Thermography in the Paper Mill - Detecting Moisture Irregularities.
INTRODUCTION The application of Infrared Thermography as a diagnostic tool, to look at the entire paper making process allows a unique opportunity to literally "see" the affects of the various processes on a paper machine have on product quality and machine efficiency.
A detailed Infrared Analysis, in most cases, can quickly determine the origin of process related problems and facilitate improvements in sheet quality and machine performance. This technical analytical service is intended to be used to optimize total machine efficiency; and in most cases, reduce unit costs.
HERE'S HOW IT WORKS The principles of infrared imaging are based on the fact that all objects emit infrared radiation. This level of radiation increases directly as temperature increases. Infrared imaging equipment provides real time presentation of temperature patterns being emitted by an object. These patterns are displayed as standard video images in either black & white, or color. The darker colors represent "cooler" temperatures, while the lighter colors would be "hotter".
SHEET MOISTURE/TEMPERATURE RELATIONSHIP The advent of portable infrared imaging equipment has proven useful in determining the cause of cross-direction and machine direction moisture variations on paper machines. Variations in temperature of the sheet at the reel directly correlate with variations in sheet moisture. Areas with higher temperatures indicate dry conditions. Conversely, areas that are cooler contain higher moisture content. We found through the use of high-resolution thermography, that the sheet temperature profiles correlate very well with the moisture profile scans at the reel.
THE SURVEY When conducting an infrared survey of a paper machine looking for moisture irregularities, I begin by looking at the sheet being wound at the reel and follow the sheet to the wet end. The following sequence of photographs, show how the cool (wet) area can be followed down the machine to determine its source. Figure 1 show a real time photograph of the sheet being wound at the reel, infrared photographs (in color and black & white) of the reel, and a copy of the mill's moisture scan of the reel. The infrared photographs correlate quite well with the poor moisture profile.
The survey continues toward the wet end looking at the sheet anywhere there is a clear unobstructed view. Figure 2 shows the top side of the sheet exiting the 3rd press, it still shows to be cooler (wetter) on the tending side, same as what was noted at the reel.
The sheet passing over the center press roll is looked at next, (figure 3) this shows the same cool (wet) front 1/4 th of the sheet, the same as at the reel.
The stock passing down the wire and over the couch roll (figure 4) shows the temperature to be quite even ahead of the couch roll, but as the stock passes over the couch roll it becomes cool on the front 1/4th
CONCLUSION The Cool (wet) front 1/4th of the sheet we followed from the reel to the former, was being caused by a worn wipe on the couch roll.
SUMMARY While infrared thermography does not replace good paper making know-how, it does provide information that can help pinpoint complicated or persistent moisture imbalance problems.
Thermographic analysis enables the mill to identify the source of irregularities without shutting down the machine or otherwise affecting production; thus making problem-solving both efficient and economical.
Typical problem areas where infrared thermography has proven to be an invaluable troubleshooting tool:
* WET/DRY STREAKS (CD and MD) * BARRING PROBLEMS * SLICE IRREGULARITIES * PLUGGED FELTS, SHOWERS, AND DRILLED ROLLS * DEFECTIVE ROLL COVERS * INCORRECT ROLL CAMBERS * UNEVEN STEAMBOX DISTRIBUTION * PLUGGED UHLE AND SUCTION BOXES * UNEVEN FELT CONSTRUCTION * STEAM CONDENSATE PROBLEMS * PRESS ROLL AND CALENDER STACK VIBRATION * GENERAL MACHINE MAINTENANCE: * STEAM LEAKS, OVER HEATED * BEARINGS, AND ELECTRICAL P/PM
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