Cast iron is a metal that typically contains a carbon content of between two and four percent which is much larger than that found in many common steels. Because of the high levels of carbon, cast iron tends to be very brittle and difficult to weld. Much of the cast iron welding done requires repairs to existing castings instead of creating new castings.
- It is suggested that cooling or heating be used when welding cast iron is required. The most important factor in welding cast iron is that it be kept out of the 150 – 500 degrees Fahrenheit range. You should preheat the cast iron, which is preferred and to also use cooling techniques as well. It is important when welding cast iron that you do not change welding methods in the middle of a weld.
- When preheating the cast iron you should heat the entire casting slowly and evenly in the range of 500 – 1,200 degrees Fahrenheit. It is crucial to the success of your weld that you do not overheat the metal, most forms of cast iron begin to crack if the temperature reaches 1,400 degrees and above. In order to minimize stress you should use a low current to perform your weld.
- It is important that you keep the cast iron you are welding cool but not cold. If the cast iron part you are working on is located on a piece of powered machinery it may be necessary to run it for a short amount of time in order to achieve the correct temperature. It is important that the casting you are working with never get so hot that are not able to touch it with your bare hand. Use short welds about one inch long to avoid the cast iron from overheating.
- When welding cast iron you should expect small cracks to form, even when the proper technique is being used. It may be necessary for you to apply a sealing compound to joints that are required to be watertight.
- To repair any major cracks that may have formed during welding it is recommended that you use studding to repair the cracks. This involves screwing steel studs into holes that have been pre-drilled and tapped into the surface that is to be welded. The studs should be between 5 and 6 mm above the surface to work correctly. Once they have been put into place they are then welded into place.