temperature control：
1. Cylinder temperature: During the injection molding process, the temperature of three places needs to be controlled, namely, the temperature of the barrel, the temperature of the nozzle and the temperature of the mold. The first two temperatures mainly affect the plasticization and flow of plastics, while the latter temperature mainly affects the flow and cooling of plastics. Each plastic has a different flow temperature. The same plastic has different flow temperature and decomposition temperature due to different sources or grades. This is due to the difference in average molecular weight and molecular weight distribution. Plastics in different types of injection The plasticizing process in the machine is also different, so the selection of barrel temperature 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 "salivation phenomenon" that may occur in the straight-through nozzle. The temperature of the nozzle should not be too low, otherwise it will cause premature solidification of the molten material and block the nozzle, or the performance of the product will be affected due to the injection of premature solidification material into the cavity
3. Mold temperature: Mold temperature has a great influence on the internal performance and apparent quality of the product. The temperature of the mold depends on the presence or absence of plastic crystallinity, the size and structure of the product, performance requirements, and other process conditions (melt temperature, injection speed and pressure, molding cycle, etc.).
Pressure control: The pressure in the injection molding process includes plasticizing pressure and injection pressure, and directly affects the plasticizing of plastics and product quality.
1. Plasticizing pressure: (back pressure) When a 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. The size of this pressure can be adjusted through the relief valve in the hydraulic system. In injection, the size of the plasticizing pressure is constant with the speed of the screw. When the plasticizing pressure is increased, the temperature of the melt will be increased, but the plasticizing speed will be reduced. In addition, increasing the plasticizing pressure can often make the temperature of the melt uniform, the color material can be mixed uniformly and the gas in the melt can be discharged. In general operation, the decision of plasticizing pressure should be as low as possible under the premise of ensuring good product quality. The specific value varies with the type of plastic used, but usually rarely exceeds 20 kg/cm2.
2. Injection pressure: In the current production, the injection pressure of almost all injection machines is based on the pressure exerted by the plunger or the top of the screw on the plastic (converted from the pressure of the oil circuit). The role of injection pressure in injection molding is to overcome the flow resistance of the plastic from the barrel to the cavity, to give the molten material a filling rate and to compact the molten material.
molding cycle ：The time required to complete an injection molding process is called the molding cycle, also known as the molding cycle. It actually includes the following parts: molding cycle: molding cycle directly affects labor productivity and equipment utilization. Therefore, in the production process, should ensure the quality of the premise, as far as possible to shorten the forming cycle in each relevant time. In the whole molding cycle, injection time and cooling time are the most important, which have a decisive influence on the quality of the product. The filling time in the injection time is directly inversely proportional to the filling rate, and the filling time in production is generally about 3-5 seconds.
The pressure holding time in the injection time is the pressure time of the plastic in the cavity, which takes a large proportion in the whole injection time, generally about 20-120 seconds (for extra thick parts, it can be as high as 5~10 minutes). Before sealing the molten material at the gate, the amount of pressure holding time has an effect on the size accuracy of the product, if in the future, it has no effect. The holding time also has an optimal value, which is known to depend on the feed temperature, mold temperature, and the size of the main channel and gate
If the size and process conditions of the main channel and gate are normal, the pressure value within which the shrinkage of the product fluctuates in the smallest range is usually taken as the norm. The cooling time is mainly determined by the thickness of the product, the thermal and crystallization properties of the plastic, and the mold temperature. The end of the cooling time, should be in order to ensure that the product does not cause changes when demoulding principle, cooling time is generally about 30~120 seconds, cooling time is too long is not necessary, not only reduce production efficiency, complex parts will also cause demoulding difficulties, forced demoulding even produce demoulding stress. Other times in the molding cycle are related to whether the production process is continuous and automated and the degree of continuity and automation.
The general injection molding machine can be adjusted according to the following procedures:
According to the temperature range provided by the material supplier, adjust the cylinder temperature to the middle of the range, and adjust the die temperature. To estimate the amount of injection glue required, set the injection molding machine to two-thirds of the estimated maximum amount of injection glue. Adjust reverse cable (glue) stroke. Estimate and adjust the secondary injection molding time, adjust the secondary injection pressure to zero.
Preliminarily adjust the primary injection pressure to half (50%) of the limit of the injection molding machine; Set injection molding speed to maximum. Estimate and adjust the required cooling time. Adjust the back pressure to 3.5bar. Remove degraded resin from cartridge. Adopt semi-automatic injection molding mode; Begin the injection procedure and observe the screw action.
It is necessary to properly adjust the injection speed and pressure, if you want to shorten the filling time, you can increase the injection pressure. As previously mentioned, the final pressure can be adjusted to 100% of the primary injection pressure due to a process prior to full filling. The pressure is eventually set high enough that the maximum speed that can be achieved is not subject to the set pressure limit. If there is overflow, you can reduce the speed.