Conditioning esp. densifying reusable plastics, esp. expanded polystyrene - by grinding and rounding particles by repeated contact with surface at temp. below m.pt., avoiding damage

摘要

In a conditioning process, esp. for increasing the bulk density of re-usable plastics material (I), esp. expanded polystyrene (PS), is first ground to particle (II) of a size suitable for the end prod. The novelty is that (II) are then rounded by repeated contact with a surface (III) at a temp. below their m.pt. (II) impinge on (III), pref. at an angle less than 90 deg. and pref. at high speed so that they rebound, and the speed and temp. pref. are selected to prevent (II) sticking to (III). The (III) temp. is above the softening temp. but at least ca. 30 deg.C below the m.pt. of (II); pref. 70-130, esp. 90-110 deg.C for PS. During rounding, (II) also impinge on a surface at or below room temp. and are rotated. ADVANTAGE - (II) are densified to the required bulk density and the surface is freed from fibrous material, which can block mould nozzles in the foaming process, so that these need cleaning up to once a week. There is no loss of foaming capacity or other damage, since rounding is carried out at a lower temp. than usual.