Processes involved in the manufacture of Grey Iron Castings
By vr foundries on 12-May-2018
In this rather short blog let us discuss the Manufacture of Grey Iron Castings & 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 mold is used into which liquefied grey iron is poured and 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 molds 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 molding or Sand casting comes as an economical and low-maintenance option that has a sandy mixture as a mold. There are four main mixtures preferred by manufacturers – no bake, skin-dried, dry sand, and green sand.
No-bake molds are disposable molds consisting of sand, a catalyst, and a quick-setting resin. A casting flask is used to make ‘no bake molds’, generally made of wood, plastic, or wood. No bake molds are made out of a heat-free, cold-setting casting process.
Dry sand molding involves mixing unbonded sand with a chemical binder or an adhesive, shaped to create a mold, and then baked at a fixed temperature to finish. Castings are made by pouring the molten grey iron into the mold, taking its shape.
In skin-dried or air-dried molding, the operator creates a mold by mixing water, bonding additives, a binder like clay, and sand, and finally dries it out using a heating lamp and torch. Greensand molds 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 a 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 cars and trucks, tractors, windmills, oil rigs, and piano harps. These are the processes involved in the manufacture of grey iron castings, along with the types of castings produced by iron casting foundries.