Gear pumps are ideal equipment for transporting high viscosity liquids and have a wide range of applications.  

At present, although domestic enterprises have produced many gear pumps suitable for transporting high viscosity liquids, there are still some problems in material selection, leakage and noise prevention due to incomplete testing methods. Especially, there is a significant gap between domestically produced high viscosity gear pumps and foreign products in terms of efficiency, reliability, and service life. Therefore, most of the high viscosity gear pumps used in China's petroleum and chemical industries still rely on imports.  

The development characteristics of high viscosity gear pumps at home and abroad are as follows:

Gear structure

The gears of high viscosity gear pumps commonly include straight teeth, helical teeth, herringbone teeth, and spiral teeth, with tooth profiles mainly including involute and circular arc forms. Usually, small gear pumps use involute spur gears, high-temperature gear pumps often use variable gears, and melt pumps that transport high viscosity, high-pressure polymer melts often use involute helical gears. The gear and shaft are integrated, and their rigidity and reliability are higher than those of gear pumps manufactured separately. The gears of low-pressure gear pumps abroad often adopt a square structure, where the tooth width of the gear is equal to the diameter of the tooth tip circle. The tooth width of high viscosity gear pumps used in high-pressure environments is smaller than their tooth tip circle diameter, in order to reduce the radial compression area of the gears and lower the load on the gears and bearings.  

Pump body and heating method

Generally speaking, the heavier the pump casing of a gear pump, the higher its temperature and pressure resistance strength. The material of the pump body is often ductile iron, which can also be cast by casting aluminum alloy hard molds or manufactured by extruding aluminum alloy profiles. When the conveyed medium is corrosive, higher cost stainless steel materials can be used. Foreign high viscosity gear pumps often use alloy steel with high nickel and chromium content as the pump casing material, which has good comprehensive performance in strength, reliability, and cost. To solve the problem of oil entrapment in gear pumps, symmetrical unloading grooves are usually opened on the pump cover, or asymmetrical unloading grooves are opened towards the low-pressure side. A conical unloading groove is used on the suction side, and a rectangular unloading groove is used on the discharge side. The depth of the unloading groove is also deeper than that of gear pumps used in the hydraulic industry.  

Due to the high viscosity of the medium conveyed by high viscosity gear pumps, heating or insulation of the medium is necessary to reduce flow resistance and improve the pump's suction capacity. Usually, electric heating elements are used to uniformly heat viscous liquids. If the temperature fluctuation is not significant and the high viscosity liquid being transported is prone to degradation, it is recommended to use fluid heating, especially for gear pumps with large displacement. Fluid heating is divided into internal and external structures. The so-called internal type refers to the design of a heat sleeve inside the gear pump body or end cover, while the external type is connected to the pump body through bolts to clamp the heat sleeve together. Whether to introduce steam, thermal oil, or cooling water into the jacket depends on the specific conditions of the medium. Built in type is suitable for situations where high temperature uniformity is required for conveying liquids, or where uniform cooling of high-temperature liquids is required. When the electric heating method lacks safety or does not require high temperature control, an external structure can be used. The internal gear pump produced by VIKING in the United States has a jacket on the pump head that can control the temperature of the conveyed fluid. It can be equipped with an external jacket in both high and low temperature environments.

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