ANALYSIS OF THE FORMATION AND REMOVAL OF GAS-BUBBLES IN ROTATIONALLY MOLDED THERMOPLASTICS

The presence of internal bubbles is a characteristic feature of thermoplastic products manufactured by rotational moulding. The bubbles in the mouldings are generally undesirable since they reduce strength and stiffness and impair the appearance of the product if they occur at the surface. The bubbles form as a result of powder particles coalescing during the heating stage of the process and they subsequently decrease in size as a function of time and temperature. This paper presents a semi-empirical model to predict the bubble size which is likely to occur under any specified processing conditions.