PE foam film extrusion melt pumps
Core Function: Stabilized delivery and metering of high temperature, high viscosity melt
In PE foam film production, the melt pump is required to pressurize, stabilize and accurately meter the high temperature polymer melt (e.g. PE) output from the extruder into the head. Its key roles include:
Flow stability
The melt pump realizes positive displacement delivery through gear meshing, and the flow rate is strictly proportional to the rotational speed, which can eliminate the flow pulsation caused by the extruder charging fluctuation and temperature change. For example, in the XPS foam production line, the melt pump will reduce the outlet pressure fluctuations to within ± 1%, to ensure the uniformity of sheet thickness.
Pressurization and Pressure Stabilization
After the high temperature melt (usually 180-250℃) is pressurized by the pump, the pressure can reach 20-70MPa, which can satisfy the strict requirements of the foaming process on the melt pressure. For example, when CO₂ blowing agent is injected, high pressure is needed to maintain gas solubility, and the melt pump can ensure that the pressure is stabilized at 20-25MPa.
Linear Extrusion Characteristics
The flow rate of the melt pump is linearly correlated with the rotational speed, which is easy to synchronize with the upstream and downstream equipments (e.g., extruders and haul-off machines). For example, by adjusting the pump speed through frequency conversion, the melt output can be precisely controlled to meet the production requirements of different specifications of PE foam film.
Second, technical parameters and selection suggestions
Working temperature and pressure
Temperature range: mainstream equipment to support ≤ 400 ℃ (conventional applications) or ≤ 510 ℃ (high-end models), covering PE melt processing needs (PE processing temperature is usually 160-230 ℃).
Outlet pressure: 0-70MPa optional, according to the foaming process pressure requirements to match. For example, XPS foaming line commonly used 20-25MPa, while microcellular foaming may require higher pressure.
Flow rate and specifications
Flow rate range: 0.1CC to 12000CC, according to the output of the extruder. For example, 0.1-100CC can be selected for small laboratory equipment, and 500-3000CC is required for industrial grade production line.
Material Selection: Gear and pump body are recommended to be made of high temperature tool steel (such as CPM tool steel) or titanium alloy, which is superior to ordinary alloy steel in abrasion resistance, and extends the service life by 3-5 times.
Seal and drive
Seal method: screw seal, packing seal or mechanical seal, need to be selected according to the melt viscosity (≤4000Pa-s) and temperature. For example, mechanical sealing is recommended for high viscosity melt (such as PA) and packing sealing is available for low viscosity melt (such as PE).
Drive system: motor + reducer + universal coupling, support frequency conversion speed control, can be linked with the extruder control.
Third. Application Scenario
XPS foam sheet production line
Case: After an enterprise adopts melt pump, the thickness tolerance of sheet is reduced from ±0.5mm to ±0.2mm, and the scrap rate is reduced by 40%.
Energy saving effect: when used in tandem with twin-screw extruder, energy consumption is reduced by 25% and screw life is extended by 2 times.
PE microcellular foaming film
Process requirements: high pressure (30-50MPa) is needed to maintain gas solubility, melt pump ensures pressure stabilization and avoids bubble merging or rupture.
Advantages: Foaming multiplication is increased to 10-30 times, film density is reduced to 0.2-0.5g/cm³, and heat insulation performance is increased by 50%.
Composite Extrusion Line
Multi-layer Co-extrusion: Melt pump can feed multiple extruders at the same time, realizing uniform extrusion of wide (≥3m) PE foam film.
Online screen changer: Equipped with automatic screen changer, the screen changing time is shortened to 5 seconds, reducing the loss of downtime.
PE foam film extrusion melt pumps need to be accurately selected according to the process temperature, pressure, flow and other parameters, giving priority to high-temperature tool steel material, frequency control drive, mechanical sealing products. In practice, the melt pump can significantly improve product stability, reduce energy consumption, is one of the core equipment of high-end PE foam film production line.
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