American Printer's mission is to be the most reliable and authoritative source of information on integrating tomorrow's technology with today's management.
Aug 30, 2001 12:00 AM
Calendering technology expands in U.S. as first online coated lines are ordered and two major lines on SC uncoated grades start up this year
Online calendering continues to transform the papermaking process worldwide, providing mills with the technology to finish a variety of grades completely on line. Most printing-paper grades and many specialty grades are currently produced with online calenders — either soft-nip or multiroll. Board mills are also increasingly looking at new sheet-finishing technology, including soft-nip and shoe calendering. Here, several top suppliers and other sources help assess the current status of calendering, and uncover important trends and innovations for the future of papermaking.
European mills were the first to incorporate online, multiroll calendering, but North American mills are rapidly adopting the technology (see table, p. 7). In North America, the main application to date has been supercalendered (SC), uncoated groundwood grades, where multiroll calenders have rapidly changed the face of the SC business. These moves have led to an upward shift in groundwood printing-paper quality, and have put tremendous cost and quality pressure on mills that rely on older technology such as supercalenders, hard-roll machine calenders or even older soft-nip calenders.
Irving Paper installed North America's first online, multiroll calender in early 1999 on an uncoated groundwood machine at its St. John, NB, mill. Irving's six-roll OptiLoad unit from Finland-based Metso Paper Inc. (formerly Valmet) has two hot intermediate rolls. Irving has been a pioneer in hot soft calendering, reportedly installing the first unit on a North American newsprint machine in 1991.
Stora Enso installed the world's first online OptiLoad, a six-roll unit, in late 1998 at its Varkaus, Finland, mill. The OptiLoad was installed on Stora Enso's 354-inch-wide No. 4 paper machine, which produces directory and newsprint papers.
In North America, a second multiroll calender was installed as part of Alliance Forest Product Inc.'s (Montreal) revamping of its two Canadian printing-paper mills. The company installed a soft calender — consisting of a pair of two-roll, soft-nip calenders — at its Dolbeau, PQ, mill in 1999. In 2000, Alliance installed a multiroll Janus calender at its Donnacona, PQ, mill. Voith Paper (Los Gatos, CA) supplied both units.
The transformation of SC paper production from traditional offline finishing via supercalendering to online operation is continuing with two key startups planned for 2001. Both orders went to Metso, and each installation has unique attributes. Abitibi-Consolidated Inc.'s project at Lufkin, TX, will utilize a six-roll OptiLoad on a southern pine furnish for SC-B grades, which offers challenges due to the high pitch content. Great Northern Paper Co. is installing a 10-roll unit on the No. 11 machine at its Millinocket, ME, mill, which is being converted to printing-paper production. The company declined to identify what grade the mill will produce, but confirmed that it is an SC paper. The 10-roll configuration, however, seems to be capable of producing SC-A grades, or even higher-quality products.
In North America, the most innovative news in calendering is its evolution in coated paper production. Pacifica Papers (formerly MacMillan Bloedel) was one of the world's first — and the first in North America — to use soft calendering to produce coated groundwood papers on line, at its Port Alberni, BC, mill. This innovative operation, installed in the mid-1990s and now somewhat dated, uses a pair of two-roll soft calenders. Newer machines with multiroll calenders have more nips and thus can develop higher gloss.
At Alliance Forest Products' Donnacona, PQ, mill, North America's first online Janus calender will produce top-of-the-line SC-A grades. Currently, no mill in the U.S. produces standard coated groundwood fully on line; all use offline supercalenders. In Europe, several coated mills produce lightweight coated (LWC) papers with online coating, including UPM-Kymmene's Rauma, Finland, mill and Haindl Papier's Augsburg, Germany, mill. The latter facility also has online calendering.
Haindl's Augsburg mill is the current standard-bearer for modern LWC technology. Its new 400,000-tpy machine, brought on line last summer, operates at a wire width of 411 inches (10.45 m) using an eight-roll calender, of which five rolls are plastic-covered and three are steel-thermo rolls. Linear load ranges from 30 kN/m to 450 kN/m at temperatures up to 200ÞC. The sheet is pre-calendered before both sides are film-coated, and then calendered using an OptiLoad. “The mill is making coated offset grades right now, and can attain 60 gloss range and a smoothness (Parker Print Surface) range of 1.5 microns,” notes Martii Tuomisto, Metso's director of North American calendering.
Online technology in coated-paper manufacturing is migrating to the U.S. via two upcoming projects that will convert existing newsprint machines to LWC paper production.
The first project will convert Madison Paper Industry's Alsip, IL, facility to a 120,000-tpy LWC mill. The mill's 240-inch machine will be converted with the addition of a Voith SpeedCoater and Janus Mark 2 (MK2) eight-roll calender. The mill will utilize significant recycled fiber in the sheet; Madison declined to specify the amount. The stock-preparation area will be rebuilt with an EcoCell flotation unit. Startup will reportedly be in late 2001 or early 2002.
The second major project, which also utilizes cutting-edge technology, is the conversion of a southern U.S. newsprint mill to coated papers. This larger project includes a major rebuild of the 390-inch machine at Bowater Inc.'s Catawba, SC, mill. Voith was unable to confirm the order due to confidentiality restrictions. Numerous sources, however, report that the project includes the addition of an online Voith SpeedCoater and Janus MK2 multiroll calender. Metso is supplying a new press section for the machine.
