Frequency Sweep

Rheological Profile

Variations in molar mass distribution alter the curve shape obtained during the test. Broad distributions shift the crossover frequency toward lower values compared to narrow distributions of the same weight-average molecular mass. Technicians observe these changes to predict how a resin will fill a cavity or exhibit die swell at the nozzle.

Deviations from an established profile indicate contamination or thermal degradation in the batch.

Tooling Interaction

Filling pressure requirements depend on the relationship between shear rate and the complex viscosity derived from these laboratory results. Injection molding machines require viscosity data at high shear rates to calculate the clamping force and holding pressure for specific cavity geometries. Material specifications often include a master curve to ensure consistency between virgin resin lots.

Moulders verify that the operating window covers the shear rates present at the gate during high speed injection.

Processing Constraint

Incorrect polymer grade selection manifests as a mismatch between the measured crossover frequency and the cooling rate of the tool. Production cycles run efficiently when the material elastic recovery matches the gate freeze time. Short shots occur if the viscosity remains too high at the peak frequency of the process.

Melt fracture arises when the test indicates high elasticity that the shear rates in the runner system cannot accommodate.