Improving the design of the extruder to improve the quality of polymer products

Abstract

The object of research is an extruder for the manufacture of polymer products. The article considers the problem of improving the quality of polymer products on the basis of improving the design of the extruder. The selected design of the extruder with the execution of a three-section worm in the compression zone with different heights of barrier gaps in each section. The ratio of the length of individual sections to the total length of the compression zone should be in the range of 0.1–0.5. In this case, the height of the barrier gap in the first section should exceed the height of the gaps in subsequent sections by 1.1 times between adjacent turns of the worm. In the first section with a larger gap, there is an intensive dissipation of the mechanical energy of the drive, which leads to the melting of the polymer and the release of heat. At the same time, a significant part of the unmolten material is retained before entering subsequent sections with a smaller gap. Thus, the worm does not experience a sharp increase in pressure in the compression zone and local overheating of the material along its length in the compression section. In subsequent sections, further separation of the melt and solid particles of the polymer occurs, and the clearance height decreases gradually, ensuring a controlled distribution of heat flows in the material. The proposed design of a worm in the compression zone with a closed barrier gap h = 0.001 m and open barrier gaps h at 0.0105 m and 0.0075 m is illustrated by the example of an extruder (D = 0.63 m; φ = 17.1°) in the processing of recycled high-pressure polyethylene. The use of open barrier gaps between the worm and the extruder body reduces heat dissipation on its working surfaces by almost three times than with closed barrier gaps, as demonstrated by the obtained dependence of the dissipation function on the worm rotation speed. This reduces the risk of material degradation, the thermal conditions of the polymer stay are mitigated, the homogeneity of the melt increases and will contribute to improving the quality of finished polymer products, in particular polymer pipes, films, etc.