The flow properties of a thermoplastic are characterized by the melt index. Depending on the test method, either the mass per unit of time (MRF measurement) or the volume per unit of time (MVR measurement) is determined. Available from ZwickRoell in Ulm, Germany, is a variety of testing instruments for determination of melt rates
. The portfolio ranges from Cflow
, a compact manually operated tester, to the modular Mflow
, with classical load weights, right up to the fully automatic all-rounder Aflow
, with electromechanical force control. The latter was developed for particularly high specimen testing rates and is designed for determination of volume and melt flow rates to Methods A, B, C and D. All established standards and methods are supported, including ISO 1133, ASTM D1238 and ASTM D3364.
Included in the outstanding functions of the Mflow and Aflow instruments is the detection of potential air bubbles in the plastic melt. Air bubbles temporarily increase piston speed, causing distortion of the flow rate. ZwickRoell testing instruments feature high-resolution time and travel measurement, enabling changes in piston speed to be detected automatically. This allows certain extrudates to be excluded from measurement to avoid errors in flow-rate calculation. The operator is also assisted by the APC (Adaptive Process Control) function, which measures the speed of the piston shortly before the start of the actual measurement. On the basis of this data the system selects the best possible type of control – travel or time-controlled – thereby setting the optimum measurement interval for the expected MVR value.
Intuitive, workflow-based touch operation allows the operator to move easily between instrument and PC. The melting process and behavior of the melt during measurement can be followed live, both directly on the instrument and in the ZwickRoell testing software