With paint lines running well in excess of 300 fpm, it is essential that a coil coater know the color of the product as early in the process as possible. With this information, adjustments can be made to increase or decrease the film thickness of the paint or the bake time required to get the desired color.
One way to achieve this goal is with an online color measurement system. Using this tool, the coated product can be compared to an unlimited number of numerical or physical standards. Color can be compared across the web for side-center-side comparison, and color changeovers can be achieved quickly. For new products, an ad hoc standard can be used, meaning that the first data point in the run is used as the standard, or some averaging of a defined number of data points. The colorimetric results typically are displayed on the instrument screen, and operators are notified through an alarm when the tolerances for these colors are exceeded. Color charts and min/max tolerances are displayed in real-time.
Some online systems have a provision for analog/digital outputs, which report color data to a plant DCS or PLC control system so that the color measurement data can be used to control line process variables. Parameters that can be controlled by this output data include chemical feeds to the line for cleaning, pretreatment, and painting; sprays; oven temperatures; and line speed.
Additionally, with the temperature compensation option offered on some models, the effects of thermochromism are eliminated because colorimetric data is automatically corrected based upon changes in product temperature. Other process variables from the line can be displayed onscreen along with colorimetric data using Windows Dynamic Data Exchange (DDE), Windows NT Public Interface Socket, or user entry. This data can be stored in the database along with the corresponding measurement data and included in batch reports. Detailed and summary reports are available for the run, including event logs, alarm conditions and process variable information.
The sensor is typically mounted on a traversing rail over the coated metal just before the exit accumulator stack. Popular options for online color measurement systems on coil coating lines include extended edge detectors, a sheet break option (so the system sensor moves off line if the sheet breaks), an analog output (four 4-20 mA outputs), an alarm relay (for visual or audio alarms) and a temperature compensation package.
With online color measurement tools, coil coaters can ensure the quality of their products in real-time.
For more information about online color measurement systems, contact HunterLab at 703.471.6870 or firstname.lastname@example.org, or visit www.hunterlab.com.
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