Melt pump - the best extruder "friend"

Melt Pump - The Best "Friend" for Extruders Melt pumps play an integral role in the extruder. It is called the best "friend" for extruders, which not only provides stable delivery of melt material, but also provides extrusion pressure more efficiently than screws, and it can be used as a mixing device to improve the quality of the melt. As the best "friend" of the extruder, the melt pump precisely controls the production of the handpiece. The melt pump consists of two gears, usually driven by a single motor. The material delivered by the extrusion screw first enters the suction end of the gear and the gear is rotated before it is fed from the other side. The principle is that a well-made gear has a very fine profile, and the amount of material in each tooth is very accurate when the gear and housing are closely mated. Gear can accurately measure the material in the discharge end, gear speed by the DC or AC motor drive control, the rate of change within 1%. Why meltblown extruder is the best "friend"? This is because, by precisely controlling the melt output, the melt pump eliminates many of the variables that affect the output stability of the extruder. Melt pumps compensate for many adverse effects on extrusion throughput, such as poor temperature control, feed discontinuities, changes in polymer blend composition (such as changes in regrind content), and extrusion accuracy due to screw design Fluctuations and so on. As these output stability issues are resolved, the operator can focus more on the nose and downstream equipment. Melt Pump Monitoring However, the operation of the melt pump requires some degree of monitoring. Important indicators observed include outlet pressure, suction pressure, inlet and outlet pressure difference, motor current, gear shaft seal, and pump temperature. Since the head flow changes with the outlet pressure, the outlet pressure should be constant. In general, the outlet pressure fluctuations can not exceed ± 10psi (1psi = 0.00689Mpa). Large fluctuations usually belong to the transmission problem, the need for motor technicians to adjust the transmission parameters. If the melt pump is heavily damaged, it can also cause such problems. Changes in suction pressure reflect changes in extruder output. Although the main function of the melt pump is to eliminate these fluctuations, the range of fluctuations that it can control is limited. Even if the melt pump keeps the output of the polymer constant, the melt temperature changes. Because the suction pressure to maintain stability, the screw speed will change, which led to fluctuations in melt temperature. Fluctuations in melt temperature will directly lead to head melt flow and product size changes. The ideal suction pressure must not fluctuate within ± 100 psi, preferably ± 50 psi, and fluctuations above this value will result in changes in head flow. For this reason, it is necessary to reduce the sensitivity of the extruder motor to the pressure fluctuation reaction. This typically gives extruder motor this feature by adding proportional control and sensing the bandwidth of the pressure. If this method is not yet able to minimize fluctuations, it is likely to be the extruder's own problems, which will have to be analyzed separately. The power required to rotate the pump gear should be constant. Even a few amps of current change during drive mean there is a problem. This can be a simple parameter setting problem, a mechanical problem in the pump body, gearbox or drive shaft, or too much suction pressure fluctuations. The bearings of the melt lubricated melt pump are self-lubricated by the melt through a leak design from the pump outlet end to the suction end and through the entire bearing. Polymer flow is very necessary to protect the bearings. This flow requires that the pump outlet pressure and inlet pressure be different, suggesting that the pressure differential between the two ports should be kept at a minimum of a few hundred psi. Because the melt pump's bearings are melt lubricated, there is a seal on the outside of the bearings to prevent the polymer from flowing to the outside of the gear shaft. In order to adapt to different melt viscosity and pump pressure, most pumps are installed water-cooled seal. This requires a reasonable amount of water to ensure that there is enough water to prevent leakage or to reduce the discharge to the micro level. However, there should not be too much water as this will reduce shaft lubrication and increase the load on the melt pump motor. After the melt pump starts, its temperature should match the melt temperature or melt set temperature. If the pump temperature is significantly higher than the set temperature or the actual melt temperature, this means that the pump's mechanical part or the temperature controller has failed. Practice has proved that the melt pump temperature below the melt temperature 3-6 ℃ is the most reasonable. In addition to being able to stably convey unexpectedly multifunctional devices, the melt pump has many other advantages: Compared to extruding the screw, the melt pump is more effective in raising the pressure, so that the pressure in the screw head is reduced, the melt temperature is decreased, and the screw output increase. In addition, the melt pump is a mixing device that improves the quality of the melt.

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