Rotational microwave moulding of expandable polystyrene

Abstract

Expandable polystyrene (EPS), a white polymeric material that is generally used for protection and containment of finished products such as domestic household appliances and computers, is moulded using the steam injection process. The process involves initially injecting the required amount of pre-expanded EPS beads into the mould chamber. Steam is then introduced into the chamber through wall perforations or vents in the mould, which causes the beads to expand and fuse together. The moulded product is then cooled before being ejected from the mould. This process is highly inefficient in energy utilisation. In search of a more efficient energy saving process, preliminary experiments conducted have found that microwave energy can be used as an alternative to steam for beam fusion in the processing of EPS. Results showed that polystyrene cushion could be moulded directly from the raw material EPS beads using a static mould. Subsequent testing of the moulded polystyrene cushions indicated that the bead fusion was acceptable, although not uniform: this may cause variation in the compressive strength of the foam. The present paper discusses a method to improve fusion of the cushion. Preliminary tests were conducted using different static orientations of the mould during processing and the effects on fusion were analysed. Subsequently, a rotational mechanism was designed and fabricated to permit the mould to be rotated during processing. The investigations conducted have found that reasonable improvement in terms of better fusion can be achieved when the rotational mechanism is used.