High-Speed Infrared Detection of Coated Roll Surface Defects, 1997 Papermakers Conference Proceedings

Cermet roll coatings have become an important component of paper machine press rolls with the increased use of cermet coatings as granite roll substitutes and recent developments in impulse drying. Given these developments, one would like to know how well cermet coatings withstand thermal and mechanical cyclic loading over an extended period of time. Using infrared thermography techniques, it should be possible to determine when and how the cermet coatings fail; coating failures are detected by temperature differentials between a defect and the surrounding coating. To establish how well the infrared thermography can detect various defects in a cermet coating, a study was conducted using a high-speed, high-resolution infrared thermal imaging and data acquisition system. A press roll rotating at 328 RPM (628 m/min, 2061 fpm), with coating defects of various shapes and sizes, was imaged. The defects were classified as either circular or line defects based on their shape and method of forming. Resolution of 2.38 mm (3/32”) was achieved with the circular defects and a resolution of 1.59 mm (2/32”) with the line defects. The dimensional accuracy of the method was also quantified. The successful identification of these defects supports the implementation of infrared imaging as a viable method of identifying coating failures at high roll speeds.