4.2 Oxyfuel Joining Processes
Figure 4-5. Oxyacetylene welding (OAW). The oxygen and acetylene gas are mixed in a torch. The mixture burns at the torch tip. The heat from this flame is used to melt the base metal and welding rod. This melted material forms the welded joint.
Oxyacetylene Welding Overview1:27
Figure 4-6. Color appearance of oxyacetylene flames. (Smith Equipment, Division of Tescom Corp.)
Image descriptionOxyfuel joining processes covered in this section include oxyfuel gas welding, torch soldering, and torch brazing. These processes combine the use of oxygen with a fuel gas to produce the source of heat required to weld, solder, and braze. The basic differences between these processes will be explained in this section. Commonly used fuel gases include acetylene, hydrogen, natural gas, butane, propane, and LP gas mixes. Acetylene and oxygen are most often used because when burned together, oxyacetylene produces a hotter flame than any other fuel gas/oxygen combination.
4.2.1 Oxyacetylene Welding (OAW)The oxyacetylene welding process combines oxygen and acetylene gases to provide a high-temperature flame for welding. This flame provides enough heat to melt most metals. The oxyacetylene flame may also be used for all types of brazing.
An oxyacetylene outfit, as shown in Figure 4-5, is used in this process. Oxyacetylene welding is a manual process. The welder must personally control the torch movement and welding rod. Acetylene is supplied from one cylinder; compressed oxygen is supplied from another cylinder. Both cylinders must be equipped with pressure-reducing regulators. Each regulator is fitted with two gauges.
One pressure gauge (high) indicates the pressure in the cylinder. This is referred to as cylinder pressure. The other pressure gauge (low) indicates the pressure of the gas being fed to the torch. This is referred to as working pressure.
Separate flexible hoses carry the gases to the torch. The torch has two needle valves, referred to as torch valves. One torch valve controls the rate of flow of the oxygen, the other controls the rate of flow of the acetylene to the torch tip. The mixed gases burn at the torch tip orifice (opening).
As shown in Figure 4-6, acetylene burns in the atmosphere with a yellow-red flame. A carburizing flame (excess acetylene with oxygen) is blue with an orange-and-red end. It may produce black smoke. A neutral flame (perfect mixture of oxygen and acetylene) has a quiet, blue-white inner cone. This is the flame used in most welding processes. An oxidizing flame (excess of oxygen) results in a short, noisy, hissing inner cone. It tends to burn the metal being welded.
Other fuel gases can be used in place of acetylene. These include LP (liquefied petroleum), natural gas, and hydrogen. Be sure to use only fuel gases approved for the equipment being used.
Welding goggles should be worn for eye protection. Gloves, nonflammable clothing, and all other required safety clothing should be worn to protect against burns. Good fire safety and prevention techniques should be employed. Proper ventilation must be provided.
See Chapters 11 and 12 for additional oxyacetylene welding information.