Here is some info on our most popular cast iron product, it is available in Tig, doesn't require preheating and can weld steel to cast !


http://webapp1.cronatronwelding.com/cronatron/showItem?itemNum=CW01034

The very best way to weld smaller castings, especially exhaust manifolds, is with the Oxy-Acetylene fusion welding process. You use a gray cast iron filler rod with a silicon base "ferro flux" (trade name). This gives you an exact base metal match, which is very important when welding components which incur vibration and excessive levels of heat. The high expansion rate of an exhaust manifold requires a filler metal that will expand at the same rate as the casting....if that doesn't happen, cracking will occur.
This process takes some practice, but if you have experience in gas fusion welding carbon steels it's not too much of a stretch. Cast iron does not puddle as fluid as carbon steel, so it's a slower process. Also, some stirring of the weld pool with the flux coated filler rod helps to float impurities to the surface. Flux is added to the rod by heating it and then dipping it into the container.
The key is even and sufficient preheat temperatures, maintaining those temperatures, and then a very slow cooling rate. A furnace is preferred, but an oxy-aceylene torch with a rose bud will work. Ideally build a firebrick dam under and around the casting and then slowly and evenly bring the casting to around 800 degrees F. About an inch either side of the prepped area will need to be brought to a dull red. It's important to bring the casting up to temperature slowing so as not to shock the casting. Post heat to at least 800 degrees and provide very slow cooling....ideally in a furnace, or covered with heated sand or fire blankets.