Factors affecting the quality of screw plasticization

Update:11-05-2019
Summary:

The main factors affecting the quality of screw plastic […]

The main factors affecting the quality of screw plasticization are: aspect ratio, compression ratio, back pressure, screw speed, barrel heating temperature, etc.

Length to diameter ratio: the ratio of the effective working length of the screw to the diameter of the screw:
If the aspect ratio is large, the feed is easy to be uniform;
Plastics with better thermal stability can be used with longer screws to improve kneading without scorching. Plastics with poor thermal stability can be used with shorter screws or screw ends without threads. Considering the plastic characteristics, the general flow length is as follows: thermoset is 14'16, hard PVC, high viscosity PU and other heat sensitivity is 17'18, general plastic is 18'22, PC, POM and other high temperature stability plastic is 22'24 .

Compression ratio: the ratio of the last groove depth of the feed section to the first groove depth of the metering section:
Considering the compressibility, filling degree, reflow and other effects of the material, the product should be dense, heat transfer and exhaust;
Appropriate compression ratio can increase the density of plastics, make the binding between molecules and molecules more tight, help to reduce the absorption of air, reduce the temperature rise caused by pressure, and affect the difference in output. The inappropriate compression ratio will It will destroy the physical properties of the plastic; c. The higher the compression ratio, the higher the temperature rise during the plasticizing process of the plastic in the material tube, the better the mixing uniformity of the plastic in the plasticizing process, and the larger the discharge amount. To reduce.
The high compression ratio is suitable for non-melting plastics, especially low melt viscosity, heat stable plastics; low compression ratio is suitable for fusible plastics, especially high melt viscosity, heat sensitive plastics.