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Views: 0 Author: Site Editor Publish Time: 2025-09-22 Origin: Site
In the selection of twin-screw extruders, "high torque" and "high speed" are often mistakenly regarded as core indicators of equipment performance. Many enterprises blindly pursue maximum parameters while ignoring the matching logic in actual production. In fact, the scientific ratio of torque to speed is more critical than individual parameter values in determining production efficiency and product quality. This article explains the intrinsic relationship between torque and speed in twin-screw extruders, reveals matching principles for different application scenarios, and helps enterprises avoid selection pitfalls.
The core performance of a twin-screw extruder depends on the synergistic effect of "torque" and "speed," similar to how a car's torque and speed must be reasonably matched to driving conditions (corresponding to production scenarios).
Torque is the maximum rotational force output by the screws (usually measured in N·m), directly reflecting the equipment's ability to "shear, mix, and convey" materials:
High-torque equipment can handle high-viscosity materials, hard recycled materials, or high-toughness materials. It overcomes material resistance through strong shear force to prevent screw "stalling."
Low-torque equipment is suitable for low-viscosity materials or easily processed materials. Excessively high torque may cause material degradation due to over-shearing.
Speed refers to the number of screw rotations per minute (measured in r/min), directly related to material processing volume per unit time:
High speed (400-600r/min) is suitable for large-scale continuous production, increasing output by accelerating material conveying.
Low speed (100-300r/min) is suitable for precision processing or heat-sensitive materials. It ensures uniform plasticization by extending material residence time and avoids high-temperature degradation.
The effective power of a twin-screw extruder can be simplified as a function of "torque × speed" . Selection requires matching their product to material characteristics:
High torque + low speed: Suitable for "high-intensity, low-output" scenarios
Medium torque + medium speed: Suitable for "balanced" production
Low torque + high speed: Suitable for "low-intensity, high-output" scenarios
Misconception Warning: Blindly choosing "high torque + high speed" equipment not only increases procurement costs by 30%-50% but also raises energy consumption due to power redundancy. Moreover, strong shear at high speeds may damage material molecular chains.
Recycled materials feature complex compositions, impurities, and fluctuating melt viscosity, requiring energy-efficient operation while ensuring plasticization quality:
Recommended parameters: Torque range 30-50N·m/cm³ (converted by screw diameter), speed 200-400r/min
Example: Φ65mm twin screw, torque 2000-3500N·m, speed 250-350r/min
Matching logic:
Medium torque handles hard impurities in recycled materials (e.g., unremoved label fragments) to avoid frequent overload shutdowns
Medium speed balances output and material residence time (typically 30-60 seconds), ensuring sufficient discharge of moisture and volatile substances
Special adjustments:
For oil-contaminated PET flakes: Increase torque by 10% (enhance shear decontamination) and reduce speed by 10% (extend thermal washing time)
For film-like soft materials: Decrease torque by 10% (avoid over-grinding) and increase speed by 10% (improve conveying efficiency)
Filled modified materials (e.g., 30% glass fiber-reinforced PP) require strong shear force to disperse fillers while avoiding fiber breakage from high-speed shear:
Recommended parameters: Torque range 50-80N·m/cm³, speed 150-300r/min
Example: Φ75mm twin screw, torque 4000-6000N·m, speed 200-250r/min
Matching logic:
High torque ensures uniform dispersion of fillers (e.g., calcium carbonate, talc) to avoid agglomeration (dispersion particle size under electron microscope can be controlled within 5μm)
Low speed reduces glass fiber length loss (e.g., 3mm fibers retain ≥1.5mm after processing to ensure mechanical properties)
Verification standard: Modified material tensile strength fluctuation ≤5%, impact strength fluctuation ≤8%
Blended materials (e.g., PC/ABS alloys, PP/PE blends) require balancing compatibility and dispersion uniformity of different resins:
Recommended parameters: Torque range 40-60N·m/cm³, speed 250-450r/min
Example: Φ90mm twin screw, torque 5000-7000N·m, speed 300-400r/min
Matching logic:
Medium-high torque provides sufficient shear force to form uniform phase structures in incompatible resins (e.g., PC and ABS)
Medium speed ensures adequate blending time (40-80 seconds) to promote interfacial reactions (e.g., grafting when compatibilizers are added)
Typical case: In PC/ABS alloy production, using 45N·m/cm³ torque + 350r/min speed increases impact strength by 20% compared to "low torque + high speed" schemes
Heat-sensitive materials easily decompose under high temperatures or prolonged shear (e.g., PVC releases HCl, POM releases formaldehyde):
Recommended parameters: Torque range 20-40N·m/cm³, speed 300-500r/min
Example: Φ50mm twin screw, torque 800-1500N·m, speed 350-450r/min
Matching logic:
Low torque reduces mechanical shear heat generation (can lower actual barrel temperature by 5-10℃) to avoid local overheating
Medium-high speed shortens material residence time (controlled at 20-40 seconds) to reduce thermal degradation risks
Key measures: Equip with forced cooling systems (e.g., barrel water cooling) to ensure melt temperature fluctuation ≤±3℃
Viscosity level: High-viscosity materials require high torque; low-viscosity materials can use low torque
Heat sensitivity: Highly heat-sensitive materials (PVC, POM) require speed control (shorten residence time); heat-stable materials (PE, ABS) have looser speed restrictions
Filler/additive content: High filling (>50%) requires high torque; pure resin processing can use standard torque
According to target output (Q), material bulk density (ρ), and screw displacement (V), approximate required speed (n) using the formula:
n ≈ Q/(ρ×V×η) (where η is the filling coefficient, typically 0.6-0.8)
Example: For target output 1000kg/h, PE bulk density 0.9g/cm³, and Φ65mm screw displacement 180cm³/r, calculated speed ≈350r/min, matching empirical values.
Torque redundancy: Handles material fluctuations (e.g., sudden hard impurities in recycled materials) to avoid frequent overload protection
Speed redundancy: Meets future output increase needs (e.g., from 800kg/h to 1000kg/h) but should not exceed 30% (to avoid cost waste)
Truth: High-torque equipment has higher costs for core components like gearboxes and bearings. However, if only 50% or less of the torque is used in actual production, it results in "overcapacity," increasing procurement costs and raising installation requirements due to greater equipment weight.
Solution: Determine minimum required torque through small-scale tests.
Truth: When speed exceeds a critical value (e.g., 500r/min), material filling rate in screw grooves decreases (causing "slippage"), actual output growth slows, and even material degradation may occur due to excessive shear heat, reducing effective output.
Solution: Check the equipment's "speed-output curve" and select speed ranges in the flat section.
Truth: Some imported equipment's high torque and speed parameters are designed for specific high-end materials. For ordinary recycled material production, they may cause excessive energy consumption due to "performance surplus".
Solution: Prioritize manufacturers offering "customized screw configurations + parameter matching schemes" rather than simply comparing parameter tables.
Selecting a twin-screw extruder essentially involves three-dimensional matching of "material characteristics-process requirements-equipment parameters." Torque and speed are like two ends of a balance; only by finding the equilibrium point suitable for your production scenario can you achieve "efficient, stable, and low-cost" production.
