Blown Film Extrusion Troubleshooting
The growing demand for global processors to keep their blown film machine(also called film blowing machine) operations operating as efficiently as they can. Making multi-layer and single layer blown films that have excellent uniformity of the film, strong tensile strength and robust barrier properties, leaves no space for errors. To ensure product consistency as well as a low amount of waste and decreased downtime, we’ve compiled some of the most frequent blow-film issues and ways to resolve these issues.
Problem:Gels, un-melts, Charred polymer
Reason: Overheated/degraded polymer, poor melting, foreign substances in the resin stream
- Reduce the melting temperature or, if it does not melt then increase the extruder barrel temperature
- Make sure you have a thermocouple installed and that you are able to make sure that the heater is controlled correctly.
- Extruder screw damaged or worn out Inspect and take measurements of the screw’s dimensions
- Damaged or worn out extruder barrel Check and measure the barrel ID
- Examine the material handling and resins for foreign contamination such as angel hair, fluff and more.
Problem:Melt fracture “Sharkskin”
Cause: Melt temperature too low or die gap too narrow
- Raise melt temperature (if possible)
- Raise die lip temperature
- Activate die lip heaters if quipped
- Increase die gap
- As as a last resort, think about the addition of the PPA (polymer processor additive)
Problem:Poor or non-uniform optical clarity
Cause: Inadequate extrudate quenching
- The melting temperature of the extrudate could be too low. increase the temperature of melt.
- Non-uniform heating of dies; test thermocouples and heaters
- IBC Air leaks be sure IBC intake and exhaust pipes are correctly installed
- The flow of air from the external or internal air ring is not even; ensure to ensure that the ring(s) are aligned. Check for blocked supply lines and dirty coil filters. broken or blocked plenums/screens, dirty or blocked plenums.
- Interfacial instability caused by co-extrusion; adjust the thickness of the layer using extruder outputs or by substituting a different resin with a different MI.
issue:Voids, “raindrops,” or gray streaks
Cause: Indicates potential moisture in resin stream
- Determine the source of the moisture problems in the material handling system.
- Examine the water condensation on the feed section for the extruder (hot humid atmosphere)
- Check that your raw materials are dry. examine the moisture content using a the heated balance of moisture
- If dryer is in use to dry clothes, is operating in a proper manner
The reason: Indicates contamination by an incompatible polymer
- Find out the source of contamination and then eliminate the source of contamination.
- Clean/purge the materials handling equipment, the hopper and dryer
- Purge extruder screen changer, purge extruder pipe and die using an un-blended, neat-base resin
- Clean and disassemble the barrel of extruder as well as feedscrew, filter changer, melting pipe, and die (if required)
The reason: Indicates the extrudate melt temperature is excessively high.
- Reduce the temperature of the barrel to the recommended levels
Issue: Poor pigment dispersion
Reason:Indicates poor mixing or uneven melting
- Residence time inadequate for accurate mixing; increase backpressure/residence time
- The melting temperature is not sufficient for precise mixing Lower temperature to increase shear
- Check the blending dosing device for precise and consistent color masterbatch feed
- Examine the feedscrew’s design and modify or change if needed.
- Assess the compatibility of the resin’s rheology
Issue: Gauge bands, die lines, film lines
Cause: Indicates contamination at die lips, die adjustment issues, uncontrolled localized tension, non-uniform cooling
- Die lip is dirty; clean (shim) die lips at localized lines
- Die is filthy; clean the area, wash and check the die
- The lip of the die is out of alignment Check the gap of the die and then re-gap
- Check the air rings on both sides for proper alignment as well as leaks, blockages, and localized high/low velocities and adjust as needed.
- Check that die is in the center of the bubble cage(s) or frames collapsing are centered. Nip roll is properly centered. that when it is closed the impression of a nip shows the same nipping gap between the chrome and rubber roll
- Verify that all the transport rollers can are able to rotate freely. Do you notice any tension differences?
- Eliminate external influences, such as drafts
issue: Wrinkles prior to the rolling of the nip
The reason: A non-uniform extrusion process that begins upstream of the tip
- Does the bubble breathe? Verify that the extrusion process is stable. The output as well as melt temperature and pressure must be in line
- Is the bubble still breathing? Examine the frost line; is it consistent and stable? If not, then check the position of IBC sensors to determine whether they are from or above the frost line.
- Does the air ring appear to be aligned and centered to maintain the stability of the bubble?
- Are the temperatures of chilled air constant? Check blower stability, chiller temp, cooling coils; look for blocked/crimped/missing supply hoses
- Are the bubble cages too tight? Examine for bubble breathing. Make sure the cage is properly centered and that it is in good interaction with the balloon. Make sure that the rollers and bubble contact surface are well-maintained and uniform.
- Is the cage too loose? If it shifts across the room, or makes a an hula-hoop, pull the cage back
- Does the collapsing frame angle appear too wide? If there are wrinkles on the edges Reduce the collapsing angle.
- Is the collapsing angle too narrow? If there are wrinkles in the center Increase the collapsing frame angle
- Are there wrinkles in the lightning bolt? Examine the nip-roll diameter from side-to-side as well as the nip-pressure variations. A lack of even pull from drive rollers with narrow drives or side guides may create wrinkles.
Reason: Indicates the winding tension or corona treatment levels could be excessively high.
- Reduce tension of the winding
- Lessen treatment levels
- Inadequate film cooling; decrease the temperature of the cooling roll or decrease the speed of the line
- Inadequate amounts of anti-block additive Increase the effectiveness of anti-block
If you need any information of blown fim extrusion,plastic bag machine,please feel free to contact us.
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