Shell Moulding

A shell mould consists of a sand shell, varying in thickness between 4-10mm. The sand particles are bonded together with phenolic resins giving a permeable mould. The production of shell moulds may be automated which lends itself to medium to high production runs. The resin coated sand is placed on a hot metal pattern; this is fired in an oven to harden the shell. After cooling, the shell is removed from the pattern and is ready for use. Molten metal is then poured into the shell mould cavity and allowed to cool. The mould material is broken off the casting. Better dimensioned tolerances are possible than with sand moulding, which reduces machining costs. Fine surface finishes equal to that of permanent moulds (12~130rms) may be obtained, and consistently reproducible thin castings with fine detail may be made. The process is more costly than sand, permanent mould or die casting.