mechanical drives system for promasidor. repaired

You are welcome to a 5 day training programme on MECHANICAL DRIVE SYSTEMS MAINTENANCE

Organised for The Staff of

PROMASIDOR NIGERIA LIMITED BY

APPLIED ENGINEERING TECHNOLOGY INITIATIVE (...total engineering solutions)

Objectives

At the end of the course, participants will be able to:• Recognize and avoid common safety hazards

associated with Mechanical Drive Systems.• Identify reasons for rotating machinery to have a

specific ratio between driver and driven components • Identify and use common Mechanical Drive train

fasteners• Properly install Belts and chains• Identify common bearings by proper name and

application2

Objectives

• Explain purpose for lubrication and interpret lube specifications to match specific applications.

• Analyze symptoms of wear to troubleshoot system failure

• Describe a basic proactive approach to implement a preventive maintenance programme.

• Proper bearing mounting and dismounting procedures

• Carry out proper lubrication on Mechanical drive components

• Identify causes of bearing failure3

COURSE CONTENTIntroduction to Mechanical Drive and Lubrication maintenance• Definition:• Safety associated with industrial activities:• Maintenance management• Types of maintenance Introduction to rotating machinery• Driving machines (engines or prime movers) • Transmission machines• Driven machines• Operation principle of rotating machinery• Mechanism• Balancing• Transmission• Alignment• Guards 4

COURSE CONTENTBushings, Keys, and Keyways• Splines• Tapered, QD and split bushings• Square, flat, tapered, Woodruff keys• Sizing and fit• Symptoms of failureShafts• Factors for designing a shaft• Classification of shaft• Actions of the load on the shaft• Characteristics of shafts• Materials for shafts• Installation of Shafting• Shaft Alignment

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COURSE CONTENTFriction• Causes of friction• Advantages of friction• Disadvantages of friction• Nature of friction• Types of friction• LubricationBelt drives• Types of Belt• Belt installation• Toothed belt and pulleys• Pulley ratio• Advantages and Disadvantages of belts• Troubleshooting and Maintenance belt drives

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COURSE CONTENTGears drives • Gears drives definition• Alignments• Lubrication• Types of gears• Major types of gear tooth wear & failures

Chain drives • Chain drives definition• Drive sprockets• Driven sprocket• Chain pitch• Centre distance• Chain length• Chain rating• Ultimate strength

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COURSE CONTENTChain drives CONTD• Pitch diameter• Installation of chain drives• Advantages of chain drives• Disadvantages• Maintenance of chain drive• Chain lubrication• Troubleshooting chain drivesCouplings• Functions of couplings• Types of couplings• Shaft alignment on couplings• Installation of couplings• Failure patterns on couplings

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COURSE CONTENTSeals• Types of seal• Gaskets• Sealing principles• Gasket materials• Methods of marking out gasket shapes• Fitting a flat seal• 0-rings• SealantsIntroduction to lubrication• Types of lubricants• Types of grease• Bearing not requiring lubrication• Characteristics of lubricants• Characteristics of grease

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COURSE CONTENTClutches and brakes• Mechanical, friction, centrifugal, and plate clutches• Clutch selection• Torque converters• Mechanical, hydraulic, pneumatic, and electric brakesVibrationOverheating

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MECHANICAL DRIVES SYSTEMS MAINTENANCE

A. Definition: Mechanical drives system’s maintenance is the study of nature, operations, maintenance and lubrication of mechanical drives components such as shafts, couplings, v-belts & pulleys, chains & sprocket, gears and bearings used in the manufacturing of goods in the industry.

B Safety associated with industrial activities: They are wide and comprehensive i.e. all inclusive legal requirements in form of written laws and what should be in place or observed in an industrial organization for the security of life and, properties.

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MECHANICAL DRIVES SYSTEMS MAINTENANCE

It's the government that is responsible for the enforcement through the factory inspectors and the observance rest on the management of any industrial concern. The laws border on: set up of the industry, safety, health, welfare, accident prevention, etc. It is the responsibility of the workers to get acquainted with these laws, which are in form of Factory Act usually pasted at a conspicuous point in industries, and keep all safety rules therein.

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SAFETY REQUIREMENTS ASSOCIATED WITH WORKING ON A PLANT

1. Generala. It is absolutely necessary that a workman be in sound mind and in

complete control of his faculties before working in the plants. b. Attempt should not be made in the operation and maintenance

of any machinery one is not familiar with until properly instructed.

c. Machines are equipped with safety guards and protection and they must not be removed unless under repairs, equipment should not be operated without the guard in place.

d. Defective, loose or inappropriate tools should not be used e.g. badly fitting spanners, loose file haft, cable, sling, hooks and blocks.

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e. Improper handling of materials and heavy object cause injuries and accident in industries. Mechanical means of handling materials should be used whenever possible instead of manual method.

f. Thorough cleanliness and orderliness of work areas is imperative to avoid slipping, bad fall or injury to legs.

2. Personal protective equipmenta. Clothing:I. Synthetic materials should not be used, as some are highly

inflammable. It should be of flame resistant material.II. Trouser legs which drag on the floor or which have cuffs that are too

wide should be avoided. Loose and flapping clothing may at any time become entangled in a belt or moving part.

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b. Hard toed protective shoes with anti-static sole should be worn. Also safety hats for the protection of the head against falling objects.

c. Rings and other items of jewelry should not be worn when working, they may catch a moving parts and CAUSE injury to hands and fingers.

d. Safety goggles should be worn especially when striking an object with another, wire brushing, chipping, grinding and working on rusty or dirty chains.

e. Earmuffs, masks and respirators should be worn to protect against noise, vibration, and inhalation of dangerous gases or fire particles.

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3. Cleaning rags and solventsa. Rags should not protrude from pockets since

they can be hazardous when working near rotating machinery.

b. Under no circumstances should wiping around revolving shafts and other moving parts be done.

c. Cleaning of machines with petrol or other flammable liquid should never be contemplated. Diesel fuel is ideal for cleaning machinery.

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MAINTENANCE MANAGEMENT

This is the organization of maintenance within unambiguous agreed policy of the top management team being its express responsibility. This policy will be communicated to the maintenance engineer defining acceptable condition of maintenance, which will serve as his terms of reference.

Objectives Of Maintenance Management1. To extend the useful life of assets where it stands to reason

to maintain rather than to replace due to lack of capital resources for replacement.

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MAINTENANCE MANAGEMENT2. To ensure maximum utility of installed equipment for production

or service, and for maximum possible return in investment.3. To ensure operational readiness of all equipment for emergency

use at all times e.g. stand by units, fire fighting units, rescue units (e.g. ambulances).

4. To ensure the safety of personnel using the production facilities.

Various forms of maintenanceMaintenance is combination of actions carried out to retain equipment or restore it to an acceptable condition i.e. whatever level is set by an organization.

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MAINTENANCE MANAGEMENTUNPLANNED MAINTENANCE1. Emergency maintenance: this is a maintenance that is necessary

immediately to avoid expensive damage to assets.2. Break down maintenance: maintenance carried out which result in non-

availability of the equipment for production or services for sometime.3. Running maintenance: this is maintenance that can be carried out when

the equipment is in service.4. Shut down maintenance: this is maintenance that can only be carried out

when equipments are out of service.PLANNED MAINTENANCEThis is a maintenance programme organized and carried out with forethought, control and records to a predetermined plant. It has two arms:

-

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MAINTENANCE MANAGEMENT1. Preventive maintenance: is the system of plant maintenance that deals

with inspection and replacement intended to eliminate the occurrence of defects.

a. Running inspection to locate loose parts e.g. vibration, misalignment, wear, leakages of lubricant and lack of cleanliness.

b. Shutdown inspection of working parts that need dismantling.2. Corrective maintenance: is a maintenance program carried out at

predetermined intervals intended to reduce the likelihood of equipment not meeting an acceptable condition.

3. To ensure operational readiness of all equipment for emergency use at all times e.g. stand by units, fire fighting units, rescue units (e.g. ambulances).

4. To ensure the safety of personnel using the production facilities.

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INTRODUCTION TO ROTATING MACHINERY

DEFINITIONSA rotating machine is one in which the main working components rotate about a fixed centre in a regular manner. Most such machines incorporate additional subsidiarymechanisms such as linkages, slides, gears and reciprocating components, and many of the operating principles that apply to the rotating assembly also apply to these other elements.Although there are many different types of rotating machines, they can all be classified into three basic groups in terms of their function.

