FILMS

PROBLEM CAUSES & SOLUTION
Poor optical properties Change compound, or run hotter. If cast film, decrease gap between die and cooling surface. If tubular, increase blow ratio raise frost line.
Improper Slip More slip agent and/or higher melt Temperature to increase slip.
Film too weak in one direction (splitting) If tubular, adjust relation of linear speed and blow ratio to correct balance. If cast minimize draw down, run hotter use shorter gap, smaller lip opening. In both methods, check for die lines which may weaken film.
Film too weak all over Both methods, change to stronger resin check for possible degradation polymer If tubular use greater blow ratio and greater linear speed or lower frost line.
Film discolored or streaked Check condition and colour of feed. Run cooler to inhibit Decomposition.
Too many fish eyes (Gala of other particles) These impair appearance and may cause bubble breaks. Review entire operation looking for source of contamination, decomposition inside the system, a major cause. Use more streamlined equipment. Follow recommended start-up/shut-down procedures. In opening bags, avoid pick up of outside dirt or paper fibers and thread. Reduce or eliminate addition of reprocessed trim, check cleanliness of the air. Keep hopper covered and full. Check plant ventilation, as dirty air must not enter extruder. Clean die often. Check raw material; if fish eye producing material there, change to another material or use fine screens (200 mesh) and/or continuous changer. Burnt plastic on Die lips may break and cause fish eyes and bubble breaks.
Bubble breaks ( not form fish eye) Draw-down limits may be exceeded, increase temperature, use different compound, get better mixing and more uniform melt. Moisture in hopper either absorbed into Plastic or introduced as contaminant can cause tiny bubbles and roughness.
Die lines (grooved) Clean die, follow proper start-up shut down procedures, avoid internal decomposition, check for nicks or burns on die lips.
Varying thickness This is evidence by an asymmetrical bubble and/or heavy spots on the finished roll. Adjust die opening. Check for defective heaters or other hot/cold spots on die. Use uniform, jet-free cooling air. In tubular film thin bends require increased cooling air flow and/or reduction in gap opening at corresponding positions on die and vice-versa for thick ends. To get neat roll, use rotating/oscillating die. Uneven roll is also possible if wound too hot.
Bubble instability vibrating or shaky Decrease blow ratio (use large die, or make smaller film) check temperature and thickness uniformity of melt at the die. If extruder is surging (watch pressure and power fluctuations) reduce screw speed increase pressure, use different screw, cool screw (last resort, as it reduce output) Check constancy of air pressure inside bubble. Improve air ring construction, aiming air more in an upward (vertical) direction. Use iris, expandable mandrel or other stabilizing device. Avoid outside drafts, shield whole system from doors, windows, other air currents.
Wrinkless These are often caused by bubble instability (see proceeding item) Also check for improper alignment of take-off, skewed rolls etc. Check for smooth drag-free passage through flattener and nip rolls. Use auxiliary expander or bowed rollers having Helical pattern diverging from center out to ends.
Blocking Improve cooling or run at lower temperature, inflate a secondary bubble just after the nip rolls. Use anti- block additives, reduce nip rolls pressure, check for excessive electrical discharge treatment for printing which can cause blocking. Use nitrogen instead of air in bubble.
Poor cooling Tubular: Increase height of nip rolls from die, use more air, better doffing inside air; ring better direction of air (smaller angle with vertical), cooling sleeves, fog sprays metal mandrels, expandable mandrels extra air ring; refrigerated air. Put cooling section in air conditioned enclosure. For cast film; use colder cooling water, large chill roll, air knife. Both methods run at lower temperature.
Puckering on cast film Run chill roll warmer.

