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Papermaking is an interesting combination of a continuous high-speed process with scheduled interruptions for reel turn-ups. So, how do paper machine operators and winder operators communicate and coordinate their activities so that the jumbo reel has exactly the right amount of paper to meet the order book?
If the machine operators lack precise information about how jumbo reels match the winder operator's needs, an excessive margin of safety is usually built into each jumbo. This overproduction-which is good salable paper-is usually left on the spool and slabbed off into the broke pit. On the other hand, when upsets occur, winder operators need to know how much paper is on a partial or orphaned jumbo so they can optimize use of the reel with minimum waste and a minimum number of splices.
Like many mills, Abitibi-Consolidated Inc. in Iroquois Falls, Ont., faced the dilemma of how to reduce the sometimes-ignored tear-off and unaccounted losses caused by imprecise information exchange between machine and winder operators. Abitibi decided to tackle this problem in a systematic fashion by setting up a multi-disciplined task force to thoroughly investigate the sources of the problem, change operating procedures if necessary, and implement new technology to support those operating procedures.
 At the Abitibi Iroquois Falls, mill, operator interfaces for the winder and reel turn-up systems are located on the machine room floor.
By combining a good team effort, diligent diagnostic work, and new technology, the Iroquois Falls task force was able to solve many of the tear-off problems, amounting to considerable cost savings. In addition, operator involvement in the reel turn-up and winding systems design has been a major factor in its success.
TASK FORCE CREATION. The task force addressing tear-off problems at the Iroquois Falls mill is part of a
corporate wide program called CHP, standing for
consistent high performance. Each mill within the company has identified opportunities that, if realized, will allow them to operate at a "world-class" level and generate a significant bottom-line return. Reducing tear-off on the 200,000 tpy No. 8 newsprint machine was selected as a primary opportunity for the Iroquois Falls CHP program.
Comprised of machine operators, supervisors, and engineering personnel, the task force team followed a systematic program that resulted in a new set of operating procedures. Some recommendations-like defining the number of sheets taken for testing or communicating customer specific final diameter tolerances to the winder operators-were straightforward to implement. However, the problem of tear-off from the spools could not be solved without more precise information about how the paper on the jumbo reels matched the winder operator's requirements.
 Figure 1: Reel density profiles before and after nip load optimization.
Stan Denault, paper mill superintendent, says that "the team saw a major opportunity to reduce waste by reducing the amount of guesswork involved in building a jumbo reel." Usually, reels were built larger than necessary because of imprecise diameter measurement, varying operator attention, and imprecise calculation of paper needed at the reel to fill a sequence of set diameter requirements.
Before the CHP program, the so-called "jackets" of paper left on the reel spools were averaging about 1.5 in., representing 2.8% of production or 14 tpd. The mill set an ambitious goal of reducing these losses by over 66% over a three month period. But the existing manual methods of tracking these losses were not very precise. The first step in achieving this lofty goal was defining the problem.
At the beginning of the Iroquois Falls CHP program, it was known that not all of the tear-off was salable paper. The problem of crepe wrinkles had to be addressed first. Primary arm nip relief and programmed nip-load had been installed to prevent excessive nip-load just after turn-up and to prevent double loading as the reel is transferred from the primary arms to the secondary arms. This was combined with new cobra jet turn-up showers and a new air assisted gooseneck to ensure a very tight wrap of the tail. The frequency of missed turn-ups was significantly reduced, but the mill was still battling crepe wrinkles.
At this stage, the mill invited LSZ PaperTech of Mississauga, Ont., to be part of the project team. This company specializes in optimizing roll structure and winding. Using a portable LSZ roll density monitor, the mill team and LSZ discovered that there was a repetitive dip in the reel density profile at the point where the primary arms release the spool.
As Denault explains, "We determined that the crepe wrinkles were occurring at the point of transfer between the primary and secondary arms. With reel density monitoring, we were able to tune the bumpless transfer system and thus reduce the susceptibility to crepe wrinkles."
This modification eliminated the dip in the density profile as shown in Figure 1. The resulting improved reel structure significantly reduced crepe wrinkles, allowing most of the jumbos to be wound down to the bare spool. It also allowed the building of jumbos with six-rather than five-40 in. sets. This reduced turn-up frequency so further reductions in the tons left on-spool were possible, as well as increased winder throughput.
PRECISE INFORMATION AND TRACKING. To provide precise information about the matching of jumbo reel production to wound roll production, the CHP team agreed to install a roll wastage monitor (RWM) provided by LSZ. The Abitibi mill team worked with LSZ to customize the system's functions so that their needs for information and operator tools were met.
With the roll wastage monitor (RWM), 80% of rolls are within 0.1 in. of target and less than 1% are more than 0.2 in. from target.
Installed on the winder, the RWM monitors the building of sets to customer-defined diameters. Set yardage, roll diameters, caliper, and densities are calculated using three tachometers located on the paper roll, the back drum of the two-drum winder, and the unwinding jumbo roll. Also, relay inputs that define the winder state are used together with the roll diameter and winder speed data from the tachometer to automatically infer the reason for a loss in paper or production time.
