Hoping to improve board formation and reduce raw material costs, manufacturers and equipment supplier are targeting the forming area

Containerboard Makers Focus on Wet End Developments

By Mark Lockie

Of the entire paperboard machine, recent developments in boardmaking technology have focused almost exclusively on the first few meters. The headbox and the former are seen as the two areas where significant improvements can be made, not just to the quality of board but also to a company's bottom line. The target is to generate quality improvements through better formation and to save on raw material costs. Put simply, as long as the same strength and stiffness values can be reached using less material, lower basis weight board can be produced to do the same job.

Board machines are getting faster as well, and this is forcing many suppliers to push their wet end technology to its limits. Among packaging grades, a number of paperboard machines already in operation are just a few meters per minute from the magic 1,000 mpm mark.

According to Valmet's vice president of board machine technology, Vesa Huovila, "In packaging grades, I believe the 1,000 mpm speed limit will be broken within a year. Within five years speeds up to 1,300-1,400 mpm could be reached. This is because packaging grades have many similarities to printing grades."

Papermakers are not able to produce cartonboard quite as quickly, and it is in this area where suppliers are demonstrating significant differences in opinion over the best manufacturing practices for the future.

AN EVEN SPREAD. At the Institute of Paper Science and Technology (IPST) in the Atlanta, Cyrus Aidun, professor of fluid dynamics, believes that one recent research and development program on headbox technology is set to dish up the goals of "higher quality" and "reduced raw material requirements." According to Aidun, "A major development is the invention of a technology to significantly reduce the anisotropy in the in-plane fiber orientation of the sheet, distributing the strength characteristics of the sheet more evenly in all directions. This results in a sheet of paper or board with higher strength characteristics and an evenly distributed fiber orientation."

The technology is being developed as a retrofit to existing headboxes as well as a feature in new headboxes. At the heart of the process is the generation of a particular flow with axial vorticity in the tube of the headbox. As Aidun explains, the idea has been developed using modern computer-based fluid flow analysis and design engineering, stereolithographic fast prototyping methods and laser-Doppler velocimeters for laboratory evaluation and confirmation of the concept. Whatever it does on an industrial scale, it certainly sounds impressive so far.

The pilot trials have been sponsored by the Containerboard Group of the American Forest and Paper Association (AF&PA), and there are plans to implement this technology on a commercial scale. Aidun predicts that the initial results from commercial test runs should be available within one year.

TAKING FORM. Moving very slightly down the production line, most other boardmaking developments are to be found in the forming section. According to board technology consultant, Seppo Seppälä, "If the grade is recycled-for example, brown paper, testliner, or fluting-all the new machines over the last three to four years have used gap former technology. Normally this has involved two formers with a stratified headbox."

It is this move toward the use of gap forming technology that has sparked the most supplier research. Although there is an element of technology transfer between paper machines used to produce printing grades and packaging papers, applying the different techniques is not always as obvious as one might imagine.

Huovila at Valmet explains some of the company's pilot plant findings: "Our gap forming development work on packaging grades has shown that the optimum process is quite different from printing grades," he says. "In packaging grades, the strength of the board is vital. Using a roll blade former, we have discovered that the emphasis should be placed on the roll dewatering side rather than blade dewatering."

Figure 1: Forming technology such as Voith Sulzer's DuoFormer Base could be used as part of a 1,000 mpm duplex
board machine.


Valmet has just sold two linerboard machines designed on the basis of these findings to SCA Packaging's mills in Obbola, Sweden, and Witzenhausen, Germany. "The Obbola machine, at 10.16 m wide, is the biggest we've ever sold, and both PMs will be installed by the end of the year. The name of the roll blade former has yet to be decided, but it will be a Speed Former P-something."

Following months of research at Valmet's pilot plant, SCA Packaging expects to run the machine at 900 mpm, which will put the machine near the top of the current speed range for this grade. This design should also allow the mill to meet its quality targets using a lower quality furnish.

Another supplier that has been busy improving an existing former design is Voith Sulzer. The design of the supplier's DuoFormer Base concept is rooted in the company's well-established DuoFormer CFD design, and will be particularly suited for packaging papers. According to Voith Sulzer's head of technology
for board and packaging, Günter Halmschlager, "Two months after the development of the new concept, two units have been sold. The DuoFormer Base is especially suitable for packaging paper machines, but it has also shown potential for board machines, as well as folding boxboard and plasterboard production."

Some of the advantages being claimed for the new former design include enhanced water discharge, less vacuum consumption, a wider speed range from 300 mpm up to 1,400 mpm, a clean design, and easier rebuilds. According to Halmschlager, "Drainage in the jet discharge channel and top wire suction box is gravity supported. This design ensures perfect water discharge for all operating conditions, which is especially advantageous during machine startup, but also during operation."

Voith Sulzer claims that the design is well suited for rebuilds since the height of the existing fourdrinier wire is not relevant. This is a departure from the supplier's previous design, which was often difficult to fit in the headbox.

In a similar way to the Valmet design, this roll blade former design places less emphasis on blade drainage. "The portion of blade drainage is significantly smaller than in graphic paper machines. This reduction in blade drainage and the reduced vacuum demand are expected to improve strength characteristics-especially burst strength," Halmschlager explains.

