Issues of Blown Film & Solution Guide Book
The problems of blown film extrusion are related to Air Ring, Die Head, Extruder, Materials, Ambient conditions of of Blown Film Plant
When bubble blown up unstably, check cooling air, environmental air flow and B.U.R.
Check 1: Problem of air ring exits
Action 1: Check if Air Ring exits position has been moved away from the last setting up. See if its air flow is to be evenly delivered; find the correct position of lip-height with air pressure properly.
**Air ring is designed with Venturi principle which is to make exit air to become a vacuum effect instead of interference by itself, for example, dual air flows. Generally when increasing air flow, the bubble will be sucked up with the wall and become stable; but the thin film might be touched with the wall and scratched. If any question, please consult with our technical service.**
Check 2: Ambient air flow interference
Action 2: Check and minimize the surrounding air flow of the ambient interference.
Check 3: Melt strength too low
Action 3: Lower the molten temperature; use lower MFI material; and increase LDPE level.
Check 4: Too high B.U.R.
Action 4. Increase die head size for suitable B.U.R.
Check 5: Too high output
Action 5: Lower output quantity.
Check 6: Extruder Surging
Action 6: See "Solution of Extruder Surging" below.
Thickness variation or gauge variation happen and require to see air ring, die head and material feeding; or B.U.R.
Check 1: Incorrect coupling between air ring and die head
Action 1: Check the position between air ring and die head to be at central line.
Check 2: Check if air flow from air ring exit not uniformly
Action 2: Check if air ring exit has been damaged, if any foreign material or dust got into air ring, air entrances to be uniformly distributed.
Check 3: Die head temperature uneven or unstable
Action 3: Check die head heater band, thermal couple, temperature indicator to be normally working.
Check 4: Material feeding unstable
Action 4: Check rotating speed and feeding area of screw or hopper of any material blockage; nipple roller evenly runs. Exchange filter of screen changer when polymer becomes blockage.
Check 5: B.U.R problem
Action 5: Check B.U.R, see if it is too large; or replace with larger die head lip size.
Check 6: Ambient air flow interference
Action 6: Stop outer air flow directly coming to working area. Apply ventilation system for air conditioning properly without affect extrusion blown film running.
Poor Optical Film
Blown film optical property is related material type and temperature and die gap size.
Check 1: Frost line too high
Action 1: Lower height of the frost line.
Check 2: Molten temperature too low
Action 2: Increase temperature of extruder and die head.
Check 3: Happenings of melt fracture
Action 3: See "Solution of Melt Fracture".
Check 4: Too wide of die gap
Action 4: Exchange narrower gap of die pins.
Check 5: Formulation issue or additives problem such as too much of anti-block agent
Action 5: Add higher flow index and lower density polymer and optimize level of additive.
Blown film output productivity is related mostly to die head and extruder; then cooling effect.
Check 1: Too high pressure of die head?
Action 1: Check screen changer blockage, consider to add higher MI polymer, add up die size or gap size or add up extrusion temperature.
Check 2: Is bubble kept stable
Action 2: Follow the "Solution of Unstable Bubble" of above.
Check 3: What about the extruder motor runs
Action 3: Exchange the malfunction motor; or increase extruder temperature, use of higher MI Polymer.
Melt fracture is also called sharkskin or surface melt fracture, mostly at die head and material.
Check 1: Too narrow of die gap
Action 1: Change larger gap die inserts.
Check 2: Melt temperature is too low
Action 2: Increase temperature of extruder and die head.
Check 3: Formulation issue
Action 3: Increase more (%) of wider molecular weight polymer(for ex. LDPE) rather than narrower one (for ex. LLDPE).
Check 4: Additives insufficient problem
Action 4: Increase additives for the processing requirement.
Check 5: Too high of output rate
Action 5: Lower down output rate.
Check 6: Die head material issue
Action 6: Choose a suitable material for die head which decreases molten slippage.
The blocking bubble means the opposite faces of film stick or adhere to each other.
Check 1: Bubble cooling not enough
Action 1: Increase cooling air supply.
Check 2: Too high pressure of nip roller
Action 2: Release nip roller pressure.
Check 3: Too high of winding tension
Action 3: Lower down winding tension.
Check 4: Rollers exposed at high heat during standby or store
Action 4: Keep the standby rollers away from high heat area.
Check 5: Is the anti-block level inadequate or improper type
Action 5: Add up anti-block level; or apply better type of agent.
Check 6: Polymer formulation issue
Action 6: Use of higher density polymer or Metallocene PE.
Poor Heat Sealing
Sealing dwelling time, sealing temperature or sealing blade clamping pressure and cooling conditions are to consider.
Check 1: Too high film thickness variation or gauge incorrect
Action 1: See "Solution of the blown film thickness variation too high"; follow the standard of B.U.R. as stated above.
Check 2: Too high of sealing temperature
Action 2: Decrease sealing temperature.
Check 3: Too high or too low sealing pressure
Action 3: Adjust sealing pressure properly; or optimize the choice of sealing knife.
Check 4: Sealing temperature or dwelling time are not enough
Action 4: Increase sealing temperature and dwelling time.
Check 5: Polymer formulation issue
Action 5: Check again that the original polymer type, see if any incorrect blending.
Check 6: Too much corona treatment
Action 6: Decrease level of corona treatment at blown film plant.
Die Lip Build-up
Die lip build-up or die line happen when die head or molten too high of temperature.
Check 1: Too high of die head temperature
Action 1: Decrease temperature of die head.
Check 2: Too high of molten temperature
Action 2: Reduce temperature of the extruder.
Check 3: Die lips damaged or scraped
Action 3: Exchange or repair die lip sets.
Check 4: Misalignment of die lips
Action 4: Re-align die lips to be neat and correct position.
Check 5: Too much anti-block agent
Action 5: Check type of anti-block agent and its level properly.
Extruder feeding and temperature setting up are to consider.
Check 1: Extruder temperature setting not properly
Action 1: Readjust and set up properly of extruder temperatures.
Check 2: Material feeding zone blockage
Action 2: Check of hopper of feeding zone and expel the blockage.
Check 3: Material feeding throat cooling insufficient
Action 3: Make sure of the cooling water for feeding zone properly.
Check 4: Polymer blending not well done
Action 4: Check of material blending equipment to be working properly.
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ISSUES OF BLOWN FILM & SOLUTION GUIDE BOOK - C.Y.
The problems of blown film extrusion are related to Air Ring, Die Head, Extruder, Materials, Ambient conditions of of Blown Film Plant. A guide book is provided to gain an in-depth understanding of blown film extrusion.
Sections of The ISSUES OF BLOWN FILM & SOLUTION GUIDE BOOK include: Unstable Bubble, Thickness Variation, Poor Optical Film, Low Output, Melt Fracture, Bubble Blocking, Poor Heat Sealing, Die Lip Build-up, and Extruder Surging.
C.Y. has been offering customers high quality air rings and die heads in Foundry Industry. Both with advanced technology and 20 years of experience, C.Y. makes sure each customer's demands are met.