PIPES

PROBLEM CAUSES & SOLUTION
Indented pock marks with direct water cooling Caused by air bubble on the pipe surface under water. Correct with large volume low velocity water cascade.
Raised pock Marks Caused by water droplets on surface in air cooling zone. Eliminate any splashing by putting up in a shield to protect hot pipe. Use water cascade instead of sprays.
Surface defects appearing
  • Moisture can cause surface marks especially with black or filled compounds. Drying prior to extrusion will help.
  • Unmixed resin or additive particles are possible and require more mixing in the extruder.
  • Foreign contamination can be reduced by new or finer screen pack. Check system for handling regrind; inspect virgin resin and sources of contamination.
  • Particles may also come from decomposition in stagnant areas within extruder, especially with PVC.
Rough surface inside
  • Can be caused by moisture or low melt temperature or dirty metal surfaces. Sticking and seizing on mandrel or sleeve surfaces can cause roughness.
  • Very high linear extrusion speeds can cause melt fracture at the die, which is caused by higher temperature, longer die lands and smaller internal entrance angles into the die-head section.
  • When roughness is observed, try to locate the exact point of its origin. A strip or roughness on the underside is caused by uneven water cascading; direct another cascade from bottom upward or cascade all around the pipe. Strip roughness on the outside can also be caused by misaligned sleeve or some foreign matter caught in the sleeve sizing plate.
  • A ripples strip of roughness can be caused by a difference in wall thickness at that at that point.
  • Roughness all over, especially in little V-shaped marks pointing away from the die arised from insufficient mixing and Occasionally also from moisture in the Melt. Better mixing is achieved by higher Melt pressure cooler screw, slower speed Or better screw design.
Discoloured material Decomposition of compound, usually PVC reduces temperature or uses a different formulation (more stable or less viscous) or improves streamlining of extruder and die interior.
Splity pipe
  • Look for visible weld marks and check if failure is along weld lines. Extrusion may too cold or too fast. Raise melt temperature or improve die design by increasing long length to develop more pressure
  • Excessive draw down can produce split pipe even with proper rewelding of split streams. Check pipe for unbalanced orientation in extrusion direction.
Circumferential Ridges Caused by periodic drag on mandrel, vibration of take-off equipment, or uneven take-off speed. This is remedied by finding proper mandrel temperature or fixing the take-off. The puller may be operating at the low and of its range, which can cause irregular pull.
Circumferential Waviness Caused by material surging on non-uniform water cascade or leaking of water through sizing plates. Use smaller first sizing plates or a more uniform flow of water around the pipe. Check plate for wear and nicks. For surging remedies, see "better mixing" under rough surfaces", above.
Unbalanced wall thickness Adjust at die. Make sure the elements of the take-off are all properly aligned and that there are no hot or cold spot in the die.
Pipe Out of round Sizing devices inadequate or out of shape especially in water trough also, pipe is too warm when it reaches the puller.
Lack of Gloss Same problems and remedies as rough surface discussed above. Raising melt temperature is most likely a remedy. Some die cores are electrically heated to give batter internal gloss. The exterior can be flame polished if linear speed is slow. Sizing sleeves can give best outside surface. Formulation can be Improved to give better gloss, e.g. Lubricants in PVC.
Poor strength
  • See `Split pipe' above. Also indented printing can weaken pipe, as can too much Draw down at low temperature. Look carefully for nicks and grooves that could concentrate stress.
  • Plastic may be degraded by thermal decomposition (PVC) ultraviolet light long storage in sunlight) or use of too much strap in the feed. Mould a plaque from the weak pipe and compare its basic physical properties with those expected from new compound.
  • Poor mixing can cause weak pipe even if appearance is acceptable, particularly with PVC. Remedies are given above under `rough surfaces' strength is very much dependent upon material formulation.

MONOFILAMENT

PROBLEM CAUSES & SOLUTION
Filament Breakage
  • Surging in extruder. Run at higher pressure, or with better mixing screw of with cooled screw, or with gear pump or more slowly. Try to determine period of the surging, and relate to drive controllers etc.
  • One or more holes partially blocked the same filament (s) will break over time
  • Uneven temperature or distribution of material in head and die. The same group of filaments will break every time. Look at blue print of die or find symmetrical construction, if any, which could cause the uneven patterns.
  • Melt too hot. Not enough ductibility to draw down. Raise temperature.
  • Melt too hot. Too fluid to hold together under drawing tension. Reduce temperature.
  • Draw down too great (use smaller holes in die) or draw down too fast (slow down whole system )
  • Contamination in material. Inspect feed stop using reground or reworked plastic
  • Moisture in material. Use a hopper dryer.
  • Oxidation and weakening of filament furnace. Run at lower temperature, or reduce the gap between die and quench bath.
  • Decomposition in extruder, head or die bits or decomposed material clog holes or come through them but weaken the filaments. Clean die, run at lower temperature, examine die change die or head if necessary, use better stabilizer plastic.
  • Too much orientation, ratio of roll speeds may be too high causing excessive tensile stress in orientation stage
  • Too hot orientation. If plastic becomes too hot, it loses ductibility and will break under the normal orientation stresses.
  • Too cold orientation. If plastic is not hot enough, too much tensile stress will be produced in the filaments.
  • Nicks or abrasive areas on any of the rolls grind them smooth or wrap them with tape.
  • Erratic drive. Check smoothness of operation of all moving parts.
All filaments varying Surging in extruder. Draw down too much or too fast or erratic drive see (a) (f) and (e) above
Some filaments different from others, in size and/ or strength
  • Temperature gradients in die. Unequal flow in die. Check for drafts, burnt-out heaters, poor die design. See (c) above.
  • Take-off not exactly aligned with die and extruder.
Poor surface appearance
  • Moisture in material. Possible with polystyrene, nylon, or any pigmented or filled plastic. Dry the feed.
  • Melt fracture. Reduce linear speed or reduce entrance angle into die holes, or use lower viscosity compound or run hotter.
  • Plastic too cold. Run hotter.
  • Compound inherently dull. Change compound or run hotter or flame polish.
Low Tenacity
  • Not enough orientation, increased ratio of roll speeds. Use proper orientation temperature. Not that changes of orientation may also change the filament size, requiring compensating adjustments else-where.
  • Degraded plastic. Use lower material temperature or change to better stabilized formula.
  • Plastic unsuitable for filaments. Check check with its manufacturers.
  • Nicks or cuts in filaments. Examine breaks and examine unbroken filaments look for a repetitive pattern and examine take-off for the source.
Heavy Filaments do not lie straights Filaments would around a roll while still warm. Adjust filament or roll cooling.
Oval Cross Section
  • Filaments too hot while passing over rolls, especially in quenching bath. The rolls themselves could be too. Hot also.
  • Die holes not truly round
  • Temperature gradients in die effect roundness. Most likely in t-type die, with all holes in a line.
  • Too much tension in wrapping around

