Bảo dưỡng và sửa chữa (maintain and repair mechanical drives and mechanical transmission assemblies)

Đây là nguồn tài liệu phục vụ cho giảng dạy và học tập môn bảo dưỡng và sửa chữa cơ khí ô tô (maintain and repair mechanical drives and mechanical transmission assemblies) . Trong tài liệu có phân tích và các hình vẽ đi kèm, đồng thời có các câu hỏi để kiểm tra kiến thức của người học.

MEM18007B

Maintain and repair mechanical drives and mechanical transmission assemblies

Reference Book

UNIT: 18007B – Maintain and repair mechanical

drives and mechanical transmission assemblies

 The State of Queensland (TAFE Queensland) 2002

Copyright protects this publication Except for purposes permitted by the Copyright Act, reproduction by whatever means is prohibited without the prior written permission of TAFE Queensland Inquiries should be addressed to the Librarian (Copyright), Library and Information Management Services, Open Learning Institute of TAFE, GPO box 1326, Brisbane Q 4001

Edition : 1 April, 2002

Template Version 5, April, 2002 by N F Lassen, Mount Isa Institute of TAFE,

PO Box 1612 Mount Isa Queensland, 4825

Acknowledgments:

Acknowledgments:

Unit Writer: N F Lassen, B Teaching (FET);

Cert.IV in Workplace Training & Assessment; Trade Qualified; Cert III InfoTech; MERSITAB Reg

Assessor; Teacher, Mt Isa Institute

of TAFE

Unit Editor/Moderator: C N Leader, B Ed; Dip.Eng; Trade

Qualified; BB; ES; Cert.IV in Workplace Training & Assessment; MERSITAB Reg Assessor; Principal Teacher, Wide Bay Institute of TAFE

Moderators Signature: C N Leader Date:

Unit contents

Page

Unit contents 3

Unit: 18007B – Maintain and repair mechanical drives and transmission assemblies 5

Pre-requisites 5

Resource Materials 6

Introduction 6

Range statement 8

Assessment 8

About the Icons 11

Check your current knowledge 11

Section 1 – Friction Belts 13

Introduction 14

Characteristics of belts 15

Flat belts 16

Vee Belts 19

Timing or synchronous belts 23

V-ribbed belts 23

Belt and pulley installation 25

Checklist 40

Summary 40

Section 2 – Working with gears and Gear drives 41

Introduction 42

Introduction to gears 42

Gear terminology 47

Worm and Worm Gears 51

Checklist 68

Summary 68

Section 3 – Chain drives 69

Introduction 70

Precision roller chain 71

Types of chain 71

Joints and spare parts 73

Chain pinions and chain wheels 77

Installation and maintenance of chain drives 78

Methods of chain lubrication 87

Checklist 92

Summary 92

Section 4 – Clutches, brakes and couplings 93

Introduction 94

Purpose of couplings 95

Installation and maintenance of couplings 106

Clutches 114

Brakes 120

Checklist 129

Summary 129

Section 5 – Shaft, drives and coupling alignment 130

Introduction 131

Types of misalignment 132

Types of misalignment 133

Principles and methods of Alignment 134

Soft foot 137

Aligning pulleys 138

Laser belt aligning tool 141

Aligning chain drives 143

Symptoms of misalignment .144

Checklist 150

Summary 150

Unit: 18007B – Maintain and repair

mechanical drives and transmission assemblies

Welcome to Unit 18007B, which is a stream unit of the National

Metal and Engineering Industry Competency Standards This unit

is designed to help you understand the maintenance and repair of

a range of mechanical power transmission and drive components and/or assemblies

This Study Guide is designed to guide you through the unit and assist in planning your study It is written in a self-paced format that will allow you to progress through at your own speed and convenience It is structured to assist you in obtaining the

necessary knowledge and skills required for this unit of

9.1A – Draw and interpret sketch

9.2A – Interpret technical drawing

18.1A – Use hand tools

18.2A - Use power tools, hand held operations

18.3A – Use tools for precision outcomes

18.6A – Dismantle/repair/replace/assemble engineering

components

18.9A – Levelling and alignment of machines and

engineering components

Resource Materials

This study guide recommends these texts to further the topics covered:

