PET extrusion melt pump speed control elements
In a continuous PET plant, the melt coming out of the final polymerization kettle is transported to the pelletizer and the corresponding downstream spinning system through the melt pump; in the actual production process, the speed of the gear pump is controlled by a frequency converter to achieve the purpose of controlling the output, and the melt pump speed is usually controlled by flow control or pressure control. In PET production, the speed control of the entire system is controlled in the reverse direction, and the slurry feed is actually determined by the PET extrusion melt pump output coming out of the final polymerization kettle, so it is especially important to control the speed of the melt gear pump for the material balance and stability of the entire PET production.
The melt gear pump is a positive displacement pump, which relies on the working volume change caused by the mutual meshing of the main and driven gears to convey the melt; the working volume is composed of the pump body, the gear grooves and the bearings with side plate function. When the gears rotate according to the design direction, the melt enters the grooves of the two gears in the suction chamber, and as the gears rotate, the melt is brought into the discharge chamber from both sides, and the gears engage again, so that the melt in the grooves is squeezed out of the discharge chamber and pressed into the outlet pipe.
In continuous PET production, it is important to keep the speed of the hot melt pump stable for the material balance and stability of the whole production. The speed of the melt gear pump can be controlled by flow control or pressure control, depending on the focus of the control. The use of flow control has the advantages of direct control, flow display intuitive, etc., the disadvantage is that cutting and spinning increase the pressure before the pump is not easy to stabilize; pressure control has the advantages of timely and sensitive pressure adjustment, the pressure stability of the back-end system; disadvantage is that the actual flow of the melt pump and the need to match the output is poor. Melt gear pump speed regardless of the use of flow sense control or pressure control, chemical melt pump flow are affected by the volumetric efficiency of the pump.
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