上海Brief introduction of working principle of bidirectional lubricating oil pump

Working principle analysis of bidirectional lubricating oil pump

Structure of bidirectional lubricating oil pump. A pair of intermeshing gears and a pump cylinder separate the suction chamber from the discharge chamber. When the gear rotates, the inter-tooth volume at the position where the teeth on the suction cavity side are disengaged gradually increases, the pressure decreases, and the liquid enters the inter-tooth under the action of pressure difference. As the gears rotate, the liquid between the teeth is carried to the discharge chamber. At this time, the volume between teeth at the meshing position of the teeth on the side of the discharge cavity gradually decreases, and the liquid is discharged. Gear pump is suitable for conveying lubricating liquid with no solid particles, no corrosiveness and wide viscosity range. The flow rate of the pump can reach 300 m3/h and the pressure can reach 3×107 Pa. It is usually used as a hydraulic pump and conveying all kinds of oil products. The gear pump is simple and compact in structure, easy to manufacture, convenient to maintain, and has self-priming ability, but the flow and pressure pulsation are large and the noise is large. The gear pump must be equipped with a safety valve to prevent the pump or the prime mover from being damaged because the outlet pressure of the pump exceeds the allowable value for some reason, such as the blockage of the discharge pipe.

Brief introduction of working principle of bidirectional lubricating oil pump

The concept of gear pump is very simple, that is, its basic form is that two gears with the same size mesh and rotate in a closely matched shell. The inside of this shell is similar to the "8" shape, and the two gears are installed inside, and the outer diameter and two sides of the gears are closely matched with the shell. The material from the extruder enters between the two gears at the suction port, and fills this space, moves along the shell with the rotation of the teeth, and then is discharged when the two teeth mesh. 　　

Technically, a gear pump is also called a positive displacement device, that is, like a piston in a cylinder, when one tooth enters the fluid space of another tooth, the liquid is mechanically squeezed out. Because liquid is incompressible, liquid and teeth cannot occupy the same space at the same time, so liquid is excluded. Because of the continuous meshing of teeth, this phenomenon occurs continuously, which provides a continuous discharge at the outlet of the pump. The discharge amount is the same every rotation of the pump. With the continuous rotation of the drive shaft, the pump also continuously discharges fluid. The flow rate of the pump is directly related to the speed of the pump. In fact, there is a small amount of fluid loss in the pump, which makes the operating efficiency of the pump unable to reach 100%. Because these fluids are used to lubricate both sides of bearings and gears, and the pump body can never fit without clearance, it is impossible to discharge the fluid 100% from the outlet, so a small amount of fluid loss is inevitable. However, the pump can still run well, and for most extruded materials, the efficiency can still reach 93% ~ 98%. 　　

For fluids whose viscosity or density changes in the process, this pump will not be affected too much. If there is a damper, such as a screen or a limiter on the discharge side, the pump will push the fluid through them. If this damper changes during operation, that is, if the filter screen becomes dirty or blocked, or the back pressure of the limiter increases, the pump will still maintain a constant flow until it reaches the mechanical limit of the weak parts in the device (usually equipped with a torque limiter). 　　

In fact, there is a limit to the speed of a pump, which mainly depends on the process fluid. If oil is conveyed, the pump can rotate at a high speed, but when the fluid is a polymer melt with high viscosity, this limit will be greatly reduced. 　　

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

The gear and shaft are integrated, and a longer working life can be obtained by adopting the whole hardening process. The "D" bearing combines the forced lubrication mechanism to make the polymer pass through the bearing surface and return to the inlet side of the pump to ensure the effective lubrication of the rotating shaft. This characteristic reduces the possibility of polymer retention and degradation. The precision machined pump body can make the "D" bearing fit with the gear shaft to ensure that the gear shaft is not eccentric and prevent gear wear. Parkool seal structure and PTFE lip seal together form a water-cooled seal. This kind of seal does not actually contact the surface of the shaft. Its sealing principle is to cool the polymer to a semi-molten state to form a self-seal. Rheoseal seal can also be used, which has a reverse spiral groove on the inner surface of the shaft seal, so that the polymer can be backpressure back to the inlet. In order to facilitate the installation, the manufacturer has designed a ring bolt installation surface to match the flange installation of other equipment, which makes the manufacture of cylindrical flange easier. The gear pump has heating elements matching the specifications of the pump, which can be selected by users, which can ensure rapid heating and heat control. Different from the heating mode in the pump body, the damage of these components is limited to one board and has nothing to do with the whole 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 gear pump outlet can be controlled within 1%. Using a gear pump in the extrusion production line can improve the flow output speed, reduce the shearing and residence time of materials in the extruder, and reduce the extrusion temperature and pressure pulsation to improve the productivity and product quality.