TABLE OF CONTENTS As described in Chapter 1, the basic principle of rotational moulding involves heating powdered (or liquid) plastic, and subsequently cooling it, inside a hollow shell-like mould. During the heating stage, the mould is rotated so that the melted plastic forms a coating on the inside surface of the mould. The rotating mould is then cooled so that the plastic solidifies to the desired shape and the moulded part is removed.
There are many methods that can be used to achieve the three essential requirements of the process that is, (a) mould rotation, (b) heating and (c) cooling. Early types of rotational moulding machine involved the heating of the rotating mould by an open flame. The mould rotation usually involved a rock and roll motion. This description was used because the mould rotated through 360 about one axis and was rocked backwards and forwards about the other axis. Few modern commercial rotational moulding machines involve direct flame heating of the mould but the rock and roll rotation mechanism is still used in some cases.
Most modern rotational mould machines involve full biaxial rotation about two perpendicular axes and use a hot air oven to heat the rotating metal mould. Other mould heating methods that are less common include electrical elements on the mould, infrared or microwave heating, or hot oil circulated in a jacket around the mould.
As stated above, the common aspects of all rotational moulding machines are that the mould...
