The modern paper machine, part 1: bigger, better board machines: paperboard machines were the first to push the limits of width. now it's speed, quality, and versatility that sets new technology apart.

Paper and paperboard may be mature commodity products, but most grades of paper and paperboard still are growing in demand--particularly on a global basis. However, profit margins and return on investment (ROI) can be very low, and that has meant that many paper companies--particularly in North America--are not investing in new paper machine technology. Older paper machines have inherently higher operating costs often coupled with lower product quality compared to current technology.

How does new paper machine technology provide competitive advantage, and how do you define the modern paper machine? "Current technology" paper machines have many of the following characteristics:

* Wider and faster

* Integration of off-line operations onto the paper machine

* Use of new technology to solve long-standing quality issues

* Use of new technology to solve long-standing operating issues

* Use of technology to reduce operating costs

These trends can best be discussed using real examples on a grade-by-grade basis.

Containerboard paper machines were the first to push the limits of width. International Paper and Weyerhaeuser both installed fourdrinier linerboard machines back in the 1960s that were approximately 10 m wide with original speeds in the range of 300-350 m/min. Linerboard machine widths are normally a multiple of around 2.5 m because modern corrugating machines are typically 2.5 m wide. That means that a number of linerboard and testliner (recycled linerboard) machines were built that were around 5 m wide. However, more recently corrugating machines are being developed that use 3.3-m wide rolls making the trim issue more complex in the future for narrow machines.

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Older technology liner machines are characterized by a rectifier roll headbox, a fourdrinier forming section with a secondary headbox, three or more straightthrough presses, a large number of conventional two-tier dryers, and a multiplenip hard calender. Updated containerboard machines typically have a hydraulic headbox, one or more top-wire formers or a secondary fourdrinier or gap former to form the top ply, conventional rolls and shoe press combination, and a single-nip hard calender. Most older containerboard machines have been upgraded to operate at 500-700 m/min.

Although some board machines have used gap former technology for the top ply of the board, the first board machine to use gap formers for both the top and bottom plies was the Republic Paperboard gypsum board machine in Lawton, Oklahoma, USA. This machine, supplied by Voith Paper, started up on November 27, 1999. Design speed is 760 m/min and wire width is 4.7 m. The machine is designed to run basis weights in the range of 75-110 g/[m.sup.2]. Gap former technology was selected primarily for enhanced paper quality, which allows a reduction in basis weight. The machine also has two straight-through, double-felted shoe presses, which have become the standard for many new board machines. Shoe presses remove much more water and reduce energy costs in drying.

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Papierfabrik Palm GmbH recently installed a new paper machine at its Worth, Germany, mill that represents current technology for corrugating medium and test liner machines (Figure 1). The new PM 6, supplied by Metso Paper, is designed for a basis weight range of 60-150 g/[m.sup.2] and has a design speed of 1800 m/min. PM 6 started on April 1, 2002, and present operating speeds are around 1000-1100 m/min due to stock limitations. Machine width is 10.5 m, which was chosen to take advantage of the emerging 3.3 m wide corrugating machines as well as the current standard of 2.5 m.

PM 6 has two gap formers that supply three plies. Although a single gap former could supply the basis weight range needed on PM 6, the use of two gap formers and a stratified headbox produces better flexibility in furnish and reduced furnish costs. The first gap former produces the bottom ply of the sheet, which is also the outer, printed surface. The second gap former has a stratified headbox, which produces the middle and top plies comprising 55% to 60% of the total sheet weight. The headbox for the second former has dilution control to correct CD basis weight variation. Strength properties of the gap-formed sheet allow a reduction in basis weight with comparable performance to fourdrinierformed sheets.

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The press section has a doublefelted, straight through configuration with two shoe presses. Dryness out of the press is reported to be 53%, which is at least 10 points better than what could be expected out of older technology roll presses. Since a 1% increase in sheet solids out of the press results in a 4% reduction in drying requirements, new tandem shoe presses can save as much as 40% of the energy needed in the dryer section over conventional long-nip presses.

Because of the higher design speeds, the dryer section is single-tier for most of the machine, except for a short, double-tier section at the end of the machine for curl control. PM 6 has a rod metering size press followed by a non-contracting gas-fired drying unit. Because of the excellent sheet uniformity, there is no need for a calender. Lack of calendering is common for corrugating machines, but uncommon for linerboard and test liner grades. The reel, rather than being a conventional surface winder, also has center-wind assist, which allows for much larger parent rolls and good reel quality all the way to the spool. Finished reel diameter is 4.3 m compared to standard reel diameter of 2.5-3 m for conventional, older technology reels. Parent roll change is fully automated, and the parent rolls are transferred to two fully automated winders for conversion to customer rolls.

