Brazing and Soldering E-Book

Richard Lofting

• Herausgeber: Crowood
• Kategorie: Lebensstil
• Sprache: Englisch
• Veröffentlichungsjahr: 2014

Beschreibung

Brazing and soldering are essential metal joining techniques for a range of jobs in the workshop. This new practical guide will introduce you to the methods and show you how to enhance these skills safely and effectively, with step-by-step photography throughout. Included in this new book is advice on equipment and building a brazing hearth; an overview of alloys and fluxes; lead loading, body and electrical soldering and pickling and cleaning. The main brazing and soldering types are also covered including soft soldering, silver soldering and brazing. There is also a range of case studies to show practical technique applications. Fully illustrated with 298 colour photographs and 2 tables.

Leseprobe

  C R O W O O D   M E T A L W O R K I N G   G U I D E S  

BRAZING ANDSOLDERING

RICHARD LOFTING

First published in 2014 by

The Crowood Press Ltd

Ramsbury, Marlborough

Wiltshire SN8 2HR

www.crowood.com

This e-book first published in 2014

© The Crowood Press Ltd 2014

All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publishers.

British Library Cataloguing-in-Publication Data

A catalogue record for this book is available from the British Library.

ISBN 978 1 84797 837 0

Disclaimer

Safety is of the utmost importance in every aspect of the workshop. The practical procedures and the tools and equipment used in engineering workshops are potentially dangerous. Tools should be used in strict accordance with the manufacturer’s recommended procedures and current health and safety regulations. The author and publisher cannot accept responsibility for any accident or injury caused by following the advice given in this book.

Acknowledgements

I would like to thank my family for their help in writing this book, in particular my son William Lofting and my niece Bethany Old, who posed for some of the photographs, my wife’s aunt, Audrey Peters, for reading through the text, and of course Pam, my wife, for the endless cups of tea. Thank you.

All photographs by Richard Lofting.

Contents

Introduction

1  Alloys and Fluxes

2  Soldering Irons and Blowlamps

3  Designing and Building a Brazing Hearth

4  Brazing

5  Silver Soldering

6  Preparation, Cleaning and Pickling

7  Soft Soldering

8  Lead Loading, or Body Solder

9  Electrical Soldering

Useful Addresses

Index

All forms of soldering or brazing require the use of heat; as long as the correct precautions are taken, these tasks can be done safely.

Introduction

Brazing and soldering are essentially the same joining technique, the difference between the two being the temperature at which each method is performed. In essence, a joint is made in metal using an alloy of two or more metals to, in effect, hot-glue the parts together. The word ‘glue’ here does not refer to just sticking something together with a sticky substance, as the items to be joined will be bonded at a molecular level to the alloy, which imparts considerable strength to the joint. The weakness will be in the strength of the brazing or soldering alloy, although the strength of some alloys that are used for filler rods are very near to the strength of the materials being joined.

In general terms, the hotter the melting temperature of the alloy, the stronger the joint. The weakest joints are made with soft solder, where the soldering alloys melt at temperatures below 450°C; in fact, some alloys will melt at extremely low temperatures and even in hot water, but these are beyond the remit of this book as they are not used for soldering. Historically, most soft solders were predominantly made from lead. However, the lead content has lately been substituted for other alloying metals, such as tin due to health concerns regarding the use of lead and its poisonous effect on the human body and of course the environment.

The middle ground is held by hard soldering, or silver soldering, where traditionally the soldering alloy contains a significant proportion of silver; details of the actual alloy contents will be given in a later chapter. Hard/silver soldering covers a temperature range of approximately 450°C through to around 850°C. As can be seen, this is already significantly higher than soft soldering, with joints effectively being made with a blow-lamp as these temperatures are beyond a soldering iron’s capability.

At the top of the temperature range is brazing, with a heat range of approximately 800°C through to 1,000°C and sometimes higher. In this process, the alloying components in the filler rod are mainly copper, tin and zinc; copper and tin form the alloy bronze, while copper and zinc form the alloy of brass, both very common alloys in everyday use. While these temperatures may seem hot, they are still a fair way below welding temperatures, which are required to melt and then fuse the component parts together; typically for mild steel this is around 1,300°C.

