How To Control Extrusion Temperature? Parameter Setting Guide for Different Plastic Materials

In the plastic extrusion molding process, temperature control is one of the core factors determining product quality. Whether producing pipes, films, or profiles, precise temperature parameter settings directly affect material plasticization, product mechanical properties, and production stability. This article systematically explains the control principles of extrusion temperature, key influencing factors, and specific parameter setting schemes for common plastic materials.

I. Core Principles of Extrusion Temperature Control

Temperature control in plastic extruders is not a single value but requires segmented regulation of barrel sections, screw, and die head, forming a gradient heating curve to achieve a smooth transition of materials from solid to molten state.

Three Core Goals of Temperature Control:

1. Complete Plasticization: Ensure materials are fully melted without unmelted particles

2. Uniform Mixing: Allow material molecular chains to fully expand and distribute evenly

3. Stable Flow: Ensure continuous and stable extrusion of molten materials under pressure

Typical Temperature Segments and Functions:

• Feeding Section: Lower temperature (usually below the material's glass transition temperature), mainly responsible for conveying materials and preliminary preheating, preventing premature melting that causes "bridging" (material caking and blocking below the hopper)

• Compression Section (Melting Zone): Temperature rises rapidly above the material's melting point, gradually converting solid materials to molten state through screw compression ratio design while expelling air from materials

• Homogenization Section (Metering Zone): Temperature remains stable or slightly higher than melting temperature, further homogenizing molten materials to provide stable melt quality for extrusion molding

• Die Head and Mold: Temperature is usually slightly lower than the homogenization section, ensuring the melt maintains good fluidity in the mold while avoiding material degradation due to overheating

Temperature Control Precision Requirements: In high-precision extrusion production, temperature fluctuations in each section should be controlled within ±1℃; for ordinary products, it should also be within ±3℃, otherwise dimensional instability and surface defects may occur.

II. Key Factors Affecting Temperature Settings

1. Plastic Material Properties
        Different plastics have significant differences in melting points and thermal stability (e.g., PE melts at 110-130℃, while PI can withstand temperatures above 300℃), which is the primary basis for temperature settings.

2. Melt Flow Rate (MFR)
        For the same plastic, higher MFR values (smaller molecular weight) generally require lower temperatures. For example, high-melt-flow PP (MFR 30) requires 10-20℃ lower processing temperature than low-melt-flow PP.

3. Screw Structure and Rotational Speed
        High-shear screws generate heat through mechanical friction, allowing slightly lower temperature settings; when screw speed increases, shear heat increases, requiring corresponding reduction in barrel temperature to prevent material overheating.

4. Product Structure Complexity
        Thin-walled, complex cross-section products require higher melt fluidity, so temperatures can be appropriately increased by 5-10℃; thick-walled products need temperature control to prevent excessive internal stress.

5. Additive Types
        Modified materials containing glass fibers or mineral fillers need 10-15℃ higher temperatures to overcome the fillers' impact on melt fluidity; materials with heat stabilizers can have a slightly expanded processing temperature range.

III. Extrusion Temperature Parameter Guide for Common Plastic Materials

1. Polyolefins (PE/PP)

Polyethylene (PE)

• Low-Density Polyethylene (LDPE): 150-180℃
       Barrel segments: 140-150℃ (feeding section) → 160-170℃ (compression section) → 170-180℃ (homogenization section) → 160-170℃ (die head)
       Characteristics: Wide melting range, low temperature sensitivity, suitable for beginners' debugging

• High-Density Polyethylene (HDPE): 180-220℃
       Barrel segments: 160-180℃ (feeding section) → 190-210℃ (compression section) → 200-220℃ (homogenization section) → 190-210℃ (die head)
       Note: Excessively high temperatures (>230℃) can cause oxidative degradation, resulting in product discoloration and reduced mechanical properties

Polypropylene (PP)

• Homopolymer PP: 180-230℃

• Copolymer PP: 170-220℃ (10-15℃ lower than homopolymer PP)
       Barrel segments: 160-180℃ (feeding section) → 200-220℃ (compression section) → 210-230℃ (homogenization section) → 200-220℃ (die head)
       Key point: PP oxidizes easily at high temperatures, requiring controlled residence time and necessary addition of antioxidants

