Research on temperature and pressure responses in the rapid mold heating and cooling method based on annular cooling channels and electric heating

Rapid heat cycle molding (RHCM) is an advanced injection molding technology for producing spraying-free plastic products with excellent appearance. Rapid mold heating and cooling is the key technique of RHCM. Despite widely used in practice, the regular rapid mold heating and cooling methods still have some obvious defects. Thus, the authors developed a new rapid mold heating and cooling method characterized by electric heating and annular cooling, and this study experimentally investigated its temperature and pressure responses in the heating and cooling periods. The results show that the tool surface temperature increases almost linearly with the heating time after a short response time. The larger the heating power or the smaller the distance from heater to tool surface, the faster the heating rate. Introducing air bubbles into working fluid can remarkably reduce the pressure growth of working fluid without affecting the heating rate. In the investigated range of flow rate, the cooling rate firstly increases significantly with the flow rate, and then reaches a plateau, while the running pressure of working fluid increases linearly with the flow rate in the whole range. The optimum flow rate is around 6.0 L/min corresponding to the Reynolds number of 6700. The heat transfer coefficient in cooling period increases sharply at the initial stage, and then reduces gradually, and finally reaches a plateau. The larger the Reynolds number the higher the heat transfer coefficient. In particular, the heat transfer coefficient and the Reynolds number show a linear relationship on the double logarithm scale. Finally, a mathematical model was developed for predicting and controlling the temperature fluctuation range of tool surface. Thus, this study can benefit the industrial application of the new rapid heating and cooling method.