Requirements and processing technology of PP plast

2022-06-23
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Requirements and processing technology of PP plastics for injection molding machines

the processing process of plastic raw materials is mainly the process of melting, flowing and cooling of rubber particles into finished products after finalization. It is a process of heating and then cooling. It is also a process of plastic changing from particles to different shapes. The following will explain the processing process from the perspective of different stages

the heater of the device allows the raw material particles to gradually melt into a fluid flow, which is mainly adjusted according to the temperature of different raw materials. Increasing the temperature will tend to increase the raw material flow by 1, but improper protection may affect the accuracy and performance of the instrument. It can always increase the efficiency with a new image, but it may not guarantee the yield. It must achieve a proper balance. In addition, the good effect and the characteristics of PP in case of high thermal cracking are that it is best to make the raw materials flow smoothly to the die head during production, so as to avoid insufficient filling or backflow. Backflow means that the raw materials flow faster than the output rate, which will eventually lead to an increase in the average flow efficiency equal to an increase in MFR. It is one of the available methods for processing, but it also causes an abnormal MFR distribution, which may lead to an increase in instability and an increase in the defect rate. However, PP finished products are not products with high dimensional precision due to application, so the impact is not significant

pp processing mostly relies on the screw to drive the fluidity, so the design of the screw has a great impact. The size of the diameter affects the output, and the compression ratio affects the pressure value, which also affects the output and the finished product effect, including the mixing effect of a variety of materials (Color Masterbatch, additives and modifiers). The flow of raw materials mainly depends on the heater, but the friction and friction of raw materials will also generate friction heat energy to accelerate the fluidity. Therefore, the small screw compression ratio will drive the small flow, and the rotating speed must be increased, resulting in more friction heat energy than the screw with large compression ratio. Therefore, it is often said that there is no master in plastic processing, and the person who carefully understands the performance of the machine is the master. The heating of raw materials is not only a heater, but also includes friction heat and retention time. So this is a practical problem. Experience is helpful to solve production problems and improve efficiency. If the mixing effect of the screw is particularly good, sometimes two-stage different screws or Twin-axis screws are designed and different types of screws are set separately to achieve various mixing effects

3. Mold or die head

plastic reshaping depends on the mold or die head. The injection molded finished product is three-dimensional, and the mold is also complex. The shrinkage rate should be considered. Other continuous product dies are plane, strip and needle. If they are special shapes, they are classified as special shapes. Attention should be paid to the problem of immediate cooling and shaping. The rigid polyurethane foam of the plastic machine has excellent heat insulation performance. Most of the meters are like injection syringes. The extrusion force driven by the screw will cause great pressure at the small outlet and improve the production efficiency. When the die head is designed as a plane, it is very important to design the coat hanger die head so that the raw materials can be evenly distributed on the whole surface. Pay attention to the extrusion opportunity to increase the stable supply of raw materials by the gill pump

in addition to pouring raw materials into the sprue gate, the injection mold also has the design of cooling raw materials by cooling water channel. Press out molding relies on the cooling water channel in the roller to achieve the cooling effect. In addition, there are also air knives, cooling water is directly sprayed on the blowing bag, and hollow air blowing and other cooling methods

finished product reprocessing and extension will enhance the effect. For example, the different speed of the packaging belt driven by the front and rear rollers will result in the extension effect. The tensile force of the finished product alignment extension is strengthened and it is not easy to tear, but it is very easy to tear horizontally. Molecular weight distribution will also affect the extension effect in high-speed production. All extruded products including fibers have different extension. Vacuum and compressed air forming can also be regarded as another form of extension

any raw material has the problem of shrinkage, which is caused by internal stress during thermal expansion, cold contraction and crystallization. Generally speaking, thermal expansion and cold shrinkage are easy to overcome, which can be done by prolonging the cooling time in processing and maintaining the pressure continuously. Crystalline raw materials tend to have greater shrinkage difference than non crystalline ones, about 16% of PP, but only about 4% of ABS. The difference is very large. This part needs to be overcome in the mold, or additives to reduce the shrinkage rate are often added. LDPE is often added to the extruded plate to improve the necking problem

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