Desiccant Dryer Operation and Basic Moisture Management in Hygroscopic Polymers
Maintaining desiccant dryers at -40°C dew point prevents hydrolytic degradation, preserving melt viscosity and mechanical performance in hygroscopic polymers.
Mass Flow Vs Funnel Flow
Meaning
Particle discharge behavior during silo unloading governs the distinction between mass flow and funnel flow. Mass flow happens when the entire contents of a hopper or silo move toward the outlet at a uniform velocity. Funnel flow occurs when material exits through a central channel while stagnant zones remain near the vessel walls.
These patterns determine whether a granular bulk solid discharges reliably or bridges across the transition zone.
Hopper Geometry
Vessel wall friction and internal angle of repose define the required hopper slope for specific mass flow regimes. Steep walls reduce the shear stress at the boundary to promote gravitational slide of the entire bed. Shallow angles encourage the development of stagnant regions because the friction force against the wall exceeds the weight of the material in those sections.
Industrial design for plastic pellets necessitates mass flow to prevent the first in first out degradation of heat sensitive resins.
Resin Degradation
Segregation of fines and additives represents a failure mode common in funnel flow configurations. Stationary material near the walls occupies space and reduces the live capacity of the vessel over time. Moisture retention within stagnant zones increases the risk of hydrolysis for hygroscopic materials like nylon or polyester.
Production batches suffer from inconsistent part properties when stagnant material eventually sloughs off into the discharge stream.
Mechanical Consistency
Consistent pellet geometry and low surface roughness minimize the risk of flow blockage during high speed injection moulding cycles. Correct silo design ensures that residence time remains predictable for every gram of resin. Proper hopper inclination eliminates zones where material settles for extended periods and creates off specification product.
Uniform discharge velocity provides the stable feed required for consistent plastification in the screw and barrel assembly.