Application of Melt Pumps in Sheet Extruders

Melt pumps serve as the core equipment in sheet extruders. By precisely controlling flow and pressure, they effectively resolve critical issues such as thickness inconsistency, high energy consumption, and poor melt quality. When integrated, thickness tolerances can be reduced to ±1% to ±2%, energy consumption decreases by 10% to 15%, melt quality improves, and compatibility with high-viscosity materials is enhanced—delivering genuine quality upgrades, cost reductions, and efficiency gains.

The core requirements for sheet extrusion are stable melt flow, constant pressure, and uniform thickness (especially in high-precision applications like food packaging, medical devices, and electronics). Traditional extruders rely solely on screw speed adjustment, making them susceptible to fluctuations in material melting, screw wear, and backpressure changes, often failing to meet stringent demands. Melt pumps specifically address these challenges, offering the following advantages:

1. Stabilizes melt pressure and flow rate, eliminating sheet thickness inconsistencies

• Core Principle: As a positive displacement pump, its flow rate depends solely on “pump speed × pump chamber volume,” unaffected by inlet pressure fluctuations (within ±10%).

• Application Effect: Traditional extruders exhibit sheet thickness tolerances of ±5% to ±8% due to screw speed fluctuations (±2%). When paired with a melt pump, flow control precision reaches ±0.5%, reducing thickness tolerance to ±1% to ±2% (or even tighter), fully meeting the demands of high-precision sheets (e.g., pharmaceutical-grade PVC rigid sheets, electronic carrier tape sheets).

• Typical Application: During PET thermoforming sheet production (for food packaging trays), melt pumps prevent uneven melting caused by raw material moisture fluctuations. This ensures consistent sheet thickness both crosswise and lengthwise, reducing scrap rates in subsequent thermoforming processes.

2. Reducing Extruder Load for “Energy Savings and Consumption Reduction”

• Traditional challenge: Extruders must simultaneously handle “melt plasticization” and “high-pressure melt delivery to the mold.” Especially with complex mold runners (e.g., wide-format sheet molds), the screw must overcome significant back pressure (typically 20–30 MPa), leading to high motor load, excessive energy consumption, and accelerated screw wear.

• Role of the melt pump: The melt pump proactively “assumes” the melt conveying task, allowing the extruder to focus its core function on “melt plasticization.” This reduces extruder screw backpressure by 30%–50%, lowers motor current by 15%–20%, and achieves overall energy savings of 10%–15%.

3. Improving melt quality to reduce sheet “cosmetic defects”

• Mixing and homogenization: Certain melt pumps (e.g., those with static mixing elements) further agitate the melt during conveyance through gear meshing or mixing chamber structures. This eliminates issues like “melt dead zones” and “uneven masterbatch dispersion,” thereby reducing sheet defects such as “color variation, streaks, and bubbles.”

• Controlling melt temperature: Melt pumps feature independent temperature control systems (typically electric heating + thermal oil cooling), enabling precise melt temperature regulation (±1°C). This prevents melt degradation caused by temperature fluctuations at the extruder outlet (e.g., PVC high-temperature degradation discoloration, PET hydrolysis) and enhances sheet mechanical properties (e.g., impact strength, tensile strength).

4. Expand process window to accommodate more materials and conditions

• High-viscosity / difficult-to-process materials: For high-viscosity materials like PPR, PC, and PEEK, conventional extruders struggle to generate sufficient pressure to force melt into the die. Melt pumps deliver higher outlet pressure, enabling stable extrusion of high-viscosity materials.

• Multiple material switching: When switching between different grades or colors during production, melt pumps rapidly evacuate residual melt from the pump chamber, minimizing “transition material” (unqualified sheets resulting from mixed materials). This reduces waste from 50–100 kg to 10–20 kg.

• Wide-width sheet production: For wide-width (over 2m) sheet molds, melt pumps ensure uniform melt distribution across all mold channels. This prevents “thick edges and thin centers,” guaranteeing consistent thickness across the entire sheet width.

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