Regrind Fractions Nobody Writes into the Grade Specification
Undeclared regrind degrades melt stability and impact strength; verify batch history using melt flow rate delta and oxidative induction time limits.
Bulk Density Segregation
Meaning
Physical phenomenon occurs when particles of different sizes or weights separate during handling or storage. Gravity and vibration cause smaller fines to sift through the gaps between larger pellets during transport. The resulting inconsistency often affects the melt flow and final part weight during injection moulding.
Material Separation
Center-flow discharge tends to pull material from the top middle, leaving stagnant zones where bulk density segregation becomes more pronounced. Funnel flow increases the risk of receiving a high concentration of fines at the end of a production run. Discharge patterns from storage bins contribute to how different particle types exit the container.
Vessel Geometry
Discharge patterns from storage bins contribute to how different particle types exit the container. Center-flow discharge tends to pull material from the top middle, leaving stagnant zones where bulk density segregation becomes more pronounced. Funnel flow increases the risk of receiving a high concentration of fines at the end of a production run.
Particle Uniformity
Variations in the ratio of fines to pellets change the packing efficiency inside the screw flights. When bulk density segregation is present, the extruder may struggle to maintain a constant pressure, leading to surging and dimensional defects. Maintaining a homogenous mix requires minimizing the drop height into storage containers.