Extruders for plastic granulation are the main devices of the granulating line, responsible for agglomeration, homogenisation and proper moulding of plastic for the further recycling stages. Depending on configuration, ranging from the single-screw systems to cascade systems, extruders are designed for extrusion of shredded, lightly and strongly printed materials such as: PP, PE, LLDPE, LDPE, PS, ABS in the form of films and plastic scrap.
The advancement of processing on extruders consists in subjecting the processed material to the appropriate physical processes such as compaction, compression and moulding at high temperatures. The material in the form of plastic scrap or film flakes is fed to the feed hopper or compactor (where it is preheated and compacted) and then transfered to the screw in the extruder cylinder. The screw rotational movement transports the material to the plasticizing (melting and metering) zone, where by the heat from the heating elements (heaters) and the friction between the screw and cylinder, it undergoes to melting and homogenisation. The obtained homogeneous material is then fed with the appropriate speed to the extruder die, where it is subjected to a proper moulding.
To ensure better plasticization of the printed waste, it is necessary to use a degassing system in the extruders of granulating lines. This system ensures effective reduction of the gas produced during the extrusion and prevents the formation of the defects in the form of air bubbles on the final product.