The single/twin screw extruder is the main equipment for polymer extrusion; it not only completes the melting and shear mixing of materials, but also completes the conveying and pressure building of the melt. Because the functions performed by the extruder are too complicated, and the processes interact with each other, the melt conveying process is not ideal; The pressure fluctuation of the extruder head leads to a decrease in the uniformity of the extruded product, which seriously affects the quality of the product.
Melt metering gear pump (referred to as "melt pump" or "metering pump") is used in series with the extruder
When the extruder melt pump is installed between the extruder and the die, its outstanding feature is that the pressure at the melt output end is hardly affected by the pressure fluctuation at the input end. It can provide a uniform and stable melt to the extrusion die. This is because the gears in the pump act as a rotating "barrier"; it can effectively block the impact of pressure fluctuations in the feed area and flow fluctuations on the discharge area. When the inlet pressure of the melt pump varies in a large range due to fluctuations of various factors, the fluctuation of the outlet pressure of the metering pump can be completely controlled within a very small fluctuation range. According to the experimental results, the reduction ratio of pressure fluctuation can reach 50:1~20:1, which can provide +-1% or better output uniformity, which can be converted into excellent product thickness uniformity; such as optical fiber, high-speed coating Coated cables, biaxially oriented films, medical special pipes and micro-foamed products have higher requirements on extrusion precision.
The main advantage of adding a melt gear pump at the end of the extruder is the consistency and quality of the output. A gear pump, also known as a melt pump, is a positive displacement device so the output per revolution is consistent and predictable. A gear pump is used for high pressure pumping; therefore, it builds the pressure (die and screen changer) needed to overcome system back pressure more efficiently than an extruder.
The volumetric efficiency of the melt pump is 98% to 99%, while the efficiency of the extruder is only 45%. This means that adding a gear pump to an extruder generally reduces overall power consumption. Wear on very expensive extruder components can also be reduced by taking on the pressure build-up by the melt pump. email@example.com