..............................................................................81

Figure 36: Example of a belt conveyor..............................................................................82

Figure 37: A basic belt conveyor transporting solid material.............................................83

Figure 38: Pneumatic conveyor systems..........................................................................84

Figure 39: A basic positive pressure pneumatic conveying system..................................85

Figure 40: Basic negative pressure pneumatic conveying system...................................85

Figure 41: Positive and negative pressure pneumatic conveying systems.......................86

Figure 42: A fluidised system............................................................................................87

Figure 43: Conveyor scale................................................................................................88

Figure 44: Platform scale..................................................................................................88

Figure 45: Storage bunker................................................................................................89

Figure 46: Silos.................................................................................................................89

Figure 47: A silo and its basic components.......................................................................90

Figure 48: Silos operating in series sharing a common filter............................................91

Figure 49: Storage hopper................................................................................................91

Figure 50: Self dumping steel hopper...............................................................................92

Figure 51: Hopper and storage bin...................................................................................93

Figure 52: Cylindrical storage bins....................................................................................94

Figure 53: A horizontal storage bin with V-shaped bottom...............................................95

Figure 54: Bulk bags.........................................................................................................95

Figure 55: An electric motor..............................................................................................96

Figure 56: Squirrel cage AC motor.....................................................................................97

Figure 57: A switchgear panel...........................................................................................97

Figure 58: Gas turbine.......................................................................................................98

Figure 59: Chain drives.....................................................................................................99

Figure 60: Gear drives......................................................................................................99

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Figure 61: Example of a belt drive..................................................................................100

Figure 62: A multi-disc clutch..........................................................................................100

Figure 63: Types of instruments......................................................................................102

Figure 64: Digital and analogue displays........................................................................104

Figure 65: Your eyes should always be level with a gauge............................................105

Figure 66: Analogue display with X100 on the display....................................................105

Figure 67: Various valves................................................................................................106

Figure 68: A control panel...............................................................................................107

Figure 69: Compressed air networks..............................................................................109

Figure 70: A steam system.............................................................................................111

Figure 71: Cooling water system.....................................................................................113

Figure 72: Electricity distribution.....................................................................................114

Figure 73: Relationship between the different levels of quality.......................................122

Figure 74: Air pollution caused by the pulp and paper industry......................................128

Manual 7 US 256282


Module overviewPlease note:

This manual deals only with the monitoring and controlling of the process and has to be

used in conjunction with the SOP / Operating Instructions manual which addresses the

pre-start up, start-up, shut-down and emergency shutdown of the equipment as well as

the process.

Introduction

Forming and pressing forms part of the wet end operations and falls within the stock

preparation section, but before the dry end of the process. The wet end receives thick

stock from stock preparation, it forms the sheet and removes the water, and then sends

the sheet to the drying section for further water removal.

Unit 1 will introduce you to the principles of the forming and pressing process. Unit 2

deals with the ancillary systems related to the forming and pressing process. In Unit 3

you will learn about the quality principles applicable to process materials. In Unit 4 you

will learn about the procedures needed to monitor and control the forming and pressing

process.

Learning outcomes

After working through this module, you will be able to:

Explain the purpose of the mechanical pulping process in terms of the final product manufactured.

Explain the principles of the mechanical pulping forming and pressing process by making use of a generic flow diagram.

Explain the forming and pressing process in relation to its supplier’s- and customer’s processes.

Trace the flow of material through the forming and pressing section and identify all equipment using standard industry terminology.

Explain the purpose and functioning of each piece of equipment used in the forming and pressing section in terms of its role in the overall process.

Explain the functions of all chemicals and additives used within the process in terms of their chemical and physical properties.

Identify and describe mechanical equipment used in the forming and pressing process in terms of purpose and application.

Identify and describe electrical equipment used in the forming and pressing process in terms of purpose and application.

Identify and describe instrumentation used in the forming and pressing process in terms of purpose and application.

Manual 8 US 256282


Identify and describe utilities used in the forming and pressing process in terms of purpose and application.

Discuss typical ancillary equipment problems within the forming and pressing process and offer solutions in accordance with workplace procedures.

Monitor ancillary systems and correct any deviations from operating parameters in accordance with operating procedures.

Explain the properties of process materials in terms of key characteristics.

Explain the purpose of process material quality control procedures as well as the consequences of not adhering to these procedures with regards to the impact thereof on the final product produced.

Explain the quality requirements of raw materials, process water, chemicals and additives or other materials according to general and workplace specifications.

Discuss typical raw material problems and its impact on the final product properties and costs.

Discuss corrective action to be taken in the case of non-conforming raw materials in accordance with workplace procedures.

Evaluate product variations and take corrective action in accordance with workplace procedures.

Monitor the forming and pressing process and record parameters in accordance with workplace procedures.

Explain the impact of process variables on the product properties in terms of final products and costs.

Discuss typical equipment problems within the forming and pressing process and offer solutions in accordance to workplace procedures.

Evaluate variations in the product and take corrective action in accordance with workplace procedures.

US specific outcomes

The following specific outcomes are covered in this module:

SO1: Explain the fundamental principles applicable to the forming and pressing

function.

SO2: Monitor and control the different ancillary systems interacting with the forming

and pressing process.

SO3: Monitor and control the quality standards of process materials in the forming

and pressing process.

SO4: Monitor and control the forming and pressing process

Manual 9 US 256282


UNIT 1: INTRODUCTION TO THE FORMING AND PRESSING PROCESS

Learning outcomes

After working through this unit, you will be able to:

Explain the purpose of the forming and pressing process in terms of the final product manufactured.

Explain the principles of the forming and pressing process by making use of a generic flow diagram.

Explain the forming and pressing process in relation to its supplier’s- and customer’s processes.

Trace the flow of material through the forming and pressing section and identify all equipment using standard industry terminology.

Explain the purpose and functioning of each piece of equipment used in the forming and pressing section in terms of its role in the overall process.

Explain the functions of all chemicals and additives used within the process in terms of their chemical and physical properties.

1.1 Instructions

Ref. No Resources Learning Methodology Workbook Assess Time

CCFO3-8 Learning materials

Workplace and other relevant procedures

It is assumed that you are competent in terms of the following outcomes or areas of learning before starting with this module:

mathematics and literacy at NQF Level 3 or equivalent.

Act. 1

N/a N/a N/a

Manual 10 US 256282

Sparrow Consulting© November 07 Rev.1 – Nov 07


SO 1, AC 1-4

CCFO 3-5, 7, 8

Learning materials

Read through Unit 1 of the learning materials and/ or refer to the generic learning materials on forming and pressing paper, board and tissue. Make notes of things you do not understand and/ or need more information on and discuss it with your facilitator.

00:00

SO1 AC1-4

CCFO 2, 3, 5, 7, 8

Lecture room

Facilitator

Multimedia

Relevant flow diagrams

Attend a lecture and/ or facilitated discussion on:

Relevant industry specific terminology with regards to the process

The purpose of the forming and pressing process

The role of the forming and pressing process in the overall functioning of the mill

The forming and pressing process in relation to its suppliers and customers

The operating principles of the forming and pressing process

The flow of material through the forming and pressing section

Ex. 1

Questions and flow diagrams

Ass. 1

Questions, sketches

and diagrams

00:00

Act. 2

All SO’s and AC’s

CCFO 1-8

Lecture room

Facilitator

White/ black board

Brainstorm the critical safety requirements as applicable to the forming and pressing process.

Act. 3

00:00

SO1 AC1-4

CCFO 2, 3, 5, 7, 8

Learning materials and workbook

Revise the work that you have done up to this point. Make sure that you have completed the CCFO checklist and obtained the required evidence for your

CCFOs CCFOs N/a

Manual 11 US xxx

Sparrow Consulting© November 07 Rev.1 – Nov 07


PoE

Facilitator/ SME

PoE. If there is anything that you do not understand, ask your facilitator. Act. 4

Total time allocated for this unit (00h00) 05:00

Manual 12 US xxx


1.2 IntroductionForming and pressing forms part of the wet end operations and falls within the stock

preparation section, but before the dry end of the process. The wet end receives thick

stock from stock preparation, it forms the sheet and removes the water, and then sends

the sheet to the drying section for further water removal.

The main objectives of the wet end are:

to dilute the thick stock

to provide final cleaning and screening of the stock

to remove air from the stock

to proportion and mix dyes, filler, internal size and retention aids into the stock

to form the sheet with a uniform cross machine basis mass profile

to remove water from the wet sheet by gravity, applied vacuum and mechanical

methods (pressing)

to consolidate the sheet

to recycle white water within the wet end process

In this module we will be focussing on the forming and pressing parts of the wet end

operations. The figure below shows where forming and pressing fits into the overall

processes of the paper manufacturing mill.

While forming and pressing may be included here as one process, it is in actual fact two

different processes. We will therefore begin by explaining the forming process after which

we will focus on the pressing process.

Manual 13 US 256282


Figure 1: Wet end processes

Manual 14 US 256282


1.3 The approach flow systemThe purpose of the approach flow system is to dilute the thick stock, clean and screen the

stock, remove air from the stock and supply a continuous and uniform stock flow to the

headbox. Different kinds of approach flow systems are used for each paper machine

depending on the requirements of the product, the available space, the machine

throughput and the capital cost of equipment. A modern approach flow system consists of

the following equipment:

Machine chest

Stuff box

Basis mass valve

Silo

Fan pumps

Multi stage cleaning systems

Air removal systems

Vacuum pumps

Dye addition systems

Pressure screens

Flow spreaders

Pulsation attenuators

Headbox

Manual 15 US 256282


Figure 2: An approach flow system

1.3.1 Functioning of the approach flow systemThe basic functioning of the approach flow system is as follows: firstly the thick stock is

pumped from the machine chest for dilution at the wire pit. The basis weight is controlled

by a thick stock pump. The stock fan pump feeds the first stage cleaner banks from

where the accept flows to the de-aeration tank. The air from the stock de-aeration tank

and the headbox dilution water de-aeration tank passes through a valve and the

condenser to the first-stage vacuum pump followed by a water separator. There are two

pressure screens equipped with an automatic shut-off valve on the feed side and manual

shut-off valve at the accept side. The stock flows from the de-aeration tank to the

headbox fan pump. From the screens, the machine stock flows to the headbox.

1.3.2 Design of the approach flow systemSmall waterfalls of water trap and absorb air that may cause foam and dirt build-up

problems throughout the system. There is no system on the forming table that can

eliminate cascading from the various de-watering elements into the collecting trays under

the forming fabric. The design and operation of the white water collecting system must

therefore set the entrained air free.

Manual 16 US 256282


The water silo should be full at all times, to eliminate cascading from the wire pit. The

vertical speed of the down flow should be low enough to allow for the removal of the

entrained air.

When flow speed is low, the liberated air tends to cling to the top inside of the pipeline. To

prevent this, all piping should be pitched slightly upward in the direction of the flow to

allow the air to escape from the system.

On the other hand, high velocities create a high load on the fan pump and other

equipment in the approach flow system.

The introduction of thick stock and make-up water into the suction of the fan pump can be

critical. Both should be introduced through the wall of the collecting silo and headed

toward the eye of the fan pump, as shown in the figure below.

The two pipes should end some distance before the pump connection so that the air will

escape upward and out before entering the fan pump. All control valves in the approach

flow piping system must also be placed below the normal liquid level in the white water

silo to prevent cascading.

Figure 3: Stock addition and mixing

The best system incorporates a variable speed fan pump that is automatically controlled.

A variable speed fan pump will pay for itself in power savings alone as no more power is

required than what is needed at the flow rate of the grade being made. There must not be

any gaskets in the flanges of the line, especially between the final screen and the

headbox manifold. Gaskets will create strings from which stock hang-ups will occur. All

Manual 17 US 256282


flanges should be of the metal to metal type with ground and polished welded joints. All

welded joints in the total pipeline must be ground and polished for smoothness to avoid

possible fibre hang-ups and consequent strings.

Screens should be located in the basement under the machine so as to keep a positive

head on the screen and an even flow to the headbox manifold. If physical space permits,

there should be a straight length of pipe equal to eight diameters between the last elbow

and the manifold transition section. This will re-blend laminar separation before the stock

and water slurry enters the manifold.

An elbow reacts like a cleaner in that the centrifugal action of the turn throws the heaviest

part of the mixture to the outside of the elbow – like clay or calcium carbonate. Unless

this is re-blended, there could be a difference of filler content from one side of the

machine to the other – the side nearest to the elbow having the greatest amount of pulp

stock.

If it is not possible to have a straight length of pipe between the last elbow and the

manifold, a hydraulic or venturi type elbow must be used to reduce the laminar separation.

1.3.3 Manifold distributor (flow spreader)All manifolds today are designed with a taper so that the cross-sectional area decreases

in about the same ratio as the flow to the headbox as it travels across the full machine

width, plus about 10% for recirculation purposes to balance out the cross-machine

pressure within the manifold. Most manifolds are rectangular in shape but there are a few

round types, both serving the same purposes. However, in both cases, round or

rectangular, the cross-machine direction has a linear decreasing cross-sectional area to

compensate for the frictional loss of the flow.

The recirculation line is piped to either the white water silo or the wire pit.

It seems logical that the best manifold be rectangular in shape with the sides of the unit

parallel to each other and the bottom or the surface directly opposite the headbox

entrance unit, tapering as the flow is reduced. This puts all of the force of the taper

compression directly opposite the tube bank entrance. The rectangular construction is

also substantially less expensive to manufacture. However, a headbox manufacturer like

Voith prefers the circular header, which tapers parabolically in the direction of flow. Voith

reserves the use of rectangular cross-section headers for special applications.

The bottom of the feed line, the round to rectangular transition and the manifold section

should be in a straight line to avoid uncontrollable turbulence.

Manual 18 US 256282


Figure 4: Manifold distribution

From an operational point, adjustment of the recirculation flows is intended to allow the

pressures in the piping to be similar between the front side and the backside of the

headbox. Too little recirculation flow will result in a higher pressure and hence a higher

flow into the headbox at the back of the machine.

It should be noted that an unequal pressure between the front and back of the headbox

could result in cross flow in the headbox. To balance the manifold or cross header, the

valve should be adjusted until the flow appears either stationary or with a slight movement

towards the discharge side. The flow should also be balanced in conjunction with the dry

basis weight of the paper.

If the profile "curve" shows a downhill slope from front to back, it means that the pressure

at the front side of the manifold is higher than at the back and the recirculation valve

needs to be adjusted accordingly. The most important part of the operation is the delivery

from the slice.

The points for and against a recirculation system are:

Advantages

Good performance at a wide range of flow rates

Construction of the manifold is made simpler

Recirculation is necessary with rectangular headers to prevent unstable flows at the

tube ends

Necessary to keep air swept from the manifold

Disadvantages

Higher cost and complexity of headbox installation

Recirculation valve is seldom adjusted or reset

Improper valve position leads to pressure fluctuations

The original concept of the tube bank was to provide tubes long enough to create a

pressure drop to assist in the balance of the manifold. The original tubes were 3 m or

more. Throughout the years it was found that tubes of much shorter length could be used

Manual 19 US 256282


if the velocity was increased accordingly. This, perhaps, led to the use of a drilled block in

place of the tube bank. Today, nearly all headboxes, both the distributor roll and hydraulic

types, use the basic tapered manifold with a tube bank or a drilled block.

The drilled block, approximately 150-mm long, depending on the builder, does not seem

to be able to cover as wide a range of flows as the tube concept but it has one advantage.

If the volumetric throughput of the headbox is increased beyond the velocity design it can

be easily replaced with one having larger holes. The tube bank concept is not as easily

replaced and it can only be done with considerable downtime.

Figure 5: Long tube bank

1.4 The headboxThe purpose of the headbox is to transfer the flow of stock from the round piping system

in the approach flow system, to a rectangular flow across the full width of the paper

machine and at uniform speed in the machine direction.

The headbox must smooth out or eliminate the flow disturbances and introduce a level of

turbulence to minimise fibre flocculation. The headbox must deliver the fibre suspension

evenly as a controlled jet onto the drainage section of the paper machine.

The primary objective is therefore to create the formation of a sheet profile with a uniform

cross machine basis mass. Therefore, the stock delivery from the headbox must be

absolutely balanced.

Manual 20 US 256282


1.4.1 Pressurised headboxThe modern pressurised headbox consists of the following components:

A cross header where the suspension is distributed evenly across the full width of the

paper machine. The header may or may not be fitted with a recirculation manifold

The step manifold where the stock velocity is increased to promote fibre

deflocculation and also to create a pressure drop between the header and the body

of the headbox

A stilling chamber where the stock velocity is reduced and made more uniform

The rectifier rolls to assist in the minimising of flow patterns

Front wall and slice arrangement where the prime purpose is to present an even jet

onto the forming or drainage zone

The control of the jet is done in one of three ways or a combination of two or even all

three methods:

Changing the consistency by raising or lowering the slice to adjust the water to fibre

ratio

By moving the complete front wall forward or back to alter the angle of discharge of

the stock onto the forming board

By discrete adjustment of the slice screws across the full width to obtain the best

possible fibre basis weight profile

The diagram below shows the side view of a pressurised headbox.

Manual 21 US 256282


Figure 6: Side view of a pressurised headbox

In the stilling chamber, the intention is to slow down the stock whilst still maintaining

sufficient turbulence to minimise re-flocculation of the fibres. It should be noted that on air

pad boxes where the throat opening is too small for the flow, vortices might be formed

which will pass through to the forming zone. In certain cases, the fibres may spin into

strings.

Where the throat is too wide, individual high velocities will be presented as basis weight

irregularities in the wet line.

Rectifier or “evener” rolls are used in air pad headboxes to even out flow disturbances or

irregularities and to minimise fibre reflocculation.

Typical problems associated with rectifier rolls are:

The effect on the basis weight profile, which should be investigated and corrected

using the on-machine gauge

Fibre scooping to be deposited as fibre bundles in the sheet

The formation of wakes which appear from the slice jet and spread out across the

table. The wakes may also have a relatively high-speed oscillation or instability. This

is a serious defect, particularly with respect to formation streaks and can be attributed

to the flow patterns through the rectifier rolls which have not been allowed to decay,

i.e., rolls with an incorrect open area.

Manual 22 US 256282


Wakes can also be produced in hydraulic headboxes and originate in the area of the

turbulence inducers and the diffusers. The overall cause is jets of stock, which have not

been sufficiently mixed and allowed to decay.

Many different roll designs are used, ranging from 50% open area down to 35% in some

rare cases and with hole diameters from over 25 mm to 12 mm. The open area of the

slice distributor roll should be 50% with holes of 19 mm to 25 mm in diameter. Holes over

25 mm in diameter are not effective and holes less than 19 mm can result in land areas so

small that stapling usually results, especially on the thick wall (10 mm) rolls more

commonly used today.

The other rolls in the headbox need to be something less than 50% open area to provide

resistance for a better and more uniform flow through the headbox.

There are two schools of thought concerning the direction of rotation, both quite valid.

One school of thought is that the roll should turn so that the bottom of the roll is turning

against the flow to create turbulence between the roll and the bottom surface of the

headbox. When doing this, the top of the roll will then be turning in the same direction as

the flow and, if there is a foam and/or dirt condition, the holes will scoop the contamination

down into the slice nozzle and out onto the forming table with resultant defects in the

sheet.

If the roll is rotated in the opposite direction, bottom with the flow, scooping action will not

be there but there will be a danger of undisturbed stock flowing between the roll and the

bottom of the headbox, especially if the gap is larger than 6.5 mm. Some headboxes

have reversing switches on the roll drive so that the roll can be operated in either

direction, depending on the circumstances. There does not seem to be a hard and fast

rule.

