Oxy-Acetylene Welding and Cutting / Electric, Forge and Thermit Welding together with related methods and materials used in metal working and the oxygen process for removal of carbon

by Harold P. Manly

It should completely use up the carbide, generating the maximum amount of gas.

Overheating.--A large amount of heat is liberated when acetylene gas is formed from the union of calcium carbide and water. Overheating during this process, that is to say, an intense local heat rather than a large amount of heat well distributed, brings about the phenomenon of polymerization, converting the gas, or part of it, into oily matters, which can do nothing but harm. This tarry mass coming through the small openings in the torches causes them to become partly closed and alters the proportions of the gases to the detriment of the welding flame. The only remedy for this trouble is to avoid its cause and secure cool generation.

Overheating can be detected by the appearance of the sludge remaining after the gas has been made. Discoloration, yellow or brown, shows that there has been trouble in this direction and the resultant effects at the torches may be looked for. The abundance of water in the carbide to water machines effects this cooling naturally and is a characteristic of well designed machines of this class. It has been found best and has practically become a fundamental rule of generation that a gallon of water must be provided for each pound of carbide placed in the generator. With this ratio and a generator large enough for the number of torches to be supplied, little trouble need be looked for with overheating.

Water to Carbide Generators.--It is, of course, much easier to obtain a measured and regular flow of water than to obtain such a flow of any solid substance, especially when the solid substance is in the form of lumps, as is carbide This fact led to the use of a great many water-feed generators for all classes of work, and this type is still in common use for the small portable machines, such, for instance, as those used on motor cars for the lamps. The water-feed machine is not, however, favored for welding plants, as is the carbide feed, in spite of the greater difficulties attending the handling of the solid material.

A water-feed generator is made up of the gas producing part and a holder for the acetylene after it is made. The carbide is held in a tray formed of a number of small compartments so that the charge in each compartment is nearly equal to that in each of the others. The water is allowed to flow into one of these compartments in a volume sufficient to produce the desired amount of gas and the carbide is completely used from this one division. The water then floods the first compartment and finally overflows into the next one, where the same process is repeated. After using the carbide in this division, it is flooded in turn and the water passing on to those next in order, uses the entire charge of the whole tray.

These generators are charged with the larger sizes of carbide and are easily taken care of. The residue is removed in the tray and emptied, making the generator ready for a fresh supply of carbide.

Carbide to Water Generators.--This type also is made up of two principal parts, the generating chamber and a gas holder, the holder being part of the generating chamber or a separate device. The generator (Figure 10) contains a hopper to receive the charge of carbide and is fitted with the feeding mechanism to drop the proper amount of carbide into the water as required by the demands of the torches. The charge of carbide is of one of the smaller sizes, usually "nut" or "quarter."

Feed Mechanisms.--The device for dropping the carbide into the water is the only part of the machine that is at all complicated. This complication is brought about by the necessity of controlling the mass of carbide so that it can never be discharged into the water at an excessive rate, feeding it at a regular rate and in definite amounts, feeding it positively whenever required and shutting off the feed just as positively when the supply of gas in the holder is enough for the immediate needs.

The charge of carbide is unavoidably acted upon by the water vapor in the generator and will in time become more or less pasty and sticky. This is more noticeable if the generator stands idle for a considerable length of time This condition imposes another duty on the feeding mechanism; that is, the necessity of self-cleaning so that the carbide, no matter in what condition, cannot prevent the positive action of this part of the device, especially so that it cannot prevent the supply from being stopped at the proper time.