Another supplier, Beloit, has been making improvements to its technology. According to the company's research and development director, David Hope, based in Bolton, U.K., "Our BelLiner was established two to three years ago. We now have seven in operation mostly for the liner ply of linerboard. We are developing this model further, though. We have reversed it to create a new model called the Reverse BelLiner. This model maximizes the primary table by extending the forming table before the two wires meet. This allows more flow from the headbox."

Hope explains that there have also been developments made to increase the BelLiner's capacity for the production of middle ply in cartonboard grades.

Like Valmet and Voith Sulzer, Beloit is looking at using roll blade forming for board grades. As Hope explains, "For corrugating medium there is a desire to move toward roll blade formers, perhaps running at speeds of up to 1,500 mpm. As well as corrugating medium, we are investigating the use of roll blade formers for other grades such as linerboard, where there is a greater percentage of virgin fiber in the furnish."

AGREE TO DIFFER. Up to a point, suppliers and academics seem to have largely similar opinions when it comes to choosing an appropriate forming technology. But moving from packaging board grades to cartonboard grades, opinions begin to differ. While all the suppliers seem to have solutions to meet their customers' needs, most agree it is necessary to take each case individually, especially considering the wide range in basis weights in board grades.

According to Huovila at Valmet, "For cartonboard grades, I think that a multi-fourdrinier is still the best choice, perhaps with top forming, and I believe it will continue to be the best choice for many years to come." The main alternative to the multi-fourdrinier is the gap former, but there are drawbacks with this system that have long been recognized. To get the fiber into the x- and y-plane and develop good strength and formation, a low stock consistency is needed. This then requires a large headbox slice opening, which is a problem in gap forming where slice openings can only reach between 20-25 mm.

At Voith Sulzer, the approach is very pro-gap forming, and the ideas being suggested seem to go against the grain. Halmschlager admits that there are difficulties in gap forming for fresh fiber grades. But as he points out, "Although one gap former is not enough, as we are limited with jet thickness, the cost of two gap formers each with a two-ply headbox is justified."

Voith Sulzer has also been looking at the future of board machines, and again the use of gap forming technology features prominently for cartonboard production. As the company's product manager of board grades, Alexander Wassermann, explains, "We have been looking at a board machine that could be feasible in the next five to ten years to produce today's quality at higher production rates. We have a customer that wants to be able to produce coated duplex board at 3,000 mtpd. This would require a 9-10 m wide board machine working at speeds of 1,000 mpm. The state of the art machine today produces around 100 mptd for every meter width on the machine at speeds up to approximately 600 mpm." Even so, the supplier is confident that it can make the step up in scale.

"The wire would be a combination of gap formers so that the board can still be multi-ply," says Wassermann. "If you want speeds up to 1,000 mpm, a multi-fourdrinier would become very long. We can build board machines with gap formers and reach the same quality levels as you would get with a fourdrinier. This type of setup will be standard in the future, especially in countries where big machines are still feasible, such as Asia. In Europe, there is not really a market."

To produce duplex board, Voith Sulzer is proposing a forming section, which combines the new DuoFormer Base and one or more of the recently introduced DuoFormer Top (also a roll blade former). The "Top" is also based on the supplier's DuoFormer CFD design (PPI, February1998, p. 45). According to Wassermann, "We have just managed to sell one such wire section setup and it is scheduled to start up by 2000."

Voith's futuristic machine continues with a press section using exclusively shoe presses, and a combination of double tier and single tier drying is being proposed in the drying section. Single tier drying has never really been talked about for boardmaking because the high speeds possible with this set up were not seen as necessary and because it would need a greater length. But Voith believes there is no real alternative if the producer is to attain higher speeds.

According to Wassermann, "Some producers have problems with smoothness at the edges of the board due to shrinkage with double tier setups. A combination of single and double tier drying will alleviate these problems, and double tier dryers would compensate for any curl," he says.

PRESSING MATTERS. The press section has witnessed few commercial developments during the last year, although a new pressing technology-impulse drying-promises to revolutionize this section in the future. Impulse drying is a very high temperature (up to 400C) pressing arrangement, where moisture and heat are driven out of the web, causing the fibers to consolidate. Although there is much research being conducted in this area, IPST in Atlanta believes it will be able to trial this technology within a year, perhaps on a linerboard machine (PPI, December 1997, p. 33). Critics of the concept point out that the technology will be very difficult to handle on a full-scale machine.

In the drying department, Valmet has been able to sell its second Condebelt drying process to Dong Il in South Korea, following the successful implementation of the first Condebelt at Enso's Pankakoski mill in Finland. The Korean board machine is a 4.5 m wide unit, running at 650 mpm. Luckily for Valmet, the Asian crisis has not delayed the startup date, which is scheduled for the end of the year.

Since the Condebelt breakthrough, no radically new technology has been introduced in the last year, and most developments have been in the form of upgrades to existing equipment designs. But if the potential of the technology waiting in the wings can be realized, the next five years could prove to be an interesting time. The only question is whether or not board manufacturers will be brave enough to take the chance, and the risk, of implementing the new ideas on a production scale.

Mark Lockie is features editor of Pulp & Paper International.