Let the Weld Guru guide you through the world of OxyFuel Cutting
The cutting torch (fig. 5-12), like the welding torch, has a tube for oxygen and one for acetylene. In addition, there is a tube for high pressure oxygen, along with a cutting tip or nozzle.
The tip (fig. 5-13) is provided with a center hole through which a jet of pure oxygen passes.
Mixed oxygen and acetylene pass through holes surrounding the center holes for the preheating flames.
The number of orifices for oxyacetlylene flames ranges from 2 to 6, depending on the purpose for which the tip is used. The cutting torch is controlled by a trigger or lever operated valve. The cutting torch is furnished with interchangeable tips for cutting steel from less than 1/4 in. (6.4 mm) to more than 12.0 in. (304.8 mm) in thickness.
b. A cutting attachment fitted to a welding torch in place of the welding tip is shown in figure 5-14.
c. In order to make uniformly clean cuts on steel plate, motor driven cutting machines are used to support and guide the cutting torch. Straight line cutting or beveling is accomplished by guiding the machine along a straight line on steel tracks. Arcs and circles are cut by guiding the machine with a radius rod pivoted about a central point. Typical cutting machines in operation are shown in figures 5-15 and 5-16.
d. There is a wide variety of cutting tip styles and sizes available to suit various types of work.
The thickness of the material to be cut generally governs the selection of the tip.
The cutting oxygen pressure, cutting speed, and preheating intensity should be controlled to produce narrow, parallel sided kerfs.
Cuts that are improperly made will produce ragged, irregular edges with adhering slag at the bottom of the plates.
Table 5-3 identifies cutting tip numbers, gas pressures, and hand-cutting speeds used for cutting mild steel up to 12 in. (304.8 mm) thick.
The oxygen and acetylene gas pressure settings listed are only approximate. In actual use, pressures should be set to effect the best metal cut.
c. Hold the torch so that the cutting oxygen lever or trigger can be operated with one hand. Use the other hand to steady and maintain the position of the torch head to the work. Keep the flame at a 90 degree angle to work in the direction of travel. The inner cones of the preheating flames should be about 1/16 in. (1.6 mm) above the end of the line to be cut. Hold this position until the spot has been raised to a bright red heat, and then slowly open the cutting oxygen valve.
d. If the cut has been started properly, a shower of sparks will fall from the opposite side of the work. Move the torch at a speed which will allow the cut to continue penetrating the work. A good cut will be clean and narrow.
e. When cutting billets, round bars, or heavy sections, time and gas are saved if a burr is raised with a chisel at the point where the cut is to start. This small portion will heat quickly and cutting will start immediately. A welding rod can be used to start a cut on heavy sections. When used, it is called a starting rod.