Meaning
Dynamic metering compensation used during polymer extrusion corrects for thermal expansion and material density variations inside the melt delivery barrel. High precision volumetric metering relies on stable melt density to maintain dimensional tolerance in moulded parts. Barrel temperature fluctuations alter polymer specific volume, creating unintended mass output shifts even when screw rotation speed remains constant.
Mass drift calibration links screw torque feedback and melt pressure sensor data to adjust motor output before dimensionally noncompliant parts enter production.
Thermal Offset
Viscosity changes alter pressure gradients along the screw flight channels during continuous compounding operations. Temperature increases reduce melt density and increase volumetric flow rates through the die head. Mathematical compensation algorithms calculate density shifts from real time thermocouple arrays located at the adapter zone.
Calibration parameters counteract these thermal gradients by scaling drive frequency against measured melt temperature deviations.
Pressure Compensation
Melt pressure variations downstream of the metering zone distort the mass output rate per revolution of the extrusion screw. Transducers monitor pressure spikes caused by screen pack contamination or filter degradation. Closed loop control routines adjust volumetric output targets dynamically to offset restriction induced flow reductions.
Material specifications differentiate between virgin resin behaviour and regrind batches containing degradation byproducts that alter compressibility under high pressure.
Tolerancing Control
Dimensional stability in finished moulded components depends on maintaining consistent shot weight throughout multi cavity production runs. Part specifications impose strict limits on wall thickness variation caused by inconsistent material delivery rates. Datasheet values assume constant ambient processing conditions that rarely match factory floor realities during extended manufacturing cycles.
Mould operators apply calibrated mass adjustments to prevent sink marks and flash formation without altering nominal cooling times.
