What are the general structural parameters of the screw

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

The aspect ratio (the ratio of the effective length to the diameter of the working part of the screw, expressed as L/D) is usually 18-25. Large L/D can improve the temperature distribution of the material, which is beneficial to the mixing and plasticization of plastics, and can reduce leakage and backflow and improve the production capacity of the extruder. The screw with large L/D has strong adaptability and can be used for the extrusion of various plastics; however, when the L/D is too large, the plastics will be degraded due to the prolonged heating time. The self-weight increases, the free end flexes and sags, which is easy to cause scratches between the material and the screw, and makes the manufacturing and processing difficult; it increases the power consumption of the extruder. A screw that is too short can easily cause poor plasticization in kneading.

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 control δ in about 0.1-0.6 mm is appropriate. When δ is small, the shearing effect of the material is large, which is beneficial to plasticization. However, if the δ is too small, the strong shearing effect is easy to cause thermomechanical degradation of the material, and at the same time, the screw is easy to be hugged or rubbed against the barrel wall. When 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.

Jiangsu Xinrongplas Machinery Co.,Ltd focus on manufacturing various plastic pipe extrusion machine such as PPR pipe extrusion machine, PVC pipe extrusion machine, PE pipe extrusion machine etc, welcome to consult. 


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