Fundamentals of Welding Skills

118 Pages·1976·22.021 MB·English

by  Peter F. Woods A.I.W. (auth.)

FUNDAMENTALS OF
WELDING SKILLS
Peter F. Woods
A.I.W.
M
Other Macmillan Titles ISBN 978-0-333-19197-2 ISBN 978-1-349-02818-4 (eBook)
DOI 10.1007/978-1-349-02818-4
Engineering Craft Studies series
©Peter F. Woods 1976
Part 1 - Engineering Bose
Reprint of the original edition 1976
Part 1 - Mechanical Engineering Complement
Part 1 - Electrical Engineering Complement All rights reserved. No part of this publication may
be reproduced or transmitted, in any form or by any means,
Part 2 -Mechanical Engineering
without permission,
Part 2-Electrical Engineering
First published 1976 by
THE MACMILLAN PRESS LT O
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Contents
Preface ix 2 Flux-Metal-Arc Welding 17
Energy Supply 17
1 Introduction 1 the electrode holder
Safety 17
General Safety 1
ventilation-clothing
cutting edges-injuries through flying objects
Electrodes 18
- correct dress - injuries through ignorance
electrode coatings- functions of electrode
or abuse-electrical safety-electric-shock
coatings - electrode types - electrode storage
treatment -lifting or moving materials-
Power Sources 21
fire hazards
electrical conductors
Principles of Fusion 2
Carbon-arc Welding 23
heat and work - the thermal reservoir-
Solubility of Gases in Metals 24
expansion and contraction
Preparation of Workpiece 25
Iron and Steel 5
Penetration 29
casting and forge welding
The Crater 29
Basic Metallurgy 7
Welding Procedures 30
alloys
tacking-presetting the joint- vertical
Fluxes 8
welding-overhead butt-and fillet-joints-
reactive fluxes- organic fluxes- fume
'stovepipe' technique-plug welding
removal
Further Study 44
Engineering Materials 9
sintered materials - non-ferrous metals -
3 Oxy-Acetylene Techniques 47
ferrous alloys-non-metallic materials
Heat Treatment 10 Oxy-acetylene Equipment 47
annealing - normalising- tempering- low-pressure system - high-or equal-
surface hardening and case hardening- pressure system - gas-pressure regulators -
nitriding oxygen and acetylene - assembly of
Surface Protection of Metals 11 equipment-lighting-up procedure -
cladding-chemical coatings-anodising- shutting-down procedure
encapsulation-metal spraying-powder- Safety 51
metal spraying-plasma-arc spraying working on tanks or vessels- working on
Elements of Drawing 11 painted surfaces
geometrical definitions-area- volume- Gases 53
line language-plane section-half-section oxy-acetylene-air-acetylene-oxy-hydrogen
-part section - revolved section - offset - hydrocarbon gases
section Oxy-acetylene Welding Techniques 54
v
vi
Cast Iron 58 Welding Aluminium and its Alloys 86
preparations for welding cast iron - welding direct-current welding
procedure Welding Stainless Steel 87
Braze Welding 59 Spot Welding 88
braze welding of cast iron - braze welding Welding Copper 89
of copper- tin and lead bronzes - Welding Titanium 89
aluminium brazing -/ow-temperature safety with titanium
brazing Further Study 90
Hardfacing 62
Flamecutting 63 6 Quality and Inspection 91
starting a cut
Visual Inspection 91
Flamehardening 65
simple aids to inspection
Flamespraying 65
Impact Testing 95
Flamegouging 65
Classification of Defects 95
Further Study 66
Structural and Design Assessment 95
stress relief-proof testing-jigs
4 Gas-shielded Metal-arc Welding 67
Summary of Other Welding Techniques and
Metal transfer in G.S.M.A. Welding 68 Processes 98
Safety 69 resistance welding-electron-beam welding
Preparation for Welding 70 - friction welding-plasma-gas metal-arc
effect of wire extension on deposition welding-plasma-cutting (transferred arc)
G.S.M.A. Welding Practice 71 -plasma-plating-plasma-cutting (non-
tracking - vertical welding-alloy steels transferred arc) - explosive welding-
Pulse-arc Welding 77 vapour plating-vacuum welding
Further Study 77 Further Study 105
Appendix 107
5 Gas-shielded Tungsten-arc Welding 78
units and symbols-conversion factors-
Electrode Geometry 79 conversion tables - travel-speed conversion
Safety 82 table - comparative diameters - tensile-
Main Parameters of G.S.T.A. Welding 82 stress equivalents-approximate flame-
electrode attitude and tracking- filler wire temperatures-properties of metals -
Jigging and Joint Preparation 84 summary of process power-sources
Preface
For the past fifteen years I have been a welding engineer, The real secret of success is enthusiasm
concerned with the invention, design, and development of new
If this book helps to instil this, then its purpose will have been
processes and equipment. Prior to this I spent some thirty
accomplished - as will yours, for you will be reaching out to
years as a practical welder, working on such diverse projects as
success ...
