Mixing Techniques for Injection Molding Machines

Injection molding is an engineering technology that involves transforming plastic into useful and functional products. The important process conditions of injection molding are the temperature, pressure, and corresponding effect moments that affect the plasticizing activity and cooling.
1、 Temperature control
1. Barrel temperature: The temperature required for controlling the injection molding process includes barrel temperature, nozzle temperature, and mold temperature. The first two temperatures primarily affect the plasticization and activity of plastics, while the second temperature primarily affects the activity and cooling of plastics. Each type of plastic has a different activity temperature, and the same type of plastic has different activity and differentiation temperatures due to its origin or brand. This is because the average molecular weight and molecular weight dispersion are different, and the plasticization process of plastic in different types of injection machines is also different, so the temperature of the selected material barrel is also different.
2. Nozzle temperature: The nozzle temperature is generally slightly lower than the upper limit of the barrel temperature, in order to avoid the "salivation phenomenon" that may occur when the molten material is in the straight nozzle. The temperature of the nozzle should not be too low, otherwise it will cause early solidification of the molten material and block the nozzle, which may affect the function of the product due to the injection of early solidification material into the mold cavity
3. Mold temperature: Mold temperature has a significant impact on the intrinsic function and apparent quality of the product. The unevenness of mold temperature depends on the presence or absence of plastic crystallinity, the size and structure of the product, functional requirements, and other process conditions (melt temperature, injection speed and pressure, molding cycle, etc.).
2、 Pressure control: During the injection molding process, the pressure includes two types: plasticizing pressure and injection pressure, which directly affect the plasticization of plastics and the quality of products.
1. Plasticizing pressure: (Back pressure) When using a screw injection machine, the pressure exerted on the top of the screw during the rolling retreat of the screw is called plasticizing pressure, also known as back pressure. The magnitude of this pressure can be adjusted through the relief valve in the hydraulic system. In injection, the size of the plasticizing pressure remains constant with the rotational speed of the screw. Therefore, adding plasticizing pressure will increase the temperature of the melt, but will reduce the plasticizing speed. In addition, adding plasticizing pressure often results in a uniform temperature of the melt, a uniform mixing of pigments, and the discharge of gases from the melt. In general operations, the determination of plasticizing pressure should be as low as possible while ensuring excellent product quality. The specific value varies depending on the type of plastic used, but generally it rarely exceeds 20 kilograms per square centimeter.
2. Injection pressure: In current production, the injection pressure of almost all injection machines is based on the pressure applied to the plastic at the top of the plunger or screw (converted from oil pressure). The effect of injection pressure in injection molding is to overcome the resistance of plastic flow from the barrel to the cavity, provide the rate of mold filling for the molten material, and compact the molten material.