Nearly all distributor roll types of headboxes have water-sealing glands on the roll

journals. It is very important that the sealing water be turned on before the rolls are

started and or the stock introduced into the unit. If it is not, there is a danger of the fibre

and or clay entering the gland resulting in wear of both the gland and the journal. The

purpose of the sealing water is to keep the fibre and filler constantly washed out and back

into the headbox. Some headboxes are equipped with an interlock so that the rolls and

the fan pump cannot be started until the sealing water has been turned on.

Manual 23 US 256282


1.4.2 Headbox showersThe purpose of the internal headbox shower is to maintain a clean surface and to prevent

the build-up of deposits, which could drop off and cause a break on the machine. The

shower is also intended to assist in the reduction of foam.

The main points of the shower operation are:

The shower must be kept clean - inside and out

During shutdowns, the shower pipe must be flushed out and cleaned out chemically

The shower temperature must be controlled at or near the stock temperature

The pressure of the shower on the surface of the stock must not cause variations with

each rotation

The water supply to the shower must be adequately filtered using a dual basket filter

positioned at the headbox

1.4.3 Total head controlMechanical feedback control, both the Hornbostle tube and the float control system,

control the headbox liquid level at the expense of total head. There are two basic

instrument control systems on the market, namely:

Airflow (pressure) is used to control the total head and stock flow is used to control the

liquid level.

The total head is controlled by stock flow and the liquid level is controlled by airflow

(pressure). For proper operation of this system a three-mode controller is required to

control the total head. Refer to the following three figures.

It should be possible to determine from tests whether for any headbox it is better to control

total head with the stock flow or air pad pressure. This depends upon the lag in

pneumatic transmission lines, the type of controllers, the valve characteristics, and the

upsets in the system.

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Figure 7: Hornbostel control system

Each system should be modelled to determine which method is best and whether or not

rate control is needed. If total head control is to be effected with the stock flow valve rate,

action will be needed for this controller.

It appears that system "noise" may be one of the principal causes of the upsets existing

on some machines. This means that high frequency variations from the screens could

very well be causing the headbox instability of much lower frequency.

Figure 8: Head control by air and level control by stock flow

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Figure 9: Total head control by stock flow and level control by air

The effectiveness of any scheme depends on the sophistication of the instrumentation

and its reliability in the paper mill environment.

One point to consider is that stock flow control is usually slower than air pad corrections;

therefore, when total head is considered more important than level control, it is usual to

control total head by automatic adjustment of air flow and level by adjustment of stock

flow. Simulation can determine optimum controller settings.

1.4.4 Air flow control systems Constant airflow pump and automatically adjusted bleed valve. This system is

straightforward and is illustrated below. This is the most common system used in

practical headbox operations.

Figure 10: Constant flow airflow pump and automatically adjusted bleed valve

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Constant pressure air fan driven by a variable speed motor. A variable speed fan

provides the airflow while the exhaust flow is via a fixed orifice. The speed of the fan

is adjusted to provide control of the total head. This is shown in below.

Figure 11: Constant pressure air fan driven by a variable speed motor

Figure 12: Constant volume air pump and twin valve system

Constant volume air pump and twin valve system. This system, shown in above, is

designed to operate with a constant flow air pump at a pressure differential which is

high when compared to the air pad pressure. The flow into and out of the air-padded

headbox is then determined by the position of the two three-way valves.

1.4.5 Liquid flow controlSome potential liquid flow control systems are considered in the following sections:

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Flow control by means of a main control valve and a by-pass valve. The flow

control is obtained by means of a manually operated main valve located on the

pressure side of the fan pump. Automatic control is obtained by means of a by-pass

valve. This method can be of limited use if the pump curve is steep, but is used on

many machines.

Figure 13: Main control valve

Figure 14: Variable speed fan pump

Flow control with a variable speed fan pump and a by-pass valve (see figure

above). The flow is adjusted by varying the speed of the fan pump to the desired

value. For automatic control, a valve is installed in the by-pass line between the

pressure and suction sides of the pump through which a part of the stock is led back

to the suction side.

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Flow control by means of a main control valve and a by-pass valve located in recirculation line back to the wire pit. Leading a part of the total flow coming from

the fan pump via a recirculation line back to the wire pit controls Headbox flow. The

main control valve with a by-pass valve is located in this line.

Figure 15: Main control valve located in recirculation line

Flow control with a variable speed fan pump. The flow to the headbox can be

controlled directly by a variable speed fan pump.

1.4.6 Stock flow control systems

1.4.6.1 System One

The air bleed valve controls total head while liquid level is controlled by a by-pass valve.

This scheme is often thought to be best for overall control because the control of the air

bleed valve is normally very quick and this gives good overall total head control.

However, the problem with this scheme is the control over the liquid level. With a by-pass

control valve, the range of control is very limited and as a result it is very easy, particularly

on start-ups, to lose control of the level with the result the headbox either floods or goes

dry. Both these results are very undesirable from the point of view of time required to start

up a machine. With machines that are equipped with a controllable variable speed fan

pump, then the problem with flooding and drying caused by the by-pass valve does not

occur and in such circumstances system one would be the preferred choice.

Error: Reference source not found shows a scheme where both the air pump and the fan

pump are driven by DC motors. The use of thiristor drives provides fast control action to

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both the total pressure and liquid level loops. The speed rise time is less than 0.1 second.

The two loops can also be electronically de-coupled; this can result in improved control

under certain circumstances. However, when the total head control has a very short

response time and the level control is not unnecessarily vigorous, de-coupling becomes

less essential.

Figure 16: Total head and level control

1.4.6.2 System Two

The liquid level control is shifted to the air bleed valve over which a much wider range of

control can be exercised. The flow by-pass line controls total head. Operationally, this

combination is found best because level control comes in easy on account of the wider

range of the air bleed valve and flooding and drying does not occur.

1.4.7 Hydraulic headboxesHydraulic head boxes (flow boxes) are used on Fourdrinier machines covering a speed

range from 300 m/min upwards. Flow boxes started off being exclusive to twin-wire

formers since the special characteristics of twin-wire formers demanded better headboxes

which eventually led to their development.

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Since twin-wire formers set the sheet very fast, there is no disturbance in the forming

zone. In these cases, fibre distribution in the jet (which is controlled by turbulence level)

and consistency in the headbox determine formation and other paper properties.

Figure 17: Hydraulic headbox (Escher-Wyss)

Hydraulic headboxes eliminate the presence of a free liquid surface and the impact of all

its disturbances. The resulting stability allows the use of stationary elements for steadying

the flow and generating turbulence at much higher flow velocities without causing surface

instability. These higher velocities and use of stationary elements have radically

increased turbulence intensity level but reduced turbulence scale, which has improved

deflocculation. In addition, hydraulic headboxes give much more stable and uniform jets.

Because of their improved performance and competitive price, hydraulic headboxes are

currently not only used for twin-wire formers, but are employed increasingly on

Fourdriniers and top-wire formers.

Short-term, periodic pulsations can be caused by sources such as:

Fan pump impeller

Pressure screen foils

Resonate motion of pipe lines

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Valve cavitation

Structural or equipment vibration

Where possible and practical, short term variations should be eliminated.

Diaphragm-type attenuators are a preferable arrangement since they attenuate over a

broad range of (0,25 to 40 Hz) without incurring a reduction in pipeline velocity as with a

surge tank or the possibility of entraining air in the stock as with a surge pipe. The effect

of a diaphragm attenuator can be seen below. The figures show machine direction basis

weight variation in the time domain.

Figure 18: Pulsation attenuators

Figure 19: MD basis weight profile, time domain

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1.4.8 Headbox designAll headboxes can be divided into three parts: the distributor, the stilling section, and

the slice. The distributor deals with the initial distribution of the flow from the pipe to the

full width of the machine. The stilling section takes the flow from the distributor and

stabilises it into a uniform flow of controlled, small-scale turbulence. The slice accelerates

the flow to a speed close to that of the wire speed and controls the slice opening and

impact conditions.

1.4.8.1 Distributor

Virtually all hydraulic flow boxes have a one-sided tapered distribution header. The flow

enters from the side and perpendicular to the machine. This header is designed with a

taper and normally with an overflow to maintain constant pressure along the header, while

turning the flow 90º in the machine direction through pipes or holes evenly distributed

across the machine.

If properly designed, this ensures constant flow through each pipe and uniform initial

distribution from a pipe to the full width of the machine, independent of width. The stilling

section and the slice will then homogenise and deliver the jet. The one-sided tapered

distributor is the standard in the industry for all types of headboxes and is used for any

width, furnish, or flow range. Different headbox suppliers use different designs. All use

an overflow, but different approaches for cross-sections, tapers and manifolds.

Figure 20: Tapered flow header

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The one-sided tapered header with a hole plate or tube bank correctly designed and

operated provides a distribution system that is applicable to all conditions and widths and

give flow uniformity and stability. The one-sided inlet tapered distributor is superior to any

other distribution system currently in use.

Many header designs use lower pressure drops through the tubes to reduce the

turbulence level, which otherwise may lead to formation of hard, small flocs. Good

distribution is assured by adding another pressure drop downstream.

1.4.9 Stationary headbox elementsHydraulic headboxes use stationary elements to dissipate kinetic energy and high-velocity jets to produce a stable, homogeneous flow. Stable flow and the generation of

suitable turbulence to disperse the fibres, are accomplished by using stationary elements.

Hydraulic headboxes are completely filled (no air pocket) with a water / fibre suspension

and can therefore tolerate much higher velocities through the box. These velocities

enable turbulence generation through deceleration, step changes in cross-sectional area,

changes in flow direction and wall shear. Three basic principles are used to accomplish

this, namely flow nozzles, step diffusers and different variations of stationary flow stilling devices.

Figure 21: Stationary flow stilling devices

Most hydraulic headboxes use a stilling chamber after the distributor followed by a

resistance element, which is a type of perforated plate, followed by a tube bundle,

honeycomb, vanes, or foils. The stilling chamber is used to mix the individual jets coming

from the distributor and thus creates a homogeneous, uniform flow across the machine.

The perforated plate acts as a resistor to further improve uniformity followed by vanes,

tubes or honeycombs sections, which eliminate cross flows and develop the desired

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amount of turbulence. This is achieved in the step diffuser headbox by the length

directional partitions that the pipes constitute.

All major suppliers have headboxes based on these general principles, and although there

is a certain amount of convergence in headbox design, individual characteristics still

determine the final performance.

Step diffusers are based on the principle that, after accomplishing the initial distribution

through a perforated plate or a tube bank, stabilisation and turbulence generation are

performed through a series of step-wise increases in the diameter of the original branch

tubes or holes. From a small open area at the entrance, which gives the necessary

pressure drop to give good distribution, the flow is decelerated in these channels with two

or more steps until they come out either through a honeycomb with 90 to 95% open area

or through holes with an open area of 60 to 70%.

Step diffusers produce a stable and uniform flow with a controlled turbulence level that

can be delivered directly to the slice over a short rectangular distance. Turbulence is

generated by separation at the steps. The length of the tubes between steps is designed

to produce a suitable turbulence level high enough to eliminate boundary layer problems.

The step diffuser is critically dependent on a good original distribution, as there is no

mechanism for evening out flow differences between the different flow channels.

Figure 22: Step diffuser

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By making these steps about 3,2 and 6,4 mm and dimensioning the length of the tubes,

step diffusers combine a stable, uniform flow without streaks and a suitable turbulence

level and scale to give good fibre distribution. The last step cross-section can either be

cylindrical or square and it is even possible to put square honeycombs in lines without

having trouble with boundary layer streaks. This very simple system has given excellent

performance.

1.4.10SliceThe function of the slice is to accelerate the flow and deliver a stable, deflocculated jet

through a well-refined rectangular lip opening. This lip opening must be adjustable but

keep its shape independently of temperature, pressure or total lip opening.

In addition to the total lip opening and its shape, the angle and point of impact must be

controllable. For a wide, high-speed machine, this is quite a difficult task, as the degree of

definition is in the order of 0.01 mm. The slice is the converging part of the headbox

taking the flow from the stilling section to the delivery of the jet.

1.4.11Headbox operation

1.4.11.1Basis weight uniformity and stability

One key to efficient paper machine operation is stable, uniform basis weight. By

observing the basis weight and moisture profiles it is possible to obtain information on the

uniformity and stability of the process and the headbox.

Modern scanning systems with computers print out standard deviation or variance

statistics in the CM, MD and the random component directions.

Machine direction variation shows the effect of consistency and flow variations entering

the headbox. Cross-machine standard deviation determines the stable, cross-machine

profile variation. This is basically a function of the slice lip profile and any stable

hydrodynamic non-uniformity’s. Random variations for a given headbox will increase with

cross machine variation and with non-uniform drainage.

A useful way of viewing these profiles is to compare all the basis weight profiles around a

line representing the average basis weight. The profiles will show the stability of the

headbox while an average profile compiled from the data will show the headbox’s basis

weight profile.

Standard deviation numbers can also be compared to industry-wide numbers to indicate

how the headbox compares to other headboxes producing similar grades. To make such

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a comparison, the effect of edge disturbances which are often not characteristic of the

headbox itself, should be excluded.

It is important to determine the reasons for poor performance if the variance analysis

shows that the headbox is not functioning satisfactorily. A number of techniques can be

used to make such a determination:

Visual observation of the jet. Use of photography or a stroboscope is of great help

as these devices allow analysis of streaks and other disturbances

Observation of the dry line provides an indication of basis weight stability and

uniformity. As with the jet, one looks for the size, location, and movement of non-

uniformities. There is normally a good correlation between the dry line and the basis

weight profile. The dry line looks much more stable at high vacuums than at low

vacuums on the dry line suction boxes. Barring is readily observed at the dry line

Observation of the sheet at the calendar and the reel. By looking through the

sheet ahead of the calender, one can see the types of streaks and non-uniformity.

Stationary, stable streaks come from the slice lip or stationary elements in the

forming area, while moving streaks are hydrodynamic and characterised by size,

dispersion, movement and pattern. In all cases, location is very important

For a more detailed study of non-uniformities and instabilities of the sheet, it is useful to

view a large full width sheet. This allows the determination of the size, position,

distribution, and stability of the streaks and a characterisation of sheet structure. Based

on these observations, one can normally determine the sources of non-uniformities and

instabilities.

In addition to observations and measurements of the basis weight profile and its stability,

it should be standard procedure to inspect the headbox. This will identify any build-ups in

the headbox or areas that can cause non-uniformities and/or instabilities. This is

especially important if there are problems with cleanliness and if there is a slow and

continuous change in the basis weight profile. Stability of the slice region can be studied

by measuring how the slice opening varies with lip opening pressure and temperature.

Recording changes in the basis weight profile at start-up and grade changes best does

this.

It is usually possible to determine the sources of non-uniformities and instabilities.

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1.4.12Headbox problems Fixed streaks: Narrow fixed streaks are caused by dirt on the slice lip or dried

fibres. Larger, stable streaks can be caused by deformations in the slice lip. These

streaks are normally easily observed in the jet and in the sheet. Similar types of

streaks, but of a different structure, can be caused by stationary elements in the

forming area and by ridges in the wire. These do not show up in the jet.

Unstable streaks and an unstable basis weight profile: These streaks are

caused by hydrodynamic sources behind the immediate slice area.

Wake effects: Hydraulic headboxes can cause narrow streaks that move around at

relatively high frequencies. These can be caused by boundary layers from vanes,

tubes, etc., and by Taylor vortices.

Large instabilities: Large flow instabilities that are wider, move more slowly and are

either varying around a centre line or randomly are caused by flow instabilities from

the distribution system or the headbox proper. These can be instabilities in the

approach to the distribution system; plugged manifold tubes or holes; air; or caused

by edges and vortices in the flow through the box. In addition to observations, it is

normally necessary to perform measurements as indicated above to identify the

cause of these instabilities and non-uniformities.

Systematic profile problems: Stable basis weight non-uniformities that show up in

basis weight analysis have a variety of causes, some of which are listed below:

On one-side tapered headers, it is necessary to keep the pressure at the entrance

and outgoing sides equal.

Audit the design and installation of the headbox to ensure that there are not

design or manufacturing mistakes that cause non-uniformities.

Dirt build-ups in the box can be a cause of stable non-uniformities.

The slice geometry can cause stable non-uniformities: The slice might not be

uniform due to manufacturing errors, deformations of the slice lip, and/or play in the

adjusting mechanisms. It is very important to make sure that the slice geometry is

stable and independent of pressure, temperature, and total lip opening. Temperature

gradients can cause warping.

Edge problem: Exact fit of the cheeking pieces and the edge deckles is very

important to give good edges. Any step change will give wakes.

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Slice profile adjustments:. The basis weight profile can be non-uniform due to over

adjustment of screws, which causes permanent deformation of the slice. It is

therefore very important to check the straightness of the slice periodically and to reset

the slice to a uniform opening.

Distribution systems: The distribution system is often the cause of large, movable

streaks, cross machine, profile instabilities, and large, stable non-uniformities. The

appearance of these non-uniformities and instabilities also depends on interaction

with the stilling section.

One-sided tapered header: This is by far the best distribution system. Normally, it

has an adjustable overflow. Pressure difference between front and back should be

zero to get a uniform profile. It is possible to get the hole plates or tube banks

plugged at too low flow rates. Plugging will cause a change in the profile with time

and make it increasingly unstable. This instability can be overcome by changing the

hole plate, plugging holes or tubes, or increasing the flow if possible.

Unstable profiles: One-sided tapered headers, pulsation and flow instabilities give

CD variations. To avoid this, one should eliminate pulsations from rotating elements

and design and install the pipeline correctly with suitable attenuators. Bends too

close to the header and transition pieces with too large divergence can cause such

problems. Another potential source of instabilities is the stilling chamber, especially if

it is used to divide the flow. Using a small number of branch pipes in the distributor

will also cause large-scale instability, as will poorly designed explosion chambers.

Hydraulic headboxes: Hydraulic headboxes use stationary elements in stilling, and

explosion chambers for stabilising and homogenising the flow. Design of the box is

critical with regard to its performance. Vanes and other elements can cause

boundary layer streaks in the jet. These are recognised form spacing and

movements of the streaks. The higher the flow rates the more unstable the flow.

There is basically nothing operational that can be done, except by reducing the flow

or rebuilding or changing the box.

Hydraulic boxes are much more sensitive to dirt and build-up on the top surfaces. In

addition to causing flow disturbances, these also cause cleanliness problems. To

keep vanes and roofs clean, velocities must be high (0.9 - 1.5 m/s). Cleanliness

problems show up as a continuous change in profile after washing-up and as an

increase in lumps. This can be seen at an inspection. These problems can be

reduced or eliminated by increasing the velocity in the box, by filling in stagnant areas

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or by increasing the flow rate. Dividing the flow in the stilling chamber can cause flow

instabilities. This can only be reduced or eliminated by redesigning the box.

Slice region: The slice region can contribute to stable non-uniformities caused by

geometry of the slice area and through deformations. The slice can become

permanently deformed through excessive adjustment and must then be replaced.

This is not a big problem for headboxes with small vertical metal strips used for

profile control. Slice lips can also be nicked or have dried fibres, which will cause

streaks.

Temperature, pressure, and slice opening can change the profile. This is a very

critical problem, which has to be dealt with. For good operation, it is very important

that the slice profile stay the same, independent of these parameters. It might be

necessary to build in pressure and temperature compensation and to eliminate

excessive play in the slice adjusting screws to take care of these problems. It is very

important that the slice area be checked for accuracy and uniformity.

