What types of screw machines are there? The screw of th […]
What types of screw machines are there?
The screw of the injection molding machine is divided into: gradual screw, abrupt screw and general screw.
1) Gradual screw:
It means that the depth of the screw groove gradually transitions from the deep screw groove of the feeding section to the screw groove of the homogenizing section. Mainly used for processing non-crystalline plastics with a wide softening temperature range and high viscosity, such as polyvinyl chloride.
2) Mutant screw:
It means that the process of screw groove depth from deep to shallow is completed within a short axial distance. It is mainly used to process crystalline plastics with obvious viscosity and melting point, such as polyethylene, polypropylene, etc.
3) Universal screw:
The length of the compression section is between the abrupt screw and the gradual screw, but the plasticization quality and energy consumption are worse than those of the dedicated one. In order to meet the requirements of crystalline and amorphous plastics melted into plastics.
4) L/D ratio of injection screw:
Compared with the extrusion screw, the injection molding machine screw has a smaller L/D ratio. The screw length-diameter ratio of domestic injection molding machines is mostly between 17-22, and usually around 20:1. The length-to-diameter ratios of foreign screws are mostly between 21-33, and the common length-to-diameter ratios are 20, 25, 30, etc.
5) Injection screw compression ratio:
If the screw groove in the homogenization section of the injection screw is deeper, the compression ratio is small, and vice versa.
The selection of the depth of the screw groove is mainly based on the factors of the processed plastic: specific heat capacity, thermal conductivity, stability, viscosity, and pressure during plasticization. But it should not be too deep, too deep will cause the screw due to excessive torque Twisting, or stalling due to overload, over to the groove of the homogenization section. The compression ratio of the injection screw is usually (1.5-3.5):1. The screw with a high compression ratio should rotate slowly, and the screw with a compression ratio of less than 2:1 can work at a higher speed.
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