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PROCESS CONTROL | IN-LINE MEASUREMENT


Right:


Masterbatches can present challenges for in-line spectroscopy measurement systems due to their high


optical density


In-line measurement presents various challenges, including finding a location to install the sapphire- tipped probe into the extruder where it will not interfere with production but where it can measure as intended. Typical probe locations are near the output area of the extruder (in the die, in an adapter piece, before or after a melt pump, or before the underwater pelletising system), Eker says. “The self-cleaning property of the sapphire window combined with the material flow prevents the lens becoming coated, which is a problem often encountered if not dealt with using the right design principles,” says Eker, who explains that sufficient shear from the material flow is needed in order to clean the lens, prevent material from coating it, and present the melt for real-time measurement in front of the window. “The sapphire tip has to penetrate into the polymer melt to achieve this cleaning effect, while avoiding moving machine parts such as screw elements at the installation location of the probe. These safeguards ensure there are no hindrances to the measurement of opaque or transparent polymers,” says Eker. For opaque polymer melts, ColVistec employs a


probe designed for reflection measurement in which six optical fibres illuminate the melt while a central single fibre directs the light reflected from the polymer melt to the spectrophotometer for analysis. For transparent or clear polymer melts, two directly opposite and aligned probes are used; one sending the light into the molten polymer and the opposite probe detecting and transmitting it to


IMAGE: SHUTTERSTOCK


the spectrophotometer. All ColVisTec probes for extruder applications are designed for a maximum of 250 bar pressure and 400°C melt temperature.


Masterbatch challenges Masterbatches, which are optically dense, present a special challenge for in-line measurement systems. ColVisTec says it is currently working on an in-line solution that will allow real-time monitoring of product quality in masterbatch production. He says that, at the present time, such dense products have to be diluted in the laboratory to reduce the optical density to be measured. Eker says that polymer melts containing glass


fibre or glass microspheres are also a challenge to measure because they scatter light. In addition, he says these abrasive components will eventually scratch the sapphire lens. For such products, it is recommended that the polymer is measured before the glass additive is introduced. The goal of in-line measurement is to monitor the process in real-time to allow problems to be rectified


Rapid metal separation cuts plant risk


Germany-based Sesotec has developed the Rapid Pro-Sense 6 metal separator to offer high detection accuracy to prevent even small metallic contaminants from entering the compounding extruder, where they can cause machine damage and


unplanned downtime as well as potential quality problems in the end product.


Sesotec says compounders


processing recycled materials face a higher risk of metallic contamination. However, the company adds that machine wear and other external sources can also present problems and recommends compounders


32 COMPOUNDING WORLD | November 2020


take a holistic approach to preventing metal contamination in the final product, including preventive maintenance, inspection


Sesotec says the Rapid Pro-Sense 6 metal separator is suited to compounding applications


of incoming materials, and metal separators at critical points in the processing line, such as after sieving and before bag filling. The Rapid Pro-Sense 6 can detect and remove both ferrous and non-ferrous metal particles in powder or granulated raw materials using high-resolution frequency technology, which the company says is more accurate than magnetic systems. It is suitable for connection to IoT and systems and is equipped with a logbook functiona so compounders can use data to identify the source of contaminants. � www.sesotec.com


www.compoundingworld.com


IMAGE: SECOTEC


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