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INTRODUCTION TO ROTATING MACHINERYDriving machines (Engines or prime movers)

This group includes all machines whose purpose is to drive other machines. Examples include: Electric motor Steam turbines Diesel engines Petrol engines Air motors The common characteristic of these machines is that they convert an energy input of varying kinds into a mechanical output in the form of a rotating drive shaft.

Transmission machinesThese are machines whose purpose is to transmit mechanical energy from a living to a driven machine. Examples include: Gearboxes, Differentials, Variable speed drives. The mechanical energy transmitted often undergoes a speed transformation and these machines often incorporate some means of drive disengagement such as a clutch. 22


Driven machinesThese machines cannot operate independently and need to be coupled to a driving machine. Examples include:

• Pumps• Compressors• Fans• Generators• Blenders• Machine tools

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This group is by far the largest and includes a large number of different types of machines. The common characteristic is that the energy input is normally in the form of a rotating drive shaft while output may be in a variety of forms including kinetic or pressure energy of a fluid, electrical energy, kinetic or potential energy of a solid materials, etc. Because of the ways in which different types of machines are sometimes combined into sets, the distinction between the separate elements is not always clear. For example, some pumping units are directly coupled through a reduction gear to an electric motor with all three elements contained in a single housing. Although such an item may be treated as a single machine it does, in fact, contain all three elements of driving, transmission and driven. 24


From a maintenance viewpoint, it is important that the function of a machine, or the elements of a machine set, is clearly understood. Troubleshooting and fault correction depend on an ability to detect deviations from normal operation, and the assessment of operating conditions demands a knowledge of the function of a machine as well as the principles on which it operates. It is recommended that technicians make sure that they are fully familiar with the function (i.e. what the machine 'does') of the particular machinery with which they are concerned.

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OPERATING PRINCIPLESA prerequisite of good maintenance practice is a critical understanding of the principles on which the satisfactory operation of rotating machinery is based. This understanding provides the foundation of the maintenance technician's ability to diagnose and correct faults. Although each machine is different in some way, and each engineering situation gives rise to special requirements, there are a number of conditions that are critical to the operation of all rotating machines. They were: -– Performance– Downtime– Service life– Efficiency– Safety– Environmental impact– Maintenance cost

If a machine is to perform 'satisfactorily' according to these criteria, then the following conditions must be satisfied.

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OPERATING PRINCIPLESMOUNTING

A rotating machine must be correctly mounted on a suitable foundation. If this condition is not met then operation of the machine may cause damage both to itself and to adjacent equipment.

MECHANISM Every rotating machine must have an internal mechanism that is operable, in good repair and capable of achieving the performance required. There are many excellent books that describe the operation and maintenance of specific types of machines and the technician should consult these for information when necessary

BALANCINGThe rotating components or assemblies of a rotating machine must be correctly balanced. Assemblies that are not balanced cause excessive vibration and high stresses. Not only does this condition cause rapid wear and frequent breakdown but sudden and dramatic failure may occur with dangerous consequences.

LUBRICATIONA rotating machine, like any mechanism where relative motion of contacting parts is involved, cannot operate satisfactorily unless it is lubricated to reduce friction and wear.

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OPERATING PRINCIPLESBEARINGS

Every item of rotating machinery requires a set of properly maintained bearings that support the mechanism and restrain its motion with minimum resistance. Bearings are an essential component and a common element in all rotating machine.

TRANSMISSIONBecause machines normally operate in 'sets' i.e. driving-driven or driving-transmission driven, some means of connecting the input and output shafts of the separate elements is required.

ALIGNMENTWhen machines are assembled in sets as described above, it is vital that the interconnecting shafts are properly aligned to each other. Poor alignment will cause vibration and lead to rapid wear of couplings, bearings, seals and other rotating elements.

SEALSRotating machines usually contain a number of fluids such as process fluids, fuels, cooling water and lubricants. At the very least there will always be a lubricant present. 28

OPERATING PRINCIPLESThe escape of any of these fluids must be prevented to avoid waste and the creation of hazards to personnel and the environment. Hence all machine joints and connections must be properly sealed. As well as containing fluids within the machine, sealing also serves to prevent contamination from external sources such as dirt and moisture.

GUARDSIn order to prevent injury to personnel, the minimum safety requirement on any rotating machine is that all exposed rotating elements should be guarded during operation. Guarding should be designed and installed in such a way that accidental interference with rotating elements is impossible. The construction of machine guards is usually straightforward and the maintenance technician should ensure that they are always secure and in good repair. No matter what specific type of rotating machine is considered, these nine conditions represent the minimum requirements for satisfactory operation and if proper attention is given to these conditions then there is every chance that satisfactory operation will be achieved.

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KEYS AND KEYWAYS

• The term fastener generally refers to a number of devices used for holding components together.

• The key and keyway is one of such devices.• Other fasteners includes; Bolts and nuts Screws Collars etc.

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Fundamental Problem inShaft Design

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Interference Fits

Hole is undersized and part is heated to allow it to slide over shaft. Compressive interface pressure develops when part cools.

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Keys and Keyseats

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Keys are used to transmit torque from a component to the shaft.

Types of Keyseats

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Keyseats are classified according to the process by which they are made.

Keyway Fabrication Methods

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Fillet Radii and Key ChamfFillet Radii and Key Chamfers

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Fillet Radii Fabrication

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Square and RectangularParallel Keys

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The hub is slightly larger than the shaft and key to allow it to slide over the shaft during assembly. The set screw is used to take up the slack. The resulting friction is used to provide resistance to axial motion. Thread adhesive may be required to ensure that vibration doesn't cause the set screw to loosen.

Square and RectangularKey Geometry

Width is approximately ¼the diameter of the shaft. Standard contains tables of recommended key sizes versus shaft diameter

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“Keys and Keyseats,” ANSIStandard B17.1-1967.

Set screwsHolding Power .Resistance to axial or rotary motion of the hub or collar relative to the shaft.Holding power is a function of friction between contactingportions of hub or collar and shaft and any penetration of the setscrew into the keyway or shaft.

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Representative HoldingPower Values

Based on alloy steel screw against steel shaft, class 3A coarse or fine threads in class 2B holes, and cuppoint socket setscrews.

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Keys and Keyways

• Keys can be classified as:I. Rectangular Keys and KeywaysII. Gibb Head KeyIII. Feather KeyIV. Woodruff Key and Keyway.

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Keys And Keyways contd.The rectangular key and keyway are the simplest key

fasteners for securing a shaft to a hub. They are easy to remove and re-install.

The Gibb key is used where a tight fit is desired. It is installed and removed with a hammer.

The feather key and keyway have a screw arrangement for securing the key to the shaft. This ensures that at all times the key is fixed to the shaft.

The woodruff key and keyway take the shape of sector of a circle. The keyway is often cut with a side and face cutter on a milling machine.

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Keyway Broach Set cuts keyways

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Shafts

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SHAFTSSHAFT is a member usually of circular section which supports gears, sprockets, pulleys, rotors, etc and which is subjected to torsion or axial loads, acting singly or in combination. It is also the principal part for transmitting power or rotary motion and torque, and is subjected to complex deformations in operation (torsion, bending, tension and compression).FACTORS FOR DESIGNING A SHAFT1. Basis of Strength: It is necessary to consider the following types of loadinga. Static loadingb. Shock loading: The weakening effects at points of stress.c. Cyclic loading: Concentration due to keyways and shoulders.2. Basis of Rigidity (a). The twisting of the shaft should be limited in order to provide accurate prescribed timing or motions. 46

SHAFTS(b) Transverse deflections should be limited to maintain proper

bearing clearances or gear tooth alignment.Classification of shaft1. Plain shaft-With constant diameter, are of the simplest

shape, but find only limited applications. 2. Stepped shaft-Are most extensively used in the engineering

industriesActions of the load on the shaft1. Torsion2. Bending3. Torsion combined with bending.4. Torsion combined with axial tension or compression

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SHAFTSCharacteristics of shafts1. Shafts are not of uniform diameter to provide shoulders for

locating gears, pulleys, bearings, and other attached or contacting parts.