Fitting and Machining, Edited by Ron Cully

Principles of Machine Operation and Maintenance, by Dick Jeffrey

Introduction

The study guide is divided up into a number of sections with Activities to work through These Activities when successfully completed will build towards competency Each section is further divided into a number of related Topics What you will cover is presented at the beginning of each section

Take the time to work through the various Activities that are included to build on your knowledge and skills They will also help to assess your current level of knowledge and to decide how much time and effort to spend on each part

The table on the page 5 shows how the Activities you need to complete in this study guide relate to the

Criteria in the Unit that will be used in your

assessment The Activities may also relate to

practical tasks used to assist in developing both

your underpinning knowledge and skills relevant to

this Unit It is recommended that you become

familiar with this table You should refer to the

Competency Unit in your training record book or in

the appendices of this study guide for additional

information if necessary

The following elements and their associated criteria

requirements are covered in this Study Guide:

Element 18007B.1 – Undertake maintenance of mechanical

drives and mechanical transmission assemblies

Element 18007B.2 – Adjust mechanical drives and

transmission assemblies

Element 18007B.3 – Diagnose faults

Element 18007B.4 – Repair mechanical

drives/transmissions

Element 18007B.5 – Final adjust and commissioning

The information provided here covers the underpinning

knowledge you will require when final workplace assessment takes place

Only when you have successfully completed both the underpinning knowledge and Activities contained in this Study Guide and any necessary final workplace

assessment if required, will you be deemed competent in this unit

Remember: If you need assistance ask! Contact your Teacher/Trainer and/or RTO at any time

Range statement

Work undertaken autonomously or in a team environment using predetermined standards of quality, safety, and workshop

procedures involving the adjustment, repair, replacement of

mechanical drives/transmission assemblies and associated

components Drive devices may include worm and worm wheel, line shafts, plumber blocks, pulleys, sprockets, belts, taper bush assemblies, roller chains, chain drives, mechanical and hydraulic couplings, compression couplings, disc type flexible couplings, spider type, chain couplings, universal joints, bevel gearing, rack and pinion gearing, dog toothed clutches, cone type clutches,

friction/plate type clutches, centrifugal clutches, toggle action linkages, magnetic clutches, sprag clutches, band type brakes, and other associated type components Spare parts replacements selected from manufacturer’s catalogues or engineering

specifications All adjustments, removal and repair, replacement and installation practices in conformance to safe workshop

practices utilising appropriate maintenance principles, methods, techniques, tools, equipment and procedures Lubrication

requirements attended to according to suppliers instructions and recommendations Assemblies tested using appropriate methods for conformance to specifications and operational requirements This unit should not be selected where either 18.42A (Diagnose and repair manual transmission) or unit 18.44A (diagnose and repair drive line and final drives) or unit 18.43A (Diagnose and repair automatic transmissions) are also selected

Assessment

Your assessment will comprise two parts, an assessment of your underpinning knowledge, and of your practical skills

Your underpinning knowledge for this unit may be assessed

by a written examination or by oral questioning A written assessment of your underpinning knowledge may include short answer, multiple choice, true or false, word or sentence completion, logical ordering, object recognition or other types

of written questions as deemed appropriate to assess your underpinning knowledge required for this unit in accordance with the criteria contained in each element of the competency unit

Assessment of your practical skills will require the completion

of one or more nominated work tasks/work pieces or projects

to specification from drawings in the Practical Task

Appendices in this guide, or, as contained in Practical Task, Project or Worksheets if being used when this unit is being undertaken concurrently with other units

You should refer to any marking criteria for practical work contained in the relevant Marking Criteria appendix of this study guide for further information

To assist you as you progress through this unit, Student Activity Recording and information pages are included in the appendices of this guide This is to record the successful achievement of both study and practical activities as you progress through this unit

It is your responsibility to ensure each successfully completed activity and underpinning knowledge test/s are entered and signed off by your teacher/trainer

When the unit is successfully completed, this page will be removed and a copy given to you to place in your training record book

