Melt Flow Index Tester ISO 1133: Principle and Testing Method

Introduction

In the plastic and polymer industry a Melt Flow Index Tester measures the amount of molten thermoplastic that comes out through a standard die under a certain temperature and applied load. ISO 1133-1 defines MFR by the weight of material that comes out and MVR by the volume measured during testing. This test is performed to understand how easily plastic flows during processing. In this guide, you will learn the tester's working method, ISO 1133 testing steps, sample preparation, MFR and MVR calculations, result understanding and common testing errors.

What Is a Melt Flow Index Tester?

The amount of melted plastic that flows through a heated chamber and standard die is measured by a laboratory instrument called a Melt Flow Index Tester. The result of the test is usually expressed as MFR, which stands for grams per 10 minutes or MVR which stands for cubic centimeters per 10 minutes.

A higher MFR means that the material flows more freely under the selected temperature and pressure, while a lower MFR suggests more resistance to flow when compared under the same test conditions.

MFR is measured by the amount of plastic that comes out, while MVR is measured by the distance the piston moves in a given time. Perfect Group India provides testing equipment for laboratories that need steady heating, stable weight and accurate results when testing plastic quality.

What Is the ISO 1133 Principle?

The ISO 1133 principle used by a Melt Flow Index Tester is based on forcing molten thermoplastic through a die with a set diameter and length. A measured quantity of polymer is placed inside a heated cylinder where the plastic becomes soft at the selected test temperature.

A piston and specified load apply pressure, causing the molten material to leave the cylinder through the die. The amount of material that comes out is then measured by weight or by piston movement, depending on the selected procedure.

ISO 1133-1 defines Procedure A as a weight-measuring procedure and Procedure B as a movement-measuring procedure. The standard defines the melt mass flow rate (MFR) in g/10 min and the melt volume flow rate (MVR) in cm³/10 min for a given temperature and load.

What Equipment Does the Test Need?

The Melt Flow Index Tester must keep temperature, load, die dimensions, timing and sample position within suitable limits during measurement.

A laboratory generally uses the following main parts for an ISO 1133 test:

Heated cylinder: Melts the polymer at the selected temperature.
Piston: Passes the applied load to the material.
Standard die: Controls the outlet size and flow path.
Test weights: Create the specified force on the piston.
Temperature controller: Keeps the selected barrel temperature steady.
Cutting device: Cuts timed material portions for weighing.
Balance: Measures material weight during Procedure A.
Displacement sensor: Records piston movement during Procedure B.
Timer: Controls the measurement time accurately.

How Is the ISO 1133 Testing Method Performed?

Before testing with a Melt Flow Index Tester, the operator selects the material standard, temperature, load and measurement procedure required for the polymer grade.The barrel, die, piston and loading parts are cleaned carefully so earlier material does not affect the sample.

A measured sample is placed into the heated barrel and allowed to reach the required temperature for the specified conditioning period. The piston and selected load are then positioned, allowing molten material to flow through the die.

For Procedure A the material that comes out is cut at defined time intervals and each portion is weighed on a suitable balance. The measured mass is used to calculate the amount of material that comes out during ten minutes using the relevant calculation formula.

For Procedure B the instrument records piston movement over a selected time or the time needed for a defined travel distance. The recorded movement is used to calculate MVR, expressed as cubic centimetres per ten minutes.

The operator should record the material name, test temperature, load, procedure, conditioning details and final result with the test report.

What Is the MFR Calculation Formula?

The MFR calculation from a Melt Flow Index Tester uses the mass of an extruded portion and the time required to produce that portion.

The commonly used expression is:

MFR = 600 × m / t

where m = extrudate mass (g) and t = cutting time (s)

The factor 600 converts the measured time interval into an expression of grams per ten minutes.

For example, if 0.35 grams of polymer is collected in 30 seconds the calculated MFR is 7.0 g/10 min. The result should also give the test temperature and load as polymers can give widely varying results under different experimental conditions.

What Is the Difference Between Procedure A and B?

Procedure A measures the weight of timed extrudate pieces, making it useful when manual mass measurement is acceptable. Procedure B measures piston movement electronically, which can reduce manual cutting and provide direct MVR data.

Procedure A: Calculates MFR from weighed material.
Procedure B: Calculates MVR from piston movement.
Procedure A result: Reported in grams per ten minutes.
Procedure B result: Reported in cubic centimetres per ten minutes.
Density link: MVR can be converted to MFR if melt density is known.
Material sensitivity: Materials affected by time and temperature might need ISO 1133-2.

The correct test method depends on the material, lab procedures, customer specifications and required reporting format.

Which Factors Affect Melt Flow Index Tester Results?

Various conditions during testing may affect the flow rate of a polymer grade even if the material remains the same. Temperature is highly important as minor changes may affect the melt thickness and flow speed.

Moisture content in hygroscopic polymers may lead to damage or bubble formation.
Incorrect load changes the pressure applied to the molten sample.
Poor cleaning allows old polymers to mix with the new material.
Wrong heating time can produce an unstable melt condition.
Damaged dies can change the flow path and measured rate.
Uneven temperature distribution can create different flow results.
Inaccurate cutting time affects the MFR calculation.
A contaminated balance can change the measured mass.
Delayed weighing can create errors in manual measurement.

For reliable results the Melt Flow Index Tester must be calibrated, cleaned and operated according to the selected ISO procedure.

How Should Results Be Interpreted?

An MFR value is only meaningful if the temperature, load, material condition and test method are clearly given. A value of 12 g/10 min at 190 °C and 2.16 kg can therefore not be compared directly with 12 g/10 min at a different load. MFR and MVR values from a Melt Flow Index Tester are used by manufacturers to compare incoming plastic material, control production batches and make material choices.

However the test is a flow-rate measurement, not a complete description of strength, toughness or final product performance. Perfect Group India recommends comparing results against the approved material details and previous confirmed laboratory records.

Final Thoughts

To measure how plastic flows through a standard die, a Melt Flow Index Tester provides controlled heat and pressure. ISO 1133 supports two main approaches: weighing plastic that comes out in a set time for MFR or measuring piston movement for MVR. Accurate results depend on clean parts, correct sample preparation, stable temperature, suitable load and precise timing. The final report should mention the material, test conditions, method and measurement unit for useful comparison. Used correctly, ISO 1133 testing gives a practical flow-rate reference for plastic quality and batch evaluation. Following the standard method carefully helps Indian manufacturers obtain clear, comparable and meaningful flow data.