TAPE PLANT

PROBLEM CAUSES & SOLUTION
Filament Breakage
  • Surging in extruder. Run at higher pressure, or with better mixing screw of with cooled screw, or with gear pump or more slowly. Try to determine period of the surging, and relate to drive controllers etc.
  • One or more holes partially blocked the same filament (s) will break over time
  • Uneven temperature or distribution of material in head and die. The same group of filaments will break every time. Look at blue print of die or find symmetrical construction, if any, which could cause the uneven patterns.
  • Melt too hot. Not enough ductibility to draw down. Raise temperature.
  • Melt too hot. Too fluid to hold together under drawing tension. Reduce temperature.
  • Draw down too great (use smaller holes in die) or draw down too fast (slow down whole system )
  • Contamination in material. Inspect feed stop using reground or reworked plastic
  • Moisture in material. Use a hopper dryer.
  • Oxidation and weakening of filament furnace. Run at lower temperature, or reduce the gap between die and quench bath.
  • Decomposition in extruder, head or die bits or decomposed material clog holes or come through them but weaken the filaments. Clean die, run at lower temperature, examine die change die or head if necessary, use better stabilizer plastic.
  • Too much orientation, ratio of roll speeds may be too high causing excessive tensile stress in orientation stage
  • Too hot orientation. If plastic becomes too hot, it loses ductibility and will break under the normal orientation stresses.
  • Too cold orientation. If plastic is not hot enough, too much tensile stress will be produced in the filaments.
  • Nicks or abrasive areas on any of the rolls grind them smooth or wrap them with tape.
  • Erratic drive. Check smoothness of operation of all moving parts.
All Filaments Varying Surging in extruder. Draw down too much or too fast or erratic drive see (a) (f) and (e) above
Some Filaments Different from others, in size and/ or strength
  • Temperature gradients in die. Unequal flow in die. Check for drafts, burnt-out heaters, poor die design. See (c) above.
  • Take-off not exactly aligned with die and extruder.
  • Poor surface appearance
  • Moisture in material. Possible with polystyrene, nylon, or any pigmented or filled plastic. Dry the feed.
  • Melt fracture. Reduce linear speed or reduce entrance angle into die holes, or use lower viscosity compound or run hotter.
  • Plastic too cold. Run hotter.
  • Compound inherently dull. Change compound or run hotter or flame polish.
Low Tenacity
  • Not enough orientation, increased ratio of roll speeds. Use proper orientation temperature. Not that changes of orientation may also change the filament size, requiring compensating adjustments else-where.
  • Degraded plastic. Use lower material temperature or change to better stabilized formula.
  • Plastic unsuitable for filaments. Check check with its manufacturers.
  • Nicks or cuts in filaments. Examine breaks and examine unbroken filaments look for a repetitive pattern and examine take-off for the source.
Heavy Filaments do not lie straights Filaments would around a roll while still warm. Adjust filament or roll cooling.
Oval Cross Section
    Filaments too hot while passing over rolls, especially in quenching bath. The rolls themselves could be too. Hot also.
  • Die holes not truly round
  • Temperature gradients in die effect roundness. Most likely in t-type die, with all holes in a line.
  • Too much tension in wrapping around