Shell Moulding Material:

Various moulds are now being made by the shell-moulding procedure that offers better surface finish than might be obtained along ordinary sand moulding, better dimensional accuracy, and a superior production rate with reduced labour needs. In many cases, the procedure can be fully mechanized and adapted for mass production. The complete shell moulding procedure has been described in the next unit.

The sand used for shell moulding consists of a mixture of the following ingredients  are following:

 (a) Dry sand grains, AFS fineness 60 to 140 distributed over 4 to 5 screens.

(ib) Synthetic resin binder, 3 to 10 % by weight. Resins that may be utilized are the phenolformaldehydes, alkyds, urea formaldehydes, and polyesters. The resin should be a thermosetting plastic, and is utilized as a powder in dry mixtures. It might also be applied as a liquid and dried on the sand grains then. For moulding, the mixture should be dry and free flowing.