Surface Flaw
In this example, a paper mill was experiencing problems with a wet front edge on the reel of a tissue machine, forcing them to cull the first set off the reel in the converting plant. Machine runnability began to suffer noticeably. Line scanned infrared imaging was used to "see" the temperature of the sheet on the Yankee dryer.

The resulting map of surface temperatures clearly showed one major wet area and several minor wet areas (which appear cold) near the edge the sheet. In other regards the temperature profile was good. Since the images were synchronized to the dryer rotation, it was possible to pinpoint the locations of the wet spots around the circumference of the dryer.

Using PROdry's surface profiling system, polar graphs of the surface near the wet areas were obtained while making paper. The inset in the figure for this example shows one such profile. Each spot was found to be the result of a wear pattern on the Yankee dryer which degraded the pressure roll nip locally. The dryer was subsequently ground, eliminating the low spots and improving the wet edge condition. A coating chemistry change improved the protection of the dryer and extended the time between grinds.