In the processing industry of polymer materials such as plastics, chemical fibers, and rubber, the melt pump serves as a critical component ensuring production continuity and product quality stability. As a positive displacement conveying machine operating under high-temperature and high-pressure conditions, it has become indispensable in processes like extrusion molding and injection molding, leveraging its precise metering capabilities and stable pressure-boosting performance. This article elaborates on the working principle and core functions of the melt pump, facilitating industry professionals to gain a comprehensive understanding of its application value.
The working principle of the melt pump is based on a positive displacement conveying mechanism, with its core structure comprising a pump body, driving gear, driven gear, transmission shaft, sealing device, and heating/cooling system. Its operational process can be divided into three key stages: First, high-temperature molten polymer materials enter the pump chamber through the feed port. At this point, the driving gear—powered by a motor—drives the driven gear to rotate at high speed in meshing motion, and the meshing gap between the gears forms a sealed cavity. Second, as the gears continue to rotate, the cavity moves from the feed zone to the discharge zone alongside the movement of the gear tooth grooves. During this process, the cavity volume remains constant, enabling quantitative material conveying and eliminating unstable throughput caused by variations in material viscosity or feed fluctuations. Finally, when the cavity reaches the discharge port, gear meshing forces the material within the cavity to be extruded. During extrusion, the squeezing action of the gears provides the material with a stable pressure boost, effectively overcoming flow resistance from downstream components such as molds and filters, and ensuring the material enters subsequent processing stages at a uniform, steady rate.
Notably, the meshing precision of the melt pump’s gears directly determines its operational efficiency and metering accuracy. High-precision gear machining and assembly techniques minimize material leakage within the pump chamber, guaranteeing volumetric efficiency. Meanwhile, the heating system integrated into the pump body enables precise control of the pump chamber temperature, preventing material solidification or abrupt viscosity changes due to temperature drops. The cooling system, on the other hand, protects the sealing device and bearings, safeguarding vulnerable components from high-temperature damage and extending equipment service life. Additionally, stepless adjustment of throughput can be achieved by regulating gear speed via an inverter motor, catering to the material conveying speed requirements of diverse production processes.
In industrial production, the core functions of the melt pump are primarily manifested in four aspects:
Precise Metering Function: Since the melt pump’s throughput maintains a linear relationship with gear speed, precise control of the motor speed allows for accurate regulation of material conveying volume, with metering accuracy typically within ±1%. This function is particularly crucial in processes demanding high product thickness uniformity—such as film extrusion and cable coating—effectively avoiding thickness deviations caused by uneven material supply and improving product qualification rates.
Stable Pressure-Boosting Function: After being conveyed by the extruder screw during processing, polymer melts often exhibit significant pressure fluctuations and struggle to meet the requirements of downstream high-pressure processing. Through the squeezing action of the gears, the melt pump can raise material pressure to the required range while significantly reducing pressure fluctuation amplitudes, ensuring the material enters the mold under a stable high-pressure state. For instance, in plastic pipe extrusion, stable pressure guarantees uniform pipe wall thickness and smooth inner/outer surfaces, eliminating defects like depressions and bubbles. Simultaneously, stable pressure reduces material flow dead zones within the mold, enhancing material plasticization uniformity.
Fluctuation Elimination Function: During extruder operation, factors such as screw speed fluctuations, material formula adjustments, and variations in raw material moisture content can all lead to fluctuations in feed pressure and flow rate. Leveraging its positive displacement conveying characteristics, the melt pump effectively buffers these fluctuations, acting as a "pressure and flow stabilizer." It converts unstable feed into consistent discharge, ensuring the continuity and stability of the entire production process and minimizing production interruptions caused by process fluctuations.
Process Adaptability Expansion: Different polymer materials exhibit substantial differences in melt viscosity. Some high-viscosity and high-hardness materials face challenges such as difficult conveying and uneven plasticization in conventional conveying equipment. The melt pump boasts strong material adaptability, capable of stably conveying various molten materials under extreme conditions (temperatures up to 400℃ and pressures up to 40MPa), including general-purpose plastics (e.g., PE, PP, PVC) and engineering plastics (e.g., PA, PC, PPS). Additionally, it can collaborate with extruders to implement complex processes such as multi-material blending modification and masterbatch addition, enhancing the flexibility and diversity of production processes.
Furthermore, the melt pump offers auxiliary energy-saving and consumption-reduction benefits. In traditional extrusion processes, extruders must increase screw speed or length-diameter ratio to overcome downstream resistance, resulting in substantial energy consumption. The melt pump directly boosts material pressure, reducing the extruder’s workload and enabling it to meet production requirements with lower energy consumption—typically achieving 10%-30% electricity savings. Simultaneously, stable material conveying minimizes waste generation during production, further lowering manufacturing costs.
As the polymer material processing industry advances toward high precision, high efficiency, and green energy conservation, melt pump technology continues to evolve. Today, intelligent melt pumps have become increasingly prevalent. By integrating pressure sensors, flow sensors, and PLC control systems, they enable real-time monitoring and automatic adjustment of conveying pressure and flow rate, further enhancing the intelligence of production processes. In the future, with the integrated development of materials science and mechanical manufacturing technology, melt pumps will play a pivotal role in a broader range of high-temperature and high-pressure operating conditions and more complex material systems, providing robust support for the high-quality development of the polymer material processing industry.