2. Stepped shaft are for motors and locating the rotor, ball bearings, fans, etc,

3.Shaft must be sufficiently rigid to ensure normal operation of the parts in transmitting motion

MATERIALS FOR SHAFTS1. Mild steel-Most common materials for shafting.2. Alloy steel-Used for high strength requirements (nickel, chromium

and vanadium).3. Low carbon steel- (SAE 1015) hot rolled and finished to size by cold

rolling, by turning or grinding for commercial shafting. Shafts for special purpose may be forged 48

SHAFTS DESIGN

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Installation of ShaftingSafetyIt is essential that the mechanism be completely isolated from its power supply while working on couplings or shafts.

Fitting a Plummer (or Pillow) Block to Shaft.(a) Thoroughly clean the shaft and remove any burrs from the ends and keyways.(b) Coat the inside of the bearing with oil to prevent scoring or scratching during assembly.(c) Slide the correct size plumber block on to the shaft to approximately the correct position.

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Fitting a Plummer (or Pillow) Block to Shaft.

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Methods of locking Plummer blocks to a shaft

Many Plummer blocks incorporate ball or roller bearings. With blocks of this type the shaft is located then locked to the inner race.

1. Some types of block use set screws to lock the shaft in position. When fitting this type of block partially unscrew the set screws to allow the shaft to pass through the inner race

2. Other types of block have the bearing mounted on a taper lock adaptor When positioning this type of block on a shaft remove the top half of the housing.Slacken off the adaptor sleeve locknut to allow free movement of the shaft through the bearing. The shaft is locked to the inner race by tightening up the locknut.

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c. Do not over-tighten the locknut as the free movement of the bearing will be affected. When the locknut has been locked in its final position by means of the tab washer check that the race moves freely

d) Align the holes in the Plummer blocks with their mounting holes

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e) Fit the bolts into the Plummer block mountings and tighten them by hand.

(f) Check that the clearances at each end of the shaft are correct.

(g) Lubricate the bearing according to the manufacturer's instructions. Note Some bearings, packed with grease by the manufacturer's, do not need any further lubrication.

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(h) Tighten the lock screws in the Plummer blocks equally to clamp the shaft.

(I) Align the shaft. See next section.

(j) Tighten mounting bolts

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Shaft Alignment

Shafts must be accurately aligned when fitted, as any misalignment will damage or shorten the life of both the bearings and the couplings. Machines bed down when they are used, so the shaft alignment must be checked regularly and corrected if necessary.

Checking AlignmentThere are several methods of checking alignment. It may be done using a straight edge, a dial test indicator or a vernier height gauge. Before beginning an alignment check:

(a) The mounting surfaces must be clean and flat.(b) The mounting bolts must be tight. Alignment must be

checked in both horizontal and vertical plane. 57

Shaft Alignment

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Shaft Alignment1. Using a straight edge.

The use of a straight edge will provide a sufficiently accurate alignment check when a flexible coupling is to be used.

Vertical alignment(a) Place the straight edge along the top of the two shafts.(b) Correct any misalignment by adding or removing shims under the appropriate

Plummer blocks. Ensure that burrs are removed from shims before placing them in position, and that the mounting bolts are tightened down before each check. An inspection lamp should be placed behind the straight edge to reveal whether shafts are aligned vertically.

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Shaft AlignmentHorizontal alignment(a) Place the straight edge along the sideof the shafts.(b) Correct any misalignment by loosening off

the Plummer block mounting bolts and moving the blocks sideways as required. Tighten the mounting bolts and re-check alignment.

(c) Repeat procedure until correct alignment is obtained.

2. Using a Dial Test Indicator. When rigid bearings and couplings are used, greater accuracy is required. Use an indicator with a vee slot in the base. Hold the vee against one of the shafts. Adjust the indicators to read on the end of the other shaft.

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Shaft AlignmentRotate the shaft carrying the base andnote the readings of the indicator for onerevolution.Adjust the position of the indicator toread further along the other shaft. Takereadings for another revolution. Adjustthe alignment as necessary. When theshafts are correctly aligned, the indicatorreading will be constant for the revolutionUsing a vernier height gaugeVertical alignment can be checked with avernier height gauge if the housings aremounted on a machined surface.

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Shaft AlignmentRotate the shaft carrying the base andnote the readings of the indicator for onerevolution.Adjust the position of the indicator toread further along the other shaft. Takereadings for another revolution. Adjustthe alignment as necessary. When theshafts are correctly aligned, the indicatorreading will be constant for the revolutionUsing a vernier height gaugeVertical alignment con be checked with avernier height Gauge if the housings aremounted on a machined surface.

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Shaft AlignmentDoweling

After correct alignment, drill and ream two holes in the Plummer block and its mounting surface. Fit dowel pin, to permanently locate the Plummer block.

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FRICTIONFriction is the resistance to movement when one surface is moved over anotherthereby creating opposition to motion. The amount of frictional resistance between the two surfaces in contact dependsupon: -(a) The roughness of the surfaces in contact. The smoother the surfaces, the lowerthe frictional resistance.(b) The metals in contact: When steel slides on steel, the frictional resistance will

be greater than when bronze slides on steel(c) The force which presses the two surfaces together. The larger the force thegreater the frictional resistance.Advantages Of FrictionThere are many instances whereby friction is advantageous. Some of these are:1. Friction is used as a driving force. Friction transmits the drive between a belt andpulley and provides the drive with friction clutches.2. Friction prevents slipping. Parts gripped in chucks and vices are prevented from

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FRICTIONmoving by friction. Clamping devices also rely on friction,3. Tools are held in position in their tool posts by friction. Milling cutters are

held in position on the arbor of the milling machine by friction,4. Friction is used on brakes.Disadvantages Of Friction

When one surface has to slide over another, friction is a disadvantage. It is therefore disadvantageous to have friction on;

1. Any part of machine tools that have to slide e.g. the shaping machine and its slides.

2. Shafts and bearings,3. The teeth of meshed gears .Obviously, dirt and grit between two moving

machine parts will increase the amount of friction, but it may also scar the surface of the parts and interfere with the operation. Rusting can increase the friction on parts that move together, but lubrication is also used to prevent rust on parts that do not move.

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FRICTIONNATURE OF FRICTION

Ball bearings and roller bearings are typical examples of rolling friction. In machine design, ball and roller you will understand the "whys" of lubrication better if you are familiar with what causes the different types of friction and how their effects can be used or overcome. The simplest way to define friction would be to stay that it is the resistance to movement that is caused when two surfaces move against each other.Even the smoothest highly polished metal surfaces still have some rough edges on the surfaces, and these rough spots will restrict the motion of the two pieces of metal when they are rubbed together. Even though they are so small that a magnifying glass may be needed to see them, they can still have some effect.

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FRICTIONTYPES OF FRICTIONThere are three basic types of friction1. SLIDING FRICTION2. ROLLING FRICTION3. FLUID FRICTION

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TYPES OF FRICTION1. SLIDING FRICTIONThe strongest friction is the SLIDING FRICTION, which is produced when two flator similar surfaces rub against each other. Two bars rubbing together, a piston, could produce this Moving against the cylinder walls, or a shaft turning in a bushing. In each of these instances, a maximum amount of surface of each part is in contact with the other one.

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TYPES OF FRICTION2. ROLLING FRICTIONIt occurs when one part rolls over the surface of the other. This type of frictionconsumes less energy than sliding friction, because there are fewer surfaces making contact at any time. Bearings are used between two surfaces to reduce theeffects of sliding friction to those of rolling friction.

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TYPES OF FRICTION3. FLUID FRICTION

It occurs when the two surfaces are separated by thin layers of fluid (or lubricant). This lubricant changes sliding or rolling friction into the much more efficient fluid friction.

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BELT DRIVE

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BELT DRIVES• In belt drives, power is transmitted by friction• The amount of power transmitted is dependent on the coefficient of friction

between the belt and pulley• The coefficient of friction depends on the materials in contact, their condition

(smooth, dry, oily), the arc of contact between the belt and pulley or sheave and the velocity at which belt operates

• It transfers power from a driver to something that is driven• Are commonly used to transmit motion between two sheaves in one direction

onlyAdvantages Of V-Belts• Compactness Of Design: Short centre distances are possible. The centre

distance between two pulleys may be small as the diameter of the larger sheave.

