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www.futuremanagers.net info@futuremanagers.net

Mechanical

Technology

Grade 12

Learner’s Book

Charles Goodwin

André Lategan

Daniel Meyer

CAPS

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Mechanical Technology

Grade 12 Learner’s Book

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FutureManagers

All rights reserved. No part of this book may be reproduced in any form, electronic, mechanical, photocopying, or otherwise, without prior permission of the copyright owner.

ISBN 978-1-77581-000-1

To copy any part of this publication, you may contact DALRO for information and copyright clearance. Any unauthorised copying could lead to civil liability and/or criminal sanctions.

Telephone: 086 12 DALRO (from within South Africa); +27 (0)11 712-8000 Telefax: +27 (0)11 403-9094

Postal Address: P O Box 31627, Braamfontein, 2017, South Africa www.dalro.co.za

First published 2007 Second edition 2012 Revised 2013

Published by

Future Managers (Pty) Ltd

PO Box 13194, Mowbray, 7705

Tel (021) 462 3572

Fax (021) 462 3681

E-mail: info@futuremanagers.net

Website: www.futuremanagers.net

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iii

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How to use this book ... iv

Chapter 1 – Safety ...1

Chapter 2 – Tools ...27

Chapter 3 – Materials ...51

Chapter 4 – Terminology ...63

Chapter 5 – Joining methods ...79

Chapter 6 – Forces ... 105

Chapter 7 – Maintenance ... 123

Chapter 8 – Systems and control ... 139

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v

Outline of the curriculum

Mechanical Technology Grade 12 Learner’s Book has been based on the new FET Curiculum for Mechanical

Technology which entails 9 topics.

Spider diagrams

Each chapter is introduced by a spider diagram which is a diagrammatical summary of the content covered in a particular chapter. The following spider diagram is an example from Chapter 6:

Concepts of stress, strain and modulus

of elasticity Advanced tests on

various mechanical principles

Calculation of stress, strain and modulus of

elasticity Calculating moments in engineering components Forces Calculation of forces in engineering components

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The following icons are used throughout the book to help you to recognise important concepts or activities.

Icon

Description

Topics

Assessment

Did you know?

Key word

Pause for thought

Caution!

Envoronmental

issues

Human Rights

Besides the various icons, explanatory notes, Pause for thought and Did you know? boxes have been placed in the margin to give further insights.

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vii

South Africa and many other countries in the world currently suffer from huge skills’ shortages and desperately need skilled engineers, technologists, technicians and artisans. An introduction to Mechanical Technology aims to produce learners who have been exposed to skills, knowledge, attitudes and values (SKAVs) which will equip them for further study in Mechanical Engineering and related sectors.

The subject Mechanical Technology focuses on technological processes from conceptual design through to the process of practical problem solving to produce or improve on products which can enhance our quality of life.

Explanation of the key words

You may encounter many unfamiliar words in this course. For this reason, key words have been included in the margins to explain the meanings of words that appear in bold print in the text. The key words also cover acronyms (words made up of the first letters of the name of something) and abbreviations that are used in the book.

Assessment activities

The assessment activities comprise individual, pair and group tasks. Some are pen-and-paper activities and some are practical tasks. The solutions to some tasks can be found in the text but others will require you to do further research. It is very important that you read the instructions carefully before attempting any of the tasks.

Message from the authors

Y

ou have the good fortune to be one of the first learners to choose Mechanical Technology as one of your FET subjects. It will definitely stand you in good stead for your future studies. To help you succeed in this subject, it is essential to apply the following principles:

• Go through your notes and make sure that you understand the work. • Learn the important concepts and definitions.

• Solve as many problems as you can.

• You will find that regular revision will help you to understand and remember the work better. Do not hesitate to refer to other relevant reading material to broaden your understanding of the subject. Above all, think and work hard.

We wish you well for your studies this year. THE AUTHORS

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Chapter 1

Safety

Topic 1

Safety

OHS Act

Grinding

machines

Shearing

machines

Press

machines

Joining

Gas

cylinder

Testing

equipment

Lathes

Milling

machines

Cutting

machines

MIG

welder

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Introduction

Safety in the workplace was introduced in Grades 10 and 11.

In Grade 12, learners must be fully aware of all the safety precautions to be taken during performance-based activities in order to avoid injuries or incidents. Learners must demonstrate an understanding of the Occupational Health and Safety (OHS) Act where applicable.

Occupational Health and Safety Act 1993 (OHSA)

The aim of the Occupational Health and Safety Act, Act 85 of 1993 (OHSA) is to provide for the health and safety of employees at work. The following groups are excluded from the Act:

• Parties covered by the Merchant Shipping Act.

• People employed in mines, mining areas or any works defined in the Mine Health and Safety Act 29 of 1996.

The provisions of the Occupational Health and Safety Act of 1993 (OHSA) are as follows:

• The employer must provide and maintain a safe working environment. • Suppliers/manufacturers must ensure that items used in the workplace do not

pose a safety or health risk.

• Employers must inform the workforce of hazards in the workplace.

Employees must:

• Take reasonable care to ensure their own and others’ health and safety.

• Carry out any lawful order and obey the health and safety rules and procedures laid down by the employer.

• Report unsafe/unhealthy situations.

• Report incidents that may affect health or which may cause injury.

The Act also refers to the following:

• The appointment of health and safety representatives. • The establishment of health and safety committees. • Reporting of incidents/diseases and inspections.

Extracts from the Occupational Health and Safety Act

of 1993 (OHSA) concerning General Health and Safety

Regulation

Personal protective equipment and facilities

1. Subject to the provisions of section 8(2)(d), every employer, self-employed person or user, as the case may be, shall make an evaluation of the risk attached to any condition or situation which may arise from the activities of such employer, self-employed person or user, as the case may be, and to which persons at a workplace or in the course of their employment or in connection with the use of machinery are exposed, and he shall take such steps or

precautionary measures as may be necessary to render the condition or situation safe and without risk to the health of persons.

