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Troubleshooting guide for blown film extrusion
 
PROBLEM
POSSIBLE CAUSES
SOLUTIONS
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 10C in 5C 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 Reduce nip height in order to collapse film at a higher temperature, 80C to 90C 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 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 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
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
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
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.
Courtesy: Mr. P.M. Jariwala, Kolsite Industries
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