With no two pieces of cast iron the same how to weld cast iron can become quite a challenge, and is most likely the most difficult material to weld. Much welding of cast iron is related to the repair and maintenance of iron casting in a multitude of industries both light and heavy.
Many cast iron repairs therefore are heavy cast components that are likely to have various contaminants such grease and soil attached. Obviously these contaminants first need to be removed by way of water pressure blasting or sand blasting before any cast iron welding can be performed.
There are two common methods of welding cast iron, the first being stick welding using cast iron electrodes and the second by brazing using bronze filler rods and using oxy acetylene gas welding techniques.
The most common repairs to cast iron are the welding of cracks in various castings. To repair iron casting cracks the area needs to be clean and free from contamination. The preferred method in how to weld cast iron is with preheating, and plenty of it. However, another way to successfully weld cast iron is to keep it cool. However, once you select either method, stick with it. Keep it hot, or keep it cool.
Preheating a casting needs to be well heated by using a heating torch and kept hot during the welding process, typically between 500 and 1200 F. For repairs using cast iron electrodes the weld run should be no longer than about 1 inch at a time and peening after the weld is most important. Allow the weld to cool very slowly, this can be done using a welding blanket or by burying the component in sand.
For welding using the cool method the casting needs to be heated but not so much as you cant put your hand on the casting. weld 1 inch at a time, peen the weld and allow to cool before proceeding.