The right extrusion plastometer for every testing volume
Extrusion plastometers, also known as melt flow index testers are used to determine the melt mass flow rate (MFR) and melt volume flow rate (MVR) of a plastic melted mass. Measurement of the flow behavior of the melted material is used to compare different grades of the same polymer and provides an important parameter for quality assurance and incoming goods inspections, for material selection and the setup of processing machines by plastics processors. Demands on these melt flow indexers vary according to which plastics processing stage is involved.
Detailed information on melt flow tests can be found here:
ZwickRoell supplies extrusion plastometers for companies serving every phase of plastics production, including raw material producers, compounders, and processors. Find the right melt flow index tester for your needs!
- The Cflow is particularly suited for incoming goods inspections, when only a few tests need to be performed.
- The Mflow is modular and features a pneumatic weight application device and piston travel transducer.
- The Aflow, with its defined pre-compaction of polymers, automatic material-dependent parameterization, fast residual material purge with a force of up to 80 kg and cleaning at the push of a button helps make your test sequence more efficient and reliable.
|0.325 - 21.6 kg
|0.325 - 21.6 kg
|0.325 - 50 kg
to ASTM D1238, ISO 1133- 1, ISO 1133-2
Method A, B, C
Method A, B, C, D
|Typical measurement range
|Level of automation
Low level of automation
Medium level of automation
High level of automation
|Range of application
Low test volume
Medium test volume
High test volume
Melt flow testing is a test method used to determine the flow properties of thermoplastic materials. The test measures how much material flows through a standardized die while subjected to a specified load and temperature. The result is referred to as melt index (MI) or melt flow index (MFI).
The melt flow test is described in standards ISO 1133-1 and ASTM D1238 (general test method), ISO 1133-2 (method for materials sensitive to time-temperature history and or/moisture, e.g. PBT, PET or PA), as well as ASTM D3364 (test method for PVC). ISO and ASTM describe the test methods (method A - MFR, method B - MVR, method C “half-die” - variation of method B, and method D multi-weight test, FRR) in a similar manner, however they differ in terms of test requirements for MFR and MVR measurement (barrel temperature, piston load).
- For testing, the die with the specified size orifice is placed in a heated barrel.
- Polymer granules are added and packed into the barrel with a piston.
- A defined heating period melts or softens the polymer.
- A weight is placed on the piston, and the molten polymer is forced through the die.
- The extrusion plastometer calculates the extruded mass per unit of time (MFR plastics) or the distance the piston travels per unit of time (MVR plastics).
At the end of the test, the die and barrel are cleaned.
Since extrusion plastometers (also referred to as melt flow index testers or MFI testers) according to ISO and ASTM standards are very similar in design and the metrologically relevant components such as the die, piston and extrusion barrel are identical, you can assume an almost identical level of the test results in terms of value, provided that the same test conditions for MVR and MFR measurement (same test load and same test temperature) are used for the respective polymer.
The methods for melt flow index testing of thermoplastics are equivalent but not identical, as they differ in some respects, especially in terms of test procedure:
- Test requirements for MVR and MFR measurement: For some polymers, test temperatures and test weights are specified differently in ISO 1133 and ASTM D1238.
- The recommended volume of polymer to be used is slightly different
- The duration of the preheating phase is set to at least 5 minutes in ISO 1133-1, but can also be significantly longer. In ASTM D1238, the duration of the preheating phase is standardized at 7 minutes with a strict tolerance of ±0.5 minutes.
- According to the ISO standard, the starting point of the test is at a piston position of 50 mm above the die, while ASTM D1238 sets this point at 46±2 mm.
- Testing of sensitive polymer types with respect to time- or temperature-dependent history and/or moisture (e.g., PBT, PET, or PA) are described in the separate ISO 1133-2 standard, while ASTM D1238 specifies a narrowly tolerated time sequence of testing for all polymer types.
- ISO 1133-1 leaves it largely up to the operator to determine suitable section or measurement intervals for the measurement procedure, while ASTM D1238 specifies very precisely over what piston travel distance or at which section interval measurements are to be made at which MFR value or MVR value.
Even the smallest amount of residue or impurities on the die, extrusion barrel or piston can lead to considerable deviations in the melt flow index measurement. For example, impurities change the glide properties of the polymer on the wall of the extrusion barrel and die, they reduce the gap between the piston and the extrusion barrel, or reduce the cross-section of the hole in the die. They mostly consist of residues of the previously tested polymer, which settles into the roughness of the wall, where it possibly degrades more and more until it forms a soot-like layer. The situation becomes particularly critical when different polymers are measured one after the other and this is associated with a change in the test temperature. Cleaning agent deposits can also cause issues, which is why the extrusion barrel is usually cleaned with an unwaxed clean cotton cloth. In cases where residue is persistent, it may be necessary to clean the tools with a brass brush or even resort to burnout of critical components.