Detail on defects

1. Defects, Causes and Remedies
in Extrusion Blow Molding
By Sunil Mor

2. Defect: Bubbles
Causes
• Moisture in resin.
Remedies
• Keep resin dry and clean.
• Reduce coolant flow to feed throat.
• Raise feed section temperature.
• Use indoor surge bins to allow
resin to warm up after transferring
from cold outside conditions.

3. Defect: Bubbles
Causes
• Extrusion rate too slow.
Remedies
• Increase back pressure.
• Increase orifice size.
• Use resin with higher Melt Index.

4. Defect: Bubbles
Causes
• Misalignment of die/mandrel.
Remedies
• Tighten die lip bolts.
• Realign die/mandrel.
• Repair die seal.
• Lengthen land between mandrel
and bushing.

5. Defect: Bubbles
Causes
• Melt temperature too low.
Remedies
• Increase feed section temperature.
• Increase die lip temperature.

6. Defect: Rolling Up (Parison Curl)
Causes
• Resin contaminated.
Remedies
• Keep resin and regrind clean.
• Proper preheating.
• Use magnet in hopper.

7. Defect: Rolling Up (Parison Curl)
Causes
• Die and mandrel misaligned.
Remedies
• Tighten die tip bolts.
• Realign mandrel and die.
• Repair mandrel seal.
• Lengthen land between bushing
and channel.
• Replace tooling.

8. Defect: Rolling Up (Parison Curl)
Causes
• Contaminants in die channel.
Remedies
• Briefly open die gap and purge
contaminate.
• Clean die and resin channel.

9. Defect: Rolling Up (Parison Curl)
Causes
• Extrusion rate too low.
Remedies
• Increase back pressure.
• Increase orifice size.
• Use resin with higher Melt Index.

10. Defect: Rolling Up (Parison Curl)
Causes
• Uneven extruder heating.
Remedies
• Melt temperature too low.
• Replace/repair heater bands.
• Replace/repair thermocouples.

11. Defect: Excessive Stretching
Causes
• Extrusion rate too high.
Remedies
• Reduce mold open time.
• Lower back pressure.
• Reduce orifice size.
• Use resin with lower Melt Index.

12. Defect: Excessive Stretching
Causes
• Melt temperature too high.
Remedies
• Lower feed section temperature.
• Lower die tip temperature.

13. Defect: Holes
Causes
• Contaminates in die channel.
Remedies
• Briefly open die gap.
• Clean die and resin channel.

14. Defect: Holes
Causes
• Contaminated resin.
Remedies
• Keep resin and regrind clean.

15. Defect: Holes
Causes
• Bridging or collaring.
Remedies
• Drop scrap directly into feed
throat.

16. Defect: Streaks
Causes
• Contaminants in die channel.
Remedies
• Briefly open die gap to purge.
• Clean die and resin channel.

17. Defect: Streaks
Causes
• Contaminated resin.
Remedies
• Keep resin and regrind clean.

18. Defect: Streaks
Causes
• Uneven extruder heating.
Remedies
• Melt temperature too low.
• Replace /repair heater bands or
rods.
• Replace/repair thermocouples.

19. Defect: Streaks
Causes
• Die and mandrel misaligned.
Remedies
• Tighten die lip bolts.
• Realign mandrel and die.
• Repair mandrel seal.
• Lengthen land between bushing
and channel.
• Replace tooling.

20. Defect: Streaks
Causes
• Extrusion rate too high.
Remedies
• Reduce mold open time.
• Lower back pressure.
• Reduce orifice size.
• Use resin with lower Melt Index.

21. Defect: Uneven Parison Thickness
Causes
• Die and mandrel misaligned.
Remedies
• Tighten die lip bolts.
• Realign mandrel and die.
• Repair mandrel seal.
• Lengthen land between bushing
and channel.
• Replace tooling.

22. Defect: Uneven Parison Thickness
Causes
• Uneven extruder heating.
Remedies
• Melt temperature too low.
• Replace/repair heater bands.
• Replace/repair thermocouples.

23. Defect: Uneven Parison Thickness
Causes
• Die swell too high.
Remedies
• Use lower die swell resin.

24. Defect: Uneven Parison Thickness
Causes
• Extrusion rate too high.
Remedies
• Reduce mold open time.
• Lower back pressure.
• Reduce orifice size.
• Use resin with lower Melt Index.

