The temperature in the
injection Mold is uneven, which is also related to the time point in the injection cycle. After the injection, the temperature of the mold cavity rises to the highest, when the hot melt touches the cold wall of the mold cavity, and when the parts are removed, the temperature drops to the lowest. The function of the mold temperature machine is to keep the temperature constant between 2min and 2max, that is, to prevent the temperature difference from fluctuating up and down in the production process or gap. The following control methods are applicable to controlling the temperature of the mold: controlling the fluid temperature is the most common method, and the control accuracy can meet the requirements of most cases. Using this control method, the temperature displayed in the controller is not consistent with the mold temperature; The temperature fluctuation of the mold is quite large because the thermal factors affecting the mold are not directly measured and compensated, including the change of injection cycle, injection speed, melting temperature and room temperature. The second is the direct control of mold temperature. This method is to install a temperature sensor inside the mold, which is used only when the mold temperature control accuracy is required to be relatively high. The main features of mold temperature control include: the temperature set by the controller is consistent with the mold temperature; The thermal factors affecting the die can be directly measured and compensated. In general, the stability of the mold temperature is better than by controlling the fluid temperature. In addition, the mold temperature control has good repeatability in the production process control. The third is joint control. The joint control is a synthesis of the above methods, which can simultaneously control the temperature of the fluid and the mold. In the joint control, the position of the temperature sensor in the mold is extremely important. When placing the temperature sensor, the shape, structure and the position of the cooling channel must be considered. In addition, the temperature sensor shall be placed at a place that plays a decisive role in the quality of injection molded parts. There are many ways to connect one or more mold temperature controllers to the
Injection Molding machine controller. It is better to use digital interface in consideration of operability, reliability and anti-interference. Information can be transferred between the control unit and the injection molding machine through software. Mold temperature machine can also be automatically controlled.
The heat balance control of injection mold is the key to the production of injection molding parts. Inside the mold, the heat brought by plastics (such as thermoplastic plastics) is transferred to the materials and steel of the mold through thermal radiation, and transferred to the heat conducting fluid through convection. In addition, heat is transferred to the atmosphere and the mold base through thermal radiation. The heat absorbed by the heat conducting fluid is taken away by the mold temperature machine. The heat balance of the die can be described as: P=Pm - Ps. In the formula, P is the heat taken away by the mold temperature machine; Pm is the heat introduced by plastic; Ps is the heat emitted by the mold to the atmosphere.
The purpose of mold temperature control and the influence of mold temperature on injection molded parts In the
injection molding process, the main purpose of mold temperature control is to heat the mold to the working temperature, and to keep the mold temperature constant at the working temperature. If the above two points are successful, the cycle time can be optimized to ensure the stable and high quality of injection molded parts. Mold temperature will affect surface quality, fluidity, shrinkage, injection cycle and deformation. Too high or insufficient mold temperature will have different effects on different materials. For thermoplastics, a higher mold temperature usually improves surface quality and fluidity, but prolongs cooling time and injection cycle. A lower mold temperature will reduce the shrinkage in the mold, but will increase the shrinkage of the injection molded parts after demoulding. For thermosetting plastics, higher mold temperatures usually reduce cycle time, which is determined by the time required for parts to cool. In addition, in plastic processing, higher mold temperature will also reduce the plasticizing time and reduce the number of cycles.
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