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PROBLEM
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POSSIBLE CAUSES
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SOLUTIONS
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| DROOP ON FILM EDGES |
Film edges rolling before the nips, due
to uneven cooling of film edges. Caused by uneven collapsing. |
Adjust gap at top of collapsing frame,
adjust collapsing board. |
| GAUGE VARIATION |
Die gap uneven, non uniform air velocity
in air ring. Uneven temperature
on die ring Extruder surge Improper nip drive speed |
Adjust die, Adjust volume of air through air ring Adjust
temperature Check extruder drive speed. Check feed section housing.
Check temperature controllers, remove screw cooling, raise temperature
in first zone up to 10°C in 5°C increments until surge is minimized
or eliminated. Check water circulation in feed section. Check nip
drive motor g/box and belts, chains or sprockets. |
| GELS & FISH EYES |
Poor mixing Contaminated resin Flaking from dirty screw
or barrel Excessive use of reclaim or off grade pellets with virgin
material Burnt polymers from improper start ups or shut downs Poor
resin quality |
Check mixing. Clean resin silos, transfer system &
hopper feeder. Clean screw & barrel. Drop ratio of reclaim &
off grade. Check for burnt polymer Check resin homogeneity |
| SAG IN FILM |
Bubble geometry wrong Bubble cooled unevenly
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Reduce nip height in order to collapse film at a higher
temperature, 80°C to 90°C before nips. Check uneven contact, check
side collapsing boards. |
| SCRATCHES IN FILM |
Surface contact of film with auxiliary
equipment |
Polish any surfaces causing problem: bubble guides,
treater, idler rolles, gusset formers, slitter blade holders |
| UNEVEN WIDTH OF FILM |
Tension varies or is too high Air leakage from bubble
Web wander prior to wind up Variable web tension in edge triming or
slitting station |
Check tension & taper it as roll builds & ensure
it is not too tight. Check collapsing frame Check for too much velocity
at air ring Check web tension. Check web tension |
| WRINKLES IN FILM |
Wide guage variation across web Insufficient cooling
of high frost line Bubble bounce Poor alignment of tent & primary
nip rolls Rolls out of alignment producing angled wrinkles Excessive
tension or unbalanced idler rollers, rough surfaces in collapsing
area Collapsing & cooling of bubble are uneven, producing wrinkles
on edges after nips |
Make die adjustments, check for uniform die temperature
and air ring velocity. Use cooler air or drop extrusion temperature
Ensure smooth collapsing in tent, eliminate air drafts around bubble
Re-align die to nip rolls Check alignment of rollers. Check tension
& speeds of downstream rollers, eliminates rough surfaces Adjust
gap at top of collapsing frame & side collapser, also minimize
bubble movement by reducing stalk height |
| PROBLEM SPLITTING OF THE FILM |
Insufficient cooling, frost line too high, blow up
ratio too high Nips set too tight, especially if old & hardened
rubber nips are used Die line or bad web lines from die Scratches
from collapsing frame, nips or idlers Degraded particles of resin
or dirt lodged under edge of die lips which make film split at weld
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Check cooling, check frost line, check blow up ratio.
