1450 Diamond Station Road, Ephrata PA 17522
After reading the article in the Readers Write column of August GEM on welding cast iron, it prompted me to share a procedure that works well for me. We have a metal working and machine shop and have yet to have a piece come back to us.
I agree with Mr. Larson on grinding the crack out far enough, because the more area you have for the weld to knit to, the better. The next step is to tack weld the pieces together properly. No preheating is required.
We use 1/8 nickel welding rods and run them at 110 or 120 amps AC. Have a small ball peen hammer handy. Now lay down about a ?' long weld bead, weaving back and forth to get a good hold on both pieces. Immediately peen the weld in while it is still red hot. The idea of peening the weld in is to relieve the casting of any stress caused by the weld shrinking and cooling thus replacing the preheating process. When you have it peened in well, repeat the welding and peening cycles till the entire weld is complete. If the crack is quite deep or wide to fill up, make more than one pass. Take your time in doing this; you will not be disappointed with your efforts. Make sure you get enough weld on it. Any excess can be ground off.
We feel this is a much simpler way to weld cast iron than trying to preheat it in a forge, which can be quite a major undertaking with a large casting. Operating a forge properly takes quite a bit of practice and learning.