Mill maintenance personnel are always on the lookout for wear changes that indicate operational problems. A maintenance superintendent at the paperboard mill in the northeast investigated the suction couch roll on the machine and found a fine groove pattern that was worn in to the tops of the two, 3/4" packing strips over their entire length.
Maintenance personnel noted that these fine grooves had sharp peaks. There were between 13 to 30 of these peaks per inch on each of the 170.5" strips.
Although the couch bore was a mirror image of the grooves on the packing strips, maintenance personnel had an obvious concern. "We had never noticed this degree of grooving before," the maintenance superintendent said.
Additionally, a suction press roll inspection of the on-coming and off-going packing strips showed some small chipping along the length of the strips. In addition, mill personnel found that a 3" piece had broken off the end of the off-going strip. Both of these observations indicated that the strip material had turned brittle during machine operation.
The technicians noted that the contacting surface on both packing strips had a similar grooved pattern as the couch strips, but they were not as pronounced. Although a look into the shell revealed slight grooving that matched the pattern on the seal strips, no major grooves were seen.
Maintenance personnel provided operating data on the breast and couch rolls to determine the cause of the excessive grooves and to identify a solution.
Vacuum Level (in. Hg)
|1st P. Bottom||22||8.5||Off|
|1st P. Top||8||9||Off|
|2nd P. Top||10||11||Off|
|3rd P. Bottom||20||11||Off|
Service technicians reviewed the data and indicated that a primary concern was that the fog showers had not been in use for some time. To minimize the amount of wear on the shell and the strips, the mill needed to turn on the fog showers. This would introduce about 7 gallons per minute of water at 20 psi into the roll's interior to lubricate the seal strips.
In reviewing the excessive grooving to the bore of the couch roll, service technicians concluded that the cause of this problem was insufficient seal strip lubrication and probably the abrasive material in the water. Because the mill was operating the paperboard machine 50-100 fpm faster this year than the previous year, the need to use fog showers to lubricate the seal strips was even greater.
Service technicians also believed that the water that was being pulled through the shell might also cause the excessive grooving. The whitewater was coming from board sheet, which was made from recycled materials. Whitewater from a recycled waste furnish can contain abrasive materials. Therefore, the technicians recommended that the mill supply filtered fresh water for the fog showers to provide good lubrication for minimum wear and friction.
By implementing the recommendations of the service technicians, the paperboard mill no longer suffered from excessive grooves in suction and couch rolls and sealing strips.
For more information on couch and suction roll maintenance and packing strips, contact your Valmet representative.