Welding E-Book

Richard Lofting

• Herausgeber: Crowood
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 235

Veröffentlichungsjahr: 2013

Beschreibung

Welding is an essential technique for a wide range of jobs in the workshop. Whether you are new to welding or ready to try the more advanced techniques, this practical guide gives a thorough introduction to the method, and suggests ways of improving your skills to achieve professional and safe results.Explains the different types of welding and when they are best used.Advises on choosing equipment and its maintenance.Demonstrates the processes with clear, step-by-step photographs.Emphasizes safety and best practice.Aimed at everyone who needs to weld and has a workshop - modellers, theatre designers, automotive repair and restorers and farmers.A practical guide to the different types of welding and advise on equipment and its maintenance.Superbly illustrated with 280 step-by-step colour photographs.The first in a new series Crowood's Metalworking Guides.

Leseprobe

Copyright

First published in 2013 by The Crowood Press Ltd, Ramsbury, Marlborough, Wiltshire, SN8 2HR

www.crowood.com

This e-book edition first published in 2013

© The Crowood Press 2013

All rights reserved. This e-book is copyright material and must not be copied, reproduced, transferred, distributed, leased, licensed or publicly performed or used in any way except as specifically permitted in writing by the publishers, as allowed under the terms and conditions under which it was purchased or as strictly permitted by applicable copyright law. Any unauthorised distribution or use of this text may be a direct infringement of the author’s and publisher’s rights, and those responsible may be liable in law accordingly.

ISBN 978 1 84797 513 3

Acknowledgements I would like to thank several people who have helped me tremendously with this e-book; without their help it would have been a lot harder than it was. My niece, Bethany Old, provided the glamour in some of the photographs, which without her input would have been rather mundane. I think all would agree she is easier on the eye than a follically challenged, fifty-something guy with a beard. My son, William Lofting, was a substantial help with the welding photographs, as he is excellent with a MIG welder. I like to think that I taught him all he knows about welding, but he makes a better, and more confident, job of it than I can! He hadn’t tried TIG welding until helping on the e-book, but now wants an AC-DC TIG welder for his own use. Thanks also go to Pat Neilson and Michael Davies for the use of their equipment, my wife’s aunt, Audrey Peters, who proof read the text for me, and of course my wife Pam, who has helped tremendously with keeping morale high when concentration lapsed. Thank you.

Contents

Title Page

Copyright

Introduction

1 A BRIEF HISTORY

2 OVERVIEW OF PROCESSES AND ANCILLARY EQUIPMENT

3 SAFETY

4 ARC WELDING

5 MIG/MAG WELDING

6 TIG WELDING

7 GAS WELDING

8 SPOT OR RESISTANCE WELDING

9 CHOOSING THE RIGHT EQUIPMENT

Useful Addresses

Index

Introduction

At one time, not so long ago, if you were looking for welding equipment for the workshop there was little choice: you either plumped for an AC electric arc welder – some more exotic ones giving DC current were available at a price – or it meant an oxyacetylene gas welding plant.

Today things are a little different. Indeed, we are possibly spoilt for choice, for as well as the examples mentioned above we now have MIG welders, TIG welders and Inverter welders, all for reasonable prices with something available to suit most people’s budgets.

If I were to say ‘Go out and buy a cheap MIG welder and practise on a few scraps of steel’, you would possibly be able to stick two pieces of metal together after a fashion, but how would you know if there had been any penetration? To be able to weld properly it will help to have some background knowledge on what is actually happening and, of course, safety concerns come to the fore as in all forms of welding today. Burns are a real risk with all types of welding and all forms of electric welding carry the risk of eye and skin damage due to ultraviolet radiation (seeChapter Three).

The first chapter outlines some of the milestones in welding development through the years that have made it possible to produce a good weld with very little effort. Chapter Two is intended to give an idea of what is actually going on in the weld pool itself and the theory behind it, so we can understand what is happening.