1.4.13Headbox operational parametersThe various forming factors involved in the sheet formation are:

Jet to wire ratio

Jet angle

L/b ratio

Forming board position

The various forming and drainage factors involved in the sheet formation, at the point of

impingement between the stock and the fabric can have a significant result on:

sheet formation

basis weight profile

Retention

sheet strength properties

1.4.14Headbox efficiency

1.4.14.1Sheet formation

Following are only a few points to be considered:

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If the head is showing a cyclic variation or random variation, the following points

should be checked:

fan pump

level control on the cleaners

deculator level control

white water silo level control

If the slice is incorrectly set, an excess water flow will require too high a head with too

fast a jet speed. Sheet formation will be poor.

If the headbox stock consistency is above that which corresponds to the critical stock

velocity for a particular fibre furnish, then the sheet formation will suffer from

flocculation

Too high a consistency in the headbox will cause the drainage rate on the forming

fabric to be too fast, affecting sheet formation.

Too high a consistency inside the headbox may cause flocculation across the rectifier

rolls in an air-padded headbox.

To improve sheet formation, reduce the headbox consistency (if the table drainage

capacity allows).

To obtain best sheet formation keep the jet / wire ratio at the optimum value as

required by the performance characteristics of the headbox.

For optimum sheet formation, it is necessary to maintain the correct:

top slice lip

bottom slice lip

breast roll gap

forming board relationship

Avoid breast roll discharge. The lower part of the discharge from the slice should just

be closed off at the forming board.

1.4.15Cross-machine basis weight profileThe following adjustments are required for variations in the cross-machine basis weight

profile:

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The slice must be adjusted carefully and not over adjusted in any one position. This

will require changes to at least three slice screws at any one-correction position

Make sure that the slice screws are correctly maintained and with the minimum of

backlash and with the position indicators correctly set

Operate the side bleeds correctly and avoid over adjusting the slice screws at the

edges of the lip

Replace sprung or distorted slice lips. Schedule slice lip replacements at regular

predetermined intervals

Maintain a balanced flow or pressure in the distribution system and ensure that both

sides of the headbox are balanced - i.e. no cross flows

Ensure that the rectifier rolls are seated correctly and with the minimum practical gap

with the sides of the headbox

Ensure that the headbox showers are operated correctly - pressure and temperature

Set-up the deckles and the deckle end to ensure that there is only minimum cross-

waves

Provided the headbox and the forming table are set up correctly, significant

improvements can be obtained by either automating the slice screws with control

through the on-line computer or by using a computer programme for manual

adjustment of the slice screws based on computer assessment of the changes

required

1.4.16The dilution headboxHeadboxes which use a slice lip to control the basis weight profile across the machine

have their limitations in achieving a flat profile. This problem is largely attributed to the

complex flow responses produced by change in the slice lip, which affects basis weight

and fibre orientation.

The dilution control headbox addresses the above problem. The diagram below shows a

typical dilution headbox.

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Figure 23: Dilution headbox

1.5 The forming sectionThe purpose of the forming section is to receive the rectangular flow of stock from the

head-box and to transform the stock flow into a wet sheet on the forming fabric. The

meshes of the forming fabric permit drainage of water while retaining the fibres. Water

removal through the fabric is accomplished with the aid of drainage elements and

vacuum. Until the late 1960’s only metal “fabrics” made from phosphor bronze wire were

used; today forming fabrics are made of polyester monofilaments which provide a longer

service life (lasts up to ten times longer) and do not damage easily. However, the old

terminology still persists and forming fabrics are usually called wires by papermakers

irrespective of its material of construction.

The different types of forming sections are: the Fourdrinier (making of paper or tissue),

twin wire formers (making of paper or board), multi wire formers (board making) and

cylinder vat formers (board making). In this module we will be focussing on the

Fourdrinier and twin wire forming sections.

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1.6 The Fourdrinier

Figure 24: Diagram of Fourdrinier section

1.6.1 Drainage principles of the FourdrinierFor the efficient running of a paper machine, it is essential to optimise the performance of

the making table since low efficiency in this area has a major effect on the overall

performance of the machine. The following diagram shows how the activities on a typical

Fourdrinier table are divided into four distinct phases:

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Figure 25: Table layout – sheet formation

1.6.1.1 Phase 1

Initially, the stock impinges onto the wire or fabric and the objective is to start forming a

mat without sealing the sheet or causing excessive loss of fines or loading.

1.6.1.2 Phase 2

In this phase, the sheet formation is started with a low drainage to prevent fibre loss, but

with sufficient agitation to prevent the formation of flocs. i.e. forming the sheet.

1.6.1.3 Phase 3

In phase 3 the sheet undergoes gentle drainage by the careful selection of the correct foil

blade angles. If the angle is too sharp and there is insufficient water being removed to

form a meniscus in the nip, the vacuum necessary will not be generated and the drainage

rate will reduce. Near the end of phase 3 the resistance to drainage becomes so high that

additional vacuum sources are essential to continue removing water, i.e. vacuum assisted

foil boxes or wet suction boxes.

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1.6.1.4 Phase 4

Water removal is now only achieved through the application of higher differential pressure

i.e. dry suction boxes. If the sheet enters this point with too high moisture content, there is

the possibility of pin-holing, streaking and an additional loss of fines. Excessive vacuum

will also increase the drag load on the fabric and cause undue wear.

1.7 Drainage profilesFor the production of good quality paper, which is as even sided as possible, the drainage

must be under control, i.e.:

Should not be excessive at the forming board

Should be even along the table and not too vigorous

Capable of variations and the introduction of micro turbulence for sheet formation

The dryness after the foil units should be 2% or more

The dryness after the low vacuum units should be at least 5%

The drainage profile presented by the first figure below is acceptable while the profile

presented in the second figure is unacceptable

Figure 26: Acceptable drainage profile

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Figure 27: Unacceptable drainage profile

In the first example, which is considered acceptable, the drainage is held up initially at the

forming board with a reasonably constant drainage to the flat boxes.

In the second example, which is considered unacceptable, the comments are:

Too high drainage at the forming board

A drainage restriction on the early part of the table

Erratic drainage for the remainder of the table

To achieve maximum efficiency, an acceptable drainage profile and good sheet formation,

the following points must be taken into consideration.

1.7.1 ConsistencyThe aim after presenting the stock at the correct consistency for good formation is to

achieve the maximum dryness from the couch. One typical layout is as follows:

Four blade forming board (Phase 1)

Three boxes of foils followed by a wet suction box (Phase 2)

Four Boxes of higher angle foils and two wet suction boxes (phase 3)

Four dry suction boxes (Phase 4)

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1.7.2 VacuumOne of the more critical areas is the vacuum level at the couch. Where the vacuum levels

are not achieved, the sheet runs wetter and as a result the wet web strength will be lower

with a significant effect on sheet runnability.

The drier sheet also places a reduced load on the press section and the pick-up is

similarly less critical.

1.8 Fourdrinier table equipment

1.8.1 Forming board

1.8.1.1 Design of the forming board

The design of the forming board tends to vary depending on the machinery manufacturer

and as will be noticed there are significant differences in the number of blades and the

open area.

The current practice is towards three bladed forming boards with, in some instances, the

second blade slightly angled to act as a foil.

From an overall design parameter, the forming board should be rigid and have adequate

strength for absolute minimum deflection. The forming board is a critical area in

papermaking and many of the formation defects originate at this point. Typical reasons

for the defects are:

Bent or sagging board with insufficient rigidity

Distorted board due to careless handling

Insufficient care taken in setting up or aligning

Poor procedures for replacing blades on a routine basis

Lack of understanding

It should, however, be noted that many of the forming board problems could be attributed

to the lack or inability to move or reposition the board, i.e. poor design of the mounting

mechanism. Associated problems are:

Forming board set too low - water being forced between the fabric and the board

causing "galvanising", worms and streaks. Air bells may also be detected

Forming board set too high - mainly excessive fabric and blade wear

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Worn foil blades - thus streaks

1.8.1.2 Forming board position

Due to the wide differences in machine speeds and manufacturing conditions, it is not

possible to give precise measurements for the position of the forming board in relation to

the slice lip.

1.8.2 Foil blades

1.8.2.1 Foil blade operation

The operation or the effect of a foil blade can be summarised in the following steps:

Water on the underside of the fabric is doctored off at the leading edge of the foil

Any remaining water acts as a lubricant between the fabric and the foil blade

At the flat land area, the mat on the fabric is subjected to a small positive pressure

pulse followed by a vacuum pulse, which pulls the water to the underside of the fabric

The releasing of the fabric upwards creates a "micro turbulence" which is used to

break up the flocs

The control actions possible for water removal are:

The angle of the blade

The blade spacing

The removal or addition of blades

With the fabric passing over the flat land area, a negative hydrostatic pressure is

generated which tends to make the fabric follow the contour of the foil. The fabric tension

also influences the degree of deflection. This action causes a pressure drop to be set-up

across the fabric/mat/slurry and water drains through to the underside.

1.8.2.2 Factors affecting foil blade drainage

The general rules for foil blade drainage are:

The higher the speed the greater the spacing

The lower the freeness, the greater the spacing

The lower the consistency, the greater the spacing

The control parameters for foil blade drainage control are:

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Foil blade angle

Foil blade width

Foil blade spacing by removing or installing foils

In selecting the blade angle and the blade, the factors to be considered are:

The water removal rates

The required sheet formation

First pass retention

The behaviour on the fabric, i.e. micro turbulence or macro turbulence due to stock

jump

1.8.2.3 Foil blade wear

With synthetic foil blades, the wear is usually progressive to give a gradual falling off in

performance. The main indicators of foil blade wear are:

A loss in the sheet formation

A reduction in the micro turbulence

Reduction in the drainage capacity

Increased drive loads due to the greater areas of contact between the fabric and the

foil

Increased fabric wear

1.8.3 Wet and dry suction boxesThe various types of wet suction boxes can be sub-divided into four main types:

The zero angled flat bladed type, which only remove water by the application of

vacuum.

The step foil box, which is totally dependent on the application of vacuum for the

water removal

A box with alternate foils of different thickness and the ability to apply vacuum

The combined foil/wet suction box where the water removal is achieved by the dual

application of foil blade angles and vacuum

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1.8.3.1 Benefits of wet suction boxes

The overall potential benefits of wet suction boxes are dependent on the type of unit

installed and the control action.

Typical possibilities are:

By adjusting the vacuum and fitting blades of different dimension, the box can be

capable of inducing turbulence for formation control

By the application of vacuum levels higher than that generated by the normal foil

blades, the de-watering rates can be increased

The higher de-watering rates permit lower head-box consistencies and possible

formation improvements

A reduction in the drag load if used to replace flat boxes

Better fines retention when used instead of flat boxes

Reduced wire side roughness with the more progressive water removal and more

gentle suction

Improved control sensitivity. Wet suction boxes operated in millimetres of water as

opposed to millimetres of mercury. This feature also permits finer control of the stock

conditions under the dandy

A potential increase in the fabric life when the wet end drag load is reduced

1.8.3.2 Layout of vacuum system

Poor vacuum box control can result in:

Pin holes

Two-sidedness

Loss of fines and fillers

Premature fabric and suction box wear

Fabric freezing

Excessive wet-end breaks, particularly on open draw machines

In the past, the major papermaking concern was the position and the state of the "dry

line". Modern thinking reflects a greater knowledge of where the maximum amount of

water can be removed from the web without upsetting the retention or reducing fabric life,

i.e., graduated vacuums at levels, which are sufficient to ensure continual water removal.

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1.8.4 Suction couchThe objectives of the suction couch roll may be defined as:

to remove the maximum amount of water

increase the sheet density or hardness for the best possible runnability. It should

be noted that it is possible for two webs to have a similar sheet consistency but a

different density. By the application of a higher vacuum, both webs become similar

for these two properties. The couch must therefore be capable of increasing sheet

consistency and density to optimise the runnability with minimum breaks at the point

of draw

As a general rule, the suction couch box should be as large as practically possible to

obtain the maximum vacuum effect and sheet strength without causing sheet disruption.

For the optimisation of the vacuum system, there are certain ground rules, which should

be designed into the system, i.e.

Independent vacuum supplies to each vacuum unit. This avoids preferential flows if

and when the stock characteristics or porosity’s change

The piping should be sized to ensure maximum vacuum at the point of application i.e.

no restrictions

Bleeding air rather than throttling the pump should control the vacuum level

1.8.5 Couch operationThe holes in the couch shell receive water from both the sheet of paper and the showers.

Both sources of water must be controlled. The vacuum boxes must deliver a low wetness

(high consistency) sheet to the couch. The showers must be controlled.

1.8.6 Suction couch - open drawThe draw or the amount of draw at the couch on an open draw machine is a critical area

of operation and can cause such defects as "wrinkles or creases" when run slack or

"excessive shrinkage or poor runnability" when run too tight. If run excessively tight, in

addition to a high break frequency at the couch, the runnability can also suffer further

along the machine due to the inability to resist snatch.

With a tight draw, the web is removed part way up the final suction zone and the fabric

speed should be increased. When the draw is slack, the fabric speed should be

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decreased. In this case there can also be a loss in runnability if there are changes in the

adhesion factors and the web runs still lower down the couch.

1.9 The twin wire formerThe mechanics of drainage in the twin-wire nip are different from that of Fourdrinier

drainage and results in different paper properties.

Consider the case of the solid roll former typical of tissue twin-wire machines, where

drainage is in one direction only, as shown belowError: Reference source not found. The

jet, at velocity Vj, impacts the twin-wire nip, generally contacting the roll side first, with jet

impingement after the breast roll/forming roll centre line. If the jet contacts the fabric on

the breast roll first, any CD jet or fabric instability will cause a table roll action, which will

strip the forming fabric off the machine. The angle between the jet and the centre line of

the breast roll/forming roll is slightly greater than 90º on the forming roll side.

1.9.1 LayeringThe building of stratified or layered sheets has been practised for many years. The

driving force for this objective is the attainment of unique physical properties, fibre

economy and /or lower cost, in spite of the increased machine complexity. Softness,

flexibility, ink absorption and strength are all properties, which can be selectively

engineered with a layered structure.

Of recent interest is the development of layered sheets with one head-box. These head-

boxes of course require segregated flow channels and formers, which segregate the water

from the various layers as they are drained. Layered tissue machines are in operation in

both Fourdrinier and twin-wire configurations. The Fourdrinier tissue machine achieves

better layering because of the ability to positively control shorter forming zone geometry.

The twin-wire manufacturers have found that higher layer purity can be achieved if the

layer of the forming roll side is operated at a higher velocity than the rest of the jet.

Consider the two sheets which have the structures shown below. The sheet on the left

would be relatively flexible, since the strong fibres are near the neutral axis. The opposite,

of course, would be true from the sheet on the right.

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Figure 28: Layered structure

1.10 Principles of modern twin wire drainage formation

For paper grades there are three basic types of twin wire formers, namely:

Roll formers

Blade formers

Hybrids and top wire retrofits

1.10.1Hybrid formersThe principles of drainage and formation will be discussed for both roll and blade formers.

The hybrids and retrofits are combinations of Fourdrinier dewatering, after which twin wire

dewatering takes place. The top wire on a hybrid former can be expected to have the

same positive effect on formation as a dandy roll. There are many hybrid designs of twin

wire formers on the market today, with practically every possible combination of roll and

blade dewatering.

Some advantages seen for hybrid formers over Fourdriniers:

Good formation

Less linting of sheet

Two-sidedness much improved

Increased drainage capacity/speed increase

Typical problems encountered with the Hybrid formers:

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Top wire locations - too far from slice and the formation improvement is minimal - too

near slice and water handling could be a problem

Trouble keeping top fabrics clean - pitch and stickies float to top on table and stick to

top fabric

Cleanliness and mist evacuation difficult

Success of hybrid formers has been an affordable installed cost for retrofits. If drainage

was limited on the Fourdrinier the hybrid former often allowed speed increases and with

less stationary vacuum units, flat boxes or wet suction boxes. These speed increases

would often be realised at lower drive loads. The real advantage of hybrid formers is

improved paper quality.

1.10.2Roll formersA twin wire roll former is one in which the free jet is injected onto one wire and

immediately contacted by a second wire or it is injected between two converging wires

and the sandwich is immediately wrapped around a roll.

Roll formers dewater due to uniform pressure from the outer fabric tension over the roll

radius. This forming pressure has been measured by using a pressure transducer located

in the forming roll surface. This forming pressure increases on the fibre mat to a constant

level until drainage is complete. Roll formers, therefore, dewater gently with a uniform or

even drainage pressure. With this even forming pressure dewatering occurs rapidly

"freezing" the fibre suspension in the jet from the head-box.

Roll formers provide some definite advantages:

lower drive power required

longer fabric life

improved drainage/speed increase

less two-sidedness

less tinting

improved printability

closed forming zone / no free surface

The disadvantages of the roll formers are:

lower retention than Fourdrinier

higher head-box consistencies

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more pinholes

grainy formation

lower internal bond

pressure pulsations are translated into MD basis weight variations

With increasing speed the dynamic effects are amplified in the sheet-forming zone. The

furrowed character of the stock jet increases with speed. Therefore, the time span

between jet impingement and stock immobilisation between jet impingement and stock

immobilisation between the fabrics has been minimised. Also, the curl tendency is very

small, as the fluid wedge is approximately symmetrical in the forming zone, so that the

orientation of the two developing fibre mats to each other is similar.

1.10.3Blade formersA twin wire blade former is one, on which the free jet is injected onto one wire and

immediately contacted by a second wire, or it is injected into two converging wires, and

the sandwich moves over bladed dewatering boxes or individual blades. This sandwich

may travel along a large radius as with the “Bel Baie II”, or it may travel in an essentially

straight path as in the “Vertiformer”.

Types of blade formers;

Black Clawson Vertiformer

Beloit Gap blade

Blade formers de-water with a pulsating drainage pressure. Maximum pressure occurs

over each blade tip, which means that inward de-watering will be restricted compared to

outwards de-watering. This pulsating de-watering over each deflector blade is not a

gentle process. These pressure pulses have a positive effect on formation due to the

shear forces acting on flocs but there is a detrimental effect on retention and an increased

fibre anisotropy in the paper, two-sidedness.

Blade formers provide the following advantages:

better formation

less linting of sheet

two-sidedness improved on Fourdrinier

increase drainage capacity/speed increase

Typical problems encountered with blade formers:

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sensitive to fabric conditions and alignment of blades and their condition in the

forming zone

very poor retention

higher drive requirements compared to roll formers

two-sidedness still evident

1.10.4Twin wire formers, practical problems Head-box defects and pressure pulsations are frozen between the two fabrics. No

opportunity to remake the sheet

Twin wire formers are sensitive to fabric conditions. The fabric must be kept clean

and free of wrinkles and creases

Blade formers cannot have any defects or misalignment in the forming zone

Twin wire formers are difficult to keep clean for efficient operation. Pay careful

attention to:

save-all system

adequate ventilation to eliminate misting

cleaning showers for fabrics and rolls

doctors working properly

fabric design to minimise fibre carry over by top fabric

slimicide dosage

Jet impingement is often critical. Do not flood the Breast Roll with excessive

drainage in front of the forming board

Clean fabric separation or the sheet following the top fabric and plastering the roof

and head-box. Fibre picking by the top fabric

Low dryness off the couch on twin wires will hydraulically overload the Press Section

Two-sided drainage can produce a sheet with a weak middle, which can de-laminate

in the printing process

Lack of visibility on many twin wires is a problem. Install strong halogen spot lights

where needed

Surface defects on sheets are often characteristic of specific twin wire designs.

