potlatch brainerd wet end training 3
DESCRIPTION
paper formationTRANSCRIPT
04/12/23 Copyright © 2001 Bill Frawley
Potlatch Brainerd Wet End Training
March 2001By
Bill Frawley
04/12/23 Copyright © 2001 Bill Frawley
Introduction
Understanding the paper forming process, equipment and chemistry
Bill Frawley and Joe Osfar Training Consultants
04/12/23 Copyright © 2001 Bill Frawley
Topics of Discussion Looking at machine as relates to
fiber mat formation. How each area impacts fiber mat Entry zone Forming zone Dewatering zone Consolidation zone Pressing
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How The Fiber Mat Develops
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The Five Zones of the Forming Table
Entry Phase Forming Zone Dewatering Zone Transition Zone Consolidation Zone
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# 5 PM Table Zones
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1 Entry Phase
Headbox Slice and Jet Pressure Forming Vs Velocity
Forming Impingement point Forming board Structuring of filtering mat
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Headbox Approach System
Approach system Fan pump Attenuator Tube bundle
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Headbox Components
Headbox Components Diffuser block Distributor rolls (holy rolls) Nozzle Slice
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Rectifier Roll
Agitates dilute stock so flocks can not form in headbox
Velocity through center of hole greater than outside do to boundary effect
Designed for fixed flow range
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Rectifier Roll Pattern in Sheet
If roll capacity is exceeded streaks will flow through nozzle
Forming board will set pattern in filtering mat
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Flow From a Vertical Slice
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Jet Angle ß, Degrees
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Contraction Coefficient
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Defect In Slice Lip
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Rush Drag
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Rushing the Jet
Jet velocity greater than wire speed
CD fiber orientation Sheet has less MD
strength.
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Dragging the Jet
Jet velocity less than wire speed
MD fiber orientation Sheet has more MD
strength.
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Pressure Vs Velocity Forming
Pressure Forming Rapid development
of fiber mat Low first pass
retention Sheet sealing Tissue applications
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Velocity Vs Pressure Forming
Velocity Forming Better filtering mat Carry lower
consistency in to forming zone
Higher first pass retention
Flat grades
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How The Filtering Mat Develops
Filtering mat developed on the forming board
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Sheet Consistency Development
Formation is over when stock consistency reaches 1.2 – 1.4%
Excessive activity past this point will degrade sheet properties!
04/12/23 Copyright © 2001 Bill Frawley
2 Forming Zone Breast Roll Shake How foils & table rolls work Harmonics
1. Machine speed
2. Foil spacing
3. Box spacing Amplitude - Function of angle All over when stock reaches 1.2-
1.4% consistency Sheet set point
04/12/23 Copyright © 2001 Bill Frawley
How The Forming Zone Develops Fiber Mat
Forming zone works fibers & fillers in upper part of suspension
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Table Rolls High activity at low
speeds Positive and
negative pressure Ever increasing nip Work up to 1200
fpm Higher
maintenance
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When Table Rolls Go Bad
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How Different Foils Work
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How Foils Work
Nose: Skives water off bottom of wire
Flat: Seals fabric so vacuum can happen
Angle: Creates gravity vacuum
04/12/23 Copyright © 2001 Bill Frawley
Nose: Skives water off
bottom of wire Creates speed bump If the nose is too