2. Taking into account the nature of the hazard that is to be countered, and without derogating from the general duties imposed on employers and users by sub-regulations (1) and (2), the personal protective equipment and facilities contemplated in sub-regulation (2) shall include, as may be necessary:

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• suitable goggles, spectacles, face shields, welding shields, visors, hard hats, protective helmets, caps, gloves, gauntlets, aprons, jackets, capes, sleeves, leggings, spats, gaiters, protective footwear, protective overalls, or any similar personal protective equipment or facility of a type that will effectively prevent

bodily injury;

• waterproof clothing, high visibility clothing, chemical resistant clothing,

low temperature clothing, chain-mail garments, waders, fire-retardant or

flameproof clothing, ice jackets, or any similar personal protective equipment of a type that will effectively protect the wearer thereof against harm;

• harnesses, nets, fall arresters, life lines, safety hooks or any similar equipment of a type that will effectively protect persons against falls;

• mats, barriers, locking-out devices, safety signs or any similar facility that will effectively prevent slipping, unsafe entry or unsafe conditions;

• protective ointments, ear muffs, ear plugs, respirators, breathing-apparatus masks, air lines, hoods, helmets or any similar personal protective equipment or facility of a type that will effectively protect against harm: provided that hearing protective equipment shall be of a type that conforms to SANS 1451; Parts I and II: provided further that respiratory protective equipment shall be of a type that conforms to SANS 033-99;

• suitable insulating material underfoot where persons work on a floor made of metal, stone or concrete or other similar material; and such personal protective equipment or facilities as may be necessary to render the persons concerned safe.

It is important to protect yourself by wearing the appropriate protective clothing. To begin with, a correctly fitting, fire-retardant overall (one- or two-piece) is the first line of defence, as it protects your body and clothing from workshop dirt and sparks. It also prevents your clothing from becoming entangled in machine parts. Steel-capped safety shoes or boots are also important as they protect your feet from falling objects. Depending on the activities you will be conducting in the workshop, the following items of personal protective wear are also necessary:

• chrome leather gloves and aprons – essential when welding or working with heated material

• protective eyewear – important when conducting any work which can be hazardous to your eyes, for example, shaded lenses should be worn when welding to protect your eyes from intense heat and light, and clear protective lenses should be worn when doing grinding work or machining operations • ear plugs or ear muffs to protect your ears – especially if you are working in a

noisy environment.

It is important to get into the habit of wearing the necessary protective equipment. Neglecting to wear the appropriate equipment even once may result in permanent injuries or worse. Figure 1.1 illustrates some basic, personal protective safety wear.

Figure 1.1: Basic personal protective wear

Overall

Safety shoes

Safety goggles

Ear plugs

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Grinding machines

Angle grinders

Figure 1.2: Angle grinder

When working with angle grinders, remember the following safety precautions:

• The same safety precautions applicable to other types of grinders are applicable to angle grinders.

• The safety guard must be in place before you start the grinding process. • Protective shields must be placed around the grinding object to protect people

passing by.

• Use the right blade for the grinding job. • Do not force the grinding stone on the object.

• Make certain that there are no cracks in the stone before you start the job. • Protective clothes and eye protection are essential when working with an angle

grinder.

• Wear ear plugs or muffs.

• Wear safety boots with steel toe caps. • Wear overalls or other close-fitting clothing. • Wear gloves.

Bench grinders

Figure 1.3: Bench grinder

Body Disc Safety guard Handle Head Wheel guard Maximum gap 3 mm Grinding wheel Stand Perspex shield Tool rest On/off switch

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When you use a bench grinder, remember the following:

• Use a machine only when the guards have been correctly fitted.

• Make sure that there is no oil or grease on the floor around the machine which could cause you to slip.

• Check that the tool rest is not more than 3 mm from the surface of the grinding wheel. Gaps exceeding 3 mm increase the risk of material being drawn in between the tool rest and grinding wheel.

• When starting the machine, do not stand in front of the wheel. Before you start grinding, let the machine idle for a few seconds. The risk of the grinding wheel rupturing is higher at start-up than when it is running at its operating speed. • If the wheel is running unevenly, dress it with an emery-wheel dresser.

• Grind only on the face of a straight grinding wheel and never on the side of the wheel.

• Use wheels for their intended purpose only. Certain types of grinding wheels should only be used for their corresponding materials. Most grinding wheels are only suitable for grinding ferrous metals. The appropriate degree of coarseness should also be selected for the finish required of the material.

• Approach the wheel carefully and gradually and do not ‘jab’ materials onto it. Jabbing puts uneven pressure on the wheel surface, causing uneven wear or structural damage to the wheel.

• Never ‘force grind’ so that you cause the motor to slow or stop. • Adjust the tool rest only when the wheel is stationary.

• Clamp workpieces and holding devices safely and firmly.

• Never allow the wheel to stand in cutting fluid as this may cause the wheel to run ‘off balance’ when you switch the machine on again.

Mounting of grinding wheels

The following steps are advised:

• Select the correct type of wheel for the job.

• Inspect the wheel for cracks and tap it to apply the ‘ringing test’. Never use a grinding wheel which is damaged or not properly dressed.

• Make sure that the wheel’s speed does not exceed the manufacturer’s recommendation.

• Never force the wheel onto the spindle.

• Use only one smooth paper spacer on each side of the wheel.

• Use true and correctly recessed flanges of the same size and at least one-third the diameter of the wheel.

• Gently tighten the grinding wheel with a spanner, only enough to hold it firmly. • Replace the guards correctly.

• Stand aside and set the machine in motion. Let the machine idle before you dress the wheel, using an emery-wheel dresser.

• Finally, stop the machine and reset the tool rest to within 2 mm of the wheel surface.

• Ensure that the tool rest is parallel to the wheel surface.

Grinding wheels

All power-operated grinding machines should be clearly marked to indicate the recommended speed (in revolutions per minute) of the spindle. This speed should not allow the peripheral speed of the wheel to exceed the manufacturer’s recommendation.

Idle

Run without any load

Exceed

Be more than

Stationary

At rest and not rotating

Spindle

The spindle of the bench grinder is the rotating shaft onto which the grinding wheel is attached

Peripheral speed

The peripheral speed of the grinding wheel is the speed along the circumference of the grinding wheel

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Other safety measures are:

• Every grinding wheel should have a guard which can withstand the force of a rupturing wheel.

• Bench grinders must have a transparent shield to protect the operator’s eyes. • Each machine must carry a notice prohibiting persons from performing,

inspecting or observing grinding work without wearing suitable protection for the eyes.

Surface grinders

Figure 1.4: A surface grinder

Remember the following safety precautions when using surface grinders:

• The safety precautions applicable to other types of grinders are applicable when using a surface grinder.

• Protective clothes and eye protection are essential when working with a surface grinder.

• Before operating the surface grinder, be sure you have been taught how to control it and are aware of the potential dangers associated with it.

• Do not operate the surface grinder unless all guards and safety devices are in place and working correctly.

• Make sure that you understand the operating instructions applicable to your machine.

• Never clean or adjust the machine while it is in motion.

• Report any dangerous aspect of the machine immediately and stop using it until it has been repaired by a qualified person.

• You may have to stop your machine in an emergency. Learn how to do this quickly and automatically.

