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What are the requirements for the screw material

Update:14 Dec 2019

It can be known from the extrusion process that the scr […]

It can be known from the extrusion process that the screw works under high temperature, certain corrosion, strong wear and high torque. Therefore, the screw must:

1. High temperature resistance, no deformation under high temperature;
2. Wear resistance and long life;
3. Corrosion resistance, the material is corrosive;
4. High strength, can withstand large torque and high speed;
5. Has good cutting performance;
6. Low residual stress and small thermal deformation after heat treatment.

The main part of the pin screw is an ordinary screw, and the pin can be set in the falling groove of the screw or metering section of the screw or a smooth cylindrical surface without a screw groove at the end of the metering section. The pins are arranged in a certain arrangement, which can vary in density and quantity. The cylindrical pin is formed by assembling the pin into the hole of the screw; the square or diamond pin is formed by milling the pin directly on the screw.

If these pins are set in the melting zone, the pins can break the solid bed, disrupt the two-phase flow, stir the solid and liquid phases together, and increase the contact area between the undissolved solid phase fragments and the contained material, and promote Melting. If the pin is set in the melt conveying area, its main function is to divide the material flow, increase the interface, change the direction of the material flow, and rearrange the flow beam. Repeatedly split and merge, change the direction of flow, and homogenize the melt composition and temperature.
The mixing section is an inwardly grooved structure provided at the end of the ordinary screw homogenizing section, and its outer diameter is equal to the outer diameter of the screw. The grooves are divided into several groups, and each group is a confluence area of ​​materials. The materials are divided by grooves, and they meet at the confluence area, and then they are divided and merged. The principle is similar to the pin type.

The characteristic of the separate type screw is that in addition to the original screw pattern (called the main screw) on the melting section, a thread (called an additional thread) is added. Its outer diameter is slightly smaller than the outer diameter of the main thread. The lead is different. The auxiliary thread starts from the end of the feeding section (and is connected to the feeding section here). After several threads, it gradually intersects with the main thread of the homogenizing section.

The screw groove depth and thread lead of this screw are gradually changed from the beginning of the feeding section to the end of the homogenization. The thread lead gradually narrows from wide and the depth of the screw groove gradually becomes shallower from the depth, so that the material can be greatly compressed.