METHOD FOR PRODUCING SUPERFICIALLY CRYSTALLINE SPHERICAL GRANULES BY MEANS OF AIR-COOLED HOT DIE FACE PELLETIZING AND APPARATUS FOR CARRYING OUT THE METHOD

摘要

The invention relates to a method and to an apparatus for producing superficially crystalline spherical granules by means of air-cooled hot die face pelletizing in a cutting chamber (2), wherein initially the crystallisable plastic material is melted and then the crystallisable plastic material is extruded through a perforated plate (3). During the air-cooled hot die face pelletizing with at least one cutting blade (5) moved relative to the perforated plate (3), the perforated plate (3) is temperature-controlled and a viscosity of the melt of the plastic material is retained within nozzle orifices (4) of the perforated plate (3). A superficial cooling of the dry-cut granules is performed by means of a centripetally inflowing process gas for cooling to a superficial crystal nucleation temperature, the crystal nucleation temperature lying below an optimal crystal growth temperature and above a glass transition temperature of the crystallisable plastic material. Then, by control of the quantity of process gas at an adiabatically set temperature, an average granule temperature is maintained in a range of an optimal crystal nucleation temperature at a level above the crystal nucleation temperature and below a melting temperature of the plastic material.