The Impact of Extruder Screw Compression Ratio on Production Efficiency

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”.

The compression ratio of an extruder screw refers to the volume ratio between the first flight channel in the feed section and the last flight channel in the homogenization section. The compression ratio affects the production efficiency of a twin-screw extruder through the following aspects:

Material Conveying and Plasticization

An appropriate compression ratio ensures that the material is effectively conveyed and compacted within the screw. In the feed section, a larger flight channel volume allows for more material to be accommodated. As the screw rotates, the material is gradually transported to the compression and homogenization sections. If the compression ratio is too small, the material cannot be adequately compacted within the channels, leading to unstable conveying and even slippage, which adversely affects production efficiency. Furthermore, a higher compression ratio facilitates material plasticization. In the compression section, the decreasing flight channel volume compresses the material, subjecting it to shear and friction, thereby raising its temperature and improving plasticization. Effective plasticization allows the material to be extruded more uniformly in the homogenization section, reducing production interruptions or product quality issues caused by poor plasticization, consequently enhancing production efficiency.

Pressure Build-up

The compression ratio directly influences the pressure build-up inside the extruder. As the material moves forward along the screw, the change in compression ratio gradually reduces the material volume, thereby establishing pressure. Sufficient pressure is crucial for ensuring the material can be smoothly extruded through the die head. If the compression ratio is insufficient, adequate pressure cannot be built up, making it difficult for the material to overcome the resistance of the die head. This limits the extrusion rate and reduces production efficiency. Appropriately increasing the compression ratio can raise the extrusion pressure, making the material more compact during extrusion, which is beneficial for improving product quality and dimensional accuracy. When producing high-precision products, such as pipes and profiles, a suitable compression ratio helps stabilize the extrusion pressure, ensuring product consistency, and thus improves production efficiency.

Mixing and Dispersion

Variations in the compression ratio affect the mixing and dispersion efficiency of the material within the screw. In the compression and homogenization sections, screw elements with different compression ratios can generate varying degrees of shear and stretching, enabling better mixing and dispersion of various components in the material. For instance, in composite materials requiring multiple additives, effective mixing and dispersion enhance product performance stability and reduce the defect rate caused by component non-uniformity, indirectly boosting production efficiency. However, if the compression ratio is too high, the material may undergo excessive shear and friction within the screw, generating excessive heat. This not only increases energy consumption but may also adversely affect the properties of certain heat-sensitive materials, potentially leading to material degradation, which in turn reduces production efficiency.

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