The gear pump is driven by an independent motor, which can effectively block the upstream pressure fluctuation and flow fluctuation. The pressure pulsation at the outlet of the gear pump can be controlled within 1%. Using a gear pump in the extrusion line can increase the flow output speed and reduce the shearing and residence time of materials in the extruder.
External gear pump is one of the most widely used gear pumps. General gear pump usually refers to external gear pump. Its structure is shown in Figure 5-14. It is mainly composed of driving gear, driven gear, pump body, pump cover and safety valve. The sealing space composed of pump body, pump cover and gear is the working room of gear pump. The axles of the two gears are respectively installed in the bearing holes on the two pump covers. The driving gear shaft extends out of the pump body and is driven to rotate by the motor. The external gear pump has the advantages of simple structure, light weight, low cost, reliable operation and wide application range. When the gear pump works, the driving wheel rotates with the motor and drives the driven wheel to rotate with it. When the meshing teeth on one side of the suction chamber gradually separate, the volume of the suction chamber increases and the pressure decreases, and the liquid in the suction pipe is sucked into the pump; The suction liquid is pushed to the discharge chamber by the gear in the tooth groove in two ways. After the liquid enters the discharge chamber, due to the continuous meshing of the teeth of the two gears, the liquid is squeezed from the discharge chamber into the discharge pipe. The driving gear and driven gear rotate continuously, and the pump can continuously suck in and discharge liquid. The pump body is equipped with a safety valve. When the discharge pressure exceeds the specified pressure, the delivered liquid can automatically open the safety valve to return the high-pressure liquid to the suction pipe.
The internal meshing gear pump is composed of a pair of meshing internal gears, crescent shaped parts between them, pump casing, etc. The function of the crescent shaped part is to separate the suction chamber from the discharge chamber. When the driving gear rotates, a local vacuum is formed at the place where the gear disengages from engagement. The liquid is filled between the teeth of the suction chamber by the suction pump, and then enters the discharge chamber in two ways along the inner and outer sides of the crescent shaped part. Where the gear teeth enter the mesh, the liquid between the teeth is squeezed and sent to the discharge pipe. In addition to the characteristics of self-priming capacity and flow independent of discharge pressure, the gear pump has no suction valve and discharge valve on the pump shell, which has the characteristics of simple structure, uniform flow and reliable operation, but has low efficiency, high noise and vibration, and is easy to wear. It is used to transport various oils without corrosion, solid particles and lubrication capacity, and the temperature is generally not more than 70 ℃, such as lubricating oil, edible vegetable oil, etc. The general flow range is 0.045 ~ 30ms/h, the pressure range is 0.7 ~ 20MPa, and the working speed is 1200 ~ 4000r/min.