Assessment 1

1. When working with an angle grinder, you must follow safety rules. Name six. 2. Name five safety precautions to observe when working with a grinding wheel. 3. Name five steps to follow when installing a grinding wheel.

4. Name five safety precautions to remember when working with a surface grinder.

Rupturing

Breaking or bursting suddenly

Prohibiting

Not allowing Vertical adjuster

Horizontal adjuster

Horizontal table

On/off switch Grinding stone

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Cutting machines

Drill presses

Figure 1.5: A drill press

Observe the following safety precautions when using a drill press:

• Choose a drill bit correctly sharpened for the type of work you need to do and the material of the workpiece.

• Do not leave the key in the chuck when you are not at the machine. • Never leave the machine running if it is unattended.

• Clamp the workpiece securely to the table and do not hold it by hand. • Never try to stop the workpiece by hand if it slips from the clamp. • A drill should run at the correct speed for the job.

• Do not force a drill bit into the workpiece – this may cause broken or splintered drill bits and possible injuries.

• Use a brush or wooden rod to remove chips from the drill. Do not use your fingers, waste material or rags.

• When reaching around a revolving drill, be careful that your clothes do not get caught in the drill or drill chuck.

• Do not use a drilling machine with a faulty switch. • Do not wear loose clothing or jewellery when drilling.

Portable electric drilling machine

Figure 1.6: Portable drilling machine

Motor and gearbox

Feed lever

Table

Column

Base Depth gauge

Did you know?

A drill press is also called a drilling machine.

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Observe the following safety precautions when using a portable drilling machine:

• Wear safety goggles.

• Choose the correct size and type of drill bit. A metal bit is used to drill into iron and a masonry bit to drill into a brick wall.

• The bit must be placed in the chuck of the drill and fixed in place by using the chuck key. Make sure that the bit is centred.

• Place the key in the key holder provided at the bottom of the drill’s handle. • If you are drilling into metal, mark the position with a centre punch.

• Stand firmly with your legs slightly apart and one leg more forward than the other.

• Hold the drill firmly and squeeze the trigger.

• If you are drilling through a metal plate you should decrease the pushing pressure when you come close to drilling through the last piece of the metal plate.

Power saws

Figure 1.7: A power saw

Observe the following precautions when using a power saw:

• Ensure that all guards are in place.

• Make sure that there is no oil, grease or obstacles around the machine. • Select the right blade for the material to be cut.

• When changing blades, ensure that the machine is switched off at the main switch.

• Remove or replace the blade gently. Quick movements, such as pulling off the blade, may result in a badly cut hand.

• Do not adjust guides while the machine is running.

• All material must be clamped properly before cutting is started. • Long pieces of material must be supported at the end.

• Always stop the machine when you leave it unattended.

Power saw switch Cutting blade

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9

Centre lathes and milling machines

Figure 1.8: A centre lathe

Figure 1.9: A milling machine

Observe the following safety precautions when working with a centre lathe or milling machine:

• Make sure that all guards are in place.

• Do not use a machine or come close to its moving parts while wearing loose clothing.

• Keep any cleaning material such as waste and rags away from rotating parts. • Check that there is no oil or grease on the floor around the machine.

• Do not leave spanners or keys on rotary parts. Always disconnect, remove or stand clear of handwheels, levers or chuck keys before setting your machine or feeds in motion.

• Never apply a spanner to revolving work.

• Always clamp workpieces and holding devices safely and firmly. A loose fit, especially of spanners and keys, may cause slipping and result in injury. • Do not use your hands to remove cuttings while a machine is in motion. Use a

wire hook or a brush once the machine has stopped. • Never adjust the cutting tool while a machine is running.

Toolpost Top slide or compound slide Cross slide Cross-feed handle Saddle or carriage Thread dial Power-feed control Leadscrew engager Feed rod Carriage handwheel Rack Leadscrew Adjustable overarm Arbor Power-feed unit Base Arbor support Machine table Knee and saddle Handwheel

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• Resist the habit of leaning on machinery. This dangerous, ‘automatic’ practice often results in serious injury.

• Do not attempt to stop a machine by placing your hand on the chuck while the machine is slowing down.

• Pay attention to cutting-fluid control before switching on a machine.

Assessment 2

1. When working with a portable drilling machine, you must adhere to safety rules. Name six.

2. Name five safety precautions to follow when working with a drill press.

3. Power saws are dangerous power tools. Name five safety precautions that must be observed when working with them.

4. Give four safety precautions to follow when working with a lathe or a milling machine.

Shearing machines

Figure 1.10: An electrical guillotine

Figure 1.11: A manual guillotine

Cutting blade Safety mechanism Push-down pedal Switch Machine platform

Blade safety mechanism

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Manual and electrical shearing machines

Where the opening at the point of operation of a pair of shears or a guillotine is greater than 10 mm, the machine should be fitted with one of the following:

• A fixed guard to prevent hands or fingers from reaching through, over, under or around the guard.

• A self-adjusting guard which automatically adjusts to the thickness of the material being worked.

• Some machines have manual or automatic moving guards which completely enclose the point of operation so that the working stroke cannot be opened unless the ram or blade is stationary.

• Another safety device is the automatic sweep-away or push-away that pushes any part of the machine operator’s body out of the danger zone when the working stroke starts. Nowadays, there is even an electronic presence-sensing device which stops the working stroke if the device senses a foreign object in the danger zone.

Hydraulic press

Figure 1.12: A hydraulic press

Observe the following safety precautions when using a hydraulic press:

• The predetermined pressure must never be exceeded. This operating pressure is always less than the maximum safe pressure and is shown by a pressure gauge on the apparatus.

• Pressure gauges must be tested regularly and adjusted or replaced if any malfunction occurs.

• The platform on which the workpiece rests must be rigid and square with the cylinder of the press.

• The platform must rest on the supports provided and should not be supported by the cable by which it is raised or lowered.

• Objects to be pressed must be placed in suitable jigs. Ensure that the direction of pressure is always at 90° to the platform.

• To prevent damage to soft material, the prescribed equipment must be applied. • Relieve the cylinder of all pressure after use by opening the valve.

Pressure meter

Plunger

Hydraulic press cylinder Return springs

Platform

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Also remember:

• The level of the hydraulic fluid in the reservoir should be checked regularly. If fluid has to be added frequently, it is an indication that there may be an internal leak.

• Regularly inspect the apparatus for rigidity and tighten all nuts and bolts. • Pins and/or other equipment that keep the platform at a desired height on the

frame must be inspected regularly for damage.