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Poor retention on blade formers can build up fines in the white water system and

overload the disc save-all and effluent treatment systems

High vacuum required to achieve decent dryness off the couch can make the porosity

of the sheet excessive

Rich white water, that should have been lean, will be difficult to use in showers and

the fibre will promote slime growth

Fabric instability and wrinkling due to wire return roll deflections has caused a lot of

grief. Valmet has crown-compensating rolls, to be used in highly wrapped positions,

to compensate for deflection at higher speeds. Hope rolls are also supplied to keep

the fabric seam lines straight

1.11 The press sectionThe primary objectives of pressing are to remove water from the sheet and to consolidate

the sheet. Other objectives are to provide favourable sheet properties, and to improve

wet web strength in order to ensure good runnability in the dryer section.

The pressing operation may be considered an extension of the water removal process

that was started in the forming section. The water remaining in the pressed sheet must be

removed by evaporation in the dryer section. It is far more economical to remove water

by mechanical means in the press section than by evaporation in the dryer section,

because the drying process is a costly operation which requires large amounts of energy.

Moreover a wet sheet going through the dryer section is at risk of damage or breaking.

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Figure 29: Water removal cost in the former, press- and dryer sections

The efficiency of the press section is therefore of absolute importance because of its

potential for increasing the productivity of machines and for reducing the cost of the dryer

section.

The primary functions of the press section are:

water removal from sheet

consolidating the sheet of paper

improving the sheet surface quality

1.11.1Water removal and paper consolidation in a wet press

The sheet leaving the former and entering the press section contains about 80% water. A

portion of water carried by the web is located in the interstices between the fibres; the rest

is contained in the lumen, pores and swollen walls of cellulose fibres.

The bulk of this water is removed when the sheet is compressed in one or several

consecutive press nips. Although press nip loads normally increase from the first, to the

second, to the third press, the amount of water removed decreases. As the sheets

become dryer, removal of the remaining water becomes more difficult.

Pressing significantly augments the tensile strength of a wet sheet by raising the solids

content. For example, solids content increases from 17% to 40% results in about a

threefold increase in the tensile strength of a newsprint sheet. Tensile strength is required

to minimise sheet breaks, especially on fast machines producing low basis weight grades.

While pressing improves the economy of papermaking and the efficiency of the paper

machine, its most important effect is the improvement in product quality. Pressing

increases the sheet's smoothness, burst strength, tensile strength and density, and

reduces its thickness and tear strength. This factor cannot be over-emphasised.

1.11.2Pressing actionThe pressing action can be divided into two distinct types:

Pressure Controlled and

Flow Controlled

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1.11.2.1Pressure controlled

Normally applies to easy draining, low basis weight sheets. Typical grades are newsprint,

groundwood grades and fine papers.

Grades such as corrugating and Kraft papers are not purely pressure controlled, but are

pressed best with a single felted installation.

With this type of pressing, the limiting factor is the amount of pressure, which can be

applied, and there will be no restriction on the flow of water in the nip.

1.11.2.2Flow controlled

The limiting factor is the rates of flow out of the nip - hence the use of double felted nips.

When the flow resistance becomes the dominating factor, dryness is reduced with

increasing basis weight. Similarly, increasing production speeds result in lower sheet

dryness. With heavy weight sheets, there is the possibility of a flow-controlled operation,

but the pressing conditions are more advantageous with a reduced possibility of crushing.

Linerboard sheets, where the compaction is controlled primarily by the outflow of water,

are said to be flow controlled. In some of the lightweight sheets, compaction is controlled

more by the compression of fibres and less by water flow; these are said to be pressure

controlled.

1.12 Water removal in a transversal flow press nip

The figure below shows a transversal flow press nip in which the press operation has

been broken down into different phases based mainly on the main mechanisms involved

in water transfer.

The transversal flow press nip consists normally of two rolls, one of which is normally

rubber covered, and which are pressed together. Through the nip defined by the rolls a

web of paper is pressed between one or two felts that are backed by a structure, either in

the roll or separately, that can accept water pressed from the felt. If this structure is a wire

mesh, the press is called a fabric press if the wire runs in a loop inside the felt, or a sleeve

press if the wire is shrunk on to the roll. If the roll surface is grooved, it is called a vented

press. In these presses, water is flowing in a plane perpendicular to paper and felt and

giving the shortest possible flow distance. Tangential flow in paper and felt is small for

transversal flow presses.

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Figure 30: Transversal flow nip

The water forced from the paper web is absorbed into the press felt in the compression

phase while a small percentage of the water is re-absorbed from the felt by the paper in

the expansion phase.

Both felt and paper are unsaturated when entering the nip. Both contain a sufficient

amount of water to reach saturation before mid-nip. The geometric configuration,

pressure distribution curves, water transfer mechanisms and thickness curves for paper

and felt are shown for the nip. The nip has been divided into four phases.

Phase 1 starts at the entrance of the nip where the pressure curve begins and lasts until

the paper has become saturated. The felt is shown unsaturated in phase 1. No hydraulic

pressure develops in phase 1.

Phase 2 extends from the point of saturation to mid-nip, or more accurately to the

maximum point of the total nip pressure curve. In this phase the felt also reaches

saturation.

Phase 3 extends from the maximum point of the nip curve to the point of maximum paper

dryness. This point corresponds to the maximum of the paper structure pressure curve

and zero hydraulic pressure in the paper. In this expanding part of the nip, the felt passes

zero hydraulic pressure and becomes unsaturated.

Phase 4 covers the point where the paper starts to expand and becomes unsaturated.

The felt is unsaturated through this whole phase and expands continuously.

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The total nip pressure curve is divided into a fluid pressure component and a fibre

structure pressure component. The sum of these two components is equal to the total

pressure. As the felt has a much lower flow resistance than the paper, the fluid pressure

component is much lower in the felt than in the paper. The size of the fluid pressure

component in the felt is dependent both on moisture content of the incoming felt and on

the amount of water being transferred from the paper to the felt.

The proportion of hydraulic pressure and pressure in the structure will vary along the nip

and through the thickness of felt and paper. Hydraulic pressure in the area of paper

facing the felt is almost identical to the total hydraulic pressure in the felt. Hydraulic

pressure in the paper will then grow with the distance from the felt surface and be at its

highest at the roll. This means that the forces compressing the fibre structure will be

largest close to the felt. Pressure gradients, therefore, exist both in machine direction and

perpendicularly to sheet and felt.

In addition to the pressure curve, areas have been marked in Error: Reference source not

found to show the type of mechanisms acting in different parts of the nip. This includes

the flow of water through compression, two-phase flow through capillary forces and two-

phase flow through compression and expansion.

1.12.1.1Phase 1

The total pressure of the sheet starts to grow through compression. In this phase, air is

flowing out of both paper and felt. No hydraulic pressure is present. Felt and paper are

both unsaturated. Transfer of water can only occur through capillary forces or two-phase

flow. Very little change in dryness in the paper can be expected in this phase. All forces

are taken up by compression of the fibre structure.

1.12.1.2Phase 2

The sheet has reached saturation and hydraulic pressure increases, squeezing water

from paper to felt. The felt reaches saturation and hydraulic pressure is generated,

resulting in the flow of water from the felt into receptacles under the felt. Compression

force acting on fibres and felt structure increases through the whole of phase 2. Fluid

pressure in the felt and paper reaches a maximum ahead of mid-nip.

In phase 2, water is flowing out of the system through compression. Before the felt is

saturated, there are capillary forces promoting water transfer from the paper to felt.

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1.12.1.3Phase 3

The total pressure curve decreases. Here Larsson and Nilsson make a new contribution

when they show that fibre structure pressure increases to a maximum point that is also

the point of maximum paper dryness, corresponding to the point where fluid pressure in

the paper is zero. This means that the paper is getting dryer after mid-nip as long as

there is a hydraulic pressure gradient between paper and felt. As phase 3 is an

expanding portion of the nip and paper in this phase gets still further compressed, the felt

must take up all expansion. Owing to some lateral flow of water through the nip, the felt is

saturated through a small part of phase 3 corresponding approximately to the felt

thickness, but soon becomes unsaturated. This creates a vacuum in the felt, forcing air

and water to enter from underneath through the fabric or grooves.

1.12.1.4Phase 4

Both paper and felt expand in this phase and the paper becomes unsaturated. A negative

pressure is created in both structures. Compressive forces on the fibre structure and felt

are larger than the total pressure. In this phase, it must be assumed that air will enter for

the same reason as air would enter the felt in phase 3. However, the vacuum due to

expansion will be larger in the paper than in the felt, creating a two-phase flow of air and

water into the felt and from felt to paper. In addition, capillary forces will act within and

between paper and felt in this two-phase system.

When paper and felt are separated at the end of phase 4, water in the interface between

them will be divided, due to film splitting.

In phase 4 the paper enters at maximum dryness and absorbs water from the felt. In this

phase, only a two-phase air-water system exists. The transfer mechanism can only be

through capillary forces existing in the interface between paper and felt and through two-

phase flow, because of a pressure difference between them due to expansion.

This analysis of nip conditions confirms basic mechanisms as being the compression of

paper in the in-going part of the nip resisted by pressure in the structure and fluid flow

through paper and felt and as re-wetting in the expanding, unsaturated area in the

outgoing part of the nip, transferring water from felt to paper. The most recent findings

included are the fact that the hydraulic pressure maximum lies ahead of mid-nip, that the

sheet continues to compress after mid-nip and that both felt and paper are saturated past

mid-nip.

In most nips, felt is a necessary component. The function of the felt as expressed by

Wahlström and Wrist is to provide a structure to which water from the paper can flow in

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the in-going part of the nip and which will retain most of this water in the expanding part of

the nip. In addition, felts must be able to uniformly distribute pressure over the paper and

provide a soft nip with a controlled pressure pulse to give sufficient time for fluid flow.

Felts, therefore, are a necessary intermediary between water receptacles of holes, wires

or grooves and the paper.

Only an elastic capillary structure like felt is able to perform this function satisfactorily.

The optimum felt should give a perfectly uniform pressure distribution, lowest possible

flow resistance in the fluid flow region, and smallest possible re-wetting in the outgoing

part of the nip. As these properties are somewhat contradictory, the quality of the felt will

become a compromise to get optimum conditions for each particular application.

The mechanical pressure of fibres and hydraulic pressure of water between the fibres

oppose the force acting on the press roll. Hydraulic pressure is greater on the roll side of

the sheet than on its felt side.

1.12.2Factors influencing press water removal performance

Water is removed from the sheet by both the compressive action of the nip formed by two

contacting rolls (or a roll and a mating shoe) and the compressive response of the sheet

under transverse load. The amount of water removed is a complex function of a large

number of factors. Among them are felt characteristics, roll covers and venting, rewet, in-

going sheet moisture, basis weight, temperature, press impulse including pressure

uniformity, and furnish properties.

A list of all the possible factors involved in the stable operation of the wet press on a paper

machine is exceedingly long. The important factors in press operation are many and

include avoidance of sheet crushing; influence on sheet quality; roll crowns and cross-

machine moisture profiles; prevention of press vibration; and others.

This diversity in the identification of primary variables and an ever-growing number of

them underscore the importance of efforts to identify the relative importance of the

principal variables governing water removal in the press. The purpose of this chapter is to

sort the primary and secondary factors that influence wet press water removal from the

long list of proposed variables. However, prioritising variables is risky, as any

classification will be based on inadequate experimental data. In addition, there always

seem to be data that are purported to be the exception to the rule.

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1.12.3Primary variablesA primary variable is defined here as one capable of influencing outgoing sheet dryness

by 4% or more where large changes in the variable can be achieved. State-of-the-art wet

presses have been designed to apply principal influence over the primary factors involved

in water removal. The extent to which the press designer or the machine operator can

exert influence over a press variable will be limited by the behaviour of the materials in the

press nip (e.g. sheet, felt, and press roll performance), and by the cost-effectiveness of

the design or operating condition.

1.12.4Press loadingNip load (Newton per metre, N/m) is the first of several primary variables. Though higher

nip loading decreases felt life and increases the presses drive load, these losses are

offset by appreciable gains in moisture removal and improved sheet consolidation leading

to the development of better, more-consistent sheet strength.

However, press action is a function of nip loading per unit area (pressure) in the nip.

Moisture removal is directly related to nip pressure. The pressure varies continuously in

the machine direction within the nip; therefore it is sometimes convenient to use average

nip pressure.

A measure of nip width or uniformity of loading across the face of the press roll may be

approximated by carbon paper impressions of the loaded nip with the press at rest.

Pressure-sensitive film is also available for the same purpose and, combined loading can

be estimated from pressure gauges connected to the pneumatic or hydraulic cylinders, or

from electronic load cells.

1.12.4.1Press load uniformity

Another press loading factor that appears to qualify as a primary variable in the wet press

nip, uniformity of pressure applied to the sheet, has not yet been broadly understood or

exploited. The uniformity referred to here is not of the type associated with variations in

felt weight over a distance of a metre or of differences in pressure in the cross-machine

(CM) profile due to an improper roll crown. Rather, the scale of uniformity being

considered is over distances of a few millimetres or less.

The largest factor in nip pressure uniformity is the felt. Measurements have been made in

the laboratory with pressure transducers rotating through a press nip. The transducer has

a sensitive area of the order of 1mm to 2mm diameter. Each revolution of the transducer

through a felted nip produces a pressure profile with a different peak pressure while the

Manual 65 US 256282


residence time, or nip width, remains constant. The difference in magnitudes of these

peak pressures, all at constant press loading, is astonishingly high.

Of more interest here is whether the felt non-uniformity or non-uniform pressure

application on the micro scale affects the sheet water removal. Qualitative surface can

control sheet dryness. If felt contact on the sheet is not uniform, then a localised high

mechanical pressure at the felt-paper interface will result in localised high hydraulic

pressures in the sheet.

These localised hydraulic pressures cause the water between the fibres to migrate to

lower-pressure areas in the sheet. This lateral transfer of water results in locally

saturating the sheet in an adjacent area where it is difficult to effectively remove it to the

press felt. Greater felt uniformity generally appears to increase outgoing press solids.

1.12.4.2Machine speed

Machine speed has a strong influence on water removal in the wet press. As speed is

increased, water removal from the sheet will decrease with other conditions held constant.

The more fundamental variable, however, is time for the water removal to occur. This

generally is called nip residence time (NRT).

Machine speeds can be measured accurately, but the measurement of nip width is

subjected to variability.

1.12.4.3Press impulse

The effects of press loading and nip residence or dwell time historically have been treated

as independent variables. Evidence suggests that the product of these variables unify

their influence on overall water removal in the press.

Campbell is the earliest investigator who equated dryness or increase in outgoing sheet

consistency as being proportional to the product of pressure per unit area and duration of

press application.

1.12.4.4Sheet temperature

The temperature of the sheet as it is being pressed can have significant effects on water

removal and thus qualifies as a primary variable.

As the temperature in the sheet is raised both surface tension and viscosity of the water

decrease, which lowers the resistance of water movement through the sheet and to

ultimate removal into a felt at the press.

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Heating the sheet can save energy. Steam showers on the press and heated press rolls

are both used to heat the stock.

1.12.4.5Felt shower temperature

Higher felt shower water temperatures increase the water removal. It should also be

noted that the higher shower temperatures permit easier water removal at the felt

conditioning suction boxes.

When the temperature of water is raised, certain properties undergo significant

changes, which are of significant benefit in the pressing operation

1.12.4.6Basis weight or grammage

Sheet basis weight or grammage is another factor that alters the water removal load at the

nip and is dependent on the product line being manufactured. Variability in sheet

grammage is a major factor in water removal, albeit a predetermined and given one.

1.12.4.7Furnish properties

The furnish properties are never at a steady state although they are primary variables in

their impact. Furnish variability begins with diversity of tree species, age, and condition of

the fibre in the chip entering the pulping process. Variability in chip thickness before

cooking and the natural instability of the pulping and bleaching operations impart

variability in the pulp not present in the native fibre. Freeness, which is largely controlled

by a few percent of fines material, is inadequate to clearly predict the sheet consolidation

and press de-watering performance.

As the sheet is consolidated on the machine-wet end, comparatively minor forces are

exerted on the fibres to compact the sheet. By contrast, the wet press represents a

significant mechanical compaction. The resistances of individual fibres to collapse are

forces, which oppose sheet consolidation.

A wet mat's resistance to being compressed is related to the individual and distributed

characteristics of the fibres in the sheet. When the contact junction of two fibres is

transversely compressed in the nip, stresses are localised in the region of the fibre-fibre

crossing.

The load required to initiate fibre buckling under the instantaneous compression in a press

will depend on the wall thickness and the outside fibre diameter. Luce developed the fibre

shape factor shown in Error: Reference source not found which estimates the relative

transverse buckling load required to promote an individual fibre's collapse. Consequently,

Manual 67 US 256282


it is not surprising that even within the same species changes in the proportion of early

wood and latewood fibres, thin-walled juvenile wood fibres, or the chemical yield of the

fibres will influence a mat's response under dynamic compression. The extent to which

the mat is compressed will directly control the amount of water expressed from the sheet.

However, if hydraulic drag of water movement inside the sheet increases, as might occur

with an increase in fibre fibrillation and fines, then water removal will be retarded. Slight

changes in the ease with which water can be removed out of sheet will depend on

whether the sheet deformation is pressure controlled or flow controlled.

When a sheet is pressure controlled, little resistance is offered to the flow of water out of

the mat and the mat elastically rebounds after the sheet emerges from the nip. This rapid

rebound of such furnishes probably influences their rewet gain. However, if the fibre

deformation rate is viscously dampened and resistance to fluid flow within the sheet is

increased due to high surface area on the fibres, higher basis weight, or more swollen

components, then pressing this sheet will be more flow controlled. Flow-controlled pulps

are thought to behave like a viscous element where the sheet resists both deformation

upon entering the nip and elastic expansion once out of the nip.

1.12.4.8Felting

The wet felt is the receptor that acts as an absorptive interface between the press roll and

the sheet. The considerations on felt surface uniformity mentioned earlier can have a

dramatic effect on sheet water removal.

Felt condition and design control felt compressive properties. The elasticity of the felt

exiting the nip will control the rate and even the direction of water transfer at the sheet-felt

interface. The difference in void volume between the compressed and relaxed conditions

is a first approximation of the felt's adsorptive capacity. Perhaps more important is the

felt's void volume at the most compressed state.

Double felting has been an effective method of increasing water removal in the press.

Perrault reported the results of a TAPPI Pressing and Drying Committee survey on

experiences with double felting on linerboard machines. Many of the results indicated an

increased dryness of 4% or more. Double felting is an important, and thus a primary,

variable on heavyweight sheets. It is less effective on lightweight sheets and is less

valuable for such applications.

Manual 68 US 256282


1.12.4.9Re-wetting

Re-wetting is probably the most controversial aspect of wet pressing. It is an effect rather

than a variable in the strict sense and probably should be treated as negative water

removal rather than as a wet press variable, but most authors include it as a variable.

Post-nip rewet is a second important aspect of re-wetting. If sheet and felt are left in

contact after leaving the nip zone, a post-nip rewet can occur. Even though rates of

transfer of water back to the sheet may be falling off, the total water transferred can be

large if a long rewet time is allowed.

1.12.5Effect on paper and the paper machineThe following summarises the effect of pressing on the papermaking operation.

Higher pressures and as a result higher nip loads, result in higher sheet dryness and

either lower steam consumption or an increased production rate

Increasing dryness increases the wet web strength and reduces the possibility of

breaks within the press section

Increased pressure reduces the final paper bulk and is therefore not always possible,

unless an alternative bulky fibre is available. In the fine writing and printing sector,

increasing use is being made of Eucalyptus pulp

Increased pressure increases the tensile value up to a critical value over which there

is no change. This is due to the improved fibre to fibre bonding, which is affected by

the degree of refining

The effect on surface strength is similar to the effect on tensile

Increased pressure reduces the sheet opacity, i.e. higher show through due to the

increased fibre to fibre bonding and a reduction in the air spaces between the fibres

Due to the more compact sheet with higher pressures, the sheet is less porous, i.e.

reduced airflow for a given air pressure

1.12.6Sheet transfer and wet web strength development

The wet and very weak mat of paper must be transferred first from the forming part of the

paper machine to the press section. After pressing, it passes on to the dryer section.

