Reliable data on viscosity are essential for achieving high melt quality in extrusion. The new Leistritz Elongational Rheometer delivers exactly these data and with more accuracy than conventional rheometers. At the core of this technology: a new, patented slotted die. It allows the operator to access two measurements for shear viscosity and one for elongational viscosity within a clearly defined shear/elongational data corridor. This provides the operator with real time analysis of product quality on the running production line. With these data, the operator is empowered to react immediately to optimize quality outcome. This saves time, expenses and resources.
One of the most common challenges in extrusion is product instability – in film manufacturing, compounding and recycling equally.
Instability can lead to both volume and surface defects, for instance when producing polyethylene films. Slightest deviations in the extrusion process can cause turbidity and may result in the shark skin effect. This has an impact on the clarity of food packaging and may make them unusable – expensive and avoidable.
It is therefore essential to avoid instabilities in order to achieve consistently high output quality and save resources. The problem is that mistakes happen more often than one thinks. Slightest changes in temperature, irregularities in material feed or moisture in the pellet have a direct impact on melt quality without being noticed immediately.
This is exactly the reason why reliable and immediate measurement of viscosity are so vital to perfect material quality control in the extrusion process. Knowing exactly what is happening enables you to govern the process more accurately and safely.
Viscosity analysis online vs. offline
In inline viscosity measurement, data are drawn directly from the extrusion process itself. To do so, a part of the melt is tapped from the production line via a bypass system and analyzed in a rheometer. Offline analysis is delegated into the laboratory, away from the actual production process.
Extrusion generally prefers inline/online analysis, since it delivers data more quickly and closer to the extrusion line. This reduces the time frame between recognizing deviations in melt quality and the opportunity to correct these, saving time and resources. The improved reaction time enables the operator to keep melt quality on a more stable and reliable quality level. Moreover, inline analysis is independent of availability of laboratory capacity. When running on shifts, this can be an important factor during off times. There is also no need for time-consuming sampling or disruption of the running process.
Even state-of-the-art rheometers provide only data on shear viscosity. Important data on elongational viscosity must be organized offline. Conventional inline rheometers are thus limited in this respect.
The Solution? The new Leistritz Elongational Rheometer. The innovative, patented slotted die is more accurate and provides data on both shear and elongational viscosity in one step. That is unique.
Core of the new Leistritz Elongational Rheometer: the innovative patented die
At the heart of this new technology is a new, patented hyperbolic die which not only measures shear viscosity, but also elongational viscosity in the melt product.
The slotted die enables constant monitoring of viscosities with shear rates from 10 to 10.000 s-1 and longitudinal extension from 5 to 75 s-1. The measurement corridor can be preset. Standard pressure sensors are used to determine the elongational viscosity in the flow channel at constant average elongation rates.
The special die geometry generates a constant elongation flow, which was previously not possible with other online measuring devices. The design consists of an inlet and an outlet section as well as two transition zones. The design of the second transition zone prevents dead zones or undesired pressure vortices in the flow channel. This prevents both unwanted material deposits and falsified measurement results.
As with other inline processes, a melt sample is extracted from the extrusion line and diverted into the rheometer, where sensor elicit exact analytic data. What is unique, is that the material is fed back into the production process, avoiding material loss. The die geometry also prevents subsequent expansion, thus avoiding pressure swirls and dead areas in the flow channel. This prevents unwanted material despots and falsification of analysis data. A special, electronically controlled melt pump ensures that the flow rate is implemented accurately.
The Leistritz Elongational Rheometer can be added on to existing extrusion lines and exchanged between various extruders, providing maximum flexibility in aligning your production layouts and opening up new opportunities in operation. And: it can be fitted to existing Leistritz extrusion lines or to other brands as a stand-alone solution. Options for going online with other data systems is the perfect basis for IoT solutions.
Innovative applications for your competitive edge
The Leistritz Elongational Rheometer was clearly developed for applications in the extrusion business, both in production and in research, designed to provide reliable analytic data in real time. This makes analysis more accurate and uncovers fluctuations in melt quality more accurately and more quickly. This is the ultimate competitive edge in improving melt quality, reducing costs and saving resources. The additional capability of eliciting simultaneous data on shear and elongational viscosity inline and upgrading existing extruder lines with this new technology offers you a range of options for improving melt quality, avoiding waste and sharpening your competitive edge.