• Smoothness: This is possible because the v-belt is endless• Bearing Life: Lower belt tensions and hence lower bearing loads are possible.

Also, since this type of belt readily absorbs shock, bearing life is lengthened72

BELT DRIVES• Dependability: When more than one belt is used in a drive, failure of one

will not cause the entire machine to stop. • Maintenance: Except for an occasional tightening of the drive, necessitated

bystretching and seating in the sheave, little maintenance is required

Why V-Belts are UsedThere has been a great increase in the use of v-belts to power industrial drives since their invention early in this century. The advantages they provide include:

• Because they can slip, v-belts cushion equipment from overload and fluctuations in load

• Alignment, although important is not as critical as with other kinds of drives

• They are relatively easy to select, install and maintain• They operate quietly (with proper alignment and tension)• They do not require lubrication

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BELT DRIVESDisadvantages • Disadvantages of using a v-belt drive which may influence selection of

another power transmission device, such as a synchronous drive or direct coupling include V-belts are reliable, relatively inexpensive and easy to install and operate

• They are subject to certain, though minimal, amount of slip making them unsuitable for applications that require invariable, constant speed• They are not as efficient as other drives, although modern technology has

reduced their inefficiency greatly• Angular-velocity ratio is not constant or equal to that of the pulley

diameters, due to slip and stretch.• Heat accumulation is present, and speed is limited to 2300rpm and power

only 500hp.• Adjustment of centre distance or addition of an idler pulley is crucial to

compensate for wear and stretch.74

Row of Flat belts

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BELTSFlat Belts

Flat belts are used early in line shafting to transmit power in factories.It is a simple system of power transmission that deliver high power for high speeds.A good use for flat belts is with small pulleys and large central distances.They come in both endless and jointed construction.They are used as conveyor belts in the food industry.

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Flat drive

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Flat drive

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Rubber belt

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BELTSRound Belts

Round belts are a circular cross section belts designed to run in a pulley with a circular (or near circular) groove.They are for use in low torque situations and may be purchased in various lengths or cut to length and joined, either by a staple, gluing or welding (in case of polyurethane).They find application in sewing machines and some other machines.

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Belt shape

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Belts

Film BeltsThey consist of a very thin belt (0.5-15mm) strip of plastic and occasionally rubber.They are generally intended for low power (7kw or 10hp), high speed uses, allowing efficiency (up to 98%) and long life.They are used in business machines, tape recorders, and other light-duty applications.

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BeltsTiming Belts

Timing belts, (also known as Toothed, Notch or Cog) belts are a positive transfer belts and can track relative movement.These belts have teeth that fit into a matching toothed pulley.When correctly tensioned, they have no slippage, run at constant speed, and are often used to transfer direct motion for indexing or timing purposes.

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Belts

Timing BeltsThey are often used in lieu of chains or gears, so there is less noise and a lubrication bath is not necessary.They run with toothed pulleys.Camshafts of automobiles, miniature timing systems, and stepper motors often utilize these belts.

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BeltsVee Belts

The V-belt was developed in 1917 by John Gates of the Gates Rubber Company.They are generally endless, and their cross-section shape is trapezoidal.The “V” shape of the belt tracks in a mating groove in the pulley (or sheave) with the result that the belt cannot slip off.The belt also tends to wedge into the groove as the load increases

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BeltsV-Belts

The greater the load, the greater the wedging action – improving torque

transmission and making the V-belt an effective solution, needing less width

and tension than flat belts.

The preferred centre distance is larger than the largest pulley diameter, but

less than three times the sum of both pulleys.

Optimal speed range is 330 to 2300 rpm.

For high-power requirements two or more V belts can be joined side by side

in an arrangement called a multi-V, running on matching multi-groove

sheaves.

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V belt

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Double angle v belt

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Notch belt

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BELT DRIVESPROCEDURE FOR INSTALLATION OF V- BELT1. Check the condition of the pulley and check for wobble.2. Check that the belt is match set.3. Align the pulleys according to the procedures outlined above.4. Reduce the centre distance of the shafts by adjusting the position of the motor.

If an idler pulley is used, release the tension on the idler so that the belt can befitted5. Fit the belt or belts taking care not to damage them in the process.6. Adjust the belt tension as recommended.7. Run the unit for a short period says 10 minutes, to allow the belt to seat

correctly in the pulley grooves.8. Readjust the tension. 9. Recheck the tension after 24 hours of operation.10. Ensure that the drive is protected with a suitable guard at all times duringoperation. The guard should be provided with ventilation and secure againstremoval by unauthorized personnel. 90

INSTALLING A SET OF V- BELTS(a) Check that the belts are a matched set.(b) Install the belts starting from the inside pulley and

working outwards.Note

Mountings must be slackened to avoid straining belts.Tensioning BeltsBelts must be tensioned correctly to transfer the drive,and prevent unnecessary wear. As they stretch in use,their tension must be regularly checked and adjusted.Measuring deflection in a slack belt(a) Check the specified deflection In the

manufacturer's instructions.(b) Find the middle of the longest span of beltbetween pulleys.(c) Push this mid-point inwards, then pull it

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Tension tester

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INSTALLING A SET OF V- BELTSout and note the total deflection, which shouldindicate the tension.d. Adjust the tension as necessary.Measuring tension in a taut belt(a) Check the manufacturers' Instructions forthe deflection used and the force needed to reach it.(b) Find the middle of the longest span of beltbetween the pulleys.(c) Attach a spring balance to this point.(d) Pull the belt out to the required deflection andnote the reading.(e) Adjust tension if necessary.

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Adjusting belt tension1. Loosen the locknuts.2. Slacken off the clamping bolts.3. Move the pulley with the adjusting screwto alter the tension. The adjusting screwsmay be turned equally to keep the pulleyscorrectly aligned.4. Check the tension5. Readjust until correct6. Tighten the clamping bolts.7. Tighten the locknuts

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INCORRECT METHOD OF INSTALLING V-BELT ON PULLEY

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TOOTHED BELT AND PULLEYSIn machines where a positive drive is essential and no slip between belt and pulleys can be accepted a toothed belt and pulleys is used as shown.Toothed belts are mainly used for timing mechanisms, where a quiet, positive (no slip) drive is required such as driving a camshafts in a motor car engine

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BELT DRIVINGSince belt driving is still used for various purposes, it is worthy of some attention. The drive from one pulley to another is caused by the frictional resistance between the belt and the pulleys. In practice a little belt slip takes place and there is a small amount of belt creep. If two pulleys of diameter d and D are connected, and if d makes N rev/min, then if we neglect slip and creep:

πd millimetres of belt pass over the small pulley per turn or πdN millimetres per minute.

This length will also pass over the large pulley i.e. pulley speeds are proportional to their diameters, with small pulleys rotating faster than larger ones in the same drive.

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BELT DRIVING

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BELT DRIVINGExample 1. The drive to a machine is as follows: A 400 mm pulley on the

mainshaft drives a 300 mm countershaft pulley. From the countershaft a 300 mm pulley drives a 230 pulley on the machine. If the mainshaft speed is 250 rev/min, estimate the speed of the machine (a) without belt slip, (b) with 5% slip.

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BELT DRIVINGThe drive is shown diagrammatically where A, B, C and D are the pulleys, A and C being the drivers.

Then with no slip:Speed of B (and C) = 250 X (400/300) = 333 rev/min.Speed of D = 333 X (300 /230)= 436 rev/min

If there is 5% slip:Speed of B and C = 333 X (95/100)=316 rev/min.Speed of D =316x (300 /230 )X (95/100)=390 rev/min

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PULLEY RATIO

101

PULLEY RATIO

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TROUBLESHOOTING V-BELT DRIVESIn case of a belt drive malfunction, look for trouble signs and correct problemsbefore replacing belts and resuming operations.

Trouble Possible Causes

Belts turn over in sheaves 1. Misaligned sheaves and shafts2. Worn sheave grooves3. Misalignment of idler sheave4. Excessive belt vibration due to improper tension5. Belt cord damage from improper installation

Bell Squeaks or screeches 1. Too high standing load, causing belt to slipbecause of improper tension.2. Overload, causing belt slippage because ofimproper tension.

Belt chirps 1. Movement of belt on a flat idler or sheave(not harmful).

