Castings Volume I, 2nd Edition

354 Pages·2003·11.6 MB·English

by  John Campbell

Castings

Castings
John Campbell OBE FREng
Professor of Casting Technology,
University of Birmingham, UK
U T T E R W O R T H
E I N E M A N N
OXFORD AMSTERDAM BOSTON LONDON NEW YORK PARIS
SAN DIEGO SAN FRANCISCO SINGAPORE SYDNEY TOKYO
Butterworth-Heinemann
An imprint of Elsevier Science
Linacre House, Jordan Hill, Oxford OX2 8DP
22 Wheeler Road, Burlington MA 01803
First published 1991
Paperback edition 1993
Reprinted 1993, 1995 (twice), 1997, 1998, 1999, 2000
Second edition 2003
Copyright 0 1991, 2003, Elsevier Science Ltd. All rights reserved
No part of this publication may be reproduced in any material
form (including photocopying or storing in any medium by
electronic means and whether or not transiently or incidentally
to some other use of this publication) without the written
permission of the copyright holder except in accordance with the
provisions of the Copyright, Designs and Patents Act 1988 or under
the terms of a licence issued by the Copyright Licensing Agency Ltd,
90 Tottenham Court Road, London, England WIT 4LP. Applications
for the copyright holder’s written permission to reproduce any part
of this publication should be addressed to the publisher
Permissions may be sought directly from Elsevier’s Science and Technology
Rights Department in Oxford, UK: phone [phone]; fax [phone];
e-mail: [email protected]. You may also complete your request on-line via the
Elsevier Science homepage (http://www.elsevier.com), by selecting ‘Customer support’ and
then ‘Obtaining Permissions’
British Library Cataloguing in Publication Data
A catalogue record for this book is available from the British Library
Library of Congress Cataloguing in Publication Data
A catalogue record for this book is available from the Library of Congress
ISBN 0 7506 4790 6
For information on all Buttenvorth-Heinemann
publications visit our website at www.bh.com
Typeset by Replika Press Pvt. Ltd, India
Printed and bound in Great Britain by MPG Books Ltd, Bodmin, Cornwall
Contents
Preface vii 6.2 Subsurface porosity 186
Dedication ix 6.3 Growth of gas pores 195
Introduction xi 6.4 Blowholes 200
7. Solidi$cation shrinkage 205
1. The melt 1
7.1 General shrinkage behaviour 205
1 .I Reactions of the melt with its
7.2 Solidification shrinkage 206
environment 2
7.3 Feeding criteria 210
1.2 Transport of gases in melts 10
7.4 Feeding - the five mechanisms 2 12
1.3 Surface film formation 12
7.5 Initiation of shrinkage porosity 222
7.6 Growth of shrinkage pores 226
2. Entrainment 17 7.7 Final forms of shrinkage porosity 227
2.1 Entrainment defects 20
2.2 Entrainment processes 3 1 8. Linear contraction 232
2.3 Furling and unfurling 54
8.1 Uniform contraction 232
2.4 Deactivation of entrained films 61
8.2 Non-uniform contraction (distortion) 237
2.5 Soluble, transient films 63
8.3 Hot tearing 242
2.6 Detrainment 64
8.4 Cold cracking 258
2.7 Evidence for bifilms 64
8.5 Residual stress 259
2.8 The significance of bifilms 67
9. Structure, defects and properties qf the
3. Flow 70
finished casting 267
3. I Effect of surface films on filling 70
9.1 Grain size 267
3.2 Effect of entrained films on filling 73
9.2 Dendrite arm spacing 270
3.3 Fluidity (maximum fluidity length) Lr 74
9.3 Compact defects 275
3.4 Continuous fluidity 95
9.4 Planar defects 279
3.5 Glossary of symbols 98
9.5 Effects of defects on properties of
castings 282
4. The mould 99 9.6 The statistics of failure 301
4.1 Inert moulds 99
4.2 Aggregate moulds 100
10. Processing 306
4.3 Mould atmosphere 105
4.4 Mould surface reactions 11I 10. 1 Impregnation 306
10.2 Hot isostatic pressing 306
4.5 Metal surface reactions 114
10.3 Working (forging, rolling and
extrusion) 309
5. Solidification structure 117 10.4 Machining 309
5.1 Heat transfer 117 10.5 Painting 310
5.2 Development of matrix structure 129
5.3 Segregation 139
1 1. Environmental interactions 3 11
5.4 Aluminium alloys 147
5.5 Cast irons 156 1 1.1 Internal oxidation 3 1 1
11.2 Corrosion 313
5.6 Steels 167
6. Gasporosity 178 References 3 18
6.1 Nucleation of gas porosity 178 Index 329