Activity Mapping Guide

Criteria No & Description Activity or Project No 18007B.1 – Undertake maintenance

of mechanical drives and

mechanical transmission

assemblies

1, 2, 3

18007B.2 – Adjust mechanical

drives and transmission

assemblies

1,2,3

18007B.3 – Diagnose faults 1,2,3

18007B.4 – Repair mechanical

drives/transmissions

1,2,3

18007B.5 – Final adjustment &

commissioning

1,2,3

-

-

-

-

-

-

NOTE: This activity mapping guide is here for your

benefit to keep track of how the activities and

underpinning knowledge relate to each assessment

criteria in each section For further information on the

criteria, refer to the Unit Competency Standard in

Appendix A

About the Icons

Activity

Activities, self-checks and examples are embedded into the Study Guide These will draw on the learning you are undertaking, your previous experiences and various workplace situations If you have any problems answering the questions, refer back to the

appropriate part of the Study Guide and revise that Section

Discuss the activities, your answers and findings to further your understanding

Self assessment

Self-assessment questions/exercises are included throughout this Study Guide They build and collect the information you will need

to put towards achieving competency You will be required to

complete successfully all of the Self-Assessment activities before formal on the job assessment begins You can do this to

suite your own learning style

Check your current knowledge

You may feel that you already have some prior knowledge and/or experience of the elements covered in this Unit Look through the various sections and if you feel that you can complete the Self-Assessment activities, do so now This will give you an opportunity

to test yourself beforehand and depending on your results, you may choose to bypass or skip the learning materials for this unit and focus on the on-the-job component of the assessment

If you cannot answer the Self-Assessment activities

comprehensively, you should now study the relevant sections of this unit and redo the associated self-assessment activities

Remember that you can come back at any time and review any part of this unit if you need to

Section 1 – Friction Belts

This section contributes to the underpinning knowledge and skills development required for the successful completion of the following criteria:

18007B.1.1 – Principles of mechanical drives and mechanical

transmission assemblies understood

18007B.1.2 – The function of the main parts of the designated

mechanical drive/transmission understood

18007B.1.3 – Using appropriate maintenance principles,

techniques, tools, and equipment, mechanical drive/transmission components checked for wear, distortion, tensions, misalignment, fatigue,

lubrication, slackness, tooth wear, breakages, and other related malfunctions

18007B.1.4 – Assembly identified as requiring further diagnosis

Repair or adjustment and findings documented by appropriate means

18007B.2.1 – Adjustment requirements determined by appropriate

means

18007B.2 -2 - Adjustment method suitable for type of drive or

transmission assembly being serviced determined from manufacturer’s instruction sheets, standard workshop manuals/procedures or other appropriate means

18007B.2.3 – Adjustment tools selected according to the type of of

assembly being serviced

18007B.2.4 – Using appropriate maintenance principles,

techniques, tools, and equipment, drive/transmission components tensioned, aligned, balanced or adjusted

to manufacturer’s specifications according to safe work practices

18007B.3.3 – Faults localised at the component level and

identified for repair or replacement

18007B.3.4 – Fault cause analysed and preventative measures to

avoid recurrence developed, documented and actioned by appropriate means

18007B.4.3 – Tools and equipment selected according to the type

of drive assembly being serviced

18007B.4.4 – Mechanical drive/transmission assembly

dismantled using appropriate maintenance principles, techniques tools, equipment and safe work practice

18007B.4.6 – Serviceable items selected using manufacturer’s

catalogues, spare parts lists, engineering specifications, and obtained by appropriate means

Introduction

Belts provide an efficient load transfer between shafts on a wide variety of applications They also perform special tasks such as speed ratio variation, power transmission in more than one plane, clutching, torque limiting, and shaft synchronization

Compared with most forms of power transmission, belts often

provide the best overall combination of design flexibility, low cost and maintenance, ease of drive assembly, and space savings

Disadvantages on some applications may include the need to tension belts periodically to avoid slippage (note: over tensioning can damage bearings on pulley system), deterioration because of severe exposure to chemicals and lubricants, and the requirement that damaged belts must be replaced, rather than repaired

re-The following topics will be covered in this section:

There are many different types of power transmission belts Depending on the requirements of these types, other characteristics are important

1 Continuous timing belts are composed of a closed round rubber or Polyurethane provided with teeth In some cases, power transmission is important In other applications, synchronization is the key element Mainly in this case, timing belts are steel cord reinforced

2 Discontinuous timing belts have the same characteristics as the continuous timing belts, but the belt is not closed Main application here is linear transport When precision is of essence, steel cord will be selected as the reinforcing material

