The casting of iron is difficult but impossible. In most times, welding of cast iron uses repairs repair to castings and without joining casting to other members. The repairs are performed in the foundry where the castings are produced. Also, the process of the repair was performed after discovering the casting defects in machining. Mis-aligned parts of cast iron require repair welding. The conditions such as when holes are drilled in the wrong place. Broken cast iron parts also require welding for its repair. Broken pieces of cast iron are unusual and give the brittleness to cast iron.
Variety of cast iron present includes white cast iron, grey cast iron, ductile, nodular, or malleable iron. Among grey cast iron is most common. Cast iron fundamentally shows 2 to 4% carbon and ten times more steel. The presence of high carbon forces the carbon to form flakes of graphite. Here, graphite offers grey cast iron fractured appearance as a fundamental characteristic.
The welding of cast iron saves time and money, but it holds several challenges. When welding fails, it results in cracking and other damages. If the welded parts are critical, then it needs a welding facility and skilled welders to obtain desired results.
The welding process involves various steps that include the following:
- Identification of alloy
Here, cast irons are the iron-carbon alloy that has high carbon. The presence of carbon offers hardness. Here, hardness comes along with ductility. Cast iron is less malleable compared to other materials. The heating and cooling process during welding creates expansion and contraction of the metal and induces tensile stress. Cast iron is non-reactive to stretch and deformation after heating and stress conditions. Instead, they become challenging to undergo welding. The spectrochemical analysis is the best way to understand the material specifications.
- Cleaning of the cast iron
Before welding, it is essential to clean the casting iron properly regardless of the alloy. During material preparation for welding, it is essential to eliminate all surface elements. The area of the weld must be clean. The weld zone from casting must be free of paint, grease, oil, and pollutant. The application of slow heat to the weld area removes trapped gas and other elements. Further, before welding cast iron, a simple testing technique is essential on the cast iron surface. The test determines the presence of impurities and the porous nature of the cast.
All cast irons are susceptible to cracking under stress conditions, and hear heat control works well to prevent cracks. For welding of cast iron requires three steps as pre-heating, low heat inputs, and slow cooling. Due to thermal expansion, heat control is a necessary factor. The metal expands after exposure to warm temperatures. Local heating brings restricted expansion around the metal.
- Welding technique
Based on the suitability to cast iron alloy, one can select a welding technique. But following are the most common welding procedures that work well on cast iron.
- Stick welding
It is also known as shielded metal arc welding or MMA. The process uses a consumable electrode that is coated with flux. The process uses various electrodes based on the application, desired colour requirement, and machining level after welding. Several filler elements that work well in cast iron welding include cast iron covered electrodes, copper alloy electrodes, and nickel alloy electrodes.
- Oxy-acetylene welding
It is a welding process involving electrodes. Here, the process uses an oxy-acetylene torch to provide the energy for welding instead of an arc generated by the current. Here, cast iron electrodes and copper-zinc electrodes are suitable. Careless welding causes silicon loss and the formation of white iron during the weld. Before welding, melting of the welding rod is necessary.
- Braze welding
It is a standard method that connects cast iron parts due to the minimal impact on the base metal. Here, a welding rod offers the filler that attaches to the cast iron. The filler material’s low melting point does not weaken with the cast iron and sticks to the surface. Also, while performing welding of cast iron, cleaning the surface is essential as the joining depends on the filler’s quality.
Thermal contractions usually cause cracking of cast iron. Also, tensile stress develops on cast iron during weld cooling and contractions. Iron cast cracks after attaining stress level. The chances of cast cracking decrease with compressive stress to resist tensile stress during cooling. Welders use a peening technique to weld a deformable bead where the weld keeps soft. Peening lowers the risk of cracking in the weld and required while working with relatively ductile weld metal.
Cooling control is the final step in the welding of cast iron. The process involves insulating materials to reduce cooling or uses periodic heat to the weld to curb the natural cooling.