What is MFR? Melt Flow Rate

Melt flow rate versus melt flow index
These are interchangeable terms, right?
They basically mean the same thing.
Am I right?
Am I right?

Yes, there is some truth in this statement.
The terms are used in an interchangeable manner when discussing material flow.

But. . .
They’re not the same.
Let’s look at the two acronyms and their respective units.

What’s up with the strange units?

MFR: melt flow rate. Units: g/10 mins
MFI: melt flow index. Units: %

The extreme difference in units gives you a clue that MFR and MFI are not the same.

Bet you are more curious about the differences now.
Aren’t you?

Here’s the plan.

We will answer the following questions for both MFR and MFI.
At the end of this exercise you will have a clear and nuanced understanding.

• Why does MFR/MFI mean?

• Where do the measurement units come from?

• Where and how is MFR/MFI tested?

• What equipment is used for testing?

• Are there any special testing procedures?

What is Melt Flow Rate?

This is the flow designation given by the material/resin manufacturer.
Check your resin data sheet to see MFR near the top of the specifications list.

In the data sheet that follows, the MFR is 12.
12g/10mins
Twelve grammes of material per ten minutes.

Yes, these are strange, strange units.
Hang in there and all will be explained in a little while.

Check out the data sheet that follows.

Data Sheet

What’s used to test material flow?

Flow is tested using a rheometer.
It’s a fancy plunger that drools material.

Rheometer Device

This fancy plunger is set up using specific controls for . . .

• Temperature

• Material sample weight

• Plunger force (weight)

• Orifice size

But . . . what about those weird units?

Remember the weird units?
g/10 mins
Grammes per ten minutes

The amount of material that squeezes through the plunger device in ten minutes . . . . is weighed.

There you have it.
It’s that simple.

MFR testing is done at the material/resin manufacturing facility.
Here’s what happens.

Virgin material is tested using the rheometer (flow tester).
It’s usual to test three or more samples and use the average.
The MFR value is then added to the material spec sheet.

Each new batch of material that gets prepared for shipment has to have its MFR tested and confirmed.
Why?

It’s critical to the molded part quality that the material flow properties are consistent batch to batch.

Sometimes, the vendor double checks incoming material just to be absolutely safe and sure.
Trust but verify.

Ok.
So what have you learnt here.

• MFR is melt flow rate

• There’s a special device and standards for testing flow

• Testing occurs at the material manufacturer site

  Now. You have a nuanced understanding of MFR.
  Well done. Congratulations.