ROTATIONAL MOULDING
Process:-
Rotational moulding is known as roto-forming. Rotational moulding is a process in which a pre determined mass of powder, usually thermoplastics, is charged in a closed mould and caused to simultaneously rotate into two planes while in hot oven. The temperature would be between 260 and 485°C depending on material and product. This causes the powder to melt and uniformly deposit on the mould surface. When the melting face is completed the moulds are moved, while still rotating, from the oven into a cooling chamber where the moulds are cooled by air circulation or water spray, internal cooling to speed the cycle by means of Nitrogen or water fog is currently being investigated as means of lowering the cost.
After the cooling cycle the moulds are opened, and moulded parts are removed. Gasoline tanks, toys, plastics balls etc. are produced by this method.
Advantages of rotational moulding are :
- Tooling is simple and inexpensive.
- Parts produced are strain free.
- Parts are usually made with uniform wall thickness.
- No weld lines, sprue marks, gate marks / ejection marks on the parts
- No scrap, or very little, is produced.
- Hollow parts are easily produced with simple tooling.
- Usually no secondary operations are required.
- Wall thickness change can be easily made without new tooling or tool modification.
Disadvantages are:
- Not suited generally for large production runs of small parts.
- Not suitable for production of parts with wall thickness less than 0.5.
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