Polymers are tested for various properties that decide its application. As plastic is most widely used product and so as the manufacturing process. And the major reason for testing is to assess whether the supplier has delivered the raw material as per the specifications or not. Melt flow index tester simply measures the flow rate of the molten polymer granules. It is also called melt mass flow rate or melt volume flow rate. MFI is the weight of molten polymer flowing through the orifice at specified temperature and pressure. It’s noteworthy that, the dimensions of the orifice are defined in the test standards.


Testing Procedure

It is a very simple test to perform. The granules are charged in the hot barrel using a spool. The granules are tightly fitted into the barrel using the charger. There should not be any empty space in the barrel. A dead weight is applied on the granules via piston. Due to the heat of the barrel, the plastic granules start to melt. The molten plastic starts to flow out of the orifice in a string. The plastic that has come out of the orifice is weighed for deriving the MFI. The test procedure is defined in the ASTM D1238 and ISO 1133.

Important accessories used for precise measurement

  • Piston for applying weight on granules
  • Spool
  • Funnel for clean charging of barrel
  • Mirror to check the outcome from the orifice
  • Plumb line for levelling the machine
  • Orifice cleaner to clean the left over raw material in the barrel
  • Dead weights for applying pressure

Why is MFI important?

  • It will help in estimating the melt flow rate of the raw material to be used in the production
  • Producers of granules can check the quality of material that is being produced
  • Comparison of new materials in a product development setting
  • Evaluation tool for new material suppliers
  • It helps in choosing the best raw material supplier for your production
  • It helps in achieving uniformity in raw material
  • Estimation of flow properties for simple extrusion processes 
  • Helps in deciding the application of raw material for the different extrusion process.


Melt flow index tester is an inseparable part of polymer industry. And with growing popularity, it is now a common sight in almost every second industry. For more information about polymer testing instrument, contact us.