Autogenous welding by oxy-hydrogen and oxy-acetylene blowpipes has, within the last few years, been applied in thousands of workshops. In spite of the fact that these applications have, at least in many cases, been undertaken without precise methods, without theoretical or practical knowledge, in a word, without technique, it has become an extremely important process capable of numerous and varied applications in all branches of metallic construction and repair. A great future can be foreseen for this process from the moment its technique becomes known to the welder, and when manufacturers who use the process realize that knowledge and reflection are at least as important as skill and dexterity of hand.

Autogenous welding is certainly the one process of construction and repair that requires, from top to bottom of its application, most reflection, intelligence, and conscientiousness.

It is, for the welder, a trade which differentiates it from the majority of others in this sense that mechanical work is completely excluded from its practice, and that an immediate judgment cannot always be passed on the realization, more or less perfect, of an intimate joining of which the metal holds the secret.

This handbook is intended for the welder as well as for all those who wish to acquire a simple and reliable technique in the art of autogenous welding. It has been simplified by the omission of all intricate scientific considerations relevant only to a more advanced study of the subject, but it has not been deprived of the fundamental and technical principles serving as the base for all the applications of the science.

Such a work should not frighten the practitioner. Even the least inexpert welder will find useful instruction relating to manipulation, methods of operation, dexterity of hand, various apparatus and their safety; he will acquire a mass of information concerning the process which he uses, sufficient technique to increase his efficiency and enable him to apply his art in a rational and easy manner.

The Union de la Soudure Autogene, by their publications and practical courses, have already disseminated the principles for obtaining work as perfect as possible, and at the same time securing absolute safety for those in charge.

In this practical handbook we continue the enterprising work by entering further into the details of the process. Its publication has been delayed because such a work should be complete. True, it is neither perfect nor final, since the technique of autogenous welding is still in its infancy. This technique, already on a solid foundation, will be enriched by further studies. Those that utilize autogenous welding have only themselves to thank for any benefits which they may derive from this book, since the work emanates from their association, the Union de la Soudure Autogene. We are only their collaborators.

In order to appreciate thoroughly autogenous welding, it is useful before studying the process to examine briefly the other methods for bringing about permanent metallic joints, to know their characteristics, their applications, their advantages and disadvantages.

All the practical methods have their own particular value, their legitimate application, their defects and good qualities. They complement each other more than they replace each other; each has its special application as none of them are universal.

SOFT SOLDERING

Soft soldering is generally used for joining pieces of thin metal together. In the majority of cases in which it is used the object is to obtain an air or water-tight joint rather than a strong joint.

As its name indicates, the "soft solder" used has a much lower strength than that of the metals to be joined; its tensile strength is extremely low, and it is necessary to increase the surface of contact so that firmness is obtained at the joint by adhesion, something like the use of gum in joining paper.

Soft soldering is principally used for tin plates, zinc, lead plates, galvanized plates, sometimes copper or brass, and wherever the joint has not to stand any serious strain.

The melting-point of the solder must, obviously, be lower than that of the metals to be joined, or the surfaces will be destroyed. The joint is always weaker than the actual metal joined, and really only constitutes a connection and never an alloy.

To apply the solder a "soldering iron" or soldering flame of "gas, acetylene, etc., is used.

A flux is always necessary to clean the joint and prevent or remove any oxide formed during the soldering. The flux used depends on the metals to be joined. Fluxes used are colphonium and sal ammoniac, zinc chloride, resin, etc.


BRAZING.

If one compares brazing to soft soldering, it can be called "hard soldering." It is characterized by the use of a metallic cement melting at a high temperature and possessing a high mechanical resistance.

Given these facts, one can see that it is necessary to heat strongly the edges to be joined and to use a cleaning flux melting at a high temperature.

The "metallic cement" used is called brazing metal, and can be applied in the form of a powder, paste, filings, or grains often mixed with the flux. Its melting-point is just below that of the metal to be joined, so that in heating the pieces to be brazed, the brazing metal melts and adheres to the edges to be joined when they reach a high temperature, thus even forming an intermediate alloy, and the joining is obtained simply by cooling.

When it is a question of joining end to end or edge to edge, the brazing is done with bevelled faces placed side by side. It is clear that this increase of surface in contact increases the resistance of the joint.

