Cast iron is not easy to weld and no two pieces are the same. It contains a high carbon content and is about 10 times that of steel. However while difficult you can learn how to weld cast iron by following some general practices.
Most cast welding evolves repairs or builds up jobs to castings such as pumps, couplings and the like. By its nature cast iron is brittle and some of the more common repairs are for cracks or broken casings. It can be welded by using stick electrodes such as Lincoln Ferroweld rods and in some cases it can be brazed using bronze filler rods.
One of the keys in learning how to weld cast iron is the heat treatment of the material. During the weld process and after the process the casting being worked on must be allowed to cool slowly if pre heating is used to avoid cracking as the weld cools. The other option is to keep the casting as cool as possible so that the rate of cooling is not so important.
Heating Cast Iron repairs.
The preferred method of repairs to castiron is to pre heat the whole casting and pre heat well. This will help to slow the cooling of the welded area. Pre heating temperatures should be around 500 to 1100 degrees F; this can be controlled buy the use of special heat crayons.
Try to keep welds small and use a low current, peening the weld is also helpful.Allow the casting to cool as slowly as possible to reduce the possibility of cracking. One method of doing this is to bury the casting in sand that will hold the heat and allow slower cooling. The other option is to use a special insulating blanket.
Non Heating Of cast Iron Repairs.
This method relies on keeping the casting as cool as possible, however getting the repair to about 100 degrees will assist, but if you find it hot to the touch then it is to hot. Using specific repair electrodes make short welds about an inch long and allow to cool naturally. Peening after the weld is an important part of the procedure to relieve stresses that can cause cracking.
Of the two methods always be sure to use only one and not to try and mix them up. Learning how to weld cast iron requires a fair amount of patience as you can see, it is often a slow and precise job that can take many hours to complete.
Joel Davis is a welding tutor and has been in the welding business for 25 years, check out other welding tips and how to weld cast iron techniques on his website, weldinghowto.com.