railway rolling-stock fabrication, pressure-vessel construction
' I would like to express my sincere appreciation to B.O.C.
armoured vehicles and aircraft, as well as motor-vehicle
Ltd, E.S.A.B. Ltd, A.G.A., U.K. Ltd, the Lincoln Electric Co.
manufacture.
Ltd, C. S. Milne and Co. Ltd, and James Neill and Co. Ltd, for
I therefore have something of a sense of dedication in
the use of photographs appearing in this book. My sincere
writing this book. I want to share, within the limitations of the
thanks and appreciation also go to Mrs Valerie Bryon, who
format of this book, my experiences in welding with you, the
typed the manuscript, and to Ruby, for her inspiration.
student.
Peter F. Woods
vii
1. INTRODUCTION
GENERAL SAFETY Injuries through Flying Objects
Constant reference to safety is made throughout this book. Into this category fall damage to the person caused by molten
Certain aspects are amplified in appropriate sections (for metal -for example, from a spot-welding machine or from
example, acetylene and oxygen are dealt with specifically in flamecutting- splinters, swarf, or grinding sparks. Wear the
part 3). Handling equipment should never encourage anything recommended safety clothing. Safety clothing includes
but respect, and careless or unauthorised use of hand or goggles, aprons, boots, gloves, welding helmets, leather caps
machine tools may not only endanger your own safety but and approved safety footwear.
that of the people around you.
It is dangerous to: interfere with machinery with which you
are not familiar; use tools or equipment for unauthorised Correct Dress
purposes; conduct experiments with apparatus or materials
Items of dress such as ties, belts, unfastened shirt-sleeves or
without being instructed to do so.
coats can be the cause of severe injury or fatal accidents. For
Some of the main causes of workshop accidents are:
example, a dangling tie or shirt sleeve could wrap around a
carelessness, ignorance, risk-taking or interference with appar
rotating shaft and pull you into machinery. Long hair is
atus or machinery; wrong use of materials, for example, using
another hazard; caps should always be worn; remember too
hardened tools, like files or drills, as hammers. Untidyness, for
that long hair is a fire risk when you are engaged in welding.
example, oil, grease, nuts, bolts, or metal parts on the floor
could cause people to stumble and fall against sharp edges,
machinery, or glass. Using any gas or combination of gases, Injuries through Ignorance or Abuse
including air, for any purpose other than that recommended is
Do not take risks with anything with which you are
dangerous; for example, the impact of a high-pressure air jet
unfamiliar-and even if you are familiar with it, do not take
on the skin can produce an embolism and death; carbon
risks. Ask if you are unsure; the person to ask is your
dioxide, nitrogen and argon can cause death by suffocation in
instructor-he has the right answers.
unventilated spaces.
Wilful misuse of equipment in a misguided spirit of fun may
Oxygen, acetylene, propane, hydrogen, natural gas, coal
cause severe injury or death to you or the people you work
gas, carbon monoxide and liquid hydrocarbons like petrol,
with. Cylinders of any compressed gas or liquid can become
volatile oils and paraffins are all explosion and fire risks if
bombs if wrongly treated; almost any material can be lethal if
handled wrongly.
used incorrectly: electricity can kill, water can drown, gases
can poison or suffocate, a single match can burn down a
Cutting Edges factory. Think, and if in doubt, ask.
