There are many indicators of the screw, such as pitch, groove depth, compression ratio, length to diameter ratio, etc., but in production, due to the difference in bulk density, temperature sensitivity, shrinkage, etc., strictly speaking, different materials should be matched with different screws. At least the temperature-sensitive material (represented by PVC) and the crystalline material (represented by PA) should use their own screws.
The characteristics of the PVC screw are that in the three sections, the feeding section and the homogenization length are short, and the compression section is very long, exceeding 50%. This is because the PVC is decomposed if it is rapidly compressed, so the compression section is long.
In terms of compression ratio, the temperature sensitivity of PVC makes the compression ratio the smallest among the screws, generally between 1.6 and 2.2, the soft PVC can be upper limit, and the rigid PVC is as small as possible.
The aspect ratio of the PVC screw is also close to the lower limit. Between 18~~22.
PA is a typical crystal material with a large shrinkage. Its screw characteristics are:
The third section is the feeding section, the compression section is very short, less than 20%, and the homogenization is short and short, less than 20%.
The compression ratio is large and can be 2.5~~3.5. At the same time, the aspect ratio also takes the upper limit, which is between 20 and 25 degrees.
Finally, PVC is corrosive, so the surface treatment requires higher corrosion resistance, and the surface is chrome-plated.