in thickness, you do not need to make a V-groove. Metal that is between 3/16 of an inch and 3/8 of an inch should have a single V-butt joint with an included angle of 60 degrees. For metal over 3/8 of an inch, use a double V-butt joint with 60-degree included angles.
Before you begin welding, preheat the entire weldment to a temperature between 750°F and 900°F The welding should be done with a neutral flame using the backhand method. Use a cast-iron filler metal and the appropriate flux. The flux is necessary, but use it sparingly as needed Add filler metal by directing the inner cone of the flame against the rod instead of dipping the tip of the rod into the puddle. The filler metal should be deposited inlayers not exceeding 1/8 of an inch thick. Upon completion of the weld, you must stress relieve the weldment by heating it to a temperature between 1100°F and 1150°F and then cool it slowly. Oxygas welding cast iron gives a good color match and good machinability; however, if color match is not essential, a cast-iron repair can be made more easily and economically by braze welding.
Oxygas welding can be used with some CHROMIUM-NICKEL STEELS (STAINLESS STEELS). As a rule, oxygas welding is used only for light sheet; heavier pieces of these steels are usually joined by one of the electric arc welding processes. On material 20 gauge (0.040 of an inch) or less in thickness, a flange equal to the thickness of the metal is turned up and the weld is made without filler metal. Before welding, you should clean the joint surfaces of the metal with sandpaper or other abrasives and then apply a stainless steel flux. The torch tip used for welding stainless steel is usually one or two sizes smaller than the tip used to weld mild steel of the same thickness. Adjust the torch so you have a carburizing flame, as seen through your goggles, with an excess fuel-gas feather extending about 1/16 of an inch beyond the tip of the inner cone. Hold the torch so the flame makes an angle of 80 degrees to the surface of the sheet. The tip of the cone should almost, but not quite touch the molten metal. Make the weld in one pass, using a forehand technique. Do not puddle or retrace the weld. A uniform speed of welding is essential. If it is necessary to stop the welding process or reweld a section, wait until the entire weld has cooled.
OXYGAS WELDING OF NONFERROUS METALS
Although brazing and braze welding are used extensively to make joints in nonferrous metals, there are many situations in which oxygas welding is just as suitable. The joint designs are the same for nonferrous metals as for ferrous metals in most cases. Oxygas welding of nonferrous metals usually requires mechanical cleaning of the surfaces before welding and the use of flux during welding. Filler metals must be suitable for the base metal being welded A separate section on aluminum and aluminum alloys is included as part of this chapter since you may need more detailed instructions in welding these materials.
Pure copper can be welded using the oxygas torch. Where high-joint strength is required you should use DEOXIDIZED copper (copper that contains no oxygen). A neutral flame is used and flux is required when welding copper alloys. Because of the high thermal conductivity of copper, you should preheat the joint area to a temperature ranging between 500°F to 800°F and use a larger size torch tip for welding. The larger size tip supplies more heat to the joint and thus makes it possible to maintain the required temperature at the joint. After welding is completed, cool the part slowly. Other than the extra volume of heat required, the technique for welding copper is the same as for steel.
Copper-zinc alloys (brasses) can be welded using the same methods as deoxidized copper; however, a silicon-copper rod is used for welding brasses. The rods are usually flux-coated so the use of additional flux is not required. Preheat temperatures for these metals range between 200°F to 300°F.
Copper-silicon alloy (silicon bronze) requires a different oxygas welding technique from that used for copper and copper-zinc. You weld this material with a slightly oxidizing flame and use a flux having a high boric acid content. Add filler metal of the same composition as the base metal; as the weld progresses, dip the tip of the rod under the viscous film that covers the puddle. Keep the puddle small so the weld solidifies quickly. A word of caution: when welding copper-zinc, you should safeguard against zinc poisoning by either doing all the welding outdoors or by wearing a respirator or by both, depending on the situation
Oxygas welding of copper-nickel alloys requires surface preparation and preheating. The flux used forContinue Reading