Troubleshooting guide for HDPE Monofilament Extrusion Applications
HDPE Monofilament Extrusion Troubleshooting
Problem
Probable Cause
Suggested Remedy
Temperature Setting
Temperature setting are crucial parameter for proper plastic processing ,hence one should check temperature controller, thermocouple and solid state relay(SSR)
- when you cold start the machine ,wait for 2hours.
Frequent filament breakage at quench bath
- Moisture in the material
- Contamination in material
- Surging of extruder
- Breakage of particular filaments due to partially blocked holes of extrusion die/spinneret
- Oxidation and weakening of filament surface
- Melt draw-down ratio too high
- Quench bath temperature too low
- Molten filaments sticking to each other
- Melt too cold which reduces ductility
- Use hopper dryer
- Inspect feed, reduce or stop using recycled material
- Run at higher pressure or with better mixing screw, try to determine period of surging and relate to drive controllers
- Clean the die holes for blockage, reduce extrusion temperature if a higher side, check for uneven temperature or material fat/lighter side, check for asymmetrical distribution in the extrusion die head, check for asymmetrical construction of the die head which can cause uneven melt flow pattern or melt stagnation
- Run at lower temperature, or reduce the distance between die head and quench bath
- Reduce melt draw-down ratio
- Increase quench bath temperature to desired level
- Separate the filaments properly after quenching
- Increase melt temperature
Frequent filament breakage at stretching oven
- Higher stretch ratio, low stretching temperature
- Stretching temperature too high
- Abrasive marks or scratches on godet rolls
- Jerks and erratic drive of the godet rolls
- Optimise stretching parameters, both of these produce excessive tension in the filaments
- Reduce stretch temperature (too high stretch temperature draw the filaments but without orientation causing filament breaks under normal stretching tension)
- Grind them smooth or wrap them with Teflon tapes
- Check smoothness of operation for all moving parts
Non-uniformity of filaments
- Contaminated polymer melt
- Non-uniform dispersion of pigments in polymer melt
- Surging in extruder
- Through-put variation
- Broken or cracked filter pack
- Temperature variation at extrusion die
- Variation in quench water temperature
- Variation in godet speed
- Jerks and inefficient pressure on nip rolls
- Inspect feed, reduce or stop using recycled material
- Use good quality pigments, use base polymer of master batch as the parent material
- Run at higher pressure or with better mixing screw, check production rate and reduce if running at higher production rate than recommended
- Check metering pump drive for variation in RPM, check for aggregate formation at feed zone
- Change filter pack, broken filter pack causes uneven melt flow to extrusion die/spinneret
- Check for actual and set temperature, check for burn out heaters
- Maintain quench water temperature at desired level
- Check godet drive for speed variation and jerks
- Check and adjust pressure on nip rolls
Poor Surface Appearance
- Moisture in the material, master batch or pigments
- Degradation of material in extruder
- Melt fracture
- Use hopper dryer at feed section
- Reduce extrusion temperature
- Reduce extrusion rate, reduce line speed, use larger die extrusion hole with the lighter melt draw down ratio, reduce entrance angle in die holes, increase extrusion temperature
Lower tenacity
- Lower stretching temperature
- Low molecular orientation
- Nicks and cuts in filaments
- All causes related to non-uniformity of filaments
- Increase stretching temperature
- Increase stretch ratio, optimise stretching temperature, too high stretching temperature reduce filament tenacity, note that changes of orientation may also change the filament diameter, requiring compensating adjustment elsewhere to maintain desired filament diameter
- Examine broken and un-broken filaments, look for a repetitive pattern and source of defect generation