Belt breaks prematurely 1. Foreign materials in sheaves2. Shock or extreme overload3. Belt damage during installation

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TROUBLESHOOTING V-BELT DRIVES

Trouble Possible Causes

Belt stretched beyond take-up 1. Drive operated with too much tension2. Wrong belt or poor storage in damp area.

Belt has short life 1. Worn sheaves2. Oil or grease on belt3. High temperatures4. Belt cover wear caused by guard or bell guardinterference5. Excessive belt slippage (inadequate tension)6. Poor Storage.

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Belts

Determination Of Belt LengthTo determine the needed length of belt, we use

the following formula;

Belt length=2C+1.57(D+d)+[D-d]² /4CWhere C = centre distance b/w pulleys D = diameter of large pulley d = diameter of small pulley.

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BELT MATERIALS

• Industrial belt drives come in a variety of shapes and materials, and are designed to perform specific tasks. They are;

Rubber Urethane Leather Canvas

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Belt Materials

• Advantages Of Rubber Beltso Made of natural or synthetic fibre core

surrounded by compound.o Resist abrasion, punctures and chemicals.o Dimensionally stable.

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Belt Materials

Advantages Of Urethane Flat Belts• Very flexible to conform to sharp bends.• Have high coefficient of friction, hence they

are used in machines that have to grip products, such as turning cartons or cans, or sorting packages.

• They can be spliced on the job, hence repairs can be made.

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GEAR DRIVES

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http://en.wikipedia.org/wiki/Image:Gears_animation.gif

Gear Drives A gear is a component within a transmission device

that transmits rotational force to another gear or device.

Gear devices can transmit forces at different speeds, torques or in different direction, from the power source.

The most common situation is for gear to mesh with another gear, but a gear can mesh with any other device having compatible teeth, such as linear moving racks.

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GearsA gear’s most important feature is that gears of

unequal sizes (diameter) can be combined to produce a Mechanical advantage.

The rotational speed and torque of the second gear are different from that of the first.

The interlocking of the teeth in a pair of meshing gears means that their circumferences necessarily move at the same rate of linear motion (e.g. m/s).

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Planetary Gear train

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Gear train

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Spur Gear train

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Gear box

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Worn and wheel gear

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Planetary Gear train

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Helical Bevel gear

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Spur bevel gear

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Rack and pinion gear

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Rack and pinion gear

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Gears

• Since rotational speed is proportional to a wheel’s circumferential speed divided by its radius, it means that the larger the radius of a gear, the slower will be the rotational speed, when meshed with a gear of given size and speed. It goes like this;

(speed A x number of teeth A) =(speed B x number of teeth B)

This is known as the gear ratio.

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Gears

1. Gear Types2. Spur Gear3. Helical Gear4. Herring-bone Gears5. Bevel Gears6. Spiral Gears 7. Worm Gears8. Rack and pinion.9. Planetary or internal Gears.10. Hypoid Gears.

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Gears

Spur GearsThe shafts run parallel with the teeth. The teeth are

straight.Helical GearOffer more refinement over spur gears. The leading

edges of the teeth are not parallel to the axis of rotation, but are set at an angle.

Since the gear is curved, this angling causes the tooth shape to be a segment of a helix.

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Gears

• Helical Gears run more silently ,since both teeth engagement take place more gradually.

• It develops an axial pressure which can be absorbed by a thrust bearing.

• Spur gears are used for applications involving high speed, large power transmission, or where noise abatement is important.

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Gears

Double Helical or Herringbone Gears• The double helix compensate for the axial

thrust.• They are applied for heavier load

transmission.

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Gears

Bevel Gears• They are essentially conically shaped, although the

actual gear does not extend all the way to the vertex of the cone that bounds it.

• The angle between the shafts can be anything except zero or 180 degrees.

• Bevel gears with equal number of teeth and shaft axes at 90 degrees are called miter gears.

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GearsSpiral Gears• They are spiral toothed gears. • The shafts cross each other.Worm Gear• A worm gear resembles a screw.• A worm is usually meshed with a disc-shaped gear

called the gear, the wheel or the worm wheel.• Worm and wheel normally have gear ratios of

between 10:1 and 100:1.• They are capable of heavy loads.

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Gears

Rack and Pinion• A rack is a toothed bar or rod that can be

thought of as a sector gear with infinitely large radius of curvature.

• Torque can be converted to linear force by meshing a rack with a pinion.

• It is used in automobile steering wheels.

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Gears

Planetary or Internal Gears• Have better load carrying capacity than external

gears.• They are safer in use because the teeth are guarded.Hypoid Gears• A variation of the spiral bevel gear is the hypoid gear

designed to transmit motion between two on-intersecting and non-parallel shafts.

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Gears

Backlash• Backlash is the error in motion that occurs

when gears change direction.• It exists because there is always some gap

between the tailing face of the driving tooth and the leading face of the tooth behind it on the driven gear.

• The gap must be closed before force can be transferred in the new direction.

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Gears

• The term “backlash” can also be used to refer to the size of the gap, e.g. 0.1mm backlash.

Gear Materials• Generally made of nonferrous alloys, cast

irons, powder metallurgy and even plastics.

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Gears Gear Tooth Wears and

Failures Normal wear Abrasive wear Scratching Overload wear Rolling and peening Rippling Scoring

Gear Tooth Wears and Failures

Pilling Spalling Corrosion Burning Interference wear Ridging Breakage Cracking failure

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CHAINDRIVE SPROCKETS - usually, the driver sprocket is the smaller of the two sprockets and the one having the highest RPM.DRIVEN SPROCKET - this is usually the larger of the two sprockets and the onehaving the slower RPM.CHAIN PITCH - this is the distance (in inches/mm) from the centre of one connecting pin to the centre of the next. In chains having a solid block link, the chain pitch is on alternate spacing.CENTRE DISTANCE - the centre distance is the distance in inches/mm between the centres of the driver and the driven shafts.CHAIN LENGTH - this is the distance from the centre line of the connecting pin at one end of the strand to the empty connecting hole at the opposite end. Chains can be measured in feet/m and inches/mm, or in pitches.CHAIN RATING - the chain rating, or recommended working load, is the load inpounds/kgs that the chain will satisfactorily handle over extended periods of time.

Most manufacturers rate their chains in maximum or average working load.134

CHAINULTIMATE STRENGTH - this is the strength of the chain before it will break. This ISNOT a governing factor in the selection of the chain. However, it gives you the shock loading capacity of the chain.PITCH DIAMETER - this is a theoretical circle described by the centre line of thechain as it passes over the sprocket. The PD of a sprocket is usually below the top of the tooth or the outside diameter (OD) of the sprocket. On drives that have shortened teeth (such as silent chains), the pitch diameter may be larger than the diameter of the circle at the top of the teeth.Installation of Chain DrivesThe following procedure is recommended when installing a Chain Drive:1. Check the condition of the Sprockets and make sure they are clean and free

from damage.

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INSTALLATION OF CHAIN DRIVES2. Align the sprockets as discussed.3. Loosen the tighteners so that the chain will fit over the sprockets.4. Remove the chain from its wrapping and bring the ends together over one of

thesprockets. Use the sprockets teeth to hold the chain and install the final link.5. Fit the side plate and spring clips or whatever device is used to secure the pins.6. Take up the slack in the drive as outlined above.7. Lubricate the chain according to the manufacturers instructions.8. Start up the machine and check that the chain runs through, without excessive

noiseand without binding or whipping.9. Ensure that the lubrication system is working properly.10. Install a suitable designed guard to prevent interference with the drive. (Do notattempt to do this while the drive is in operation).

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MAINTENANCE PRACTICESThese are the following points to be taken into account in the maintenance of chain drives:

1. Alignment and proper tensioning are critical to the operation of the drive.2. Chain drives should be provided with an adequate supply of a suitable

lubricant.3. New links should not be installed in chains that have been significantly

lengthened by wear.4. New chains should not be installed on badly worn sprockets. Sprockets may

be reversed on the shaft to extend their life if necessary.5. New chains should be stored in protective wrappings until ready for use

and protected from excessive heat and moisture.6. Chain drives, like belt drives should be properly guarded and protected

from interference.

