Multiple Surface Flaws

In this example, a high-speed tissue machine was experiencing a wet front edge and a high frequency of sheet picking at the blade, leading to frequent sheet breaks and lost production. A precision line-scan infrared image of the Yankee dryer was acquired by PROdry under normal papermaking conditions. The result showed there to be several cold spots that were synchronous to the Yankee rotation and the likely causes of the runnability problems. The mill had previously found two low spots in the Yankee shell, but were unaware of the remaining spots revealed by the PIR image.

In order to quantify the location and depth of the wear spots on the Yankee surface, PROdry Technology engineers used a cable-mounted, eddy current probe coupled to their proprietary to measure Yankee surface topography while the machine was making paper. The resulting topography map is shown below in 3-D projection. Several low spots were present in the shell. Each was well defined, and coincidentally aligned with the Yankee's internal condensate removal system geometry. The overall range of shell runout was about 15 mils (0.015").

The profile shown in the figure is a cross-section of the dryer at the low spot 15" from the dryer centerline. The nature of the distortion is clearly defined by the topographic data, and the head bolt reference positively locates the spot on the dryer. Due to the number and depth of the flaws, the Yankee dryer was ground to remove all surface irregularities and restore the papermaking surface. It was started up afterwards with no signs of the picking problems that had been the cause of much lost production. A regimen of testing has been established to provide early warning should these spots redevelop.

© 2007 PROdry Technology, Inc. Site last updated 3/7/07