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Skills Tech Australia School of Engineering Technology Fitting and Machining Student Resource Book MEM18055 Disassemble replace assemble engineering components MEM18006 Disassemble Repair Replace Assemble Fit Replace Assemble Engineering Components Student Name: Contents Section 1: Power Transmission Systems Flexible Belt Drives Key factors enabling belt drives to transmit power Advantages of belt drives (compared with chains) Disadvantages of belt drives (compared with chains) Types of belts Flat Belts V-Belts Timing belts 10 Pulleys or Sheaves 12 Types of Pulleys 12 Pulley Faults 12 Pulley alignment 13 Belt adjustment 14 Belt maintenance 15 Variable speed drives 15 Summary of Belt Drives 16 Chain Drives 17 Chains 17 Advantages of chains (compared to belts) 17 Disadvantages of chains (compared to belts) 17 Uses of chain drives 17 Types of chains used in chain drives 17 Chain Classification 20 Chain Drive Maintenance 21 Sprocket Alignment 24 Installing and Removing Chains 25 Chain Wear 26 Sprocket Wear 27 Hunting Tooth Sprockets 28 Troubleshooting Chain Drive Systems 28 Shaft Couplings 28 Principles of Operation 28 Types of Coupling 30 Maintenance Practices 32 Failure Patterns of Couplings 33 Shaft Alignment 34 Principles of Alignment 35 Methods of Alignment 37 Review Questions – Section 45 Section 2: Fastening and Locking Devices 46 Types of Fasteners 46 Bolts and Nuts 50 Thread Form 50 Tensile Strength 51 Bolt Identification 53 Nuts 53 Problems encountered when fastening nuts and bolts: 54 Machine, Set and Cap screws 55 Screws 56 Self-tapping and Drive Screws 56 Locking Devices 60 Lock wire 60 Liquid Locking Materials (Anaerobic resins) 61 Pins 62 Retaining Rings and Circlips 64 Washers 65 Rivets 65 Review Questions – Section 67 Section – Plain & Anti-friction Bearings .68 Overview of Bearings 68 Purpose of Bearings 68 Principle Classes of Bearings 68 Types of Loads that can be applied to Bearings 68 Design of Bearings 69 Bearing Material Requirements 70 Specific qualities of bearing materials 70 Bearing materials 71 Bearing materials – suited to heavy loading 71 Lubrication of Heavy Duty Bearings 71 Friction 73 Nature of Friction 73 Factors affecting friction 74 Plain Bearings 75 Sliding Contact Bearings 75 Bushes 75 Types of Plain Bearings 76 Installation of Bushes 77 Removal of Bushes 77 Anti-friction bearings 78 Bearing designations 79 Parts of an anti-friction bearing 81 Types of anti-friction bearing 82 Fitting anti-friction bearings 88 Inspection of bearing journals and housing bores 90 Installation Methods - Force fitting 93 Installation Methods - Shrink fitting 96 Installation Methods - Freeze fitting 98 Advantages and Disadvantages of Shrink and Freezing Methods 98 Other installation methods 99 Setting of bearings – Preloading and Endplay 101 Methods of measuring preload 102 Preloading of duplex bearings 104 Removal of Bearings 105 Do’s and Don’ts when working with bearings? 108 Review Questions – Section 109 Section 4: Lubrication 112 Lubrication in General 112 Fluid Lubrication: 112 Types of Lubricants 113 Oils 113 Greases 113 Types of Greases 114 Lubrication delivery systems 115 Oil-Bath Lubrication 115 Wick-Feed Lubrication 116 Drip-Feed Lubrication 116 Oil-Splash Lubrication 116 Circulating-Oil Lubrication 117 Oil-Jet Lubrication 117 Oil-Mist Lubrication 117 Pressure and Pressure Spray 118 Grease Lubrication 118 Grease packing of Bearings 118 Lubricant selection 119 Viscosity 119 Viscosity Index 119 Pour Point 119 Lubricant additives 121 Review Questions – Section 122 Section 5: Sealing Mechanisms 123 Introduction 123 Static sealing mechanisms 124 Types of static seals 124 Gaskets 124 Desirable characteristics of gaskets 125 Gasket materials 125 Metallic Gasket Designs 126 Metallic O-rings 128 Working with Gaskets 129 Sealing compounds with gaskets 132 Gasket failures 132 Static sealing with O-rings 134 Sealants 135 Dynamic sealing mechanisms 136 Dynamic O-rings 136 Radial Lip Dynamic Seals 137 Exclusion Type Dynamic Seals 141 Clearance Type Dynamic Seals 144 Compression Packing Type Dynamic Seals 146 Molded Packing Type Dynamic Seals 147 Face Type Dynamic Seals 149 Diaphragm Type DynamicSeals 151 Diaphragm Type DynamicSeals 152 Review Questions – Section 154 Section 6: Gearing Systems 156 Definitions 156 Types of Gears 162 Enclosed Gear Systems - Fixed Ratios 166 Enclosed Gear Systems – Selectable Ratios 172 