Oxy Acetylene Welding and Cutting

The Oxy-acetylene flame is now used to advantage in welding practically all metals, as steel, cast iron, malleable iron, brass, bronze, copper, aluminum, sheet iron and silver. Its success has been proved beyond a doubt. Engine and machine parts of any metal, automobile castings and the like are as strong as any part of like dimensions when welded.

A brief description of all principal kinds of welding is given, including fire welding, welding by water gas, thermit welding, brazing and blowpipe welding. The advantages and disadvantages of each are discussed.

Manufacturers, contractors, machine shops, garages, blacksmiths, boiler makers, repair shops, foundries, steel mills and railroad shops are rapidly adding the oxy-acetylene process to their equipment. In cutting beams, girders, steel sheeting, heavy piston rods, steel plates, gates from steel castings, wrecking steel building frames or bridges, the work can be done much cheaper and in less time than by the old methods.

In the preparation of this book the author has endeavored to cover every practical point in the process of welding and cutting and the removal of carbon with oxygen. Enough of the theory has been included to enable the practical man to acquire a thorough understanding of the subject.

The fusion or welding of metals is accomplished by an intense heat concentrated at the location of the weld. The temperature of the oxy-acetylene flame taken at the extremity of the white jet has been calculated to be 4000° Centigrade, or 7232° Fahrenheit.

In practice a temperature of approximately 6500° Fahr. is obtained by means of the oxy-acetylene process, and this temperature is more than sufficient to melt any of the commercial metals. By the application of this temperature the metal at the point of treatment is rapidly reduced to a liquid molten state, flowing together and thoroughly mixing with a proper quantity of metal added by the operator to fill up all the crevices. The fluid mass thus formed does not result in merely cementing the two pieces of metal together; it fuses them into one piece.


VARIOUS METHODS OF WELDING

In order to appreciate the advantages of oxy-acetylene welding as compared with other methods it is well to consider, briefly, the leading methods of uniting pieces of metal by the weld, most of which are still used to some extent.

Welding at the Forge. - This method has been known from the most remote time. Its application, however, is practically limited to iron and steel. A joint is obtained by energetic hammering together of the two pieces of metal which have been previously brought to a welding heat in the furnace or forge fire. The important points connected with this method consist in the ability to recognize the welding heat and to avoid burning the metal by going beyond this point, and the difficulty of so joining the metal pieces that the weld is perfect over the entire surfaces that are to be joined. Metals can only be welded between certain exact limits of temperature, and it requires skill and experience to be able to know these temperatures.

The success of a fire weld depends on the exact external observation of temperature and the state of the surfaces to be united, because all interposition of slag or oxide hinders complete welding.

It is therefore necessary to sprinkle the surfaces to be welded with a flux capable of dissolving the oxide of iron and to form with it an extremely fluid compound which can be expelled by hammering. As for the brazing of iron, the materials used for fire welding are generally white sand and borax. Certain special materials, of satisfactory composition and easy use, are sold and give excellent results.

Fire welding has the following disadvantages:

(1) It is necessary to heat a large portion of the articles to be united and this causes deformation, hence the necessity for considerable working of the metal after welding.

(2) Large quantity of heat wasted, rendering the process costly.

(3) Difficulty of insuring uniform success and impossibility of exact control.

Forge welding is done, where possible, by joining the two sections after the edges or ends have been beveled, known as a scarf weld. This increases the surface in contact and the strength of the joint. The strength of these welds very seldom exceeds 70 per cent of the original strength of the metal.

The elongation of forge welds is always very low, that is, the portion welded will break apart before stretching to any extent under strain. From the point of view of brittleness, forge welds show a very low average of results, and frequently in tests under shock, separation takes place at the weld. The results obtained are notably inferior to those obtained with well-executed oxy-acetylene welds.

Welding by Water Gas, - This constitutes a more perfect form of forge or fire weld. Instead of raising the edges to be joined to a welding heat by fire, they are submitted to the action of a blowpipe fed by water gas. This gas is chosen because it can be produced on the spot very economically. It is made by passing steam over red-hot coke, and consists of carbon monoxide and hydrogen, which produce a very high temperature by their combustion. Pneumatic tools rapidly hammer the two edges of the weld when they have been raised to a welding heat by the flame.

Welding by water gas necessitates a very costly installation, and does not pay unless it is used continuously on a very large scale. It is not practically applicable unless the plates have a thickness of at least inch.

