In HDPE pipeline production, double shaft drive melt pump is the core equipment to improve process stability, product quality and production efficiency, especially suitable for high viscosity melt transportation, high pressure difference scene and large pipe extrusion. The following is a specific analysis:
First, the core advantages of dual-shaft drive melt pump
High viscosity melt handling capacity
HDPE melt viscosity is usually between 10,000-40,000 Pa-s, dual-shaft drive design through the forced shear effect of gear meshing, to ensure that the melt is uniformly transported to avoid the flow fluctuations due to uneven loading of single-axis pumps. For example, in the production of HDPE double-wall corrugated pipes, the twin-shaft pumps provide stable delivery of highly filled (e.g. carbon black) melts, preventing flow marks or uneven thicknesses in the inner wall of the pipe.
High differential pressure and high pressure stability
Twin-shaft pump can withstand inlet pressure 0-30MPa, outlet pressure 0-40MPa, differential pressure up to 25MPa, to meet the needs of extrusion of large HDPE pipes (such as diameter ≥ 1200mm). Its double gear synchronous drive structure can balance the axial force, reduce gear wear, ensure pressure stability under long-term high-pressure operation, and reduce the deviation of pipe wall thickness (within ±3%).
Flow rate accuracy and process control
Through the precise control of gear speed (deviation ≤ ±1%), the twin-shaft pump can realize linear adjustment of melt flow rate from 20-3200 cc/rev, eliminating the influence of extruder screw speed fluctuation, temperature change and other factors on the flow rate. For example, in the production of HDPE water supply pipe, the flow stability is directly related to the pipe's ring stiffness and burst pressure, biaxial pumps can control the flow fluctuation within ±1%, which significantly improves the product qualification rate.
Energy savings and equipment protection
Twin-shaft pumps transfer the extruder's depressurization function to the pump body, allowing the extruder to operate at lower back pressure (15-25% lower) and temperature (10-15°C lower), reducing the risk of melt degradation and lowering energy consumption by 15-25%. In addition, low back pressure operation extends screw life by 30-50%, reducing equipment downtime and maintenance costs.
Typical application scenarios in HDPE pipe production
Large pipe extrusion (≥630mm)
In the production of HDPE water supply pipes with a diameter of more than 1200mm, the biaxial pump stabilizes the melt pressure and flow rate, preventing the pipe from being deformed due to sagging melt or pressure fluctuations in the form of a “bamboo joint”. For example, in one company, the wall thickness deviation of a 1200mm pipe was reduced from ±8% to ±3% after the adoption of a dual-axis pump, and the production speed was increased by 20%.
High-pressure pipes (e.g. gas pipes)
HDPE gas pipes need to withstand a pressure of PN16 or more, the high differential pressure capability (25MPa) of the twin-axis pump ensures that the melt is fully filled in the high-pressure molds, avoiding air holes or delamination of the inner wall of the pipe. For example, in the production of SDR11 series gas pipes, the biaxial pump stabilizes the melt pressure at 8-10MPa, which meets the standard requirement of pipe burst pressure ≥4 times the working pressure.
Co-extrusion of multi-layer composite pipes
When producing HDPE pipes with three-layer structure (e.g. corrosion-resistant layer + structural layer + wear-resistant layer), the biaxial pumps can accurately control the flow rate and pressure of the melts in each layer to ensure that the bonding strength of the interlayer ≥2.5 N/mm, avoiding delamination or peeling defects.
Technical Parameters and Selection Recommendations
Key Parameters
Material: pump body and gears are made of high temperature tool steel (HRC 60-62), with nitriding treatment on the surface, resistant to the corrosion and wear of HDPE melt (with additives).
Sealing method: Screw seal or packing seal is recommended to prevent leakage of high pressure melt, especially suitable for toxic or flammable HDPE compounds (e.g. PE-RT).
Heating system: electric heating zone control (±1℃), to avoid the melt in the pump body localized overheating degradation.
Selection basis
Pipe diameter: 50-100 cc/rev pumps for pipes below 630mm; 1000-2000 cc/rev pumps for pipes above 1200mm.
Production speed: High-speed production lines (≥15 m/min) need to be equipped with high-flow pumps (e.g. 2000 cc/rev) to compensate for pressure loss.
Melt viscosity: If the viscosity of the HDPE melt exceeds 30,000 Pa-s, a pump with a larger gear module (e.g., module 5 or higher) is required to increase the shear capacity.
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