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#107 Melt Flow Rate (MFR) of Plastics

Category : Molding Technology
January13, 2012

In the injection molding of plastics resin, you may all have experienced that the settings of the molding conditions, particularly of the injection pressure or the injection speed, and of the mold temperature are greatly affected by whether or not the fluidity of the molten plastic is good or bad.
While there are several methods for evaluating the fluidity of plastics, the easiest method which is being used as a guideline is the Melt Flow Rate (MFR) method.

The melt flow rate is measured by putting the plastic resin under test in a testing equipment called a melt low indexer, heating the plastic resin, making the molten plastic resin with a prescribed weight to flow, and measuring the weight of the plastic that flows out as an index of the melt flow rate. The method of this test has been stipulated in JIS and ISO standards.
A plastic resin with a high value of melt flow rate is evaluated as one with good fluidity. The flow is poor of a plastic resin whose melt flow rate is low.
However, the melt flow rate evaluates the fluidity in a static condition, whereas in actual injection molding the plastic resin flows in a very short time through a very narrow gate, so it is necessary to understand well the fact that the melt flow rate as it is does not fit in the case of injection molding.

As explained above, the melt flow rate is used as an index of the fluidity of the plastic resin for grasping the properties of the plastic resin in a simple manner.

Name of plastic resin Melt flow rate
Polypropylene 5 to 60
Polystyrene 5 to 25
AS resin 10 to 40
ABS resin 5 to 60
Acrylic resin 1 to 35
Polyamide 6 10 to 80
Polyamide 66 10 to 80
Polyacetal 3 to 70
Polycarbonate 2 to 30
PBT 20 to 100
PPO 7 to 30
PSU 7 to 18
PES 17 to 30
Cyclo olefin polymer 7 to 60
TPX 21 to 80
PEEK 1 to 20