Views: 0 Author: Felix Publish Time: 2026-05-08 Origin: Site
Plastic extrusion defects can quickly reduce product quality, increase material waste, and cause costly production downtime. Common issues such as bubbles, burn marks, melt fracture, unstable pressure, and uneven thickness are especially common in plastic recycling and high-output extrusion lines.
This guide explains the most common plastic extrusion problems, their root causes, and practical troubleshooting solutions used in industrial extrusion production.
Whether you process PE, PP, HDPE, LDPE, PVC, or recycled plastics, understanding these extrusion defects helps improve line stability, reduce scrap rates, and increase production efficiency.
Most plastic extrusion defects originate from three key areas:
Poor raw material quality directly affects melt stability and surface finish.
Typical material-related extrusion problems include:
Moisture contamination
Inconsistent melt flow index (MFI)
Mixed polymers
Contaminated recycled flakes
Improper material blending
Recycled plastics are especially sensitive to moisture and contamination, which often leads to bubbles, unstable pressure, and die build-up.
Improper machine parameters can create unstable extrusion output and surface defects.
Common process-related causes include:
Barrel temperature too high or too low
Excessive screw speed
Improper back pressure
Inconsistent cooling
Incorrect die settings
Even small parameter changes can significantly affect extrusion quality and dimensional stability.
Worn or poorly maintained equipment is another major source of extrusion defects.
Typical equipment problems include:
Worn screws and barrels
Dirty dies
Weak vacuum degassing
Poor filtration systems
Inconsistent feeding systems
These issues become more severe in recycled plastic extrusion applications.
Quick Troubleshooting Table
Extrusion Problem | Main Cause | Recommended Solution |
Bubbles in extrusion | Moisture or trapped gas | Improve drying and vacuum degassing |
Burn marks and yellowing | Overheating or degradation | Reduce temperature and clean screw |
Rough surface / sharkskin | Excessive shear stress | Lower output speed |
Melt fracture | High pressure and unstable flow | Optimize die design and melt temperature |
Uneven thickness | Cooling or die imbalance | Adjust die gap and cooling system |
Die build-up | Material contamination | Improve melt filtration |
Unstable pressure | Screw wear or inconsistent feeding | Inspect screw and feeding system |
Bubbles usually form when moisture, trapped air, or gas cannot escape during melting.
This problem is extremely common in recycled plastic extrusion lines.
Wet raw materials
Insufficient drying
Weak vacuum degassing
Air trapped inside recycled flakes
Excessive extrusion speed
Use an industrial plastic drying system
Install a vacuum degassing extruder
Reduce screw speed if gas removal is insufficient
Improve feeding consistency
Use stable recycled material sources
For recycled plastics, efficient degassing systems are often essential for stable extrusion output.
Burn marks are signs of material degradation caused by excessive heat or long residence time inside the barrel.
Yellow streaks
Brown discoloration
Black particles
Burnt smell
Barrel temperature too high
Material staying too long inside the screw
Dead zones inside the die
Carbonized contamination
Lower processing temperature gradually
Clean screws and dies regularly
Reduce melt residence time
Avoid excessive back pressure
Use accurate temperature control systems
Frequent burning may also indicate poor screw design or uneven heating zones.
Sharkskin defects create rough or ribbed surfaces on plastic products.
This issue is common in PE and HDPE extrusion processes.
Excessive shear stress
Melt temperature too low
High extrusion speed
Poor die surface finish
Increase melt temperature carefully
Reduce line speed
Polish or replace worn dies
Optimize extrusion pressure
Improve resin flow stability
Stable melt flow usually improves surface quality immediately.
Melt fracture appears as distorted or cracked surfaces caused by unstable polymer flow under high stress.
Excessive output rate
High melt viscosity
Poor die design
Low melt temperature
Increase melt temperature moderately
Reduce screw RPM
Improve die flow transition
Optimize material balance
Use resins with suitable melt flow properties
For high-output extrusion lines, die optimization is often more effective than simply lowering speed.
Uneven thickness can create major quality problems in pipes, sheets, and films.