25. Defect: Uneven Parison Thickness
Causes
• Melt temperature too high.
Remedies
• Lower feed section temperature.
• Lower die lip temperature.

26. Defect: Uneven Parison Thickness
Causes
• Contaminants in die channel.
Remedies
• Briefly open die gap.
• Clean die and resin channel.

27. Defect: Bad Pinch-Off
Causes
• Molds misaligned.
Remedies
• Realign molds.
• Use pre-blow cushions and slam.
• Replace or repair mold.

28. Defect: Bad Pinch-Off
Causes
• Melt temperature too low.
Remedies
• Lower feed section temperature.
• Lower die lip temperature.

29. Defect: Bad Pinch-Off
Causes
• Pinch-off too thin.
Remedies
• Widen pinch-off land.
• Eliminate knife edges and burrs
on mold.
• Repair damaged mold.

30. Defect: Bad Pinch-Off
Causes
• Flash volume too high.
Remedies
• Reduce flash size.

31. Defect: Blowout
Causes
• Melt temperature too high.
Remedies
• Lower feed section temperature.
• Lower die tip temperature.

32. Defect: Blowout
Causes
• Blow pressure too high
Remedies
• Lower blowing pressure.
• Delay air start time.

33. Defect: Blowout
Causes
• Extrusion rate too high.
Remedies
• Reduce mold open time.
• Lower back pressure.
• Reduce orifice size.
• Use resin with lower Melt Index.

34. Defect: Blowout
Causes
• Pinch-off too wide.
Remedies
• Reduce pinch-off.

35. Defect: Blowout
Causes
• Mold temperature too high.
Remedies
• Increase mold cooling.
• Clean cooling channels.
• Increase mold close time.

36. Defect: Blowout
Causes
• Parison too short.
Remedies
• Increase mold open time.
• Increase extrusion rate.

37. Defect: Blowout
Causes
• Blow up ratio too high.
Remedies
• Use larger diameter die.
• Eliminate mold hang-ups.

38. Defect: Blowout
Causes
• Poor parison clamping.
Remedies
• Increase clamp pressure.

39. Defect: Blowout
Causes
• Mandrel/die misaligned.
Remedies
• Tighten die tip bolts.
• Realign mandrel/die.
• Repair mandrel seal.
• Lengthen land between mandrel
and bushing.
• Replace tooling.

40. Defect: Blowout
Causes
• Contaminants in die channel.
Remedies
• Briefly open die gap.
• Clean channel and die.

41. Defect: Blowout
Causes
• Contaminated resin.
Remedies
• Keep resin and scrap clean.

42. Defect: Breakage at Part Line
Causes
• Molds misaligned.
Remedies
• Realign molds.
• Increase pre-blow cushion time.
• Replace or repair mold.

43. Defect: Breakage at Part Line
Causes
• Melt temperature too high.
Remedies
• Lower feed section temperature.
• Lower die tip temperature.

44. Defect: Breakage at Part Line
Causes
• Poor parison clamping.
Remedies
• Increase clamp pressure.

45. Defect: Ejection From Mold
Causes
• Not enough draft in mold.
Remedies
• Clean blow pins.
• Eliminate mold hang-ups.
• Align blow pins.
• Redesign mold (increase draft).

46. Defect: Ejection From Mold
Causes
• Mold temperature too high.
Remedies
• Increase mold cooling.
• Clean cooling channels.
• Increase mold close time.

47. Defect: Ejection From Mold
Causes
• Melt temperature too high.
Remedies
• Lower feed section temperature.
• Lower die tip temperature.

48. Defect: Weak Weld Line
Causes
• Mold temperature too high.
Remedies
• Increase mold cooling.
• Clean cooling channels.
• Increase mold close time.

49. Defect: Weak Weld Line
Causes
• Melt temperature too high.
Remedies
• Lower feed section temperature.
• Lower die tip temperature.

50. Defect: Weak Weld Line
Causes
• Pinch-off too thin.
Remedies
• Widen pinch-off land.
• Eliminate knife edges and burrs.

51. Defect: Flash
Causes
• Pinch-off too wide.
Remedies
• Reduce pinch-off.

52. Defect: Bubbles
Causes
• Moisture in resin.
Remedies
• Keep resin dry.
• Reduce coolant flow to feed
throat.
• Raise feed section temperature.