Often, similar transfers are necessary within the press section itself. If the transfers don't

Manual 69 US 256282


work, no paper is made. If they fail frequently, excessive downtime occurs and the

operating economy of papermaking suffers greatly.

1.12.7Rolls of the press sectionThe press section of the paper machine can be very simple in design for low-speed

speciality machines, or very complex in design for high-speed paper production. The type

and design of the rolls of the press part play a very important part in the function of the

press.

1.12.7.1Plain press roll

The plain press roll consists of a shell body of bronze, cast iron, stainless steel, or chilled

iron, which may or may not be covered. Plain press rolls are also referred to as solid

press rolls, even though the shell body is hollow cored. The plain press roll can be

covered with rubber, polyurethane, or fibreglass material. The plain press roll is the oldest

type of press roll used in the press section. All other types of press rolls were derived

from the plain press roll.

1.12.7.2Suction roll

The first major improvement in the design of press rolls was the suction roll, which

consisted of a through-drilled bronze shell body, fitted with an internal, stationary suction

box assembly connected to a vacuum source. The vacuum connection was designed to

be from the front or rear of the roll assembly, depending upon the particular requirements.

The principle of the suction roll has not changed since its introduction into the press

section to aid in the removal of water from the paper web. The mechanics of actual water

removal in the nip have changed with the evolution of press felt design. Suction roll shells

are now manufactured from bronze, aluminium bronze, and stainless steel. The internal

components of the roll may be constructed of cast iron, mild steel with resin coatings, or

solid stainless steel.

Depending on the application, the suction roll can be operated with or without a cover

material. The style of the drilling pattern and amount of open area are dependent upon

the application into which the suction roll is to be placed.

Suction rolls are typically used in pickup, top, bottom, multi-roll, and transfer positions in

the press section. The suction roll is usually a driven roll, with the vacuum discharge

taken from the front side of the roll.

Manual 70 US 256282


Depending upon the application, a suction roll shell has an open area of 15% to 30%.

Drill pattern are carefully selected to avoid stress concentrations, as well as to provide the

optimum pattern for de-watering and low noise levels.

The application of the suction roll, grade of paper, speed, and nip load will determine the

final construction of the suction roll assembly.

For the machine speed and loading applications, some mills have opted for suction rolls

manufactured completely from stainless steel material for maximum strength and

corrosion resistance.

When designing for suction press nips, care must be taken to select the proper inlet and

outlet geometry of the nip and the type of press felt to avoid shadow marking.

The suction roll has been an integral part of the press section for a number of years.

With the advent of jumbo presses and shoe-type presses, it has sometimes been

predicted that the suction roll would vanish from the press section. This has proven false,

with the suction roll still playing an integral part in the design of modern press sections.

1.12.7.3Granite roll

A granite press roll consists of a heavy-walled, granite roll body, which is machined from

quarried block of granite. The granite roll body is fitted to steel through-shafts, tie rod

assemblies, or journal assemblies to complete the assembly.

The granite roll is a plain press roll that is in direct contact with the wet paper.

It imparts smoothness to the side of the paper with which it is in contact. Wet paper wants

to stick to a smooth surface and considerable pull or tension is needed to peel off the

paper. The non-homogeneous, yet smooth surface releases the paper relatively easily.

Granite has found widespread use in the press section, particularly in newsprint

production, because of its excellent release properties, which are now being duplicated by

manmade coverings.

Granite rolls are sensitive to thermal shock, which may cause breakage. Also, granite is

not uniform in all directions and it may expand non-uniformly, leading to press vibration.

The search for good manmade material is intense, and paper technologists should follow

new developments closely because of the promise of significant economies in press

operation.

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1.12.7.4Grooved press roll

The grooved press roll was the first variation applied to the plain rubber cover material of

a plain press roll. Grooves of a uniform depth and width, and an axial pattern, were cut

into plain rubber covers to reduce the hydraulic resistance to flow in the press nip and

consequently enhance water removal in the press nip.

Grooving is also used on press rolls with stainless steel covers, polyurethane covers, and

fibreglass covers. The pattern of the roll grooving will vary depending upon the roll

position, cover hardness, and roll supplier.

1.12.7.5Blind drilled roll

The blind drilled press roll was the next step after the grooved cover in the evolution of

rubber cover design. The principle of suction roll drilling was applied to a solid roll cover,

where the solid cover is drilled to a partial depth to provide open area similar to a suction

roll. The open area of a blind drilled roll is greater than that of a grooved roll.

1.12.7.6Combination grooved/blind drilled roll

After the grooved and blind drilled covers became accepted cover designs, the two drilling

patterns were applied to the same press roll cover to obtain the maximum benefit of open

area from both designs. This design has proven successful in several last-bottom

positions of highly loaded press positions.

1.12.7.7Self-peeler roll

Self-peeler press rolls are plain press rolls, supplied with a rubber cover material that is

designed to enhance the release of the paper web from the roll. This design is used as an

alternative to the granite press roll.

1.12.7.8Steam heated roll

The steam heated press roll is a plain press roll, designed as a pressure vessel to accept

internal steam pressure as well as an external nip load force. The steam is used to

increase the roll and cover temperature in an effort to transfer this heat to the sheet to

improve the pressing action in the nip. Increasing the sheet temperature in the press nip

lowers the viscosity of the water in the sheet and greatly improves the rate of water

removal from the sheet.

The steam-heated roll can be covered with a temperature resistant, rubber cover material,

or a special sprayed-on release material.

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1.12.8Shoe with belt type pressA departure from the use of the rolls in the press section to create a nipping action to

remove water from the sheet has led to the development of the shoe-type press. The

shoe-type press consists of a top plain press roll and a bottom, hydraulically actuated

shoe surrounded by an impervious belt. This is typically a double-felted press, designed

to provide a long nip effect at pressure levels far higher than those achievable with

conventional press rolls.

A shoe with belt type press can develop a nip that is up to seven times wider than a nip

using conventional press rolls.

Nip loads up to 42 bar have been achieved with the shoe with belt type presses to achieve

wide nips.

The greatest success to date for this press style has been on heavyweight grades such as

linerboard and corrugating medium, where high volumes of water must be removed in the

press nips at high speeds.

1.12.9Shoe with elastomeric sleeve rollIn a development similar to the shoe with belt type press, an elastomeric-covered press

roll, consisting of a fixed shaft, rotating shell, hydraulic shoe, and flexible rotating sleeve or

blanket, was conceived.

Elastomeric covers have physical properties that permit the cover to deform under the

great pressure of the press nip. This creates a wide nip, longer dwell time, and increased

water removal capability, similar to the shoe with belt type press.

The cover design is proprietary and varies with the supplier of the roll and cover. These

covers represent some of the more advanced developments in roll coverings and roll

design.

Typically, the elastomeric-covered roll will operate against a solid rubber covered roll as a

double-felted press.

1.12.10 Roll crowningThe rolls of the press must be crowned in order to obtain uniform pressing and sheet

profiles from press nips. Roll crowning is the international placement of a profile into the

outside diameter of a press roll to compensate for the deflection of the press roll, due to

externally applied nip forces and its own weight.

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1.13 Press nipsDwell time in the press nip is an important factor in press design. The selection of the

style of press roll could have a dramatic effect on operating nip width. Conventional

presses are those presses utilising roll diameters up to approximately 1.8 metres with

suction rolls, plain rolls, bind drilled, granite, or grooved rolls. Nip widths up to 40 mm are

obtainable with conventional press rolls. Jumbo presses are defined as those presses

with roll diameters up to 1.8m, which can utilise plain rolls or blind drilled rolls.

Nip widths up to 100 mm are obtainable with jumbo press rolls. Long nip presses are the

shoe type with belt presses and elastomeric covered presses. Nip widths up to 250 mm

are obtainable with long nip presses. Jumbo presses can create press nips, which are 2.5

times as wide as conventional press nips. Press nips selection is a function of sheet

grade, properties and speed. For slower-speed machines, conventional nip presses

deliver enough dwell time in the nip for satisfactory de-watering of the sheet.

As speeds increase and reduced nip dwell time becomes a critical factor, the jumbo and

long nip presses become the effective methods of maintaining nip dwell time for optimum

press performance.

As press roll technology advances, so will the operational limitations of the various roll

designs. Press roll design must stay in step with the increasing demands for quality paper

products, produced at the highest attainable machine speeds.

Manual 74 US 256282


UNIT 2: MONITOR AND CONTROL ANCILLARY SYSTEMS

Learning outcomes


Identify and describe mechanical equipment used in the forming and pressing process in terms of purpose and application.

Identify and describe electrical equipment used in the forming and pressing process in terms of purpose and application.

Identify and describe instrumentation used in the forming and pressing process in terms of purpose and application.

Identify and describe utilities used in the forming and pressing process in terms of purpose and application.

Discuss typical ancillary equipment problems within the forming and pressing process and offer solutions in accordance with workplace procedures.

Monitor ancillary systems and correct any deviations from operating parameters in accordance with operating procedures.

2.1 Instructions


SO1 AC5

SO2 AC1-6

CCFO 3, 4, 5, 7, 8

Learning materials


Act. 5

N/a N/a 00:00

Manual 75 US 256282

Sparrow Consulting © September 08 Rev.1 – Sep 08


SO1 AC5

SO2 AC1-4

CCFO 3, 4, 5, 7, 8

Lecture room

Facilitator

Multimedia

SOPs, workplace and other relevant procedures

Attend a lecture and/ or facilitated discussion on the various ancillary equipment (i.e. mechanical, electrical, instrumentation) and utilities relevant to the forming and pressing process. This includes:

Mechanical equipment e.g. bulk handling, conveying, weighing, storage, transport, packaging equipment

Electrical equipment e.g, electrical motors, switchgear, drive equipment,

Instrumentation e.g. process indicators, control valves, controllers

Utilities e.g. air, steam, electricity and cooling water

Function/ purpose

Application

Operating principles

Ex. 2

Questions

Ass. 1

Questions, sketches

and diagrams

00:00

Act. 6

SO2 AC5, 6

CCFO 1, 3, 4, 5, 7, 8

Lecture room

Facilitator

Multimedia


Attend a lecture and/ or facilitate discussion on:

Ancillary equipment problems and solutions to these problems

Process parameters

Deviations from operating parameters and solutions to these deviations

Ex. 3

Questions Ass. 1

Questions, sketches

and diagrams

00:00

Act. 7

SO2 AC1-6

CCFO2, 4-8

Lecture room

Facilitator

In a group, discuss the interaction between the various ancillary systems, utilities and the forming and pressing process and the effect of non-conformities on the final

00:00

Manual 76 US 256290



product properties e.g. strength, appearance and surface properties of the paper as identified by the workplace quality control system

Act. 8

SO2 AC1-6

CCFO 1, 3, 4, 5, 7, 8

On-site

Facilitator/ SME

PPE/ PPC

Notebook and pen


On-site, identify the main ancillary equipment and utilities and observe how these processes are monitored and controlled.

Take notes of the step-by-step procedures. Discuss your notes with a SME and draw up a checklist(s). Verify the checklist(s) for correctness.

Notes

Ass.2

Monitor & control

00:00

Act. 9Ex. 4

Checklist

SO2 AC1-6

CCFO 1, 3, 4, 5, 7, 8

On-site

SME

PPE/ PPC


Under supervision monitor and control the ancillary and utility equipment and processes per SOPs and/ or other relevant workplace procedures

Act. 10

Ex. 5

Practical

Ass.2

Monitor & control

00:00

SO1 AC5

SO2 AC1-6

CCFO 3, 4, 5, 7, 8


PoE

Facilitator/ SME

Revise the work that you have done up to this point. Make sure that you have completed the CCFO checklist and obtained the required evidence for your PoE. If there is anything that you do not understand, ask your facilitator.

CCFOs CCFOs 00:00

Manual 77 US 256290




Manual 78 US 256290


2.2 IntroductionYou should now have a very good idea of the forming and pressing process and the

equipment used in the process. However, you also need to be familiar with a whole range

of ancillary systems related to the forming and pressing process. In this unit we are going

to discuss the mechanical and electrical equipment, instrumentation and utilities that are

relevant to the forming and pressing process.

2.3 Mechanical equipmentThe mechanical equipment relevant to the forming and pressing process includes, for

example, bulk handling equipment, conveying equipment, storage equipment, transport

equipment and packaging equipment.

2.3.1 Bulk handling equipmentA variety of bulk handling equipment may be used, depending on the mill and the

requirements of the process. It would serve you well to become very familiar with all the

bulk handling equipment used in the forming and pressing process so that you know what

the purpose is of each and how it should be used correctly.

2.3.1.1 Chutes

A chute is a passage through which material goes, usually from one operation to another.

Chutes are used, for example, to move material from storage to the conveying system and

to the processing area. Chutes do not have specific forms as they purpose designed.

The figure below shows a spiral chute.

Figure 31: Spiral chute

Manual 79 US 256282


Below are a few examples of other types of chutes and their applications.

Figure 32: Examples of other chutes

2.3.1.2 Bucket elevator

Bucket elevators are used to lift bulk loads. There are three common types of bucket

elevators namely centrifugal-discharge bucket elevators, positive-discharge bucket

elevators and continuous bucket elevators.

Centrifugal-discharge bucket elevators are use for material that is fine and loose. The

buckets are loaded by scooping vessels that have spaces in-between them. The material

that is carried is discharged at the top.

Figure 33: A centrifugal discharge bucket elevator

Manual 80 US 256282


Positive-discharge bucket elevators are used to handle light, sticky or fragile material such

as sand or clay. This type of elevator is similar to a centrifugal discharge bucket elevator

but the buckets in this case is attached between a chain. The material is discharged into

a chute at the top.

Figure 34: Positive discharge bucket conveyor

Continuous bucket elevators are used for all types of material. In this case, the buckets

are close together and material is fed directly into the buckets from a loading chute. The

material is also discharged from the top.

Figure 35: Continuous bucket elevator

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2.3.2 Conveying equipmentConveyor mechanisms are used as components in automated distribution and

warehousing. This allows for more efficient transportation of raw materials such as logs,

woodchips, minerals, powders, catalyst, etc. as well as final products such as fertiliser,

paint, etc. to the warehouse. It is a labour saving system that allows large volumes to

move rapidly through a process. Conveying systems are used to transport material

upwards, downwards and horizontally over a long or short distance. There are different

types of conveyors such as belt conveyors, pneumatic conveyors and screw conveyors.

2.3.2.1 Belt conveyors

The belt conveyor is the most well-know type of conveyor and is often found in a range of

different workplaces.

A belt conveyor is a machine that is used to move large tonnages of solid materials from one place to another over paths beyond the range of any other mechanical conveyor.

Figure 36: Example of a belt conveyor

A conveyor belt or belt conveyor consists of two end pulleys, with a continuous loop of

material (belt) that rotates about them. The pulleys are powered, moving the belt and the

material on the belt on an inclined surface, either down, up against gravity or horizontally.

Manual 82 US 256282


The following figure shows the basic principles of a belt conveyor.

Figure 37: A basic belt conveyor transporting solid material

In the above figure, the belt runs between two cylindrical drums of which one (anyone) is

driven by a motor.

2.3.2.2 Pneumatic conveyors

A pneumatic conveyor uses air to move bulk materials, either from storage facilities to a

process unit, or between process units.

This type of bulk solid transport equipment moves material that is suspended in a stream

of air. This movement can either be vertically or horizontally over a short or long distance.

Different systems of pneumatic conveyors are found in the manufacturing and processing

industry. The main ones are classified as follows:

Pressure system

Vacuum system

Pressure-vacuum system

Fluidising system

The first three types are defined by the type of pressure, namely gauge pressure, that is

used to move the material. Gauge pressure is the pressure that can be seen on

measuring instruments. These instruments are called pressure gauges.

Manual 83 US 256282


Figure 38: Pneumatic conveyor systems

Pressure system

This type of system, which is also known as a positive pressure system, uses air that is at

high pressure above atmospheric pressure to deliver the material. Fans or compressors

are used to blow the air that is used to transport the material. A blower delivers air at high

pressure into the pipeline that is used for conveying material. Material is fed into this

pipeline by a feeder that is situated underneath the storage medium. The bulk material is

suspended in the air by the high velocity of the stream of air until it reaches the receiving

vessel. An air filter or cyclone separator that is situated above the receiving vessel, is

used to separate the material from the air.

Manual 84 US 256282


Figure 39: A basic positive pressure pneumatic conveying system

Vacuum system

This type of system is characterised by an air stream that has pressure less than

atmospheric pressure. In the following figure, a blower is used to suck air from the filter.

The suction continues to the conveying line. The feeder that is connected to the storage

medium feeds material into the line that is under suction. This material is pulled to the

filter where it is separated from the air.

Initially the air that is fed into the conveying line is filtered before entering into the pipeline.

Figure 40: Basic negative pressure pneumatic conveying system

Manual 85 US 256282


Pressure-vacuum system

This is a combination of the pressure and the vacuum system. The material is sucked into

the conveying pipe by the vacuum and is moved a short distance to a cyclone separator

which separates the material that is conveyed from air. Air is passed through a filter and

then into the suction side of a positive displacement blower while the solids move into an

intermediate storage tank. In this tank, material is stored temporarily. The positive

pressure is caused by the blower that is connected to the separator.

Figure 41: Positive and negative pressure pneumatic conveying systems

The non-return valve that is situated after the blower ensures that the air does not move

back to the cyclone separator.

Material is fed into the pipeline by the feeder that is situated below the storage medium

and is blown by the air that comes from the bower. Material is then moved to the

receiving hoppers.

The configuration that is shown is not the only one that is used in industry. Other

complicated configurations are also used.

Fluidising system

Fluidisation is when material is suspended (floating) on air. The material is suspended by

the air that is moving upwards. Fluidised material tends to display properties of liquids like

the ability to flow from a lower to higher level. For example, a powder that was fluidised in

a vessel would flow from a hole that is situated on the sides of that vessel through a pipe

Manual 86 US 256282


that is fitted in the hole of the vessel. This will happen, provided the pipe is not so long

that the material is completely defluidised.

The fluidising system uses the principle of fluidisation. A blower is used to blow air into

the pipeline just below the storage structure. Material that comes from the storage

medium is suspended in the air by air from the blower. Material is then moved along the

pipeline still in a suspended form to the discharge.

The fluidising system conveys material that is pre-fluidised over a short distance such as

from storage vessels, bins or transportation vehicles to the entrance of a main conveying

system.

Figure 42: A fluidised system

Manual 87 US 256282


2.3.3 Weighing equipment

Figure 43: Conveyor scale

The following figure illustrates the type of scale you might also encounter in a processing

environment.

Figure 44: Platform scale

2.3.4 Solids storage methodsOnce the production process is complete, the end products – usually solids – have to be

conveyed, and sometimes temporarily stored. Here not only dosing, flow measurement

and fill-level measurement, but explosion protection and plant safety also have to be taken

into account.

Bulk storage containers, such as bunkers, silos, bins and hoppers, and their ancillary bulk

handling equipment, are important to operations in a range of industries including, petro-

chemical, chemical, pulp and paper, agriculture, etc. Bulk containers are used in many

Manual 88 US 256282


industries to store a range of substances such as cement dust, paper pulp, plastic pellets,

farm products and fertilizer

2.3.4.1 Bunkers

A bunker is a cost effective, high volume storage system for various types of solids such

as fertilisers and pulp and paper raw materials such as wood chips.

