In-line color measurement
Color Measurement with Integrated Process Control
Since plastics are being colored increasingly directly at the injection molding machine, quality assurance is also gaining in importance. In-line color measurement of the (still hot) molded parts would be an ideal approach, except for one problem: the color depends not infrequently on the temperature - a phenomenon known as thermochromy. To address this issue, the SKZ - Das Kunststoff-Zentrum in Würzburg, Germany, and ColorLite GmbH, Katlenburg-Lindau, Germany, have developed a solution. To compensate for the effect of thermochromy, the temperature and spectral values are measured simultaneously at exactly the same location on the molded part’s surface. With this approach, it is possible to match the color to the desired value in the course of the production process.
At the most recent Fakuma, Arburg GmbH + Co KG, Lossburg, Germany, demonstrated how this type of quality assurance can be incorporated into an injection molding facility. By checking the color continuity of the molded parts produced on a hydraulic Allrounder 520 S advance with a clamping force of 1,300 kN, off-color parts can be detected and diverted immediately. This is accomplished by a Multilift Select linear robot that removes the molded part from the mold, transports it to the inspection station for optical in-line color measurement and subsequently places the good parts on a conveyor belt. The three-zone screw used in the plasticating unit is equipped with an additional mixing section to ensure uniformly colored melt. Both the machine and part handling unit are controlled by the Selogica controller, which features built-in process control. This relatively simple configuration provides an effective safeguard against poor quality parts in high-volume production.
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