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During tough economic times, it is tempting to reduce quality control to cut costs. However, Dolph Beyer, an engineer with Mohawk Fine Papers in Madison, N.J., asserts doing this is actually counterproductive. He has determined that using pressure-indicating sensor film as a quality control tool actually decreases costs while significantly improving product quality.
“By taking nip impressions with pressure-indicating film every couple of weeks, we have extended roll life by a few months in many cases,” says Beyer. ”This quality control measure not only lowers costs for the replacement of these covers, but also minimizes equipment downtime.”
Pressurex sensor film reveals pressure from two to 43,200 pounds per square inch (0.14 to 3,000 kilograms per square centimeter). When placed between contacting rollers, the sensor film instantaneously and permanently changes color directly proportional to the actual pressure applied. Precise pressure magnitude is then easily determined by comparing color variation results to a color correlation chart (conceptually similar to interpreting Litmus paper). Variations in pressure that lead to defects in papermaking, converting and printing can be quickly and accurately detected and corrected, improving yield, decreasing scrap and increasing productivity.
By examining pressure variations in the nip, corrections in alignment and crown profiles can be made. The film is effective on virtually all roller compositions and surfaces. A visual pressure mapping profile of an engraved pattern or drilled roll can be effortlessly produced that exposes minute surface defects and other imperfections.
Pressure indicating sensor film is cited by Beyer as being especially helpful with calendar rolls, which are swim rolls that have mechanisms to allow the center of the rollers to exert a different level of pressure.
“Similar to crown rolls, swim rolls need to be carefully monitored to ensure even and exacting pressure is being applied to achieve optimum nip conditions,” he says. “We use the film to create just the right nip and improve the roll shape and crown to deliver better sheet uniformity.”
Mohawk Fine Papers uses Pressurex to take static nip impressions on its press section and dynamic nip impressions on its calendars. Dynamic nip impressions are inspected for uniformity and static nip impressions for uniformity and nip pressure. Image results of Pressurex are archived and used as a control to compare tools and processes.
Pressurex is extremely thin (4 to 8 mils) and flexible, which allows it to conform to curved surfaces. It is ideal for invasive intolerant environments and tight spaces not accessible to conventional electronic transducers. While recommended for tests in non-operating conditions, the sensor film can be used at temperatures exceeding 200 degrees Fahrenheit (93 degrees Celsius) for brief intervals.
For more information, visit www.sensorprod.com or call 973-884-1755.