Posted by Joe Lorenzino on Friday, March 05, 2004 at 1:29AM :
In Reply to: OT- Cast Iron Fusion welding posted by Jack Cain on Thursday, March 04, 2004 at 6:11PM :
We still fusion weld cast iron exhaust manifolds at work. The process is easy to learn, as it is just another form of oxy-acetylene welding. The hard part, is finding the proper welding supplies, and coping with the heat. Cast fusion rods (they look like round or square sticks of cast iron) are hard to find, and the GOOD ones are quite expensive. Most welding suppliers can get fusion rods, but few stock them, and the last time I had to buy a 50# box as the smallest quantity. Arctec Alloys make a good one (I think it is Cast Iron # 1), and the local Grainger supply has a fairly good one as well. The other main ingredient is the proper flux. The best I have found is/was "Hemitox" made by Liquid Air. It is no longer available here, but MWP (Maintenance Welding Products) makes a workable flux.
Heads are fixed because they will fit in most preheat ovens, and warpage is not as much of a concern as with a block. The closer the area to be repaired is to an edge or end of the casting, the easier it is to fix. Cracks in the middle of a large chunk present more of a problem to repair, as they require the whole piece to be hot, rather then just at one end. I have fused parts for fancy old wood stoves, so as thin as 1/8" material is repairable.
We always use a reducing (fuel rich) flame on the torch, and lots of flux on CLEAN metal.(preferably sand blasted, and don’t forget to descale the rods too) Preheat with an oven or Tiger Torch, and keep it running until after you are done. If the part is not going to see thermal shock in operation, wrap it in insulation, or bury it in Vermiculite to help anneal it after welding. Good Luck J.V.L.