JOINT EDGE PREPARATION

Sheet metal is easily melted and does not require special edge preparation. In welding operations involving plate, joint edge preparation and proper spacing between edges are important factors. The thickness of the plates determines the amount of edge preparation required. The faces of square edges can be butted together and welded You can use this type of joint on plate up to 3/16 of an inch thick. For plate 3/16 to 1/4 of an inch thick, a slight root opening between the parts is necessary to get complete penetration. Plate more than 1/4 of an inch thick requires beveled edges and a root opening of 1/16 of an inch. For oxygas welding on plate more than 1/4 of an inch thick, bevel the edges at an angle of 30 degrees to 45 degrees, making the groove included angle from 60 degrees to 90 degrees. You can prepare the edges by flame cutting, shearing, flame grooving, machining, chipping, or grinding. In any case, the edge surfaces should be free of oxides, scale, dirt, grease, or other foreign matter.

Plate from 3/8 to 1/2 of an inch thick can be welded from one side only, but thicker sections should be welded by preparing the edges on both sides. Generally, butt joints prepared on both sides permit easier welding, produce less distortion, and ensure better weld qualities.

Heavy steel plate is rarely welded with oxygas unless other types of welding equipment are not available. The welding of heavy plate is just not cost effective because of the amount of gas consumed and time used to complete a weld. If at all possible, use a form of electric arc welding because the joint can be welded faster, cheaper, and there is less heat distortion

OXYGAS WELDING OF FERROUS METALS

Low-carbon steel, low-alloy steel, cast steel, and wrought iron are easily welded by the oxygas process. A flux is not necessary with these metals because their oxides melt at a lower temperature than the base metal.

During the welding process, you should enclose the molten puddle with the flame envelope to ensure the molten metal does not contact the air. If the metal is exposed to the air, it will oxidize rapidly. You also should avoid overheating the metal.

The proper flame adjustment is required to make a good weld Adjust the flame to a neutral or slightly reducing (carburizing) flame. Do not use an oxidizing flame. Manipulate the torch and rod so the tip of the oxygas cone is about 1/16 to 1/8 of an inch from the surface of the metal. Melt the end of the filler rod in the puddle, not with the flame. The welding of low-carbon steels and cast steels presents no special problems other than the selection of the proper filler rod Low-alloy steels usually require prewelding and postwelding heat treatment. This heat treatment relieves the stresses developed during the welding phase and produces the desired physical properties of the metal.

As the carbon content of a steel increases, welding becomes more difficult. Steels whose carbon content is within the 0.3-percent to 0.5-percent range are welded with a slightly carburizing flame. These low-carbon steels require postwelding heat treatment to develop their best physical properties.

High-carbon steel and tool steel require a slightly different technique. While protecting the parts from drafts, slowly preheat them to about 1000F. Complete the weld as rapidly as possible using a carburizing flame and no flux. Do not manipulate either rod or torch and add the filler metal in small amounts, as it is needed. You should use a smaller flame and lower gas pressure than that used for low-carbon steel. This is to ensure you do not overheat the steel. You must heat-treat high-carbon steels and tool steels after welding to develop the physical properties required.

The procedure for oxygas welding of WROUGHT IRON is the same as that for low-carbon or mild steel; however, you should keep several points in mind. Wrought iron contains a slag that was incorporated in it during the manufacturing stage. This slag gives the surface of the molten puddle a greasy appearance. Do not confuse this greasy appearance with the appearance of actual fusion. Continue heating until the sidewalls of the joint break down into the puddle. Best results with wrought iron are obtained when the filler metal (usually mild steel) and base metal are mixed in the molten puddle with a minimum of agitation

Oxygas welding of CAST IRON is not difficult, but does require a modification of the procedure used with steel. For material that does not exceed 3/16 of an inch 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 750F and 900F 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 1100F and 1150F 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.

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