Paper 360
It was five years ago in July, 2013, when the first roll of lightweight linerboard came off a machine at Cascades’ new mill near Buffalo, New York. Sure, the nearby Niagara Falls are impressive—but so is this 100 percent recycle Greenpac Mill.
Cascades’ Greenpac Mill is a sustainable recycling operation that includes a modern, large linerboard machine. The machine has a 356-inch (9.03 m) trim and produces extra-performance packaging grades.
“We basically produce two linerboard grades here,” says Murray Hewitt, Greenpac’s general manager. “One is a high performance (HP) grade that is basis weight driven. The other is a grade we introduced called XP (extra performance), which is sold based on its ability to meet strength guarantees. The fact that we make the sheet lighter while adding starch for crush resistance is an added plus, as it also reduces transportation costs for our customers.”
The machine and related auxiliaries were supplied by a European supplier that also negotiated a multi-year agreement for the machine clothing. There were limited exceptions for Greenpac to run trials with other suppliers, meaning mill management had to carefully consider and prioritize which machine positions and which suppliers to run trials with.
A couple of spots took clear priority for fabric trials: the pickup (press) felt position and the base-ply forming position. As Tony Newman, production manager at Greenpac, explains, “Stability and consistency throughout our operation is a very high priority. We just weren’t achieving these things in critical forming and pressing positions.”
Hannu Korhonen and David Hufnagel from Greenpac (left and center), with Steve Lachacz from AstenJohnson, on the 356-inch (9.03 m) trim linerboard machine at the Greenpac Mill.
A PRESSING MATTER
According to David Hufnagel, junior process specialist at Greenpac, the issues with the pickup felt were that it was widening out, sometimes wrinkling, and occasionally popping at the seams. “Cleanliness was also an issue, as we had to shut down and do caustic washes a few times a month,” he says.
Greenpac elected to try an AstenJohnson AccuFlow press felt in the pickup position. “You only get one chance to make a good first impression,” says Steve Lachacz, AJ’s sales/service representative for the region. “Getting a trial for AccuFlow was the entry point we were hoping for.”
AccuFlow is the first four-layer woven press fabric with high void volume and a single seam without lamination. “Right off the bat, the fabric didn’t widen, didn’t fill in, and dewatered well,” Hufnagel says. “The performance was as good as we hoped.”
TRACKING TRUE
Greenpac’s machine is one of North America’s largest packaging machines. Yet from day one, the forming fabric for the base-ply (top) position had a severe guiding issue, “running off the rails” during every start-up or shutdown. “We struggled keeping the wire on the machine,” Hewitt says. “The supplier couldn’t resolve the issue in a timely manner, so we began looking at alternatives.”
The stock-on, stock-off guiding issue is not uncommon on wide and fast fourdrinier packaging machines like Greenpac’s, according to Mike Boettcher, forming product manager for AstenJohnson. “I’ve seen it quite often,” Boettcher says. “However, Greenpac’s situation was one of the more clear-cut examples and could have been catastrophic—losing an expensive forming fabric and/or damaging other machine components.”
According to Hufnagel, “We had operators keeping the wire from running off the back side by adjusting the hand guides with wrenches until it settled into a range that could be handled by the automatic guides. Just to verify that it wasn’t a machine issue, we ran a wire with the twill in the other direction and it ran off the front side of the machine.”
When invited to do a trial, AstenJohnson recommended its KraftStar fabric with a unique, patent-pending option called TruTrac. TruTrac has a modified twill pattern on the machine side to eliminate guiding problems for positions that are sensitive to high hydraulic flows.
“There is an inherent imbalance in the twill angles of the yarns creating the wear surface on the bottom side of a forming fabric,” Boettcher explains. “Normally, this small imbalance has only a minor effect on guiding, but on certain machines, the unbalanced twill angles are enough to cause guiding issues when stock is put on the wire. TruTrac has the same number of CD yarn floats going in both directions, ensuring that the drainage forces generated by each set of twills cancel each other out. It solves problems on even the most guide-challenged machines.”
“On the day of the trial, even before the fabric was installed, three AJ guys inspected the machine and found two rolls that were causing wear problems that we had been struggling with since start-up,” Hufnagel says. “It was refreshing for a fabric supplier to look at the whole machine, not just the fabrics. From the moment KraftStar with TruTrac was put on, it was obvious that AJ nailed it. The tracking was phenomenal, and the caliper profile was exactly as we wanted it.”
Greenpac is now also running an AJ wire on the finish ply (bottom) forming position. “We are trying to improve our ply bond, and our thinking is that by having compatible wires top and bottom from the same supplier, we will get that improvement working with a single supplier,” Newman says.
Operator performing edge crush test to verify the strength characteristics of the linerboard.
Boettcher points out that modifying an existing product such as KraftStar with the TruTrac capability is a challenge. “Papermakers expect a certain performance and don’t want a change that alters machine performance,” he says. “So, we had to figure out a way to add TruTrac capabilities without detracting from KraftStar’s benefits.”
Hufnagel agrees. “Our experience is that some fabrics will do one thing extremely well—say, dewatering or seam integrity—but will fall down in the other areas that are important,” he says. “Product consistency and performance across-the-board are extremely important to us.”
DRYING AND DRAWING
Greenpac also ran a trial with AstenJohnson in the dryer section. “In the first UniRun, we had problems with fabric cleanliness and edge cracking,” Hufnagel explains. “With 100 percent recycle, contaminants can ultimately make their way into dryer fabrics. We were changing dryer felts every three or four months due to losses in permeability.”
According to AJ’s Lachacz, “We put our SpeedTec fabric on in the first UniRun position. Later, when it came off, there were no visible signs of wear or of the fabric filling in.”
Switching to SpeedTec also enabled Greenpac to reduce draw in the first position by 28 percent. While many dryer fabrics have a neutral line with equal distance between paper side and machine side, SpeedTec shifts the neutral line to the sheet side. According to Lachacz, “This minimizes stretch and draw forces on the sheet as it passes through the dryer cans. This design excels on higher speed machines, especially in the early sections where abrasion and contamination are highest.”