General

Lest the variations in practice and the variety of apparatus about to be described should prove confusing, it is well to state that the oxy-acetylene welding process depends on the high heat of combustion of oxygen and acetylene. The apparatus primarily consists of:

1. Apparatus for storing or generating oxygen.

2. Apparatus for storing or generating acetylene.

3. A burner or blowpipe, with leading tubes, for the combustion of oxygen and acetylene.

This is the simple story, of which there are many details. The advantages and limitations of the processes here described are as follows:

1. The apparatus is fairly light, easily portable, and can be installed permanently.

2. For repair work, the cost is light and the results satisfactory.

3. On account of the intense heat of the flame, any substance or metal can be melted locally at once.

4. The high heat of the flame represents a limitation in so far as it is difficult to adjust and dangerous to use unless the operator knows his business.

5. The weld, being a melt-weld, is subject to oxidation and carbonization from the flame, and to crystallization on cooling.

The merits of the oxy-acetylene process greatly outweigh its possible faults. There is no process that will compare with it for welding job work of all kinds of metals and for repair work.

The present use of the oxy-acetylene flame in welding and autogenous soldering is the outcome of the discoveries of many experimenters. It is a step beyond the oxy-hydrogen process: the flame has an opproximate temperature of 3500 deg. Cent., while the oxy-hydrogen is about 2250 deg. Cent. But this high heat and the explosive nature of acetylene complicate the problem. Special apparatus had to be devised; special instructions worked out for its use in practice. As one writer states, its practical value was at first overestimated by those interested in it. And when obstacles arose their ardor was checked and the process suffered a temporary relapse. At the present writing, however, the oxy-acetylene process is in a state of rapid development, and it has passed the critical stage. It is a recognized repair and welding process. It is being used to weld or solder almost all the metals, both to themselves and to one another; it is also used to cut through steel and iron plate, bars, etc., with six times the rapidity of a saw.

There are several items in the apparatus for this process that have advanced its use. One of them is the compounds for producing oxygen in situ and at less expense than by the ordinary electrolytic process. The Industrial Oxygen Company of New York sold until recently a powder called "Epurite," probably sodium dioxide, which produced oxygen when wet with water. In 1906 the Industrial Oxygen Company withdrew this compound and advanced a second, called "Oxygenite." Oxygenite necessitates special combustion, cleaning and storing tanks, but cost of these is small in comparison with the cost of an electrolytic plant, and brings it into competition with the storage oxygen made by the electrolytic and liquid-air processes.

The Davis-Bournonville Company have recently adopted the potassium-chlorate method of generating oxygen in cases where tanked oxygen is inconvenient. As with Oxygenite, special tanks are required for generating, washing, and storing. Their oxygen compound is not combustible and requires the external heat of a gas flame. Fuller particulars of these two chlorate processes are given on pages 86 and 87.

Since 1880 industrial oxygen has been sold in increasing quantities by the firms using apparatus for the electrolysis of water. France and Germany have been specially active in projecting methods. The processes of Schuckert, Garuti, Schoop, and Schmidt are worthy of mention. In late years oxygen obtained by the Linde liquid-air process has come into competition with electrolytic oxygen. It is most largely used in this country, while the company claims to supply 90 per cent of the world's demand for oxygen.

Acetylene was discovered in 1837. It was first recognized as a valuable illuminant, more especially in France, where it is used by hundreds of municipal plants at the present day. France is also foremost in oxy-acetylene welding inventions, among the most important being those of Fouche.

Acetylene can now be had in two forms: stored acetylene in steel cylinders, such as are used for carbon dioxid; and calcium carbid, which produces acetylene when wet with water, according to the formula CaC2+H20 = C2H2+CaO.

Stored acetylene was originally a dangerous commodity. It was liable to explode under pressure. The railroads objected to handling it. So the acetylene producer, calcium carbid, held the market. The gas was generated at the place where it was to be used and kept in a tank under less than 10 pounds' head. In 1897, the acetone-absorption process was patented, and since then stored acetylene has been in active competition with the carbid (see p. 92).

At the present writing a repair shop desiring to set up an acetylene welding department is offered a number of alternatives:

1. The acetylene can be bought in storage tanks or it can be generated from the carbid.

2. The oxygen can be bought in storage tanks or it can be generated from Oxygenite or by the other chlorate method.

3. Oxgyen can be dispensed with and atmospheric air substituted. For this purpose a pressure pump and air gasometer are needed. Under the second head it might be added that oxygen could be produced by the electrolysis of water. But this would require a large, costly outfit, running up into thousands. Under the third head, oxygen air and acetylene are sometimes used in a three-way burner.