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Diverse grades demand stringent quality control - Part II

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Diverse grades demand stringent quality control - Part II

March 04, 2012 - 18:01

BRUSSELS, March 5, 2012 (RISI) -Versatility is a word that comes to mind when describing the product portfolio of Port Townsend Paper, a company that managing quality control issues across a diverse range of products. Read Part Ihere.

Profiles dramatically improved

With flat basis weight profiles established the next step was to tackle the moisture profile, which is in many cases the most critical parameter affecting sheet quality. The previous manually-operated steam shower was replaced by a Metso IQSteamPro located on the suction roll of a triple nip press. The suction through the felt provides good sheet penetration, promotes an optimum condensing rate in the sheet and therefore high heat transfer and sheet temperature rise. It is this rise in temperature that provides increased dewatering throughout the press. A response test, as shown in Fig. 1 shows the sheet temperature rise immediately after the profiler and the carry-through effect after the second nip. The sheet temperature rises by more than 20°F to more than 70°F, indicating the high range of profiling capability.

Depending on the actuator opening, the steam profiler raises sheet temperature from over 20°F to over 70°F, promoting good sheet dewatering and profile control

The multi-variable CD control has resulted in a "dramatic improvement " in CD moisture profiles as attested by Harke. Statistics in Fig. 2 indicate that over a two-month period, 2-sigma variability averaged less than 0.5% and that is a significant improvement from before-control numbers. Also, the spread of the data is less, indicating a more consistent product. The precise control by the steam profiler has allowed the mill to to turn off the water spray moisture profling system, thereby avoiding the energy required to remove the extra water.

With control on 100% the 2-sigma variability averaged less than 0.5% over a two-month period. That is a significant improvement from the before-control numbers

Operators give "thumbs up"

Machine operators are never short of words and usually give very forthright evaluations of new products. In this respect, the new QCS, steam profiler and CD controls are an unqualified "thumbs up". Machine tenders Ernie Pelham and Tim Reandeau, who have more than 70 years of combined experience at the Port Townsend mill, are enthusiastic about the new equipment. First, Pelham offers his observations and comments: "Unlike the old one the new steambox adjusts the profile exactly the way you want it. Also, we notice there is no more steam spillage in the machine room." He also notes the new scanner flies across the sheet at about twice the speed according to his estimate, and that is good for control, in his opinion.

Reandeau picks up on the steam spillage issue:"With the old one it seemed like 25% of the steam came out into the room. Now, you hardly know the new one is on. This makes life a lot easier threading the sheet through the press section on a hot summer day," he quips. "This new steam box really impressed me since, with the old one, the actuators were sticking." Now the control is positive and sure.

Regarding CD weight control, Reandeau says, "With the old control worked only on the lightweight grades. After that, it got saw-toothed. Now, it runs well on all grades regardless of weight."

Altogether, the improved control and extra dryness from the press has made a major difference in machine productivity as well as quality. Tim estimates that the production rates of the benchmark 23-lb medium grade has been increased from 38 to 42 tons/hr - slightly better than 10%.

Customers better served

Kevin Wright, general sales manager, has seen a positive impact in how product quality consistency has improved the company's market position. "It's our competitive strength to use the control equipment and our personnel effectively to make our product consistently. It allows us to make product quality transitions more effectively to serve our niche application customers, and that provides us with a more stable market."

Kevin Wright: "Industry standards keep changing and customers are installing faster converting equipment so we must produce better quality paper. We need to do this to keep up with progress in the industry"

"Industry standards keep changing and customers are installing faster converting equipment so we must produce better quality paper. We need to do this to keep up with progress in the industry," he concludes.

Port Townsend Paper at a glance
Port Townsend Paper, located in the Puget Sound, WA, area, produces 220,000 tons/yr of containerboard and specialty kraft papers on the 240-in. trim PM 2. Basis weights of the containerboard grades range between 17 to 35 lb/1,000 ft2 for linerboard and 18 to 33 lb/1,000 ft2 for corrugating medium. Specialty kraft paper basis weights range from 30 to 100 lb/3000 ft2. The machine furnish comprises high yield kraft pulp and 20% to 50% recycled OCC, both produced on-site. The mill's kraft paper is used for a wide variety of end product including paper bags, paper moving pads, gumming kraft for paper tape, paper trash bags, laminated roll wrap for fine paper, poly-coated products for lumber wrap, protective papers for construction and painting, envelopes, raisin trays and padding for industrial packaging.
The mill also produces unbleached kraft pulp on PM 1. The pulp is a blend of northwest long fibers designed for consistently high strengths, bulk and uniformity. The northwest softwood fiber species (Douglas fir, hemlock, red cedar and spruce) enable Port Townsend Paper to manufacture pulp from blends of these species for specific end uses which include kraft sack paper, kraft paper specialties and as enhancing fibers for recycled furnish sheets.

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