3 Flat belts are used in the mining industry, in the metallurgical industry and in ports For heavy duty applications, steel cord is the preferred tension member

4 V-belt products are widely used in transmission equipment

of petrochemical industry, light industry, mine metallurgy, textile, automotive etc The stress of this application is on transfer of power, so the breaking strength is the most important feature

Flat belts

Flat rubber belts were developed around the turn of the century, primarily as replacements for leather belts With the advent of V-belts, fewer machines were designed to use flat belts, and their production became largely a matter of supplying replacement parts

Recent developments in flat-belt technology have overcome their previous drawbacks of high tension and mis-tracking New designs and advances in materials have made both low and high-power transmission practical and cost efficient, and at speeds that usually exceed other belt designs

Higher power flat belts

Developments here include sticky, yet abrasion-resistant rubber compounds that eliminate the need for high tension to grip pulleys These materials also allow lower shaft and bearing loads to transmit significant amounts of power The strongest flat belts now transmit over 3Kw per centimetre of belt width

Different flat belt surface patterns serve different transmission requirements For example, in high-power applications and outdoor installations, longitudinal grooves in the belt surface reduce the air cushion that flat belts generate when they run at speed onto a pulley An air cushion reduces friction between pulley and belt In addition, the longitudinal profile nearly eliminates the effect of dirt, dust, oil, or grease Furthermore, the grooves reduce the noise level of an already quiet power transmission design even more

Perhaps the most significant advantage of flat belts is their high efficiency nearly 99%; about 2.5 to 3% better than V-belts

Three factors account for the good efficiency:

 lower bending losses due to the thin cross section,

 low creep because of special friction covers and

 high modulus of elasticity traction layers, and

 no wedging into pulleys like V-belts Without the wedging action as in V-belts, flat-belt and pulley wear is minimal

Flat belts offer greater design freedom than standardized designs because they are available in almost any width (increments of 2

mm are common) and length, This means drives can be sized closer widths to optimum rather than the next size larger

Pulley alignment is equally important

to flat belts as it is to other types of

belts Crowning of at least one

pulley, usually the larger one,

improves belt tracking Flat belts are

more tolerant of misalignment;

however, proper alignment improves

belt life sand efficiency

Low-horsepower drives with small pulleys are usually more expensive than comparable V-belt drives But once the larger pulley diameter reaches 750mm or more, flat-belt drives become less expensive Despite initial cost of smaller flat-belt drives, their efficiency gain makes up for the cost differential within a few years

Joining flat belts

Flat belts are joined by a variety of fasteners, depending on the type of material, the width of the belt, and the amount of power to

be transmitted These include:

Tensioning of flat belts

Tensioning of flat belts constructed of synthetic materials is important Incorrect tension may reduce the amount of power transmitted, shorten belt life and damage equipment A simple tensioning method that can be used to tension a flat belt correctly

is as follows:

After joining the belt, place it flat on a table and draw two lines 0.5

to 1m apart across the belt at 900 to the edge of the belt This distance may be shorter if the belt is very short

Mount the belt and gradually increase the tension by increasing the centre distance until the required increase in distance between the gauge marks is reached Rotate the pulley and belt as you make the adjustments to ensure an even spread of tension throughout the belt

The increase in elongation required should be obtained from the belts manufacturer’s specifications This is normally expressed as

a percentage increase and you may have to calculate the increase

in distance required using the gauge distance you have marked on

Classical section vee belts

These are the most widely used type of vee belt and have a range of sizes designated M, A, B, C, D, and E The classical vee belt is

designed to drive on the sides only of the belt and pulley sheave They have an include angle on the sides of 40o

Narrow section vee belts

The narrow or “wedge” design belt provides more tensile support the classical Vee belt design Narrow belts of this design handle an equivalent load, but with a narrower face width and smaller diameter pulley sheaves than the classical vee belt These features allow the use of smaller or fewer belts to transmit the power, enable lighter drive weights and sizes

