What are the general structural parameters of the screw


Ningbo Fangli Technology Co., Ltd. is a mechanical equipment manufacturer with nearly 30 years’ experiences of plastic pipe extrusion equipment, new environmental protection and new materials equipment. Since its establishment Fangli has been developed based on user’s demands. Through continuous improvement, independent R&D on the core technology and digestion & absorption of advanced technology and other means, we have developed PVC pipe extrusion line, PP-R pipe extrusion line, PE water supply / gas pipe extrusion line, which was recommended by the Chinese Ministry of Construction to replace imported products. We have gained the title of “First-class Brand in Zhejiang Province”.


The common screw diameter D is 45-150 mm. With the increase of screw diameter and processing capacity, the productivity of extruder is directly proportional to the square of screw diameter D.


The length diameter ratio (the ratio of the effective length of the working part of the screw to the diameter, expressed as L / D) is usually 18-25. Large L / D can improve the temperature distribution of materials, facilitate the mixing and plasticization of plastics, and reduce leakage and countercurrent. Improve the production capacity of the extruder. The screw with large L / D has strong adaptability and can be used for the extrusion of a variety of plastics. However, when the L / D is too large, the plastic will be degraded due to the increase of heating time. At the same time, due to the increase of screw weight and the deflection and sagging of free end, it is easy to cause the scratch between barrel and screw and make manufacturing and processing difficult; the power consumption of the extruder is increased. Too short screw is easy to cause poor plasticization in mixing.


Half of the difference between the inner diameter of the barrel and the diameter of the screw is called the gap δ, which can affect the production capacity of the extruder. With the increase of δ, the productivity decreases. Usually, it is advisable to control δ at about 0.1 to 0.6 mm. When δ is small, the shearing effect of the material is large, which is conducive to plasticization. However, if the δ is too small, the strong shearing effect is easy to cause thermo-mechanical degradation of the material. , δ is too small, there is almost no leakage and reverse flow of the material, which affects the mixing of the melt to a certain extent.


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