410 Modern Welding thermal units (Btu) or joules. This is called the heat of combustion. The heat of combustion helps to keep the metal in the cutting area at the ignition temperature, so that cutting can progress smoothly. 14.2 Oxyfuel Gas Cutting Process A special torch and tip is used in the oxyfuel gas cutting process. See Figure 14-1. Cutting tips have one or more preheating orifi ces (holes) to provide the fl ames used to heat the metal being cut to its igni- tion temperature. Cutting oxygen exits from a central orifi ce when the welder presses the cutting oxygen lever. See Figure 14-2. The ignition temperature of steel occurs when its color is cherry red and its temperature is about 1300°F to 1400°F (704°C to 760°C). The oxyfuel gas preheating fl ames are adjusted and used in the same manner as the fl ames used for welding. The preheating fl ames are used to heat a spot on the base metal to its ignition temperature. When the ignition temperature is reached, the operator depresses the oxygen lever, and a stream of pressur- ized oxygen burns the metal and blows it away from the base metal. As the torch is moved along a prede- termined line, the metal is cut, forming the cut or kerf. The preheating fl ames are kept burning throughout the entire cutting process. These fl ames are required to ensure that the base metal never drops below its ignition temperature during cutting. 14.3 Cutting Outfi t An outfi t used for manual oxyfuel gas cutting is similar to an oxyacetylene welding outfi t. The outfi ts differ only in the torch and possibly the oxygen regu- lator used. The term cutting outfi t is used to include all equipment required to perform a cut. A cutting station would include the outfi t, lighting, ventilation, a cutting table, and possibly a booth. Since the cutting torch must provide an oxygen cutting jet, it is quite different from a welding torch. Because the oxygen pressures for cutting are usually higher than the pressures employed when welding, an oxygen regulator with a higher working pressure should be used. Also, the inside diameter of the oxygen hose should be larger to provide a higher rate of fl ow. Carefully review Chapters 11 and 13 before connecting and operating the oxyfuel gas cutting outfi t. Information in those chapters concerning cylin- ders, manifolds, regulators, hoses, torches, and tips also apply to oxyfuel gas cutting outfi ts. 14.4 Cutting Torch A cutting torch is similar to a welding torch, however, a cutting torch has a separate passageway for the oxygen jet. As in welding, the cutting torch is Figure 14-1. Oxyacetylene cutting outfi t. Oxygen cylinder valve Acetylene regulator Acetylene cylinder Safety chain Oxygen regulator Twin hoses Welding/ cutting torch Oxygen cylinder Figure 14-2. A cutting torch with fl ashback arrestors built into the torch body. (Victor, a division of Thermadyne Industries, Inc.) Torch oxygen valve Cutting oxygen lever Body Torch acetylene valve Flashback arrestors