Rotational Moulding involves a heated hollow mould which is filled with a charge or shot weight of material. It is then slowly rotated (usually around two perpendicular axes) causing the softened material to disperse and stick to the walls of the mould. In order to maintain even thickness throughout the part, the mould continues to rotate at all times during the heating phase and to avoid sagging or deformation also during the cooling phase.
The process was applied to plastics in the 1940s but in the early years was little used because it was a slow process restricted to a small number of plastics. Over the past two decades, improvements in process control and developments with plastic powders have resulted in a significant increase in usage.
Normally all rotation moulding systems have a number of parts including moulds, oven, cooling chamber and mould spindles. The moulds are used to create the part, and are typically made of aluminium. The quality and finish of the product is directly related to the quality of the mould being used.
The oven is used to heat the part while also rotating the part to form the part desired. The cooling chamber is where the part is placed until it cools, and the spindles are mounted to rotate and provide a uniform coat of plastic inside each mould.