Injection Velocity

Shear Rate

Viscous heating during cavity filling depends directly on velocity profiles across the runner system. Programmed stepped injection velocity maintains a constant melt front speed as cavity cross-sectional area changes. Viscosity reductions achieved via shear rate adjustments allow lower melt temperature settings on the barrel.

Excessive shear stresses introduce molecular orientation that increases anisotropic part shrinkage.

Switchover Point

Velocity-to-pressure switchover timing prevents overpacking of cavity gates while ensuring full part density. Machine hydraulic pressure spikes when velocity is maintained beyond ninety-nine percent cavity volume. Position-based switchover points yield more consistent part weights than time-based transfer methods.

Defect Mitigation

Jetting defects occur when low injection speed allows polymer melt to snake through thick wall sections without contacting mold surfaces. Gas entrapment and sink marks result when slow filling allows premature skin formation near gate entrances. Moulding technicians establish optimum velocity profiles by conducting viscosity curve studies across multiple injection speeds.

Part weight consistency improves when injection speed profile remains repeatable within zero point five percent across production runs.