The effect of mold temperature on the injection molding process


    1. To achieve a thermal balance of the mold surface […]

    1. To achieve a thermal balance of the mold surface to continue to produce stable quality injection molded products.
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, the heat from the plastic 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.

    2. The main purpose of controlling the mold temperature is to heat the mold to the operating temperature and keep the mold temperature constant at the operating temperature.
The cycle time can be optimized to ensure a consistently high quality of the injection molded part. 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.

    3. Pre-conditions for effective control of mold temperature The temperature control system consists of three parts: mold, mold temperature machine and heat transfer fluid.
In order to ensure that heat can be added to the mold or removed, the various parts of the system must meet the following conditions: First, inside the mold, the surface area of ​​the cooling passage must be large enough to match the pump's capacity. The temperature distribution in the cavity has a large influence on the deformation and internal stress of the part. Properly setting the cooling runners can reduce the inherent stress and thus improve the quality of the molded parts. It also reduces cycle times and reduces product costs. Secondly, the mold temperature machine must be able to keep the temperature of the heat transfer fluid constant within the range of 1 ° C - 3 ° C, depending on the quality requirements of the injection molded parts. The third is that the heat transfer fluid must have good heat transfer capacity, and most importantly, it must be able to introduce or export a large amount of heat in a short time. From a thermodynamic point of view, water is significantly better than oil.