Describe Shell Molding Process with applications.

Describe Shell Molding Process with applications.
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Answer :

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Shell Molding:

[1] Fine Silica sand with liquid catalyst is dumped onto a hot pattern.

[2] Box is inverted so that the sand and resin fall on to a hot pattern, due to which a layer of mixture cures on the surface to form a hard shell.

[3] Box is repositioned so that loose uncured particles drop away.

[4] Dump box removed and then Mold is removed

[5] Clean the mold using sand blasting.


Shell Molding Applications:

Body panes, truck hoods, small size boats, bath tubs, shells of drums, connecting rods, gear housings, lever arms, etc. are cast using Shell Molding process.

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Answer :

Shell Moulding: It is a process in which the sand mixed with a thermosetting resin is allowed to come into contact with a heated metallic pattern plate, so that a thin and a strong shell of mould is formed around the pattern. Then the shell is removed from the pattern and the cope and drag are removed together and kept in an flask with the necessary back up material and the molten metal is poured into the mould. Generally dry and fine sand which is completely free from clay is used for preparing the shell moulding sand .

The first step in preparing the mould is the preparation of sand mixture in such a way that each of the sand grain is thoroughly coated with resin. Only metal patterns with the associated gating are used. The metallic pattern is heated to a temperature of 200 to 3500 C. The heated pattern is securely fixed to a dump box, as shown in fig. a, wherein the coated sand in an amount larger than required to form the shell of necessary thickness is already filled in.

Then the dump box is rotated as shown in fig. b, so that coated sand falls on the heated pattern. The heat from the pattern melts the resin adjacent to it thus causing sand mixture to adhere to the pattern. When a desired thickness of shell is achieved, the dump box is rotated backwards by 1800 so that the excess sand falls back into the box, leaving the formed shell intact with the pattern as shown in fig.d.

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Applications of shell moulding:

1. Cylinders and cylinder heads for air cooled IC engines

2. Automobile transmission parts

3. Cast tooth bevel gears

4. Brake beam

5. Transmission plannet carrier

6. Gear blanks

7. Small crank shafts

8. Refrigerator valve plate

9. Chain seat bracket

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