As a positive displacement pump, the mechanism of melt transport depends on the continuous change of the volume of the feed area and discharge area. Because the volume of discharge area is always in a state of decreasing, so the melt must be extruded to achieve the pump pressurization function. At the same time, the gear of the pump can effectively block the fluctuation of the pressure and flow in the feeding area, thus realizing the function of stabilizing the pressure.
When calculating the flow rate of the melt pump, the empirical formula is usually applied to deal with the actual application. At the same time, due to the characteristics of the gear itself, the pump will inevitably produce a certain flow fluctuation in the process of transportation, that is, the flow is not uniform. Therefore, various factors affecting the flow fluctuation should be fully considered in the design to minimize the flow fluctuation of the designed melt pump. In addition, due to the existence of various clearances in assembly, often resulting in a certain leakage, so in the design should be reasonable to select clearances, so as to achieve the best volume efficiency of the melt pump.
Generally speaking, the three technical parameters of displacement, working temperature and pressure determine the transport and pressurization capacity of the melt pump. In the case of a certain maximum output, it is particularly important to control the speed of the pump. Excessive speed may cause the melt to decompose due to high shear. The three performance characteristics of the melt pump are: linear output characteristics, pressurization characteristics, low energy efficiency and high volumetric efficiency.