Requirements for the purpose, internal structure, and material of the melt pump

The melt pump can operate continuously at high temperatures of 350C and pressures of 35MP or higher. Its main function is to pressurize and stabilize the high-temperature plastic melt from the extruder, ensuring accurate and stable flow of the melt into the extruder head. When the melt at the inlet of the pump experiences significant pressure fluctuations due to various reasons, the pressure fluctuations caused at the outlet are minimal. Its ability to stabilize melt pressure and flow rate is superior to various types of extruders. Its main characteristics are simple and compact structure, reliable operation, and long service life.

The composition of the melt pump mainly includes the pump body, front and rear side plates, two meshing gears, bearings, and seals. The space formed by the tooth profile of two gears, pump body, and side plate forms the inlet area, conveying area, and discharge area of the pump. Gears are the core components of melt pumps, with various structural forms that can be divided into internal and external meshing modes according to the meshing mode; According to the tooth profile curve, it can be divided into involute gears, circular arc gears, cycloidal gears, etc; According to the tooth direction, it can be divided into spur gears, helical gears, and herringbone gears. But in the process of conveying plastic melt, the most commonly used is an external meshing gear pump with involute straight or helical teeth.

Due to the continuous operation of the melt pump under high temperature and pressure conditions, and the transported plastic melt generally has high viscosity, some of which also have certain corrosiveness. Therefore, high requirements are placed on the material of the melt pump, which needs to have characteristics of temperature resistance, wear resistance, corrosion resistance, and sufficient strength and dimensional stability. Usually, melt pumps are mainly made of alloy tool steel, with gears and shafts integrated, making them more reliable to operate under high torque conditions.

The lubrication and sealing issues of the melt pump are quite complex. In order to prevent contamination of plastic melt, it cannot use ordinary lubricating oil or grease for lubrication, but relies on the transported plastic melt for self-lubrication. Therefore, the bearing and sealing structure of the melt pump must adapt to the special performance of plastic melt. For small and medium-sized melt pumps, electric heating is generally used for insulation, while for large melt pumps, a jacket type pump body is used for fluid temperature control.

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