These belts are typically designated 3V, 5V, and 8V

Caution! The narrow section and classical vee belts are not

interchangeable and will not run on the same pulley sheaves

Narrow wedge vee belt

Raw edge vee belts

Unlike conventional fabric-covered

V-belts, raw-edge belts have no

cover Thus, the cross-sectional area

normally occupied by the cover is

used for more load- carrying cord

Cogs on the inner surface of the belt

increase airflow to enhance cooler

running They also increase

flexibility, allowing the belt to

operate with smaller sheaves With

classical V-belts, certain

under-designed or problem drives can be

upgraded to "satisfactory" by substituting classical cogged belts for classical envelope belts without replacing sheaves

Because of their higher coefficient of friction, cogged belts tend to

be more sensitive to alignment While envelope vee belts can tolerate some misalignment, cogged belts are more likely to turn over under the same conditions Cogged belts should not be used

in clutching drives, drives with severe shock loads, and drives that have changing centre distances, such as shaker screens In these applications, the aggressive nature and flexibility of cogged belts can cause vibration, belt turnover, and belt breakage Cogged belts should also be avoided in drives that require slippage during frequent stops and starts

Double vee belts

A variation of the classical belt, double vee

or as they are sometimes called, Hex belts,

come in AA, BB, CC or a deep CCP cross

section These belts transfer power from

either side in serpentine drives A drive

design using Hex belts is more complicated

and manufacturer’s V-belt engineering

manuals should be consulted when

replacing or troubleshooting these drives

Joined (Multi-strand) belts

This type of vee belt is commonly

used in applications where shock,

pulsating loads, or extreme

vibration occurs where single vee

belts could turn over on the

pulleys They are tied together

permanently with a single tie

band layer to provide lateral

rigidity This keeps the belts

running in a straight line in the

pulley sheaves

T Link vee belts

This belting is widely used in industry for coupling transmission systems together Although considerably more expensive than ordinary V belts, it does have some important advantages:

It can be installed without having to dismantle the drive system and spend hours pulling apart well set-up or bedded in components

 It "absorbs" vibration and is

recommended for drives where

the transmission of vibrations

from the motor or other sources

are undesirable, in precision

grinding machines and high

speed lathe spindles, for example

 It is of very high quality and

claimed by the manufacturers to

have improved shock loading

capacity and improved abrasion, oil, chemical, damp and heat resistance

 It fits all standard pulleys - there is no need to replace or modify the existing pulleys

Timing or synchronous belts

These belts are used where drive

speeds of two shafts must remain

synchronised They can also be used

to in place of roller chain drives

eliminate noise and maintenance

problems associated with chain drives

They are ideally suited for use in

situations where space is limited This

type of belt is also extremely efficient

when compared to the average

classical vee belt

The three important dimensions of a synchronous belt are:

 Belt pitch in mm– the distance between two adjacent tooth centres

 Belt pitch length in mm – Circumference as measured along the pitch line

 Tooth profile (obtained from manufacturer’s catalogue)

This type of belt runs on sprockets that are specified by the following:

 Pitch – distance between grove centres

 Number of sprocket grooves

 Width – the face width

Vee ribbed belts have the following advantages:

 Transmit 30% more power under the same conditions as a classical vee belt

 Occupied space is 25% smaller than common V belt

 Suitable for not only transmission of power with small pulley diameters, but also high-speed transmission with speeds of 40m/s at low vibration levels

 Low elongation and long life

Ribbed belt Dimensions

The important dimensions for a ribbed belt are:

 The pitch (shown as Pb)

 The height (shown as h)

 The included angle (shown as a)

Belt and pulley installation

Installing and aligning pulleys

Pulleys may utilise a parallel bore with a plain parallel key seat and sunken key in the shaft, and, in other instances, utilise a taper lock hub and pulley that is also keyed likewise to the shaft

Taper lock hubs give the advantage of having a standard sized pulley that can be fitted to a range of shaft sizes by selecting the appropriate sized bush for the shaft They also provide ease of fitment and removal during maintenance operation

When fitting keys for taper lock

bushed pulleys, it is essential that the

correct top clearance between the key

and the key seat in the bush is within

the specified range If insufficient

clearance is present, the taper lock

bush may be cracked through from

the base of the key seat to the external

face of the bush

Fitting a taper lock bush and pulley

1 Match the plain holes of the bush to the pulley (not the

threaded holes)

2 Slip the entire assembly onto the shaft

3 Insert the screws into the holes that are threaded in the

pulley only

4 Lightly tighten the screws

5 Check the total height of the keyway and key seat in the

pulley and width of key

6 Consult manufacturer’s manual or engineering reference book for the correct key clearance for the size of key being used

7 If necessary, machine or file to correct height for the

required clearance

8 Loosen screws and remove assembly from shaft and fit key to shaft

9 Slip the assembly back into position and tighten the screws

to the manufacturer’s torque requirement for the sized bush

being used DO NOT OVERTIGHTEN!

