A common method of molding is to use pre-expanded beads, in which beads are partially expanded by steam (although hot air. hot water, or an oven can also be used) in an open top chamber. The beads are then placed in a storage bin and allowed to stabilize tor a period of from 3 to 12 hours. They can then be molded into shapes in the manner described above. /////
Polystyrene beads are available in three sizes: small, for cups; medium, for molded shapes; and large, for the molding of insulating blocks (which can then be cut to size). The bead size selected depends on the minimum wall thickness of the product Beads can also be colored prior to expansion, and they are available integrally colored
Polyurethane foam processing, for products such as cushions and insulating blocks, involves several processes. Basically, it starts with the mixing of two or more chemical components; the reaction forms a cellular structure which solidifies in the mold Various low-pressure and high-pressure machines, having computer controls for proper mixing, are available.