• When the apparatus is equipped with cables to alter the working height of the platform, the cable and pulleys must be inspected for damage and lubricated with grease.

Assessment 3

1. A hydraulic press is an important tool in the workshop. Name five precautions to observe when working with this equipment.

2. Which safety devices are used in conjunction with guillotines?

Joining (arc, spot, gas)

Arc welding

Safety rules to observe when working with arc welders

• Always wear personal protective equipment.

• Make sure the area where you are going to work is clear of obstructions. • Use as small a rod as possible when tackling the job. This will ensure a much

better and neater weld upon completion of the job. • Only weld in well-ventilated areas.

• Seek medical attention if someone suffers a burn. • Do not weld near flammable materials or liquids.

• Do not weld on petrol tanks or any containers that contain flammable liquids or gas.

• Radiation from the arc is dangerous to the eyes. Always wear a welding mask. • Avoid striking an arc when other people are close to you.

• An electric shock is always a possibility.

Spot welding

Figure 1.13: Spot welding machine

Safety rules to observe when working with a spot welder

• Wear protective clothes. • Wear goggles.

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• The area must be cordoned off when the machine is being used.

• Make certain that the time and current settings are appropriate to the type and thickness of the material being welded.

• Make certain that the alloy tips are kept in good condition and are not damaged during operation.

• Make certain that the copper tips are constantly cooled (through the circular liquid cooling system) to prevent overheating.

Gas welding

Figure 1.14: Oxy-acetylene welding plant

The following are some safety precautions that should be followed when using oxy-acetylene apparatus:

• Welding or flame-cutting operations may not be undertaken unless:

– An operator has been instructed on how to use the oxy-acetylene welding plant safely.

– The workplace is effectively partitioned off. – An operator uses protective equipment.

– Effective ventilation is provided and maintained.

– Masks or hoods maintaining a supply of safe air for breathing are provided and used by the persons performing such operations.

• The following precautions must also be considered:

– Any vessel that contains a substance which, when subjected to heat, may ignite or explode (or react to form dangerous or poisonous substances) must not be welded or heated until it has been properly cleaned.

Oxygen regulater

Oxygen flashback arrestor

Acetylene regulater Acetylene flashback arrestor

Acetylene hose Oxygen hose

Acetylene cylinder

Parallel hose clips

Torch mounted flashback arresters

Oxygen cylinder

Cylinders secured in a cylinder trolley

Nozzle

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– Where hot work involving welding, cutting, brazing or soldering operations is carried out at places other than workplaces, steps must be taken to ensure proper and adequate fire precautions. When in doubt, the manufacturer’s instructions are always the final authority on safety precautions and

procedures. African Oxygen (Afrox) supplies safety booklets on all aspects of welding safety, free of charge, at their outlets and depots.

– Never use damaged equipment.

– Never use oil or grease on or near oxygen equipment.

– Never use oxygen or fuel gas to blow dirt or dust off clothing or equipment. – Never light a torch with matches or a lighter. Always use a striker.

– Always crack cylinders before assembling the regulators to remove any dust. – Always make sure regulators have their adjusting screws released by turning them anticlockwise untill free before opening the cylinder valves. Stand to the side of a regulator and not in front of it when opening cylinder valves. – Always wear proper welding goggles, gloves and clothing when operating oxy-acetylene equipment.

– Always have a fire extinguisher handy when operating oxy-acetylene equipment.

– Always use the proper regulator for the gas in the cylinder. – Always use cylinders in the upright position only.

– Always keep the valve wrench on the acetylene cylinder valve when in use. – Open the cylinder valve a maximum of 1½ turns.

– Do not carry lighters, matches or other flammable objects in your pockets when welding or cutting.

– Always be aware of others around you when using a welding torch.

– Be careful not to let welding hoses come into contact with the torch flame or the sparks from cutting.

Assessment 4

1. Name four safety precautions to observe when working with an electrical welder.

2. Name four safety rules that should be considered when working with a spot welder.

3. Name six safety precautions to be observed when welding with a gas welding apparatus.

Handling gas cylinders

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15

Every gas cylinder should have a label which contains the following particulars:

• name of the manufacturer • country of origin

• year of manufacture

• manufacturer’s serial number

• name, number and date of the standard of design • design gauge pressure in pascals

• maximum permissible operating pressure in pascals • operating temperature

• mark of an approved inspection authority.

No portable gas container should be used, filled, handled, modified, repaired or inspected in any way other than in compliance with standards set by the South African Bureau of Standards (SABS).

The following safety precautions must be observed when handling gas cylinders:

• Store full cylinders and empty ones separately.

• Keep cylinders in a cool place and protect them from sunlight and other sources of heat.

• Always store and use acetylene cylinders in an upright position. • Store oxygen cylinders and acetylene cylinders separately. • Never stack cylinders on top of one another.

• Do not bang or work on cylinders. • Never allow cylinders to fall.

• Do not allow oil or grease to come into contact with oxygen fittings as this forms a flammable mixture.

• Keep the caps on the cylinders for protection.

• The thread on an oxygen cylinder is a right-hand thread. • The thread on an acetylene cylinder is a left-hand thread.

Cylinder testing register

The following are the requirements for cylinder testing:

Pressure vessels must be tested every 4 years, inspected every 2 years, tested before commissioning, tested after each major repair and tested after being out of use for longer than 2 years.

Location: Record of inspections and tests

Manufacturer’s particulars:

Manufacturer: Country of origin: Maker’s number: Year of manufacture: Hydraulic test pressure: Capacity:

Name and number of code of manufacture: Maximum permissible working pressure: Inspection/test date:

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The following form is used by inspection authorities when testing cylinders.

Items Checked Remarks

Clean and free of carbonised oil and other matter Yes No Chemically reactive matters

Internal surfaces and all seams External and internal plates: cleaned All plates hammer tested

All welds checked

Corrosion, internal and external Internal pitting

Oil deposits

Red mark on pressure gauge (P.W.P.) Safety valve set, locked or sealed Liquid level indicator

Reducing valve Leaks detected Other defects detected Remarks

I certify that this pressure vessel has been inspected and/or tested in accordance with legal requirements and that the employer/manager has been informed of all weaknesses and defects.

Vessel

May be used  May not be used  Signature of competent person ________________________ Date

Hydraulic pressure test Y/N Inspection Y/N Commissioning test Y/N Major repair/out of use Y/N

Assessment 5

1. Which nine particulars must be visible on a gas cylinder?

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17

Specific safety measures when dealing with the

following machines and equipment

Metal-arc gas shield welders

Figure 1.16: Metal-arc gas shield welders

The following safety measures must be adhered to:

• An operator should be instructed to use a machine safely. • A workplace is effectively partitioned off.