All the various welding disciplines will be covered in separate chapters, starting with setting up the equipment to get you going, with step-by-step photographs of the whole process and examples showing the effects of current settings that are too high or too low and other problems. This will enable you to dive straight into whichever chapter is relevant to your welding needs, with all the information that you require to get you going and able to tackle workshop projects as they arise with proficiency and confidence. Specific safety concerns that are critical to each method will be mentioned in the various chapters, but they are covered in depth in Chapter Three.

As with all things practical, while written theory is all well and good, getting someone skilled and proficient to demonstrate how to go about a task and guide you through your first attempts will save you time and frustration as you get to grips with the practicalities of whichever welding discipline you are learning. A friend or colleague may be able to help, but if they have picked up bad habits then these will inevitably be passed on to you and in your ignorance will be perpetuated. The best help and guidance can be found on courses run at local colleges, some of which also provide evening courses to guide you in the correct ways. Health and safety, of course, will be instilled right from the start. When using gas welding equipment, in particular, things can get out of hand extremely quickly, and knowing what to do instinctively in these situations can keep a minor incident from developing into a major one. As stated elsewhere in the book, acetylene can be unstable and in fact is classed as an explosive, but when treated with proper care and attention it is safe to use.

The last chapter will advise on how to choose equipment for your intended purposes and where to purchase it. There is also some discussion of the quantities of shielding gas required and the costs involved.

Throughout the book will be found useful tables on such subjects as welding rod selection and recommended gas pressures. There are also addresses where equipment, consumables and useful advice can be sought.

1

A Brief History

The first evidence for welding dates from not long after the discovery that metals could be extracted from ore by heat. Examples of iron items being hammer welded in a hearth are known from before 1000BC. Under this process the two parts to be joined are heated to just below melting temperature and then quickly hammered together. The extra heat and pressure generated by the hammering enables the surfaces of the two components to fuse and become one.

Forge welding has been the mainstay of welding for centuries.

During the forge welding process, heat and pressure are used to join the parts as one.

One fine example of the ancient craft of forge welding is now at the Quwwat al-Islam Mosque in Delhi, to where it was moved at some point in its long history. Known as the Delhi Pillar, it is reputed to have been forge welded, by hand, from several billets of almost pure iron. It stands 23ft 8in (7m) above the ground with a further 3ft (1m) or so buried below, and weighs in the region of 6½ tonnes. It is 16in (400mm) in diameter at its base, tapering upwards to 11½in (300mm) with a fancy finial at the top, although it is believed that an ornate figure in the form of Garuda (Sunbird), the Vahana of the Hindu god Vishnu, originally stood on top of the column. According to the Sanskrit inscription at the base, the pillar was constructed during the fourth century AD in honour of the Gupta ruler Chandragupta Vikramaditya. In all the time that the pillar has stood at the mosque, there is little evidence of any rust appearing on the column. While this is a very arid region, it is now believed that this is the result of its phosphorus content, incorporated into the iron from charcoal used in the smelting process. This has caused an extremely thin oxide coating to form, preventing further rusting.

ELECTRIC WELDING

Forge welding and riveting remained the mainstay methods used by blacksmiths to join metal objects until the 1800s. Around this time it was found that carbon electrodes connected to an accumulator (battery) produced an arc. The DC current stored in the accumulators could then be utilized to make a brittle and porous weld. Since the introduction of mains electricity and AC current was still about a century away, recharging would have been carried out with a dynamo, possibly driven by a steam engine or waterwheel.

Coated electrodes were designed in the early twentieth century but did not become popular until 1927, when mass production techniques were used to drop the price.

In 1881 the French engineer Auguste de Méritens was awarded a patent for a method by which the plates of lead accumulators might be welded together with the carbon arc. In 1885 two of his Russian pupils, Nikolai Benardos and Stanislav Olszewski, obtained the first British patent in welding practices. Patent No. 12984 described the method of using the carbon arc with an electric power source to weld metals together. The apparatus used to achieve this was named the ‘Electrogefest’. Patents followed in Russia and the USA in 1886 and 1887, respectively.

