Screw elements play a vital role in twin screw extruder. They are not only the driving force for material transportation, but also the key factor in the plasticizing, mixing and homogenizing processes. The following are the specific functions of screw elements in extruders:
- Conveying function: The basic function of screw elements is to push the material along the axial direction of the screw. The forward screw element is consistent with the extrusion direction and is responsible for conveying the material from the feed port to the rest of the screw; while the reverse screw element hinders the forward flow of the material, which helps to prolong the residence time of the material in the barrel and improve the filling degree and pressure.
- Plasticization: Through the rotation of the screw element, mechanical energy is converted into heat energy, which gradually melts the plastic particles into a uniform molten state. This process is crucial for plastic processing because it directly affects the quality and performance of the product.
- Mixing ability: The design of the screw element enables distributive mixing and dispersive mixing of materials during the extrusion process. Distributive mixing is achieved by rearranging the position of the materials, while dispersive mixing increases its surface area by breaking up the material agglomerates, thereby promoting more uniform mixing.
- Shearing action: Specific screw elements such as kneading blocks provide high shear forces to break up agglomerates in the material and ensure sufficient mixing between the components. This is particularly important for the production of high-quality composite materials or modified plastics.
- Exhaust function: In the exhaust section of the extruder, the screw element design helps to remove gases and volatiles from the material, improving the performance and appearance quality of the product.
- Pressure establishment: The screw element is also responsible for establishing the necessary pressure in the extruder, which is essential to ensure the stable flow of the material and the shape stability of the final product.
- Adaptability adjustment: According to different processing requirements, the screw element can adjust its performance by changing its parameters such as lead, pitch and depth to adapt to different materials and process requirements.
In general, screw elements are an indispensable component of the extruder, and their design and configuration are directly related to the production efficiency of the extruder, product quality and suitability for the end use. Through the precise control and optimization of the screw element, the efficiency of the extrusion process and the product quality can be significantly improved.