53. Defect: Bubbles
Causes
• Moisture in mold.
Remedies
• Increase mold temperature.
• Vent molds.
• Eliminate cooling water leaks.
• Dehumidity molding area.
• Wipe mold surface.

54. Defect: Bubbles
Causes
• Misaligned die/mandrel.
Remedies
• Tighten die tip bolts.
• Realign die/mandrel.
• Repair mandrel seal.
• Lengthen land between mandrel
and die.
• Replace tooling.

55. Defect: Bubbles
Causes
• Extrusion rate too low.
Remedies
• Raise back pressure.
• Increase orifice size.
• Use resin with higher Melt
Index.

56. Defect: Flashing on Product
Causes
• Mold Misaligned.
Remedies
• Realign mold.
• Use pre-blow cushion and slam.
• repair or replace mold.

57. Defect: Flashing on Product
Causes
• Melt temperature too high.
Remedies
• Lower feed section temperature.
• Lower die tip temperature.

58. Defect: Product Breaks Weld Line
Causes
• Poor parison clamping.
Remedies
• Increase clamp pressure.
• Check pinch-off areas.

59. Defect: Product Breaks Weld Line
Causes
• Mold misaligned.
Remedies
• Realign mold.
• Use pre-blow cushion and slam.
• Repair or replace mold.

60. Defect: Product Breaks Weld Line
Causes
• Melt temperature too low.
Remedies
• Lower feed section temperature.
• Lower die tip temperature.
• Reduce cycle time.

61. Defect: Shrinkage
Causes
• Melt temperature too high.
Remedies
• Lower feed section temperature.
• Clean cooling channels.
• Increase mold close time.

62. Defect: Shrinkage
Causes
• Extrusion rate too high.
Remedies
• Reduce mold open time.
• Lower back pressure.
• Reduce orifice size.
• Use resin with lower Melt Index.

63. Defect: Shrinkage
Causes
• Blow pressure too low.
Remedies
• Increase blowing pressure.
• Increase blowing time.
• Increase blow pin size.
• Eliminate air leaks.

64. Defect: Surface Roughness
Causes
• Blow pressure too low.
Remedies
• Increase blowing pressure.
• Increase blowing time.
• Increase blow pin size.
• Eliminate air leaks.

65. Defect: Surface Roughness
Causes
• Moisture in mold.
Remedies
• Increase mold temperature.
• Vent molds.
• Eliminate cooling water leaks.
• Dehumidify molding area.
• Wipe mold surface

66. Defect: Surface Roughness
Causes
• Misaligned mold.
Remedies
• Realign mold.
• Raise pre-blow cushion.
• Repair or replace mold.

67. Defect: Surface Roughness
Causes
• Incomplete melting.
Remedies
• Do not use resins/regrind with
different MIs

68. Defect: Specks
Causes
• Die/mandrel contaminated.
Remedies
• Briefly open die gap.
• Clean channel and die.

69. Defect: Specks
Causes
• Resin contamination.
Remedies
• Keep resin and regrind clean.

70. Defect: Warpage
Causes
• Melt temperature too high.
Remedies
• Lower feed section temperature.
• Reduce die tip temperature.

71. Defect: Warpage
Causes
• Mold temperature too high
Remedies
• Increase mold cooling.
• Clean cooling channels.
• Increase mold close time.

72. Defect: Warpage
Causes
• Poor product design.
Remedies
• Redesign mold.
• Use parison programmer.

73. Defect: Uneven Wall Thickness
Causes
• Poor product design.
Remedies
• Redesign mold.
• Use parison die tip temperature.

74. Defect: Uneven Wall Thickness
Causes
• Extrusion rate too low.
Remedies
• Raise back pressure.
• Increase orifice size.
• Use resin with higher Melt
Index.

75. Defect: Uneven Wall Thickness
Causes
• Melt temperature too high.
Remedies
• Lower feed section temperature.
• Reduce die tip temperature.

76. Defect: Uneven Wall Thickness
Causes
• Extruder heating uneven.
Remedies
• Repair/replace heater bands.
• Clean/replace thermocouples.
• Set melt temperature not
reached.

77. •Thank you