1. The heat balance of the injection mold controls the heat conduction of the injection molding machine and the mold is the key to the production of injection molded parts. Inside the mold, the heat brought by the plastic (such as thermoplastic) is transferred to the material and the steel of the mold through thermal radiation, and transferred to the heat transfer fluid through convection. In addition, heat is transferred to the atmosphere and the mold base through thermal radiation. The heat absorbed by the heat transfer fluid is taken away by the mold temperature machine. The thermal 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 emitted by the mold to the atmosphere.
2. The purpose of controlling the mold temperature and the influence of the mold temperature on the injection molded parts. In the injection molding process, the main purpose of controlling the mold temperature is to heat the mold to 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 high quality of injection molded parts. Mold temperature will affect surface quality, fluidity, shrinkage, injection cycle and deformation. Excessive or insufficient mold temperature will have different effects on different materials. For thermoplastics, a higher mold temperature will usually improve the surface quality and fluidity, but will extend the 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 part after demolding. For thermoset plastics, a higher mold temperature usually reduces the cycle time, and the time is determined by the time required for the part to cool. In addition, in the processing of plastics, a higher mold temperature will also reduce the plasticizing time and reduce the number of cycles.
3. Preparatory conditions for effective control of mold temperature The temperature control system consists of three parts: mold, mold temperature controller, and heat transfer fluid. In order to ensure that heat can be added to or removed from the mold, each part of the system must meet the following conditions: First, inside the mold, the surface area of the cooling channel must be large enough, and the diameter of the runner must match the pump’s capacity (pump pressure). The temperature distribution in the cavity has a great influence on part deformation and internal pressure. Reasonable setting of cooling channels can reduce the internal pressure, thereby improving the quality of injection molded parts. It can also shorten cycle time and reduce product costs. Secondly, the mold temperature machine must be able to keep the temperature of the heat transfer fluid within the range of 1°C to 3°C, depending on the quality requirements of the injection molded parts. The third is that the heat transfer fluid must have good thermal conductivity, and most importantly, it must be able to import or export a large amount of heat in a short period of time. From a thermodynamic point of view, water is clearly better than oil.