High-Temperature Brazing in Controlled Atmospheres PDF
Preview High-Temperature Brazing in Controlled Atmospheres
THE PERGAMON MATERIALS ENGINEERING PRACTICE SERIES Editorial Board Chairman: D. W. HOPKINS, University College of Swansea J. R. BARRATT, British Steel Corporation T. BELL, University of Birmingham G. E. SHEWARD, UKAEA, Springfields Laboratories A. J. SMITH * Secretary: A. POST OTHER TITLES IN THE SERIES ALLSOP& KENNEDY Pressure Diecasting, Part 2 BYE Portland Cement DAVIES Protection of Industrial Power Systems HENLEY Anodic Oxidation of Aluminium and Its Alloys HOLLAND Microcomputers for Process Control LANSDOWN Lubrication MORGAN Tinplate and Modern Canmaking Technology NEMENYI Controlled Atmospheres for Heat Treatment PARRISH & HARPER Production Gas Carburising UPTON Pressure Diecasting, Part 1 WILLIAMS Troubleshooting on Microprocessor Based Systems NOTICE TO READERS Dear Reader An Invitation to Publish in and Recommend the Placing of a Standing Order to Volumes Published in this Valuable Series. If your library is not already a standing/continuation order customer to this series, may we recommend that you place a standing/continuation order to receive immediately upon publication all new volumes. Should you find that these volumes no longer serve your needs, your order can be cancelled at any time without notice. The Editors and the Publisher will be glad to receive suggestions or outlines of suitable titles, reviews or symposia for editorial consideration: if found acceptable, rapid publication is guaranteed. ROBERT MAXWELL Publisher at Pergamon Press THE PERGAMON MATERIALS ENGINEERING PRACTICE SERIES Editorial Board Chairman: D. W. HOPKINS, University College of Swansea J. R. BARRATT, British Steel Corporation T. BELL, University of Birmingham G. E. SHEWARD, UKAEA, Springfields Laboratories A. J. SMITH * Secretary: A. POST OTHER TITLES IN THE SERIES ALLSOP& KENNEDY Pressure Diecasting, Part 2 BYE Portland Cement DAVIES Protection of Industrial Power Systems HENLEY Anodic Oxidation of Aluminium and Its Alloys HOLLAND Microcomputers for Process Control LANSDOWN Lubrication MORGAN Tinplate and Modern Canmaking Technology NEMENYI Controlled Atmospheres for Heat Treatment PARRISH & HARPER Production Gas Carburising UPTON Pressure Diecasting, Part 1 WILLIAMS Troubleshooting on Microprocessor Based Systems NOTICE TO READERS Dear Reader An Invitation to Publish in and Recommend the Placing of a Standing Order to Volumes Published in this Valuable Series. If your library is not already a standing/continuation order customer to this series, may we recommend that you place a standing/continuation order to receive immediately upon publication all new volumes. Should you find that these volumes no longer serve your needs, your order can be cancelled at any time without notice. The Editors and the Publisher will be glad to receive suggestions or outlines of suitable titles, reviews or symposia for editorial consideration: if found acceptable, rapid publication is guaranteed. ROBERT MAXWELL Publisher at Pergamon Press HIGH-TEMPERATURE BRAZING IN CONTROLLED ATMOSPHERES G. SHEWARD Formerly of UKAEA, Springfields Laboratories, Preston, UK Now consultant on joining processes PERGAMON PRESS OXFORD · NEW YORK · TORONTO SYDNEY · FRANKFURT U.K. Pergamon Press Ltd., Headington Hill Hall, Oxford OX3 0BW, England U.S.A Pergamon Press Inc., Maxwell House, Fairview Park, Elmsford, New York 10523, U.S.A. CANADA Pergamon Press Canada Ltd., 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 FEDERAL REPUBLIC Pergamon Press GmbH, Hammerweg 6, OF GERMANY D-6242 Kronberg-Taunus, Federal Republic of Germany Copyright© 1985 Pergamon Press Ltd. All Rights Reserved. No part of this publication may be repro duced, 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 1985 Library of Congress Cataloging in Publication Data Sheward, G. High temperature brazing in controlled atmospheres. (The Pergamon materials engineering practice series) Includes bibliographies and index. 1. Brazing. I. Title. II. Series. TT267.S49 1985 671.5'6 85-3626 British Library Cataloguing in Publication Data Sheward, G. High temperature brazing in controlled atmospheres. — (Pergamon materials engineering practice) 1. Brazing I. Title 671.5'6 TT267 ISBN 0-08-026170-1 (Hardcover) ISBN 0-08-026169-8 (Flexicover) Printed in Great Britain by A. Wheaton & Co. Ltd., Exeter Materials Engineering Practice FOREWORD The title of this series of books "Materials Engineering Practice" is well chosen since it brings to our attention that in an era where science, technology and engineering condition our material standards of living, the effectiveness of practical skills in translating concepts and designs from the imagination or drawing board to commercial reality, is the ultimate test by which an industrial economy succeeds. The economic wealth of this country is based principally upon the transformation and manipulation of materials through engineering practice. Every material, metals and their alloys and the vast range of ceramics and polymers has characteristics which require specialist knowledge to get the best out of them in practice, and this series is intended to offer a distillation of the best practices based on increasing understanding of the subtleties of