Melt pumps hold significant application value in PP (polypropylene) filament production lines. Their core functions, selection criteria, and practical application outcomes are as follows:
I. Core Functions of Melt Pumps in PP Filament Production Lines
Stabilizing Melt Pressure
During PP filament drawing, melt pressure fluctuations can cause uneven filament diameter and breakage. The melt pump employs gear meshing to forcibly convey the melt, eliminating pressure variations caused by extruder screw pulsation (pressure fluctuations can be controlled within ±1%, far superior to the ±5%-10% typical of conventional extruders). This ensures consistent filament diameter and stable quality.
Precise Flow Control
The flow rate of the melt pump is strictly proportional to its rotational speed (controlled via a variable frequency drive motor). This enables precise matching to the melt requirements of the filament drawing process, preventing material waste while enhancing production efficiency. For instance, in PP woven bag filament drawing machines, the melt pump reduces material loss and adapts to diverse filament drawing process demands.
Reduced Risk of Filament Breakage
By stabilizing pressure and flow, the melt pump minimizes filament breakage caused by melt fluctuations, extending production continuity. This is particularly advantageous for high-output, high-precision PP filament production lines.
Adapting to High-Temperature, High-Viscosity Conditions
PP melt typically operates at temperatures between 180-250°C (356-492°F) with viscosities ranging from 100-10,000 Pa·s. Constructed from high-temperature-resistant materials (e.g., nitrided steel, 316L stainless steel) and featuring specialized seal designs (e.g., spiral seals or combination seals), melt pumps ensure stable operation in demanding high-temperature, high-viscosity environments.
Selection Criteria for Melt Pumps in PP Filament Production Lines
Flow Rate Requirements
Determine the melt pump's displacement (CC value, i.e., displacement per revolution) based on the production line's output demand. For example, if the line requires processing 120-240L of melt per hour, a 100CC displacement pump can be selected (yielding 120L/H at 20 RPM or 240L/H at 40 RPM). Common displacement specifications: 5CC, 50CC, 800CC, 1200CC, etc., covering requirements from small-scale lab equipment to large industrial production lines.
Pressure Parameters
Inlet Pressure: PP filament production lines typically operate from vacuum (-0.08MPa) to atmospheric pressure.
Outlet Pressure: Standard melt pumps have outlet pressures ≤40MPa, while high-pressure models reach 70MPa. Selection depends on mold resistance and process requirements.
Maximum Pressure Differential: Standard models: 25 MPa; High-pressure models: 50 MPa. Ensure the pump's pressure rating exceeds actual operating conditions.
Temperature Adaptability
PP melt operating temperature: Typically ≤250°C. Conventional melt pump operating temperature: ≤350°C. High-temperature models: Up to 510°C. Fully covers PP filament drawing requirements.
Temperature Control Methods: Electric heating or thermal fluid circulation (jacketed/vacuum insulation). Matching must align with the production line's heating method.
Viscosity Adaptability
PP melt viscosity ranges from 100 to 10,000 Pa·s, accommodated by standard melt pumps. For processing highly filled or glass-fiber reinforced PP (potentially higher viscosity), select high-viscosity pumps (≤30,000 Pa·s).
Materials and Sealing
Body Material: Nitrided steel for standard applications; 316L stainless steel or Hastelloy for medical or highly corrosive environments.
Sealing Type: For low PP melt viscosity (<1000 Pa·s), gland packing or combined seals (spiral + packing) are recommended for balanced leak prevention and wear resistance.
Installation and Drive
Installation Space: Select compact or split-body pumps based on the distance between the extruder and mold.
Drive Method: Connect the motor via universal or flexible couplings. Speed adjustment range must cover 5-500 rpm (small pumps operate at higher speeds, large pumps at lower speeds).
Practical Application Cases and Outcomes
PP Woven Bag Filament Extruder: After adopting a melt pump, a company achieved 15% improvement in filament diameter uniformity, 30% reduction in filament breakage rate, and 10% overall production cost reduction.
Glass-fiber reinforced PP filament drawing: Through specially designed slotted gears, the melt pump prevents fiber breakage, maintaining a 15-20% fiber retention rate and significantly enhancing product strength.
Nonwoven fabric production: When used with metering pumps, the filament fineness CV value is <2%, improving spinning stability by 30% compared to traditional methods.
The melt pump is a core component in PP filament production lines. By stabilizing pressure, precisely controlling flow, and reducing breakage risks, it significantly enhances product quality and production efficiency. During selection, key parameters such as flow rate, pressure, temperature, and viscosity must be prioritized, while material compatibility and seal configuration should be chosen based on actual operating conditions.
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