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MAINTENANCE PRACTICESADVANTAGES OF CHAIN DRIVES• Chain drives are efficient and do not slip.• Chain drives are fairly flexible and reasonably inexpensive.• Chain drives keep fixed speed ratio without slipping.• Chain withstands heat and dirt better than some other drives.• Chain is less affected by weather.• Chain drives can carry heavier loads.

DISADVANTAGES• Chain drives are fairly noisy.• Most chains require frequent lubrication.• Most chains tolerate very little misalignment.• Chains cannot be used if the drives must slip.

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MAINTENANCE OF CHAIN DRIVECleaning and Oiling a ChainChains that are not totally enclosed with an automatic oiling system must be cleaned and oiled regularly to minimise wear.Cleaning a chain(a) Remove the chain from the drive.(b) Roll up the chain and leave it to soak in

a bath of cleaning agent.(c) Remove the chain and hang it vertically.(d) Scrub the chain with a stiff brush,

rinsing the brush in the cleaning agent frequently.

(e) Rinse the chain in fresh cleaning agent139

MAINTENANCE OF CHAIN DRIVEOiling a chain(a) Check that the chain is thoroughly clean.(b) Roll up the chain and leave it to soak in a bath of oil for several hours. If possible, heat the oil so that it flows into the links more easily.Chain Drive WearWorn chains or sprockets will cause the chain to jump, and possibly come off the sprockets, this will damage the machine and cause a breakdown. Therefore chain drives must frequently be checked for wear.Checking chain wearChains do not wear evenly, so check the complete lengths for wear, if any part is worn replace the complete chain. Chains must be thoroughly cleaned before checking for wear.(a) Stretching Compare the compressed and stretched lengths of the chain. The difference between the lengths indicates the amount of wear.

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MAINTENANCE OF CHAIN DRIVE(b) Bending: Bend the chain sideways.The amount of curvature indicates the amount of wear.Note This check is only for simple chainsSprocket wearExamine the teeth on the sprocket. If the teeth are pointed or hooked, the sprocket is worn and should be ReplacedChain Sprocket AlignmentChain sprockets must be correctly aligned tominimize chain wear and prevent the chain fromjumping off the sprockets. Sprocket alignment must always be checked before a chain is fitted, by placing a straight edge against both faces of the sprocket. Ensure the sides of the chain sprockets are clean

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COUPLINGS

• Coupling is the joining of two rotating shafts together to transmit a rotary motion.

• Couplings compensate for any misalignment between the rotating coupled shafts.

• They allow axial and end movement of the coupled shafts.

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Couplings

• Types of Couplings1. Flanged coupling2. Universal joint

coupling3. Simple coupling4. Gear coupling5. Disc coupling]6. Rubber tyre coupling

Types of Couplings7. Barrel coupling8. Muff or split coupling9. Chain coupling10. Sleeve coupling11. Pin and rubber bush12. Spider coupling

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CouplingsAlignment

• Alignment is very crucial when using a coupling to transmit motion because;

• It prolongs the life of the coupling, bearing, shaft, and the entire machinery.

• It eliminates vibration.TOOLS

1. Straight edge2. Dial indicator3. Vernier height gauge.

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Coupling

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Shaft coupling drive coupling

Coupling

146

Shaft coupling

COUPLINGS

147

Jaw couplings

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Couplings

• Installation For Different Types of Couplings Chain Coupling• If the coupling has a cover, it must be packed

with grease.• Take care to prevent damage to the seals

during fitting.• When the coupling is in use, the grease must

be replenished regularly.

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Couplings

• Gear Couplingo The sleeve have to be placed on the shafts

before the hubs are fitted.o Take care to avoid damage to the seals in the

sleeves during assembly.o The coupling must be lubricated according to

the manufacturer’s instruction after assembly.

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Couplings

• Sleeve Couplingo The shafts must be correctly aligned before

the coupling is fitted.o Hooke’s or Universal Jointo Check the manufacturer’s instruction for

details of lubrication.o On all the following couplings avoid

contamination of the rubber component by oil or grease.

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Couplings• Disc Couplingso When in use, the rubber disc must be regularly

checked. o If it is worn or torn, it must be replaced. Pin and Rubber Bush Couplingo Check the manufacturer’s instruction to see which

half of the coupling is fitted to the driving shaft and which to the driven.

o When in use, the rubber bushes should be checked regularly and replaced if worn or streched.

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Couplings

• Spider Couplingso Care must be taken to avoid damage to the

spider during fitting.o Barrel Couplingso When in use the flexible tyre must be checked

for signs of wear.

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Couplings

• Symptoms Of Failure• Noise• If coupling hubs are not tight and wear begins to

develop, it develops clicking or a rattling noise.• Vibration• Once a coupling begins to vibrate, not only its

condition, but the conditions of other machine elements, such as bearings, seals will begin to deteriorate.

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Couplings

• External Damage• Causes are; • Misalignment.• Inadequate lubrication• Improper Assembly• Interference• Contamination• Overload.

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Seals• Seals are used to prevent the leakage of fluids from

items of rotating machinery and other types of industrial equipments.

• Seal Types• Static seals are those used for sealing surfaces

between which there is no relative motion. A gasket is a static seal.

• Dynamic Seals• They are used where relative motion occurs.

Dynamic seals are often referred to as packing or gland packing.

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Seals

• Gasket Materials1. Rubber Bonded Cork2. Rubber3. Compressed Asbestos fibre4. Plastics5. Metals

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Seal/Bearing Housing Assembly

158

Seal/Bearing Housing Assembly

159

1. Prior to reassembling the Seal/Bearing Housing, carefully check the inner surfaces of the housing and pump shaft. They should be free of rust and scratches. If necessary use fine sandpaper to clean up the surfaces before reassembling. Loosen the eccentric on bearing and set screw on yoke assy in next door above the Seal/ Bearing Housing.

Seals

• Installation of Static Seals• Most times it is necessary to make a leak-

proof joint between assembled joint.• Perfectly matched surfaces are needed to

make such a seal.• Flat seals and gaskets are either provided cut

to shape, or have to be cut from sheets of gasket materials.

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Seals• Installationa. Thoroughly clean the surfaces.b. Check that the surfaces are not buckled, dented or

cracked.c. Put the seal on the surface.d. Check that the gasket lies flat and is the correct size

and shape.e. Position the mating surfaces carefully and gently.f. Check that the seal is still correctly positioned

between the seating.

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Seals

g. Fit the nuts or bolts and screw them up by hand.h. Check the manufacturers instructions to see if

there is a special order for tightening the bolts and a recommended torque value.

i. Check the joint for leaks.j. New gaskets bed down. When the machine has

been running for a short time, re-tighten the bolts.

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Seals

• O-Rings• Elastomeric o-rings is one of the most versatile forms

of static sealing arrangements and can also be used as a dynamic seal.

• The o-ring is normally contained in a groove machined into one of the flange faces.

• The elasticity of the materials allows a good seal to be achieved with relatively low contact pressure.

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Seal

• Crane Mechanical seal

• Conical spring seal

164

Multi spring reversed balanced balance seal

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BEARING INSTALLATION , LUBRICATION AND MAINTENANCE

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CONTENTS1. INTRODUCTION TO BEARINGS2. BASIC CONCEPT OF BEARINGS3. INTRODUCTION TO TRIBOLOGY4. FRICTION IN BEARINGS5. BEARING AND TYPES OF LOAD6. PARTS OF BEARINGS7. CATEGORIES OF BEARINGS8. BALL BEARINGS9. ROLLER BEARINGS10. THRUST BEARINGS11. NEEDLE BEARINGS12. TAPERED ROLLER BEARINGS13. BEARING SELECTION PROCESS AND MOUNTING SKILLS14. BEARING PART NUMBERING15. BEARING MAINTENANCE

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INTRODUCTION TO BEARING

The bearing makes many of the machines we use every day possible. Without bearings, we would be constantly replacing parts that wore out from friction.

168


Have you ever wondered how things like inline skate wheels and electric motor spin so smoothly and quietly? The answer can be found in a neat little machine called a bearing.

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MOTOR BEARING TO EASE MOTION

170


We are going to look how bearings work, look at some different kinds of bearings and explain their common uses as well as its lubrication, and explore some other interesting uses of bearings.

