How does the structural design of the conical screw barrel affect the quality and efficiency of plastic extrusion?

In the field of plastic extrusion processing, the structural design of the conical screw barrel as a core component directly determines the stability of the extrusion process, the melt quality and the production efficiency. With the increasing market demand for high-performance plastic products, optimizing the design of the conical screw barrel has become the key to improving the competitiveness of enterprises.
1. Compression ratio and thread depth: the core of melt uniformity
The compression ratio of the conical screw (the ratio of the screw groove depth between the screw feed section and the metering section) is the core parameter affecting the melt quality. A higher compression ratio can enhance the shear and mixing effect of the material in the screw groove, promote the uniform plasticization of the polymer chain, and reduce the generation of unmelted particles. However, too high a compression ratio will cause a sudden increase in the pressure in the barrel, increase energy consumption and accelerate screw wear. For example, when processing high-viscosity engineering plastics (such as PC, PA), a progressive compression ratio design (such as 3:1 to 2.5:1) can not only avoid degradation caused by excessively high melt temperature, but also improve melt density.
In addition, the gradual design of the thread depth directly affects the shear rate distribution. The shallow groove area (metering section) improves the melt fluidity through high shear, while the deep groove area (feeding section) ensures the stability of solid conveying. If the gradient design is unreasonable, it may cause melt reflux or local overheating, reducing the dimensional accuracy of the extruded product.
2. Aspect ratio and temperature field: the balance point between efficiency and energy consumption
The aspect ratio (L/D) of the conical screw is the key to determining the material residence time and plasticization efficiency. Longer screws (L/D>25) can extend the material heating time and are suitable for processing materials with poor thermal stability (such as PVC), but will significantly increase equipment costs and energy consumption. On the contrary, short screws (L/D<20) can reduce energy consumption, but may cause surface defects of products due to incomplete plasticization.
The coordinated control of the temperature field is also crucial. The zoned heating design of the conical barrel needs to match the geometric characteristics of the screw. For example, a lower temperature is used in the feeding section to prevent the material from melting and sticking prematurely, while the temperature is gradually increased in the compression section and metering section to ensure sufficient plasticization. The use of dynamic temperature control technology (such as PID algorithm) can reduce melt temperature fluctuations and control the temperature difference within ±1.5°C, thereby avoiding product warping or cracking caused by thermal stress.
3. Material adaptability: Extending life and reducing maintenance costs
The surface treatment process of the conical screw barrel (such as nitriding and bimetallic alloy spraying) directly affects its wear resistance and corrosion resistance. For example, when processing reinforced plastics containing glass fiber, the use of tungsten carbide (WC) coating can extend the life of the screw by more than 30%, while reducing the pitch change caused by wear and maintaining a stable extrusion pressure. In addition, the material selection of the barrel lining (such as boron steel or high-temperature nickel-based alloy) needs to match the corrosiveness of the processed material to avoid contamination of the melt due to chemical reactions.
The structural design of the conical screw barrel needs to find a balance in multi-objective optimization: it must meet the high standards of melt quality and minimize energy consumption and costs. With the popularization of simulation technologies (such as CFD and finite element analysis), accurate prediction of screw performance through digital modeling has become an industry trend.