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IN-LINE MEASUREMENT | PROCESS CONTROL


Measuring up in real time


Data from measurements taken in-line with the compounding process allow users to monitor and make adjustments to improve quality. Jennifer Markarian reports


The traditional approach to process control relies on monitoring of equipment parameters — such as temperature, pressure, or feeder rate — to ensure that production is running as expected. Off-line laboratory testing is then used to ensure compound and masterbatch product quality has been met. By the time that quality determination has been made a lot of product may have been produced. In-line analysis during processing provides an alternative that allows “real time” process adjustments to be made to improve product quality and reduce or eliminate out-of- specification product. “The ongoing automation of traditional manufacturing requires the use of smart technology that can measure, analyse and diagnose issues without the need for human intervention,” says Jaime A Gómez, President and CEO of US-based Equitech, which offers in-line colour measurement solutions. He says that the pandemic has driven an increase in automation this year as many companies have had to restrict access to their facilities and looked for ways to reduce employee interaction. Equitech’s colour measurement solution uses optical fibre probes connected to a spectrophotometer. A sapphire-tipped probe is inserted into the melt through a die adapter, allowing the melt to be illuminated and the light


www.compoundingworld.com


reflected to the spectrophotometer, where it is measured and output as colour values (L*, a*,b*, C*, h). The probes allow measurement in reflectance mode for opaque materials and transmission mode for transparent materials. The company says that measurement intervals as short as one to two seconds are possible, but adds that 10 to 60 second intervals are recommended for continuous process monitoring. Gómez says the L* measurement feedback can be used to provide immediate adjustment of the colorant feeder to maintain the final product in specification throughout the product run. “With a more sophisticated pigment library, closed loop on a* and b* can also be achieved,” he says. He explains that laboratory and in-line colour instruments will produce numerically different results because of differences in the instruments and in the measurement environment. He says that a best practice for harmonising these numbers is straight-forward. “We use the offline (laboratory) measurement values to adjust our in-line measurements by making an offset that matches the laboratory. In this way, when the offline measurement is done (every two or three hours) we use it to adjust our in-line measurement and eliminate any drift in in-line data.” Equitech reports a growing trend to use real- time data for more comprehensive analysis of the


Main image: in-line measurement technology promises to help plastics compounders improve product quality and reduce material wastage


November 2020 | COMPOUNDING WORLD 29


IMAGE: SHUTTERSTOCK


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