Many apparently harmless materials can be highly
These can cause severe injury and the first rule is always to
dangerous under certain conditions. For example, rubber,
keep both hands behind the cutting edge. Where machinery is
flour, sugar, metal and cork (to name but a few common
concerned, for example, saws, guillotines, lathes, shapers,
substances) can produce violent explosions if mixed with air or
millers or grinders, a further point should be noted
oxygen. Some rare-earth metals will spontaneously ignite if
Never operate any machine without making sure that the sprinkled in the air. Vapour or powder residues in containers
safety guard is correctly fitted and in good order (oil drums are a classic example) are capable of producing
7
2 Fundamentals of Welding Skills
explosions if ignited. Even a soldering iron can initiate an external cardiac massage may be necessary. If a doctor or
explosion with volatile liquids like high-octane petrol. nurse is present he or she will perform this. If someone who
To apply a heat source of any kind to a vessel is potentially knows how to perform external cardiac massage is in attend
dangerous, no matter whether the vessel is full or empty. ance, this task should be delegated to him. For further details
Filling an exhausted container, tank or vessel with water, see the electricity regulations contained in the Factories Act,
leaving only the immediate working area out of contact, is 1961.
usually safe. Large vessels require steam-cleaning which may in
some cases take as long as twenty-four hours, depending on
the nature and amount of contaminating substance to be
Lifting or Moving Materials
removed. Even after this, it is best to ventilate the vessel with
air for a few hours. Injuries to the spine can easily be caused by incorrect
body-posture when lifting. The correct stance is
Electrical Safety 1. Feet slightly apart
2. Knees slightly bent (so that the weight will be taken
Even low voltage can kill under certain circumstances, so never
by the powerful leg and thigh muscles)
believe it is safe to take risks with electricity. Never interfere
3. Take hold of the load, keeping the back straight
with any electrical apparatus; if something has gone wrong,
4. Lift by straightening the legs
report it to your supervisor.
Fire Hazards
Electric-shock Treatment
Before welding or cutting in any environment obtain author
To free the victim from contact with the electricity, switch off
isation from your supervisor. Note where fire extinguishers are
the current immediately or get someone to do so; do not
kept; read operating instructions; make sure that fire emer
attempt to remove a person from contact with a high-voltage
gency exits are unobstructed; warn people in the area before
source unless suitable equipment, insulated for the system
starting work; use the correct dress and equipment.
voltage, is available. When attempting to free a person from
contact with low or medium voltage use rubber gloves, rubber
boots and a rubber mat, or an insulated stick, but if these are
not available use a loop of rope, a cap, or a coat to drag the
PRINCIPLES OF FUSION
person free. Whatever is used must be non-conducting.
After release, do not waste time moving him. Lay the The joining and fabrication of metals by brazing and casting
patient down on something dry, if possible, and if there is no are ancient arts whose origins are lost in remote antiquity
sign of breathing immediately proceed with artificial respir yet they are still used today, although in more diverse and
ation and send someone for a doctor and ambulance. sophisticated ways. The principles of forge welding for
Artificial Respiration: Mouth-to-mouth Method example, are uti Ii sed in resistance spot-welding but with
Remove any foreign material -false teeth, vomit, etc. - that electrical-resistance heating taking the place of the black
may be blocking the air passage. To open the air passage, tilt smith's hearth and an air cylinder doing the work of his
the patient's head back as far as possible. Use one hand to hammer. (For a detailed description see the section on
push the patient's head backwards and the other to pull the resistance welding, p. 98.) In forge welding, metal is heated
jaw forwards, thus slightly opening the patient's mouth. to a temperature at which it becomes soft and malleable, and
Take a deep breath, place your mouth over the patient's the parts are then welded together by hammering. (Forge
mouth and blow. Then press firmly on his chest to expel the welding is not the same as forging, which is a method of
air. Repeat this about five times a minute. shaping parts in a die or on an anvil using power- or
External Cardiac Massage hand-operated hammers or rams.)
