Web monitoring - Breaks reduced by 40%
"This is the best accepted project by production operators that I have ever seen," says Pierre Hudon, Production Manager at the Paperboard Jonquière Division of Paperboard Industries Corporation. He was referring to the installation of a Sensodec Web Runnability Monitoring System (WRM) supplied by Metso Automation. The web break analysis system, which is based on digital image processing technology, was installed in January 2000 on their folding boxboard machine in Jonquière, Québec, Canada. The mill produces 140,000 tonnes per year of double-coated, three-ply board with calipers ranging from 250 to 600 microns. The machine trim is 3.43 metres and the maximum speed is 450 mpm.
Hudon goes on to explain why the project was such a success: "The operators took ownership of the system and that helped to develop teamwork." That teamwork plus the valuable information from the WRM has added up to major reductions in break lost time and a significant return on investment. And the returns were achieved by making several small mechanical changes that didn't require major capital investments.
It's About Visibility
If you can define or see a problem, then you can solve it. It's an old engineering adage that aptly describes the breakthrough in problem definition achieved by the so-called camera system. Before its installation, the machine's efficiency was limited by many web breaks and the long times required to rethread the machine. The "break committee", which was formed to look at this major productivity issue, concluded that the operators had no real visibility into the causes of the breaks.
Hudon says, " The causes of the breaks were mainly unknown. We felt that breaks were coming from the presses. But sometimes we would take downtime to change a press felt with no results. At that time, we had no information to target our actions."
The committee decided to invest in a web runnability monitoring system which would give the operators a continuous view of key board machine locations where breaks might occur or originate. The system would also store those images so a series of break events at any time of the day or night could be reviewed many times over to determine the exact causes. To ensure the success of the new system, the mill implemented a continuous improvement program in which engineering and production people would regularly review the system's information and decide on the right corrective actions.
Fifteen Camera Locations
The Metso Automation system is comprised of fifteen digital cameras located strategically on the board machine. The environmentally protected cameras are supplied with lights to illuminate the web. Several image-processing modules are networked to a WindowsNT -based computer and operator video terminal in the machine's control room. The operators can see the board web on the system's video terminal or through a black and white monitor that can be switched from camera to camera.
During the evaluation process, the mill preferred the simplicity of the Sensodec WRM's operator interface. Using the main terminal, operators can review break events several times, playing them back and forth and stopping the images much like a video tape. All cameras are synchronized in the machine direction so that the upstream causes of a break can be related exactly to a downstream break.
The machine wet end is comprised of three fourdriniers followed by three presses. Prior to the double-sided coating, a liquid starch solution is applied to the sheet by a liquid application system (LAS).
The web monitoring locations include:
· Wet lines on all three fourdriniers
· Trim squirts, front and back
· Open draw between the couch and the first press, front and back
· Exit of the first press, front and back
· Exit of the third press
· Two locations in the enclosed dryer hood
· Liquid application system, front and back
· Into the first coater
The wet line monitors are used by the operators to react quickly - before a break occurs - by adjusting the slice opening or polymer flow.
Small Investments, Big Returns
Break cause information is gathered by engineer Pascal Dubé and formatted into monthly reports. The improvement team then makes decisions to change operating procedures or add new equipment to reduce breaks.
Before the system's installation, the presses were suspected as being a major source of breaks. Analysis of the break images disproved that theory. In the wet end, the major source of breaks was isolated to fiber clumps that gathered on the deckle boards and periodically broke loose. Installing low-flow showers on the deckle boards has eliminated this problem. In another case, accumulated stock was dropping from a pan overhanging one of the wires. The stock was being thrown from a wire turning roll by cenfrifugal force. Re-balancing the roll and adding edge showers on the wire solved the problem.
At the liquid application system, starch accumulation on the sheet edges was causing breaks. The edges of the applicator roll are now wetted using a trickle of water, thereby reducing breaks. Also, re-balancing the LAS rolls reduced wrinkles in the sheet.
The returns from the WRM system and the break improvement program have been dramatic, especially in the wet end and at the liquid application system. Overall, the number of breaks has been reduced by about 40% from 1999 levels. Hudon reports that the break reduction has been achieved at a relatively low cost: "Most of the break reductions have come from little changes, a shower or adjustment here or there. At most, we have invested $10,000 for our break reduction program."