Bowater declined to comment on or confirm this information. It is likely, though, that the Janus calender would be an eight-roll unit, based on technology deployed at similar mills. Startup is scheduled for Q3 2002 at a cost of $106 million, according to published reports.
“ON HIGH-QUALITY BOARD, SHOE CALENDERING MAKES SENSE BEFORE COATING. ON LESS DEMANDING GRADES, IT COULD BE USED AS A FINAL CALENDER.”
Haindl has installed Metso OptiConcept technology on its Augsburg mill's No. 3 paper machine, including online coating and an eight-roll calender.
In the original Janus calender, as installed at Alliance, the rolls were arranged in a vertical stack, but in the Janus Mark 2, the system is inclined at a 45-degree angle. “This facilitates roll changes and sheet threading, and allows increased operator access to both sides of the stack,” notes Paul Martin, Voith product manager.
Voith's first MK2 unit was installed on the No. 5 machine at Lang Papier's Ettringen, Germany, mill. The machine also has a double shoe press — the first shoe press on magazine papers, and key to the machine's design speed of 2,000 m/min. The Madison Paper order for its Alsip mill is a Mark 2 Janus calender.
Küsters GmbH is also a major supplier of soft-nip calenders, with more than 300 units running worldwide, according to Hans Hendrix, vice president, and Mark Sorensen, product manager. The company's ProSoft multiroll calender operates in Europe on coated woodfree grades. There are currently 10 ProSoft units running, including one in the U.S. at a confidential location.
Another noteworthy calendering development involves the startup of Metsa Serla's rebuilt No. 4 paper machine. The former copy-paper producer has been converted to a 225-inch-wide, 3,937-fpm, coated free-sheet machine in a major rebuild that includes a Metso OptiCoater with two jet blade-coating stations and an online OptiLoad calender. It is the first machine in the world with online blade coaters and an online OptiLoad multiroll calender. Several machines produce coated groundwood papers on line, but these use film coaters rather than traditional blade coating. A new shoe press was also added as part of the project.
Although Metsa Serla's No. 4 paper machine is the first to incorporate this particular technology combination, coated woodfree has been produced on line for some time, according to various sources. Mills in Europe make coated woodfree using online soft calendering. SAPPI Ltd. (Johannesburg, South Africa), formerly S.D. Warren, pioneered online production in the U.S. in the 1980s with its patented “thermal gradient” calendering. Reportedly these soft-roll calenders had multiple rolls, but not of the same number or physical arrangement as the current generation, exemplified by the OptiLoad or Janus calenders. Both SAPPI's Skowhegan, ME, and Muskegon, MI, mills employed this technology. Exact details on the calenders' setup are unavailable.
Other developments in calendering include further application of the “shoe” or “nip” calender. Metso now has two installations running at its Korsnas, Sweden, mill, with the original installation now joined by a second unit on the No. 4 paper machine. The company has also delivered on two confidential orders, notes Metso's Tuomisto.
While installations are currently limited to four operational units, the company knows of other possible shoe-calendering applications. “On high-quality board, such as coated SBS, we think shoe calendering makes sense before coating. On less-demanding grades, such as uncoated, it could be used as a final calender. It could also be used to replace the Yankee on boxboard machines,” explains Mikko Tani, Metso's product manager, calendering.
Soft calendering and multiroll calendering didn't really develop until polymer roll covers were designed. Polymer covers can withstand temperatures up to 200ÞC and loads up to 400 kN/m. All three major roll-cover producers — Metso, Voith and Stowe Woodward — are reportedly working on the development of more durable covers that keep machines up and running. The business continues to be highly competitive, with many mills shopping around and switching suppliers.
There are ongoing efforts to find roll-cover material that can supply the longest life at extreme operating temperatures. “We've developed a new cover named Ivory that has enhanced durability,” notes Scott Bowman, composite product manager with Stowe Woodward (Westborough, MA). “It's a new type of enhanced composite material.” Composite roll covers essentially consist of a polyurethane matrix or glue that is reinforced with fiber and/or particulate. Manufacturers continue their search for the best combination of materials for improved durability.
Rebuilds and retrofits of existing supercalenders continue to attract interest, as well as online applications for multiroll calendering. Metso is rebuilding three supercalenders with its multiroll technology at St. Marys Paper Ltd. (Sault Ste. Marie, ON). It also has completed work at Mead Paper's Escanaba, MI, plant and has started up two offline OptiLoad units at a mill in Wisconsin on release papers (one a rebuild and one a new unit).
In addition to improved cover performance and continued growth in online applications, key advances in calendering technology center on roll developments.
“Caliper control is another major development,” notes Voith's Martin. “CD caliper control using internal pistons has come a long way, with an increased number of zones across the role for caliper control. Pistons can be bundled together for control in a specific area, with the advantage of instantaneous hydraulic pressure control, compared to using heat to adjust the roll and, in turn, affecting sheet caliper.”
(# of rolls)
|Great Northern Paper||Millinocket, ME||320||SC||10||2001||Valmet|
|Madison Paper||Alsip, IL||244||LWC||8||2001/2002||Voith|
|Pacifica Papers||Port Alberni, BC||328||LWC||two 2-roll
|Stora Forest||Port Hawkesbury, NS||400||SCA||offline||1998||Voith|
|Irving||St. John, NB||346||SCB||6||1999||Valmet|
|Alliance||Dolbeau, PQ||248||SCB||two 2-roll||1999||Voith|
|1 Not all units listed. All are online unless specified|