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BASIC CONCEPT OF BEARING

The concept behind a bearing is very simple: Things roll better than they slide. The wheels on your car are like big bearings. If you had something like skis instead of wheels, your car would be a lot more difficult to push down the road.

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That is because when things slide, the frictions between them causes a force that tends to slow them down. But if the two surfaces can roll over each other, the friction is greatly reduced.

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BEARING USED TO REDUCE FRICTRION

174


Bearings reduce friction by providing smooth metal balls or rollers, and a smooth inner and outer metal surface for the balls to roll against. These balls or rollers "bear" the load, allowing the device to spin smoothly.

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TRIBOLOGY

During these interactions, forces are transmitted, mechanical energy is converted, physical and chemical nature including surface topography of the interacting materials are altered.

Understanding the nature of these interactions and solving the technological problems associated with the interfacial phenomena constitute the essence of tribology.

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FRICTION

Friction is the resistance to motion that is caused when two surfaces move against each other.

Even highly polished metal surfaces still have rough edges on their surfaces, and these rough spots will restrict the motion of the two pieces of materials when they move relative to each other.

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FRICTION

• There are three basic types of friction;I. Sliding frictionII. Rolling friction III. Fluid friction

• Sliding friction is the strongest among them and is produced when two flat or similar surfaces rub against each other

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ROLLING FRICTION

• This occurs when one part rolls over the surface of the other.

• This type of friction consumes less energy than sliding friction, because there are fewer surfaces making contact at any time.

• Ball and roller bearings are used to reduce this kind of friction.

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ROLLING FRICTION

180

FLUID FRICTION

• Fluid friction occurs when the two surfaces are separated by thin layers of fluid (or lubricant).

• This lubricant changes sliding or rolling friction into the much more efficient fluid friction.

181

BEARING FRICTION• Plain bearings are very widely used, and use

surface in rubbing contact.• With lubrication they often give entirely

acceptable life and friction.• Low friction bearings are important for

efficiency, to reduce wear and to facilitate extended use at high speeds.

• Bearings can reduce friction by virtue of its shape, material, or

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BEARING FRICTION

o By Shape, gains advantage usually by using spheres or rollers.

o By Material, exploits the nature of the bearing material used.

o By Fluid, exploits the low viscosity of a layer of fluid, such as lubricant of as a pressurized medium to keep the two solid parts from touching, or by reducing the normal force between them.

183

BEARING FRICTION• By Fields, exploits electromagnetic fields,

such as magnetic fields, to keep solid parts from touching.

A combination of these can even be employed within the same bearing

184

BEARING LOADS

Bearings typically have to deal with two kinds of loading, • RADIAL and • THRUST. Depending on where the bearing is being used, it may see all radial loading, all thrust loading or a combination of both.

185

RADIAL LOADS

The bearings that support the shafts of motors and pulleys are subject to a radial

load.

186

RADIAL LOADS

The bearings in the electric motor and the pulley pictured above face only a radial load. In this case, most of the load comes from the tension in the belt connecting the two pulleys.

187

THRUST LOAD

The bearings in this stool are subject to a thrust load

188

THRUST LOAD

The bearing above is like the one in a barstool. It is loaded purely in thrust, and the entire load comes from the weight of the person sitting on the stool.

189

RADIAL AND THRUST LOAD

The bearings in a car wheel are subject to both thrust and radial loads.

190

RADIAL AND THRUST LOAD

The bearing above is like the one in the hub of your car wheel. This bearing has to support both a radial load and a thrust load. The radial load comes from the weight of the car, the thrust load comes from the cornering forces when you go around a turn.

191

Common motions permitted by bearings

• Axial rotation e.g. shaft rotation.• Linear motion e.g. drawer.• Spherical rotation e.g. ball and socket joint. • Hinge motion e.g. door.

192

BEARINGS

Exploded View Of A Bearing

http://en.wikipedia.org/wiki/File:Four-point-contact-bearing_din628_type-qj_120-ex.png

193

BEARING PARTS

The outer race

The inner race

The balls or rollers

The cage

194

END VIEW OF A SHAFT SUPPORTED BY A BALL OR ROLLER BEARING

195

HOW BEARING WORKS

196

THERE ARE MANY TYPES OF BEARINGS, EACH USED

FOR DIFFERENT PURPOSES.

197

CATEGORIES OF BEARINGS

There are two categories of bearingsPLAIN BEARINGS In this kind of bearings the surface of one

component slides over the surface of another.The surfaces in contact are specially prepared in other to minimize friction or wear.

198

CATEGORIES OF BEARINGSROLLING ELEMENT BEARINGS

In this category of bearings a set of rolling elements i.e. either balls or rollers of various shapes are interposed between the two surfaces in order to facilitate movement of one with respect to the other.The relatively small contact area of the rolling elements helps to reduce the resistance to relative motion.

199

BALL AND ROLLER BEARINGS

• Ball and roller bearings do not rub, but rather roll between the ball or rollers and their races.

• The inner race is fixed to the shaft and the outer race is mounted in a hub or bearing support housing.

• A cage is usually there to prevent adjacent balls or rollers from rubbing against one another.

200

BALL AND ROLLER BEARINGS

• The races and balls or rollers are made from special quality steel suitably hardened.

• Cages are made from softer materials, like bronze, aluminum or mild steel.

• A single row bearing with the balls running in grooves in the races is sometimes called a ball race and is intended for carrying mainly radial loads.

• Double row bearings of this type are intended for carrying heavier loads.

201

ROLLING ELEMENT BEARINGS

Ball Bearings,

Roller Bearings,

Ball Thrust Bearings,

Roller Thrust Bearings and

Tapered Roller thrust bearings.

202

BALL BEARINGS

Ball bearings, as shown below, are probably the most common type of bearing. They are found in everything from inline skates to hard drives. These bearings can handle both radial and thrust loads, and are usually found in applications where the load is relatively small.

203

CUTAWAY VIEW OF A BALL BEARING

204

BALL BEARINGS

In a ball bearing, the load is transmitted from the outer race to the ball, and from the ball to the inner race. Since the ball is a sphere, it only contacts the inner and outer race at a very small point, which helps it spin very smoothly.

205

BALL BEARINGS

But it also means that there is not very much contact area holding that load, so if the bearing is overloaded, the balls can deform or squish, ruining the bearing.

206

ANGULAR BALL BEARING

207

ANGULAR BALL BEARING

• Angular contact bearings are capable of taking radial loads, and axial loads in one direction only.

• They are used in pairs and must be fitted the correct way.

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ROLLER BEARINGS

• Roller bearings like the one illustrated below are used in applications like conveyer belt rollers, where they must hold heavy radial loads. In these bearings, the roller is a cylinder, so the contact between the inner and outer race is not a point but a line.

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ROLLER BEARINGS

This spreads the load out over a larger area, allowing the bearing to handle much greater loads than a ball bearing. However, this type of bearing is not designed to handle much thrust loading.

210

CYLINDRICAL ROLLER BEARINGS

• A variation of this type of bearing, called a needle bearing, uses cylinders with a very small diameter. This allows the bearing to fit into tight places.

211

NEEDLE BEARING

212

NEEDLE BEARING

213

NEEDLE BEARING

214

FEATURES OF NEEDLE BEARING

* Extremely High Speed * Extremely Low Rolling Friction * High Load Capacity * High Lubrication Capacity * Low Profile, Lightweight Caged * Low Sensitivity to mismanagement * Caged Needle Bearings offer up to 3X the

speed of unchanged designs * Needles have high length to diameter

215

CUTAWAY VIEW OF A ROLLER BEARING

216

BALL THRUST BEARING

Ball thrust bearings like the one shown below are mostly used for low-speed applications and cannot handle much radial load. Barstools and Lazy Susan turntables use this type of bearing.

217

BALL THRUST BEARING

218

ROLLER THRUST BEARING

Roller thrust bearings like the one illustrated below can support large thrust loads. They are often found in gear-sets like car transmission between gears, and between the housing and the rotating shafts..

219

ROLLER THRUST BEARING

The helical gear used in most transmissions have angled teeth -- this causes a thrust load that must be supported by a bearing

221

TAPERED ROLLER BEARINGS

• The working surfaces of both races and rollers are conical.

• Tapered roller bearings are always used in pairs facing each other.

• They are capable of dealing with considerable axial and radial loads.