Uneven die gap
Inconsistent cooling
Pressure fluctuation
Screw wear
Poor calibration
Adjust die alignment
Stabilize cooling water temperature
Inspect screw wear
Improve haul-off synchronization
Monitor melt pressure continuously
Consistent extrusion pressure is critical for dimensional accuracy.
Die build-up occurs when degraded material accumulates around the die lips.
This reduces surface quality and production stability.
Contaminated recycled plastic
Low-quality additives
Poor filtration
Material degradation
Install efficient melt filtration systems
Use continuous screen changers
Improve material cleanliness
Reduce overheating
Schedule regular die cleaning
In plastic recycling lines, filtration quality directly affects long-term extrusion stability.
Pressure fluctuation often leads to inconsistent product quality and lower production efficiency.
Inconsistent feeding
Screw wear
Blocked filters
Material inconsistency
Incorrect temperature settings
Inspect feeding systems regularly
Replace worn screws and barrels
Monitor melt pressure continuously
Improve filtration efficiency
Use stable material blends
Pressure instability is often an early warning sign of equipment wear.
Recycled plastic extrusion introduces additional processing challenges compared to virgin materials.
Recycled flakes and films absorb moisture during washing and storage, causing:
Bubbles
Silver streaks
Surface defects
Pressure instability
Proper drying and vacuum degassing are essential.
Recycled materials may contain:
Paper
Metal particles
Wood fibers
Adhesives
Mixed polymers
Without proper filtration, contaminants can damage dies and reduce product quality.
High-efficiency melt filtration systems are especially important in plastic recycling extrusion lines.
Preventive maintenance and process control significantly reduce extrusion defects.
Store materials properly
Prevent moisture exposure
Use reliable recycled plastic suppliers
Separate contaminated materials
Monitor melt pressure
Stabilize barrel temperatures
Avoid excessive screw speed
Adjust cooling gradually
Routine maintenance reduces:
Carbon build-up
Die contamination
Burn marks
Pressure fluctuation
Modern extrusion recycling lines often use:
Vacuum degassing systems
Laser filters
Continuous screen changers
Automatic pressure monitoring
These systems improve extrusion stability and reduce downtime.
Many extrusion problems are related to equipment design and system stability.
When selecting a plastic extrusion machine, manufacturers should evaluate:
Equipment Feature | Why It Matters |
Vacuum degassing | Removes moisture and gas |
Stable temperature control | Prevents burning |
Efficient filtration | Reduces contamination |
Wear-resistant screw design | Improves long-term stability |
Automatic pressure monitoring | Reduces pressure fluctuation |
Energy-efficient systems | Lowers operating costs |
For recycled plastic processing, extrusion systems specifically designed for recycling applications usually deliver better long-term performance.
What causes bubbles in plastic extrusion?
Bubbles are usually caused by moisture, trapped air, or insufficient vacuum degassing during extrusion. Wet recycled materials are one of the most common reasons.
How do you prevent melt fracture in extrusion?
Melt fracture can be reduced by lowering extrusion speed, increasing melt temperature, and improving die flow design.
Why does plastic burn during extrusion?
Plastic burns when material overheats or remains too long inside the barrel. Poor screw cleaning and dead zones inside the die can also cause degradation.
How do you improve extrusion surface quality?
Stable temperature control, optimized extrusion speed, proper die maintenance, and balanced melt flow help improve surface quality.
Can recycled plastic be extruded efficiently?
Yes. With proper drying, filtration, and degassing systems, recycled plastics can achieve stable extrusion performance and good product quality.
How often should extrusion dies be cleaned?
Cleaning frequency depends on contamination level, material quality, and operating hours. Recycling extrusion lines usually require more frequent die cleaning.
What is the most common plastic extrusion defect?
Bubbles, surface defects, unstable pressure, and uneven thickness are among the most common extrusion problems in industrial production.
Looking to improve extrusion stability, reduce material waste, or optimize recycled plastic processing?
Our engineering team provides customized plastic extrusion and recycling solutions, including:
Plastic recycling extrusion lines
Vacuum degassing extruders
Melt filtration systems
Screen changers
Process optimization support
Contact us to discuss your production requirements and improve long-term extrusion performance.