ANOTHER MODERN MACHINE

Another modern corrugating medium machine is SAICA PM 9 in Zaragoza, Spain. This Voith machine has a wire width of 8.1 m and a design speed of 1500 m/min. It started up in October 2000 and set a speed record of 1260 m/min. on 110 g/[m.sup.2] corrugating medium. PM 9 has a single gap former, a 4-roll, cluster press with a shoe press for the third nip, single-tier drying, and a metering size press.

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PACKAGING BOARD

Although gap formers are the technology of choice for higher speed and medium to lighter weight board applications, multi-ply fourdrinier machines still represent the best technology for many packaging board grades. Gap formers are limited to about 170 g/[m.sup.2] per former, so a tandem gap former would be limited to about 340 g/[m.sup.2] basis weight--lighter than many packaging board applications.

CMPC's new machine in Maule, Chile, is a good example of a modern multi-ply coated folding boxboard machine (Figure 2). Built by Voith, it has a wire width of 5.4 m, a design speed of 650 m/min, and a basis weight range of 150 to 450 g/[m.sup.2]. What makes this machine exceptional is its furnish flexibility. As Figure 3 shows, the sheet has a bottom layer of chemical pulp and OCC, an intermediate layer of mechanical pulp and OCC for good bulk, another intermediate layer of mechanical pulp and mill broke, and a final top surface of high quality bleached chemical pulp for surface characteristics. This multi-ply structure minimizes fiber cost, maximizes the bulking potential of mechanical pulp, and provides a high quality surface for coating and printing.

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The top surface is further prepared for coating by drying on a Yankee cylinder, followed by a metering size press, and finally a hard nip calender. The sheet can be reeled at this point or threaded under the first reel to the coaters, final soft nip calender, and second reel.

There is also an alternative emerging technology in packaging board technology calendering called shoe nip calendering (SNC). SNC extends the concepts used in shoe presses to the area of calendering. There are currently three SNC units running on packaging grades and a fourth on woodfree fine paper. Two of the SNC installations are in the Korsnas mill in Gavle, Sweden, on coated liquid packaging board and uncoated packaging board. These units were supplied by Metso.

SNC consists of a "shoe-type roll" similar to the shoe found in a press section and an opposing conventional heated roll (Figure 4). In current production units, the shoe is either 50- or 70-mm long, which is much shorter than the shoes used in press sections. Normal loading of the shoe is between 100 and 400 kN/m, which is lower than the linear loading used in most shoe presses.

In SNC units, there is no felt between the sheet and the shoe roll, as would be found in a press section. Since the sheet is in direct contact with the shoe's polymeric belt, the construction of the belt has a big impact on sheet properties. Soft belts can be used for bulk sensitive board grades at low nip pressure, and harder belts can be used for lighter weight paper grades requiring higher pressures.

Since the length of the shoe determines the nip width, SNC produces longer dwell time than either hard nip or soft nip calendering, but at reduced maximum nip pressure. SNC therefore results in higher sheet bulk at equal or better surface uniformity. Higher bulk means higher stiffness and potential for reduction in basis weight and therefore a reduction in fiber cost.

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. Many paper machines produced by a number of suppliers would fit the definition of "best current technology."

Editor's Note: This article appears in two parts. Part One, published here, deals with paperboard machines. Part Two, scheduled for publication in December, focuses on coated and uncoated paper machines.

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ACKNOWLEDGEMENTS

The author appreciates the assistance provided by Metso Paper and Voith Paper. This includes both technical and graphical material and the direct support of technical and marketing personnel.

ADDITIONAL RESOURCES:

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

* 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.

REFERENCE

1. Todorovic, A., and Hamalainen, T., "Shoe nip calender possibilities for board and paper," 2003 TAPPI Spring Technical Conference Proceedings, TAPPI Press, Atlanta, Georgia USA.

RELATED ARTICLE: IN THIS ARTICLE YOU WILL LEARN:

* How new paper machinery technology provides competitive advantage.

* Definitions of the modern paper machine.

* Current technology for boardmaking machines.

* Examples of modern board machine technology.

JAMES W. 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].