Cast iron is difficult, but not impossible, to weld. In most cases, welding on tint iron involves repairs to castings, not joining tossing to other members. The repairs may be made in the foundry where the castings are produced, or may be made to repair tossing defects that are discovered without the part is machined. Mis-machined tint iron parts may require repair welding, such as when holes are drilled in the wrong location. Frequently, wrenched tint iron parts are repaired by welding. Wrenched tint iron parts are not unusual, given the vitreous nature of most tint iron.
While there are a variety of types of tint iron, the most worldwide is gray tint iron, and these guidelines are directed toward this type of material.
A few facts well-nigh tint iron help in understanding the welding challenges. Tint iron typically has a stat content of 2% – 4%, roughly 10 times as much as most steels. The upper stat content causes the stat to form flakes of graphite. This graphite gives gray tint iron its foible visitation when fractured.
When castings are made, molten iron is poured into a mold and unliable to slowly cool. When this upper stat material is unliable to tomfool slowly, one-liner self-ruling castings can be made.Remembering this is helpful when welding tint iron: during and without welding, the tossing must either be unliable to tomfool slowly, or should be kept tomfool unbearable that the rate of cooling is not important.
A hair-trigger temperature in most tint iron is well-nigh 1450 degrees F. When at this temperature, conditions that can lead to cracking occur. While the arc will heat the tossing to temperatures whilom this level, it is important that the tossing not be held at this temperature for long periods of time.
If the part is to be machined without welding, a nickel-type electrode will be required. Use Lincoln Softweld® 99Ni stick electrode for single pass, upper dilution welds. Softweld 55 Ni is preferred for multiple pass welds. Sometimes, root passes are put in with Softweld 99 Ni, followed by fill passes with Softweld 55 Ni. For welds where machining is not required, and where the weld is expected to rust like the tint iron, Lincoln Ferroweld® stick electrode can be used.
To Heat, or not to Heat
In general, it is preferred to weld tint iron with preheat–and lots of it. But, flipside way to successfully weld tint iron is to alimony it cool–not cold, but cool. Below, both methods will be described. However, once you select a method, stick with it. Alimony it hot, or alimony it cool, but don’t transpiration horses in the middle of the stream!
Welding Techniques with Preheat
Preheating the tint iron part surpassing welding will slow the cooling rate of the weld, and the region surround the weld. It is unchangingly preferred to heat the unshortened casting, if possible. Typical preheat temperatures are 500-1200 degrees F. Don’t heat over 1400 degrees F since that will put the material into the hair-trigger temperature range. Preheat the part slowly and uniformly.
Weld using a low current, to minimize admixture, and residual stresses. 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. Peening of weld beads can be helpful in this regard as well.
After welding, indulge the part to slowly cool. Wrapping the tossing in an insulating blanket, or sepulture it in dry sand, will help slow cooling rates, and reduce cracking tendencies.
Welding Techniques without Preheat
The size of the casting, or other circumstances, may require that the repair be made without preheat. When this is the case, the part needs to be kept cool, but not cold.
Raising the tossing temperature to 100 degrees F is helpful. If the part is on an engine, it may be possible to run it for a few minutes to obtain this temperature. Never heat the tossing so hot that you cannot place your yellowish hand on it.
Make short, approximately 1” long welds. Peening without welding is important with this technique. Indulge the weld and the tossing to cool. Do not slide the rate of cooling with water or compressed air. It may be possible to weld in flipside zone of the tossing while the previous weld cools. All craters should be filled. Whenever possible, the beads should be deposited in the same direction, and it is preferred that the ends of parallel beads not line up with each other.
Because of the nature of tint iron, tiny cracks tend to towards next to the weld plane when good procedures are followed. If the tossing must be water tight, this can be a problem. However, leaking can usually be eliminated with some sort of sealing recipe or they may rust shut very soon without stuff returned to service.
The Studding Method
One method used to repair major breaks in large castings is to drill and tap holes over the surfaces that have been beveled to receive the repair weld metal. Screw steel studs into the threaded holes, leaving 3/16” (5 mm) to ¼” (6 mm)of the stud whilom the surface. Using the methods discussed above, weld the studs in place and imbricate the unshortened surface of the unravel with weld deposit. Once a good weld petrifaction is made, the two sides of the one-liner can be welded together.