Handbook-Welding Ferrous Metals

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Preparation for Welding. When faced with the problem of welding a broken steel casting, first consideration should be given to correcting any permanent distortion the casting may have suffered before it broke. Any heating and bending required to restore a casting to its original shape and alignment should be done before beveling and welding. Small steel castings usually require no more preparation than beveling of the edges to be welded, and good cleaning of the surfaces. Beveling can be done with a chipping hammer, portable grinder, or cutting torch. Follow oxy-acetylene beveling with grinding or wire-brushing. Large or intricate castings will often require preheating before welding, in order to eliminate the chance of permanent distortion. So much depends on the shape of the casting and the location of the place where welding must be done that it is impossible to provide guidelines which can be broadly applied to determine whether general preheating, local preheating, or no preheating is required. If general preheating is done, the casting should be heated bright red, and allowed to cool slowly after welding is completed. Welding Technique. Welding the casting, whether preheated or not, should usually be done in a series of passes, following the normal practice for heavy steel plate. If you are repairing a break which occurred in service, watch closely for evidence of sand holes or inclusions which may have been the primary cause of the break. These will show up as bright spots or unexpected craters in the molten metal. Work on these with the flame so that any inclusions (sand or slag) will be brought to the surface of the puddle, and then worked over to the edge of the puddle with the welding rod. When a break between a thin section and a thick section is being welded, take pains to direct more of the heat from the flame onto the heavier section. Building-Up and Filling-In Operations. Welding on steel castings often falls into two categories rarely encountered in work on rolled steel: the building up of lugs or bosses which may have emerged incomplete from the mold, or the filling-in of holes which cropped up unexpectedly. (These defects are more common in cast steel than in cast iron, because molten steel isn’t quite as fluid as molten cast iron; on the other hand, they can be corrected far more easily in cast steel than they can in cast iron.)