• They are connected with axial adjustments to control the amount of play.

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TAPERED ROLLER BEARINGS

Cutaway view of (left) a spherical roller thrust bearing and (right) a radial tapered roller bearing

223

SELF-ALIGNING BEARINGS

• Self-aligning bearings allow the shaft to run at a right angle to the housing axis and are used where precise alignment cannot be maintained.

224

BEARING SELECTION PROCESS

Roller Bearing Selection Process• Bearing selection is a process for evaluating

the suitability of bearings for specific industrial application.

• The first step in bearing selection is identifying the proper bearing type, whether it is a cylindrical, spherical or tapered roller bearing.

225

ROLLER BEARING SELECTION PROCESS

• Check size constraint or available space.• Consider minimum shaft diameter.• Consider maximum housing bore.• Check available width within the application

for the bearing.• After the bearing envelope has been defined,

search the catalog for bearings with bores, outer diameters and widths that will fit within the bearing envelope.

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ROLLER BEARING SELECTION PROCESS• There may be several bearings with different

load-carrying capacities available that fit within the envelope.

• Determine which of these bearings will give the desired life in the application by performing a bearing life analysis for each bearing.

• Once you have chosen the right bearing to handle the load requirements of the application, the bearing selection is completed with the selection of the design options.

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SPHERICAL ROLLER BEARING PARTS NUMBERING

• Timken uses a part numbering system based on the established world numbering system for spherical roller bearings.

• The system consists of a five-digit number, to which a variety of prefixes and suffixes are attached, are attached, indicating application –specific design customization.

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SPHERICAL ROLLER BEARING PART NUMBERING

Example:

T3 2 30 40 CAW33

T3 Designate carburized steel for rollers.

2 The number (2) designates a spherical roller bearing.

30 The next 2 digits (30) are referred to as the dimension series.

They define the width and outer diameter of the bearing envelope.

The first digit, which is the width series, ranges from 8,0 1,2,3,4,5,6,

with 6 being the widest.

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40 The fourth and fifth digits of the part number (40) represents the bore size in mm.

• Multiply this number by 5 to get the actual bore size.• If there is a slash (/)between the third and fourth

digits, the actual bore size would follow.• This (/) rule only applies to bearings with a bore of

500 mm or larger.• Spherical roller bearing 230/500 CAW33 has a

500mm bore.

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• The system consists of cylindrical bearing design type prefixes, dimension series, bore size, and variety of suffixes that identify design and application specific customization.Example: T3 NU 22 80 MA

T3 The first prefix (T3) designates the cylindrical bearing design having two machined flanges on the outer ring and no flanges on the inner ring.

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CYLINDRICAL ROLLER BEARING PARTS NUMBERING

22 The digits (22) are dimension series.80 The next two digits (80) represents the bore size in mm.

• Multiply this number by 5 to get the actual bore size.

• If there is a slash (/) between the third and the fourth digit, the actual bore size would follow.

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CYLINDRICAL ROLLER BEARING PART NUMBERING

• This (/) rule only applies to bearings with bore of 500mm and larger.

• Example; SRB 239/500 CAW33 has a bore of 500mm.

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BASIC SKILLS FOR BEARING MOUNTING

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PRECONDITIONS OF FAULTLESS BEARING MOUNTING

1. Keep bearings well stored in their original packing. Unpack them only at the mounting site immediately prior to mounting.

2. Do not wipe off or wash out anticorrosive oil of new bearings, since the oil combines with the lubricant and provides for sufficient lubrication in the initial running period (oil mating faces, wipe off surplus oil).

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3. Do not perform any modification on two bearings Subsequent drilling of lubricating holes, machining of grooves, flats and the like will disturb the stress distribution in the rings resulting in premature bearing failures. There is also the risk of chips or grit entering the raceway and destroying it within a short period.

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4. The mounting site must be clean and dry, since even the smallest particles may damage the rolling surfaces and humidity leads to corrosion.

Avoid cleaning with compressed air. Do not mount near right angle grinders, floor stand grinders, lathes etc

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5. Check mating parts for dimensional and form accuracy prior to mounting, non-observance of the tolerances for shaft and housing seat diameters, out of roundness of these parts, out-of-square of abutment shoulders etc may impair bearing performance and lead to premature failure.

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6. Mounting procedure and dismounting possibilities should be planned before the actual assembly.

7. Compare bearing number on package or bearing with data on drawing or parts list.

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ARBOR PRESS

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TYPICAL CAUSES OF BEARING DAMAGE

A. Faulty mounting

B. Faulty lubrication

C. Foreign matter in the bearing

D. Water in the bearing arrangement

E. Inaccuracies of form of the shaft or housing seating

F. Vibration

G. Metal fatigue

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MAINTENANCE OF ROLLER BEARING

Roller bearing Is a robust mechanical component which

will give long service life particularly if the bearing is correctly mounted and well

maintained. This Simply means that they should be protected

from dirt, moisture, and correctly lubricated.

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ROUTINE CHECKS DURING OPERATION

Listen,

Feel,

Look and

Lubricate- grease/ oil lubrication.

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LISTENListen - A piece of wooden listening rod or screw driver or similar object against the bearing housing as close to the bearing as possible. Place the ear against the other end and listen. If all is well, a soft purring sound will be heard.

A damaged bearing gives out a loud noise, often irregular and rumbling.

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LISTEN

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FEELCheck the temperature of the bearing arrangement by using a thermometer (digital thermometer) or often simply by placing a hand on the bearing housing. If the temperature seems usually high or suddenly changes it is an indication that something is wrong. The reason may be:

a. Insufficient or excess lubricant b. Impurities c. Overloading.

d. Bearing damage e. Insufficient clearance f. Pinching

g. High friction in the seals or heat supplied by an

external source.

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FEEL

Note :Immediately after lubrication there will be a natural rise temperature which may persist for one or two days.

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LOOK

Ensure that lubrication does not escape through defective seals or insufficiently

tightened plugs. Impurities generally discolour the lubricant, making it darker. Check the

condition of the seals near the bearings to ensure that they will not, for example, permit

hot or corrosive liquids and gasses to penetrate the bearing arrangement.

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LOOK

Any automatic lubricating devices should also be checked to see they function correctly.

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GREASE LUBRICATION Relubricate the bearing arrangements according to the instructions provided by the machine manufacturer

a. Wipe lubricating nipples clean before fresh grease is injected.

b. The housing cap or end cover must be removed, the used grease taken out and fresh grease added.

c. The used grease should be removed and replaced with fresh grease from time to time.

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GREASE LUBRICATION

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OIL LUBRICATION

a. Check the oil level and replenish if necessary

b. Ensure that the air vent of the oil level gauge is not blocked.

c. When the oil is to be changed, it is drained off and the bearing arrangement rinsed with fresh clean oil of the same type before refilling to the required level.

d. Check the oil if it is already contaminated

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OIL LUBRICATION

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MAINTENANCE OF BEARINGS

• There are a number of recommended maintenance procedures for most bearings.

• These maintenance procedures are aimed at preventing premature failure.

1. As with plain bearings, cleanliness is very vital to the satisfactory operation of rolling element bearings. Bearings should be kept free of dust and dirt particles, be kept dry and protected at all times.

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MAINTENANCE

2. Bearings should be handled with clean, dry hands or with clean gloves.

3. It is very important when mounting and dismounting bearings that the correct tools are used and that they are in good condition.

4. Bearings should be wrapped in oil-proof paper when not in use.

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MAINTENANCE

5. Only clean solvents and flushing oils should be used for bearing cleaning.

6. Before installing a rolling element bearing both the housing and shaft should be carefully inspected for burrs, nicks and scratches that may interfere with the fitting of the bearing.

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MAINTENANCE

7. Bearings that are dry and un-lubricated or have not been cleaned should not be spun.

8. Cotton waste or dirty rags should not be used to clean bearings, but only clean lint-free rags.

9. The slushing compound used to protect a bearing in storage need not be removed if it is petroleum based, unless it has gone hard.

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Maintenance10. The force applied when mounting or dismounting a bearing should always be applied to the ring with the interference fit and should never be applied in such a way that the force is transmitted through the rolling elements.

11. Never strike a bearing directly with a hammer or mallet.

12. Bearings should never be heated with a naked flame.

mechanical drives system for promasidor. repaired

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