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Gear pump design concept

11 Jan 2022Email

       The concept of a gear pump is very simple, that is, its most basic form is that two gears of the same size mesh with each other in a tightly fitting shell. The inside of the shell is similar to the "8" shape, and two gears are installed in it. The outer diameter and both sides of the gear are tightly matched with the housing. The material from the extruder enters the middle of the two gears at the suction port, and fills the space, moves along the housing with the rotation of the teeth, and is finally discharged when the two teeth mesh.

      In fact, there is a small amount of fluid loss in the pump, which makes the pump's operating efficiency unable to reach 100%, because these fluids are used to lubricate the bearings and both sides of the gear, and the pump body can never fit without clearance, so The fluid cannot be discharged from the outlet 100%, so a small amount of fluid loss is inevitable. However, the pump can still run well, and for most extruded materials, it can still reach an efficiency of 93% to 98%.

   For fluids whose viscosity or density changes during the process, this pump will not be affected too much. If there is a damper, such as a strainer or a restrictor on the side of the discharge port, the pump will push the fluid through them. If this damper changes during operation, that is, if the filter screen becomes dirty, clogged, or the back pressure of the limiter rises, the pump will still maintain a constant flow rate until the mechanical limit of the weakest part of the device is reached (Usually equipped with a torque limiter).

There is actually a limit to the speed of a pump, which mainly depends on the process fluid. If the oil is conveyed, the pump can rotate at a very high speed, but when the fluid is a high-viscosity polymer melt In practice, this restriction will be greatly reduced.

It is very important to push the high-viscosity fluid into the two-tooth space on the side of the suction port. If this space is not filled, the pump will not be able to discharge the accurate flow rate, so the PV value (pressure × flow rate) is another limiting factor, and It is a process variable. Due to these limitations, gear pump manufacturers will provide a series of products, that is, different specifications and displacement (amount discharged per revolution). These pumps will be matched with the specific application process to optimize the system capacity and price.

   The gear and shaft of the PEP-II pump are integrated, and the whole body hardening process is adopted to obtain a longer working life. The "D" type bearing incorporates a forced lubrication mechanism that allows the polymer to pass through the bearing surface and return to the inlet side of the pump to ensure effective lubrication of the rotating shaft. This feature reduces the possibility of polymer retention and degradation. The precision-machined pump body can accurately match the "D" type bearing with the gear shaft to ensure that the gear shaft is not eccentric to prevent gear wear. Parkool seal structure and PTFE lip seal together constitute a water-cooled seal. This kind of seal does not actually touch the surface of the shaft. Its sealing principle is to cool the polymer to a semi-molten state to form a self-sealing. Rheoseal seal can also be used, which has reverse spiral grooves on the inner surface of the shaft seal, so that the polymer can be back pressured back to the inlet. In order to facilitate installation, the manufacturer has designed a ring bolt mounting surface to match the flange mounting of other equipment, which makes the manufacture of cylindrical flanges easier.

  PEP-II gear pump has heating elements that match the pump specifications, which can be selected by users, which can ensure rapid heating and heat control. Unlike the heating method in the pump body, the damage of these components is limited to one board and has nothing to do with the entire pump.

  The gear pump is driven by an independent motor, which can effectively block the upstream pressure pulsation and flow fluctuation. The pressure pulsation at the outlet of the gear pump can be controlled within 1%. Using a gear pump on the extrusion production line can increase the flow output speed, reduce the shear and residence time of the material in the extruder, and reduce the extrusion temperature and pressure pulsation to improve productivity and product quality

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