Flow Rate Ratio

Meaning

A physical property defined as the quotient of mass flow rates determined at two distinct shear stress levels provides an estimate of the molecular weight distribution of thermoplastic resins. This flow rate ratio quantifies the non-Newtonian behavior of a polymer melt under varying levels of mechanical deformation. The metric applies exclusively to linear and branched polymers processed through extrusion or injection moulding where shear sensitivity dictates the ease of flow.

Processing Sensitivity

Precise adjustments to screw speed during manufacturing depend on the sensitivity of the resin to shear forces. Higher values for flow rate ratio suggest a broader distribution of chain lengths which typically allows for easier processing in complex mould geometries. Resins with lower values require higher temperatures or increased pressures to achieve the same fill consistency.

Operators monitor these shifts to avoid flash or short shots on finished parts.

Material Specification

Datasheet values offer a baseline for quality control during the procurement of virgin material. These laboratory measurements utilize standardized equipment to maintain consistency between batches from a supplier. Regrind additions often alter the effective melt rheology and shift the observed performance away from the initial specification.

Production teams track these variances to maintain wall thickness and surface finish requirements.

Economic Consequence

Increased cycle times result from improper viscosity matches between different material grades. Costs accumulate when an inconsistent melt index forces technicians to lower injection speeds to compensate for material drag. Parts fail to meet tolerance standards if the rheology of the resin does not align with the original gating design.

Stable flow profiles optimize the throughput of every production cell.