Melt Volume Flow Rate

Measurement Method

Standardized testing utilizes an extrusion plastometer to perform this evaluation under controlled conditions. During a melt volume flow rate test, the polymer is heated in a heated barrel and extruded through a standardized die by a piston driven by a specific load mass. Optical or mechanical displacement sensors measure the distance the piston travels over a set time interval.

This displacement is then converted into the volumetric flow rate.

Rheological Signification

Viscosity of the polymer melt under low shear conditions is inversely related to this flow value. A high melt volume flow rate indicates a lower molecular weight or a broader molecular weight distribution, allowing the polymer to flow easily under stress. This behavior is important for injection molding complex or thin-walled parts where high flowability is required.

Conversely, a low value indicates a high molecular weight resin suitable for extrusion where melt strength is necessary to maintain part profile.

Processing Utility

Industrial molders rely on this metric to monitor resin consistency across different material lots. Fluctuations in the melt volume flow rate can indicate thermal degradation, moisture absorption, or variation in additive levels, all of which disrupt the molding process. Adjusting process settings like injection pressure and barrel temperature helps compensate for these variations to maintain part weight and dimensions.

This monitoring is especially important when blending virgin and regrind resins, where the average flow behavior can change unpredictably. It ensures that the process window remains stable and reduces scrap rates during high-speed production runs.