Plaster Moulding : In this method, the mould is prepared in gypsum or plaster of paris. In practice, the plaster of paris is mixed with tale, asbestos, fibers, silica flour and a controlled amount of water to form a slurry. This plaster slurry is poured over the metallic pattern confined in a flask. The mould is vibrated and the slurry allowed to set. The pattern is removed after about 30 minutes, when the setting is complete and the mould is dried and backed by slowly heating it to about 200ºC in a conveyer oven.
Ceramic Moulding : In ceramic moulding, a thick slurry consisting of specially developed ceramic aggregates and a liquid chemical binder (alcohol based silicon ester) is poured over the reusable split and gated metal pattern which is usually mounted on a match plate.
Vacuum Process : In this process the mould is made from reclaimable dry sand and is vacuum sealed in a plastic film. Due to application of vacuum the surface finish is excellent and vacuum holds the mould rigid during the pouring and solidification of casting.
Permanent Mould Casting : While in the sand casting the moulds are destroyed after solidification of castings, the moulds are reused repeatedly in the permanent mould castings. This requires a mould material that has a sufficiently high melting point to withstand erosion by the liquid metal of pouring temperature, high enough strength not be deform in repeated use and high thermal fatigue resistance to resist premature crazing (the formation of thermal fatigue cracks) that would leave objectionable marks on the finished castings.
Pressed Castings : It is another method of producing hollow castings from permanent moulds but differs from gravity die casting and slush casting in operation. In this case a definite amount of molten metal is poured into the mould and then close fitting cores are pushed in the cavities, so that the molten metal can be forced into the mould cavities.