2. Polyesters and Polyamides (PET/PA)

Polyethylene Terephthalate (PET)

• Recycled PET bottle flake granulation: 250-280℃

• Virgin PET: 270-300℃
       Barrel segments: 230-250℃ (feeding section) → 260-270℃ (compression section) → 270-280℃ (homogenization section) → 260-270℃ (die head)
       Essential condition: Must be equipped with a vacuum venting system; temperatures exceeding 290℃ can cause thermal degradation, producing acetaldehyde that causes product odor

Polyamide (PA6/PA66)

• PA6: 230-260℃

• PA66: 260-290℃ (higher melting point)
       Barrel segments: 210-230℃ (feeding section) → 240-260℃ (compression section) → 250-270℃ (homogenization section) → 240-260℃ (die head)
       Special requirement: Must be fully dried before processing (moisture content <0.05%), otherwise molecular chain breakage will occur at high temperatures

3. Polyvinyl Chloride (PVC)

Rigid PVC (UPVC): 160-190℃
Flexible PVC (SPVC): 150-180℃ (lower processing temperature due to plasticizers)
Barrel segments: 120-140℃ (feeding section) → 150-170℃ (compression section) → 170-190℃ (homogenization section) → 160-180℃ (die head)
Critical point: PVC has poor thermal stability; temperatures exceeding 190℃ can cause decomposition producing HCl gas, requiring strict temperature control and addition of heat stabilizers; low-shear screw design is recommended

4. Other Common Engineering Plastics

Polystyrene (PS): 170-210℃
Characteristics: Good melt flowability; excessive temperature can cause product yellowing

Acrylonitrile-Butadiene-Styrene (ABS): 180-240℃
Note: The butadiene component degrades easily at high temperatures; temperatures exceeding 250℃ can cause black spots on product surfaces

Polycarbonate (PC): 260-300℃
Requirement: Requires high-temperature drying (120℃/4 hours); wide processing window but sensitive to moisture

Polyoxymethylene (POM): 170-200℃
Warning: Decomposition occurs at temperatures exceeding 210℃ with prolonged residence time, producing toxic formaldehyde gas; temperature must be strictly controlled

IV. Troubleshooting Guide for Temperature Abnormalities

1. Poor Material Plasticization (with unmelted particles)

• Causes: Low temperature settings, insufficient screw shear, short material residence time

• Solutions: Increase homogenization section temperature by 5-10℃, reduce screw speed (increase residence time), check if screw compression ratio matches

2. Silver streaks/bubbles on product surface

• Causes: High material moisture content, poor venting, degradation due to excessive temperature

• Solutions: Enhance drying, check vacuum system, reduce homogenization section temperature

3. Large fluctuations in melt pressure

• Causes: unreasonable temperature gradient, uneven feeding, filter blockage

• Solutions: Optimize temperature segment settings, check feeding system, replace filters promptly

4. Unstable product dimensions

• Causes: Large temperature fluctuations, uneven die head temperature

• Solutions: Calibrate temperature control instruments, check if heating coils are damaged, add die head insulation

V. Advanced Temperature Control Techniques

1. Gradient Setting Principle: Temperature should gradually increase from the feeding section to the homogenization section, with each segment's temperature difference controlled at 10-20℃ to avoid sudden changes

2. Test Molding Debugging Method: For initial production, set temperatures at the lower end of recommendations first, then gradually increase based on observing melt status (smooth continuous strips), with each adjustment not exceeding 5℃

3. Energy-Saving Control Strategy: Under the premise of ensuring plasticization quality, use lower temperature settings as much as possible to reduce energy consumption by 10-15% while reducing material degradation risks

4. Intelligent Temperature Control Application: Adopt PID (Proportional-Integral-Derivative) temperature control systems combined with infrared temperature sensors to monitor melt temperature in real-time, achieving closed-loop automatic adjustment

Mastering extrusion temperature control logic requires combining theoretical parameters with practical production experience. It is recommended that enterprises establish corresponding databases of "temperature-screw speed-product quality" for main processing materials, and form standardized operating instructions through continuous optimization, which can ensure product stability while maximizing equipment lifespan and reducing production costs.