In Plastic Industries, three main processes are known to the industries (1) Extrusion (2) Blow Moulding (3) Injection Moulding.
In all these processes, the main drawback is the high tooling or die cost of the equipments against the single piece weight of the product. For the large Hollow Component the Rotational Moulding is most economical process. The basic advantages of the process are as below.
Economic tooling costs
Single piece Construction
Weight reduction as compared to most Processes
Uniform wall thickness
Variety of finishes and colours
The ability to produce multi-wall Mouldings
Metal inserts as integral parts
Minor undercuts are possible with no draft angle required
Products from this process can offer excellent load-bearing and resistance to stress cracking and corrosion
Ease of Operation.
Rotational Moulding, also called Roto Casting or Roto Moulding is a unique process because the heating, shaping and cooling process take place inside a mould with no application of pressure. The process is carried out at the ambient pressure, which makes the products withstand environmental stress and crack resistant during use.
- A predetermined quantity of blended polyethylene resin powder is placed inside a cold mould (usually of aluminum or steel sheet metal).
- The mould is then rotated (Bi Axially) and gradually heated inside the oven. As the metal mould gets heated, the polymer resin powder melts and the molten resin eventually get distributed (Coated) along the inner surface of the mould. When all the powder has melted & distributed, the mould is transferred to a cooling chamber keeping the mould rotating.
- The Bi-Axial rotation is continued until the cooling process is finished and the polyethylene has solidified. The mould is then opened and the finished product is removed. Given process chart helps understand the system.
LLDPE / MDPE / HDPE (Roto Moulding Grade)
MFI Between 3.0 to 4.5 and Density
Between 0.92 to 0.95 are widely used.