It may be possible to weld in another area of the casting while the previous weld cools. Do not accelerate the rate of cooling with water or compressed air. Peening after welding is important with this technique. Never heat the casting so hot that you cannot place your bare hand on it. If the part is on an engine, it may be possible to run it for a few minutes to obtain this temperature. Raising the casting temperature to 100 degrees F is helpful. When this is the case, the part needs to be kept cool, but not cold. The size of the casting, or other circumstances, may require that the repair be made without preheat. Wrapping the casting in an insulating blanket, or burying it in dry sand, will help slow cooling rates, and reduce cracking tendencies. Peening of weld beads can be helpful in this regard as well.Īfter welding, allow the part to slowly cool. In some cases, it may be necessary to restrict the welds to small, approximately 1-inch long segments to prevent the build up of residual stresses that can lead to cracking. Weld using a low current, to minimize admixture, and residual stresses. Don’t heat over 1400 degrees F since that will put the material into the critical temperature range. Typical preheat temperatures are 500-1200 degrees F. It is always preferred to heat the entire casting, if possible. Preheating the cast iron part before welding will slow the cooling rate of the weld, and the region surround the weld. Keep it hot, or keep it cool, but don't change horses in the middle of the stream. However, once you select a method, stick with it. But, another way to successfully weld cast iron is to keep it cool-not cold, but cool. In general, it is preferred to weld cast iron with preheat-and lots of it. For welds where machining is not required, and where the weld is expected to rust like the cast iron, Lincoln Ferroweld® stick electrode can be used. Sometimes, root passes are put in with Tech-Rod 99, followed by fill passes with Tech-Rod 55. Use Tech-Rod® 99 stick electrode for single pass, high dilution welds. Tech-Rod® 55 is preferred for multiple pass welds. If the part is to be machined after welding, a nickel-type electrode will be required. While the arc will heat the casting to temperatures above this level, it is important that the casting not be held at this temperature for long periods of time. When at this temperature, conditions that can lead to cracking occur. Remembering this is helpful when welding cast iron: during and after welding, the casting must either be allowed to cool slowly, or should be kept cool enough that the rate of cooling is not important.Ī critical temperature in most cast iron is about 1450 degrees F. When this high carbon material is allowed to cool slowly, crack free castings can be made. When castings are made, molten iron is poured into a mold and allowed to slowly cool. This graphite gives gray cast iron its characteristic appearance when fractured. The high carbon content causes the carbon to form flakes of graphite. Cast iron typically has a carbon content of 2% - 4%, roughly 10 times as much as most steels. While there are a variety of types of cast iron, the most common is gray cast iron, and these guidelines are directed toward this type of material.Ī few facts about cast iron help in understanding the welding challenges. Broken cast iron parts are not unusual, given the brittle nature of most cast iron. Frequently, broken cast iron parts are repaired by welding. Mis-machined cast iron parts may require repair welding, such as when holes are drilled in the wrong location. The repairs may be made in the foundry where the castings are produced, or may be made to repair casting defects that are discovered after the part is machined. In most cases, welding on cast iron involves repairs to castings, not joining casting to other members. Cast iron is difficult, but not impossible, to weld.
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