7/28/2019 16962_fm

1/6

CastingsJohn Campbell, QBE, FEng

Professor of Casting TechnologySchool of Metallurgy and Materials, andInterdisciplinary Research Centre in Materials for Advanced Applications,University of Birmingham

OXFORD AUCKLAND BOSTON JOHANNESBURG MELBOURNE NEW DELHI

7/28/2019 16962_fm

2/6

Butterworth-HeinemannLinacre House, Jordan Hill, Oxford OX2 8DP225 Wildwood Avenue, Woburn, MA 01801-2041A division of Reed Educational and Professional Publishing Ltd"@^ A member of the Reed Elsevier pic groupFirst published 1991Paperback edition 1993Reprinted 1993, 1995 (twice), 1997, 1998, 1999, 2000 Reed Educational an d Professional Publishing Ltd 1991All rights reserved. No part of this publication may be reproducedin an y material form (including photocopying or storing in anymedium by electronic means an d whether or not transiently orincidentally to some other use of this publication) without thewritten permission of the copyright holder except in accordancewith the provisions of the Copyright. Designs an d Patents Act 1988or under the terms of a licence issued by the Copyright LicensingAgency Ltd, 90 Tottenham Court Road, London, England W 1P OLP.Applications for the copyright holder's written permission to reproducean y part of this publication should be addressed to the publishersBritish Library Cataloguing in Publication DataCampbell, JohnCastings.

I. Title669.028ISBN 0 7506 1696 2

Library of Congress Cataloging in Publication DataCampbell, JohnCastings/John Campbell,p. cm.Includes bibliographical references an d index.ISBN 0 7506 1696 21. Founding. 2. Metal castings. I. Title.TS230.C284 1991671.2-dc20 91-18848CIP

Composition by Genesis Typesetting, Laser Quay, Rochester, KentPrinted in Great Britain by Martins the Printers Ltd, Berwick on Tweed

FOR EVERY TITLE THAT WE PUBLISH, BUTTERWORTH-HEINEMANNWILL PAY FOR BTCV TO PLANT AND CARE FOR A TREE.

7/28/2019 16962_fm

3/6

Acknowledgements

Dr Peter Beeley of Leeds University has made asignificant contribution to this work in the form ofkind and valuable advice during its whole course.Professor John Knott and Dr Paul Bowen ofBirmingham University have given me valuableassistance on parts of the section on properties.On a longer time scale, I am grateful to my forme rsupervisor and good friend, Dr Voya Kondic, ofBirmingham and Warwick Universities, whoseenthusiasm for castings has been an inspiration. Eric

Brandes was my first encounter with an impressivemixture of unassuming technical competence, pas-sionate conviction, an d forthright exposition ofmaterials processing. Alf Vickers, as ManagingDirector of the Cos worth Group, had the foresightand steadfastness to support th e development of theCos worth process through good and bad years. Thiswas a turning point for me, and possibly for thecasting industry. Time will tell.

7/28/2019 16962_fm

4/6

Dedication

This book is dedicated to James A. Doel, Chairmanof Triplex-Lloyd pic, who volunteered the sponsor-ship which supported me during the writing of thework. I trust it will be a fitting tribute to suchgenerous philanth ropy wh ich in time will prove to becommercial vision.The development of Triplex-Lloyd pic has beenbound up with the advance of casting technology.Triplex Foundry was established in the 1930s tomanufacture domestic fire grates in grey iron. Todayit is part of the Automotive and Engineering

Division which is at the forefront of commercialcastings. T he Deritend International Division pro-duces sophisticated aluminium and magnesiuminvestment castings for the aerospace market .It has been my privilege to have worked withfoundries from both Divisions. This happy andinvaluable experience has been a trial by fire for theconcepts contained here, and has contributed in nosmall way to the completeness and practicality ofthis volume.

7/28/2019 16962_fm

5/6

7/28/2019 16962_fm

6/6

Introduction

Castings can b e difficult to get right. Creating thingsnever is easy. But sense the excitement of this newarrival:The first moments of creation of the new castingare an explosion of interacting events; the release ofquantities of thermal and chemical energy trigger asequence of cataclysms.The liquid metal attacks and is attacked by itsenvironment, exchanging alloys, impurities, andgas. The surging an d tumbling flow of the meltthrough the running system can introduce clouds ofbubbles an d Sargasso seas of oxide film. The mouldshocks with the vicious blast of heat, buckling anddistending, fizzing with the volcanic release of

vapours which flood through the liquid metal bydiffusion, or reach pressures to burst the liquidsurface as bubbles.During freezing, liquid surges through th e den-drite forest to feed the volume contraction onsolidification, washing of f branches, cutting flowpaths, and polluting regions with excess solute,forming segregates. In those regions cu t of f from theflow, continuing contraction causes the pressure inthe residual liquid to fall, possibly becomingnegative (as a tensile stress in the liqu id) and suckingin the solid surface of the casting. This will continueuntil the casting is solid, or unless the increasingstress is suddenly dispelled by an explosive expan-sion of a gas or vapour (shrinkage) cavity. Thesurface sinks are halted, but the internal defects nowstart.The subsequent cooling to room temperature isno less dramatic. The solidified casting strives tocontract whilst being resisted by the mould. Themould suffers, and may crush and crack. The castingalso suffers, being stretched as on a rack. Silent,creeping strain an d stress change an d distort thecasting, and may intensify to the point of catas-trophic failure, tearing it apart, or causing insidiousthin cracks. Most treacherous of all, the strain maynot quite crack the casting, leaving it apparentlyperfect, but loaded to the brink of failure by internalresidual stress.

This book is an attempt to examine these events,treating them as rapidly changing dynamic inter-actions. It is this rapidity, this dynamism, whichcharacterizes the first seconds and minutes of thecasting's life. An understanding of them is crucial tosuccess.This is the story of the casting from melt tofinished product. It is an attempt to provide aframework of knowledge to guide understanding; toavoid the all too frequ ent disasters; to cultivate thetargeting of success; to encourage a professionalapproach to the design and manufacture of castings.T he reader w ho learns to guide th e productionmethods through this minefield will find th e rarereward of a truly creative profession. The studentwho has designed th e casting method, and who ispresent when the mould is opened for the first timewill experience the excitement and anxiety, and findhimself asking the q uestion asked by all found rym enon such occasions: 'Is it all there?' The castingdesign rules in this text are intended to provide, sofar as present knowledge will allow, enoughpredictive capability to know that the casting will benot only all there, but all right!The clean lines of the finished engineeringcasting, sound, accurate, and strong, are a pleasureto behold. The knowledge that th e casting containsneither defects nor residual stress is an additionalpowerful reassurance. It represents a miraculoustransformation from the original two dimensionaldrawing to a three dimensional shape, from a mobileliquid to a permanently shaped, strong solid. It is anachievement worthy of pride.T he reader will need some backgroundknowledge. The book is intended for final yearstudents in metallurgy or engineering, for thoseresearching in castings, and for casting engineersand all associated with foundries who have to makea living creating castings.Good luck! JCWorcesterSeptember 1990