Tensioning vee belts

There are several methods with which correct belt tension can be set The amount of tension required depends on the size of the belt and the span length of the belt These are:

 Rule and calculated deflection of belt

 Mechanical tension tester

 Electronic meter

The span length of a drive belt is the distance from the belt contact point on one pulley to the belt contact point on the other as shown

The general deflection is calculated as 1.5 mm per centimetre of span length or, in the imperial measurement system, one sixty-

fourth of an inch per inch of belt span length

Mechanical tension tester

1 Measure the span length

2 Position the lower of the two

indicator o-rings using either

of the following methods:

(a) On the scale reading

“Deflection Inches” (or

mm as the case maybe)

to show a deflection equal to one sixty-fourth

of an inch per inch of span length (t)

(b) On the scale reading

“Inches of Span Length

*(or cm as the case maybe) set the indicator o-ring to show a

deflection equal to the measured span length in inches

or cm as required Read the scales at the bottom edge

of the o-rings

3 At the centre of the span (t) apply force with the tester

perpendicular to the span large enough to deflect one belt

on the drive until the bottom edge of the lower o-ring is even with the tops of the remaining belts A straight edge across the tops of the belts will ensure accuracy

4 Find the amount of deflection force on the upper scale of the tension tester The sliding o-ring slides down the scale

as the tool compresses and stays down for accurate

reading of pounds or newtons of force as the case may be

5 Compare the deflection force with the range of forces in the tables supplied with the tester If the force is less than then minimum specified deflection force, the belts should be further tensioned and retested

If more than the deflection force specified, the belts are over-tensioned and need to be adjusted and retested

Electronic meters

These work by sensing the fundamental frequency of vibration of a cable or belt under load when lightly touched on the moving belt A sensor automatically converts this frequency to an analog voltage The computed tension is then displayed on a high contrast LCD display With one keypad entry you can also program to read only the vibration frequency The basic meter is fully portable, weighs approximately 2 Kg and does not require in-line installation

There will normally be a drop in belt tension during the run in period of the belts It is suggested that new belts should be

tensioned to a value a half greater than the maximum deflection force recommended by the tables

Installing synchronous belts

The following is a general procedure for installing this type of belt

1 Ensure the unit to be serviced is isolated using appropriate tag out/lock out procedures

2 Remove any belt guards or machine covers

3 Loosen any tensioning devices until the belt is slack

NEVER PRY A BELT OFF!

4 Remove the old belt and check for wear patterns or

7 Inspect sprockets after cleaning for wear patterns, unusual wear or damage

8 Check other drive components such as bearings and shafts for alignment, lubrication or wear

9 Install the new belt over the sprockets Do not pry the new belt on!

10 Adjust the tensioning device until the correct tension is obtained on the belt using a belt tension tester Rotate the drive and belt several times to ensure even distribution of tension

11 Secure any bolts or retaining devices to correct tension Ensure that all drive components are secure as any change

in the drive centres will effect the belt tension

12 Start the unit and observe performance Listen for any unusual noise or vibration

13 Shut down the unit and check bearing and or motor unit

Installing new vee belt(s)

The following is a general procedure for installing this type of belt

1 Ensure the unit to be serviced is isolated using appropriate tag out/lock out procedures

2 Remove any belt guards or machine covers

3 Loosen any tensioning devices until the belt is slack NEVER

PRY A BELT OFF!

