Melt Volume Rate

Meaning

Resin flow metrics measure the volume of polymer melt extruded through a specified capillary die under a designated piston load and temperature. In plastics characterization, melt volume rate is used to quantify the flow behavior of a resin in a way that directly accounts for melt density. This value is particularly useful for co polymer blends or filled compounds where the addition of high density fillers makes melt mass flow rate difficult to compare.

It is measured in cubic centimeters per ten minutes.

Metric Application

Converting melt volume rate to melt mass flow rate requires multiplying the value by the melt density of the polymer at the test temperature. For molders running glass filled polyolefins, melt volume rate provides a more accurate picture of how the resin will fill the mold cavity than mass based metrics. This helps in predicting the required injection pressure and clamp force during tool trial runs.

Quality Control

Incoming material checks utilize this flow measurement to detect variations in molecular weight between different resin lots. A high melt volume rate indicates a lower molecular weight resin, which fills the mold easily but may yield parts with lower impact strength. Slower flowing grades are selected for extrusion blow molding where high melt strength is required to prevent parison sag.

Run Tolerance

In production, the value measured on the molding floor can vary from the datasheet value due to the presence of moisture or regrind. If the melt volume rate of the resin rises during production, it indicates that the polymer is degrading during the molding cycle.