How to choose high-quality screws and barrels for plastic extruders

The extruder screw and barrel are the core components of plastic extrusion processing, and their quality directly affects the quality and production efficiency of the extruded products. So, how to choose high-quality screws and barrels?

1. Material selection

Screw material: Generally, high-strength, wear-resistant and corrosion-resistant alloy steels such as 38CrMoAlA are used. After nitriding or hard chromium treatment, the wear resistance and service life of the screw can be further improved.

Barrel material: Similar to the screw material, high-strength and wear-resistant alloy steel is also used. The inner wall is usually nitrided or hard chromium plated to improve wear resistance and finish.

2. Processing accuracy

Screw straightness: The straightness of the screw directly affects the conveying and mixing effects of the material. Generally, the screw straightness is required to reach 0.015mm or higher.

Screw surface roughness: Excessive surface roughness can easily cause material retention and decomposition, affecting product quality. Generally, the surface roughness Ra≤0.4 is required.

Barrel inner wall finish: The roughness of the barrel inner wall will also affect the flow and heat transfer of the material. The barrel inner wall is required to have a high finish to reduce the adhesion and decomposition of the material. The accuracy requirement should meet or exceed the 8-level accuracy requirement.

3. Screw design

Screw groove design: The depth, width, pitch and other parameters of the screw groove have an important impact on the plasticization, mixing and conveying of the material. The design should be optimized according to different material properties and product requirements.

Transition section design: The transition section design of the screw should be smooth to avoid stress concentration and extend the service life of the screw.

Vent design: For materials that need to be vented, reasonable vents should be set on the screw to ensure that the moisture and gas in the material can be discharged in time.

4. Manufacturing process

Forging process: The screw blank adopts the forging process to obtain better organizational structure and mechanical properties.

Heat treatment process: The heat treatment process of the screw and barrel directly affects its hardness, strength and wear resistance.

Surface treatment process: Surface treatment processes such as nitriding and hard chrome plating can significantly improve the wear resistance and service life of the screw and barrel.

If the barrel and screw need to be installed with a water cooling channel, a water pressure test must be performed in advance, and there must be no water seepage for 5 minutes under a water pressure of 0.3Mpa.