Melt Pump: Core Equipment for High-Temperature Melt Conveying and Precision Control
In the processing industry of polymer materials such as plastics, chemical fibers, and rubber, the melt pump is a key equipment ensuring production continuity and product quality stability. As a positive displacement conveying machine operating under high temperature and pressure, it has become an indispensable core component in processes like extrusion molding and injection molding, relying on its precise metering capability and stable pressure boosting effect. This article will elaborate on the working principle and core functions of the melt pump, helping industry practitioners gain an in-depth understanding of its application value.
The working principle of the melt pump is based on the positive displacement conveying mechanism, with its core structure consisting of a pump body, driving gear, driven gear, transmission shaft, sealing device, and heating/cooling system. Its working process can be divided into three key stages: Firstly, high-temperature molten polymer materials enter the pump chamber through the feed port. At this time, the driving gear, driven by a motor, drives the driven gear to rotate at high speed in meshing motion, and the meshing gap of the gears forms a sealed cavity. Secondly, as the gears continue to rotate, the cavity moves from the feed zone to the discharge zone along with the movement of the gear tooth grooves. During this process, the volume of the cavity remains constant, thereby realizing quantitative conveying of materials and avoiding unstable conveying capacity caused by changes in material viscosity or feed fluctuations. Finally, when the cavity moves to the discharge port, the gear meshing forces the material in the cavity to be extruded. During the extrusion process, the squeezing action of the gears provides the material with a stable pressure boost, effectively overcoming the flow resistance of downstream components such as molds and filters, and ensuring that the material enters subsequent processing links at a uniform and stable speed.
It is worth noting that the meshing precision of the melt pump's gears directly determines its working efficiency and metering accuracy. High-precision gear processing and assembly technology can minimize material leakage in the pump chamber and ensure volumetric efficiency. Meanwhile, the heating system equipped on the pump body can precisely control the temperature of the pump chamber, preventing materials from solidifying or experiencing sudden viscosity changes due to temperature drop; the cooling system is used to protect the sealing device and bearings, avoiding damage to vulnerable parts caused by high temperature and extending the service life of the equipment. In addition, stepless adjustment of conveying capacity can be achieved by adjusting the gear speed through an inverter motor, meeting the requirements of different production processes for material conveying speed.
In industrial production, the core functions of the melt pump are mainly reflected in four aspects. Firstly, the precise metering function. Since the conveying capacity of the melt pump has a linear relationship with the gear speed, precise control of the motor speed can realize accurate regulation of the material conveying capacity, with the metering accuracy error usually controlled within ±1%. This function is particularly important in processes requiring high product thickness uniformity, such as film extrusion and cable coating, as it can effectively avoid thickness deviations caused by uneven material supply and improve product qualification rates.
Secondly, the stable pressure boosting function. After being conveyed by the extruder screw during processing, polymer melts often have large pressure fluctuations and are difficult to meet the requirements of downstream high-pressure processing. Through the squeezing action of the gears, the melt pump can raise the material pressure to the required range and significantly reduce pressure fluctuation values, allowing the material to enter the mold in a stable high-pressure state. For example, in the plastic pipe extrusion process, stable pressure can ensure uniform wall thickness and smooth inner and outer surfaces of the pipe, avoiding defects such as depressions and bubbles. At the same time, stable pressure can also reduce flow dead zones of materials in the mold and improve the plasticization uniformity of materials.
Thirdly, the fluctuation elimination function. During the operation of the extruder, factors such as screw speed fluctuations, changes in material formulas, and differences in raw material moisture content can all lead to fluctuations in feed pressure and flow rate. Relying on its positive displacement conveying characteristics, the melt pump can effectively buffer these fluctuations and play a role of "pressure stabilization and flow stabilization". It acts like a "flow buffer", converting unstable feed into stable discharge, ensuring the continuity and stability of the entire production process, and reducing production interruptions caused by process fluctuations.
Fourthly, the function of expanding process adaptability. Different polymer materials have significant differences in melt viscosity. Some high-viscosity and high-hardness materials are prone to conveying difficulties and uneven plasticization in conventional conveying equipment. The melt pump has strong material adaptability and can stably convey various molten materials under high temperature (up to 400℃) and high pressure (up to 40MPa) conditions, including general-purpose plastics such as PE, PP, and PVC, as well as engineering plastics such as PA, PC, and PPS. At the same time, it can cooperate with extruders to realize complex processes such as multi-material blending modification and masterbatch addition, improving the flexibility and diversity of production processes.
In addition, the melt pump also has an auxiliary function of energy saving and consumption reduction. In traditional extrusion processes, to overcome downstream resistance, the extruder needs to increase the screw speed or the length-diameter ratio of the screw, resulting in a significant increase in energy consumption. The melt pump can directly boost pressure for materials, reducing the workload of the extruder, enabling the extruder to meet production requirements with lower energy consumption, usually saving 10%-30% of electricity consumption. At the same time, stable material conveying reduces the generation of waste during production, further lowering production costs.
With the development of the polymer material processing industry towards high precision, high efficiency, and green energy saving, the technology of melt pumps is constantly upgrading. Today, intelligent melt pumps have gradually become popular. By integrating pressure sensors, flow sensors, and PLC control systems, real-time monitoring and automatic adjustment of conveying pressure and flow rate can be realized, further improving the intelligence level of the production process. In the future, with the integrated development of materials science and mechanical manufacturing technology, melt pumps will play an important role in a wider range of high-temperature and high-pressure working conditions and more complex material systems, providing strong support for the high-quality development of the polymer material processing industry.