sharp fibers will staple over and cause streaks (like a rock in a river)
Foil Nose
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Foil Flat Flat seals fabric to
bottom of wire so vacuum can happen This can tell us how
foils is wearing or aligned
Wear should be from nose back
If wear starts on back of flat t-slot is wrong or tilted
04/12/23 Copyright © 2001 Bill Frawley
Foil Angle Foils won’t work under 400
FPM Angle draws water through
filtering mat as nip moves away from wire
Vacuum brakes when water can’t fill nip
Wire is pulled down with water
When vacuum brakes, wire snaps back causing activity
04/12/23 Copyright © 2001 Bill Frawley
Harmonics
Speed ÷ Spacing ÷ 5 = CPS 1500 fpm ÷ 5 = 300 ÷ 5 = 60 CPS Sweet spot for formation is
around 80 Cycles per second If activity stops for an instant
flocculation will occur
04/12/23 Copyright © 2001 Bill Frawley
Foil Box Spacing
Box spacing has to be set to the blade spacing of the proceeding box Example: Foils are spaced 5” center to
center the next box has to set 5” 10” or 15” from the tip of the last foil to the tip of the first foil on the next box
04/12/23 Copyright © 2001 Bill Frawley
3.00 3.25 3.50 3.75 4.00 4.25 4.50 4.75 5.00 5.25 5.50 5.75 6.00
ft/min in /sec
500.00 100.00 33.33 30.77 28.57 26.67 25.00 23.53 22.22 21.05 20.00 19.05 18.18 17.39 16.67
600.00 120.00 40.00 36.92 34.29 32.00 30.00 28.24 26.67 25.26 24.00 22.86 21.82 20.87 20.00
700.00 140.00 46.67 43.08 40.00 37.33 35.00 32.94 31.11 29.47 28.00 26.67 25.45 24.35 23.33
800.00 160.00 53.33 49.23 45.71 42.67 40.00 37.65 35.56 33.68 32.00 30.48 29.09 27.83 26.67
900.00 180.00 60.00 55.38 51.43 48.00 45.00 42.35 40.00 37.89 36.00 34.29 32.73 31.30 30.00
1000.00 200.00 66.67 61.54 57.14 53.33 50.00 47.06 44.44 42.11 40.00 38.10 36.36 34.78 33.33
1100.00 220.00 73.33 67.69 62.86 58.67 55.00 51.76 48.89 46.32 44.00 41.90 40.00 38.26 36.67
1200.00 240.00 80.00 73.85 68.57 64.00 60.00 56.47 53.33 50.53 48.00 45.71 43.64 41.74 40.00
1300.00 260.00 86.67 80.00 74.29 69.33 65.00 61.18 57.78 54.74 52.00 49.52 47.27 45.22 43.33
1400.00 280.00 93.33 86.15 80.00 74.67 70.00 65.88 62.22 58.95 56.00 53.33 50.91 48.70 46.67
1500.00 300.00 100.00 92.31 85.71 80.00 75.00 70.59 66.67 63.16 60.00 57.14 54.55 52.17 50.00
1600.00 320.00 106.67 98.46 91.43 85.33 80.00 75.29 71.11 67.37 64.00 60.95 58.18 55.65 53.33
1700.00 340.00 113.33 104.62 97.14 90.67 85.00 80.00 75.56 71.58 68.00 64.76 61.82 59.13 56.67
1800.00 360.00 120.00 110.77 102.86 96.00 90.00 84.71 80.00 75.79 72.00 68.57 65.45 62.61 60.00
1900.00 380.00 126.67 116.92 108.57 101.33 95.00 89.41 84.44 80.00 76.00 72.38 69.09 66.09 63.33
2000.00 400.00 133.33 123.08 114.29 106.67 100.00 94.12 88.89 84.21 80.00 76.19 72.73 69.57 66.67
2100.00 420.00 140.00 129.23 120.00 112.00 105.00 98.82 93.33 88.42 84.00 80.00 76.36 73.04 70.00
2200.00 440.00 146.67 135.38 125.71 117.33 110.00 103.53 97.78 92.63 88.00 83.81 80.00 76.52 73.33
2300.00 460.00 153.33 141.54 131.43 122.67 115.00 108.24 102.22 96.84 92.00 87.62 83.64 80.00 76.67
2400.00 480.00 160.00 147.69 137.14 128.00 120.00 112.94 106.67 101.05 96.00 91.43 87.27 83.48 80.00
2500.00 500.00 166.67 153.85 142.86 133.33 125.00 117.65 111.11 105.26 100.00 95.24 90.91 86.96 83.33
2600.00 520.00 173.33 160.00 148.57 138.67 130.00 122.35 115.56 109.47 104.00 99.05 94.55 90.43 86.67
2700.00 540.00 180.00 166.15 154.29 144.00 135.00 127.06 120.00 113.68 108.00 102.86 98.18 93.91 90.00
Foil Frequency Chart
04/12/23 Copyright © 2001 Bill Frawley
Foil Amplitude
Function of wire speed and foil angle
Lower angle lower pulse Higher angle higher pulse 4-5 Degree foils maximum Turbulence making foils
04/12/23 Copyright © 2001 Bill Frawley
Activity Rating Chart
1. Flat Clam
2. Calm
3. Ripples
4. Small Waves
5. Small Waves
6. Wave action
7. Micro turbulence
8. Micro turbulence
9. Necking
10. Stock Jump
04/12/23 Copyright © 2001 Bill Frawley
Calm to Small Waves
No shear in stock suspension
Flocculation Mat can get so
dense that it will retard drainage
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Wave Action
Shear starts to begin
Fibers in upper suspension move
Filtering mat stays open
Formation can improve
04/12/23 Copyright © 2001 Bill Frawley
Micro Turbulence
