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What paper machine clothing issues are currently of concern to papermakers? Pulp & Paper asked a group of papermakers to submit anonymous questions that they would like answered by clothing suppliers. These papermakers came from mills producing a variety of grades, including uncoated freesheet, specialty papers, and linerboard-both recycled and kraft.
The majority of submitted questions were about clothing design as it relates to press technology, clothing life and materials, dryer technology, and other factors. However, in this era of supplier consolidation and low product prices combined with cost cutting efforts at mills, many questions related to service and pricing. The following questions, with answers, are a sample of those submitted by the papermakers, while the sidebar on pg. 58 lists additional questions. For the complete Q&A, visit www.paperloop.com and follow the pg. 58 sidebar instructions.
Two fine paper machines have been announced that will start up with or rebuild to a single shoe press. What kind of felt designs will it take for success?
The evolution in press section design to the single shoe press concept is, in many ways, a natural progression based on the success of the existing shoe press configurations. The advances in technology and fundamental knowledge, both in belt design and press fabric design, which have accompanied the growth and success of shoe presses will have to be optimized on the single shoe configurations.
Shoe press fabrics demand special considerations in terms of maintaining the proper void volume, flow resistance, and pressure uniformity. Recognition of the sensitivity of these properties to the success of shoe presses led to the development of Albany's PressPrint product line. The steady-state behavior of these fabrics will be key to a smooth operation and the operation philosophy of the press will have to take this into account.
The potential loss of efficiency for running clothing beyond optimum life will be greater with only one press. The total void volume of the fabrics will have to be engineered to not only handle the large volume of water throughout life, but to also account for an unequal split from top to bottom. The reliance on the press fabrics for sheet smoothness and two-sidedness will demand excellent pressure uniformity in the fabrics. The ability to maintain a uniform cross machine direction profile, both through fabric cleaning and uniform pressing, will be highlighted in this configuration. The fabrics must have good conditioning properties to reduce the tendency for streaks.
In the past, some of these fabric properties have been achieved with laminated monofilament designs. However, the demands of shoe presses and, in particular, single shoe press configurations, are better met with multiaxial laminated technology. The multiaxial technology allows high mesh count constructions to be used without limiting water flow. This construction eliminates the loss in void volume due to nesting of yarns that occurs with standard laminated designs. The result is the better steady-state behavior necessary for these new applications. This technology, along with processes for improved sheet finish, have made the PressPrint product line successful.
-Bill Maddock, technology specialist, high speed publication grades, U.S. press fabrics, Albany International
Without the benefit of consecutive pressing, these presses will require press fabrics that offer non-compromising pressure uniformity. Fortunately, the relatively low peak pressures and water flow velocity will allow us to apply very smooth and dense fabrics. Flat fiber technology is perfectly suited for this purpose. Press fabric uniformity will also be very critical. Suppliers who have invested in new manufacturing equipment while focusing on quality improvement will have a distinct advantage in this area.
-Daniel Hedou, press product business leader, AstenJohnson
Pin seamed forming fabrics have been run with varying success on relatively slow, narrow knockdown fourdriniers producing kraft paper grades. These fabrics are comparable in construction to the base cloth in a pin seamed press felt in that the seam is formed on the weaving loom, and, generally, the material used is polyamide (nylon). There are major limitations to the application of these fabrics due to the instability of polyamide versus polyester.
-Jim Taylor, executive v.p., sales and marketing, Cristini, North America
We strongly believe that our newest felt designs, the Ecostar felts, will be the designs that are successful in single shoe press sections. These felts are laminated felts. The construction has a very fine base fabric on the paper side, whereas the type of the base fabric underneath can be selected based on the needs of each individual position and machine. There are no woven knuckles in the paper side surface and the contact area of the base fabric surface is 10% to 20% higher than the contact area of other existing base fabric surfaces.
A good example of the life potential for Ecostar felts is the case of a shoe press position in a demanding kraft paper machine where earlier felt designs ran only 30 to 35 days before they needed changing. With the first Ecostar felt trial, the customer ran for 105 days without any problems and the felt was still in very good shape when removed, with high openness and low impurities. So far, there have been 45 deliveries of Ecostar press felts for shoe press positions.
