Which characteristics of the exhaust screw determine the quality of the extruded product?

1. Exhaust capacity
The core function of the exhaust screw is to remove gases and volatiles from the molten material. Its exhaust capacity directly determines the amount of residual gas and volatiles in the extruded product. Efficient exhaust capacity can significantly reduce defects such as bubbles and cracks in products, thereby improving the quality and appearance of products.

2. Screw diameter and aspect ratio
Screw diameter:
The choice of screw diameter directly determines the quality of the extruded product. A screw with a larger diameter can handle more material, but it may also increase the extrusion pressure and affect the uniformity of the product. Therefore, when selecting the screw diameter, it is necessary to comprehensively consider the characteristics of the material, the specifications of the extruder and the quality requirements of the product.

Aspect Ratio:
The aspect ratio (the ratio of the effective length of the screw to its diameter) is also an important factor affecting the quality of the product. A larger aspect ratio can provide more melting and mixing time, which helps the materials to melt and mix more fully, thereby improving the uniformity and quality of the product. However, an excessively long aspect ratio may also lead to excessively high extrusion pressure, increasing energy consumption and machine wear.

3. Screw structure and geometry
Exhaust section design:
The exhaust section is the key part of the screw responsible for removing gas. Its design includes the shape, quantity and position of the exhaust channels, which directly affect the exhaust efficiency and product quality. Reasonable exhaust section design can ensure smooth gas discharge while avoiding material leakage and product defects.

Screw groove depth and conveying capacity:
The depth of the screw groove is closely related to the conveying capacity of the screw. In the exhaust section, the groove depth is usually larger to accommodate more gases and volatiles. At the same time, the conveying capacity of the pumping section also needs to be greater than that of the metering section to ensure that the material can be discharged smoothly from the exhaust port to avoid stagnation and leakage.

4. Screw material and wear resistance
The material and wear resistance of the screw also directly affect the quality of the extruded products. High-quality screw material can provide better wear resistance and corrosion resistance, extend the service life of the screw, and reduce the adhesion and clogging of materials on the screw surface, ensuring the stability of the extrusion process and the quality of the product.

5. Screw speed and temperature control

Screw speed:
Screw speed has an important influence on the quality of extruded products. Appropriate rotation speed can provide sufficient shear force and mixing effect, which helps the materials to melt and mix more fully. However, too high a rotation speed may cause the material to overheat, degrade, or generate excessive frictional heat, affecting the quality and performance of the product.

Temperature Control:
Temperature is one of the key factors affecting the quality of extruded products. Reasonable temperature setting can ensure that the material is fully melted and mixed in the screw while avoiding overheating or degradation. Therefore, the temperature of the screw and barrel needs to be strictly controlled during the extrusion process to ensure the quality and performance of the product.