Fig. 19.
(30) Acetylene is the fuel gas, and is one of the greatest containers of heat known. Burning in a free state, its carbon content is so rich that complete combustion is impossible, and stringy black particles will be noticed floating through the air. In order to fully combust this gas, oxygen is introduced under pressure and a temperature of over 6000 degrees Fahrenheit is obtained. (Acetylene contains about five times as many B. T. U.’s (British Thermal Units) as hydrogen.) This gas, unlike oxygen, becomes very dangerous when in a free state it is subjected to an excessive pressure. The slightest jar may cause its disintegration and a violent explosion follows. On account of this danger, acetylene is not stored in a free state; neither is it subjected to very high pressures. Its cylinders are put out by various manufacturers to comply with the laws and regulations of the Interstate Commerce Commission. Some of these cylinders have been welded, but the most modern method is to make them of one piece of drawn steel. They are then filled with an absorbent of some kind to take up the gas and prevent any portion of it being left in a free state. Acetone is the popular absorbent, and is a liquid capable of absorbing twenty-five times its own volume of acetylene gas at normal pressure. The filling material varies with each of the manufacturers, but charcoal, asbestos and mineral wool are in very common use. Acetylene is obtained from calcium carbide brought in contact with water, or vice versa, and is compressed and then stored in the cylinders at a pressure varying from 150 to 250 pounds. When fully charged this pressure will vary almost directly with any change of temperature. Acetylene cylinders for welding are available in 100, 200, 225, and 300 cubic foot sizes.
Fig. 20.—A Generator for Producing Acetylene under Pressure.
(31) In setting up apparatus for the first time, the regulator containing the 3000-pound gauge is attached to the taller of the cylinders, which holds the oxygen gas, and the other regulator is fastened to the shorter cylinder. The hoses, which should be cleared of all powder or scale on their interior, are then added. The black hose should connect the oxygen regulator to the torch valve, marked “OX” and the red hose, the acetylene regulator to the torch valve stamped “AC.” In attaching regulators to full cylinders the “cross-bar” on the regulator should always be turned out, that is to the left, until it turns freely, to insure all pressure being released from the diaphragm, before the cylinder pressure is turned on. Another precaution that should be observed is the “cracking” of the cylinder valves, before attaching the regulator, in order to blow out any dirt or foreign particles that may be lodged there, otherwise they will be carried into the regulator seat, or lodged in some small passage, which will impair the working of the apparatus. Then too, if no truck or clamping device has been provided, both the oxygen and acetylene cylinders should be securely clamped or wired together, a rule which should be insisted upon at all times, whether in a job shop, manufacturing concern, or training school, or any place where top-heavy oxygen cylinders are being used. No particular harm results if these cylinders are turned over, which is very easily done on account of their rounded base, if no regulator is attached, but very frequently regulators are attached and the hose connecting the same to torch is found in the operator’s way. The slightest pull or tripping on this hose will upset the cylinder, usually demolishing the regulator and expensive gauges and at times causing much confusion among the workmen, on account of the loud hissing noise given off by the escaping gas. Always secure the drums or the cylinders in a safe manner.
(32) In turning on the gas, the oxygen valve is opened wide until seated and the acetylene valve is only partially opened. Often the question is raised as to where the operator should stand, especially when dealing with high-pressure oxygen. It is recommended that the operator should stand at the side and towards the rear when performing this operation, for sometimes an unreliable gauge may be attached, which if bursting, would send the glass into the operator’s face.
Fig. 21.—Acetylene Flame Blowing away from Tip.
Fig. 22.—Addition of Oxygen to Acetylene Flame.