• An operator uses protective equipment.

• Effective ventilation is provided and maintained.

• Masks or hoods maintaining a supply of safe air for breathing are provided and used by the people performing such operations.

• The insulation of electrical leads is satisfactory.

• The holder which contains the wire is completely insulated to prevent accidental contact with current-carrying parts.

• The operator is completely insulated by means of boots, gloves and rubber mats. • The argon gas cylinder is fixed in an upright position.

• When welding operations are carried out at places other than workplaces, steps must be taken to ensure proper and adequate fire precautions. When in doubt, the manufacturer’s instructions are always the final authority on safety precautions and procedures.

Hardness tester

Figure 1.17 (a): Rockwell hardness tester Figure 1.17 (b): Brinell tester

Hardness indicator meter

Platform Platform height adjuster

Activating knob Gas hose

Flow meter

Regulator

Shielding gas cylinder

Continuous wire reel

Wire-feed unit Power cable Gun conduit Welding gun Arc Power cable Platform Platform adjuster Activating panel

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The following safety measures must be adhered to:

• The area around the tester must be cordoned off. • Only one person should be in the confined space. • The person should wear protective clothing (an apron). • The tester should wear safety goggles.

• The tester should wear gloves.

• The hardness tester should be mounted on a rigid spot on a worktable.

• A cover should be placed around the area where the metal ball will be launched onto the material to be tested.

Tensile tester

Figure 1.18: Mini tensile tester

The following safety measures must be adhered to:

• The area around the tester must be cordoned off. • Only one person should be in the confined space. • The person should wear protective clothing (an apron). • The tester should wear safety goggles.

• Make certain that the dial indicator is mounted properly.

• Ensure that the front section of the indicator touches the bottom section of the tester.

• Move the protective cover over the specimen that must be tested.

• For steel and duralumin, use half-turn increments of the handwheel moving through the range.

• For aluminium, one-fifth turn increments are acceptable.

• For plastics, one-fifth turn increments for the first three turns are acceptable. Thereafter, use increments of two turns until the material is crushed.

Handwheel

Test specimen

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Torsion tester

Figure 1.19: Torsion tester

The following safety measures must be adhered to:

• Fasten the tester to a workbench.

• Determine the strength of the bolts keeping the framework together.

• Get the specification (torsion) of the different materials and of the rod size you would like to test.

• When you add pieces of different mass, you should attach them very gently otherwise you could get a skew reading of the torsion on the rod.

Moments and forces testers

Figure 1.20: Moments and forces testers

The following safety measures must be adhered to:

• Determine the strength of the bolts keeping the framework together. • Get the specification.

• When you add different mass pieces, you should attach them very gently otherwise you could get a skew reading on the tester.

Twisitng indicator Rod clamp Frame Mass pieces Twisting rod Bearing Mass pieces Moment of a force Frame Beam

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Beam-bending tester

Figure 1.21: Beam-bending tester

The following safety measures must be adhered to:

• Ensure the beam is clamped parallel to the backboard.

• Do not leave plastic beams loaded for any length of time. (They tend to creep if left loaded.)

• Gently drop the weights onto the hanger. This helps to ‘bounce’ the beam and reduces inaccuracies due to friction.

• To get true deflection, take 10 mm off the dial gauge reading at each step.

Assessment 6

1. Name three safety precautions to observe when working with a metal-arc gas shield welder.

2. Name three safety precautions that must be considered when the following testing equipment is used:

• Brinell tester • Tensile tester • Torsion tester • Beam-bending tester

Cylinder leakage tester

Figure 1.22: Cylinder leakage tester

Mass pieces

Frame Dial indicator

Bending bar

Air hose coupler

Air hose

Plug adaptor Pressure indicator

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21

The following safety measures must be adhered to:

• Get the specifications of the engine to be tested.

• The cylinder to be tested should be on Top Dead Centre.

• The crankshaft should be locked so that it cannot turn during the testing procedure.

• Predetermined compressed air should be used or else the machine will be damaged.

• Do not play with compressed air.

• Make certain that the dipstick is in its hole.

• Make certain that the radiator cap is screwed onto the radiator. • Make certain that the oil filler cap is screwed on.

• The adaptor which screws into the plug hole must be tightened, otherwise all the compressed air will escape.

Pressure testers

Figure 1.23: Compression tester

The following safety measures must be adhered to:

• Make certain that the connections (pipes) are not broken. • Screw the adaptor into the plug hole without stripping the hole. • Do not over-tighten the adaptor.

• Do not store the tester when the meter still contains pressure. • Always release the pressure before it is stored.

• Do not drop the meter. You will damage it and impede its accuracy.

Radiator tester

Figure 1.24: Radiator tester

Pressure meter indicator

Spark plug adaptor

Rubber pipe Pressure relief valve

Radiator adapters Connector to the radiator

Radiator pump

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Safety measures when working with the instrument

• Make certain that all adaptors have no cracks.

• Make sure that the pipes are leak-free and that the connections are tightened properly.

• Determine the specifications for the objects you want to test first.

• Never pump the radiator to a point that exceeds the predetermined pressure of the radiator or the cap.

Assessment 7

1. Name three safety precautions to consider for each of the following testers: • Cylinder leakage tester

• Compression tester • Radiator tester

Spring compressors and testers (valve and coil)

Figure 1.25: Valve lifter

The following safety measures must be adhered to:

• Make certain that the front part is adjusted to fit tightly over the valve retainer. • Tighten the adjuster behind the valve lifter.

• Determine the specifications of the cylinder head valve spring.

• Do not stretch or compress the spring further/more than indicated in the specification. You could damage the spring.

Figure 1.26: Valve spring compressor Figure 1.27: Coil spring compressor

Lever

Valve adjuster

Valve cotter clamp

Load cell

Crosshead Scale Spring

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23

The following safety measures must be adhered to:

• Make certain that the diameter of the compressor bolts can take the pressure of the coil spring.

• If the pressure exceeds the strength of the coil spring, the puller will snap and damage the car and/or people may be hurt.

Assessment 8

1. Name two safety precautions to observe when using the following testers: • Valve lifter

• Coil spring compressor

Gas analysers

Figure 1.28: Gas analyser

The following safety measures must be adhered to:

• The inlet hose should not be stepped on or restricted in any way.

• The hose connections must be airtight and the valve on the condenser should be in the horizontal position (closed).

• The vehicle being tested should have no leaks in the exhaust, manifolds or vacuum systems. (This will result in the analyser giving lean readings or no readings at all. If you are unsure, test the analyser on another ‘good’ vehicle.) • From time to time, condensate should be blown out of the hoses and pickup

probe with compressed air.