-Jukka Lehto, product mgr., press felts, Tamfelt
The impact of an individual press felt on the runnability of the press section becomes more evident as press sections are being developed with fewer nips and fewer press felts. The single shoe press is a great example of this. On today's machines, a press felt that is not performing optimally may be covered up by the next press nip. On the single shoe press, there are no other presses to overcome the deficiencies of a press felt that is not performing due to age or design.
The press felts for these types of presses need to work as a system with the shoe press sleeve. This system has to have the proper void volume capacity for the grade of paper being made and the resulting amount of water being removed. This system has to optimize water removal up and down in order to control sheet properties. The uniformity of the press felt (batt structure and base structure) is critical, since dwell time has increased. The felt uniformity has a major impact on pressure uniformity in the nip, as well as sheet handling into and out of the press.
At Voith Fabrics, we have a strategic partnership with Voith Paper that allows us to develop press felt and sleeve technologies for the new press sections as those sections are being designed, rather than after the design is complete.
-Tony Relich,design mgr.,press fabrics, Voith Fabrics
The single shoe press section incorporates characteristics of the shoe press and the roll press. While the nip impulse is significantly increased, peak pressures can approach levels similar to a conventional roll press. High water loads, not typical of printing and writing grade shoe presses, significantly add to the demands of press fabrics. The press fabric must optimize water load for desired life, prevent rewet, and provide nip dewatering and pressure uniformity.
-Steve Cole, dir. of marketing and product management, Weavexx
We have two separate machines that typically run the same pulp to make different groundwood grades, both closely related in specifications. There is one correlation that seems very similar and that it is the clothing for each machine. However, one machine has a clothing cost per ton of $2.00 and the other of $10.00. How can clothing suppliers offer expertise toward addressing such a cost disparity?
Clothing cost per ton has to be one of the most confusing measures of overall machine profitability ever introduced. If one machine runs all clothing for six months but averages 24 breaks a day after the first month, they will win the cost per ton game but lose the profit game. With clothing accounting for an industry average of less than 5% of total paper manufacturing costs, machine uptime has a much larger impact on overall profitability. Several factors would have to be considered to make an analysis of the situation in the example. However, if machine efficiencies were similar, then the answers might be found in operator training and preventive maintenance procedures, as a high percentage of clothing on some machines is removed due to damage.
-Thomas H. Curry, v.p., sales and marketing U.S., Albany International
Two possible reasons can explain this cost disparity: high usage of clothing or significant difference in productivity. In both cases, a paper machine clothing supplier can help. The first step would be to investigate the reason(s) for the excessive usage of clothing. This investigation should focus on the study of stationary equipment surfaces (for wear related issues), returned fabric analysis (for wear and filling related issues), or just plain housekeeping issues (for damaged fabrics).
Some clothing suppliers are still staffed with skilled technical and practical personnel who can help improve a paper machine's performance. Those services vary from basic tools to close a mass balance around sections of the paper machine (gamma gauge, wet and dry, steam and condensate survey, etc.) to more elaborate diagnostic services (machine direction variability study, infrared thermography, etc.). Furthermore, clothing suppliers are still offering the services of experienced papermakers to help with the operation of any paper machine on any grades.
-Jeff Landry, forming product business leader, AstenJohnson
The whole clothing performance has to be analyzed in detail. It is important to get detailed feedback on the performance of the clothing on each position. The data has to be analyzed and compared with similar machines to make a development proposal.
-Martti Heinola, product group mgr., forming fabrics, Tamfelt
In reality, clothing cost control is a component of the bigger issue of optimizing the overall performance of the machine to insure a maximum return on fixed and working capital. As with any pulp and paper process, machine optimization is complex and requires in-depth and long-term investigation resulting in a series of process and cost improvement projects.
Voith Fabrics has a process for evaluating paper machine performance called Machine Economic Analysis (MEA). If implemented properly, this process-in conjunction with extensive technical data-makes it possible to thoroughly evaluate paper machine performance and make quantitative recommendations for improvement.
