Copyright Goodheart-Willcox Co., Inc. Chapter 15 Oxyfuel Gas Cutting 431 Summary „ An oxyfuel gas cutting torch tip has one or more preheating orifices arranged around a central oxygen orifice. The preheating orifices provide the flames that heat the metal to its ignition temperature. „ Cutting occurs when the ignition temperature is reached and the operator depresses the cutting oxygen lever. A stream of pressurized oxygen from the tip’s central orifice burns the metal and blows it away from the base metal. As the torch is moved along a predetermined line, the metal is cut, forming the kerf. „ Because the oxygen pressures for cutting are usually higher than the pressures for welding, an oxygen regulator with a higher working pressure should be used for OFC. „ A cutting attachment can be connected to a combination torch body to change the torch from a welding torch to a cutting torch. „ One-piece cutting tips are used for oxyacetylene cutting only. Two-piece tips are used for all other gas cutting. „ Setting the correct working pressure on each regulator is critical. Acetylene should never be used at a working pressure above 15 psig (103 kPa). „ A slag stream that lags excessively behind the torch tip travel may be due to incorrect flame adjustment, low cutting oxygen pressure, or tip travel that is too fast. „ The cut should proceed just fast enough to provide a slight amount of drag at the line of cutting. „ For cutting steel that is 1/8″ (3.2 mm) or less in thickness, the tip is usually pointed in the direction the torch is traveling. In effect, the increased travel angle lowers the torch body closer to the workpiece and so increases the thickness of metal being cut. „ Steel over 1/2″ (13 mm) thick should be cut by holding the torch so the tip is perpendicular to the surface of the base metal being cut. „ Oxyfuel cutting is used to prepare the edges of bevel-groove and V-groove joints prior to welding. „ More heat is required to preheat the surface for piercing than for starting a cut on an edge. The welder should use at least the next larger tip in relation to the thickness of the metal than would be used for cutting. „ For oxyfuel gas gouging, a lower oxygen cutting pressure and a larger-diameter cutting tip orifice are used than for oxyfuel gas cutting. „ In an automated cutting process, a controller or computer is programmed with the path and speed of the torch, torches, or cutting equipment and no manual adjustments are required during cutting. „ Semiautomatic cutting is cutting with a torch that is held and moved by a mechanical device and adjusted manually. The welder manually adjusts the equipment controls as needed in response to visual observations of the cut being made. „ Cutting operations result in a considerable number of flying globules of molten metal. All safety guidelines must be followed to help prevent accidents during cutting operations. Technical Terms automatic cutting cutting outfit cutting oxygen lever drag gantry gouging heat of combustion ignition temperature oxygen jet pierce semiautomatic cutting Review Questions Answer the following questions using the information provided in this chapter. Know and Understand 1. True or False? The lowest temperature in a normal atmosphere at which a given material will ignite spontaneously, without any external spark or flame, is called heat of combustion. 2. The color of steel at ignition temperature is _____. A. black B. pale yellow C. dark red D. cherry red 3. True or False? A two-piece cutting tip is used for oxyacetylene cutting. Select the icons to access Drill and Practice activities. Ch15.indd 431 7/11/2019 3:29:58 PM