Shell Moulding

Shell Moulding:

• Shell mould casting is recent invention in moulding techniques for mass production and smooth finish.

• Which is generally used for mass production of accurate thin castings with close tolerance of ±0.02 mm and with smooth surface finish.

• It consists of making a mould that has two or more thin lines shells [shell line parts, which are moderately hard and smooth].

• Moulding sand is prepared using thermosetting plastic dry powder and fine sand are uniformly mixed in a muller in the ratio 1:20.

• In this process the pattern is placed on a metal plate and silicon grease is then sprayed on it.

• The pattern is then heated to 205°C to 230°C and covered with resin bonded sand.

• After 30 second a hard layer of sand is formed over the pattern, Pattern and shell are then heated and treated in an oven at 315° for 60 sec.

• Then, the shell so formed as the shape of the pattern is ready to strip from the pattern.

• The shell can be made in two or more pieces as per the shape of pattern.

• Similarly core can be made by this process.

• Finally shells are joined together to form the mould cavity.

• Then the mould is ready for pouring the molten metal to get a casting.

• The shell so formed has the shape of pattern formed of cavity or projection in the shell.

• In case of unsymmetrical shapes, two patterns are prepared so that two shell are produced which are joined to form proper cavity.

Advantages of Shell Moulding:

• Accurate castings with good surface finishing.

• Machining is not required.

• Thin wall sections.

• Small holes can be created.

• Shell can be reused repeatedly.

• Thin wall sections.

Disadvantages of Shell Moulding:

• Cost of resin is high.

• High cost of metal pattern.

• Casting size is limited.

 

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