Gear pump is ideal for conveying high viscosity liquid equipment, its wide range of applications.
At present, although domestic enterprises have produced many gear pumps suitable for conveying high-viscosity liquids, some problems still exist in material selection, leakage and noise prevention due to imperfect testing methods. Especially domestic high-viscosity gear pump in the efficiency, reliability and service life and other aspects of foreign products there is a big gap. Therefore, the majority of high-viscosity gear pumps used in China's oil and chemical industries still rely on imports.
The development of high-viscosity gear pumps at home and abroad are as follows:
Gear structure
High-viscosity gear pump gear are common spur, helical, herringbone, helical teeth, tooth profile are mainly involute and arc type. Usually small gear pump to use more involute spur gear, high temperature gear pump often use variable gear, conveying high viscosity, high pressure melt polymer melt more use of involute helical gears. Gear and shaft made of one, its rigidity and reliability is higher than gear and shaft separately manufactured gear pump. Foreign low-pressure gear pump gear is often used square structure, that gear tooth width equal to the addendum circle diameter. The high-pressure occasions used in high-viscosity gear pump gear tooth width less than its tip diameter, which is to reduce the gear radial compression area, reduce gear, bearing load.
Pump body and heating method
In general, the heavier the pump gear pump casing, the higher temperature resistance, compressive strength. Pump material commonly used ductile iron, cast aluminum alloy can also be cast using hard cast, or extruded aluminum alloy profiles manufacturing. When the medium is corrosive, high-cost stainless steel can be used. Foreign high viscosity gear pump to use more nickel, chromium alloy steel as the pump casing material, this material in the strength, reliability and cost of the overall performance is better. In order to solve the trapped oil phenomenon of the gear pump, a symmetrical unloading groove is usually provided on the pump cover, or an asymmetric unloading groove is opened to the low pressure side, a taper unloading groove is adopted on the suction side, and a rectangular unloading Depth of the groove, unloading groove than the hydraulic pump used in industrial gear deeper.
Due to the high viscosity of the medium fed by the gear pump, the media must be heated or insulated in order to reduce flow resistance and increase the suction capacity of the pump. Heating elements are usually used to make viscous liquid heat evenly. If the temperature fluctuations, the delivery of high-viscosity liquid prone to degradation, it is recommended to use fluid heating, especially large displacement gear pump. Fluid heating is divided into built-in, external structure. The so-called built-in gear pump pump body or cover the internal design of the sudden heat jacket, the external is through the screw clamp jacket and pump body together. Into the jacket into the steam, HTF, or cooling water, according to the specific circumstances of the media. Built-in for the delivery of liquid temperature uniformity is higher, or require uniform cooling of high temperature liquid occasions. When the lack of electrical heating or security requirements of the temperature control is not high, the external structure can be used. American VIKING company's internal gear pump, pump head part of the jacket can be transported fluid temperature control, either in high temperature or low temperature environment, can be equipped with an external jacket.
Bearing Materials, Construction and Lubrication
High-viscosity gear pump bearings are usually used in plain bearings and non-bearing surface of the bearing wall specially designed spiral flow path, spiral groove and the steering shaft gear rotation the same. The outer end of the bearing communicates with the inlet of the pump, and the spiral groove at the inner end of the bearing communicates with the root of the gear (vacuum part). As the shaft rotates, the low temperature liquid outside the bearing is drawn into the bearing by means of the helical action and the pressure difference between the two ends of the bearing. After the bearing is lubricated and cooled, it flows into the tooth just disengaged to form a fully lubricated and heat-dissipating screw Self-priming low-pressure lubrication system. The advantages of the lubrication method are as follows: all the lubricating liquid entering the bearing is a low-temperature medium, and the viscous lubricating liquid tends to form a dynamic pressure oil film with a strong carrying capacity. A large number of lubricating fluid circulation continue to take the heat of the bearing, the bearing play a good role in lubrication and cooling. Because there is sufficient liquid to fill just off the meshing gear roots, greatly improving the pump self-priming performance, to avoid the phenomenon of suction, not only can improve the volumetric efficiency, but also help to reduce cavitation and reduce noise. Sichuan Machinery Research and Design Institute of the use of sliding bearings immersed in the medium, and forced lubrication through special channels, the technology has been in the vinylon, polyester, rubber, resins, fertilizers and other fields gear pump successfully applied.
Bearing materials commonly used tool steel, and hardened to improve its anti-gluing capacity. If the conveying medium contains abrasive particles, a hard bearing material such as ceramic should be used. In recent years, GS-1 PTFE steel composite is considered as the ideal sliding bearing material. It is made of cold-rolled steel plate (substrate), sintered spherical porous bronze powder or copper mesh (intermediate layer), PTFE (surface layer) three layers of composite materials, both metal and PTFE plastic advantages. On the basis of this material, Shanghai Institute of Materials has also developed a better performance SF-type three-layer composite self-lubricating material, which uses bronze wire instead of bronze powder layer, the surface of the plastic formula carefully selected. This bearing material fatigue resistance, high load capacity, low friction coefficient, long service life, is to improve the technical performance of gear pump new bearing material.
Suction drain port
High-viscosity gear pump suction port diameter is generally larger, sometimes using diffuse-shaped suction port to expand the volume of low-pressure zone to reduce the inlet liquid flow rate, reducing the pump suction resistance. This structure can also reduce the radial force on the journal and bearings to extend the service life of high viscosity gear pump.
Check valve and safety valve
A check valve is installed on the output pipe of the gear pump so that the liquid in the system will not flow backwards when the pump is being serviced and the output pipe is in place. When the gear pump is under a load stop, a partial vacuum is generated in the output pipe to prevent the pump reverse. High viscosity gear pump outlet pipe also set safety valve and other protective devices, so once the pump outlet channel blockage, you can open the safety valve pressure relief. The safety valve can be cast in one piece with the pump body or pump head and can also be assembled separately.
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