The screw is the main component of the extruder and can be said to be the heart of the extruder. Mainly plasticizing plastics. The technical characteristics of the screw: the smaller the pitch, the larger the positive thrust of the screw and the less the plastic flow. At present, most of the single-screw extruders use a single-start thread. Thread groove depth has a large effect on shear rate and thermal conductivity. For PVC plastics, because its viscosity in the molten state is very sensitive to temperature, it is necessary to use a screw with a deep groove. The groove of soft quintal chloride is more rigid than that of rigid polyvinyl chloride.
The groove depth is larger. Generally, the aspect ratio is (20~24): when the compression ratio is 1 to 2.8, the compression ratio is usually 3 when the aspect ratio is 18:1. The larger the aspect ratio, the more complete the material is re-mixed in the screw and the better the degree of plasticization. Screw cooling device: The extrusion process requires that the friction of the material to the material is greater than the friction of the material when the screw is used. Therefore, it is necessary to keep the temperature of the screw lower than that of the cylinder.
Head of the screw: Since the melting temperature of the PVC heavy material is close to the processing temperature, it is important to properly select the screw head to maintain normal operation of the extruded polyvinyl chloride plastic, especially the hard polyvinyl chloride plastic. of. The plastic head must be designed to smoothly melt the plastic nose from the screw into the forming head. Generally, the volume between the screw head and the filter plate is close to the volume of a groove of the extrusion section. The distance between the screw head and the filter plate is generally taken as (0.07~0.1) D (D is the screw diameter).
There are many types of twin-screw structures, such as ordinary screw, vented screw and non-compression ratio screw.
