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Injection Mold Features
Aug 20, 2018

The temperature in the injection mold is uneven at each point and is also related to the time point in the injection cycle. The role of the mold temperature machine is to keep the temperature constant between 2min and 2max, which means to prevent the temperature difference from fluctuating up and down in the production process or gap. The following control methods are suitable for controlling the temperature of the mold: controlling the fluid temperature is the most common method, and the control accuracy can meet most of the requirements. Using this control method, the temperature displayed on the controller and the mold temperature are not uniform; the temperature fluctuation of the mold is quite large, because the thermal factors affecting the mold are not directly measured and compensated for these factors including the injection cycle change, injection speed, melting temperature and Room temperature. The second is the direct control of the mold temperature. The method is to install a temperature sensor inside the mold, which is adopted when the mold temperature control accuracy requirement is 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 mold can be directly measured and compensated. Typically, mold temperature stability is better than by controlling fluid temperature. In addition, mold temperature control is more reproducible in production process control. The third is joint control. Joint control is a combination of the above methods that simultaneously controls the temperature of the fluid and the mold. In joint control, the position of the temperature sensor in the mold is extremely important. When placing the temperature sensor, the shape, structure, and position of the cooling passage must be considered. In addition, the temperature sensor should be placed where the quality of the molded part is decisive. There are many ways to connect one or more mold temperature machines to the injection molding machine controller. It is best to use a digital interface from the standpoint of operability, reliability and immunity.

The thermal balance of the injection mold controls the heat transfer of the injection molding machine and the mold is the key to the production of injection molded parts. Inside the mold, heat from plastics (such as thermoplastics) is transferred to the steel of the material and the mold by heat radiation, and is transferred to the heat transfer fluid by convection. In addition, heat is transferred to the atmosphere and the formwork by thermal radiation. The heat absorbed by the heat transfer fluid is carried away by the mold temperature machine. The heat balance of the mold can be described as: P = Pm - Ps. Where P is the heat taken away by the mold temperature machine; Pm is the heat introduced by the plastic; Ps is the heat that the mold emits to the atmosphere. The purpose of controlling the mold temperature and the influence of the mold temperature on the injection molded part In the injection molding process, the main purpose of controlling the mold temperature is to heat the mold to the working temperature, and the second is 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 high quality of the injection molded parts. Mold temperature affects surface quality, fluidity, shrinkage, injection cycle and deformation. Excessive or insufficient mold temperature can have different effects on different materials. For thermoplastics, higher mold temperatures generally improve surface quality and flow, but extend cooling time and injection cycle times. A lower mold temperature will reduce shrinkage in the mold, but will increase the shrinkage of the molded part after demolding. For thermoset plastics, a higher mold temperature typically reduces cycle time, and the time is determined by the time required to cool the part. In addition, in the processing of plastics, a higher mold temperature will also reduce the plasticizing time and reduce the number of cycles.

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