Meaning
Crammer class designates the volumetric feeding capacity rating assigned to industrial extrusion screws used for compounding brittle engineering polymers. Polypropylene pellets undergo continuous volumetric feeding when this machine parameter dictates the maximum throughput capability of the grooved feed throat barrel zone. Screw rotation speeds must match the material consolidation rate specified by the crammer class to prevent hopper bridging or downstream pressure surges during high output compounding runs.
Feed Throat Dynamics
Granular materials demand precise dimensional matching between the feed screw flight depth and the barrel housing diameter. Processing temperatures rise sharply if the crammer class rating underestimates the bulk density variations found in recycled engineering resin flakes. Unplasticized polyvinyl chloride compounds generate extreme frictional torque on the drive shaft whenever feed rates exceed the geometric limitations established by the original equipment manufacturer.
Pressure transducers mounted immediately below the feed section detect mechanical overload conditions before barrel wall degradation occurs.
Resin Density Variance
Virgin polymer pellets exhibit uniform bulk density distributions that align directly with standard volumetric feed charts. Regrind flakes introduce irregular particle geometries that reduce overall material mass flow through the throat opening. Extruders processing post-consumer recyclate must reduce screw RPM values below nominal crammer class limits to avoid starving the compression zone of the barrel.
Melt fracture defects appear in extruded profiles whenever material starvation alternates with overfed surges during long production runs.
Melt Uniformity Limits
Thermal stability within the metering zone depends entirely upon consistent solid conveying rates established upstream. Viscosity fluctuations manifest as dimensional variations along the extruded sheet when feed inconsistencies disrupt the steady melting profile. Process technicians adjust barrel temperature setpoints to compensate for minor feed rate deviations without altering the primary machine classification parameters.
Output torque measurements verify whether the selected screw geometry maintains adequate pressure generation for high viscosity polycarbonate resins.
