TABLE OF CONTENTS A moulded plastic part must satisfy the customer s requirements in terms of functionality, longevity, aesthetics and economics. In all moulding methods for plastics, the interrelationships between moulding conditions, mechanical properties and part quality are very important. This chapter focuses on the mechanical aspects of the performance of rotationally moulded parts. It also considers other factors that are relevant to the quality of the moulded part, such as the wall thickness distribution of the plastic, the ways in which rotomoulded parts can be made stiffer, and the shrinkage, warpage and residual stress in the moulded part. Decoration technologies, such as in-mould graphics and painting, are also important ways of improving part quality, and so these are considered towards the end of the Chapter.
It is apparent from the preceding chapters that rotational moulding has characteristics that make it uniquely different from any other moulding method. For example, to make changes to the wall thickness distribution in the end product it is not necessary to make changes to the mould this can be achieved by changing the moulding conditions. Also, in rotational moulding it is possible to change the cooling rate, either deliberately or unintentionally, by quite significant amounts. Such changes can make significant differences to the mechanical properties and the tolerances in the end product. In particular, the shrinkage of plastic mouldings is very sensitive to the rate at which they are cooled from the melt state to the solid state.
It is important that moulders understand the...