Figure 45: Storage bunker

2.3.4.2 Silos

Silos are structures for storing bulk materials for the chemical, pulp and paper, mineral,

food, grain and plastics industries and can be constructed from steel, concrete, wood or

plastic.

Silos provide the ultimate in product protection during storage and their vertical design

allows maximum product storage in minimum space.

Figure 46: Silos

Silos are usually 4 to 8 meters in diameter and 10 to 25 meters in height.

Manual 89 US 256282


Silos can be constructed with hopper bottom, flat bottom or composite bottom, which is a

combination of both the hopper and flat bottoms.

Figure 47: A silo and its basic components

For smooth operation in conveying lines that take material from a silo, the flow from the

silo itself must be smooth and continuous.

All silos have access throughout their height so that maintenance can be done on them.

Most of the designers provide a series of vertical ladders whereas some prefer spiral

stairways. At the silo roof level, handrails and toe plates are provided for safety.

For access to the inside of the silo manholes are made at / or just above the cone (the

bottom section of a silo). This is done for inspection and maintenance of the lower parts

of the silo. One must make sure that these manholes are closed properly when the silo is

in operation to prevent material from escaping.

Silos can also be operated parallel to each other. The following figure shows silos that

are connected to each other by vents. In this way they use the same dust filter that is

located at one of the silos. In other operations each silo has its own dust filter.

Manual 90 US 256282


Figure 48: Silos operating in series sharing a common filter

Silos can be hazardous with people dying every year in the process of filling and

maintaining the silos or by falling from the ladders or work platforms.

There have also been cases of silos exploding. If the air inside becomes laden with finely

granulated particles, such as grain dust, a spark can trigger an explosion powerful enough

to blow a concrete silo apart.

Industrial silos are used to store a great variety of materials, from food products to

concrete mixture to roofing chemicals. Depending on the products being stored, silos

need to be cleaned out periodically.

2.3.4.3 Hoppers

A hopper is a wide bin-/ funnel like discharge feeder - used for holding various solids

materials - that is open on top and tapers to the bottom where it is thinner to feed into

another process system, such as a silo or conveyor system.

Figure 49: Storage hopper

Manual 91 US 256282


Hoppers are manufactured from various materials. Aluminium or steel hoppers are used

for heavy duty applications whereas plastic made hoppers are used in light duty

applications.

Hoppers are available in different shapes and sizes such as wedge, pyramidal or conical

shape as well as in bottom or tilt type. In bottom type hoppers, the materials are released

from the hopper bottom. The bottom type hopper may use augers or screws to discharge

the materials. In tilt type hoppers, materials are dumped just by tilting the hopper.

Storage hoppers can be carbon steel or stainless and round, square or rectangular in

shape, with a conical or flat bottom. Their design is such that the material can be easily

discharged from the bottom in such a way that the flow does not affect other operations

negatively.

Commercial hopper tanks are typically used in applications where routine clean-out is

required, or simply to reduce the energy and labour cost of material handling.

Hoppers are available in a variety of configurations, capacities and drive methods, such

as:

Self dumping hoppers: This type of hopper is useful in in-plant housekeeping

applications. Self dumping hoppers are used to handle heavy loads. Self dumping

hoppers can be used for forklift or roller applications.

Figure 50: Self dumping steel hopper

Conical shaped hoppers: Conical shaped hopper is a funnel shaped hopper that

flow materials. Conical shaped hoppers are available in stainless steel or aluminium.

They are more efficient than pyramidal shaped hoppers.

Wedge shaped hoppers: Wedge shaped hoppers are most often used in

mechanical engineering and chemical engineering.

Vibratory bulk hoppers

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Hoist hoppers using the standard vibratory hopper drive unit, but with the advantage

of floor level loading. This makes a large capacity hopper available, even at an

above normal height, while eliminating overhead lifting.

Horizontal belt hoppers are very similar to vibratory units but featuring a conveyor

belt in place of the vibratory tray. This is an ideal solution for either heavy parts that

would overload a vibratory tray, or fragile parts that could be damaged by vibratory

motion.

Bottom hoppers discharge material from the bottom. Bottom hoppers are used

extensively in solids handling operations and are classified into core flow, mass flow,

and composite hoppers

Hopper tanks for “dry” chemical storage are available with custom slope hoppers

designed for the desired discharge pattern

With materials that have the tendency to be cohesive (such as those having high moisture

content or fine particles) there is a coincidence of the bulk material acquiring strength to

obstruct flow. These can happen by the material “bridging “across the hopper opening.

Figure 51: Hopper and storage bin

2.3.4.4 Bins

A bin is a storage vessel used for storing and transporting both raw materials and finished

product.

Manual 93 US 256282


Cylindrical storage bins

Cylindrical storage bins that have conical bottoms and gravity discharge outlets are

commonly used in pneumatic system applications. However, material tends to stick or

flood when handled by this type of a bin.

Cylindrical storage bins are found in a range of standard sizes (diameters and heights)

that suit any locations. They can either be made free-standing or be set on columns to

make space for other equipment.

The cylindrical storage bins have the following attachments and accessories:

Manholes for maintenance, cleaning and inspection of equipment.

Ladders and platforms to provide a way to manholes and various parts of the bin.

Removable bars for safety in the manholes.

Small doors for observation of levels or level indicators and conditions inside the bin

near these small doors.

Figure 52: Cylindrical storage bins

Horizontal indoor bins

The horizontal indoor bin is rectangular with v-shaped bottom and is also used in the

pneumatic system operations. The figure following shows a horizontal indoor bin.

Manual 94 US 256282


Figure 53: A horizontal storage bin with V-shaped bottom

2.3.4.5 Bags

Bulk bags can be manufactured from paper, plastic, flat woven or circular woven fabrics

and can be uncoated or coated depending on the application and are used in just about

every industry, but most often associated with food and chemical packaging.

A bag is typically a flexible container that may be used for holding, storing or carrying

materials.

Figure 54: Bulk bags

In the pulp and paper industry, bags are for example used to store granular products such

as nickel sulphate crystals and powders such as sodium thiosulphate.

Manual 95 US 256282


The main advantages of storing the materials in bags are that the materials can easily be

loaded onto flat-bed trucks and it flows easily from the bags.

2.4 Electrical equipmentDuring the forming and pressing process you will work with a range of electrical

equipment, for example electric motors, switchgear and drive equipment.

2.4.1 Electrical motorsElectrical motors are used to convert electrical energy into mechanical motion and have a

multitude of different uses. There are two types of electrical motors, namely, an

alternating current (AC) motor and a direct current (DC) motor. An example of an electric

motor is shown in the following figure.

Figure 55: An electric motor

There are two types of AC motors, namely squirrel cage and single phase. Squirrel cage

AC motors are the most widely used constant-constant speed drives. These motors are

cheap, simple and efficient and also have a simple construction.

Manual 96 US 256282


Figure 56: Squirrel cage AC motor

Single–phase AC motors are also called synchronous AC motors and are often used to

drive smaller pumps.

Synchronous: Occurring at the same time

Direct current or DC motors have adjustable speed which means that they can be used for

a wide range of applications with variable speeds. These motors remain effective over

their whole speed range.

2.4.2 SwitchgearSwitchgear refers to devices used to de-energise equipment (i.e. to switch off the

electricity) so that work can be done on them safely and to clear downstream faults.

Switchgear consists of electrical disconnects, fuses and circuit breakers to isolate

electrical equipment. Switchgears can be placed anywhere that protection and isolation is

needed such as generators, transformers, electrical motors and electrical substations.

Below is an example of a switchgear panel.

Figure 57: A switchgear panel

Manual 97 US 256282


2.4.3 Drive equipment

2.4.3.1 Turbines

While it is true that electrical motors are also forms of drive equipment, there are also

other types of drive equipment such as turbines. Turbines are devices used to generate

electricity. There are many different types of turbines such as steam turbines and

electrical turbines. Turbines are purpose built and will therefore differ from process to

process. Below is an example of a gas turbine.

Figure 58: Gas turbine

2.4.3.2 Internal combustion motors

An internal combustion motor is another form of drive equipment. Diesel engines are

used for driving small transportable pumps. Internal combustion engines run on petrol or

diesel which makes them expensive to use.

2.4.3.3 Chain drives

Chain drives are used in instances where space is limited. They are in common use and

are often employed where the drive speed differs from the speed of the pump. Chain

drives can be used at any length.

Manual 98 US 256282


Figure 59: Chain drives

2.4.3.4 Gear drives

Gear drives are sets or systems of gears arranged to transfer rotational torque between

parts of a mechanical system.

Figure 60: Gear drives

2.4.3.5 Belt drives

Belt drives are alternatives to chain drives and are used to transfer power from the motor

to the needed mechanism.

Manual 99 US 256282


Figure 61: Example of a belt drive

2.4.3.6 Clutches

Clutches transfer power from engines to devices like drive equipment or transmission

wheels. Clutches are also useful because when they are disengaged no power is

transmitted but the engine continues to run. Clutches can be used in equipment like

cranes and hoists.

Figure 62: A multi-disc clutch

2.4.4 Electrical safetyWhen working with any electrical equipment it is essential that you practise safe work

practices. Electrical current can be the direct cause of injury to a person if it passes

through any part of the body. It can also be the indirect cause, due to its heating and

burning effects, which are manifested by electric shock, explosion, fire, and arc eye.

Electric shock can cause muscular contraction, thus increasing the period of contact. If

the current passes through the heart, it upsets its pumping action and in this case death is

almost certain. A less serious shock may cause a reaction, which results in loss of

balance and a subsequent fall, which could have serious results. In addition to causing an

Manual 100 US 256282


electrical shock, the accidental contact with live terminals may create a flash-over

between them and the consequent arc produced will dissipate considerable energy in the

form of intense heat which can cause extensive and serious burns, possibly contaminated

and vaporised metal. High frequency currents, if allowed to pass through the body, can

cause internal burns although little sensation of shock is experienced at the time.

The following guidelines will help you to work safely with any electrical equipment:

Always assume that electrical wires, switches, conductors, etc. are live and

dangerous.

Never touch any electrical equipment with wet hands or while standing in wet areas

Visually inspect all electrical equipment before use: especially check for exposed

wires and worn electrical cables and take any defective equipment out of service.

Ensure that power supply systems, electrical circuits and electrical equipment have

been grounded.

2.4.5 Isolation of electrical, hydraulic and air driven machines or equipment

No person is allowed to work on any machine or equipment, unless it is properly

isolated.

Only a qualified electrician or millwright or a person who has been authorised to do

so in writing can do isolation of electrical driven machines and equipment.

Air-driven and hydraulic machines (equipment) can be isolated by qualified

millwrights, fitters or a person who has been authorised to do so in writing.

Lockout and/or permit to work procedures should be adhered to.

2.5 InstrumentationThere are four basic instrument types which are frequently used in process plants,

namely:

pressure instruments

temperature instruments

flow instruments

level instruments



Figure 63: Types of instruments

In the forming and pressing process you also have to be familiar with the working of key

process indicators, control valves and a range of different controllers that are used to

monitor and control the process.

Apart from these instrument types, there are also a number of other instruments that

measure variables on a pulp and paper mill; some of which use very complicated

instruments.

Examples of these variables that need to be measured are:

Concentration - the amount of a substance in a specific volume liquid or gas.

Humidity - the amount of moisture in the air.

pH - a measure of the acidity of a substance.

Viscosity - a measure of how easily or difficult a fluid flows.

2.5.1 Key functions of instrumentationWe can illustrate the function of instrumentation by using the following example: John

wants to take a bath. Before he opens the tap, he decides that he only wants the bath to

be half full. Thus he marks the half-full point. Then he opens the tap and looks at the

water as the level in the bath rises. When the water reaches the ½-full mark, he closes

the tap.

This example illustrates the connection between the role instruments play in a process

and the way a person uses his or her senses in daily circumstances. The following points

illustrate this connection:



Instruments measure the value of a process variable (e.g. pressure, temperature,

flow or level) that we want to know. John measures the level of the water by looking

at it.

The measured values are indicated on a gauge and stored or recorded on paper so

that we can use it when required. In the same way, John can record (remember or

even write down) the level of the bath.

The measured value can then be compared to the value that we aim to reach. The

value that we aim for is called the set point. In John’s case, the set point (his aim)

may be a half-full bath.

If we compare the measured value with the set point, it will tell us whether we should

take action, for example change something or leave it as it is. In John’s example, he

will compare the bath level with his set point of half-full. While the bath is still below

the half-full mark, he will not take any action, but as soon as it reaches the half-full

mark, he will close the tap. Adjusting a process based on the comparison between

the set point and the actual value is called process control.

Our example shows the four key functions of instrumentation:

Measurement

Indication, storage or recording of the measurement

Comparison of the measured value with the set point

Applying process control

2.5.2 Methods of displayWe want to identify the value that is measured by an instrument. For this reason, there is

something called a display which shows the value in such a way that we can interpret and

understand the reading.

Displays might be digital, or analogue.

2.5.2.1 Digital display

A digital display is a numeric display, or in other words, a series of numbers, like the

distance indicator on a car. This means that it shows a number that is equal to the value

of the measured variable at the moment. A digital display only shows the value of the

measurement at certain times. These times will have a fixed gap in between. The display

therefore changes every second (depending of what the time interval is). The following

figure shows some examples of digital displays.



Figure 64: Digital and analogue displays

2.5.2.2 Analogue display

An analogue display is a display that indicates the value of the variable with a pointer or

needle on a scale that may be horizontal, vertical or circular. It shows the value of the

measurement at every instant in time (continuously). The analogue display will therefore

change smoothly; it does not jump through the values as a numerical display.

2.5.3 How to read a gaugeWhen taking any readings off the display, it is important to do it using the right technique.

A gauge reading must always be read face on or at the same height as the display, and

not at an angle.

With some gauges (especially analogue displays) the pointer or mark is not level with the

numbering on the display. When reading this at an angle, the wrong value ends up being

aligned with the mark. Exactly the same happens when reading a liquid level in

glassware. Because the level rises slightly against the side of the glass, it is important to

have your eyes level with the liquid level.



Figure 65: Your eyes should always be level with a gauge

Some machinery with mounted gauges vibrate. These vibrations can cause the needle to

jump around. To protect the gauge and make gauge readings easier the gauge should be

fitted with a damping adaptor or the gauge can be filled with oil. If the needle still jumps

around too much, it is best to take an average reading. This means that we take a

reading in the middle of the values that the needle vibrates between. When the needle

jumps between zero and a reading, like with a pulsating pump, the bigger value must be

reported.

The following figure shows an analogue pressure gauge. The X100 in the middle of the

gauge means that any value read from the gauge should be multiplied by 100. This is

done to get the reading in the units indicated on the gauge (kPa). If, for example, the

needle points a value of 6.6, the actual value is 660 kPa.

Figure 66: Analogue display with X100 on the display



When recording the reading (writing it down or filling it in on a sheet), you must never

report more significant numbers (the numbers that show the value of the reading) than

necessary. If a gauge is accurate to only 1 unit, it doesn’t make sense to write down a

reading with a value of 4.542 for example, because the gauge cannot accurately measure

a value of 4.542. This reading will just be reported as 5 (rounding the value up). The

amount of significant numbers that the gauge is calibrated in (marked in) shows how

many numbers should be reported.

2.5.4 Control valvesValves are used to regulate the flow of liquids and are similar to household taps. Valves

can be use to open or close the path of flow, to direct the flow, to regulate the speed of the

flow and to regulate the pressure of fluid inside a pipe. There are many different types of

valves available, depending on the use. Each different kind of valve has its own

advantages and disadvantages as well as specific applications. In your plant environment

you will learn about all the different types of valves on the plant along with their

advantages, disadvantages and use. Below are examples of various kinds of valves.

Figure 67: Various valves

2.5.5 ControllersControllers are used to control applications. There are many different types of controllers,

some of which only have on and off buttons or speed control and others that have a



multitude of controls. Controllers may also be installed into panels where they may be

used to control entire systems that are monitored trough valves that are either on the

control panel or at the device being controlled or monitored.

Figure 68: A control panel

It is your duty to become familiar with all the instruments that you have to work with so

that you are confident that you can read them accurately.

2.6 UtilitiesThe processing industry requires utilities (services) like air, steam, electricity and water to

be able to convert raw materials into a final product.

In this section, we will be looking at the types of energy and services required in the pulp

and paper industry.



2.6.1 Compressed air supplyCompressed air has a wide range of industrial applications, each with specific

requirements concerning the quality of the air. For example, instrument and control

systems need air at a relatively low pressure but free from water, oil and dirt. If an air

consuming unit is to achieve optimum performance and maximum working life, the

compressed air must be properly prepared.

The properties of the air are normally measured in terms of:

Pressure

Dryness

Purity

Lubricant content

The proper maintenance of the distribution network is essential if the system is to be

efficient and reliable. All piping, valves, hoses and connections must be in good condition

to ensure undisturbed air delivery. The following are key elements of an efficient and

reliable system:

Correct air pressure at points of consumption

Minimum air leakage

Adequate flow rate

Correct air quality

2.6.1.1 System components

A compressed air system consists of two main items – the compressor centre and the

distribution networks. There are normally two independent networks, one for

instrument air and the other for process operating air.



Figure 69: Compressed air networks

The compressor centre consists of the following:

Oil free compressor

Desiccant dryers

Refrigeration air dryer

Air receivers

Dust filters

Instrument air is used for the remote opening and closing of valves and controlling a

range of other equipment in the plant. Without air to this system, it is impossible to control

the plant from the control room.

The supply of instrument air is always given priority and controlled by a regulator. Should

there be a drop in air system pressure, the system will first cut back on the supply of

process air in order to maintain control of the plant instruments with the remaining

instrument air.

Process air is the air physically used in the process itself – for example the air used in

chemical reactions.

The process and operating air is dried in a refrigeration dryer and led to an air receiver before being distributed to the points of consumption. The instrument air is led via a

desiccant dryer and dust filter to another air receiver.



When compressed air is cooled, its ability to retain water is reduced. In the refrigeration

dryer, the air is cooled to about 2C at which temperature most of the water condenses.

The temperature at which water begins to condense is called the dew point of the

compressed air. The condensed moisture is collected and removed.

Desiccant dryers eliminate moisture in the instruments and control valves. This drying is

done by absorption. Water vapour in the compressed air is attracted to the surface of

solid absorbent materials (desiccants). The desiccant used is usually silica gel. This

method of drying produces the compressed air with the lowest dew point. Absorption

dryers handle only water vapour. Silica gel is reactivated by oven drying to drive off the

absorbed moisture.

Silica gel used as a desiccant is treated with a dye that is blue when the silica gel is dry

and pink when it needs regenerating.

2.6.2 Steam systemsSteam is used extensively in two main areas of pulp and paper manufacturing:

To provide the heat necessary for pulping wood chips

Drying of pulp and paper

2.6.3 Steam generationIn most cases steam is produced by burning coal, oil or gas but is sometimes produced

electrically. Steam is produced in two ways which are unique to the pulp and paper

industry. They are:

The burning of waste liquors

Burning of bark and wood waste

A boiler system provides the means for converting fuel energy (chemical energy) into

steam (heat energy). Steam is a very efficient form of energy to perform work and

transfer heat. It can also be converted into electrical energy by means of a turbo-

generator (electrical energy).

The following figure shows a typical flow distribution for steam in an integrated pulp and

paper mill.



Figure 70: A steam system

2.6.3.1 Waste boiler

The boiler itself consists of a series of drums and tubes which hold and transport water

and steam under pressure. A boiler system includes a furnace (where the fuel is burned).

Forced draught and induced fans are used for controlling combustion air.

