Essential for Modified Plastic Production: Detailed Explanation and Application Guide of Four Screw Cleaning Methods
Practical Application Guide to Four Screw Cleaning Methods for Modified Plastic Production
In modified plastic production, screw cleaning is a critical step to ensure product quality—but it’s often overlooked by manufacturers. Residual carbides, pigments, or cross-contamination between different materials can cause defects like black spots and streaks, leading to significant losses.
This guide dives into the principles, key operations, and precautions of four mainstream twin-screw extruder cleaning methods. It offers actionable insights for industry professionals.
01 Resin Cleaning Method
Resin cleaning is a common technique using polyester resin, epoxy resin, or specialized screw cleaners. It works well for initial cleaning of new equipment or daily maintenance.
Working Principle:
When heated to a molten state, cleaning resin physically displaces and chemically bonds with residues inside the machine. Mechanical scouring and interface peeling gradually remove contaminants from screw and barrel surfaces. The process completes when the extrudate fully switches from processing resin to clean resin.
Operation Process:
Close the feeding plate and the discharge port at the bottom of the hopper.
Reduce the screw speed to 15-25r/min and maintain it until the melt flow at the front end of the die stops.
Set the temperature of all heating zones of the barrel to 200°C.
Add the cleaning material from the discharge port until the color of the extruded strand is the same as that of the cleaning material pellets.
Stop feeding, empty the materials, and stop the screw rotation of the twin-screw extruder.
Open the die, rotate the screw, take out the orifice plate, and discharge the residual cleaning material in the barrel.
Precautions:
Speed Control: Keep screw speed below 20r/min during cleaning. For final residual removal, set it to around 10r/min.
Pressure Monitoring: Watch extrusion pressure closely to avoid overpressure. Remove the die if needed to reduce front-end pressure risks.
Temperature Management: Follow recommended temperatures strictly to prevent resin degradation from overheating.
Effect Evaluation: Judge the cleaning degree by observing the color change of the extruded strand to ensure complete conversion.
Main Limitations:
Ordinary resin may lack sufficient cleaning power and waste raw materials. It often fails to remove stubborn carbonized residues. Specialized cleaners improve efficiency via softening and peeling, but results vary by equipment condition and operating parameters.
02 Disassembly Cleaning Method
Disassembly cleaning involves fully taking apart extruder components for manual thorough cleaning. It suits deep cleaning needs or when switching to special materials.
Working Principle:
This method uses physical contact to directly remove stubborn residues from screws, orifice plates, dies, and other parts. Manual operation with special tools reaches every corner—ideal for severe carbonization or gelling residues.
Operation Process:
Stop the screw rotation, open the extruder die, and start gradual disassembly.
Rotate the screw of the twin-screw extruder, take out the orifice plate, and discharge the residual cleaning material in the barrel.
Carefully clean the residues on the orifice plate to ensure unobstructed flow holes.
Stop and pull out the screw to check if it is clean.
Manually remove the residual material on the screw with appropriate tools.
Reinstall the screw in the correct order, add new materials to flush out the residual cleaning material in the barrel.
Install the orifice plate and die to complete the entire cleaning operation.
Precautions:
Disassembly Sequence: Strictly follow the disassembly sequence required by the equipment manual to avoid damage to precision components.
Tool Selection: Use special tools such as copper scrapers and copper brushes to prevent damage to the surface of the screw and barrel.
Cleaning Thoroughness: Ensure that residues on the surface of all components are removed, especially threads and gap areas.
Reassembly: Check all seals during reinstallation to ensure assembly accuracy and equipment tightness.
Main Limitations:
This method requires professional operators. It risks irreversible damage to screws and barrels, and cannot clean the inner barrel wall.
03 Flame Cleaning Method
Flame cleaning is a traditional method that uses high-temperature flame to remove stubborn plastic residues from screw surfaces. It’s widely used in plastic processing facilities.
Working Principle:
High-temperature flame instantly heats and carbonizes solidified plastic residues on the screw. This decomposition makes stubborn deposits brittle and easy to remove by breaking down polymers quickly.
Operation Key Points:
Timing Selection: Clean immediately after the screw is used. At this time, the screw has residual heat from the processing process, and the heat distribution is uniform.
Temperature Control: Use a blowtorch for cleaning to avoid excessive temperature.
Uniform Heating: Keep the flame moving to ensure uniform heating of the screw and avoid local overheating.
Precautions:
Prohibit Acetylene Flame: Acetylene burns at 3000°C, damaging screw metal properties and mechanical tolerances.
Prevent Metal Structure Change: Persistent blue flame on any area indicates altered metal structure, reducing wear resistance.
Avoid Screw Bending: Local overheating causes uneven thermal expansion, leading to screw deformation.
Material Protection: Most screws are made of 4140.H.T. steel with tight tolerances (≤0.03mm) and high straightness (≤0.01mm). Improper heating causes irreversible damage.
Main Limitations:
Improper operation poses high risks. It demands experienced operators and is not suitable for all screw materials.
04 Water Washing Cleaning Method
Water washing uses hydraulic rotational kinetic energy for comprehensive screw cleaning. It’s an eco-friendly, efficient modern solution.
Working Principle:
Automatic screw washers use rotating water flow combined with counterforce from screw rotation to achieve 360° dead-angle-free peeling. Precisely controlled water pressure, temperature, and flow remove polymer residues effectively without damaging the screw’s physical structure.
Technical Advantages:
Comprehensive Cleaning: Rotating water flow can reach all gaps and complex structures to ensure thorough cleaning.
Material Protection: Hydraulic cleaning does not damage the screw base material, maintaining the original mechanical properties and tolerance accuracy.
High Efficiency and Energy Saving: The cleaning process is fast, suitable for forced peeling and removal of various polymer materials.
Environmental Protection and Safety: Using water as the medium, there is no chemical pollution, and the working environment is safer and healthier.
Precautions:
Applicability Check: Confirm the screw’s material and structure are suitable for water washing.
Parameter Setting: Adjust water pressure, temperature, and duration based on residue properties.
Equipment Matching: Choose a washer compatible with the screw’s size and cleaning requirements.
Subsequent Treatment: Dry in time after cleaning to prevent rust of metal components.
Environmental Compliance: Treat wastewater properly to meet environmental standards.
Main Limitations:
Water washing may not fully remove some stubborn residues. Narrow gaps and complex meshing areas of twin screws can trap residues, leading to incomplete cleaning.
Conclusion
Choosing the right screw cleaning method requires balancing material properties, equipment condition, product quality requirements, and cost-effectiveness. In practice, combine multiple methods flexibly based on production stages and contamination levels for optimal results.
Regardless of the method, standardized operation and regular maintenance are key to effective cleaning and extended equipment life. Establishing scientific cleaning cycles and standard operating procedures not only improves product quality but also reduces production costs—delivering greater economic benefits for modified plastic manufacturers.
