The melt pump is mainly used for the transfer, pressurization, and metering of high-temperature and high-viscosity polymer melts. It is widely applied in the extrusion molding of plastics, resins, rubber, and chemical fiber products, such as granulation, films, pipes, plates, sheets, artificial fibers, optical fibers, and medical plastic catheters.

The melt pump is a positive displacement transfer device, where the flow rate is strictly proportional to the pump’s rotational speed. It mainly consists of a pump casing, driving gear, driven gear, sliding bearings, front and rear end plates, and packing seals. The tooth profiles of the two gears, the pump body, and the side cover plates form the feeding zone, transfer zone, and discharge zone of the pump. During operation, it relies on the working volume change caused by the mutual meshing of the driving and driven gears to transfer the melt. The working volume is composed of the pump body, gear tooth grooves, and bearings with side plate functions (i.e., the feeding zone). When the gears rotate in the specified direction, the melt enters the tooth grooves of the two gears in the feeding zone. As the gears rotate, the melt is brought into the transfer zone from both sides. The re-meshing of the gears extrudes the melt in the tooth grooves out of the discharge zone and pumps it to the outlet pipeline. As long as the pump shaft rotates, the gears continuously pump the melt to the outlet side, so the pump outlet can reach a very high pressure. At the same time, the melt pump requires front-end equipment (such as an extruder) to provide a stable and sufficient inlet positive pressure to ensure that the tooth grooves are completely filled and to provide lubrication for the internal bearings, thereby achieving smooth, pulsation-free high-pressure extrusion at the outlet end.

Functions & Benefits

The main function of the melt pump is to pressurize and stabilize the high-temperature plastic melt from the extruder, and deliver it stably to the extruder die head. Its ability to stabilize melt pressure and flow is superior to various types of extruders. When used in series with a single-screw or co-rotating twin-screw extruder, the efficiency of the entire production line is significantly increased. The main benefits of applying a melt pump are:

• Reduced Dimensional Tolerances: Minimizes the dimensional tolerance of extruded products, making more products per unit weight of material. Using a melt pump is highly necessary and valuable when strict dimensional tolerances are required or when raw material costs are high.
• Improved Compounding & Output: Combining a co-rotating twin-screw extruder with a melt pump to form a compounding extrusion and granulation line significantly improves mixing quality and output compared to a standalone twin-screw granulating line. Energy consumption per kilogram of processed material can generally be reduced by about 25%.
• Simplified Process & Energy Savings: By adding a melt pump and extrusion dies (for pipes, plates, films, etc.) to an existing single-screw or co-rotating twin-screw granulating extruder, products can be extruded directly, eliminating the granulation step. This system is very suitable when the material of the extruded product needs to be blend-modified. In addition to the second advantage above, this system also achieves energy savings by simplifying the production process and shortening the production cycle.
• Multi-Extruder Feeding: Enables multiple small and medium-sized extruders to supply material to a single melt pump simultaneously. After being pressurized and metered by the melt pump, the melt is supplied to the die head to extrude large products (large-diameter pipes, wide plates, films, etc.). This configuration results in a compact production line with a small footprint, and the cross-sectional dimensions of the extruded products are accurate and easy to control.
• Excellent Venting Extruder Performance: Equipping a single-screw venting extruder with a melt pump allows for free operation and excellent performance. Under high die head pressure and high output, the extrusion volume can be adjusted freely without the occurrence of surging or material overflow.