• The hoses should be disconnected from the analyser or else the pump will be damaged.

• The condenser should be drained after each test, using the valve.

• When the paper filter becomes light grey, it should be changed. (Take care when inserting filter paper into the housing. Make sure the window is properly located before tightening the large nut.)

• The fuel filter on the condenser stand should be changed regularly. • On a 12-volt analyser, the battery clamps should be clean.

Pipe to the exhaust system Filter

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Multimeters

Figure 1.29: Multimeter

The following safety precautions should be taken:

• Keep the meter dry.

• Keep the meter away from dust and dirt.

• Use and store the meter in environments where the temperature is normal. • Do not drop the meter as it could be damaged and this will affect its operation. • Use only charged cells of the correct size. (Always remove old batteries as they

can leak and corrode the wiring.)

Assessment 9

1. Name three safety precautions to observe when using the following special tools:

• Gas analyser • Multimeter

Bearing and gear puller

Bearing pullers are used to remove and replace bearings and bushes.

Figure 1.30: Bearing and gear pullers

LCD display screen

Range selector switch

10A DC terminal socket

VΩmA terminal socket Common terminal socket

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25

Figure 1.31: Bearing and gear pullers

The following safety measures must be adhered to:

• Make certain that the puller is the right one for the job.

• Make certain that the puller is strong enough to remove the bearing or gear. • You must tighten the clamps or fingers around the object, otherwise it could slip

and damage the objects or hurt you in the process. • Do not use a hammer on the puller.

• Use the right spanner to tighten the clamps and to pull off the object.

• Make certain that the puller is at a 90º angle to the horizontal before you start to pull.

Assessment 10

1. Name four safety precautions to consider when working with a bearing and gear puller.

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Chapter 2

Tools

Topic 2

Gas

analyser

Beam

tester

Hardness

tester

Multimeter

Leakage

tester

Torsion

tester

Pressure

testers

MiG/MaG

machines

Compression

tester

Spring

tester

Depth

micrometer

Thread

micrometer

Tools

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Introduction

Tools are very important to complete different tasks in the workplace.

In Grade 10, hand tools was explained. In Grade 11, power tools and machines were explained. In this chapter in Grade 12, we will explain advanced engineering equipment in the workplace.

Gas analyser

Function

To analyse the gas emitted by the exhaust pipe of a motor car and determine the amount of CO (carbon monoxide) being processed by the engine. The reading will determine whether the petrol mixture of the engine is adjusted according to the manufacturer’s specifications.

Figure 2.1: a CO gas analyser

The test procedure

• Connect the analyser to the 12-volt battery terminals of the vehicle. Polarity does not have to be observed.

• The LCD will display ‘000’ during the 30-second, preheat period and will go through the auto-zero self-test programme for 35 seconds, until 0.00 is displayed.

• Do not connect the armoured hose of the condenser pickup to the rear of the machine until 0.00 is displayed.

• Insert the silicone hose probe and clamp it onto the exhaust tailpipe with the stand to the right or left of the exhaust fumes to prevent the heat from affecting the stand.

• Unroll the armoured hose and press it onto the brass inlet at the back of the analyser.

• Observe the readings on the display and make adjustments according to the vehicle manufacturer’s specifications.

• It is important to use the analyser with the condenser stand otherwise you will damage the analyser.

• If the analyser is accidentally switched off at any time, the pickup hose must be removed from the back of the analyser. This allows the analyser, when switched on again, to auto-zero without containing exhaust gas in the pump chambers and hose. If the pickup hose is not removed, the auto-zero will start above 0 and give inaccurate readings.

Never connect and disconnect clamps without removing the pipe at the back of the analyser.

In addition, attention should be paid to the following:

• The inlet hose should not be stepped on or restricted in any way.

Pipe to the exhaust system Filter

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29

• The hose connections must be airtight and the valve on the condenser must be in the horizontal position (closed).

• From time to time, condensate must be blown out of the hoses and pickup probe with compressed air.

• The hoses should be disconnected from the analyser to avoid damage to the pump. • The condenser should be drained after each test, using the valve.

• When the paper filter becomes light grey, it should be changed. (Take care when inserting filter paper into the housing. Make sure the window is properly located before hand-tightening the large nut.)

• The fuel filter on the condenser stand should be changed regularly. • On a 12-volt analyser, the battery clamps should be clean.

Assessment 1

1. Explain the function of a gas analyser.

2. Explain how you would connect the gas analyser to a motor car’s engine to test the CO of the exhaust gas.

Brinell hardness tester

Function

• To test how hard different types of materials are.

• Hardness refers to a material’s ability to resist plastic deformation, usually by penetration. The term ‘hardness’ may also refer to a material’s resistance to bending, scratching, abrasion or cutting.

• The Brinell Hardness Test involves indenting the test material with a 10 mm piece of hardened steel or a carbide ball, by subjecting it to a load of 3 000 kg. (For softer materials, the load can be reduced to 1 500 kg or 500 kg to avoid

excessive indentation.) The full load is normally applied for 10 to 15 seconds, in the case of iron and steel, and for at least 30 seconds in the case of other metals. The diameter of the indentation left in the test material is measured with a low-powered microscope.

Rockwell Hardness Test

The Rockwell Hardness Test method involves indenting the test material with a diamond cone or hardened steel-ball indenter. The indenter is forced into the test material under a preliminary minor load (F0), usually 10 kgf. Kgf is a method of expressing load in terms of mass. The permanent increase in depth of penetration, resulting from the application and removal of the additional major load, is used to calculate the Rockwell Hardness Number.

Figure 2.2 (a): Rockwell hardness tester Figure 2.2 (b): Brinell tester

Hardness indicator meter

Platform Platform height adjuster

activating knob

Platform

Platform adjuster activating panel

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Procedure to use the Brinell hardness tester

• The hardness of a material cannot be measured in standard units like the those used to measure mass, length or time. We can only define hardness.

• For many years, the hardness of a material has been assessed by its resistance to scratching or cutting, for example, if material B scratches material C but not material A. The relative hardness of minerals can be assessed by referring to the Mohs’ scale, which ranks the ability of materials to resist scratching by other materials.

• Similar methods to assess hardness are still used today. An example is the file test. In this test, a file, tempered to a desired hardness, is rubbed on the test material’s surface. If the file slides without biting or marking the surface, the test material is considered harder than the file.

• Hardness tests like these are limited and do not provide accurate numeric data or scales, particularly for modern metals and materials. The usual method to achieve a hardness value is to measure the depth or area of an indentation left by an indenter of a specific shape when a specific force is applied for a specific time.

