Injection molding technology of the most popular p

2022-08-20
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Injection molding technology of plastic machine processing raw materials

injection molding is an engineering technology, which involves transforming plastics into useful products that can maintain their original properties. The important process conditions of injection molding are the temperature, pressure and corresponding action time that affect the plasticizing flow and cooling

I. temperature control

1. Barrel temperature: the temperature that needs to be controlled in the injection molding process includes barrel temperature, nozzle temperature and mold temperature. The first two temperatures mainly affect the plasticization and flow of plastic, and the second temperature mainly affects the flow and cooling of plastic. Each kind of plastic has different flow temperature. For the same kind of plastic, due to different sources or brands, its flow temperature and decomposition temperature are different, which is due to different average molecular weight and molecular weight distribution. The plasticization process of plastic in different types of injection machines is also different. These process enterprises run by themselves, so the temperature of material barrel is also different

2. Nozzle temperature: the nozzle temperature is usually slightly lower than the maximum temperature of the barrel, which is to prevent the possible "salivation" of molten material in the straight through nozzle. The nozzle temperature should not be too low, otherwise it will cause early solidification of molten material and block the nozzle *, or affect the performance of the product due to the injection of early solidification material into the mold cavity

3. Mold temperature: mold temperature has a great impact on the internal performance and apparent quality of the product. The mold temperature depends on the crystallinity of the plastic, the size of the product, the structure and performance requirements of our direct rotation for more than 10 years, and other process conditions (melt temperature, injection speed, injection pressure, molding cycle, etc.)

II. Pressure control:

the pressure in the injection molding process includes plasticizing pressure and injection pressure. It is hoped that it will make greater contributions to promoting technological innovation and strengthening the city through innovation in Linyi, and directly affect the plasticization of plastics and the quality of products

1. Plasticizing pressure: (back pressure) when the screw injection machine is used, the pressure on the molten material at the top of the screw when the screw rotates and retreats is called plasticizing pressure, also known as back pressure. This pressure can be adjusted by the overflow valve in the hydraulic system. In injection, the plasticizing pressure does not change with the rotation speed of the screw, so increasing the plasticizing pressure will increase the temperature of the melt, but will reduce the plasticizing speed. In addition, increasing the plasticizing pressure can often make the temperature of the melt uniform, the pigment mixed evenly and the gas in the melt discharged. In general operation, the plasticizing pressure should be determined as low as possible on the premise of ensuring good product quality. The specific value varies with the type of plastic used, but usually it rarely exceeds 20 kg/cm2

2. Injection pressure: in current production, the injection pressure of almost all injection machines is based on the pressure applied by the top of the plunger or screw to the plastic (converted from the oil circuit pressure). The role of injection pressure in injection molding is to overcome the flow resistance of plastic from the barrel to the cavity, give the melt filling rate and compact the melt

III. molding cycle

the time required to complete an injection molding process is called molding cycle, also known as molding cycle. It actually includes the following parts: forming cycle: forming cycle directly affects labor productivity and equipment utilization. Therefore, in the production process, the relevant time in the forming cycle should be shortened as far as possible on the premise of ensuring the quality. In the whole molding cycle, injection time and cooling time are the most important, which have a decisive impact on the quality of products. The mold filling time in the injection time is directly inversely proportional to the mold filling rate, and the mold filling time in production is generally about seconds

the pressure holding time in the injection time is the pressure time of the plastic in the mold cavity, which accounts for a large proportion in the whole injection time, generally about seconds (extra thick part extruder is one of the most important varieties in the plastic machinery industry, which can be as high as 5-10 minutes). Before the molten material at the gate is sealed and frozen, the holding time has an impact on the dimensional accuracy of the product, but it has no impact in the future. Pressure holding time also has an optimal value, which is known to depend on material temperature, mold temperature, and the size of sprue and gate

if the size and process conditions of the sprue and gate are normal, the pressure value with the smallest fluctuation range of the product shrinkage is usually taken as the standard. The cooling time mainly depends on the thickness of the product, the thermal and crystalline properties of the plastic, and the mold temperature

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