The fully automatic Aflow
Melt index testing of plastic granulate
Method A, MFR
Method B, MVR
This method determines the extruded volume of the polymer melt at regular intervals as opposed to the mass of the extrudate. The extrusion plastometer must be equipped with a piston displacement transducer. The MVR result is the extruded material volume per unit of time. It is specified in cm³/10 min and is calculated from the distance the piston travels per unit of time.
When meltingwith a homogeneous density distribution, the melt density can be used to convert the MVR value to an MFR value. If the plastic is unfilled, this is often not possible to do with a high level of accuracy due to the inhomogeneous distribution of the filler.
A significant advantage of this method is the elimination of mechanical cutting. The entire test sequence can be performed without any additional operator influence.
Method C to ASTM D1238, halved die dimensions
Method D to ASTM D 1238, multi-step test
With many polyolefins it is common to state the MVR value for different load levels and determine the flow rate ratio (FRR). This requires measurements from several fillings when simple extrusion plastometers are used. Extrusion plastometers equipped with an automatic load change unit can measure measurement series across multiple load levels from a single filling of the extrusion barrel.
ZwickRoell produces straightforward extrusion plastometers for Method A, together with instruments which feature automatic displacement measurement and can be used for measurements to Methods A and B.
The APC function – automatic optimization of measurement intervals
When measuring flow rates, measurement intervals must be set so that the measurement times are as great as possible, and in the case of MVR measurement, the measurement travel is as great as possible. This makes the method highly accurate. When outside of the optimal range, the number of measurement errors increases rapidly.
The Mflow and Aflow extrusion plastometers are equipped with the APC function. This function measures the speed of the piston shortly before actual measurement begins. Using this information, the best possible type of control, meaning travel or time control, is selected and set for the best suited measurement interval for the expected MVR value. Time-consuming pretests are no longer necessary and the process required for programming tests is reduced to setting a few test parameters that apply to all materials to be tested.