Boilers are manufactured in many sizes depending on the required pressure, temperature

and quantity of steam to be produced. There are two types of boilers, the water tube and

the fire tube.

Most boilers are of the water tube design where water circulates within tubes and heat

transfer occurs from the hot gases on the outside of the tube to water inside the tube.

Water is heated in the tube nearest the furnace bed and then rises to the steam drum

where vapour is separated from the water. The water travels down connecting tubes to a

lower drum, called a mud drum. Here sludge formed from the concentration of mineral

impurities is removed by "blowdown".

A super heater is used to raise the temperature of the steam to some specified level

above the normal boiling point of water (100C). This “super heated” steam is used by

turbine generators.

2.6.4 Steam applicationsSteam is utilised in the pulp and paper industry in the following ways:



Paper, board and pulp drying.

Heating chips in TMP refiners, heating chemical pulp digesters.

Electrical power generation.

2.7 Mill cooling waterCooling water in a pulp, board and paper mill serves many purposes. As the name

implies it is a cooling medium. This water is used in ventilating systems, cooling of pump

glands, condensing flash steam and turbine condensers.

In a cooling water system, the product or process being cooled is the source of heat and

the cooling water the receiver. Cooling water does not usually have direct contact with the

source. The two materials are normally separated by a barrier that is a good conductor of

heat, usually metal. The barrier that allows the heat to pass from the source to the

receiver is called the heat transfer surface. The barrier is a containment vessel and is

called a heat exchanger. Most sources and receivers in heat exchangers are liquids. If

the source is steam or another vapour that is liquefied the heat exchanger is called a

condenser. If the source is a liquid that is vaporised the exchanger is called an

evaporator.

Once the receiver has done its job in having cooled the source, it contains heat. This heat

now needs to be removed again and the water cooled for reuse. In the pulp and paper

mills an open recirculation system is used. In this system cooling towers or evaporation

ponds are used to dissipate (remove) the heat it has absorbed from the source. In this

process, water from the cooling tower basin passes through the process equipment that

needs cooling, then returns the warm water through the evaporation unit (cooling tower)

where the water is cooled. A certain amount of water evaporates. To replace this loss,

fresh water is used as a make up to the cooling tower basin or pond.

Cooling towers are designed to evaporate water by bringing the water into contact with air.

Cooling towers are classified by the method of induced air flow, either by counter flow or

cross flow, depending on the flow of the water. Induced draft cooling towers are either

counter or cross flow with fans on top pulling cooling air up through or horizontally across

the falling water.

The following figure shows a flow diagram of a typical water system for an integrated pulp

and paper mill.



Figure 71: Cooling water system

2.8 Electrical powerElectrical power in pulp and paper mill operations may be a combination of purchased

power and self generated power. However, small operating mills often depend only on

power supplied by the national electricity grid.

The following figure shows how electricity is distributed in an integrated pulp and paper

mill. Electricity is brought into the mill from the national electricity grid, and/or it can be

produced in the mill from the steam from power boilers. Steam is fed to turbo-generators

that produce electricity for the processes.



Figure 72: Electricity distribution

Electrical energy is a very expensive commodity and all operations endeavour to use the

electrical energy produced, or purchased as efficiently as possible.

2.9 Monitor the ancillary systemsTo monitor and control the ancillary systems you need to understand the following

terminology:

Parameters,

Variables

Deviations

2.9.1 What is a parameter?A parameter is a value for a variable that is kept constant to measure a process. When

a process is monitored over time, the variables are adjusted and the parameters are kept

constant.

A parameter can also be described as conditions, guidelines, settings, measurable characteristics, features, fixed boundaries or limits.



2.9.1.1 Why should parameters be monitored?

Quality in the process industry means that the finished product meets the requirements that are set out for it at all times. In every phase of the production process, quality and

costs need to be controlled from the moment the raw product enters the production

process until the finished product is sent to the customer. Defective products are one of

the main factors that increase cost.

Every pulp and paper mill aims to produce quality products at the lowest possible cost.

Product parameters should thus be monitored to keep quality consistently high and to

keep costs low.

2.9.2 What is a variable?A variable is a measurable characteristic that can change during a process. Examples of

variables are temperature, pressure, flow, input materials and environmental conditions.

A process variable is the current value of a variable in a controlled process, for example;

the temperature of a furnace. Variables thus need to be controlled to ensure that the

process produces quality products.

Variables can also determine how smoothly the process will run. An increase in

environmental temperatures might cause a cooling process to happen with more difficultly

as the process has to work harder to compensate for the rise in temperature.

2.9.3 What is a deviation?A deviation is the difference between an observed value and the expected value of a

variable or function. Deviation can be either positive or negative, this means that the

deviation is either larger (positive) or smaller (negative) than what is should be. If there is

too much deviation, the quality of the product will suffer.

2.9.3.1 What can cause deviations?

Even though a process normally consists of a specific series of operations, the following

factors can influence it.

People. Different operators might perform specific operating tasks in different ways.

These differences, however small, can cause variations in the process.

Material. If the raw material differs slightly from what is normally used, there might

be certain variations in the process.



Equipment can influence a process. If machinery doesn’t work properly, it can

cause deviations.

Environment. Factors such as temperature can influence the process. On a very

hot day, the cooling capacity of certain steps in the process might be much lower

than usual.

The requirements of the end product. If the requirements are more restrictive, it

may be more difficult to produce a product that meets all the specifications.



UNIT 3: PROCESS MATERIALS

Learning outcomes


Explain the properties of process materials in terms of key characteristics.

Explain the purpose of process material quality control procedures as well as the consequences of not adhering to these procedures with regards to the impact thereof on the final product produced.

Explain the quality requirements of raw materials, process water, chemicals and additives or other materials according to general and workplace specifications.

Discuss typical raw material problems and its impact on the final product properties and costs.

Discuss corrective action to be taken in the case of non-conforming raw materials in accordance with workplace procedures.

Evaluate product variations and take corrective action in accordance with workplace procedures.

3.1 Instructions


SO3 AC1-6

SO4 AC2, 4

CCFO 1, 2, 4-8

Learning materials


Act. 11

N/a N/a 00:00

SO3 AC1-6

SO4 AC2, 4

Lecture room

Facilitator

Attend a lecture and/ or facilitated discussion on:

Industry terminology such as specifications,

00:00




CCFO 1, 2, 4-8

Multimedia

Quality policies/ procedures

variations and deviations, properties, characteristics, etc.

Process materials, i.e papermaking stock and the wet, pressed paper, board or tissue, products (including papermaking stock and the wet, pressed paper product) and chemicals forming part of the forming and pressing process.

The purpose of quality control procedures as well as consequences of not adhering to these procedures ito impact on final products.

Ex. 6

Questions

Ass. 1

Questions, sketches

and diagrams

Act. 12

SO3 AC1-6

SO4 AC2, 4

CCFO 1, 2, 4-8

Lecture room

Facilitator

Multimedia

Specifications

SOPs and other relevant workplace procedures

Attend a lecture and/ or facilitated discussion on raw materials:

Papermaking stock and the wet, pressed paper, board or tissue properties in terms of key characteristics

Quality requirements of papermaking stock and the wet, pressed paper, board or tissue

Specifications defined by machine or mill operating instructions. Specifications may include, but are not limited to fibre properties, additive contents and concentrations, particle size and shape

Raw material problems are problems associated with the properties of pulp, fillers and chemicals

Corrective action to be taken in the case of non-conforming papermaking stock and the wet, pressed paper, board or tissue

Ex. 6

QuestionsAss. 1

Questions, sketches

and diagrams

00:00

Act. 13




SO1 AC6

SO3 AC6

CCFO 1-8

Lecture room

Facilitator

Multimedia

Specifications


Attend a lecture and/ or facilitated discussion on chemicals and additives

Functions

Properties in terms of key characteristics

Quality requirements of chemicals and additives Ex. 7

Questions

00:00

Act. 14

SO3 AC5

SO4 AC4

CCFO 1-8

Lecture room

Facilitator

Multimedia

Specifications


Attend a lecture and/ or facilitated discussion on final product:

Product properties such as strength, appearance and surface properties of the paper as identified by the workplace quality control system

Quality requirements of final product

Product variations/ deviations such as freeness/wetness, porosity, formation, tensile, tear, burst, fold, deckle, calliper, smoothness, grammage, moisture, roughness, ash, opacity, strength, tensile energy absorption, scuff resistance, softness where applicable to paper, board or tissue.

Corrective action to be taken in the case of non-conforming final product

Ex. 8

QuestionsAss. 1

Questions, sketches

and diagrams

00:00

Act. 15




SO4 AC2

CCFO 1-8

Lecture room

Facilitator

Multimedia

In groups, discuss the impact of process variables on the product properties in terms of final product and cost. Process variables include but are not limited to machine speed, flow, drying capacity, pressing capacity, chemical addition rate, consistency, vacuum, wetness/freeness, process pH and temperature where applicable to paper, board or tissue

Act. 16 Notes

00:00

SO3 AC1-6

SO4 AC2, 4

CCFO 1, 2, 4-8

On-site

SME

PPE/ PPC


On-site, observe the various raw materials, chemicals, additives and products applicable to the process. Make a list of possible problems and corrective actions.

Also make sure that you know where you can find the various specifications and quality standards.

Notes

Ass.2

Monitor & control

00:00

Act. 17Ex. 9

Checklist

SO3 AC3-6

SO4 AC2, 4

CCFO 1-8

On-site

SME

PPE/ PPC


Under supervision, monitor the material and product specifications and identify and correct problems as per SOPs and/ or other relevant workplace procedures

Act. 18Ex. 10

Practical

00:00

SO3 AC1-6

SO4 AC2, 4


Revise the work that you have done up to this point. Make sure that you have completed the CCFO checklist and obtained the required evidence for your

CCFOs CCFOs 00:00




CCFO 1-8 PoE

Facilitator/ SME

PoE. If there is anything that you do not understand, ask your facilitator.




3.2 IntroductionBefore we discuss the quality requirements of the process materials entering the forming

and pressing process, we should first discuss the general principles of a quality

management system so that you can understand how important it is.

3.3 What is a Quality Management System?Most companies implement quality management systems

that meet international standards. The international

standards are generally referred to as ISO standards. The

ISO standards were developed from the system

implemented by the International Organisation for Standardisation and this is also what the acronym refers to.

When a company meets the ISO standard for quality

management systems, it means that they have a system in

place to control quality that will assure that the required standards are achieved all the

time.

A quality management (QM) system includes quality control (QC) and quality assurance

(QA), as shown in the figure below.

Figure 73: Relationship between the different levels of quality

3.3.1 Quality controlQuality control is used during the production of products. It includes control measures

and various techniques and activities to measure product quality against specific


Sparrow Consulting © January 2009 Rev.1 –Jan 09

standards. The aim of quality control is to provide quality that is satisfactory, adequate,

dependable, and economic.

Quality control means that a product is inspected, tested or analysed to see how it

measures up to the quality standards or specifications. Products that do not conform to

the desired product standard or specifications are rejected as non-conforming products.

This means that the quality of a product is determined at a specific stage in manufacturing

by taking samples of the product to determine whether the batch conforms to

specifications. If the sample does not meet the required standards, the batch is rejected

and corrective actions are taken to ensure that a good quality end product is produced.

The corrective actions might include a re-work of the product, i.e. the product might go

through the system again to see if the problem can be fixed. Sometimes the problem

cannot be corrected and this can lead to a total reject resulting in the product being

discarded (thrown out). In essence, quality control asks the question “Are we doing

everything correctly during all the production stages?”

3.3.1.1 Setting of standards

Setting of standards (as part of quality control) is one of the first steps of managing

quality. Setting of standards can become quite a complex matter in the pulp and paper

manufacturing industry.

The following factors all play a role in setting the quality standards:

Products must meet standards specified by law.

Products must meet standards set by the South African Bureau of Standards (SABS

Codes)

Products must meet standards set by various international bodies

Products must satisfy the market requirements or the standards set by the consumer

Setting of standards alone however will not ensure that we achieve the quality we aim for.

We need to do more than this. A business must also develop a system to manage quality.

This system must focus on all the different factors that ensure that we achieve the quality

standards we aim for. It is also not acceptable if the desired quality standard is achieved

some of the time. We must do better than this and achieve quality standards all the time. Such a quality management system will be made up out of many controls and

policy and procedure documents that will ensure that we meet the desired quality

standards.



3.3.2 Quality assuranceThe term “assurance” can be explained as a promise or reassurance that something is

right.

Quality assurance is a management function which includes quality control measures.

Quality assurance can be described as the management processes that provide us with

confirmation or assurance that our quality control measures are in fact working. The

answers we get through quality assurance must tell us that we are producing products to

the required standard that meet the need of the customer. Quality is more than only doing

things right, it also asks if we are in fact doing the right things, the things the customers

expect from us. Quality assurance provides us with these answers.

Quality shows us whether an item or process measures up to the expected requirements.

Quality assurance is those actions that measure whether quality was in fact achieved.

Quality assurance is made up out of various management controls; checks and tests that

prove to us that our quality control measures are working, and in fact ensuring that the

products we produce meet the required standard.

It can be said that quality assurance prevents mistakes, whereas quality control detects and corrects mistakes.

3.3.3 Quality managementQuality management is the overall management function that ensures that Quality Control

and Quality Assurance together with all the other organisational policies and procedures

are implemented in the workplace. Quality Management can also be described as the

general management function which lays down the quality policy, aims and

responsibilities. Quality Management also includes the planning and control of quality and

ensuring and improving the quality.

3.4 The quality standards of process materialsIt is important to remember that the term “process materials” refers to all the raw

materials, process water, products, chemicals and any additives or other materials

forming part of the forming and pressing process.

The quality of the raw materials and ingredients used in the manufacturing process has a

major influence on the quality of the final product. If we are using poor quality raw

materials or ingredients we will never manufacture a good quality final product.



Remember the saying:

3.4.1 Quality of raw materials and ingredientsThe raw materials and ingredients must always conform to quality specifications. Raw

material and ingredients should always be tested and inspected at receiving in

accordance with quality control procedures. It is also common practice to insist on a

quality certificate from the supplier as proof that it is of good quality.

3.4.2 Quantities of raw materials and ingredientsWhen manufacturing a product the correct quantities of raw materials and ingredients

should be used as indicated by the product specifications. Quantities of raw materials

used will influence the composition (make up) and the effectiveness of the final product

being manufactured. If the correct quantities are not used the product will not conform

and be of poor quality.

3.4.3 ContaminationPoor quality products will be the end result if the raw materials or final products are

contaminated. Contamination is when your product comes into contact with something

that spoils the quality of the product, foreign matter like metal shavings in a liquid product.

Chemicals used as raw materials or ingredients must also be pure. Therefore there

should be strict control measures during the manufacturing process to prevent

contamination. You don’t want a white paint to be contaminated with a red dye which will

spoil it.

Make sure that you understand the quality control measures and procedures that are

followed by your workplace to ensure quality raw materials and ingredients at all times.

3.4.4 Raw material problemsYou may encounter problems with the forming and pressing process that are directly

related to the quality of the incoming material. In such a case you must ensure that you

are very familiar with the properties of acceptable raw materials. You must also make

certain that you use the correct workplace procedures to reject the raw materials.

In the same way you must ensure that you are familiar with the quality standards that the

outgoing products must meet.



3.5 Consequences of poor quality control

3.5.1 Consequences for the customersQuality control always seeks to keep the customer happy. We have to be very clear on

who our customers are. Customers can be divided into two groups:

Internal customers

External customers

3.5.1.1 Internal customer

Every section or department in a production line produces products or renders services

used by the other departments or sections as inputs into their production activities. These

departments or sections rely on the quality of your products or services. These sections

or departments are your internal clients. If you do not meet their standards, they will not

be able to do their work to the quality standard expected from them. This will also result in

poor production. Production targets can only be achieved if every section in the

production chain performs to the expected standard. Non-conformance to quality

standards in one section has an impact on the ability of the rest of the production chain to

meet their targets.

In the same manner we all have internal suppliers. Those colleagues on whom we rely for

inputs in order for us to do our work. We are their internal customers.

Will you be able to do our work to the standard expected from you if the colleagues you depend on do not meet their standards? Does the same hold true for the colleagues that depend on you?

3.5.1.2 External customers

We produce products for a specific market and specific customers who purchase our

products. We must have a clear understanding of who these customers are and what

their expectations are.

External customers will expect products and services from us that meet standards such

as:

Products that meet technical specifications

Product packaging that meets specifications

Delivery on time



Delivery of their complete order

Delivery of the volumes they ordered

Delivery at the price they were quoted

In many instances, external customers depend on the quality of our products or services

for the success of their own business ventures. In the same way we also depend on our

suppliers for the success of our business. We are seen as suppliers by these customers

and we must meet their quality specifications. The quality control function in a

manufacturing business will establish clear communication channels with the customers.

Any quality problems or questions experienced by the customer will be channelled to the

quality control function and corrective measures will be taken to correct the situation to the

satisfaction of the customer.

What do you think will happen if we do not satisfy the needs of our external customers? Will you continue to support a specific product or business if your needs are not satisfied?

3.5.2 Consequences for the organisationIf the quality of products and services rendered by a workplace are not properly controlled,

the general efficiency of, and the ability of the organisation to stay in business can be

seriously affected.

Quality control measures that are poorly executed or managed can result in:

High costs to correct errors during manufacturing e.g. by re-working or rejection of

the product.

Lower productivity as the staff are re-working products and not manufacturing new

products.

Lower sales and less profit as their external customers take their business elsewhere.

An unhappy external customer can do a lot of damage to a company by “word of

mouth”. (Telling other potential customers of the poor quality products sold).

Contamination or pollution of the natural environment resulting in serious

consequences and expenses to rectify the situation.



3.5.3 Consequences for the individual and colleaguesWorkplace where quality problems are regularly experienced will find that the general

morale of the work teams and of individuals are low. This means that the employees will

not be motivated to work hard and do their best.

One member in a work team that does not comply with the expected quality standards can

mean failure for the whole team.

If a company has experienced financial losses due to poor quality control the people

working at the company may not have job security which will lead to low morale amongst

all employees.

3.5.4 Consequences for the community

Figure 74: Air pollution caused by the pulp and paper industry

If quality control in a company is poor there will be many defects and non-conformances

during manufacturing. One way to correct non-conformances is to reject the product

which will lead to a great deal of unnecessary expense and a loss of profits.

Pulp and paper mills all produce effluent and waste that has to be treated before the

material is released into the natural environment or discarded of. The effluent and waste

material pose specific hazards to the environment and can result in serious pollution

problems if not managed. Specific quality control measures should be applied by the

workplace to control effluent and waste treatment to ensure that the operation does not

have a detrimental impact on the environment and the community directly affected by the

pulp and paper mill.



UNIT 4: MONITOR AND CONTROL THE FORMING AND PRESSING PROCESS

Learning outcomes


Monitor the forming and pressing process and record parameters in accordance with workplace procedures.

Explain the impact of process variables on the product properties in terms of final products and costs.

Discuss typical equipment problems within the forming and pressing process and offer solutions in accordance to workplace procedures.

Evaluate variations in the product and take corrective action in accordance with workplace procedures.

4.1 Instructions

Ref. No Resources Learning Methodology Workbook Assess Tim

e

SO1 AC5

SO2 AC1-6

SO4 AC3

CCFO 3, 4, 5, 7, 8

Learning materials

Read through Unit 4 of the learning materials and/ or refer to the generic learning materials on forming and pressing paper, board and tissue. Make notes of things you do not understand and/ or need more information on and discuss it with your facilitator. Act. 19

N/a N/a 00:00

SO1 AC5 Lecture room

Facilitator

Attend a lecture and/ or facilitated discussion on the main equipment relevant to the forming and pressing

00:00




e

CCFO 3, 4, 5, 7, 8

Multimedia


process. This includes:

Types and components

Function/ purpose

Application

Operating principles

Ex. 11

Questions, sketches

Ass. 1

Questions, sketches

and diagrams

Act. 20

SO4 AC1, 3

CCFO 1, 3, 4, 5, 7, 8

Lecture room

Facilitator

Multimedia


Attend a lecture and/ or facilitate discussion on:

Equipment problems and solutions to these problems

Process parameters and variables.

