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What is a screw? What is it for?

2021-07-13

Introduction of plastic plasticizing screw
The solid plastic raw material enters the screw channel from the feed hopper. Due to the high-speed rotation of the screw, it produces a shearing effect with the barrel. The plastic raw material is mixed and transported along the screw channel to make it solid. The plastic raw material is heated by the electric heating plate outside the melt cylinder and the shear heat generated by the screw, so that the inside of the melt cylinder is heated and melted into a melt state.
The plasticizing screw can be divided into four zones according to its function:
1. Solid conveying zone (solid conveying zone)
This section is connected with the feed hopper, and the plastic solid particles are tightly compressed to form a solid bed, which is subjected to the shearing effect of the melt cylinder. In addition to gradually increasing the temperature of the plastic, the plastic is transported forward.
2. Delay of melting
This section is the area from the end of the solid conveying area to the area before the formation of the melt pool. Its main feature is that a thin film layer composed of melt is formed on the surface of the solid bed and the melt cylinder. The melt in the film layer is affected by the melt cylinder. The drag force accumulates in the front screw groove, and the pressure formed at the end of this zone is large enough to deform the solid bed, and the accumulation in the front screw groove gradually forms a melting pool.
3. Melting zone
This zone is the end of the melting delay zone until the plastic is completely melted. This zone can be divided into two parts to discuss, one is plastication, and plasticization mainly comes from the shear effect of the melt barrel, and the other It is melt conveying, which conveys the melt to the melting tank.
4. Melt conveying zone
When all the plastics are completely melted, they begin to enter this section and end at the end of the plasticizing screw to maintain a uniform temperature of the melt and stabilize the flow of the melted plastic.
Plastic plasticizing screw is divided into three sections according to its geometric shape:
This section is the groove depth of the fixed screw groove, and its function is to be responsible for preheating and plastic solid transportation and pushing. It must be ensured that the plastic begins to melt at the end of the feed section (that is, to be preheated to the melting point).
The length of this section is divided into crystalline (POM, PA‧‧, etc.)>non-crystalline (PS, PU, ​​ABS, etc.)>thermal sensitivity (PVC, etc.).

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