Brazing necessitates the use of a forge or blowpipe. The use of a forge is costly, inconvenient, and cannot be applied to articles of all shapes and dimensions. The blowpipe requires, for brazing, great skill in manipulation, because the localization of the heat tends to "burn" the metal, especially in the joining of brass. Note, however, that the use of blowpipes giving high temperatures, oxy-acelytene for example, enables one to use brazings less fusible, red copper among others, for joining pieces of cast-iron. Brazing rarely fulfils the conditions required for perfect joining, the following being the chief disadvantages: the part brazed possesses a different colour to that of the metal; this same part has different chemical, physical, and mechanical properties from that of the piece; electrolytic action may little by little disintegrate the joint thus constituted; the operation is risky; success is not controllable, etc.

The cleaning fluxes generally used for brazing are : white sand, used for brazing iron which forms with the oxide of the metal a very fusible ferrous silicate; and borax, which is more generally employed and which acts as a kind of solvent for the metallic oxide. Brazing mixtures for various purposes are sold ready for use.


WELDING AT THE FORGE

Fire welding has been known from the most remote time. It is practically only applied to iron and steel. One obtains a joint by energetic hammering of two pieces together which have previously been raised to welding heat.

The chief difficulty of fire welding consists in the exact appreciation, at a glance, of the welding temperature by the colour of the metal, because iron can only be welded within certain definite limits of temperature. This peculiarity was well known to the ancients, and the engraving which we reproduce, drawn from a fresco, shows an antique Greek smith very attentive to the colour of. the metal which he is about to weld.

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 hinder 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, hence deformations and necessity for working after welding.

(2) Large quantity of heat lost, hence process costly.

(3) Difficult to ensure success, and impossibility of control.

Fire welding is, where possible, done by joining the two sections obliquely, known as a scarf weld, thus increasing the surface of contact and the resistance of the joint. The adherence of fire welds very rarely exceeds 70 per cent, the resistance of the metal.

The elongation of fire welds is always very low. From the point of view of brittleness, fire welds give very mediocre results, and frequently in tests by shock separation at the welded line takes place under extremely weak shocks. The results obtained are notably inferior to those obtained for oxy-acetylene welds well executed.


WELDING BY WATER-GAS

Welding by "water-gas" constitutes a kind of perfect fire welding. 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 T 5 g inch.


ELECTRIC WELDING.

It is more than thirty years since electricity was proposed for the autogenous welding of metals. The process, however, is not largely used, and its application remains limited to special industries, viz. manufacture of chains, utensils in thin plate, etc. The rapid development of other processes of welding indicates that they are superior in many respects. Electric welding is obtained by two processes which are quite different, resistance welding and arc welding. The latter system is the one which is most used; it can be applied to work of all kinds and to repairs. Resistance welding is used in the manufacture by machinery of articles of small dimensions in large quantities.

Resistance welding modifies the mechanical properties of the metals, which lose their elongation; if the surfaces to be welded are not perfectly clean there must always be interposition of oxide or dirt, which reduces the solidity of the joint.

Arc welding is generally difficult to apply; the localization of the heat is not favourable to the perfect joining of the metal, and unless one uses judiciously a satisfactory flux, there will be an interposition of oxide in the joint. Lastly, blowholes are almost inevitable, and these considerably lower the strength of a joint which in appearance may be perfect.


THERMIT WELDING

This process is only applicable for the joining of iron and mild steels of great 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, whilst 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 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 under the action of the flame of a blmvpipe.

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 flames 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).

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.

It gives incontestable advantages from all points of view over similar processes. Its one defect is that its use is too easy, or at least appears too easy, so that it is applied by all sorts without previous study, without care, and without technical ability. Hence the failures.

It requires a long apprenticeship for joining two pieces at the forge, for brazing, even for welding tin, and in all cases one can judge whether the work is good or bad. On the contrary, after an hour's trial one can join iron by melting with the blowpipe, and after a few days one can produce good-looking welds. But are they perfect, even passable 1 ? Incontestably no, and that is, we repeat, the very great defect of the process. The reader's attention is drawn to this question in the course of the chapters which follow.


DOWNLOAD FREE BOOK:
A practical manual of autogenous welding