Gearbox Installation 176 Maintaining and Rebuilding a Gearbox 176 Review Questions – Section 178 Section 7: Pumps 180 Introduction 180 Centrifugal Pumps 181 Concepts For Centrifugal Pumps 184 Trouble shooting a pump 189 Preventative maintenance 190 Other types of pumps 197 Review Questions – Section 200 Section 8: Maintaining Mechanical Equipment 202 Introduction: 202 Methods of Performing the Maintenance Function 202 Prevention of Breakdown: 203 Evaluating Mechanical System Problems: 205 System Disassembly 208 Disassembly Procedures 208 Examples of Specialised Tools 209 System Reassembly 211 Tasks for System Reassembly 211 Review Questions – Section 214 Section 9: Repairing Mechanical Components 215 Mechanical Component Failure 215 Types of Failure 215 Modification of Components 215 Repairing Mechanical Components 216 Keyway Damage 216 Seal Damage 217 Bearing Location Damage - Shaft 217 Bearing Location Damage - Housing 218 Shaft Centre Damage 219 Shaft Sealing Surface Damage 219 Damage to end of an otherwise serviceable Shaft 219 Broken gear teeth 220 Broken casting 220 Cracks in casting 221 Broken bolts or studs 221 Broken taps 222 Damaged threaded holes 222 Section 10: Risk Assessment .224 Hazard Identification, Risk Assessment And Control Procedure 224 Section 1: Power Transmission Systems Flexible Belt Drives Key factors enabling belt drives to transmit power Flexible Belt drives transmit power by contact between the belt and the driving and driven pulleys by friction The design of belt drives is usually arranged to enable the transmission of power between two parallel shafts The ability of belts to transmit power depends on: The tension holding the belt to the pulleys The friction between the belt and pulleys The arc of contact or “wrap” of the belt on the pulleys The speed of the belt Advantages of belt drives (compared with chains) Do not require lubrication Generally operate with less noise Flat belt drives can be used where extremely long centre distances make chain drives impractical Flat belts are advantageous for extremely high speeds Single belt drives will accept more misalignment than chain drives Many belt drives are less expensive for low power and lower ratio applications Disadvantages of belt drives (compared with chains) Belts are more easily damaged by oil, grease and heat Belts cannot be used where exact timing or speed is required (Unless a special toothed belt is used) Belts are not suitable for very high load, low speed applications Types of belts There are six major types of belts used in modern heavy machinery Flat belts Linked V-belt V-belts Banded V-belts Timing belt Ribbed V-belt Flat Belts Use of flat belts has decreased because most machines today have gear drives or use V-belts A common use is where high power is needed to drive a separate machine eg Agricultural tractor auxiliary drive to a saw bench, irrigation pumps etc In this example where high speed is required, the pulley has a crown in the centre to keep the belt from slipping off Ref Fig 1(b) A more common use of flat belts is as a conveyor (medium speed) where the belt itself does the work eg Combine harvester grain conveyor, trencher soil conveyor Ref Fig 1(a) Flat belts are usually made from fabric or cord impregnated with natural or synthetic rubber Ref Fig 1(a) Some types use cotton or synthetic fibre fabric without rubber impregnation Disadvantages of flat belts: They need larger pulleys and so take up more space They are also less flexible than some other belts Advantages of flat belts: Simplicity of operation Strength – larger cross section, often reinforced Low initial cost Resistance to extreme dust V-Belts V-belts are the most common way of driving loads between short-range pulleys Their uses in heavy equipment apply to water pump, generator/alternator, fan and accessory drives on engines, as a transmission on smaller machines, and in combine harvesters, industrial sweepers, etc They may be used in single or multiple belt drives They have power ratings from fractions of a kW for the smaller belts, up to 35-40 kW per belt for the larger belts The simple wedging action of the belt against the sides of the pulley groove is the outstanding feature of V-belts A greater pull or load merely results in a tighter belt grip “Pulleys” used with V-belt drives are often called “sheaves” Either term is correct Disadvantages of V-belt drives compared to flat belt drives: The only