4 Remove the old belt

5 Clean pulley and sheaves with a

rag dampened with a non-volatile

solvent and check for belt wear or

unusual conditions

6 Check the pulley sheaves for wear patterns or unusual wear

or dishing The following are typical indicators of problems:

(a) Ruptured, polish or damaged belt covering

(b) Worn or dished walls on the pulley sheave(s) This

reduces the ability of the belt to drive correctly (c) Check to ensure that the vee belt is not bottoming

out on the base of the pulley sheave

(d) Check belt(s) for “spin burn” This looks similar to

a ruptured cover, except surfaces are shinier and smoother and have a glazed appearance This condition is normally caused by insufficient belt tension allowing belt slippage on pulley sheaves (e) Check the pulley and sheaves for wobble This

condition may be caused by a bent shaft or the pulley having coming loose on the shaft

7 Check other drive components such as bearings and shafts for alignment, lubrication or wear

8 Select and install the new belt over the pulley sheaves Do

not pry the new belt on with levers!

9 Adjust the tensioning device until the correct tension is obtained on the belt using a belt tension tester Rotate the drive and belt several times to ensure even distribution of tension

10 Secure any bolts or retaining devices to correct torque

settings Ensure that all drive components are secured as any change in the drive centres will effect the belt tension

Replace all guards or covers

11 Start the unit and observe performance Listen for any

unusual noise or vibration Shut down the unit and check

bearing and or motor unit

For photographic examples of the failures in the tables on the

following pages, please refer to a recommended reference text, or a belt manufacturer’s catalogue or manuals

Symptoms Probable Cause Corrective Action

Broken belts 1 Belt rolled or pried

onto the sheave

2 Severe shock loads

3 Power to be transmitted greater then the belt design

1.Use appropriate installation practices 2.Redesign drive to accommodate shock loads

3.Redesign drive capacity Belts fail to carry the

load

1 Under designed drive

2 Damaged tensile cord in belt

3 Worn sheave groove

4 Centre distance movement

5 Incorrect belt tension

1 Redesign drive for correct power transmission

2 Replace belt

3 Check for groove wear

4 Check drive for centre distance movement during operation

5.Check belt tension with belt tester Edge cord failure 1 Pulley mis-aligned

2 Damaged inner tensile cord

1 Check and correct alignment

2 Follow correct installation procedure Belt de-lamination Too small diameter

sheaves

Check drive design/replace with larger pulleys Wear on top surface of

Use correct size belt or replace pulley with correct size

Wear on sidewalls of belt 1 Belt slip

Wear on bottom surface

of the belt

1 Belt bottoming on sheave groove

2 Worn sheaves

3 Debris or foreign material in sheave groove

1 Use correct size belt sheave combination

Under cord or side wall

Belt surface flaking,

sticky or swollen

Oil or chemical contamination

Do not use belt dressing and eliminate sources of grease, oil, or chemical contamination