Shear occurs Flock size is
significantly smaller and more uniform
Fibers in upper suspension move
Filtering mat stays open
Formation improves
04/12/23 Copyright © 2001 Bill Frawley
Good Micro Turbulence
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Stock Jump
Filtering mat is destroyed
Retention drops Droplets can
rain on your parade (rings in sheet)
Chunks of filtering mat could cause large flocks
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Dewatering Zone
Gravity Foils Vacuum Foils Top Wire Units
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Thickening The Stock
Add a little flour and stir over low heat
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Thickening The Stock
Keep mat open Remove water Graduate low
vacuum levels to prevent sheet sealing
Finish top side of sheet
Consistency levels form 1.4 – 13%
04/12/23 Copyright © 2001 Bill Frawley
Gravity Foils
In the dewatering zone angles should be a compromise between water removal and stock activity
Need to keep mat open for drainage
Need to carry harmonic activity to last gravity unit
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Activity on Gravity Foils
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Low Vacuum Foils
Low vacuum foils are need to remove water when the filtering mat has thickened to a point where gravity foils become inefficient
Control consistency coming in to top wire unit 1.8 – 2.1%
04/12/23 Copyright © 2001 Bill Frawley
Low Vacuum Foils Vacuum measured in
inches of water Blower supplies
negative pressure Water on top of fiber
mat creates air tight seal
Open area = dwell time Ramp up vacuum To much vacuum to
soon will seal sheet
04/12/23 Copyright © 2001 Bill Frawley
Controlling Low Vacuum Foils
Ramp vacuum Drop leg seals
bottom and determines how much vacuum is possible
It is better to use narrow 0º blades and adjust t-bar spacing for open area (less drag)
04/12/23 Copyright © 2001 Bill Frawley
BEL
BOND
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Bel Bond Advantages
Fiber mat is sandwiched between two forming fabrics
Dewaters up Finishes top of sheet Structures mat uniformly Less two sidedness Increases consistency of sheet
from 2 – 11%
04/12/23 Copyright © 2001 Bill Frawley
Bel Bond Lead-in Detail
04/12/23 Copyright © 2001 Bill Frawley
Lead-in Box Four adjustments for
controlling H2O
1. Height of roll
2. Raise or lower trailing edge of lead-in box
3. Raise or lower vacuum of lead-in box
4. Raise or lower vacuum of lovac box
04/12/23 Copyright © 2001 Bill Frawley
Impingement Point of Two Wires
Water is forced up through top wire on lead-in box
Water is vacuumed down in to lead-in box up to 25” H2O vacuum
Curvature of lead-in box helps force water up
Adjusting height of trailing edge of lead-in box has affect on formation
Lead-in roll has biggest impact on dewatering
04/12/23 Copyright © 2001 Bill Frawley
Curved Inverted Vacuum Box
04/12/23 Copyright © 2001 Bill Frawley
Auto Slice Vacuums free water and air from
inside of top wire 20-25” H2O vac Roof is adjustable by hand Setting is determined by closing
roof until slice rejects some water then opened back up a smidge so all water is removed
Roof regulates only amount of air removed NOT amount of water
04/12/23 Copyright © 2001 Bill Frawley
1st Vacuum Chamber 15 two inch ceramic
blade vacuum zone under auto slice box
Vacuum level shifts to 3 – 5” Hg
Connected to a vacuum pump
Water is move up channel to a weir
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2nd Vacuum Chamber 14 two inch ceramic
blade vacuum zone under auto slice box
Vacuum level shifts to 4 – 6” Hg
Connected to a vacuum pump
Water is move up channel to a weir
04/12/23 Copyright © 2001 Bill Frawley
Transfer Box
Transfer box keep the sheet on the bottom wire
Wires separate on curved surface
Begins sheet consolidation zone
8 slots pulling 4-6 inches of mercury
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Suction Boxes
Ramp up vacuum from 4-10” of mercury
Boxes have adjustable deckles
Dries sheet from about 12-17% consistency
Vacuum supplied by Nash vacuum pump
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Suction Couch Roll
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Function of Suction Couch Roll