If a patient's condition does not improve after one full minute For centuries the only available source of heat for metal
of apparently adequate artificial respiration and you can see working was provided by the burning of charcoal or wood and
that the patient's lips remain blue and his skin pale and you not until much later by coal or coke. The temperature of the
feel sure that the heart has stopped beating effectively, early blacksmith's forge was increased by forcing air through
Introduction 3
the fire with hand- or foot-operated bellows, this task being using a consumable steel electrode. This technique was
undertaken usually by the apprentice. employed for many years, its main applications being the
The first inkling of things to come occurred when oxygen repair of blowholes, etc., in steel castings. Arc welding really
was isolated by Joseph Priestley in 1774, who prepared it by came into prominence commercially with the invention (by
heating mercuric oxide. By the mid-nineteenth century, Oscar Kjellberg of Sweden) of the flux-coated electrode in
progress was being made in steel making and the possible use 1907. Arc welding was, up to the Second World War,
of the electric arc for welding. At the turn of the century, the something of a Cinderella in engineering but the war forced its
Brin brothers tried to produce oxygen on a commercial scale use and development by sheer necessity. Today a whole family
by heating barium oxide but the process was abandoned in of processes have grown out of the original concept of
favour of the liquifaction and fractional distillation of air, a metal-arc welding and much more development lies ahead.
process in which control of temperature is used to separate the
component gases of air. This method was first used on a large
Heat and Work
scale by C. Linde in 1902, in Germany.
The gas was mainly used for medical purposes and as a In the use and understanding of every branch of sciences and
source of illumination in conjunction with lime, to give arts, there are disciplines and laws that must be observed;
'lime-light'. Then came a more significant discovery- it was fusion welding is no exception. It is therefore most important
found that by mixing oxygen with coal gas the flame that we have a fundamental appreciation of thermodynamics,
temperature produced enabled iron to be melted and cut with perhaps better known as the science of heat and work.
ease. Unfortunately, the first people to take advantage of it in Let us begin by describing a simple experiment that
the United Kingdom were the criminal fraternity in illustrates the principle of heat flow or thermal conduction.
Warrington where they used it to open a safe. The event Figure 1.1 shows a tank containing hot water; projecting from
caused a sensation and the authorities were quite alarmed at the sides of the tank are metal bars and on the end of each one
the threat that this new 'secret weapon' posed against security. is a piece of paraffin wax. Heat flows along the bars, at a rate
Acetylene was first discovered by Edmund Davy in 1836. In depending on the thermal conductivity of the particular metal,
1892 T. L. Willson, a Canadian working in the United States, eventually melting the wax. Next to silver, copper is the best
while trying to smelt aluminium ore using a mixture of conductor and compared with these, iron and lead, for
bauxite, coke and lime, discovered a technical process of example, are poor conductors.
acetylene production. (His experiment in producing alu
Hot water
minium by electrolysis was a failure and he threw the material
away, but some days later he became aware that the substance
was emitting a gas which, on subsequent analysis, proved to be
acetylene, C2 H2 .) This first found use in lighting and was
manufactured by adding water to calcium carbide in a small
vessel or gasometer. Eventually a blowpipe was developed for
the controlled combustion of oxygen and acetylene and a new
era in the fabrication of metals had arrived. Early attempts to
compress acetylene met with disastrous results until 1897 Figure 7.7 Thermal conduction in solids; A-copper, 8-
when the chemist G. Claude discovered that the gas was zinc, C - brass, D - lead, E -slate, F- wood. Thermo
soluble in acetone and the solution could safely be absorbed in couples connected to galvanometers may be used instead of
a porous material like asbestos, carbon, or diatomaceous earth, wax
packed into a cylinder. About the same time, the fractional
distillation technique for manufacturing and storing oxygen as Heat is not necessarily transmitted by conduction alone -
a liquid was developed. Fractional distillation of liquid air is it can also travel by convection and radiation. Heat is
still the method used today to obtain oxygen, as well the gases conducted at a constant rate through a homogeneous solid; the
argon, krypton and neon. rate of heat transfer, mostly by convection, in a liquid or a gas
Arc welding was first investigated in 1881 by Auguste de is not constant.
Meritens who experimented with arcs using carbon rods, and Figure 1.2 shows hot liquid rising and the colder liquid
in 1888 the Russian, N. G. Slavianoff, developed a process sinking because of its greater density. In practice it is by no