temperature control

1. Barrel temperature: The temperature to be controlled during injection molding process includes barrel temperature, nozzle temperature and mold temperature. The first two temperatures mainly affect the plasticization and flow of plastics, while the latter one mainly affects the flow and cooling of plastics. Each kind of plastic has different flow temperature. Due to different source or brand, the flow temperature and decomposition temperature of the same plastic are different. This is due to different average molecular weight and molecular weight distribution. The plasticizing process of plastic in different types of injection machines is also different, 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 "salivation" that may occur when the molten material is in the straight-through nozzle. The nozzle temperature shall not be too low, otherwise the nozzle will be blocked due to the early solidification of the molten material, or the performance of the product will be affected due to the injection of the early solidification material into the mold cavity.

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

pressure control 

The pressure in the process of injection molding includes plasticizing pressure and injection pressure, which directly affects the plasticizing of plastics and the quality of products.

1. Plasticizing pressure: (back pressure) When the screw injection machine is used, the pressure that the molten material at the top of the screw is subjected to when the screw rotates backward is called plasticizing pressure, also called back pressure. The pressure can be adjusted by the overflow valve in the hydraulic system. In injection, the size of the plasticizing pressure needs to change with the design of the screw, the requirements of the product quality and the type of plastic. If these conditions and the rotational speed of the screw remain unchanged, increasing the plasticizing pressure will strengthen the shearing effect, that is, it will increase the melt temperature, but it will reduce the plasticizing efficiency, increase the countercurrent and leakage flow, and increase the driving power.

In addition, increasing the plasticizing pressure can often make the temperature of the melt uniform, the color mixture uniform and the gas in the melt discharged. In general operation, the plasticizing pressure should be determined as low as possible under the premise of ensuring the good quality of the product. The specific value varies with the type of plastic used, but usually it rarely exceeds 20 kg/cm2.

2. Injection pressure: In current production, almost all injection machines have injection pressure of plunger or screw top to plastic