Care

• Oil the platform adjuster to avoid rust.

• When the tester is used, it should be mounted properly to ensure the correct reading.

• Do not exceed the pressure that is prescribed for testing certain materials. The machine could be damaged.

• The vice in which the sample material is clamped should be stable to ensure a correct reading.

Assessment 2

1. Explain the principles of the Brinell hardness tester.

Multimeter

Function

• The meter can be used to test different electrical components and concepts. • The switch on the meter selects the function and desired ranges and also turns

the meter on and off. To extend the life of the battery, the switch should be in the ‘OFF’ position when the meter is not in use.

• To test current, voltage, resistance, continuity, transistors and diodes.

Panel description

Figure 2.3: Multimeter

LCD display screen

Range selector switch

10a DC terminal socket VΩma terminal socket Common terminal socket

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31

Use of a multimeter

How to test current flow

DC current measurement

• Connect the black test lead to the COM jack and the red test lead to the VΩmA jack. (If the current is equal to or greater than 200 mA, use the 10A jack instead.) • Set the range switch to the desired current range.

• Open the circuit in which the current is to be measured and connect the test leads in series with the circuit.

• Read the current value on the LCD display along with the polarity of the red test lead.

How to test voltage

DC voltage measurement

• Connect the red test lead to the VΩmA jack and the black test lead to the COM jack.

• Set the range switch to the desired range. If the voltage is not known beforehand, set the range switch at the highest range position and then reduce the range in increments until the resolution is satisfactory.

• Connect the test leads across the device or circuit to be measured.

• Read the voltage value on the LCD display along with the polarity of the red test lead.

How to test resistance

Resistance measurement

• Connect the red test lead to the VΩmA jack and the black test lead to the COM jack.

• Set the range switch to the desired Ω range.

• If the resistor to be measured is connected to a circuit, disconnect the circuit’s power and discharge all capacitors before measuring the resistance.

• Connect the test leads across the resistor to be measured and read the resistance value on the LCD display.

How to test transistors

Transistor test

• Set the range switch to the hFE range.

• Determine whether the transistor to be tested is a PNP or NPN type and locate the emitter, base and collector leads. Insert the leads into the proper holes of the hFE socket on the front panel. The meter will display the approximate hFE value.

How to test continuity

Diode and continuity measurement

• Connect the red test lead to the VΩmA jack and the black test lead to the COM jack.

• Set the range switch to the range.

• Connect the red test lead to the anode of the diode to be tested and the black test lead to the cathode of the diode.

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• The approximate forward voltage drop of the diode will be displayed in mV. If the connection is reversed, only the figure ‘1’ will be shown on the LCD. • Connect the test leads to the two terminals of the circuit to be tested. • If the resistance is less than about 50 Ω, the buzzer will sound.

Care of the multimeter

The following precautions should be taken: • Keep the meter dry.

• Keep the meter away from dust and dirt.

• Use and store the meter in environments where the temperature is normal. • Do not drop the meter as it could be damaged and its operation could be affected. • Use only charged cells of the correct size. (Always remove old batteries as they

can leak and corrode the wiring.)

Assessment 3

1. Explain how to use a multimeter to test for DC current.

2. Explain how you would measure DC voltage using a multimeter. 3. Explain, step-by-step, how you would test resistance using a multimeter. 4. Describe, step-by-step, how you would use a multimeter to test diodes and continuity in a wire.

5. Name four points that have to be considered in the care of a multimeter.

Pressure testers

Cooling tester

Function

• A pump is used on a cooling system to test the system for leaks.

• To pump compressed air into the cooling system of a motor car to determine whether there are any water leaks in the system.

• To test if the pressure cap on the cooling system operates according to the prescribed pressure of the system.

Figure 2.4: Cooling pressure tester

Radiator adapters Connector to the radiator

Radiator pump

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33

Use of the cooling pressure tester

• Unscrew the radiator cap. Determine the type of adaptor to be used for testing the radiator.

• Fix the adaptor to the tester and screw it onto the radiator.

• Pump the tester to the predetermined pressure of the radiator cap. • Let the tester stand for a while.

• Note the reading on the meter. If the reading drops, it indicates that the cooling system has a leak.

• You can use the cooling tester to determine if a cylinder-head gasket is leaking. • Screw the tester into the cooling system.

• Pump until the predetermined pressure is reached. • Start the car.

• Rev the engine and note the meter reading on the tester.

• If the meter reading increases, it indicates that the cylinder-head gasket is leaking.

Care

• The meter should always be stored in its container to protect it from damage. • Check the connecting pipes regularly to determine if there are any leaks or if the

pipes are damaged.

• Determine the pressure of the cooling system before pumping air into the system. You could damage the pressure meter gauge if you exceed the predetermined pressure.

Oil tester

Function

• To use an indicator to determine the operating oil pressure in an engine.

• To test the operating pressure of the oil in the lubricating system of an engine by means of an oil pressure meter.

Figure 2.5: Oil pressure gauge and oil pressure tester

Procedure to use an oil pressure meter

An oil pressure gauge can provide an excellent indication of the health of various systems in an engine. The key is to establish baseline readings when the engine is healthy and then to be aware of any changes perceived over time.

Oil pressure meter Oil pressure meter pipe Pressure meter Meter connector

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How to test the oil pressure of an engine

• Remove the oil sender unit.

• Connect the oil pressure gauge to the hole of the sender unit. • Start the engine.

• Activate the pump. • Check the reading.

• Check the reading and compare it to the vehicle’s specifications. • If the reading is incorrect, replace the oil pump.

Care

• The meter should always be stored in its container to protect it from damage. • Check the connecting pipes regularly to determine whether there are any leaks

or whether the pipes are damaged.

• Make certain that the connector hole, where the oil sender unit is situated, has been screwed in correctly and is not crooked.

• Make certain that the relief valve is deactivated before the meter is stored.

Assessment 4

1. Explain how you would test the cooling system of an engine. 2. Explain how you would test the oil pressure of an engine.

Fuel pressure tester/meter

Function

• To use an indicator to determine the fuel operating pressure in the system.

• To test the pressure of the fuel in the fuel line that runs to the direct injection

system.

Figure 2.6: Fuel pressure tester

Procedure to use the fuel pressure tester

• Disconnect the pipe running from the tank to the fuel pump. • Connect the fuel pump pressure meter to the inlet.

• Activate the pump. Note the reading.

• Keep the pump at the predetermined stroke and check whether the reading decreases.

Pressure relief valve

Connectors

Pressure meter

Rubber pipe

Return pipe to tank

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35

• If it does, the inlet valve in the pump is leaking. • Remove the pressure gauge.

