Handbook-Welding Cast Iron

12 Practice. The bevelled edges of the pieces should be filed thoroughly. If the bottom of the bevelled edge is sharp, it should be filed to give you square edges, at least 2 mm (3/32 in.) deep, at the root of the weld. The pieces should be positioned so that there is a gap of about 1.6 mm (1/16 in.) at the weld starting point and about 5 mm (3/16 in.) at the finishing point. For fusion welding of cast iron, a neutral flame should be used, not the slightly oxidizing flame suggested for braze welding. First preheat the entire weld zone thoroughly with the torch flame. Try to reach dull red heat along the entire length of the welding vee. Then heat the bottom of the vee, at the starting end, until the actual melting has started. Angle the torch flame as you did in steel welding; keep the inner cone at least 3 mm (1/8 in.) from the metal, however. When a small puddle has formed at the base of the vee, move the flame from side to side to melt down the sides of the vee gradually. Only after you have a fair-sized puddle should the rod, which has been preheated in the flame and dipped in the flux until it is well-coated, be introduced into the puddle. From this point on, your aim must be to keep the rod in the puddle, and to allow the heat from the puddle, not the flame itself, to do the actual melting of filler metal. Try to avoid withdrawing the rod from the puddle except when more flux is needed on the rod. Never hold the rod above the puddle and allow it to melt into the puddle drop by drop. Direct the flame against the puddle, and against the sides of the vee. You must make the weld in one pass, not two or three. Therefore, you must not allow the puddle to advance too rapidly along the root of the vee. Keep the rod in the puddle, fill the vee completely for a length of perhaps one inch, then redirect the flame to melt the lower edges of the vee and allow the puddle to advance. You will find the puddle more fluid than the puddle you handled in steel welding, since cast iron does not have the fairly wide ”mushy” range which make steel welding quite easy. Therefore, extra care to avoid letting the puddle run ahead and roll onto metal which has not yet reached fusion temperature is required. While making the weld, you may see gas bubbles or white specks in the puddle. During your first weld, we suggest that you ignore them. Thereafter, you must take pains to work them out as you go along, by adding flux to the rod, and by playing the flame around the specks until they float to the very top of the puddle. Once they float to the top, skim them off with the tip of the welding rod, and tap the end of the rod gently on the welding table to dislodge them. Removal of such visible particles (usually dirt, or impurities in the base metal) is essential if a full-strength weld is to be secured. Continued on next page...