Method and apparatus for a - or repeated preexpansion of particles from driving means hold strength thermoplastic material

摘要

Expansion of thermoplastic particles or pellets contg. a blowing agent is effected by passing them through a heated chamber in which mechanical agitators are operated at =2 different speeds. Pref. the chamber is a vertical cylindrical tower with coaxial agitator shafts driven so that feedstock pellets near the base of the tower are agitated by paddles turning quickly relative to paddles moving in the upper zones of the tower from which the fully expanded particles discharged. Suitable for expanding e.g. polystyrene granules incorporating pentane to bulk densities of 10-15 kg/m3 in a single pass through the tower. Provides sufficient agitation to prevent agglomeration during the initial expansion from about 800 g/l to about 40-60 g/l together with agitators moving sufficiently slowly not to damage the more fragile particles with densities in the range 15-40 kg/m3.