material properties and behaviour and on improving experience internationally. Thus the series covers or will cover such diverse areas of practical interest as surface treatments, joining methods, process practices, inspection techniques and many other features concerned with materials engineering. It is to be hoped that the reader will use this book as the base on which to develop his own excellence and perhaps his own practices as a result of his experience and that these personal developments will find their way into later editions for future readers. In past years it may well have been true that if a man made a better mousetrap the world would beat a path to his door. Today, however, to make a better mousetrap requires more direct communication between those who know how to make the better mousetrap and those who wish to know. Hopefully this series will make its contribution towards improving these exchanges. MONTY FINNISTON v Preface Although silver brazing and soldering, using low temperature filler metals, have been used for joining materials to produce decorative articles and engineering constructions since before the birth of Christ, it is only in recent years that it has been possible to join together modern high strength materials by this method to produce high quality joints for high temperature applications. It was in the early 1950s that work in the United States and the United Kingdom demonstrated the possibility of applying this method to produce constructions for use in the aerospace, nuclear and other similar industries, where quality requirements are demand ing and the cost of failure is high. The brazing industry has grown at a fast rate, and the annual turnover is now many millions of pounds, producing products with a range of size from a pin head to massive constructions such as a high integrity steam generator. The aim of this book is to provide technicians, designers and engineering students with some basic knowledge and to suggest how the potential of the process can be realised. There is, at the present time, considerable development and assessment of the metallurgy of the process, and this book has not discussed in great depth such aspects as filler metal parent material interactions, and mechanical and corrosion properties of brazed joints. I would thank my colleagues in the UKAEA, the British Associa tion for Brazing and Soldering, and many other friends in the industry, for their assistance and their contributions to this book. G. E. SHEWARD vii Glossary Flow point. The temperature above which the filler metal becomes liquid and flows readily. Faying surfaces. The surfaces that are to be joined in an assembly. Getter. A metal used in a controlled atmosphere system to react preferentially with oxygen and nitrogen. Heat-affected zone. Those parts of a component that are heated during the brazing cycle. Inert gas. Gases that form no compounds with metals, used in systems to reduce vaporisation. Jigs. Used to align the parts during brazing. Joint clearance. The gap between the faying surfaces to accommo date the brazing metal. Liquation. Separation of the solid and liquid components of a melt ing filler metal. Liquidus. The lowest temperature at which an alloy is completely liquid. Melting point. The temperature at which a metal becomes liquid on heating or solid on cooling. Metallographic examination. The sectioning and examination at various magnifications of selected samples to give data about quality. Pre-placed filler metal. Filler metal manufactured to produce a shape that can be fitted into the sub-component assembly. Self-jigging. Self-supporting components that can be brazed without the use of jigs. Solidus. The highest temperature at which an alloy is completely solid. Step brazing. The making of joints sequentially by using filler metals of decreasing flow temperatures. Stop-off. Material used to restrict the flow and wetting of the parent metal of filler metal. Surface finish. Degree of roughness of the surface of a component. Thermal expansion. The change in dimensions of a component when heated. Vacuum. The removal of gases from an enclosed space to enable brazing to proceed without the aid of a flux produces a vacuum. XII Chapter 1 General Bonding Techniques 1.1 INTRODUCTION Early man was able to live without recourse to any of the joining processes. His utensils were hewn from the solid and eventually, when his ambitions exceeded his ability to fabricate from the solid, he increased his constructural boundaries by binding and forging compo nent parts together to produce larger assemblies. Brazing was one of the earliest of the metal-joining processes, and examination of some Indian temple work suggests that it was used about 4000 B.C. The modern joining engineer can use many processes to build up assemblies. The great majority of these are fusion processes. By this we mean that the "parent" materials are melted locally and then joined together by alloying at the joint interface. These processes may either utilise simple melting or, alternatively, a suitable "filler" metal may be added to the joint to assist the process, either by melting the filler as part of the component or by adding metal to the molten zone, usually as wire of a suitable composition. The mechanical and