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TESTING | MATERIALS


the company’s services for labs and manufacturing plants to get the most out of their testing and analysis efforts and invest- ments.


Measured flow There are numerous


developments in equipment to measure flow properties of materials, in both the melt and the solid phase. ZwickRoell’s marketing team member Wolfgang Mörsch says the company’s portfolio of melt flow testing instruments ranges from the Cflow compact manually operated tester, through the modular Mflow with classical load weights, to the fully automatic Aflow with electromechanical force control. The latter system 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. Mörsch says functions of the Mflow and Aflow instruments include detection of any air bubbles in the plastic melt (air bubbles temporarily increase piston speed, causing distortion of the flow rate). “ZwickRoell testing instruments feature high-reso- lution time and travel measurement, enabling changes in piston speed to be detected automati- cally,” he says. “This allows certain extrudates to be excluded from measurement to avoid errors in flow-rate calculation.” The operator is also assisted by a function called APC (Adaptive Process Control), which measures the speed of the piston shortly before the start of the actual measurement. The system uses this data to select the most appropriate type of control, travel or time-controlled.


Thermodynamic systems Also at the AMI Polymer Testing and Analysis conference, Moritz Göttfert, Technical Sales Manager at Göttfert Werkstoff-Prüfmaschinen discussed different systems for measuring PVT (pressure, volume, temperature) characteristics in materials. This included the company’s PVT500, which he described as a self-sufficient system for determining the thermodynamic behaviour of various materials. In the PVT500 specific volume is determined as a function of variations in pressure and temperature, with resulting data being used for such things as shrinkage prediction in mould-


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PHOTO: TA INSTRUMENTS


ings and extrusions. The PVT500 operates according to ISO17744, which distinguishes between isothermal measuring (when the sample is exposed to different pressures at a constant temperature) and isobaric measure- ment (carried out at constant pressure, with the sample being cooled at a defined rate). The isothermal measur- ing method is still one of the most common applications, but the isobaric measuring method describes the


process significantly better, says Göttfert. “This is especially


the case in injection moulding because the mould- ing cools down at constant pressures until the freezing point of the sprue system,” he explains. Göttfert says the new PVT500 offers several advantages over one of its Rheograph capillary rheometers fitted with an add-on for PVT measure- ment. Firstly, it is more accurate. In addition, the test barrel, with a diameter of just 9.5mm, allows faster cooling of the sample with better tempera- ture homogeneity. And less amount of sample material is necessary, providing more homogene- ous stress state in solid state range (especially with amorphous plastics), Figure 2.


Online rheometry Speaking at last year’s ANTEC in Orlando in the US, Dynisco Rheological Scientist Azadeh Farahanchi said online rheometers are being increasingly used in order to capture a continuous data stream of rheological properties and real-time information on the extrusion process without any delay for the offline laboratory testing. “Online rheometers have extensive applications in automatic processing, product development, and quality control,” he said. “Online rheometers can monitor the effect of different operating conditions or different formula-


Right: ZwickRoell equipment for measuring flow properties of plastic materials ranges from manual to fully automatic


Left: The benchtop


Discovery TMA 450 Thermo- mechanical Analyzer from TA Instruments


April 2019 | COMPOUNDING WORLD 83


PHOTO: ZWICKROELL


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