The modern paper machine, part 2: coated and fine paper.

EDITOR'S NOTE: This article appears in two parts. Part 2, published here, deals with fine and coated paper machines. Part 1, focusing on paperboard machines, was published in the Nov. 2003 issue of Solutions!

In today's market it is more important than ever that new paper machinery provide competitive advantage, but what exactly provides this advantage? How do you define the modern paper machine? "Current technology" paper machines typically are wider and faster, integrate off-line operations, solve long-standing quality and operating issues, and reduce operating costs. These trends can best be discussed using real examples on a grade-by-grade basis.

UNCOATED WOOD-FREE FINE PAPERS

Copy paper and publication grades have been produced on gap formers for around four decades. Modern gap formers for these grades use a combination of initial roll forming followed by blade forming to allow good retention, control over machine direction/cross direction (MD/CD) ratio, and good formation.

Asia Pulp & Paper's Dagang (China) PM 1 and PM 2, which were supplied by Voith Paper, are representative of modern uncoated fine paper machines (Fig. 1). Installed in 1998, these machines are each 10.5 m wide and have an operating speed of more than 1400 m/min. PM1 and PM 2 have a gap former followed by a four roll cluster press with a shoe press in the third nip position. As on all high-speed machines, the main dryer section is single tier. The metering size press is followed by an air turning device and heated non-contact drying. There is a short single-tier section followed by a two-tier section for curl control.

Soporcel PM 2 Figuera da Voz, Portugal, also supplied by Voith Paper, is another example of a modern fine paper machine. Started up in July 2000, PM 2 has a wire-width of 9.35 m and an operating speed around 1500 m/min. PM 2 produces copy paper and offset. Although it is similar to Dagang PM 1 and PM 2, there are several evolutionary changes. First, the press section of Soporcel PM 2 consists of two straight-through, double-felted shoe presses in place of the cluster presses at Dagang. Second, while the Dagang machines have two hard-nip calenders, the Soporcel machine has two soft-nip calenders. On-machine soft-nip calendering provides a better printing surface while preserving sheet bulk.

In August 2002, Weyerhaeuser's mill in Kingsport, Tennessee, USA, started up its K1 paper machine. This machine was originally built by Metso Paper for Asia Pulp & Paper, but later resold to Willamette before Willamette became part of Weyerhaeuser. K1 has a design speed of 1450 m/min and a trim width of 8.76 m. Top speed to date has been 1314 m/min.

The machine has a horizontal gap former followed by a single-nip shoe press (Fig. 2). This is the first application of a single-nip shoe press on a completely new paper machine, although a similar press was installed at Weyerhaeuser's mill in Johnsonburg, Pennsylvania, USA, in December 2000 as part of a rebuild.

The advantages of the single-nip shoe press over a tandem two-nip shoe press are lower capital and operating costs along with ease of operation and reduced maintenance expenses. However, felt life is reduced because the two felts must now do the job of the four felts found on a tandem two-nip shoe press.

Following the press section, K1 has single-tier drying and a metering size press. There is two-tier drying after the size press for curl control and two-nip soft calendering, a first in North America on uncoated, wood-free papers.

LIGHTWEIGHT COATED (LWC) PAPERS

LWC papers are an excellent example of the trend toward inclusion of previously off-machine operations on to the paper machine (1). Older generation LWC papers were manufactured in three separate operations: first the paper was made on the paper machine, then coated on an off-machine coater, and finally calendered in a separate supercalendering operation. This was a costly manufacturing process in terms of both capital and operating costs. The first simplification, which occurred some years ago, was to put the coating operation on the paper machine. Supercalendering has still been performed in a separate operation because the filled roll covers on supercalenders cannot stand the abuse that they would receive if located before the reel of the paper machine.

The development of polymeric covers for on-machine, soft-nip calendering was the first step in bringing the LWC manufacturing process completely on-machine. Metering size presses can film-coat both sides of the sheet in a single operation, and a two-nip, heated soft calender can finish the surface. Although LWC produced in this type of operation is suitable for offset printing, the print quality is still not as good as paper supercalendered off-machine. The final step, then, was to develop on-machine supercalenders with polymeric roll covers. These new generation supercalenders were first used for uncoated SC papers.

Haindl Papier PM 3 was the first LWC machine to integrate both on-machine coating and true multi-nip supercalendering in the machine operation. PM 3, supplied by Metso Paper, started up in June 2000 in Haindl's Augsburg, Germany, mill (now part of UPM-Kymmene). The machine has a wire width of 10.45 m and a design speed of 2000 m/min. This machine has a gap former, shoe press, and single tier main drying section.

However, the dry end is the most innovative part of this machine (Fig. 3). Following the main dryers, the sheet is pre-calendered on a two-roll hard nip stack. This pre-calender uses the latest advances in narrow-zone profiling to correct CD caliper profile through hydraulic activation of each piston. Individual piston control has allowed much tighter control over narrow streaks and a resulting substantial improvement in 2-sigma CD caliper.

[FIGURE 1 OMITTED]

After the sheet is pre-calendered, it is film-coated in a metering rod size press. At typical coat weights below 10 g/[m.sup.2]/side, film-coating can provide similar gloss, but somewhat higher PPS roughness than offset LWC produced with blade coating and off-machine supercalendering. There is a substantial advantage in capital and operating costs for film-coat presses compared to blade coaters, so for now, film-coat presses are the preferred technology.

Coating is dried after the film coater by non-contact hot air and a short single-tier dryer section before entering the 8-roll on-machine supercalender. This multi-nip calender can be viewed as an extension of on-machine heated soft nip calendering. The stack loading is controlled by cylinders at the bottom of the calender. Roll deflection is controlled by top and bottom narrow piston controlled crown rolls. The top and bottom rolls are polymer covered as are the third, fifth, and sixth rolls. The remaining second, fourth, and seventh rolls are oil-heated, thermo rolls.