Vee belts turn over or

come off pulley

1 Shock loading or severe vibration

2 Foreign material in sheave grooves

3 Worn sheave grooves

4 Damaged tensile cord member in belt

5 Mismatched belt set

6 Mis-aligned pulleys

1 Check drive design

2 Shield drive pulley

3 Replace pulley

4 Use correct belt installation procedure and storage practices

5 Replace with matched belt set

6 Re-align drive Multiple belt sets stretch

unevenly

1 Mis-aligned drive

2 Debris in sheave grooves

3 Broken tensile cord member

4 Mismatched belt set

1 Realign and tension drive

re-2 Clean sheave grooves

3 Replace all belts using correct installation procedure

4 Install matched belts

redesign guard Grinding sound Damage bearings on

pulley shaft

Replace and align Unusually loud drive 1 Incorrect belts

2 Worn sheaves on pulley

3 Debris in sheave grooves

1 Use correct belt size

If synchronous drive, use correct belt tooth profile for sprockets

2 Replace pulley

3 Clean sheave grooves and belt

Belts flopping 1 Loose belts

2 Mismatched belts

3 Drive out of alignment

1 Re-tension drive

2 Install matched set

3 Re-align drive Excessive vibration 1 Incorrect belt

2 Pulley worn out of round

3 Loose pulleys or bent shaft

1 Use correct belt cross section

2 If synchronous drive, used correct tooth profile and pitched sprocket

3 Check machine components Broken or damaged

pulley

1 Incorrect pulley installation

2 Foreign object falling onto drive

3 Excessive RPM

4 Incorrect belt installation

1 Do not over-tighten bushing retainer bolts or screws beyond

recommended torque settings

2 Use adequate drive guards

3 Keep pulley speeds within recommend limits

4 Install belts correctly

Bent or broken shaft Extreme tension on belts Set belts to correct

tension

Problems with synchronous belts

Unusual noise from drive 1 Misaligned drive

2 Belt tension too low

or too high

3 Worn sprocket

4 Bent guide flange

5 Belt speed too high

6 Incorrect belt profile for sprocket

7 Excess load on drive

1 Re-align drive

2 Adjust to recommended value

handling and installation

2 Guide flange damage

3 Belt too wide

4 Belt tension too low

5 Rough guide flange finish

6 Belt hitting drive guide or guard

7 Improper tracking of belt

1 Follow proper handling and installation instruction

2 Repair flange or replace sprocket

3 Use correct width sprocket

4 Adjust tension

5 Replace or repair flange

2 Extended exposure

to chemicals

3 Out of alignment pulley or shaft bushings

1 Redesign drive with correct size

2 Protect drive

3 Install bushings and pulley correctly and realign drive

Premature tooth wear on

2 Re-align drive

3 Use correct belt/sprocket combination

Teeth shearing off belt 1 Excessive shock

2 Re-design drive

3 Replace sprocket

4 Use correct belt/sprocket combination

5 Re-align drive

6 Adjust belt tension to recommended value Belt tracking incorrectly 1 Centres exceed 8

times the small sprocket diameter with both sprockets flanged

2 Excessive belt edge wear

3 Belt running off flanged sprocket

un-1 Check and correct parallel alignment of drive

2 Correct alignment

3 Check and correct alignment

Vibration 1 Incorrect belt profile

2 Too low or high a belt tension

3 Sprocket, key or bushing loose

1 Use proper belt/sprocket combination

2 Re-tension drive to specification

3 check and re-install

to specifications

Activity - Practical Project

You should now undertake and complete Project 1 - Vee belt drive installation in your projects book For information on the methods for alignment of pulleys, refer to Section 5 on alignment of Drives and Shafts

Self-Assessment

The self-assessment questions in this section relate to the following criteria and the assessors requirements contained in the Competency Unit contained in Appendix A of this guide

18007B.1.1 – Principles of mechanical drives and mechanical

transmission assemblies understood

18007B.1.2 – The function of the main parts of the designated

mechanical drive/transmission understood

18007B.1.3 – Using appropriate maintenance principles,

techniques, tools, and equipment, mechanical drive/transmission components checked for wear, distortion, tensions, misalignment, fatigue,

lubrication, slackness, tooth wear, breakages, and other related malfunctions

18007B.1.4 – Assembly identified as requiring further diagnosis

Repair or adjustment and findings documented by appropriate means

18007B.2.1 – Adjustment requirements determined by appropriate

means

18007B.2 -2 - Adjustment method suitable for type of drive or

transmission assembly being serviced determined from manufacturer’s instruction sheets, standard workshop manuals/procedures or other appropriate means

18007B.2.3 – Adjustment tools selected according to the type of

assembly being serviced

18007B.2.4 – Using appropriate maintenance principles,

techniques, tools, and equipment, drive/transmission components tensioned, aligned, balanced or adjusted

to manufacturer’s specifications according to safe

18007B.3.3 – Faults localised at the component level and

identified for repair or replacement

18007B.3.4 – Fault cause analysed and preventative measures to

avoid recurrence developed, documented and actioned by appropriate means

18007B.4.3 – Tools and equipment selected according to the type

of drive assembly being serviced

18007B.4.4 – Mechanical drive/transmission assembly

dismantled using appropriate maintenance principles, techniques tools, equipment and safe work practice

18007B.4.6 – Serviceable items selected using manufacturer’s

catalogues, spare parts lists, engineering specifications, and obtained by appropriate means

Question 6

Describe the difference in features that distinguish a narrow

section vee-belt from a classical section vee-belt

Explain why it is necessary to ensure a correct key fit when

installing taper lock hubs with a pulley

Describe two ways in which you could determine the correct

tension for a vee-belt

Checklist

 Are you able to identify the types of power transmission belts used?

 Can you correctly remove and fit the range of power

transmission belts used and described?

 Are you able to correctly identify the range of belt problems and possible corrective actions

Summary

The correct selection, fitting and maintenance of the range of power transmission belts is an essential skill in a wide range of

applications in industry