disadvantage with V-belts and V-pulleys is that they cost more than flat belts and pulleys Advantages of V-belts drives compared to flat belt drives: Wedging action permits a shorter arc of contact on small pulleys and hence greater speed ratios Shorter centre distances can be used for a compact drive and use of streamlined belt guards Absorb shocks to cushion motors and bearings against load fluctuations Vibration and noise levels are low Maintenance and replacements are quick and easy Power transmission efficiency is as high as 95% V-belt Construction V-belts are made in several types (Fig 2), but each one is made up of four sections The top section of the belt is known as the tension section (Fig 2) It is rubber and stretches as the belt forms around the sheave The bottom section is called the compression section because it compresses when wedged into and shaped around the sheave (Fig 2) The centre section is known as the strength section These cords give the belt its tensile strength (Fig 2) The complete belt is covered by a cover section of tough fabric and rubber that protects the inner parts Some belts (called “raw edge”) have no fabric cover Note that the heavy-duty belt has more strength cords and a heavier fabric cover than the standard-duty type Double-angle V-belts are used for drives where both the top and the bottom of the belt must contact the sheaves as in a serpentine drive The strength cords are in the centre Tension or compression forces exist on either side of the strength cords while the belt bends either way Some V-belts also have corrugated under sides for greater flexibility Operation of V-belt drives Due to the wedging action of their angled sides, V belts pull well even when wet The section going around a pulley tends to bulge as it bends, hugging the flanges tightly See Fig The angle between standard belt sides is 40 degrees The angle between the two sides of the pulley groove is somewhat less to ensure full wedging contact The groove is much deeper than the belt, for a standard V-belt must never ride the bottom of the groove If it does, it loses almost all grip, no matter how tight Banded V-belts Banded V-belts are multiple belts, which have been permanently vulcanised to a tie band See Fig This reduces problems on drives where belts may whip, turn over or jump off Other than the tie band they are the same as conventional V-belts Fig Construction of a banded V-Belt Linked V-belts Link type V-belts simplify assembly of multiple belt drives where it would be difficult to match the length of each belt or where replacement of a standard belt would be very troublesome Links can be added or removed to lengthen or shorten the belt See Fig The flexible links are laminated to tough fabric and rubber and are held together by metal studs secured with washers The links are shaped so that the sides of the complete belt fit a standard sheave groove Fig Linked V-Belt V-Ribbed Belts V-ribbed belts combine the simplicity of the flat belt with the positive tracking of V-belts They eliminate the matching problem in multi-V-belts, although the pulleys must be grooved to mate precisely with the belt The pulleys must also be precisely aligned V-ribbed belts are made of moulded rubber A ply of strength cords run along the “flat” section of the belt See Fig Most of these belts are oil and heat resistant Unlike V-belts, which depend on wedging action to transmit power, V-ribbed belts depend entirely on friction between pulley and belt Tension is somewhat greater than for conventional Vbelts These belts are suitable for very high speeds with power ratings up to 7.5kW (10 H.P.) V-belt sizes and selection There are many different types and sizes of V-belts used in heavy equipment We will look at common sizes for standard V-belts that are shown in Figure They range from 10mm wide up to 32mm wide ... must be replaced If not they will be mismatched with one new belt taking more drive than the remaining older stretched and worn belts Keep an eye out for cracks, splitting, tears etc and replace. .. assembly of multiple belt drives where it would be difficult to match the length of each belt or where replacement of a standard belt would be very troublesome Links can be added or removed to lengthen... V-belts that are shown in Figure They range from 10mm wide up to 32mm wide Figure When ordering replacement V-belts, it is important to select the correct size, length and duty The Vbelt must