The use of oxygen and hydrogen as the gases for welding and cutting is older than the oxy-acetylene process and dates back to before the production of oxygen by either electrolysis or liquefaction of air. Oxygen was probably generated in those days from potassium chlorate and manganese dioxide, or perhaps from potassium and sodium peroxides and water,* and the hydrogen from hydrochloric acid and zinc. The oxy-hydrogen process was developed by Newman who used detonating gas (pure oxygen and hydrogen mixed) at a pressure of about 3 atmospheres. This gas is still used to some extent in welding platinum, lead, and precious metals but it is rapidly being superseded by apparatus designed to use the oxygen and hydrogen from separate cylinders.
The apparatus required for oxy-hydrogen welding is similar to that in use for oxy-acetylene welding and consists primarily of the two steel cylinders for the oxygen and hydrogen (at pressures of 1500 to 2000 pounds per square inch); a mixer and insulator of the gases, together with a regulator; high pressure reducing valves for each of the gases; armored hose; and the special blowpipe, or torch. When the blowpipe is used, there are two tubes leading to it, one for the oxygen and the other for the hydrogen, and the blowpipe is made with an inner and an outer tube. The oxygen is carried through the inner tube and the hydrogen is carried through the outer tube and lighted first. After the oxygen is turned on, the flame is adjusted to suit the work in hand and the mixing is done in the tip of the blowpipe just before the gases enter the flame. Hydrogen and air can be used with the same sort of blowpipe for light work requiring but moderate heat, such as lead burning, but the process is much slower and more expensive than with the oxy-hydrogen flame.
For commercial welding another type of torch is used and the gases are combined in the mixer and carried to the burner through a single tube. This torch has an enlargement, where the gases enter, which reduces their velocity; from this chamber the gases pass through the smooth tubular body to the nozzle. The latter diminishes in size toward the tip and causes the gas to increase in speed up to the proper velocity.
The oxy-hydrogen flame is pale blue, almost colorless in fact, and has a temperature of about 2000 degrees centigrade. When lighting the torch, the hydrogen should be turned on about two-thirds and ignited; the oxygen should then be turned on enough to give a pale blue conical flame, and then the hydrogen should be turned on full. This will take but a few seconds, and a flame, which will not melt the metal too rapidly, is better than one of such intensity as to burn the work. The end of the cone of oxygen in the flame should never touch the work or that will burn it also. When through welding, the oxygen should be turned off first. Theoretically, two parts of hydrogen should be used for each part of oxygen but experience shows that it is desirable to use about three parts of hydrogen to one of oxygen. Some operators advocate using even more hydrogen, but this is not necessary when the gases are properly mixed before entering the flame.
The process of welding with oxy-hydrogen is similar to other hot-flame processes and the joints must be beveled in the same way to make them accessible for filling. The work should be heated first, in order to prevent chilling of the filling material, and the melt bar fused in to make the joint. In Germany this gas is used to heat plates and then they are welded by hammering, as in blacksmith work, this operation being used to a large extent in making large steel pipes. Iron, steel, copper, lead, zinc, and the other industrial metals can be welded by this process; the cost is similar to that for work done by the oxy-acetylene process, although somewhat higher for most operations. Each metal requires its own special method of treatment and the operator will soon learn the best ways of handling each job, but this process requires a skilled workman and the success or failure of the weld will depend largely on the man who does it.
The time required for welding seams in steel plates will vary from two minutes per foot on 1/32-inch sheets up to five minutes on ¼-inch plates. It is claimed that the oxy-hydrogen flame does not affect the ductility of the metal like the oxy-acetylene flame and, if this is true, it should be good for boiler repairs and other work in which this quality is desirable.