Kingplas as one of Chinese plastic blow molding machine manufacturers, we tell you the correct choose of screw for the plastic blow molding machine.
Each resin has its own characteristics. To achieve the desired yield and quality of the molded product, it is impossible to meet the needs of all plastic molding with the same screw. The screw should be selected according to the characteristics of the raw material.
The compression ratio, aspect ratio and the form of the screw of the screw are selected in accordance with the plasticizing temperature, stability, viscosity and melt flow rate of the extruded material.
(1) Form of screw
In order to improve the extrusion efficiency and plasticizing ability of the extruder, a single screw extruder is often used.
The screw form is selected according to the type of material to be extruded, such as the raw material is a crystalline high polymer,
Should use a pitch-type mutant screw, such plastics have PE, PA, POM, etc.;
For crystal high polymer, a pitch-grading type screw should be used. These plastics are FVC, PS, ABS.
PC, etc. Various new types of screws have also been developed for use.
1 separate type screw. This kind of screw is to add a thread to the compression section of the screw. The two threads divide the groove formed by the original thread into two groove grooves, one groove communicates with the groove of the feeding section to transport solid materials; the other thread The trough is in communication with the homogenization section for transporting the viscous fluid material. This avoids the temperature fluctuation caused by the single-thread solid state and the viscous flow state coexisting in one screw groove.
2 barrier type screw. The so-called barrier type screw is a kind of screw that establishes a barrier section in a certain part of the screw to make the unmelted solid material fail to pass and promote the solid material to melt.
3 split type screw. This kind of screw is a part of the snail, which is provided with a number of protruding parts, grooves or holes, which divides the flow in the groove to change the flow state of the material, improve the molten state, enhance the mixing and homogenization, such as Pin screws are their representative. According to the role of the pin, the pin is generally set in the compression section. If it is for uniform mixing and low temperature extrusion, the pin is usually placed in the homogenization section.
(2) Determination of screw diameter
The screw diameter is an important parameter that indicates the amount of extrusion from the extruder. China's extruder screw has been standardized, and its screw diameter series are ø30mm, ø45mm, ø65mm, ø90mm, ø150mm, ø200mm. The size of the screw diameter is generally determined by the size of the article to be processed, the type of processed plastic, and the required productivity. Generally, a large-diameter product selects a screw with a large diameter, and a product with a small cross-sectional area selects a screw with a small diameter, which is advantageous for product quality, equipment utilization, energy consumption, and the like.
(3) Selection of screw length to diameter ratio
The aspect ratio of the screw is also an important parameter of the screw. If it is combined with the screw speed, it indicates the plasticizing ability and plasticizing quality of the screw in a certain sense. The common aspect ratios are 11:1, 15:1, 20:1, 25:1, 30:1, etc. After the aspect ratio is increased, the length of the screw increases, and the material stays in the barrel for a long time. The material is plasticized more evenly and fully, and the yield and quality can be improved. However, after the aspect ratio is increased, the processing and assembly of the screw and the barrel are difficult and complicated, the cost is also increased, and the extruder is lengthened to increase the floor space of the plant. In addition, after the aspect ratio is increased, the screw sag will increase the bending of the screw, resulting in uneven gap between the screw and the barrel. In severe cases, the screw will scrape the barrel and reduce the life of the extruder. Therefore, we should strive to obtain high quality and high yield under the conditions of small aspect ratio.
(4) Selection of compression ratio
The purpose of determining the compression ratio is to compress and vent the material and establish the necessary pressure. The choice of compression ratio is related to the nature of the material, the requirements of the product, and the like.