The process of casting, or molding of cast iron, is relatively easy and it goes as follows.
- Initially, normal iron that has been purified in the blast furnace, is poured out into casts and a good amount of carbon is mixed in, as it starts cooling down.
- This process of mixing takes place when the iron is in a semi-molten form. The temperature of the molten metal is about 1450° F. This prevents the carbon from burning and helps it blend with the molten matter.
- The iron which has now become cast iron is allowed to cool down gradually and properly.
- This process of cooling down makes the surface of the cast iron smooth and prevents it from cracking. A disturbance in the cooling process produces cracks or uneven breaks in the surface. The carbon that is present in the molten iron, forms flakes of graphite throughout the alloy that gives it the characteristic of brittleness.
Though cast iron has many uses, its brittle nature becomes a headache, when it comes to repairing objects made up of cast iron. Here are some of the processes that prove to be useful while repairing and welding it.
The application of preheat makes the process a bit complicated as appropriate heating equipment is also required. Most of the time the whole object that is to be welded, is heated up till a temperature that ranges between 500 to 1200 degrees Fahrenheit. However, one must avoid heating more than 1400 degrees, as the metal starts melting.
After the metal reaches the high temperature, start welding it using a low current. The low current should be used, to minimize admixture and residual stress. Sometimes it also becomes necessary to restrict the width of the welds. Ideally the welds must be minimized to about an inch long segment. An excessive weld can also lead to cracking of the surface.
The cooling process is extremely critical in the preheated welding process. The object must not be disturbed and must be allowed to cool down gradually. For gradual cooling, the object can be buried in sand or can even be covered with an insulation blanket.
It is also very important to let the welds cool down gradually. After the cooling process is complete, it is important to peen the extra welds that are deposited on the surface.
Cracks in the surface of cast iron tend to be very troublesome. It is advisable to use the preheated technique to seal cracks. One can also peen the metal, in order to make the welded crack smooth and even.
The studding process is an extremely complex process due to the fact that one requires a lot of skill for this method. The first step is to drill and tap holes on the surface that has been beveled.
The next step is to put in steel studs and weld them into the surface. The steel studs will help in covering the entire surface of the cracked location. The welded deposit can be further used to reinforce the crack.
It is recommended that one resorts to the non-preheating cast iron welding procedure for domestic purposes. While welding cast iron to steel, the preheating procedure proves to be highly effective.