Step by Step Guide to Cleaning Extrusion Equipment and Removing Carbon Buildup (2026)
- UniTemp
- 9 hours ago
- 4 min read
Extrusion systems operate continuously under high heat and pressure. Over time, polymers degrade, color pigments accumulate, and carbonized residue forms inside the screw and barrel. These contaminants eventually cause quality defects, long startup scrap runs, and costly production downtime.
Purging an extruder is one of the most effective ways to remove this contamination without disassembling the machine. Bernd Krebs CEO UniTemp
This guide explains:
why extruders need purging
how purging compounds work
the step by step process for cleaning an extruder
when purging should be performed
how proper purging reduces maintenance downtime
For plastics processors running extrusion equipment, understanding proper purging procedures can significantly improve production efficiency and product consistency.
Why Extruders Need to Be Purged
During normal production runs, molten polymers travel through the screw flights and barrel under intense heat and pressure. Over time, several forms of contamination build up inside the machine.
Common contamination sources include:
Polymer degradation
Plastic that remains inside the barrel at high temperatures can break down and form carbonized residue.
Color pigment residue
Pigments used for colored plastics often remain trapped in the screw root and barrel surface.
Additives and fillers
Stabilizers, fillers, and lubricants can accumulate during frequent material changes.
Burned material
Dead zones inside the screw geometry can trap material that eventually burns and contaminates the melt stream.
These residues lead to production problems such as:
black specks in finished products
inconsistent color during changeovers
extended startup scrap
reduced product quality
Purging removes these contaminants and restores clean processing conditions.
What Is an Extruder Purging Compound?
A purging compound is a specialized material used to clean plastic processing equipment.
Unlike production resin, purging compounds are engineered to remove contamination from internal machine surfaces.
Their purpose is to:
displace residual polymer
loosen carbon buildup
remove color contamination
prepare the machine for the next production run
Purging compounds are commonly used during:
material changeovers
color changes
machine shutdowns
maintenance preparation
When used correctly, purging compounds can clean extrusion systems in minutes rather than hours.
Mechanical vs Chemical Purging Compounds
Purging compounds typically fall into two categories.
Chemical Purging Compounds
Chemical purges rely on additives that react under heat to release gases or chemical agents that loosen contamination.
While effective in some applications, chemical purges may produce:
fumes or odor
chemical residue inside the machine
limited temperature operating ranges
These characteristics can make them less suitable for some production environments.
Mechanical Purging Compounds
Mechanical purging compounds clean equipment using physical cleaning action rather than chemical reactions.
During processing, the material softens into a dense thermoelastic mass that:
forms a purge plug inside the screw flights
presses against barrel surfaces
loosens contamination
pushes residue out through the die
Mechanical purging compounds are particularly effective in extrusion systems because they maintain pressure inside the machine while removing contamination.
Industry publications such as Plastics Technology have described this type of purging compound as producing a “soft scrub” cleaning action inside extrusion equipment.
Step by Step: How to Purge an Extruder
The exact procedure varies depending on machine design and polymer type, but the general method is consistent across most extrusion operations.
Step 1
Increase the barrel temperature to the recommended purge temperature.
Maintaining proper temperature ensures that the purging compound softens correctly and flows through the screw geometry.
Step 2
Stop feeding the current production resin.
Allow the machine to run until most of the material currently inside the barrel has been processed.
Step 3
Introduce the purging compound into the hopper.
Feed the purge material into the machine in the same way as standard production resin.
Step 4
Run the screw at moderate speed.
Allow the purge compound to move through the screw flights while maintaining pressure inside the barrel.
During this stage the purge will begin displacing existing material and loosening contamination.
Step 5
Continue purging until the extrudate appears clean.
Contaminants such as carbon residue and color pigments will exit the machine through the die.
Continue purging until the discharge material runs clear.
Step 6
Switch to the next production material.
Once the purge material has removed contamination, normal production resin can be introduced into the machine.
Production can typically resume immediately after the purge exits the system.
Visual Overview: How Purging Works Inside an Extruder
The purge compound moves through the screw flights as a dense cleaning plug, physically removing contamination and pushing degraded material out of the extrusion system.
When Should You Purge an Extruder?
Routine purging should be performed during several key production scenarios.
Common purging situations include:
• color changeovers
• switching polymer materials
• removing carbon buildup
• preparing machines for shutdown
• troubleshooting contamination issues
Regular purging helps prevent long term contamination buildup that can lead to major maintenance procedures.
How Purging Reduces Downtime
Without purging, contamination buildup can require complete machine disassembly.
In many cases this involves removing the extrusion screw and manually cleaning internal components.
Screw pulls are labor intensive and can require many hours of downtime.
Effective purging compounds can significantly reduce the need for these maintenance procedures by removing contamination during normal machine operation.
Processors often experience:
shorter changeover times
reduced startup scrap
fewer screw pulls
improved product consistency
For high volume extrusion operations, these improvements can translate directly into increased productivity.
Extrusion Purging Best Practices
To achieve the best results when purging an extrusion system:
follow recommended temperature ranges
maintain moderate screw speeds
allow sufficient purge material to pass through the machine
purge regularly during changeovers
Routine purging keeps extrusion equipment cleaner and reduces long term contamination buildup.
Learn More About Purging Compounds
For a complete overview of purging compound technology, including injection molding applications and material compatibility, read our guide:
What Are Purging Compounds? Complete Guide for Plastics Processors (2026)
Mechanical purging compounds are sometimes described as producing a soft scrub cleaning action inside processing equipment, as noted by the plastics industry publication Plastics Technology.
Request a Sample of PEKUTHERM®
Every extrusion system operates under different materials, temperatures, and production conditions.
If you would like to evaluate how PEKUTHERM® mechanical purging compounds perform in your extrusion equipment, the UniTemp team can help identify the correct formulation for your process.
Carbon contamination is often the underlying cause of black specks in extrusion runs. This guide explains how carbon buildup forms and how processors remove it.
Request a sample or technical consultation: https://pekutherm.org/contact-us
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