Metal Casting: Appropriate Technology in the Small Foundry PDF
Preview Metal Casting: Appropriate Technology in the Small Foundry
This technical introduction to small-scale non-ferrous casting provides practical information and advice for metalworkers, engineers and manufacturing entrepreneurs who are interested in metal casting on a small scale. Illustrated instructions are provided on how to make equipment using local materials, and on the various casting techniques. These include green sand moulding - low- cost and relatively simple, encompassing different methods of sand casting appropriate to various types of product - and investment casting, which is an older, more versatile and precise technique but is more time-consuming. These and other methods are described and compared along with advice on design and pattern making, core mixtures, the use of wax, metal preparation and melting, fault finding and remedies, and kilns and furnaces. The emphasis is on local construction of equipment, often using recycled materials - there is a useful section on scrap materials and how to identify and use them - and on presenting a wide range of methods, traditional and modern, based on the author's extensive practical experience. This is an essential addition to the bookshelf of the small rural workshop or urban engineering business. ISBN 1 85339 197 2 Steve Hurst has his own small foundry in Oxfordshire, UK. He works as a foundry consultant to various overseas charities and as a visiting lecturer in the UK, and produces sculpture which is exhibited widely. The Intermediate Technology Development Group was founded by the late Dr E.F.Schumacher. Intermediate Technology enables poor people in the South to develop and use skills and technologies which give them more control over their lives and which contribute to the sustainable development of their communities. Intermediate Technology Publications is the publishing arm of the Intermediate Technology Development Group and is based at 103/105 Southampton Row, London WC1B 4HH, UK. Pouring gun-metal (bronze LG2) into moulds for Pelton turbine wheels, using the Roman technique of lost-wax casting METAL CASTING Appropriate technology in the small foundry STEVE HURST INTERMEDIATE TECHNOLOGY PUBLICATIONS 1996 Intermediate Technology Publications Ltd, 103-105 Southampton Row, London WC1B 4HH, UK © Intermediate Technology Publications 1996 A CIP record for this book is available from the British Library ISBN 1 85339 197 2 Typesetting by Diamond People, Bromyard Printed in UK by SRP, Exeter Contents Preface ix Acknowledgements x 1 Introduction 1 Making a choice of production method 1 Advantages and disadvantages of each process 4 Examples 8 2 Setting up the workshop 10 The small workshop or sand foundry 11 The workshop for a lost-wax foundry 12 Examples of foundry designs 13 3 Pattern making 15 Materials 15 Skills 18 Designing the pattern 18 Storing patterns 23 4 Flexible moulds for the mass-production of wax patterns . . .. 25 Making the case for a flexible mould 26 Making a rubber mould 28 Gelatine moulding 32 Mixing plaster 35 Summary 36 5 Sand casting 38 Essential moulding equipment 39 Making a simple, solid casting 40 Making a simple casting using a split pattern 47 Hollow casting 49 The nature of moulding sand 54 Other sand processes 58 6 Lost-wax casting 60 Waxes 62 Moulding the wax 65 The block investment process 67 Kiln firing (de-waxing) 76 The clay slurry investment method 78 Inca silver 83 4 7 The ceramic shell process 85 Equipment 86 The ceramic shell process in outline 87 The process in detail 87 8 Die casting 102 Examples of the technique 102 Finding and correcting faults in the castings 104 9 Melting and pouring metal 107 Summary 107 Safety precautions 110 10 Metallurgy and the low budget foundry Ill The structure of metals Ill Selection of scrap metals for casting 114 Alloying 117 Metal melting 119 Metal flow and solidification 122 11 Kilns and furnaces 126 The furnace drum 127 Kilns 135 Crucibles 141 Conclusion 146 12 Faults, fettling and finishing 147 Common faults in castings 147 Fettling and finishing 151 Appendices A Newar casting in Patan, Nepal 157 B Bamoum lost-wax casting, western Cameroon 163 C The Dedza crucible 171 D Sand conditioning and testing 175 E Other sand processes 181 F Summary of ceramic shell investment processes 185 Further reading 195 Glossary 199 VI "The founder is always like a chimney sweep, covered with charcoal and distasteful sooty smoke, his clothing dusty and half burned by the fire, his hands and face plastered with soft muddy earth. To this is added the fact that for his work a violent and continuous straining of all a man's strength is required, which brings much harm to his body and holds many definite dangers to his life. In addition, this art holds the mind of the artificer in suspense and fear regarding its outcome and keeps the spirit disturbed and almost continuously anxious. For this reason they are called fanatics and are despised as fools. But, with all this, it is a profitable and skilful art and in large part delightful.' From Biringuccios De la Pyrotechnia, Venice, 1559 vii Traditional Newar method of lost-wax casting using a clay-dung slurry investment viii Preface Dr E.F. Schumacher was one of the first economists to understand and consider the wisdom and skills which were cast aside or destroyed in the rush to develop higher and higher technology, and to have the wisdom to revitalize and record these skills. In Small is Beautiful, Dr Schumacher used the symbols of capital value to illustrate levels of technology: 'If effective help is to be brought to those who need it most, a technology is required that would range in some intermediate position between the £1 technology and the £1000 technology. Let us call it- symbolically speaking - a £100 technology'. He continued: 'Such a technology would be immensely more productive than the indigenous technology (which is often in a condition of decay), but it would also be immensely cheaper than the sophisticated highly capital-intensive technology of modem industry'. If you look at the small investment casting foundries of India, South-East Asia and West Africa you find models of the type of technology that Dr Schumacher describes. Using the minimum capital, abundant skilled or semi-skilled labour, simple machinery and materials found locally, these traditional co-operatives and small family businesses manufacture objects of great precision. The objects that they make, usually religious or tourist sculpture, have sometimes blinded engineers and business advisers to the possibility of making other objects, such as irrigation, agricultural, micro-hydro electric or medical items, which are within their wide range of skills. The technique we now call sand casting, or green sand moulding, was developed much later than investment (or lost-wax) casting. The former is now common to cities and small towns all over the developing world. It was introduced in the nineteenth or early twentieth century, invariably for the repair or replacement of railway or river-boat engines, or the replacement of weapon or vehicle parts. Investment casting, by contrast, is indigenous. Though it developed in all the early civilizations, it is now only found in its original form in a few places. Its grandchild, the ceramic shell technique, is to be found wherever there is an aerospace or weapons manufacturing industry. If I concentrate on Nepal, South-East Asia, North and West Africa, it is because I observed and researched foundries in these areas. Another observer might have cited Sri Lanka, China or Indonesia. Although in the pre-Colombian civilizations South America possessed sophisticated and highly developed metal casting industries, these were destroyed, together with agricultural and irrigation systems. Today only small fragments of these technologies remain. iX
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