Modern methods of welding as applied to workshop practice

In presenting this book to the welding industry, I may say that I have devoted my whole time to the welding processes and the materials used, and they are all concisely described in their various chapters. If the readers will give attention to the following pages, they will find many points that will help them in their studies and guide them to a knowledge of the processes. In the course of eighteen years' experience of the welding industry I have found that such a book as the present is badly needed. I now make an endeavour to supply the deficiency. It is my desire to do all in my power to raise the status of welders in this country; and this will be best achieved if they can be induced to pursue a course which will make them proficient.

Some time ago an effort was made to establish a system of certificates of proficiency for operators, but unity between the associations interested is not yet sufficient to allow this.

In the comparatively limited space available for my purpose, I have attempted to give a clear and consecutive description of the principles upon which an industry of unsurpassed importance is based. With the object of accomplishing my task, however, in a manner at once agreeable and instructive, I have now and again departed from the general plan to dwell on some particular point.

While sensible of the defects in my book, I venture to hope that to those practically engaged or interested in the conduct of numerous processes covered by its title it may prove to be of service.

It is well known to everyone who takes an interest in welding and welding processes that the existing opinion as to the value of the processes and the practical results obtained is in a state of uncertainty. The chief ground for this uncertainty lies in the fact that these new processes have only been introduced recently into industrial practice, and rest entirely on an empirical basis. Although oxy-acetylene welding is now extensively used, and is of great theoretical and practical interest, it has never been made the object of systematic and exhaustive research.

The author has had eighteen years' experience of welding, and has made exhaustive tests and long studies, not only of what is being done in this country, but also of the progress made in the United States and Germany. The latter country is far more advanced than Great Britain. The Germans have carried out systematic and exhaustive researches. Their operators are scientifically trained, are taught metallurgy and chemistry, including the chemical compositions and melting-points of all metals and oxides, make test-pieces for experimenting with the chemical and mechanical tests, and employ microscopic and macroscopic examinations, both of the melted zone and the neighbouring parts. Their welding, as a rule, is very neat, as they are not allowed to execute commercial work until they have become fully proficient.

The introduction of oxy-acetylene welding has opened up an enormous field, in which any metal can be dealt with, and such an article as a cracked motor frame or cylinder can be rapidly welded. In these directions there seems to be ample scope for the application of engineering skill, and recent developments have shown that it is difficult to put a limit to the purpose to which engineers may yet apply the process.

To-day the business has grown beyond the limits of personal supervision. The necessity for organized instruction of operators is becoming more and more obvious in the interest of both workmen and employer. Several welding schools have now been started in various centres about the country, whence a stream of qualified welders is already beginning to flow to the workshops, where most of them are able to turn their training to practical use.

They teach the operator under practical conditions the right flame for different work, the principles on which the blowpipe is constructed, the way to handle it, and a variety of technical and theoretical points, which are always useful to him in his subsequent career. He is also taught thoroughly the construction, working, and maintenance of the plant. It is the operator of to-day, well instructed in the points, whom we hope to find the professional welder of to-morrow. The time is not far off when employers will refuse to engage a welder unless he can produce the certificate of proficiency. This cannot be obtained unless the operator possesses thorough knowledge and practical experience of the process.

The author has undertaken many investigations in this process. The oxy-acetylene method, when properly worked, possesses numerous marked advantages. In the first place, the operating flame can easily be controlled, and the temperature attained at various zones can be readily regulated. Secondly, the work can be easily accomplished, owing to the high temperatures reached
(3600°C), and the appliances are convenient to handle and reliable in operation.

The most important conditions for securing good results are:

1. The use of the purest acetylene possible.

2. The use of a blowpipe so designed as to ensure accurate adjustment in the proportion of the mixed gases and to secure their exit at a velocity capable of keeping the metal sufficiently fluid without the melting flame being too rigid.

3. The use of an absolutely pure welding-rod.

4. The provision of an absolute neutral zone in the melting flame, neither oxidizing nor reducing.

5. The edges must be free from all impurities, and, if over inch thick, must be bevelled.

6. The use of deoxidising agents eliminating the oxides, in view of unavoidable oxidation of the metal subject to the melting process. It is necessary to bear in mind the relation between the melting-points of the oxides and of the metal itself, which is a most important matter.

