Working principle of single screw plastic extruder

Writer： admin Time：2020-02-19 14:14 Browse：℃

With the extensive application and development of plastic extruder molding technology, the types of plastic extruder are increasing, and the classification methods are also inconsistent. According to the space position of the screw, it can be divided into horizontal and vertical extruders; according to the speed of the screw, it can be divided into ordinary extruders, high-speed and ultra-speed extruders; according to the number of screws, divided into none screw extrusion machine, single-screw extruder, twin-screw extruder, multi-screw extruder, etc., the following introduces the working principle of single screw plastic extruder.

When the extrusion system is heated to a given process temperature and held for a certain period of time, start the motor and provide the required torque and speed to the screw through the reducer. The plastic in the hopper enters the screw groove through the feeding port under the effect of the weight or the thrust of the feeder. With the rotation of the screw, the plastic is transported forward under the friction of the barrel screw.

After the plastic enters the screw from the feed port, under the action of the rotating screw, it is transported forward by the friction between the inner wall of the barrel and the surface of the screw. In the molding process, after the material is added to the plastic extruder from the hopper in powder or granule form, the process of transportation, compaction, compression, melt plasticization, and homogenization to a homogeneous melt must be completed. In the screw feeding section, loose solid granules (or powder) fill the screw groove. As the material is continuously transported, the material begins to be compacted. When the material enters the compression section, due to the shallower depth of the screw groove and the resistance of the machine head, the plastic gradually forms a high pressure and is further compacted. At the same time, the material is heated outside the barrel and the screw and the inner surface of the barrel face the material. Under the action of the internal frictional shear heat generated by the strong stirring, mixing, and shear friction, the temperature of the plastic continuously increases, and at a certain point of contact with the barrel, the temperature of the plastic reaches the melting point and begins to melt. As the material is conveyed and heating continues, the amount of molten material gradually increases, while the amount of unmelted material decreases accordingly. At the end of the compression section, all the materials have changed to a viscous flow state, but at this time, the temperature at each point has not been uniform, and the homogenization effect of the homogenization section is relatively uniform. * The screw will quantify the molten material at a constant pressure and temperature. Squeeze into the nose. The middle die of the plastic extruder head is a forming part. The material passes through it to obtain a certain cross-sectional geometry and size. After cooling and shaping and other processes, a shaped product can be obtained.