Elongational Rheometer for Fast and Efficient Process Monitoring
Measuring Shearing and Stretching Viscosities Online
At the Fakuma 2017 trade show, Leistritz Extrusionstechnik GmbH based in Nuremberg, Germany, presented a novelty in the area of process monitoring. They showed an elongational rheometer that supplies solid data making it possible to prove even the slightest deviation in the production process.
In a joint project with Johannes Kepler University in Linz, Austria, Leistritz developed an online elongational rheometer with a patent die geometry. The range of applications comprises all types of plastics. The novelty enables good process reliability when processing high-viscosity pipe compounds as well as in the production of low-viscosity products for fiber and injection molding applications.
Part of the melt flow is diverted via a bypass system during the extrusion process, passing through the slit die of the rheometer. The die features a new patent geometry with a hyperbolic bottleneck. In a downstream step, the system allows for the material to re-enter the main process, thus preventing material loss.
The rheometer enables online measurement of shear viscosity at shear rates between 10 and 10,000 s-1, as well as of stretching viscosity at elongation rates of 5–75 s-1. The novel type of die geometry yields a constant stretching flow, which used to be impossible to achieve with available online measuring units. During continuous measurement, the user can obtain two measured values at the same time, i. e. shear viscosity and stretching viscosity, at ranges of shear and stretching rate precisely defined.
What is more, the Leistritz elongational rheometer can display the melt flow index and the IV value, while the feature of online melt density determination enhances the wide range of analysis.
From the mechanical view, the new online elongational rheometer can easily be integrated into any type of extrusion process, requiring no major changes to the system. The software, as well as the visualization of measured results, is either part of the Leistritz extruder control unit, or can be obtained as a standalone version.
Leistritz Extrusionstechnik GmbH
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