Shear Rate

Melt Behavior

Polymer chains uncoil and slide past neighbouring segments when subjected to strong velocity fields inside processing equipment. Viscosity decreases non-Newtonian fluids during rapid flow stages, lowering injection pressure requirements. Molecular weight distribution governs how severely a polymer reacts to changing velocity fields.

High molecular weight grades experience greater flow resistance reduction than low molecular weight equivalents. Temperature interacts directly with velocity gradients, lowering the energy required for chain disentanglement.

Thermal Degradation

Excessive mechanical working generates frictional heat within the polymer melt stream. Molecular bonds break apart when localized thermal energy exceeds polymer stability thresholds. Degradation products alter shrinkage rates and reduce impact strength in finished mouldings.

Uncontrolled barrel temperatures combine with high velocity fields to scorch sensitive engineering resins. Process technicians adjust injection profiles to keep mechanical working below thermal damage limits.

Economic Control

Virgin material costs demand precise processing window management to avoid scrap generation during continuous production. Regrind incorporation narrows the allowable velocity window because degraded polymer chains tolerate less mechanical stress before breaking down. Laboratory melt index tests fail to predict how a resin behaves under high-speed manufacturing conditions.

Moulders establish processing limits through trial runs rather than relying solely on supplier documentation. Finished part rejects decrease when operators monitor machine feedback loops instead of assuming stable material behaviour.