The screw of a single screw extruder mainly includes th […]
The screw of a single screw extruder mainly includes the following basic parameters:
① Screw diameter (Ds).
The screw diameter is used to indicate the size of the extruder, and it indicates the size of the extruder in a certain sense. The size of the screw diameter can generally be selected reasonably according to the cross-sectional size of the product, the processing performance of the material, and the required productivity and processing capacity, that is, the extruder model is selected. The screw diameter of the extruder in our country has been serialized, with specifications of 30mm, 45mm, 65mm, 90mm, 120mm, 150mm, 200mm, etc. The more widely used screw diameter is 65-150mm. Generally, large-diameter screws should be used for products with large cross-sectional area, and small-diameter screws should be used for products with small cross-sectional area.
②L/D ratio (L/D).
The aspect ratio of an extruder refers to the ratio of the effective length of the screw to the diameter of the screw. The aspect ratio is another important parameter of the extruder. If the screw length-to-diameter ratio and the screw speed are considered together, it indicates the plasticizing capacity and plasticizing quality of the screw in a certain sense. The national standard series stipulate that L/D has 15, 20, 25, 30, etc., and the maximum can reach 43. The extruder with a moderate aspect ratio should be selected according to the properties of raw materials and production efficiency. If the aspect ratio is increased, as the length of the screw increases, the residence time of the plastic in the barrel is prolonged, and the material is plasticized more fully and uniformly, so the output and quality can be improved. But this makes the processing and assembly of the screw and barrel more difficult, and the cost increases accordingly, the screw is easy to deform, and the gap between the screw and the barrel is easy to be uneven. Therefore, we should try our best to obtain high quality and high yield with a smaller aspect ratio. For example, when processing polyolefin and polyvinyl chloride materials, the ratio of screw length to diameter is 20 and 25.
③Compression ratio (ε).
The ratio of the volume of the first groove of the screw feeding section to the volume of the last groove of the homogenization section is called the compression ratio. The size of the compression ratio has a great influence on the compactness of the product and the ability to remove the air contained in the material. It also affects the output of the extruder and the mechanical strength of the screw.