1) In the formula H1 (D H3) H3, H1 and H3 are the depth of the first screw groove in the screw feeding section and the depth of the last screw groove in the homogenization section, respectively. There is also a physical compression ratio, which refers to the ratio of the density of the plastic after heating and melting to the density of the loose state. From the above formula, I (40 - 5.4) - 5.4 1.9 (40 - 6) . 6 because of the small compression ratio, it is beneficial to improve the plasticizing ability, while the shear effect is poor, but it is sensitive to the back pressure regulation. Therefore, the compression ratio of injection screw is smaller than that of extrusion screw. This kind of screw has high plasticizing ability and strong processing adaptability. Therefore, the screw compression ratio i =. (7) The strength injection screw of screw works under the bad condition. It not only needs to bear the high pressure of injection, but also suffer the corrosion of molten material and the frequent load start during pre molding. The wear of injection screw is very serious (especially the processing of glass fiber reinforced plastics), and the fatigue fracture of small diameter screw often occurs. This requires the selection of corrosion-resistant, high-strength materials. At present, most of the materials used for screw are nitriding steel (38CrMoAl) or other alloy steel.<br>
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