Handbook-Welding Cast Iron

11 Fusion Welding The general rule for the oxy-acetylene fusion welding of gray iron castings is that the entire casting be preheated in a furnace to dull red heat (about 800⁰C), that the actual welding be done under conditions which will allow the retention of most of the preheat, and that the casting be allowed to cool slowly after the welding. Whenever possible, the casting should be reheated to a uniform temperature of about 750-800⁰C after welding, and cooling to room temperature should require at least one full day. When these conditions can be met, the results should be good. In some cases, depending on the size of the casting, and the thickness of its various sections, fusion welding can be done successfully with only local preheating to a dull red color. However, it would be unwise to attempt fusion welding without full preheat unless you have had considerable experience in the fusion welding of cast iron, and feel thoroughly competent to assess the effects of expansion and contraction on the whole casting. Few oxy- acetylene welders get the chance to acquire that kind of experience. You do not, however, require previous experience, or a preheating furnace, to acquire the basic skills involved in making a fusion weld. The welding action is quite different from that with which you are familiar (if you have previously welded only steel, or braze welded cast iron) so we suggest that you make a few practice welds in small pieces of cast iron. Materials Required for Practice Welds. You will need two or more pieces of 13mm (1/2-in.) cast iron, about 3 by 6 in. in area, with edges bevelled to an angle of 45 degrees (the same as suggested for braze welding practice). Torch tip size should be the same as that you used for braze welding 13-mm (1/2-in.) cast iron. Filler metal should be cast iron rod especially formulated for welding (either gray iron or nodular iron). A flux designed specifically for fusion welding of cast iron is required, such as OXWELD Ferro Flux. (Do not attempt to use a brazing flux. It will not serve this purpose.)