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Injection mold features
Apr 27, 2018

Injection mold features

The temperature inside the injection mold is uneven, and it is also related to the point in time during the injection cycle. The function of the mold warmer is to keep the temperature constant between 2 min and 2 max, that is to prevent the temperature difference from fluctuating above and below the production process or gap. The following several 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 in the controller does not agree with the mold temperature; the mold temperature fluctuations are considerable because the thermal factors affecting the mold do not directly measure and compensate for these factors including changes in injection cycle, 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 will be used when the mold temperature control accuracy requirements are relatively high. The main features of the mold temperature control include: the temperature set by the controller is consistent with the mold temperature; the thermal factors that affect the mold can be directly measured and compensated. In general, 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 synthesis of the above methods, it can control the temperature of the fluid and the mold at the same time. 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 should be placed in a place that is decisive for the quality of the injection molded part. There are many ways to connect one or more mold temperature controllers to the injection molding machine controller. It is best to use a digital interface in terms of operability, reliability, and anti-jamming.

The heat 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 by heat radiation to the steel of the material and the mold and is transferred to the heat transfer fluid by convection. In addition, heat is transferred to the atmosphere and the mold frame by thermal radiation. The heat absorbed by the heat transfer fluid is taken away by the mold warmer. The heat balance of the mold 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 the plastic; Ps is the heat that the mold disperses to the atmosphere. The purpose of controlling the temperature of the mold and the influence of the temperature of the mold on the injection molded part The main purpose of controlling the temperature of the mold in the injection molding process is to heat the mold to the operating 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 high quality of injection molded parts. Mold temperature will affect the surface quality, fluidity, shrinkage, injection cycle and deformation and other aspects. Excessive or insufficient mold temperature can have different effects on different materials. For thermoplastics, a higher die temperature generally improves surface quality and flow but increases the cooling time and injection cycle. A lower mold temperature lowers the shrinkage in the mold but increases the shrinkage of the molded part after demoulding. For thermosetting plastics, a higher mold temperature usually reduces the cycle time, which is determined by the time required for the part to cool. In addition, in the plastic processing, a higher mold temperature will also reduce the plasticization time and reduce the number of cycles.