Development was rapid. Another Russian, Nikolai Slavianov, developed arc welding with an iron electrode in 1888. Similar experiments in the United States led to Charles L. Coffin of Detroit obtaining patents in 1889 for flash-butt welding and in 1890 for spot welding equipment that he had been developing.

The first few years of the twentieth century saw further improvements to these techniques, including the use of hollow carbon rods, filled with metal particles, to act as filler in the carbon arc process. These never gained much popularity, however, although they were later used in specialized processes in the 1940s and ’50s. The great leap was made during the 1920s. The effective introduction of thick armour plating during the First World War, for example on warships and battle tanks, led to a demand for similar armaments. The riveting of such plating, however, was somewhat slow and a faster, more efficient, production method was urgently required. Alternating current (AC) was developed in the early 1920s and power stations were built to supply industry and homes with electricity, although steam power remained the main motive force for many more years.

It was understood that a means had to be found to protect the weld pool from oxygen and nitrogen in the atmosphere is required, since it was this lack of isolation of the weld pool from the atmosphere that made welds brittle and porous. In addition, the welding arc produced by the use of alternating current was shown to be very unstable.

THE COATED ELECTRODE

At the turn of the twentieth century Swedish engineers were developing coatings to cover filler rods: A. P. Strohmenger used clay and lime, while Oscar Kjellberg used carbonates and silicates. The coated electrode was found to do the job. The heat of the arc vaporizes the coating of various clays and silicates into gases that shield the weld pool from the detrimental effects of the atmosphere until the liquid metal beneath has cooled and solidified, leaving a deposit from the remains of the rod coating and any impurities, known as slag, on top of the weld. Coated electrodes were originally produced by dipping lengths of filler wire into a liquid mixture of the coating and setting them aside to dry. The use of these rods did not become widespread until around 1927, when an extrusion process was designed to speed up production, so reducing the price and extending the range of tasks covered.

GAS WELDING

The English scientist Edmund Davy discovered acetylene, a hot burning gas, in 1836. This was followed in 1900 by the development by two Frenchmen, Edmond Fouché and Charles Picard, of an oxyacetylene torch able to create a flame of 3500°C that is ideal for welding. The acetylene obtained for this early development was produced by dripping water on to calcium carbide to release acetylene, just as early carriage lamps used the acetylene gas liberated by this method to produce a bright white light.

In 1904 Percy Avery and Carl Fisher founded the Concentrated Acetylene Company in Indianapolis to develop ways of storing acetylene as a gas. Acetylene is extremely unstable and, unlike other gases, cannot be directly compressed into an empty cylinder since it quickly becomes unstable at a pressure in excess of around 20 psi and explodes. The cylinder is instead filled with a porous medium, such as balsa wood or asbestos fibre. This is then saturated with acetone, a common solvent. The acetylene gas is very slowly introduced into the acetone and is readily absorbed, like ink on blotting paper, as the pressure is increased. When the pressure in the cylinder is released during burning of the gas, the acetone gives up the acetylene, leaving just the acetone-soaked medium behind in the cylinder, ready for its next charge of gas. Even with the porous medium and acetone in the cylinder, the acetylene gas must be introduced very slowly if it is not to become unstable.

HELIARC PROCESS

From the early days of the Second World War lighter non-ferrous materials, such as aluminium and magnesium, were increasingly used in the new fighter and bomber aircraft and techniques were soon developed to weld these newfangled materials.

Acetylene was not available in a cylinder until 1913, when Avery and Fisher developed a cylinder with a porous mass inside, soaked in acetone.

Today the engineering world is fairly familiar with the term TIG welding and it is generally supposed that it was developed after the modern MIG welder. Its origins, however, go back to work during the 1920s on using inert gases to shield the weld pool from the atmosphere. It was known as the Heliarc process, after patents taken out in 1941 using helium as the inert shielding gas and a tungsten electrode, as in the modern TIG welder (although nowadays the shielding gas is argon). Modern equipment, of course, is now more compact than the original machines and a lot more versatile.

