Processes involved in the manufacture of Grey Iron Castings

Processes involved in the manufacture of Grey Iron Castings

In this rather short blog let us discuss the three different grey iron casting processes: Die Casting, Centrifugal Casting and Ductile Iron Casting.

Centrifugal casting is usually a method employed to cast cylindrical parts and components giving outer surfaces that are finely grained with uniform dispersion. To work, a mould is used into which liquefied grey iron is poured into and is rotated at full speeds as it is introduced. Centrifugal casting is unique in many ways as it is generally used to make stock materials for further machining, in contrast to parts shaped for particular applications. Grey iron castings produced through this method come in a range of specifications – length, diameter, thickness and length.

Die casting features fast production or a continuous cycle of iron castings. Reusable moulds are used that are made to go in the shape of the desired finished piece. Manufacturers die cast the metal by injecting it into the die and applying pressure. This method is applicable for small to medium parts that need impeccable surface quality, meticulously produced details and good dimensional stability.

Sand moulding or Sand casting comes as an economical and low maintenance option that has a sandy mixture as a mould. There are four main mixtures preferred by manufacturers – no bake, skin-dried, dry sand and green sand.

No bake moulds are disposable moulds consisting of sand, a catalyst and a quick- setting resin. A casting flask is used to make ‘no bake moulds’, generally made of wood, plastic or wood. No bake moulds are made out of a heat-free, cold-setting casting process.

Dry sand moulding involves mixing of unbonded sand with a chemical binder or an adhesive, shaped to create a mould and then baked at a fixed temperature to finish. Castings are made by pouring the molten grey iron into the mould, taking its shape.

In skin-dried or air-dried moulding, the operator creates a mould by mixing water, bonding additives, a binder like clay, and sand, and finally dries it out using heating lamp and torch. Greensand moulds are done in the same way, except for the addition of the heat drying process and the bonding additives.

Ductile iron casting or spheroidal graphite casting, nodular iron casting or SG iron casting was developed by Keith Mills in 1943. The casting process involves ductile iron (iron alloys having controlled microstructures) and melting process, plus the use of one of the elements (like magnesium, yttrium or cerium) making it quite ductile.

Ductile iron castings, when compared to grey iron castings, have a greater tensile strength and increased ductility. Ductile iron castings are used to produce sewer pipes, water pipes and components of car and trucks, tractors, windmills, oil rigs and piano harps.