Melt booster gear pump for extrusion granulator in polyolefin plant
The melt boosting gear pump is a key dynamic equipment in the extrusion granulation system of polyolefin plants. Currently, most large-scale extrusion granulation series will be equipped with a melt boosting gear pump, which completes the homogenization and pressure building function. The melt boosting gear pump is installed between the driving valve and the screen changer. Its function is to mix and melt the polyolefin powder and additives in the extruder. The melt is pressurized by the melt boosting gear pump and transported, filtered by the screen changer and molded by the template. Finally, it is cut into pellets in the underwater granulation device. Therefore, the smooth operation of the melt boosting gear pump directly affects the smooth operation of the entire extrusion granulation production line.
In the meshing area of the two gears in the melt boosting gear pump, near the pump inlet, the teeth and grooves of the two gears are in a separated state, forming a low-pressure zone. At this time, the molten material of the extruder fills the grooves with less pressure. As the two gears rotate synchronously in reverse, the material is continuously transported to the pump outlet side in a sealed cavity formed between the teeth and the pump body. The teeth and grooves of the two gears enter a closed state, and the material is squeezed out. This cycle is repeated to achieve continuous transportation of the material. This mechanical forward displacement conveying principle has better flow control performance than the conveying principle of single screw relying on solid friction and viscous drag. At the outlet of the melt boosting gear pump, due to the resistance generated by the screen changer and the machine head template, the pump gear will further compress the discharged material to achieve boosting.
The melt boosting gear pump mainly consists of a variable frequency motor, gear reducer, coupling, gear pump body, reducer lubrication system, etc. The gear pump body is composed of upper and lower gear rotors, sliding bearings, sealing sleeves, gear pump housing, etc. The gear rotor adopts a straight tooth structure, with the upper and lower gears rotating in opposite directions without meshing. The material is continuously sucked in from the input end and discharged under high pressure from the output end. The pump body bearing is self-lubricated by molten material, and the lubricated material returns to the inlet side of the pump.
A large extruder equipped with a melt boosting gear pump has the following main advantages compared to an extruder without a gear pump:
(1) Reducing the axial compliance of the twin-screw extruder, reducing the design difficulty of the matching gearbox of the extruder, improving the reliability and service life of the extruder, and reducing energy consumption. The quality of plastic particles in the products of the extrusion granulator is closely related to the stability of the extrusion flow rate and pressure. When the extruder is not equipped with a melt boosting gear pump, in order to overcome the resistance of the mesh changer and granulation template, it generally needs to have a pressure building capacity of up to 40MPa or less. However, the extruder equipped with a melt boosting gear pump only needs to provide a pressure of 1-3Mpa to meet the pump inlet needs.
(2) Strong material adaptability, successful granulation and high filtration. The color, shape, size and other parameters of the pellets produced by the extrusion granulator have different requirements according to the brand. The primary condition for successful pelletizing is to obtain a stable polymer melt flow with pressure, flow rate, and temperature at the extruder head template. The melt booster gear pump can be precisely controlled, so it has stronger adaptability to the material and higher filtration rate for successful pelletizing compared to extruders without a melt gear pump.
(3) Has higher production efficiency.
(4) With lower