What exactly does the aspect ratio of a screw mean
DATE：2023/9/1 10:04:38 / READ： / SOURCE：This station
The length to diameter ratio of a screw refers to the ratio between the length of the working part of the screw and the diameter of the screw. Increasing the aspect ratio means increasing the length of the screw. A larger aspect ratio helps with the mixing and plasticization process of plastics, allowing them to be heated in the barrel for longer periods of time, thereby improving the quality of plasticization.
1. The screw is pressurized more fully, which can improve the physical and mechanical properties of the product.
2. Plastic has better plasticization effect and higher appearance quality of products.
3. The extrusion process is more stable, and the extrusion amount can be increased by 20% to 40%.
4. It is beneficial to adjust the temperature gradient along the axial direction of the material barrel to meet the needs of special polymer processing.
5. It is beneficial for the formation of powder.
When selecting the aspect ratio, it is necessary to consider the requirements of plasticization quality and extrusion amount. While maintaining the same requirements for plasticizing quality, increasing the aspect ratio can increase the rotational speed of the screw, thereby increasing the extrusion amount of plastic. However, choosing an excessively large aspect ratio will increase the power consumption of the screw, increase the difficulty of processing and assembling the screw and barrel, and increase the possibility of screw bending, leading to scraping and reduced service life. Therefore, when selecting the aspect ratio, it should not be blindly increased, and it needs to be considered based on the performance of the processed material and product quality requirements.
For heat sensitive materials such as PVC, a smaller screw aspect ratio is more suitable, as excessive aspect ratios can lead to prolonged residence time and decomposition. For materials that require high temperature and pressure, a larger aspect ratio should be selected. If the product quality requirements are not high (such as recycling and granulation of waste materials), a smaller aspect ratio can be chosen, otherwise a larger aspect ratio should be chosen. Materials with different geometric shapes also have different requirements for the aspect ratio of the screw. For granular materials, a smaller aspect ratio can be selected after plasticization and granulation, while for powder materials without plasticization and granulation, a larger aspect ratio is required. Generally speaking, the length to diameter ratio of the screw is 20-30.
In addition, for screws with larger aspect ratios, if the screw speed needs to be increased, the torque will be increased. For small diameter screws, strength verification is required to ensure that they meet the requirements.
Author：admin