In addition, the RWM consolidates winder production data into a database. From this data, reports are generated that summarize paper losses and lost time by categories such as splices, snap-offs, bad starts, and, most importantly, the jackets left on the spools.
CONSISTENT ROLL DIAMETER, REDUCED LOSSES. The RWM system was initially installed to precisely monitor and define tear-off and unaccounted losses. Using the information supplied by the system, the baseline level for tear-off was verified to be 2.8% of production. Now, with the operators' confidence established and the problem precisely defined, it was time to implement the new procedures and operator tools in order to begin reducing losses.
To build sets with a consistent amount of paper, the stop-on-diameter feature was added to the RWM. Under manual control, stopping the winder to a diameter target depended on the operator. Also, searching for the correct stopping point took all of the operators' attention during the final few minutes of the set.
With the new feature, the RWM system calculates when the stop should be initiated using precise diameter, caliper, speed, and drive deceleration characteristics. Figure 2 shows how the stop-on-diameter feature improved the accuracy of final roll diameter. Now, 80% of rolls are within 0.1 in. of target and less than 1% are more than 0.2 in. from target.
 Figure 2: The stop-on-diameter function has reduced variations in set diameters.
With the improvement in wound roll diameter, the amount of paper consumed to build a set is now more predictable. Jacket losses that were due to undersized sets can be reduced. Also, the operators can further reduce jacket losses, since they no longer have to build in a safety margin to allow for larger-than-target wound roll diameters.
In addition, the RWM gives the winder operator the ability to define sets with a minimum of splices. With a complete inventory of available jumbo reels on the computer screen, the operator can use the "cookie cutter" function to test and try combinations of jumbo reels that will produce the required sets with a minimum number of splices. "Orphaned" reels that were taken off the paper machine because of a break can now be more efficiently used with less waste cut down into the broke pit pulper.
ACCURATE TURN-UP TIMING. Once loss tracking and consistent winder operation were achieved, Abitibi attacked the problem of how to build a reel with just the right amount of paper required for the order. The profusion of charts and tic marks on the reel and scrawled calculations on cigarette packages were replaced with an LSZ reel turn-up trigger (RTT). The RTT precisely monitors the amount of paper in the building reel and assists the backtender in turning up at the precise moment to match the amount of paper needed for the winder orders.
Tachometer inputs from the reel drum and the building jumbo reel are used to calculate yardage, diameter, and density. While the target reel diameter is approached, the "countdown clock"-a large character video display-shows the operator the minutes and seconds left before turn-up. Countdown relays are programmed to prompt or initiate a turn-up sequence at predefined times. Two minutes and thirty seconds before turn-up, a warning light is activated, providing the operator with sufficient time to prepare for the turn-up when the countdown reaches zero. With the RTT as an aid, the turn-up sizes are accurate and repeatable. This allows for consistent operation, even when less experienced workers are on the job.
Figure 3: Tear-off reduction has resulted in bottom-line savings at the Iroquois Falls mill.
Figure 4: Left-on-spool losses were reduced by three factors: improving reel quality, implementing new standard operating procedures, and reel turn-up timing.
Backtenders build the reel to targets defined by the mill order system. They enter additional data into the RTT to accommodate a defined amount of tear-off for testing, a minimum jacket size, and a safety factor for bad starts. Backtenders also add the precise amount of extra paper on the jumbo to complete a partial set at the winder or to account for grade transition or off-spec paper at the reel.
With the RTT, the separate reel turn-up and winder systems are data linked for information transfer. The linking of the systems has improved the communication between the winder operators and the machine backtender so that their activities are coordinated, allowing for more comprehensive reporting of time and paper wastage.
RETURN ON INVESTMENT. With the wastage monitoring and control functions of the LSZ systems, tear-off losses have been dramatically reduced from the baseline levels-from 2.8% to less than 1%. Figure 3 shows the trends in tear-off during the period when the CHP practices and LSZ systems were being implemented. The operator tools were implemented sequentially.
The end result for Abitibi's 550 mtpd newsprint machine is an ongoing savings of about 10 mtpd. This translates into a sustainable return on investment of over $1 million dollars/year for the Iroquois Falls mill. A follow-up CHP study conducted in early 1998 verified continued savings with tear-off losses dropping from 2.8% absolute efficiency in 1994 to 1.7%, 1.8%, and 1.1% in the three following years.
Because of the success of the RTT on the No. 8 machine, Abitibi has decided to introduce similar systems on its No. 1 groundwood specialties machine.
BETTER ROLL DENSITY CONTROL. In addition to the wastage monitoring and operator tools, the winder system also includes a roll density control function. The system controls wound-in density based on target rider roll load, drum torque differential, and tension curves that are often grade dependent.
Abitibi's No. 8 machine produces many different wound roll sizes with diameters up to 50 in. The mill reports that the system has been useful in providing an insight into roll structure, diagnosing winding problems, and achieving stability in roll quality-especially in the larger roll sizes. Paul Rowlandson, technical assistant at Iroquois Falls, reports that "the RDC allowed us to improve a chronic problem of tight outer wraps on large diameter rolls."
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