Main parameters of screw in melting section

Compression ratio ε : Generally refers to the geometric compression ratio, which is the ratio of the volume of the first screw groove in the feeding section to the volume of the last screw groove in the homogenizing section.
Epsilon = (Ds - H1) H1 / (Ds - H3) material H1 / H3
Where, H1 is the depth of the first screw groove in the feeding section
H3 -- depth of the last spiral groove in the homogenization section
Melt section length L2 is determined by the empirical formula:
Non crystalline polymer L2=55% ~ 65%L
For crystalline polymer L2=(1 ~ 4)Ds
The function of the homogenizing section (metering section) is to feed the molten material into the head at constant volume (quantitative) and constant pressure so that it can be formed in the die. The volume of the spiral groove in the homogenization section is as constant as that in the feeding section. In order to avoid material retention in the dead Angle of the screw head, resulting in decomposition, screw head is often designed into a cone or semicircle; Some are homogenized with a perfectly smooth surface called the torpedo head, but others are notched or milled. Torpedo head has the function of stirring and controlling materials, eliminating pulsation (pulse) phenomenon when flowing, and with increasing the pressure of materials, reducing the thickness of the material layer, improving the heating condition, and can further improve the plasticizing efficiency of screw. This section can be 20 25% of the total length of the screw.