corrosion properties of the joint can be improved by selection of a suitable filler material. The most modern methods of joining use glues and resins. These can be applied to the joint area at slightly above ambient temperature, and produce joints of such a quality that they can be used in critical parts of aircraft and in the automotive industry. However, there is a major disadvantage in the limited service temperature to which the assembly can be used. This may be only slightly above ambient temperature, and at the best about 300°C. Another family of processes used for joining metals, ceramics and dissimilar materials includes soldering and brazing. In this technology a suitable filler metal with adequate properties for the particular application is applied to the joint. So that flow and wetting will occur, the joint interface must be cleaned and kept clean, either by means of 1 2 General Bonding Techniques TABLE 1.1 THE BRAZING PROCESSES (classified by source of heating) Heating method Principal applications Torch brazing Silver-based filler metals, copper-phosphorus. Automated production machines. Furnace brazing High-production brazing. Copper, nickel-based, gold- based, palladium-bearing filler metals. Vacuum brazing of high quality components. All processes applied in custom-designed continuous or batch type furnaces. Induction brazing Component parts heated by alternating current carried by a suitably designed coil. Rapid brazing cycle. All filler metals used. Resistance brazing Components form part of the circuit. Parts held between electrodes. Used for joining large copper leads to transformers. Dip brazing Chemical or molten metal baths. Heat exchangers (aluminium). High-energy sources Infrared-honeycomb structures, pipe joints. Electron beam/laser. Joining of ceramics and ceramics to metals. a flux or by covering with a suitable atmosphere, so that oxidation does not occur; it is then heated so that the filler metal melts, wets and joins the unmelted parent materials. The process is divided into two major sections—soldering and brazing, which is again subdivided into smaller classifications (Table 1.1). Soldering is defined as a process used at temperatures below 450°C. The higher temperature process is called brazing, because originally the filler metals used were basically brasses. The American Welding Society defines the brazing process as follows: (1) The parts are joined without melting the base metals. (2) The filler metal must have a liquidus temperature above 450°C. (3) The filler metal must "wet" the base metal surfaces and be drawn into or held in the joint by capillary attraction. We are already using several unfamiliar words, and so that we can proceed with understanding, and not too great a recourse to the dictionary, the new basic words used so far and others that may be useful are further defined in the Glossary at the front of the book. The Processes of Soldering and Brazing 3 1.2 THE PROCESSES OF SOLDERING AND BRAZING 1.2.1 The low-temperature processes There are many textbooks (Allen, 1969; Fry's Metal Foundries Ltd) that describe the various soldering processes. Soldering is widely used in the electronics industries where millions of joints are made as parts of electrical circuits. These may be made either manually or automatically, by such methods as wave soldering, reflow or infrared heating. Invariably, fluxes are used to aid flow and to ensure that the joint is made to an acceptable quality. Because of the basic properties of the solder itself, these joints are not very strong mechanically and so the designer must use his ingenuity to minimise the stress on them. For high-risk applications, such as in navigation equipment and where the cost of failure is high, considerable care in control of the process is essential. However, many soldered joints are still made by using the traditional soldering iron or the gas torch. The filler metals are based upon tin, and the most common ones are 40/60 tin/lead, used for making and repairing metalware where the basic materials are brass, copper, steel or tinplate. 63/37 tin/lead is more expensive because of the higher tin content. Its advantages are that it melts at a lower temperature and is stronger mechanically than the 40/60 alloy. It is used extensively in dip soldering of electronic components. 63/37 tin/lead is sometimes modified by adding a small amount of copper to the alloy. This helps the solderability of electronic compo nents, particularly when the soldering operation involves the use of a copper soldering bit, and also diminishes the corrosion of the soldering iron. 1.2.2 "Low-temperature" brazing This can be considered as an "open-air" operation. It is used to join copper and copper alloys, low carbon and stainless steels. Aluminium alloys can also be joined together using special filler metals. For joining copper, steels, stainless steels, etc., the silver-based filler metals are widely used. These have a melting range from 610° to 880°C depending upon composition. Care must be taken in their application as many of them contain cadmium and must not be used in an "open-air" situation without adequate fume extraction; advice must be sought from the manufacturer before use. Other filler metals
The list of books you might like