End of consolidation zone Dries sheet to 18-22% Helps drive forming fabric At speeds over 1200 FPM
water never penetrates shell Liquid ring seal Highest vacuum element on
machine
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Forming Section Review
Stock delivery system Forming zone Dewatering zone Top wire unit High Vacuum Couch Sheet development
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Press Section
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Press Section Functions
To remove water by squeezing or wringing sheet against a felt
Felts act like a sponge Pressing make sheet denser Press nips squeeze sheet and
felt or just sheet to remove water or to smooth sheet
Overloading can crush and mark
04/12/23 Copyright © 2001 Bill Frawley
4 Phases of Press Roll Nip
04/12/23 Copyright © 2001 Bill Frawley
4 Phases of Press Roll Nip
Phase 1: Felt and sheet compresses sheet becomes saturated
Phase 2: Water is squeezed from sheet to felt
Phase 3: Felt expands faster pulling more water from sheet
Phase 4: Sheet rewets as it partially expands
04/12/23 Copyright © 2001 Bill Frawley
PLI Vs PSI
Pli is used measure force of mating rolls
Pli is the number used for press loading
Psi is used when discussing force of nip on sheet or felt & sheet
04/12/23 Copyright © 2001 Bill Frawley
Why Press are Crowned
Crown is needed to
Even out pressure under nip loading
Compensate for Sag & deflection
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Press Loading
1st Press 450 PLI 2nd Press 600 PLI Smoothing 450-500 PLI Excessive pressure will crush or
shadow mark sheet
04/12/23 Copyright © 2001 Bill Frawley
Combi-Roll The Combi roll is a pickup &
suction first press roll in one
Low vacuum area lifts sheet off wire and holds it on the felt until the high vacuum zone under first press nip
Low vac area doesn’t remove water
High vac holds water in felt until sheet can get away
04/12/23 Copyright © 2001 Bill Frawley
Combi-Roll Operation Vacuum must be off to move
into wire Low vacuum is set about 8” Hg
Low vac zone doesn't remove water
High vacuum is set at 20” Hg And holds water in felt until sheet is clear of nip
Box alignment critical 1st press loaded to 450 Pli
04/12/23 Copyright © 2001 Bill Frawley
Suction Felt Roll
Acts like an anti-blow box Sucks sheet tight to
felt to prevent flutter entering 2nd press
Doesn't remove water from sheet only air
Stabilizes sheet after open draw from pickup felt
04/12/23 Copyright © 2001 Bill Frawley
2nd Press 2nd press uses a venta-
nip grooved bottom roll Grooves in rubber cover
act like tread on your car tires
Water is squeezed from sheet through felt and in to voids of grooves
Too much pressure can cause shadow marking and crush sheet
04/12/23 Copyright © 2001 Bill Frawley
Smoothing Press
Smoothing press as it’s name says smoothes the sheet for better drying
No water is removed so nip load has to be lower that 2nd press
Both rolls are hard
04/12/23 Copyright © 2001 Bill Frawley
Press Roll Showers
Showers in suction rolls are invisible
Venta-nip shower keeps grooves clean and open
04/12/23 Copyright © 2001 Bill Frawley
Press Felts Act as a blotter or sponge Absorb water + dirt, fines, pitch ash, minerals…
at nip Cleaned with showers &
chemicals (batch wash) Dried on uhle boxes Trade line needs to run square Change when filled and worn
04/12/23 Copyright © 2001 Bill Frawley
Press Section Felt Showers
Each felt has Batch chemical and
flushing shower High pressure
cleaning shower Uhle box lube
shower
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Uhle Boxes
Shop-vac for felts 4 milliseconds dwell minimum to
dry and clean Be careful of edges outside
sheet they will dry out first Adjust deckles to sheet width Vacuum will start around 10” Hg
when felt is new and increase to 15-17” when felt is filled
04/12/23 Copyright © 2001 Bill Frawley
Press Section Review To remove water by squeezing
sheet against an a felt Felts act like a sponge Uhle boxes & showers clean and
dry felts Pressing make sheet denser Press nips squeeze sheet and
felt or just sheet to remove water or to smooth sheet
Overloading can crush and mark
04/12/23 Copyright © 2001 Bill Frawley
Thank You, Any Questions?