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  • 1. The Use of Silica-Fume and PEG toEnhance Sintering of LLDPE Powders in Rotomolding ProcessTU BerlinUniBw München
  • 2. What is?ROTATIONALMOLDING
  • 3. a technology for manufacturing hollow seamless articles
  • 4. byheating, melting, sintering
  • 5. of powder
  • 6. 1 mm raw reactor powder of LLDPE
  • 7. Problems
  • 8. manybubbles
  • 9. cr c e ac ta n s is is low k re
  • 10. overheating
  • 11. to
  • 12. ExperimentalRESULTS
  • 13. Set-up forblending
  • 14. Set-up forsintering
  • 15. UniaxialRotomolding
  • 16. 1 mm PE powder
  • 17. after10 min of heating 1 mm
  • 18. Dissolving the bubbles Patm Pi ΔP = Pi - Patm = 2T/rIf melt is in diffusion equilibrium with atmospheregas in the bubble tend to flow outwards becauseof pressure difference ΔP until radius r of thebubble diminishes to zero.
  • 19. 1 mm PE powder + SF (800 ppm)
  • 20. after10 min of heating 1 mm
  • 21. o 42.5PE powder + SF (800 ppm): very good free-flow
  • 22. PE powder: good free-flow o 45
  • 23. Example ofGas Permeable Polymers:Silicone Rubber: high flexibility ofthe silicon-oxygen chain in siloxaneprovides “openings” which are freevolume and permit gas diffusion, seeZhang and Cloud (2006).
  • 24. Gas Permeation
  • 25. Siloxane – high flexible chain (Si-O-Si bond) PEG – high flexible chain (C-O-C bond)
  • 26. Gas Permeation of Polymers, Barrer1000000 100000 10000 N2 1000 O2 CO2 100 H2O 10 1 LDPE Silicone PEG est.
  • 27. 1 mm PE powder + PEG (0.4%)
  • 28. PEG beadsafter10 min of heating 1 mm
  • 29. o 70PE powder + PEG (0.4%) o at 72 C: no free-flow
  • 30. PEG + Silica Fume
  • 31. 1 mm PE powder + PEG (0.4 %) + SF(800 ppm)
  • 32. after10 min of heating 1 mm
  • 33. o 60PE + PEG(0.4%) + SF(800ppm) o at 72 C: free-flow properties
  • 34. 1 mm PE powder + PEG+CA (0.4%)
  • 35. after10 min of heating 1 mm
  • 36. 1 mm PE powder + PEG+CA (0.4%) + SF (800ppm)
  • 37. after10 min of heating 1 mm
  • 38. SilicaFume
  • 39. Novel PPA: PEG Silica+ Fume
  • 40. PEG +Carboxylic AcidsSilica +Fume
  • 41. What are micro-pellets? • Small regular oval shaped plastic granules with a diameter between 500-600µm. • Produced from the same base material as powder, i.e. Qenos 711UV etc. • Differ from powder by way of the manufacturing process and particle size distribution.
  • 42. Process comparison PELLETS POWDER and MICRO-PELLETS Cyclone Process Water PE pellets Oversize Centrifugal Dryer Particles Sieves Cutter Dust Collector PDV PE Powder Powder 190-210oC Grinding Blower Water Head Bath Bag 85-105oC Extruder Bag Customer Source: Practical Guide to Rotational Moulding Die Plate Process WaterSource: Gala Industries by R Crawford & M Kearns Pump
  • 43. Particle size distribution comparison. 70 Ave = 550 µm 60% By Weight 50 Ave = 300-350 µm 40 30 20 10 0 0 50 106 150 212 250 425 500 600 710 850 1000 Particle Size, Micron Powder MicroPellets
  • 44. What are the benefits of micro pellets? Manufacturing Process • Consistent quality and size • Less contamination • Dust free during mould filling Shape and Particle Size Distribution • Potential for faster cook times • Potential for lower peak internal air temperature • Greater bulk density (0.51kg/m3 cf. 0.34 kg/m3) • Improved flow (10 sec cf. 32 sec) • Potential for improved mechanical properties • Improved filling and definition of difficult to fill mould areas • Moulded parts with more uniform wall thickness • Maintained / improved surface finish Other • Cheaper raw materialIMPROVED ECONOMICS AND MORE OPTIONS FOR THE MOULDER
  • 45. Micro Pellet Tank TrialOven machine, Tank Size = 2,250L, Shot Weight = 55kgs, Wall thickness = ~5mm, Colour = Merino. 50 Cycle Time (mins) 45 40 35 30 25 > 12% 20 Powder Tank - 1 Tank - 2 Tank - 3 Cool Time (min) 17 16 16 17 Cook Time (min) 28 24 25 24 Cook Time (min) Cool Time (min) Meet requirements of tank standard impact testing with no ductile or brittle failures using a 9.06kg drop dart @ 1.4m.
  • 46. Rotomolding PPAs:Silica Fume (SF): "Free-Flow"Agent.PEG+SF: Densification &Processing Aid (D&PA).PEG + Carboxylic Acids (CA):Advanced D&PA.Novel Processing Additives:PEG + CA + SF.
  • 47. Extrusion PPAs:Silica Fume (SF): ThickeningAgent.PEG+SF+Anti-Oxydants:Processing Aid (PA).PEG + Carboxylic Acids (CA):Advanced PA.Novel Processing Additives:PEG + CA + SF.
  • 48. Process comparison MICRO-PELLETS MICRO-PELLETS WATER COOLING AIR COOLING Process Water Centrifugal Dryer Cutter Cutter PDV PDV Powder Powder 190-210oC 125-135oC Water Bath Bag Extruder Extruder Die Plate Die PlateSource: Gala Industries Process Water Pump Bag Air Cooler
  • 49. Little things can make BIG CHANGES
  • 50. Cost Effective patent pending
  • 51. Acknowledgements:Financial support:the German Science Foundation(DeutscheForschungsgemeinschaft).Technical support(PE powder samples):ExxonMobil ChemicalSCG Chemicals