Handbook-Welding Cast Iron

14 Practical Hints If you are preheating a casting with the torch, or in an improvised furnace, watch carefully to make sure that you do not overheat any part of the casting. It should never get more than dull red. If it gets too hot, it may warp from its own weight, and become completely unrepairable. Try to keep the thinner sections farthest from the heat source if an improvised preheating furnace is being used. Just as the foundryman must rely on experience, and the use of correct foundry practices, to feel quite sure that a finished casting with no visible defects is sound, so a welder must follow correct procedures, with emphasis on proper preheating and cooling, if he is to feel confident that a good-looking fusion weld in cast iron will stand up in service. Of course, he can leak- test a weld in a water jacket. A weld which must be leaktight, but cannot be tested under pressure in the repair shop, can be checked rather well by applying kerosene to one side of the weld. Kerosene will work its way rapidly through even a slightly porous weld. But such tests cannot be conclusive as to the overall soundness of the weld, and the final condition of the repaired casting.