Thermit Welding, - This process is only applicable to the joining of iron and mild steels of considerable thickness. It consists essentially in burning in a crucible a mixture of powdered aluminum and iron oxide. The temperature of combustion is excessively high, and can attain 3000° C. (or over 5400°F.). The aluminum unites with the oxygen to form alumina, while the iron which is set free accumulates in a molten state at the bottom of the crucible.

This is made to flow, by the aid of a suitable mould, round the parts to be joined, and its temperature is high enough to melt the edges to be joined; thus a weld which might be called autogenous is obtained.

It will be understood that the process, which requires costly material, can only be used for important or repetition work. It has chiefly been used for the welding of rails and the repair of very large steel castings. Oxy acetylene welding is largely replacing it.

Blowpipe Welding - Blowpipe welding consists in uniting the metal pieces by means of a flame of appropriate temperature with the addition of metal of the same composition. The joint thus obtained is called autogenous.

Strictly speaking, the welds obtained by the fire, water gas, or electricity can be called autogenous, since they have been obtained without the interposition of a metallic cement whose properties differ from that of the metal joined.

In current language the name autogenous welds is understood to mean those which are obtained by melting the metal imder the action of the flame of a blowpipe.

The blowpipe is an instrument in which the flame is produced and projected on to the metallic parts to be welded.

Blowpipe welding has been known for a long time, at least for the joining of metals whose melting-point is not very high, and was easily obtained by combustible gases burning in air or in a current of air. The autogenous welding of lead was thus obtained by the Egyptians, the Greeks, and the Romans.

The autogenous welding of metals with high melting-points was not possible until the industrial manufacture of oxygen permitted the use of this gas for the production of flames of high temperature.

First of all the oxy-hydrogen (oxygen and hydrogen) flame, then the oxy-acetylene (oxygen and acetylene) were thought of. After these oxy-coal gas (oxygen and coal-gas), oxy-benzene or oxy-benz (oxy-gen and vapour of benzol), etc. Autogenous welding by means of the blowpipe is the process that has been most developed in recent years. This is proved by its use in the majority of workshops for construction and repairs. The one defect in connection with blowpipe welding is that, owing to the apparent ease with which the work is done, it is, in many cases, applied by persons who have made no previous study of its requirements. Proper care is not used in the work and the result is many failures.

Welding at the forge, brazing, or even soldering, all require special knowledge on the part of the operator in order that he may be able to do reliable work. The easy appearance of blowpipe welding often leads an unskilled workman to attempt to do a job which, while often appearing perfect on the outside, is defective and unsafe.

The manufacturer or workman who wishes to apply autogenous welding should study the various systems which are offered, and find which gives him the most advantages.

The principal points to which he should direct his attention are the following: - Adapting the System to the Type of Work; Safety; Quality of Work; Economy; Convenience; Cost of Material.

Adapting the System to the Type of Work - When a process is no longer applicable to the work under consideration all interest in the process lapses. In reality, the value or economy of any particular system of blowpipe welding depends upon the type of work. Among the processes enumerated, it is first of all necessary to discern which is best applicable to the type of work.

Safety. - It can be considered that all the processes of blowpipe welding have been sufficiently studied and developed as not to offer any serious danger if the usual precautions are observed. The systems using benzol or other combustible liquids have become safe, and are practically free from danger.

Quality of Work - The quality of the work produced by blowpipe welding is not the same in all systems. According to the metal and its thickness, the weld may be more or less well finished and sound, and a process which may be satisfactory, in one case may not prove so in another. It is therefore necessary the each system should be kept in its particular sphere usefulness.

Economy - The factor of economy may differ according to the application of autogenous welding contemplated. In certain cases the cost of the work of first importance, while in other cases this may be a secondary consideration. A certain process appear to be economical and yet be expensive, or economical under certain conditions or for certain welds and not for others. The question of the net cost of welding must be considered with reference to the quality of work and convenience.

Convenience. - Convenient application is important in the choice of a method and should be carefully studied from all points of view, such as installation, maintenance, supervision, etc. A system which seems to offer great simplicity and convenience may not prove so in practice. Good judgment is therefore necessary, followed by a comparison of the different methods with reference to the kinds of work to be done.

Cost of Material - The various systems of blowpipe welding do not have the same purpose in view, and the importance that is attached to some of them is only on account of the facility and economy of their installation. They may be applicable where others are not, and it is only from this point of view that they deserve attention.

On the other hand when it is a question of regular or important work, the question of first costs will not be so important, the extra cost of material being soon recovered owing to more economical working, greater convenience and better results.


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