MVR is the volumetric flow rate of molten polymer through the standard MFI die, reported in cm³/10 min; relates to MFR through melt density at test temperature.
Melt Volume Rate
MVR is the volumetric flow rate of molten polymer through the standard MFI die, reported in cm³/10 min; relates to MFR through melt density at test temperature.
Formula
MVR = MFR / ρm
ρm is melt density at the test temperature (g/cm³). MVR in cm³/10 min equals mass flow rate divided by melt density when consistent units are used; standards specify measurement and temperature control.
Melt volume rate (MVR) expresses the same extrusion experiment as MFR but in volumetric rather than mass units. It is advantageous when comparing materials of different densities at process temperature—such as filled versus unfilled grades—because volumetric throughput often correlates more directly with screw recovery in injection molding.
MVR is measured using piston displacement and timed cuts, with melt density either measured or taken from tabulated values for the resin family. Small errors in temperature or pressure head propagate to MVR uncertainty; machines require regular verification of die dimensions and temperature uniformity.
Conversion between MFR and MVR demands accurate melt density ρm, which itself varies with temperature, pressure, and molecular architecture. Using room-temperature solid density instead of melt density introduces systematic bias.
Processors may specify MVR limits alongside MFR in material datasheets for high-cavitation molds where volumetric shot control dominates short-shot defects.
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