In reality, there is no division between silver soldering and brazing – you cannot say that on one side of a temperature line it is silver soldering and the other side of the line it is brazing. All the preparation is the same, from thorough cleaning through to heating; the only difference is in the alloys being used to complete the joint. The technique of silver soldering and brazing covers an enormous field in modern engineering, as it enables the joining of dissimilar metals. For example, it is possible to braze hard tungsten carbide tips into a steel circular saw disc or lathe tool, thus giving the best of both worlds – the tips are hard and so retain their cutting edge for longer, but the centre disc or tool holder is made from steel, giving the flexibility to stand the forces produced while cutting. With the relatively new important materials like ceramics entering the field of engineering, new ways to join these have had to be devised. Originally, they were given a metallic coating to which brazing alloys would adhere, but by accident it was discovered that with an active element in the alloy, usually titanium, used in the right atmosphere, ceramic substances could be brazed directly.

With the increasing temperature range that has just been shown, so the relative strength of the joint correspondingly increases with it. This is due, mainly, to the alloying metals used in the brazing rods or sticks of solder, as stronger materials generally have a higher melting temperature than the weaker, or softer, ones. This is the derivation of the terms ‘hard’ and ‘soft’ solder. The soft solders contain lead and tin, while the hard solders contain harder metals in the alloys such as silver. Once past the hard soldering metals and into brazing, the metals used in the alloys contain brass, which in itself contains copper and zinc. At the top of the temperature and strength range alloys using nickel are used. An in-depth overview of soldering and brazing alloys will be looked at in Chapter 1, along with the fluxes that are available and their attributes.

A soft-soldered lap joint. Soft soldering is performed at the lowest of the temperature range, but will give a moderately strong and air-tight joint.

Brazing is the strongest joining technique, without melting the parent metal; this allows dissimilar metals to be joined.

Particularly with hard soldering and brazing, where a brazing torch/blowlamp is to be used, this must be carried out in a safe environment, away from inflammables. The hotter the temperature used for the process, the more oxides are produced from not only the parent metal but also the alloy bearing rods. Chapter 3 is dedicated to building a brazing hearth. Although this sounds rather grandiose, it is nothing more than a frame made from angle iron or sheet steel with the working area lined with commercially available firebricks.

When heating metals, or anything else for that matter, the increase in temperature has the effect of increasing the production of surface oxidation, so in all forms of soldering and brazing a flux is required. In general terms, a flux keeps the metal from oxidizing during heating and removes any that has already formed, from both the item being joined and the soldering/brazing rod. The exception is specialist brazing rods that are available for joining copper to copper, which are in effect self-fluxing due to their phosphorous content.

The technique of lead loading automotive body panels with lead solder has now been, mainly, superseded by the use of plastic fillers, although there is a niche in the vintage and classic car world where originality is important. Plastic fillers are very good, being easy to mix and apply and then contour to the desired shape, but they are not as permanent as lead loading. A higher skill level is required with lead loading, as the vagaries of the alloy are exploited during the application process, spreading the lead alloy like butter with wooden paddles, unlike polyester fillers, which are mixed with a hardener; the only skill here is to get the mix on to the panel before it sets. Once again, the poisoning effect of the lead content rears its ugly head. The finish cannot be done with power tools, as this will fill the air with lead particles, but is done by hand with body files and abrasives.

At the end of the book, Chapter 9 is dedicated to electrical soldering. Although it is basically just soft soldering, there are several criteria that need to be considered to produce a satisfactory electrical joint.

Alloy rods and fluxes required for soldering and brazing operations.

1  Alloys and Fluxes

The three categories of soldering and brazing are:

◆  soft soldering, which is mainly carried out with a soldering iron and low temperature alloys

◆  silver soldering, also known as hard soldering, which is performed in a brazing hearth using alloys containing silver

◆  brazing, which is also performed in a brazing hearth, but using higher temperatures and higher temperature melting alloys, producing the strongest joints.

SOLDER AND BRAZING RODS

To help understand the process of soldering it will be advantageous to look at the composition of the alloys used in the rods for each process. First, the basic question needs to be answered: what is solder? Traditionally, soft solder was mainly based on alloys predominantly made of lead, but with the increasing awareness of the poisonous effects of lead on persons and the environment, lead solders are no longer used in plumbing. In addition, lead-based electrical solders are now virtually banned worldwide due to the possibility of the lead content leaching into water supplies from landfill rubbish sites, as a result of the ever increasing amount of discarded electronic equipment. European Union directives are now in place to prohibit the use of lead in various industrial processes and the construction industry, with it being replaced by other non- or less poisonous metals such as tin, copper and silver as the main alloy. Apart from the attributes that lead gave to solder alloys, such as good wettability, it was a cheap and readily available commodity, whereas the alternatives are relatively more expensive to source and extract from the ore containing the metal.