Zwick Offers Significant Improvements in Melt Index Measurement
Zwick's new Aflow extrusion plastometer offers 24-hour operation. “With this instrument we have demonstrated that new developments leading to significant improvements are possible even for really classical methods such as MFR/MVR determination,” states Florian Liebert, who as product manager oversaw development of the new plastometer. A glance at Aflow confirms that it does indeed represent a new direction in melt index measurement. Designed for 50 kg test loads, the instrument presents a compact appearance. Florian Liebert explains: “This is basically because the instrument uses state-of-the-art force control in place of the usual individual weights. We have been installing force and position-controlled drives in testing machines at Zwick for many years and they are also commonly employed in rheometer construction. It seemed logical to apply this proven technology to high-quality extrusion plastometers as well.” The advantages of this technology are that it makes melt index determination significantly easier and more reliable. It offers the option of controlling the start position specified in the standards by means of superimposed force and speed control. At the start of measurement the instrument identifies the amount of polymer in the extrusion barrel and determines independently, on the basis of pre-set limit values, the load to be used in the pre-heating phase. This is a crucial advantage when polymers with unknown MFR are being tested, and also when operators have not adhered precisely to the specified charge quantity. Load application via electromechanical drive provides greatly improved load control during the test. Weight application in classical instruments almost always involves percussive loadings; these are greatly reduced with Aflow. Multi-stage tests in particular, i.e. tests with various test loads, are largely impact-free using this instrument. Residual material at the end of the test can easily be extruded using the maximum test load of 50 kg, saving testing time. The new Aflow is equipped with a pneumatic device for cleaning the extrusion barrel. This is a simple and fast two step process — the operator positions a cleaning pad and presses a button. Admittedly many polymers require the procedure to be repeated several times, but it is still considerably easier than manual cleaning. This device can also be used for pre-compacting the test material directly after charging. The advantage is that pre-compacting is performed in a uniform manner, reducing operator influence and giving more consistent results.
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