A method for preexpansion of beads made of thermoplastic synthetic resin materials as well as a method and apparatus for the formation of the optionally foamed nsta ends of thermoplastic synthetic resin materials

摘要

Thermoplastic resin beads containing a blowing agent are continually agitated in a heated pre-expansion chamber to a temperature near the fusion point of the beads and above the boiling point of the blowing agent at substantially atmospheric pressure; the beads soften and expand; a dry gaseous medium may be swept over the beads to remove moisture and any blowing agent which has escaped. Thereafter the chamber is evacuated until a substantial amount of blowing agent is removed from the beads and the expanded beads are then allowed to return to atmospheric pressure. As a preferred embodiment of the invention, steam may be injected into the chamber prior to evacuation. This serves to further expand the beads, and facilitates the removal of the blowing agent. This embodiment also provides a means of manufacturing particularly stable low- density foam. The expanded beads, after they are restored to atmospheric pressure are discharged to a storage facility and maintained at an elevated temperature for immediate use in a molding apparatus. The expanded hot beads may be fed directly by air injection conveyors to mold cavities and molded into the desired articles. Apparatus comprising heating, mould and transfer means is disclosed and illustrated.