The paper machine superintendent shook his head in disgust as he examined the wear on the seal. “Not another wear problem with the seal on the couch roll,” he said. He told the maintenance coordinator that they should look at changing out the couch roll and the seal every 160 days instead of the usual 181.
The seal problem on the couch roll had plagued the machine’s operations for quite some time. After more than five years of operation and despite the best efforts of mill personnel, the wear problem wouldn’t go away.
“We had a chronic problem that was getting no better as we continued to operate our paper machine at design speeds,” the maintenance coordinator said. He explained that this seal was the only one causing a problem on the entire machine, and it stymied the best efforts of mill personnel and equipment suppliers to identify the cause of the problem and come up with a successful solution.
The machine superintendent noted that the mill had actually looked to exchange the packing seal once a year, but wear concerns prompted the mill to alter this schedule to once every six months. In explaining the wear problem, the machine superintendent said that the seal wore down to less than 1/8” from the 1-1/4” when it went on the machine. “You could almost see through it,” he said. He added that the sheet release line on the wire was skewed.
At wit’s end as to what to do with the seal, the maintenance coordinator performed trials using the two most expensive seal strips and got the same results - extreme wear. In desperation, the maintenance coordinator suggested installing a locking device that would stay on the couch roll to keep the seal in place. The machine superintendent said that the mill even explored the option of regrinding the machine rolls and installing ceramic seals, but the cost of this alternative was too expensive.
Because the machine’s couch roll packing was wearing predominantly on the wet-end side, the mill thought the problem was a question of vacuum level. They tried reducing the load tube pressure to less than 2 lbs. but this didn’t work very well. In recent scheduled maintenances, the maintenance coordinator and machine superintendent noted that wear on the wet-end side was down to less than 1/8-inch in some cases.
Then the machine operator and the maintenance coordinator learned about a new seal, one that Valmet introduced to the North American marketplace. Valmet Seal Strip Flex was flexible and could be contoured to the operating space of the couch roll.
At the suggestion of a service technician, the mill installed the seals on a trial basis. The service tech said that Valmet Seal Strip Flex was made of heat resistant material, was flexible, and could reduce the friction and heat buildup that was causing the seal strips to wear out.
The mill did nothing to the machine other than substituting the new packing for the original packing. The trial results speak for themselves. After six months on the machine, the mill removed the Valmet packing and sent it out to determine wear. In the same amount of runtime that had brought the old seal strip from new thickness down to only 1/8-in. remaining, the Valmet Seal Strip Flex had only worn .030-in., the maintenance coordinator told the machine superintendent.
Based on the trial run, the mill installed Valmet Seal Strip Flex on the couch roll for another six months, and later extended the changeout to one year. According to the paper machine superintendent, preliminary results from the seal installation indicated they could extend its life to two years.
This paper mill experienced immediate cost saving results from the Valmet Seal Strip Flex installation. The maintenance coordinator notes that the mill no longer needs to schedule six people to make roll changes every six months, plus the cost of a roll rebuild.
The paper machine superintendent sings a different tune these days when it comes to the couch roll seal packing. He no longer wonders about the chronic wear problem on the seal, but instead has doubled the life of the couch roll and achieved significant cost savings.
For more information about seal strips and how to schedule a trial run of Valmet Seal Strip Flex, contact your Valmet representative.