• Remove the pipe from the fuel pump at the delivery side of the pump. • Connect the fuel pressure gauge on the delivery side.

• Activate the pump.

• Keep the pump at the predetermined stroke and check whether the reading decreases.

• If it does, the delivery valve in the pump is leaking.

• Check the reading and compare it with the vehicle’s specifications. • If the reading is incorrect, replace the pump.

Care

• Store the pressure meter in its container.

• Make certain that the pipes are in good condition.

• Check the clamps around the pipes to ensure that they are tight. • The fuel pump sucks the fuel from the petrol tank and pumps it to the

carburettor under pressure.

• If the fuel pressure in the petrol pump is too high, the pipes could burst. • If the pressure is too low, the vehicle will not move due to fuel starvation.

Assessment 5

1. Explain how you would test the pressure in the fuel system.

Cylinder leakage tester

Function

• Use a meter with compressed air to determine if any compressed air escapes the engine.

• The function of the cylinder leakage tester is to check whether gases leak from

the cylinder in the engine during the compression stroke.

Figure 2.7: Cylinder leakage tester

Procedure to use the cylinder leakage tester

• Turn the engine until both valves on cylinder 1 are closed. (Piston 1 is on the power stroke.)

• Unscrew the spark-plug.

• Screw the spark-plug adaptor into the spark-plug hole.

• Use a spanner to lock the crankshaft pulley so that it cannot turn. • Close the relief valve on the tester.

• Connect the compressed air pipe to the tester and to the adaptor in the spark-plug hole.

air hose coupler

air hose

Plug adaptor Pressure indicator

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• Connect the compressed air hose to the main supply. • Open the relief valve on the tester slowly.

• Note the reading on the tester. The reading will determine the amount of gas leakage occurring in the engine.

Determining the leakage

• Listen to the carburettor for a hissing noise. (Inlet valve is leaking.) • Listen to the exhaust pipe for a hissing noise. (Exhaust valve is leaking.) • Listen for a hissing noise in the dipstick hole. (Piston ring is worn.)

• Remove the filler cap on the tappet cover and listen for a hissing noise. (Rings are worn.)

• If you see bubbles in the radiator water, the cylinder-head gasket is blown or the cylinder block is cracked.

Care

• Store meter in a dry place.

• Check the thread on the adaptors regularly. • Check pipes for damage.

• Check that the clamps on the pipes are tight.

• Always relieve the pressure on the tester after performing a test on a cylinder.

Assessment 6

1. What is the function of a cylinder leakage tester?

2. Explain, step-by-step, how to connect a cylinder leakage tester.

3. How would you determine where the leakage is when using a cylinder leakage tester?

Torsion tester

Function

A torsion tester allows you to investigate the relationship between the momentum or torque applied to material and the influence of the material or member length on torsional deflection. To test how torque and the material type affect the torsional deflection.

Figure 2.8: a torsion bar used in a car’s suspension

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37

Figure 2.9: Torsion tester

How to use a torsion tester

• Measure the diameter of the material using a vernier caliper or a micrometer. • Place the material between the two drill chucks, allowing a length of 500 mm

between centres.

• Zero the protractor using the pointer arm.

• Add masses in 50 g increments to the load arm, noting the angle of twist (to the nearest 0,25°) on the protractor until either the load arm hits the end stop or a maximum load of 500 g has been used.

• Plot a graph depicting the angle of twist versus load. • Repeat the above and use different materials. • Compare the results.

Care

• All nuts and bolts on the tester should be secured properly.

• Do not over-tighten the chuck where the sample material is clamped. • Store the equipment in a dry place to prevent rust.

• When adding different mass pieces, work very carefully or you could obtain an incorrect reading of the torsion of the specimen.

• Before you store the tester, remove all mass pieces.

Moments and forces tester

Principles

In order to understand moments and forces testers, it is necessary to know what the terms ‘force’ and ‘moment’ mean. There are two types of forces acting on a body: • Load – Loads are caused by acceleration due to gravity. (The weight of a body is

termed a load.)

• Shear – Shear stress refers to a state where the stress is parallel or tangential to the face of the material as opposed to normal stress.

Function

To determine the reactions on either side of a simply loaded beam. To illustrate the concept of the triangle of forces.

Twisitng indicator Rod clamp Frame Mass pieces Twisting rod

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Procedure to use testing equipment

By using this equipment, you can test the reaction on either side of a simply loaded beam.

Figure 2.10: a supported-beam kit

• Assemble the equipment as indicated in Figure 2.10. • Zero the load cells.

• Apply loads to the beam at any position via the plastic hangers. • Record the load cell reading.

• Repeat for other loads and load positions.

Use the calculation methods you learnt in Grade 11 to confirm your findings.

Triangle of forces

Figure 2.11: Equilibrium of three forces

Load cells Frame Reaction of a supported beam Mass pieces Supported beam Load cells Frame Pulleys Equilibrium of three forces Mass pieces on a string

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39

Mass pieces

Frame Dial indicator

Bending bar

• Assemble the equipment as indicated in Figure 2.11. • Zero the load cell and compression cell.

• Put the weight hanger in any position along the string and add a known mass (300 g).

• Take the reading on the load cell.

• Obtain the geometry of the system of forces by measurement and then by calculation.

Ensure that the pulley is free-running. Try other geometries by rearranging the pulleys and load cells (as long as the pulleys allow the string to be attached to the load cell vertically).

Care

• All nuts and bolts on the tester should be secured properly. • Store the equipment in a dry place to prevent any rust.

• When adding different mass pieces, do so very gently or you could obtain an incorrect reading on the load cells.

• Before you store the tester, remove all mass pieces. • Do not bump the load cells as this may cause damage.

Beam bending

Function

To use a tester to determine the deflection of various given pieces of material. To investigate the deflection of beams. In the simplest case, the equipment can be used as an illustration of Young’s modulus for a material. For example, an aluminium beam will deflect roughly three times more than a steel beam of the same section, under the same load conditions, since the modulus for aluminium is a third of that of steel.

Figure 2.12: a beam-bending test kit

Procedure to use the beam-bending test kit

• Assemble the equipment as directed in the kit, selecting an appropriate beam. • Using a ruler and a dry-wipe marker, draw a line across the beam 200 mm from

the root.

• Add a 10 g weight hanger to the dial indicator and slide the dial gauge down onto the beam until it reads 10 mm. Remove the weight hanger and zero the outer scale using the bezel. With plastic beams, this may take several attempts. • Add a 100 g mass to the dial indicator and record the dial indicator reading.

References

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