Shell molding is the expandable mold metal casting process in which mold is a thin shell of sand held together by the binder usually a thermosetting resin. It was invented by the German in about 1940s. Thickness of the shell mold is about 9 mm
Steps involves in Shell molding
A metal plate is used to make the pattern. Shape of the patter is like the shape of shell mold you need. Metal plate is heated and they fixed on a container containing the sand and the thermosetting resign.
Container is inverted so that the sand and thermosetting resign may came into contact with each other. Heated plate melts the resign and makes a shell of sand around the pattern.
In order to remove the extra sand and uncured resign container is reposition again and plate is detached from it
Shell made is not properly cured yet so it is heated in a heater for proper curing.
After proper curing shell mold is removed from the patter.
Same process is preformed to make the other half of the mold and then both halves are attached in a box and supported by the sand. Molten metal is poured.
Finish metal product is removed from the shell mold
Advantages of shell molding
- Smother surface of the mold,
- Ease for the molten metal to flow.
- Good dimensional accuracy.
- Machining is not required.
- Usually no cracks in casting.
- Mechanizing for mass production gives good results
Disadvantages of Shell Molding
- Most expansive metal pattern.
- Takes more time.
- Not suitable for small production