MIG WELDER

The now ubiquitous MIG welder was developed in 1948. The fixed tungsten electrode in the handset of the Heliarc process was replaced by a continuously fed wire electrode from a roll within the machine. In its initial form it was used for non-ferrous metals, but in the early 1950s it became popular for use with ferrous metals after it was discovered that carbon dioxide – much cheaper and more easily obtainable – made a very suitable shielding gas on steel, although technically it is an active gas and is known as MAG welding (Metal Active Gas). The other main advance was the development of much thinner electrode wires, which made the process more versatile across the range from thin sheet work to heavier sections.

EXOTIC TECHNIQUES

During the 1950s technological advances in the world of welding were being made almost on a daily basis as new ways were developed to produce welds fit for harsher and more extreme environments.

Electron Beam Welding

It was revealed during this decade that electron beam welding was being used in France’s growing nuclear power industry, for which good, reliable welds are a necessity, not just desirable. Plasma arc welding, first experimented with in the 1920s, was also developed for industrial use in the 1950s. In this process a stream of gas is heated in a tungsten arc, creating plasma that is half as hot again as a tungsten arc alone can produce. There are many specialist uses and high-grade steels, in particular, benefit from these techniques. The process can also be used for cutting. The plasma cutter itself has now developed into a portable machine that can be used to cut not only steel, but also stainless steel, aluminium, brass and copper. The plasma heats a spot on the surface of the item to be cut and the molten metal is blown clear by compressed air, producing a very tidy kerf, or cut. Oxyacetylene, on the other hand, which has been the principal means of cutting steels, cannot cut metals that do not contain iron, as it is the iron’s affinity for oxygen at red heat that allows the cutting to take place. Other applications for the plasma arc, such as metal spraying, have become popular. This technique can be used to give a soft component a harder and tougher outer layer: the outer bearing surface of an engine crankshaft, for example, needs to resist wear, but if the core is too hard the crankshaft might perhaps snap in service.

Laser Welding

The use of lasers for welding has been a fairly recent development. Several individuals and teams were behind the development of the laser. Although Gordon Gould had a working example in 1958, for instance, he failed to patent his device and the first patent was obtained in 1960 by Theodore Maiman. The word ‘laser’ is an acronym derived from Light Amplification by the Stimulated Emission of Radiation. In very basic terms this describes a substance, solid or gas, being excited by external means. It is this stimulation that coerces the substance into emitting light at one particular frequency, which can then be focused by lenses into a very small beam with extremely high energy levels. This creates a very clean weld with little distortion, which is well suited to use by robots on an industrial production line. This is especially useful in car manufacturing as the laser beam can be directed through fibre optics to the point where the weld is required without requiring the whole machine to be moved as well. The quality of the weld produced is comparable with electron beam welding, but the method is cheaper and has the distinct advantage that it is carried out in air with a shielding gas, so protecting the weld pool from the atmosphere. Electron beam welding is much more sophisticated, but needs to be performed in a vacuum.

The now ubiquitous MIG welder, developed in 1948, became popular for mass car production in the 1950s.

With experience and improved equipment, what was once a narrow specialist field has now become fairly common knowledge. Welding in the home workshop has never been so easy. The equipment available has become compact, relatively easier to use and, of course, much more affordable. The available choices have never been so good or as varied.

A modern inverter welder, for example, which uses electronic means to alter the voltage/current ratio rather than a heavy transformer, is not much bigger than a lunch box. It comes with DC welding current as standard for mmA stick welding with rutile and low hydrogen rods, and is suitable for welding stainless steel with the correct rods. It is also possible to fit an optional hand torch and regulator for the shielding gas to create a TIG welding set-up, further increasing its scope and versatility for thinner materials. A typical 150 amp model is capable of mmA welding with 4mm diameter electrodes. Together this versatile kit has an overall weight of less than 5kg.

The inverter welder uses electronic control of voltage and current to give DC output. It is light and transportable.