Zhengzhou Haike Industrial Technology Co., Ltd. is a professional manufacturer and supplier of melt pumps, high-temperature melt extrusion pumps, screen changers, high-precision filters, and precision control systems (PLC).
Zhengzhou Haike Industrial Technology Co., Ltd. is a professional manufacturer and supplier of melt pumps, high-temperature melt extrusion pumps, screen changers, high-precision filters, and precision control systems (PLC).
During the operation of a melt pump, melt leakage may occur due to improper operation, harsh working conditions, and other factors. Zhengzhou Heiko, as a professional melt pump manufacturer, analyzes the causes of melt pump leakage from the following four aspects.
Leakage at the gear end faces accounts for the major part of the total leakage. Radial leakage caused by the clearance between the gear tips and the pump body, as well as bearing clearances, constitutes a secondary portion of the total leakage. Leakage resulting from clearances between gear tooth flanks accounts for only a very small fraction of the total leakage and can be neglected.
Leakage caused by designed clearances—intended to compensate for manufacturing tolerances, elastic deformation, thermal deformation of components, and lubrication of bearings by the melt—is unavoidable. The leakage rate can only be limited by optimizing all clearances as much as possible and improving the machining precision of the melt pump.
For polymer melts that follow power-law fluid flow behavior, the leakage flow rate is inversely proportional to the "effective" viscosity of the fluid within the clearances. Obviously, low-viscosity polymer melts are more prone to leakage than high-viscosity melts. Relatively speaking, the volumetric efficiency of a melt pump is higher when conveying high-viscosity polymer melts.
The "effective" viscosity of the fluid in the clearances is a function of melt temperature and the shear rate of the fluid within the clearances. On the one hand, changes in the effective melt viscosity occur: as temperature rises, melt viscosity decreases and leakage increases. On the other hand, the shear rate of the fluid in the clearances is proportional to the gear rotational speed, which further affects the effective fluid viscosity and leakage rate in the clearances, thus influencing the volumetric efficiency of the melt pump.
The leakage rate is highly related to the pressure difference between the inlet and outlet of the melt pump. Under this pressure gradient, polymer melt leaks from the high-pressure zone to the low-pressure zone through passages formed by various clearances. For melts following power-law fluid characteristics, the pressure differential is a comprehensive parameter affected by multiple variables including melt temperature, pump speed, inlet flow rate, and others.