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Foundryman's Handbook, 8th Edition
GABE
Principles of Metal Surface Treatment and Protection, 2nd Edition
GILCHRIST
Extraction Metallurgy, 2nd Edition
HULL
Introduction to Dislocations, 2nd Edition
PARKER
An Introduction to Chemical Metallurgy, 2nd Edition
PARKIN & FLOOD
Welding Craft Practice, Volume 2
SARKAR
Wear of Metals
SMALLMAN & ASHBEE
Modern Metallography
BISWAS & DAVENPORT
Extractive Metallurgy of Copper
WILLS
Mineral Processing Technology
PEACEY & DAVENPORT
The Iron Blast Furnace
WELDING
CRAFT PRACTICE
VOL UME 2: Electric Arc Welding and
Related Studies
BY
N. PARKIN, M.I.P., M.R.S.H., M.R.P.A.
Lecturer in Welding and Plumbing
Canterbury Technical College
AND
C. R. FLOOD, A.M.INST.W.
Lecturer in Welding and Metal Plate Work
Canterbury Technical College
SECOND EDITION
PERGAMON PRESS
OXFORD · NEW YORK · TORONTO · SYDNEY ■ PARIS · FRANKFURT
U.K. Pergamon Press Ltd., Headington Hill Hall,
Oxford OX3 OBW, England
U.S.A Pergamon Press Inc., Maxwell House, Fairview Park,
Elmsford, New York 10523, U.S.A.
CANADA Pergamon of Canada, Suite 104, 150 Consumers Road,
Willowdale, Ontario M2J 1P9, Canada
AUSTRALIA Pergamon Press (Aust.) Pty. Ltd., P.O. Box 544,
Potts Point, N.S.W. 2011, Australia
FRANCE Pergamon Press SARL, 24 rue des Ecoles,
75240 Paris, Cedex 05, France
FEDERAL REPUBLIC Pergamon Press GmbH, 6242 Kronberg-Taunus,
OF GERMANY Hammerweg 6, Federal Republic of Germany
Copyright © 1980 Pergamon Press Ltd.
All Rights Reserved. No part of this publication may be
reproduced, stored in a retrieval system or transmitted in
any form or by any means: electronic, electrostatic,
magnetic tape, mechanical, photocopying, recording or
otherwise, without permission in writing from the
publishers
First edition 1969
Reprinted 1974
Second edition 1980
British Library Cataloguing in Publication Data
Parkin, Newton
Welding craft practice. - 2nd ed. - (Pergamon
international library).
Vol. 2: Electric arc welding and related studies
1. Welding
I. Title II. Flood, Charles Richard
671.5'2 TS227 79-40237
ISBN O-08-024260-X (Hardcover)
ISBN O-08-024259-6 (Flexicover)
Printed in Great Britain by
Biddies Ltd., Guildford, Surrey
Introduction
IN A rapidly developing welding industry there is a constant
demand for skilled craftsmen capable of producing high-quality
work with first-class equipment. The wide range of modern welding
work makes it necessary for the operator to be as capable of
controlling expensive automatic machines as he is of performing
skilful manual welding. The need is for adequately trained person-
nel with a sound understanding of the various processes and
materials to be used, a keen appreciation of the importance of the
correct, careful use of equipment and a completely "safety-
conscious" outlook.
The two volumes of this book cover the ground necessary for
the acquisition of the essential basic skills and safe working
methods, sufficient technology and related studies being included
to provide a suitable background to the practical work and form a
basis for further, more advanced studies. It is intended for all who
wish to learn to weld and the ground covered will enable the
beginner to obtain a sound knowledge of the equipment, a keen
appreciation of safety and, by means of a graduated series of
practical exercises, a good standard of skill.
The intention has been to cover the requirements of the syllabus
of the City and Guilds of London Institute, Courses 165; 200,
215/216; 217, the relevant information being given for the
production and testing of the specimen welds required in this
course, and it is hoped that all would-be welders will aim at
obtaining a suitable qualification.
Volume 1 deals with Oxygen-Acetylene Processes and Weld
Defects, Testing of Welds and Welding Science, Volume 2 with
Electric Arc Processes and Elementary Electricity, Classification of
VII
INTRODUCTION
Electrodes, Welding Symbols, Engineering Drawing, Metal Plate
Surface Development and Workshop Calculations.
We wish to express our appreciation to Messrs. Hancock and
Company (Engineers) Ltd., Air Products Ltd., Lincolm Electric
Company Ltd., Murex Welding Processes Ltd., for allowing the
reproduction of photographs and diagrams of their welding
equipment.
Material from B.S. 1295; 1959: Tests for Use in the Training of
Welders, B.S. 639; 1976: Specification for Covered Electrodes for the
Manual Metal Arc Welding of Carbon and Carbon Manganese Steels
and B.S. 499; Part 2, 1965: Welding Terms and Symbols, is repro-
duced by permission of the British Standards Institution, 2 Park
Street, London, W.l, from ^hom copies of the complete standards
can be obtained.
The student is advised to make a further study of the British
Standards referred to.
