Nozzle Sizes.--The size of opening through the nozzle is determined according to the thickness and kind of metal being handled. The following sizes are recommended for steel:
Davis-Bournonville. Oxweld Low
Thickness of Metal (Medium Pressure.) Pressure
1/32 Tip No. 1 Head No. 2
1/16 2
5/64 3
3/32 3 4
3/8 4 5
3/16 5 6
1/4 6 7
5/16 7
3/8 8 8
1/2 9 10
5/8 10 12
3/4 11 15
Very heavy 12 15
Cutting Torches.--Steel may be cut with a jet of oxygen at a rate of speed greater than in any other practicable way under usual conditions. The action consists of burning away a thin section of the metal by allowing a stream of oxygen to flow onto it while the gas is at high pressure and the metal at a white heat.
The cutting torch (Figure 23) has the same characteristics as the welding torch, but has an additional nozzle or means for temporarily using the welding opening for the high pressure oxygen. The oxygen issues from the opening while cutting at a pressure of from ten to 100 pounds to the square inch.
The work is first heated to a white heat by adjusting the torch for a welding flame. As soon as the metal reaches this temperature, the high pressure oxygen is turned on to the white-hot portion of the steel. When the jet of gas strikes the metal it cuts straight through, leaving a very narrow slot and removing but little metal. Thicknesses of steel up to ten inches can be economically handled in this way.
The oxygen nozzle is usually arranged so that it is surrounded by a number of small jets for the heating flame. It will be seen that this arrangement makes the heating flame always precede the oxygen jet, no matter in which direction the torch is moved.
The torch is held firmly, either by hand or with the help of special mechanism for guiding it in the desired path, and is steadily advanced in the direction it is desired to extend the cut, the rate of advance being from three inches to two feet per minute through metal from nine inches down to one-quarter of an inch in thickness.
The following data on cutting is given by the Davis-Bournonville Company:
Cubic
Feet Cost of
Thickness of Gas Inches Gases
of Cutting Heating per Foot Oxygen Cut per per Foot
Steel Oxygen Oxygen of Cut Acetylene Min. of Cut
1/4 10 lbs. 4 lbs. .40 .086 24 $ .013
1/2 20 4 .91 .150 15 .029
3/4 30 4 1.16 .150 15 .036
1 30 4 1.45 .172 12 .045
1 1/2 30 5 2.40 .380 12 .076
2 40 5 2.96 .380 12 .093
4 50 5 9.70 .800 7 .299
6 70 6 21.09 1.50 4 .648
9 100 6 43.20 2.00 3 1.311