Deviations from operating parameters and solutions to these deviations

Recording process parameters

Ex. 12

Questions, Ass. 1

Questions, sketches

and diagrams

00:00

Act. 21

SO4 AC2

CCFO 1-8

Lecture room

Facilitator

Multimedia

In groups, discuss the impact of process variables on the product properties in terms of final product and cost. Process variables include but are not limited to machine speed, flow, drying capacity, pressing capacity, chemical addition rate, consistency, vacuum, wetness/freeness, process pH and temperature where applicable to paper, board or tissue

Act. 22Notes

00:00

SO4 AC1, 3, 4

CCFO 1, 3,

On-site

Facilitator/ SME

PPE/ PPC

On-site, identify the main forming and pressing equipment and observe how the process is monitored and controlled.

Notes Ass.2

00:00




e

4, 5, 7, 8 Notebook and pen


Also observe how to evaluate variations in the product and take corrective action.

Take notes of the step-by-step procedures. Discuss your notes with a SME and draw up a checklist(s). Verify the checklist(s) for correctness.

Monitor & control

Act. 23Ex. 13

Checklist

SO4 AC1, 3, 4

CCFO 1, 3, 4, 5, 7, 8

On-site

SME

PPE/ PPC


Under supervision, monitor and control the forming and pressing process as per SOPs and/ or other relevant workplace procedures

Act. 24

Ex. 14

Practical

Ass.2

Monitor & control

00:00

SO1 AC5

SO2 AC1-6

SO4 AC3

CCFO 3, 4, 5, 7, 8


PoE

Facilitator/ SME

Revise the work that you have done up to this point. Make sure that you have completed the CCFO checklist and obtained the required evidence for your PoE. If there is anything that you do not understand, ask your facilitator.

CCFOs CCFOs N/a

Total time allocated for this activity (00h00) 30:00



Practical - Monitor and control the forming and pressing of paper, board or tissue


All SOs, ACs and CCFOs

On-site

SME

PPE/ PPC


Work under an experienced worker (SME) and apply all the procedures you have learned. When you feel competent that you have acquired the expected knowledge and skills, you can apply for the summative assessment. You will be assessed on your ability of:

Monitoring and controlling the various ancillary systems

Monitoring and controlling the quality standards of process materials

Monitoring and controlling the forming and pressing process

Recording parameters in accordance to workplace procedures

NOTE: Throughout the above procedures you should comply with relevant health, safety and environmental standards

Act. 25

N/a Ass.2

Monitor & control

00:00

Total time allocated for this activity (00h00) 55:00



4.2 IntroductionThere are no hard and fast rules that apply to how you monitor and control forming and

pressing process. Having said that, however, you should remember that there are a

whole range of workplace instructions and procedures that you have to adhere to while

doing your job.

In this unit we will discuss some of the factors that will help you work more efficiently.

4.3 Normal operating conditionsNormal operating conditions can be defined as the range of operating conditions within

which a device is designed to operate and for which operating limits are stated.

The main responsibility of a machine operator is to make sure that the machine performs

according to specified requirements, ensuring normal operating conditions. Although this

basic responsibility has not changed in recent years, factors such as technological

advancements and government regulations have resulted in significant changes in facility

requirements. Processes, equipment and policies have also changed to the point where

an operator's actions can have an increasingly significant effect on the total mill

operations.

By understanding and following standard operating procedures, as well as detecting and

correcting abnormal operating conditions, you can help to prevent problems that could

result in personal injury or equipment damage. Remember, you as an operator, perform

an important function to ensure the success of the whole operation. In most respects,

operators are the eyes and ears of process facilities.

4.4 Maintaining process variablesSome of an operator's responsibilities, such as maintaining process variables within

narrow ranges and maintaining logs, apply to both batch and continuous process

operations. In some processes, it is essential to maintain certain process variables, such

as pressure or temperature, within close limits. If process variables are outside these

limits during system operation, the product could be of low quality or completely ruined.



4.5 Deviations from normal conditionsTo make sure that a process produces quality products, control limits are set and various

controls used to show an operator when a process comes too close to these limits as well

as the corrective action that he/ she needs to take before any problems occur.

Control limits: calculated statistical points which form boundaries within which a process should be managed.

To reduce deviation in a process, you have to keep the process stable. When a process

is stable, the products will be produced to the same specifications most of the time. The

reason why the term “most of the time” is used, is because it is almost impossible to

produce a product that is exactly the same all the time. Factors like temperatures, the

specific operator’s actions and small changes in the raw material can affect the process.

These small changes are called “common cause deviations”. So it is normal for a process

to be constantly changing.

However, stable processes are much more valuable as it helps to reduce the total

deviation in the process and make the process more predictable.

After achieving stability in a process, the next step is to make sure that the deviations that

occur are safely inside the specified limits, making it thereby a capable process.

4.5.1 Detecting problems in a processA little deviation in a process is normal, but as soon as it exceeds certain limits, the

deviation becomes harmful to the company or customer. This is called an abnormal

deviation which is another way of saying that a problem has occurred in the process.

Abnormal deviations can have disastrous effects on the quality of your product, and have

to be corrected as quickly as possible.

Your workplace must have procedures and work instructions on how to deal with these

problems that are relevant to the specific equipment and raw materials in use. It is

essential that you familiarise yourself with these to help you perform your duties better.

4.6 Abnormal conditionsAn abnormal operating condition is a condition that consists outside the normal range of

operations. However, to determine whether something is normal or abnormal, you need

to know the normal ranges for the instruments associated with the system as well as



recognise the sounds that each component makes when it is operating properly. Only

after you have become familiar with these conditions, will you be able to observe

abnormal conditions quite easily.

Other abnormal conditions, such as an insufficient supply of lubricating oil or grease, and

physical damage, such as broken gauges or pipes, are also obvious enough to be

detected during a basic inspection.

Most process variables have critical operating parameters. If the value of a process

variable is outside of the established parameters, the safety of the process could be in

jeopardy. As such an abnormal condition can occur at any time, you must be ready and

able to respond correctly by knowing your unit’s standard operating procedures (SOP's)

as well as participating in emergency response drills and fire fighting drills.

When abnormal conditions occur, you must know what actions to take to protect

personnel health and safety and to prevent or minimise equipment damage. It may also

require that you make sure that everyone in the unit is accounted for.

When abnormal conditions occur, your primary responsibility is to operate the unit in a

way that will minimise danger to personnel. You can do this by following the specific

operating procedures for any piece of equipment, for example, you may need to perform

an emergency shutdown.

Any upset in your workarea increases the potential for injury and lost profits. Therefore

the combined efforts of all personnel are often needed to correct these abnormal

conditions and to resume normal operations.

You should also report abnormal conditions or potential problems immediately. Finding

and solving potential problems reduce downtime and production loss.

4.7 A problem solving strategyBy now you may realise that operating the machine is plain sailing as long as everything

works well. However, it is when things start going wrong that you need to fall back on

your training to solve the problem. Understanding and being able to implement a problem

solving strategy is of utmost importance to help you perform your tasks more efficiently.

The haphazard problem solving methods followed by some of us at home are not

necessarily the best way to address problems at work.

Following are the basic problem solving steps you have to follow to solve and address

problems in your workarea:

Identify all the symptoms



Define all the possible causes

Minimise the number of possible causes through elimination

Identify the most probable cause

Define a number of possible solutions

Select an optimum solution

Implement the solution

Verify the success of the solution



ANNEXURE 1: RESOURCES

Primary Resources IPM 101-P Study Guide

PTL 101-P Study Guide

http://en.wikipedia.org/

http://www.vanderbilt.edu/

http://nue.clt.binghamton.edu/intro1_6.html

http://www.customelec.com/glossary.asp

http://www.engineeringtoolbox.com

http://www.engineering.uakron.edu

http://www.arrowtank.com/ArrowHome.htm

http://www.cbi.com/services/hortonsphere.aspx

http://www.grengg.com/mounded-vessel.htm

http://www.tanksystems.nl


This manual was developed by

Sparrow Research and Industrial Consultants CC

e-mail: [email protected]

Tel: 012 – 460 9755


ANNEXURE 2: US 256282

SOUTH AFRICAN QUALIFICATIONS AUTHORITY

REGISTERED UNIT STANDARD:

Monitor and control the forming and pressing of paper, board or tissue.

SAQA US ID UNIT STANDARD TITLE

256282 Monitor and control the forming and pressing of paper, board or tissue.

ORIGINATOR REGISTERING PROVIDER

SGB Pulp and Paper

FIELD SUBFIELD

Field 06 - Manufacturing, Engineering and Technology

Engineering and related design

ABET BAND UNIT STANDARD TYPE NQF LEVEL CREDITS

Undefined Regular Level 4 15

REGISTRATION STATUS

REGISTRATION START DATE

REGISTRATION END DATE

SAQA DECISION NUMBER

Registered 2008-02-06 2011-02-06 SAQA 0875/ 08

LAST DATE FOR ENROLMENT LAST DATE FOR ACHIEVEMENT

2012-02-06 2015-02-06

This unit standard replaces:

US ID Unit Standard Title

NQF Level

Credits Replacement Status

246713 Form and press paper, board or tissue

4 15 This is only acceptable as a replacement if 246713 has

the following statuses: Pending; Never Was

Offered; Inactive. Please check that this is the case, and inform the Data Quality



Coordinator if not.

114261 Form and press paper, board or tissue

4 30 Complete

PURPOSE OF THE UNIT STANDARD Learners who demonstrate competence as described in the outcomes of this unit standard will be able to monitor and control the forming and pressing of paper, board or tissue in the wet end of a paper machine.

The qualifying learner is able to:

Explain the fundamental principles applicable to the forming and pressing process.

Monitor and control the different ancillary systems interacting with the forming and pressing section of a paper machine.

Monitor and control the quality standards of process materials in the forming and pressing section of a paper machine.

Monitor and control the forming and pressing process.

LEARNING ASSUMED TO BE IN PLACE AND RECOGNITION OF PRIOR LEARNING Learners accessing this unit standard will have demonstrated their competence against Mathematics and Literacy at NQF Level 3 or equivalent.

UNIT STANDARD RANGE The typical context of this unit standard covers the process from the headbox to first drying cylinder.

Range statements, which are applicable to the unit standard titles, specific outcomes and assessment criteria are found beneath the applicable assessment criteria.

Specific Outcomes and Assessment Criteria: SPECIFIC OUTCOME 1 Explain the fundamental principles applicable to the forming and pressing process.

ASSESSMENT CRITERIA ASSESSMENT CRITERION 1 The purpose of the forming and pressing process is explained in terms of the final product manufactured.

ASSESSMENT CRITERION 2 The principles of the forming and pressing process are explained by making use of a generic flow diagram.

ASSESSMENT CRITERION 3 The relationship of this functional area is explained in relation to the supplier`s- and customer`s processes.

ASSESSMENT CRITERION 4



The flow of material through the forming and pressing section is traced and all equipment is identified using standard industry terminology.

ASSESSMENT CRITERION 5 The purpose and functioning of each piece of equipment used in the forming and pressing section is explained in terms of its role in the overall process.

SPECIFIC OUTCOME 2 Monitor and control the different ancillary systems interacting with the forming and pressing section.

OUTCOME RANGE Ancillary systems refer to the interface between mechanical equipment, electrical equipment, instrumentation and utilities and the forming and pressing section. It only includes those parts of each ancillary system which interact directly with the forming and pressing section and not the full ancillary system.

ASSESSMENT CRITERIA ASSESSMENT CRITERION 1 Mechanical equipment used in the forming and pressing section is identified and described in terms of purpose and application.

ASSESSMENT CRITERION RANGE Mechanical equipment may include bulk handling equipment, conveying equipment, weighing equipment, storage equipment, transport equipment and packaging equipment.

ASSESSMENT CRITERION 2 Electrical equipment used in the forming and pressing section is identified and described in terms of purpose and application.

ASSESSMENT CRITERION RANGE Electrical equipment may include electrical motors, switchgear and drive equipment.

ASSESSMENT CRITERION 3 Instrumentation used in the forming and pressing section is identified and described in terms of purpose and application.

ASSESSMENT CRITERION RANGE Instrumentation includes the key process indicators, control valves and controllers used to monitor and control the process.

ASSESSMENT CRITERION 4 Utilities used in the forming and pressing section are identified and described in terms of purpose and application.

ASSESSMENT CRITERION RANGE Utilities may include air, steam, electricity and cooling water.

ASSESSMENT CRITERION 5 Typical ancillary equipment problems within the forming and pressing section are discussed and solutions offered in accordance with workplace procedures.

ASSESSMENT CRITERION 6



Ancillary systems are monitored and any deviations from operating parameters are corrected in accordance with operating procedures.

SPECIFIC OUTCOME 3 Monitor and control the quality standards of process materials in the forming and pressing section.

OUTCOME RANGE Process materials include the papermaking stock and the wet, pressed paper product.

ASSESSMENT CRITERIA ASSESSMENT CRITERION 1 The properties of papermaking stock and the wet, pressed paper, board or tissue are explained in terms of key characteristics.

ASSESSMENT CRITERION 2 The purpose of process material quality control procedures as well as the consequences of not adhering to these procedures are explained with regards to the impact thereof on the final product produced.

ASSESSMENT CRITERION 3 The quality requirements of papermaking stock are explained according to specifications.

ASSESSMENT CRITERION RANGE Specifications are defined by applicable general, machine or mill operating instructions. Specifications may include, but are not limited to, fibre properties, additive contents and concentrations, particle size and shape.

ASSESSMENT CRITERION 4 Typical stock problems and its impact on the final paper, tissue or board properties and costs are discussed in terms of the purpose of the process.

ASSESSMENT CRITERION RANGE Stock problems include the problems associated with the properties of pulp, fillers and chemicals. Paper, tissue or board properties include but are not limited to the strength, appearance and surface properties of the paper as identified by the workplace quality control system.

ASSESSMENT CRITERION 5 Corrective action to be taken in the case of non-conforming stock is discussed in accordance with workplace procedures.

SPECIFIC OUTCOME 4 Monitor and control the forming and pressing process.

OUTCOME NOTES The monitoring and controlling of the forming and pressing process should be performed according to operational requirements and standard operating procedures.

ASSESSMENT CRITERIA ASSESSMENT CRITERION 1



The forming and pressing process is monitored and parameters recorded in accordance with workplace procedures.

ASSESSMENT CRITERION 2 The impact of process variables on the product properties is explained in terms of final products and costs.

ASSESSMENT CRITERION RANGE Process variables include but are not limited to machine speed, flow, drying capacity, pressing capacity, chemical addition rate, consistency, vacuum, wetness/freeness, process pH and temperature where applicable to paper, board or tissue.

ASSESSMENT CRITERION 3 Typical equipment problems within the forming and pressing process are discussed and solutions offered in accordance with workplace procedures.

ASSESSMENT CRITERION 4 Variations in product parameters are evaluated and corrective action taken in accordance with workplace procedures.

ASSESSMENT CRITERION RANGE Product deviations include but are not limited to freeness/wetness, porosity, formation, tensile, tear, burst, fold, deckle, calliper, smoothness, grammage, moisture, roughness, ash, opacity, strength, tensile energy absorption, scuff resistance, softness where applicable to paper, board or tissue.

UNIT STANDARD ACCREDITATION AND MODERATION OPTIONS An assessor, accredited with a relevant NQF Level 4 or higher qualification, will

assess the learner`s competency.

Only an Assessor with considerable first hand experience in process operations will assess the learner`s competency.

Anyone assessing a learner or moderating the assessment of a learner against this Unit Standard must be registered as an Assessor with the relevant ETQA.

Direct observation in simulated or actual work conditions is required.

UNIT STANDARD ESSENTIAL EMBEDDED KNOWLEDGE Qualifying learners understand and can:

Explain the names, functions and locations of:

All items of installed equipment.

Raw material/s.

Finished product/s.

Describe the properties and characteristics of:

Raw material/s.

Product/s.

Process equipment.

Auxiliary equipment.

Process system/s.

Explain the purpose of the:



Process, in terms of product/s, efficiencies and quality.

Explain the causes, effects and implications of:

Process variables.

Raw material variables (suppliers).

Product variables (customers).

Not complying with quality standards.

Not complying with standard operating procedures.

Demonstrate procedures and techniques of:

Monitoring and controlling the process.

Recording and reporting data.

Explain the regulations, legislation, agreements and policies related to:

Standard Operating procedures.

Quality specifications.

UNIT STANDARD DEVELOPMENTAL OUTCOME N/A

UNIT STANDARD LINKAGES N/A

Critical Cross-field Outcomes (CCFO): 1. UNIT STANDARD CCFO IDENTIFYING The learner is able to identify and solve problems in which responses display that responsible decisions, using critical and creative thinking, have been made by:

Identifying and addressing variations in ancillary system operation.

Identifying and addressing variations in material quality.

Identifying and addressing variations in the forming and pressing process.

Bringing all deviations into control.

Refer to the following Specific Outcome(s):

Monitor and control the quality standards of process materials in the forming and pressing section.


2. UNIT STANDARD CCFO WORKING Work effectively with others as a member of a team, group, organisation or community by:

Maintaining sound relations with co-workers.




3. UNIT STANDARD CCFO ORGANISING



The learner is able to organise and manage himself and his activities responsibly and effectively by:

Working to achieve consistent results required by the process/customers.




4. UNIT STANDARD CCFO COLLECTING Collect, analyse, organise and critically evaluate information by:

Using various sources of information pertaining to the forming and pressing process, including basic scientific and engineering theory.

Monitoring and recording process, product and equipment variables.

Carrying out physical quality checks and tests.

Explaining the impact of non-conforming materials in terms of final products and costs.

Describing the relationship of the process to suppliers, customers and the overall forming and pressing process.

Refer to all Specific Outcomes.

5. UNIT STANDARD CCFO COMMUNICATING Communicate effectively by using mathematical and/or language skills in the modes of oral and/or written presentations during:

Recording of variables and actions taken to rectify.

Responding to questions and requests for additional information.

Liaising with relevant operational support units.

Drawing and interpreting diagrams and sketches.

Completing relevant documentation in accordance with workplace requirements.


6. UNIT STANDARD CCFO SCIENCE Use science and technology effectively and critically, showing responsibility towards the environment and health of others by:

Monitoring the process.

Bringing process, product and equipment variables into control.




7. UNIT STANDARD CCFO DEMONSTRATING Demonstrate an understanding of the world as a set of related systems by:

Explaining the purpose of the process as well as the relationship to the supplier and customer`s processes.




8. UNIT STANDARD CCFO CONTRIBUTING Contribute to the full personal development of each learner and the social and economic development of the society at large by:

Understanding the role of monitoring plant and process in a processing environment and the effect it has on the growth and development of the organisation, its customers and employees.


Icons

Icon Description

Know

-le

dge

Und

er-

stan

d

Skill

Develop a Checklist

Observe a Demonstration X X

Observe an Experiment X X

Participate in an Experiment

Participate in Group work/ discussions, role-play, etc. X

Attend a Lecture X X

Conduct a Presentation

Multimedia X

Use Multimedia as learning tool

Practical

Self-study / Individual activity



Site visit X

Theoretical – all types of questions X

Make sketches, write reports, case studies, etc.


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