Check & adjust nips, replace old & hardened rollers. Decrease
temperature to build up pressure to reduce die or weld lines (Note:
this will not decrease output) Eliminate sources of scratches Clean
die lips |
| STRENGTH OF FILM IS POOR |
Not enough blow up ratio Thin spots in film Extrusion
temperature too high or too low |
Increase blow up ratio Check for guage variations Gradually
adjust temperature. |
| APPLE SAUCE |
Poor mixing Extrusion temperature too high or too low
Poor resin quality |
Use water cooling in screw to improve mixing, increase
screen mesh to increase back pressure. Gradually adjust temperature
Check resin. |
| BLOCKING |
Insufficient amount of antiblock additive Winding tension
too high Frost line too high resulting in a higher film temperature
at collapsing, which may increase take-up nip roll temperature thus
applying more pressure on film from roll expansion Inadequate cooling
or ambient temperature too high, causing inner surfaces to block as
they pass through nips Overtreatment Excessive static electricity
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Check amount of anti-block Adjust winding tension Check
frost line level, adjust temperature. Reduce output, raise nips, use
chilled air. Check & control environmental temperatures which
may cause this condition Avoid overtreatment Check & control static
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| CHATTER IN FILM OR BUBBLE |
Air ring velocity excessive Air ring lip gap too narrow
Friction in collapsing frame |
Decrease air rate Increase lip gap Modify the surface
to decrease friction or decrease melt temperature |
| CLARITY OF FILM IS POOR |
Poor resin quality or wrong resin grade Extrusion temperature
too high or too low Inadequate film cooling Low blow up ratio Poor
mixing due to low shear extruder & die |
Check resin Gradually adjust extrusion temperature
Check cooling system Check cooling system Check extruder & die
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| DIE LINES OR TRARS IN FILM |
Oxidization of the polymer on die lip caused by polymer
resting on lip for prolonged periods after shut down Hard gel or foreign
matter inside die Insufficient blending of molten polymer as it flows
around die leaving a weld line in its path |
Stop the screw. With copper pad, clean die up. Carefully
scrape edges of lip with brass shim. Apply coat of silicone grease
Clean mandrel & upper portion of die, clean area of die land &
below Increase mixing in extruder, increase adaptor & die temp
rature and / or increase screen mesh to increase back pressure |
| BUMPY ROLLS |
Guage variation Excessive lay - on pressure Web too
warm at wind up |
Check for guage variation symptoms Decrease lay - on
pressure Decrease temp. of chill roll |
| CORE COLLAPSE |
Film too warm Film wound too tight Excessive lay -
on pressure |
Decrease temp. of chill roll Reduce winding tension.
Increase taper tension if available Decrease lay - on roll pressure
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| FUZZY ROLL ENDS |
Dull cutting blades Poorly aligned blades which are
not parallel or perpendicular to web Edge of sheet is slitting because
blade is not in centre of edge fold |
Check and replace as necessary Check blade adjustment
Check film guiding. |
| GUAGE BANDS (HUMPS) IN ROLL |
Uneven cooling of film Uneven flow out of die because
of temperature variation |
Rotate die & air ring Eliminates air drafts around
bubble. |
| ROLL IS TOO HARD |
Excessive tension at winder Excessive lay - on pressure
Web too warm (shrinks at cooling) |
Lower winder tension. Lower roll pressure Decrease
temperature of chill rolls |
| ROLL IS TOO SOFT |
Winding tension insufficient |
Increase roll pressure. |
| SYMETRICALLY DEFORMED ROLLS (tapered
convex or concave) |
Heat rising from extruder causes roll with face near
extruder to have concave face Drafts caused by air intake of air ring
blower; an open door, hot air heaters or floor fans A tipped die and
/ or air ring causes film to be pulled unevenly through nips |
Check & control heat rising from extruder Locate
& eliminate sources of air currents Check position of die and
/ or air ring |
| TELESCOPING (UNIVENROLL WIDTH) |
Improper winding tension Extruder surge (can be caused
by user or scrap or fluff.) Slippage between core &shaft. Air
draft around bubble. Lateral displacement of bubble in collapsing
tent. Incorrect nip drive tension Inconsistent contact between Lay
- on roll & film roll. Lay - on roll pressure too low Roll not
aligned. Taper in winding incorrect |
Maintain uniform winding tension control, dancer position.
Film tension before & after each nip roll should be even. Watch
for fluctuating tension. Check extruder feeding. Check all possible
problem causes; In the event of excessive slip, treat only side of
film which contacts rollers. Rotation of die will cause wrinkle problems
for deep gussetted film. Check nip drive belt of chains. Check &
correct Increase roll pressure. Check alignment of all rolls and contacting
web in turret & winding areas. Adjust taper tension. |
| WRAP UPS IN DOWN - STREAM NIPS |
Improperly cooled film or improper tension control. |
Stop nip drive, turn screw speed down to minimum, open
nips & unwrap. Do not cut against rolls or they may be damaged. |
| VARIATION IN FILM OPACITY WHILE USING
WHITE M. B. |
Heavier M. B. granules move faster than lighter basic
polymer granules when hopper is partially filled up |
Keep hopper completely filled up. Keep small difference
of level between minimum & maximum level in hopper. Install dosing
mixing unit. |
| GSM VALUE OF FRONT ROLL DIFFERENT FROM
REAR ROLL |
Winding tension unequal |
Check winding tension. |
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Courtesy: Mr. P.M. Jariwala, Kolsite Industries
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