7. Rapidity in melting, in order to avoid excessive heating, which not only alters and deteriorates the original structure of the metal, but would even favour the occlusion of the gases (particularly hydrogen) and so occasion the formation of blowholes in the melted zone.

In addition to these considerations, care should be taken that no sudden cooling occurs. The conditions may have to be modified on account of the conductivity and special dilation of the material, as well as in relation to the thickness, size, and shape of pieces operated upon.

For those who are familiar with this process of welding and cutting it is not difficult to appreciate its varied applications. The ease and rapidity with which experienced welders can carry out repairs in situ, and the portability of the plants, make the process valuable, if not indispensable. The service rendered by it in many workshops, where the welding of articles of all kinds is a daily necessity, is calculable. The oxy-acetylene process occupies a leading place in all aeroplane and airship industries. It is used with advantage in welding sheet steel stampings, cylinders, aluminium crank cases and machinery parts, steel tubes, stamped steel water-jackets for cylinders, broken cast iron. Moreover, for cutting iron and steel this process has no rival whatever. It will cut wrought iron or steel plate 20 inches thick. The flame has been applied to the case- hardening of steel, and some firms are using this on a large scale. It is well known that the flame containing an excess of acetylene is a very energetic carboniser.

When the process of acetylene welding was first introduced, its apparent simplicity led many engineers wrongly to assume that welding appliances might be regarded as general workshop tools which any inexperienced but handy man could operate with success. Consequently much work was condemned wholesale because of the defects in the weld. The author would emphasise that this is not the fault of the process, but of inefficient workmen.

It is estimated that there were, during the recent war, 33,000 employed in this country in welding processes, of whom 25,000 entered the field during the war. Of the total number, 90 per cent, are not fully skilled - that is, they are incapable of executing satisfactory welds on all metals, being mostly employed on sheet steel. The impetus that has been given under war conditions should stimulate employers to investigate and exploit this revolutionary process, the possibihties of which have no obvious limits.

In the shipbuilding trade this process can be utilised very much more than at present - for instance, in making knee brackets, stays, and frames. These can all be cut and welded by blowpipes, with present costs reduced 50 per cent, and output increased. A blowpipe only requires one man; but an anglesmith, when welding a knee bracket, requires two or three assistants. Most shipyards have plants, but they are not utilised to advantage.

In all welding it is most important that the work should be adequately prepared before commencing to weld, as all time spent in this way is amply repaid afterwards in the easier execution, and also by the homogeneous nature of the weld. It is, however, a subject on which it is impossible to lay down any hard-and-fast rules, the varying nature of the work accomplished making it impossible to do so. The general principles obtained in the best practice point out that the line of weld must be opened out - that is, the two edges must be bevelled to an angle of 45 degrees, to make certain that the weld is well penetrated, not merely sealed over, and to strengthen the weld by increasing the surface of contact.

One of the most important things to do in the preparation is to arrange the pieces to be welded in such a position that there shall be no deformation, breaks, or cracks, or internal strains, and that they may be Unable at the conclusion of the operation. This is a point in which the skill and experience of the operator are revealed, as there are no rules to guide him, and upon any work but that of the simplest character failure to grasp and apply the laws of expansion and contraction means the partial or total ruin of the work. It is impossible to control expansion and contraction by physical force, so the only way to prevent disastrous results is to foresee the probable direction and extent of the phenomena, and nullify the effects by preheating certain parts of the work, either by the blowpipe or the welder's furnace.

It is good practice to raise the temperature to nearly red heat in the furnace and weld, then allow to cool slowly and uniformly in sand or asbestos; but all cold currents of air must be avoided. All castings should be preheated bodily. This is a great advantage, for not only does it save gases, but it prevents any irregular expansion, and hence no fractures.

The cutting of iron and steel by the oxy-acetylene flame is being very extensively used. This involves the use of a blowpipe of a different design, which provides for the oxy-acetylene flame and an auxiliary jet of pure oxygen to be impinged on the line of cutting. The principle underlying this method consists of taking advantage of the fact that, when heated, iron and steel can be oxidized very quickly by a Jet of oxygen, which jet, delivered at high pressure, blows away the oxide that is made, leaving a narrow, clear cut, as dean as a saw cut.


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Modern methods of welding as applied to workshop practice