General screw is divided into three sections: feeding section, compression section, homogenization section.
1. Feeding section
-- The bottom diameter is small, the main function is to transport raw materials to the rear section, so it is mainly a problem of transportation capacity, parameter (L1, h1), h1=(0.12-0.14)D.
2. Compression section
- Bottom diameter change, the main role is to compact, melt the material, build pressure. Parameter compression ratio ε=h1/h3 and L2. The exact gradient should be A=(h1-h3)/L2.
3. Homogenization section (metering section)
-- Squeeze the fused material in the compression section to the front end of the screw at a fixed quantity and temperature, and the parameters (L3, h3), h3=(0.05-0.07)D.
For the whole screw, the parameter L/D- length-diameter ratio
L/D Pros and cons: L/D and speed n are important factors for the plasticizing ability and effect of the screw. Large L/D is a long time for the material to stay in the barrel, which is conducive to plasticization. At the same time, the pressure flow and leakage flow are reduced, which improves the plasticizing ability. At the same time, it is beneficial for materials with higher temperature distribution requirements, but after large, it has negative effects on the manufacturing and assembly use. But there is a growing trend.