N. PARKIN
C. R. FLOOD
VIII
CHAPTER 1
Plant, Procedure and Equipment
ELECTRIC arc welding is carried out by transmitting electrical
energy from one point to another and then turning the electrical
energy into heat. The heat is then used to melt the metal to be
welded (generally referred to as the parent metal) and the elec-
trode (sometimes called the filler rod). The melting of the parent
metal and the electrode is effected by an arc of high temperature
jumping from the electrode across to the parent metal and so
giving a source of heat energy (Fig. II. 1).
FIG. II. 1. Metallic arc welding of mild steel.
To transmit electrical energy efficiently, good conductors are
essential. All metals are conductors of electricity, although some
are more effective than others. This difference is shown, for
3
WELDING CRAFT PRACTICE-VOL 2
example, by comparing copper and steel: the former is the better
conductor of the two, because it wastes less energy. Most electrical
wiring is of copper wire.
The chief insulating materials consist of paper, rubber, p.v.c. and
oil, and these must resist the flow of electricity. Thus it is possible
to wrap a length of copper wire with rubber and pass electrical
power along its length, because the rubber coating will confine
the flow of electricity along the desired path.
MANUAL ELECTRIC ARC WELDING PLANT
The term "manual electric arc welding" means arc welding
carried out by one man using an electrode in a holder, the operator
being entirely responsible for the deposition of the weld metal.
Two types of plant may be used: direct current (d.c.) plants
or alternating current (a.c.) plants. The choice of plant depends
upon certain factors, but generally both types are suitable for the
welding of all metals, except for some non-ferrous metals which
require a d.c. plant. A typical arc welding circuit diagram is
shown in Fig. H.2.
Switch fuse
-·>—CED-
Mains
Input leads
supply
Welding lead
Electrode
Earth
FIG. 11.2. Circuit diagram for arc welding.
4
PLANT, PROCEDURE AND EQUIPMENT
A.C. Plants (Fig. Π.3; Plate II.l)
The welding power for a.c. plants is obtained from a step down
transformer. This means that the incoming voltage supply, which
may be in the nature of 230—250 volts, is stepped down to less than
100 volts in the transformer. The transformer is also equipped with a
current control regulator, enabling the operator to select the correct
current (amp) for the size of electrode being used. The sets may be
either air cooled or oil cooled. The air-cooled sets have an electric fan
blowing cool air on to the transformer, whilst the oil-cooled sets have
the transformer immersed in a thin oil. From the point of view of
simplicity and efficiency, the a.c. welding equipment is ideal.
Some of the advantages offered by a.c. over d.c. may be sum-
marised as follows:
1. Cheaper to buy than d.c. sets. The initial cost is approxi-
mately one-half of that required for a d.c. set of equivalent
rating.
From switch fuse box
Primary winding
tappings
Transformer
Variable reactance
Secondary windings
Current selector
switch
-•HI—^TL—i_v ~
Electrode holder
Earth ' \
■ Work piece
FIG. II.3. Circuit diagram of an a.c. welding transformer.
5
WELDING CRAFT PRACTICE-VOL 2
PLATE II. 1. a.c. arc welding transformer.
{Courtesy, Murex Welding Processes Ltd.)
2. Little or no maintenance necessary. This is because there
are no moving parts in an a.c. transformer.
3. The phenomenon of "arc blow" does not exist with a.c. (see
d.c. plants for an explanation of this).
4. The a.c. transformer may be used in the open without further
protection from the weather being necessary.
5. The quality of the weld metal is equal to that of the d.c.
process when welding steels.
6
PLANT, PROCEDURE AND EQUIPMENT
Some disadvantages are as follows:
1. Non-ferrous electrodes are not so well deposited.
2. Thin gauge sheet metal is better welded with d.c.
3. The electric shock hazard is generally recognised to be more
pronounced with a.c. than with d.c.
D.C. Plants (Plate Π.2)
Direct current welding power may be obtained from a rectifier
or generator set.
A rectifier is a means of changing the a.c. input to d.c. output.
A generator is a machine that generates or "makes" electricity
and before this can take place some form of energy is required
to drive the machine. This may take the form of a petrol or
diesel engine, an a.c. electric motor or even a d.c. electric motor.
Where no electrical supply is available (on site or on field repairs)
then the petrol or diesel motor is used. When a.c. supply is avail-
able it is, of course, most beneficial to use the a.c.-driven generator.
Some of the advantages offered by d.c. sets may be summarised
as follows:
1. They can be used to deposit both ferrous and non-ferrous
electrodes.
2. Smoother welding giving an advantage when welding thin
sheet metal.
3. Safer to use in damp conditions, where the risk of an
electric shock is great.
Some disadvantages are as follows:
1. More expensive to purchase than a.c. sets.
2. Periodic maintenance of the generator type of plant is necessary,
because of the moving parts.
3. Troubles from "arc blow".
Magnetic Arc Blow
This is a condition encountered only with d.c. welding equip-
ment. The arc is forced away from the weld point, notably when
7
