Design and construction principle of screw of plastic extruder

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”.

Feeding area of plastic extruder: the groove depth of the screw groove of the fixed screw. Its function is to be responsible for preheating, plastic solid transportation and extrusion. It must be ensured that the plastic begins to melt at the end of the feed section - that is, preheat to the melting point. The general length is: amorphous (as, ABS, PS) about 48 ~ 58% L, crystalline (PA, POM, PE, PP, CA) about 48 ~ 58% L, and glass fiber added about 45 ~ 55% L.

Compression area of plastic extruder: the thread groove of the gradually shrinking screw is deep, and its functions are melting, mixing, shear compression and pressurized exhaust of plastic raw materials. The plastic will completely dissolve in this section and the volume will be reduced, so the design of compression degree is very important. The general length is: amorphous (as, ABS, PS) about 25 ~ 35% L, crystalline (PA, POM, PE, PP, CA) about 22 ~ 32% L, glassy about 28 ~ 40% L, heat sensitive (PVC) 100% L.

Metering area of plastic extruder: the screw groove is fixed deep. Its main functions are mixing, melt conveying and metering. In addition, it must also provide sufficient pressure to maintain the uniform temperature of melt and stabilize the flow of molten plastic. The general length is: amorphous (as, ABS, PS) about 15 ~ 58% L, crystalline (PA, POM, PE, PP, CA, etc.) about 48 ~ 58% L, glassy about 45 ~ 55% L.

Although the screw of plastic extruder can be distinguished according to function or geometric shape, in the actual plasticization process, the functions of each section overlap, so it is difficult to distinguish the interval. The study of plasticizing screw is nothing more than to improve the shear mixing effect, improve the uniform mixing, improve the plasticizing ability and improve the temperature uniformity of melt. When the tooth depth of the feeding section is deeper, the conveying capacity is larger, but the torque required by the screw is larger; The tooth depth of the feeding section is too shallow, the conveying capacity is not enough, and the compression ratio is not enough. When the tooth depth of the metering section is too deep and the compression ratio is insufficient, the required feeding force is large; It is easy to burn if it is too shallow. The general tooth depth is about 0.03 ~ 0.07 times the screw diameter. Therefore, plastic plasticizing screw has the functions of conveying, melting, mixing, compression and metering, and plays a very important role in plasticizing quality.