Feeding section: The feeding section is composed of a f […]
The feeding section is composed of a feeding zone (also called a cooling hopper zone), a solid conveying zone and a transitional lag zone. Its function is mainly to compact and convey the plastic. The working process of this section is as follows:
After the plastic is fed into the hopper, the plastic is conveyed and compacted by the friction of the inner wall of the barrel and the surface of the screw under the action of the rotating screw. Typically, the plastic is conveyed forward in the feed section. According to experimental observations, usually near the end of the feeding section, due to the strong frictional heat, the plastic in contact with the inner wall of the barrel has reached the viscous flow temperature and begins to melt, and a transition zone appears.
The role of this section is to further compact and plasticize the plastic, so that the air enclosed in the plastic is pressed back to the feed port to discharge and improve the thermal conductivity of the plastic. The groove of this section should be compressed. The working process is as follows:
After the plastic enters the melting section from the feeding section, as the plastic continues to feed forward, and due to the gradual shallowening of the screw groove, and the obstruction of the filter screen, the manifold and the head, the plastic gradually forms a high pressure and is further Compaction. At the same time, the material is subjected to external heating from the barrel and strong stirring, mixing and shearing of the screw and the barrel. The temperature of the plastic is continuously increased, and the amount of molten plastic (called liquid phase or molten pool) is increasing. Unmelted solid plastics (called solid or solid beds) are decreasing. At the end of the melting section, all or most of the plastic melts and transforms into a viscous flow state.
After the plastic enters the metering section, the molten material in the compression section is quantitatively and temperature-extruded to the foremost end of the screw, further plasticized and homogenized, and the pressure, the quantitative and the constant temperature are determined. The parameter L/D is the aspect ratio, L/D and speed n, which are important factors for the plasticizing ability and effect of the screw. When L/D is large, the material stays in the barrel for a long time, which is beneficial to plasticization. At the same time, the pressure flow and leakage flow are reduced, the plasticizing ability is improved, and the material with high temperature distribution is favorable. Generally L/D is (18-20), but there is an increasing trend. For the whole screw, the longer the homogenization section, the better the plasticizing effect.