Litmus test for nip impression
Pressure-indicator sensor film helps extend roll life, improve product quality for Mohawk Fine Papers.
-- Converting Magazine, 2/1/2010 2:00:00 AM
Pressurex pressure-sensing film lets printers and converters measure nip impression.
“By taking nip impressions with pressure-indicating film every couple of weeks, we have extended roll life by a few months in many cases,” Beyer says. “This quality-control measure not only lowers costs for the replacement of these roll covers but also minimizes equipment downtime.”
Mohawk Fine Papers is the largest privately-held, premium-paper maker in North America. Recognized for its technical innovation and environmental focus, the Cohoes, NY-based company produces materials for the commercial and package-printing fields, including specialty and digital-printing papers.
When placed between contacting rollers, Pressurex sensor film instantly and permanently changes color directly proportional to the pressure applied. Precise pressure magnitude is then 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 detected and corrected—improving yield, decreasing scrap and increasing productivity, the supplier says.
Map out a pressure profile
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 produced that exposes minute surface defects and other imperfections.
Beyer cites Pressurex as being especially helpful with calendering rolls, which have mechanisms to allow the center of the rolls to exert a different level of pressure. “Similar to crown rolls, these '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.”
Pressurex is extremely thin (4 to 8 mils) and flexible, which allows it to conform to curved surfaces. The material is said to be ideal for harsh operating 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 deg F for brief intervals.
Mohawk Fine Papers uses Pressurex to take static nip impressions on the pressing section and dynamic nip impressions on the calenders. Image results of Pressurex are archived and used as a control to compare tools and processes.
| MORE INFO: | ||
| CONVERTER: | ||
| MOHAWK FINE PAPERS, INC., 800/843-6455, www.mohawkpaper.com | ||
| SUPPLIER: | ||
| SENSOR PRODUCTS, INC., 973/884-1755, www.sensorprod.com | ||
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