Sq

Thermal Degradation

Molecular weight breakdown occurs when residence time inside the barrel exceeds thermal stability limits. Excessive heat history cleaves polymer chains, lowering viscosity and shifting the melt flow rate upward beyond acceptable processing windows. Regrind material undergoes repeated thermal cycles, accumulating chain scission that differentiates its rheological behaviour from virgin pellets.

Virgin resin maintains predictable molecular weight distributions, whereas heavily processed regrind exhibits erratic flow characteristics that destabilise clamping tonnage balance.

Tooling Geometry

Runner diameters and gate dimensions dictate shear rates during the injection phase. A resin with high melt flow rate fills thin walled sections rapidly without excessive injection pressure. Thick sections suffer from sink marks and volumetric shrinkage when low viscosity grades solidify unevenly against colder tool surfaces.

Part specifications dictate shrinkage allowances, whereas material specifications establish the baseline flow index required to satisfy those volumetric tolerances.

Resin Viscosity

Shear thinning behaviour alters apparent viscosity as polymer melts accelerate through restricted gate orifices. Datasheet values describe resin behaviour under laboratory conditions that rarely match industrial injection speeds and barrel temperatures. Moulders verify incoming resin batches by measuring melt flow rate variations on factory floors to predict part weight consistency.

Viscosity fluctuations alter final dimensions, scrap rates escalate when operators fail to adjust packing pressures to compensate for material drift.