Basic structure of single screw extruder
It mainly consists of five parts: extrusion system, transmission system, heating and cooling system, control system, head and die. The extrusion system consists of a screw, a barrel and a forming head; the transmission system consists of an electric motor, a speed reduction mechanism and a bearing; the heating and cooling system consists of a heater and a cooling water jacket. Although the single-screw extruder has been improved, its capacity efficiency is always low, and the output is largely determined by the extrusion pressure. The pressure of the single-screw extruder increases with the increase of the screw speed, so that the reflux pressure is also increased accordingly. If the powdery or very lubricated granular material is used for feeding, the forward thrust is small, so that the return pressure is small. Slips close to the previous thrust.
In the middle of the screw and the head, there is a filter or a filter plate, and its function is to increase the back pressure of the flow, so that the product is pressed tightly.
In order to improve the plasticizing effect, the flat filter plate is often used. When the plastic with high viscosity and poor thermal stability is extruded, such as hard polyvinyl chloride, the filter is not placed, only the filter plate is placed, and the perforation of the filter plate is arranged. For concentric circles or hexagons, the opening area is 30%~70% of the total area, the hole diameter is 3~7mm, and the screw diameter is large. The distance between the filter plate and the head of the screw is typically 0.1D. The heating and cooling of the barrel are generally controlled in stages, each length is 4 to 7 times the screw diameter, and the head and die are separately controlled. There are three methods for barrel heating: heat carrier (oil, steam) heating, resistance heating and induction heating.