Preface
Metal castings are fundamental building blocks, materials science, where breadth of knowledge has
the three-dimensional integral shapes indispensable to take precedence over depth of understanding.
to practically all other manufacturing industries. This work makes the case for process metallurgy
Although the manufacturing path from the liquid as being a key complementary discipline. It can
to the finished shape is the most direct, this directness explain the properties of metals, in some respects
involves the greatest difficulty. This is because so outweighing the effects of alloying, working and
much needs to be controlled simultaneously, heat treatment that are the established province of
including melting, alloying, moulding, pouring, physical metallurgy. In particular, the study of
solidification, finishing, etc. Every one of these casting technology is a topic of daunting complexity,
aspects has to be correct since failure of only one far more encompassing than the separate studies,
will probably cause the casting to fail. Other for instance, of fluid flow or solidification (as
processes such as forging or machining are merely necessary, important and fascinating as such focused
single parts of multi-step processes. It is clearly studies clearly are). It is hoped therefore that in
easier to control each separate process in turn. time, casting technology will be rightly recognized
It is no wonder therefore that the manufacture as a complex engineering discipline, worthy of
of castings is one of the most challenging of individual attention.
technologies. It has defied proper understanding The author has always admired those who have
and control for an impressive five thousand years only published what was certain knowledge.
at least. However, there are signs that we might However, as this work was well under way, it became
now be starting to make progress. clear to me that this was not my purpose. Knowledge
Naturally, this claim appears to have been made is hard to achieve, and often illusive, fragmentary
by all writers of textbooks on castings for the last and ultimately uncertain. This book is offered as
hundred years or so. Doubtless, it will continue to an exercise in education, more to do with thinking
be made in future generations. In a way, it is hoped and understanding than learning. It is an exercise
that it will always be true. This is what makes in grappling with new concepts and making personal
casting so fascinating. The complexity of the subject evaluations of their worth, their cogency, and their
invites a continuous stream of new concepts and place amid the scattering of facts, some reliable,
new solutions. others less so. It is about research, and about the
The author trained as a physicist and physical excitement of finding out for oneself.
metallurgist, and is aware of the admirable and Thus the opportunity has been taken in this
powerful developments in science and technology revised edition of Castings to bring the work up to
that have facilitated the progress enjoyed by these date particularly in the new and exciting areas of
branches of science. These successes have, quite surface turbulence and the recently discovered
naturally, persuaded the Higher Educational compaction and unfurling of folded film defects
Institutes throughout the world to adopt physical (the bifilms). Additional new concepts of alloy
metallurgy as the natural materials discipline theory relating to the common alloy eutectics Al-
required to be taught. Process metallurgy has been Si and Fe-C will be outlined. At the time of writing
increasingly regarded as a less rigorous subject, these new paradigms are not quite out of the realm
not requiring the attentions of a university of speculation, but most areas are now well grounded
curriculum. Perhaps, worse still, we now have in about 200 person years of effort in the author’s
viii Preface
laboratory over the last 12 years. Furthermore, many It is intended to follow up this volume Castings
have been rigorously tested and proved in foundries. I - Principles with two further volumes. The next
This aspect of quoting confirmation of scientific in line is Castings II - Practice listing my ten rules
concepts from industrial experience is a departure for the manufacture of good castings with one
that will be viewed with concern by those academics chapter per rule. It concentrates on an outline of
who are accustomed to the apparent rigour of current knowledge of the theory and practice of
laboratory experiments. However, for those who designing filling and feeding systems for castings.
persevere and grow to understand this work it will It is intended as a more practical work. Finally, I
become clear that laboratory experiments cannot wish to write something on Castings III - Processes
at this time achieve the control over liquid metal because, having personal experience of many of
quality that can now be routinely provided in some the casting processes, it has become clear to me
industrial operations. Thus the evidence from that a good comparative text is much needed. I
industry is vital at this time. Suitable laboratory shall then take a rest.
experiments can catch up later. Even so, as I mentioned in the Preface to
The author has allowed himself the luxury of Castings, and bears repeat here, the rapidity of
hypothesis, that a sceptic might brand speculation. casting developments makes it a privilege to live
Broadly, it has been carried out in the spirit of the in such exciting times. For this reason, however, it
words of John Maynard Keynes, ‘I would rather be will not be possible to keep this work up to date. It
vaguely right than precisely wrong.’ This book is is hoped that, as before, this new edition will serve
the first attempt to codify and present the New its purpose for a time, reaching out to an even
Metallurgy. It cannot therefore claim to be wider audience, and assisting foundry people to
authoritative on all aspects at this time. It is an overcome their everyday problems. Furthermore, I
introduction to the new thinking of the metallurgy hope it will inspire students and casting engineers
of cast alloys, and, by virtue of the survival of alike to continue to keep themselves updated. The
many of the defects during plastic working, wrought regular reading of new developments in the casting
alloys too. journals, and attendance at technical meetings of
The primary aim remains to challenge the reader local societies, will encourage the professionalism
to think through the concepts that will lead to a to achieve even higher standards of castings in the
better understanding of this most complex of forming future.
operations, the casting process. It is hoped thereby
to improve the professionalism and status of casting
JC
technology, and with it the products, so that both West Malvern, Worcestershire, UK
the industry and its customers will benefit. 1 September 2002
Dedication
I dedicate this book to my wife, Sheila, for her Although it may be true that, following P. G.
encouragement and support. I recognize that such Wodehouse, without Sheila’s sympathy and
acknowledgements are commonly made at the encouragement this book would have been finished
beginnings of books, to the extent that they might in half the time, it is also true that without such
appear trite, or hackneyed. However, I can honestly long-suffering efforts beyond the call of duty of
say that I had no idea of the awful reality of the any wife, it would never have been finished at all.
antisocial problems reflected by these tributes.