Oxy-acetylene welding manual

by Lorn Campbell

Fig. 81.—End Views of Cutting Tips, Showing Possible Arrangements of Preheating Flames in Regard to Oxygen Jet. The Black Circles Represent the Preheating Flames, which Vary in Number and Arrangement According to the Nature of the Work, the Possible Limit being a Continuous Circle, as Shown. The White Circles Illustrates the Oxygen Jet, which, too, Varies in Size According to the Work.

(147) The cutting torch differs from the welding torch in many respects. The tip itself, when looking at its end, may resemble any one of the views shown in [Fig. 81]. In the welding torch, but one hole is to be found in the tip; in the cutting tips, two or more holes are to be found. In all cases the center hole passes pure oxygen, whereas in the surrounding holes, both oxygen and acetylene mix and when lighted give a neutral flame. This will hereafter be called the preheating flame. The gases issuing from these openings are controlled by three valves, one of which may have a trigger or lever arrangement for quick action, and it will control the center jet of oxygen which really does the cutting. This is under much higher pressure than the preheating flame. The other two valves will control the oxygen and acetylene gases used for the preheating flame. In lighting such a torch, the acetylene is turned on in the same manner as has been taught when welding, until it just leaves the end of the tip. Then the oxygen valve is opened, which controls the preheating flame, and enough is permitted to pass to produce a neutral flame. As soon as this has been accomplished, the third valve should be quickly opened and held so a moment, to see if the neutral flame has been changed. Generally this operation will deprive the neutral flame of some of its oxygen, and a feather flame, showing too much acetylene and not enough oxygen gas, can be noticed. This will necessitate turning on slightly more oxygen at the torch valve. The third valve is then shut off and the torch is ready to start cutting.

(Courtesy of the General Welding & Equipment Co.)

Fig. 82.—Cutting a Heavy Shaft.

Fig. 83.—Position to Hold Torch in when Cutting Metal.

(148) On small cutting jobs, about as much acetylene pressure is used on the line as there would be if it were a welding job. The oxygen pressure, however, is generally much greater, and a pressure anywhere from ten to two hundred pounds should be used, depending upon the thickness of the metal and the conditions which must be met. In extreme cases where very heavy cuts are to be made, a much higher pressure than has been mentioned should be used, but the limitations given will cover a wide range of work. To start a cut it is necessary to bring the preheating flame in contact with one edge of the metal to be cut and play it there until the metal is red hot. As soon as this condition is reached the torch is held steady—the neutral flame just touching the metal; then the third valve controlling the cutting jet of oxygen is opened. This oxygen, under high pressure, quickly acts upon the hot metal and severs it instantaneously, melting and oxidizing the metal so that it will not flow together, in one and the same operation. As soon as this occurs the torch should be advanced as rapidly as possible in the direction the metal is to be cut. The more rapid the advancement and the steadier the torch is held the cleaner the cut will be; and incidentally, less gas consumed in the execution of the job. In cutting, as in welding, it is always well to give the torch a chance, and when the operator sees much molten metal splashing directly back on the torch, he should change the angle slightly to avoid his apparatus becoming overheated. It has been found that if the cutting torch is held at the angle shown in [Fig. 83], the most satisfactory results can be expected.

(149) At the present time only such metals as steel and wrought iron can be successfully cut. When it comes to cast iron no method has yet been discovered to cut it with any degree of success by the oxy-acetylene flame, on account of the high melting-point of the oxide and various other matters. The day is looked forward to, however, when after sufficient time and study has been devoted to this subject, that cast iron can be as successfully cut as any other metal, by introducing another gas or agent to destroy some of the reactions which retard its application at the present time.

(150) The use of the cutting torch in preparing steel work, for welding of large size, plays an important part, in quickly and efficiently “V-ing” out and getting it ready for use. Care should be taken, after its use, to see that the heavy oxide which it leaves is largely destroyed, before any more metal is added.