This arrangement of hard and soft rolls means that the bottom of the sheet is in contact with the heated rolls in the top of the stack followed by a reversing set of soft rolls. In the bottom portion of the stack, the top of the sheet is against the heated rolls. Since the polymer roll covers are easily damaged, the calender must be threaded in the open position and all the rolls must be individually driven. Typical loading is 450 kN/m, with heated roll temperature as high as 160[degrees] C.

Only a few months after Haindl PM 3 was commissioned, another LWC machine with on-machine supercalendering started up in October 2000: Perlen Papier's PM 4, which has a wire width of 5.9 m and a design speed of 1500 m/min (Figure 4).

Perlen PM 4, a Voith machine, is similar to the Haindl machine in that it has a gap former and tandem shoe press; single-tier drying; hard-nip, narrow-zone control pre-calender; metering size press coater; and non-contact air-drying.

[FIGURE 2 OMITTED]

The supercalender is unique. It is comprised of six rolls with a gap between the third and fourth rolls, in effect making it a set of two three-roll calenders. The top and bottom rolls and the third and fourth rolls are soft-covered; the remaining rolls are heated.

This arrangement allows for greater flexibility over top and bottom smoothness. Voith has also supplied on-line 8-roll supercalenders (with no center gap), which were used for conversion of two newsprint machines to LWC at Madison Paper and Bowater in the United States.

ADVANCES IN AUTOMATION

Increasing use of automation on the paper machine has been responsible for reductions in operating costs and improvements in quality. Although there are numerous examples of automation on the paper machine, one of the more obvious and important ones has been the whole area of reel parent roll transfer, and winder operation (2), (3).

Automation of this area of the operation is vital for several reasons. First, this can be a dangerous area of the paper machine. Minor accidents, such as cuts from slitter blades, have been common and more serious accidents are possible. Second, this is a labor-intensive area. Older machines may require three or more operators for reel transfer and winder operations.

Finally, as paper machine speeds increase, some winders cannot keep up. New lightweight grade paper machines are now running in the 1800-2000 m/min range, while top winder speed is around 3200 m/min. That means most new machines will require two winders. However, paper machines running 1300 m/min or more can get by with one winder, provided the winder efficiency is high.

Winder automation began 30 years ago with automatic slitter change and has now progressed to full automation, which is referred to as "continuous winding." That means automated control of the following steps in the reel/winding process.

* parent reel transfer and spool return

* parent reel splicing 

* full width web threading

* slitter and wind-up stand positioning

* core feeding

* gluing or taping the web to the core

* set change and web cutoff

* attaching the tail to the finished roll

* roll transfer and labeling

Complete automation means that the winding operation can proceed without operator intervention and the associated downtime waiting for operator input. Full automation means that only a single operator is needed to monitor the process.

STEADY EVOLUTION

Paper machines are much more cost effective than those of only a decade or so ago. Faster, wider machines require fewer man-hours per ton of production.

Modern press sections offer substantial reductions in energy usage. Combining operations that were previously off-machine results in higher efficiency, lower capital costs, and of course lower labor costs.

New technologies, such as on-machine supercalendering, open the door for new products and product differentiation. Multi-ply forming and stratified headboxes provide the means to engineer the product to better meet customer needs, while at the same time reducing furnish costs. Increasing automation offers the benefits of consistent product quality, improved efficiency, increased safety, and reduced labor costs.

[FIGURE 3 OMITTED]

DISCLAIMER

Although specific paper machines and suppliers were used in the article, this does not infer that these examples represent the best or only technology available.

[ILLUSTRATION OMITTED]

There are many paper machines produced by a number of suppliers that would fit the definition of "best current technology."

[FIGURE 4 OMITTED]

ACKNOWLEDGEMENTS

The author appreciates the assistance that was given for this paper by Metso Paper and Voith Paper. This includes technical and graphical material and the direct support of technical and marketing personnel.

REFERENCES

1. Roberston, R., and Tani, M., "Development of advanced on-machine calendering for film coated LWC papers," 2003 TAPPI Spring Technical Conference Proceedings, TAPPI Press, Atlanta, Georgia, USA.

2. Daul, M., and Patton, W., "The fully automatic winder," TAPPI 99 Proceedings, TAPPI Press, Atlanta.

3. Daul, M. "New winding technology boosts the limits of conventional winding," 2003 TAPPI Spring Technical Conference Proceedings, TAPPI Press, Atlanta.

RELATED ARTICLE: WHAT YOU WILL LEARN

* How new paper machinery technology provides competitive advantage.

* Definitions of the modern paper machine.

* Current technology for fine paper machines.

* Examples of fine and coated paper machine technology.

ADDITIONAL RESOURCES

* Note: The following articles are available online at www.tappi.org. TAPPI and PIMA members can download these articles for free.

* "The modern paper machine, Part 1: Bigger, better board machines," Jim Atkins, Solutions!, November 2003, p. 30.

* "Papermaking in 2035: What will the paper machine look like?," Jim Atkins, Solutions!, March 2003, pp. 25-27.

* "Building the future: Engineering in 2015," Robert Kinstrey, Solutions!, October 2003, pp. 35-37.

* "Single-nip shoe press: The single choice," Jim Atkins, Solutions!, July 2002, pp. 40-41.

BY JIM ATKINS, ATKINS INC.

ABOUT THE AUTHOR

Jim Atkins is president of Atkins Inc., and a member of the Solutions! Editorial Board. Contact him at + 1 908 806-8689 or [e-mail].