When choosing screw, the compression ratio should be chosen according to the performance of plastics, such as density change before and after melting, compression of molten material under pressure.

Generally, the compression ratio of materials with high density is relatively small, and the compression ratio of materials with low density can be selected relatively large.

At present, the compression ratio is mostly chosen according to experience.

The following are some compression ratio data collected by KALSHINE for reference only.

from: 

Single Screw And Barrel