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.
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).
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.
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
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
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.
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.
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.
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