-Andy Lilburn, paper machine productivity analyst, Voith Fabrics
Our continuous improvement program offers expertise toward addressing clothing cost disparity. By teaming with mills, we can identify key performance indicators and compare them to industry benchmarks. From there, data is tracked and evaluated to flush out machine inconsistencies. The team can then address each key performance indicator independently and collectively until the objectives are met.
-Steve Cole, dir. of marketing and product management, Weavexx
The new Valmet OptiPress design often calls for a non-permeable "belt" in the second bottom position. What type of "belt" is used there and what could the future hold for such belts?
Transbelt consists of a woven base coated with a non-porous and durable multi-component polymer. The sheet is typically transferred on the surface of the belt through the nip of the shoe press in the OptiPress. Then, it is delivered to the first dryer section fabric. The Transbelt allows completely closed draws between the press and the dryer sections, which is crucial for allowing machines to run at high speeds. The surface of the this belt gives smooth support to the sheet, which can improve smoothness and micro-roughness. The impermeable surface of the Transbelt also prevents any rewetting in the nip, giving higher sheet dryness and ensuring even moisture profile throughout its life.
-Peter Slater, dir. of sales and product application for North and South America, process belts, Albany International
The use of a transfer belt to eliminate the last open draw will likely see greater usage to achieve increased machine speeds or improved sheet bulk. Use of a belt on the bottom position of the last shoe press before the dryer section considerably eliminates the post nip rewet that occurs with a conventional press felt on lighter paper grades. Optimizing sheet pick-up and subsequent release performance will be the critical area for development by clothing suppliers in the near future.
-Graham Jackson, v.p., business leader for advanced products, AstenJohnson
In the new Valmet OptiPress design, the second press is a shoe press. After the shoe press, the paper sheet is in contact with the bottom fabric (transfer belt), which transports it into the dryer section. This sets several demands on the properties of the transfer belt. It must be non-permeable, because it would otherwise cause rewetting after the nip. Also the surface must be very smooth, like on the central roll, for good adhesion. On the other hand, the adhesion must not be too strong, because the transfer belt must release the paper sheet on the dryer section pick-up roll with minimum draw.
Tamfelt's transfer belt is a felt-like product and its surface properties are based on a certain polymer chemistry. It provides better dryness and runnability compared with a normal press felt. The heavier the paper sheet is, the better the dryness is with the transfer belt. Further, machine speeds will increase in the future, meaning that runnability will play an even more important role. We believe that, in the future, there will be more belt-like products replacing felts, especially in press nips with high loads.
-Jukka Kaipila, product group mgr., belts, Tamfelt
The type of belt used is a substrate consisting of a forming, press, or dryer base fabric with a non-permeable top surface. This surface has very specific wear, smoothness, and release characteristics. The belts are used in a variety of applications, transfer of the sheet being just one. Voith Fabrics sees transfer as a small section of the market, used to overcome machine limitations. However, using non-permeable belts with wide-nip presses to affect sheet properties (smoothness) is a major growth area. Belt-press-felt systems is the approach we are pursuing.
-John McEwen, mgr. sleeves/belts, press fabrics, Voith Fabrics
In the OptiPress configuration, the second bottom position transfers the sheet out of the nip to the dryer section in a closed draw arrangement. Rewet from the second bottom position is the limiting factor in being able to realize maximum water removal potential. Conventional press fabric application does not overcome this factor. Studies have shown that the use of non-permeable urethane-impregnated felts, similar to the belts used in the Valmet Transbelt, are able to minimize the rewet factor.
However, non-permeable structures increase the potential for sheet two-sidedness. Future structures for these positions will be derivations of endless and/or seamed products that will blend non-permeable membranes with that of conventional press fabric technology. These structures will minimize the rewet factor without sacrificing sheet two-sidedness.
-Steve Cole, dir. of marketing and product management, Weavexx
| More Q&A on www.paperloop.com
Here are some additional questions from papermakers. To see the answers,visit the "technology and mill operations" area of http://www.paperloop.com and click on "extra edition".
&$149; How do you select a wet felt to balance the upward and downward water removal for optimum smoothness?
• Will suppliers avoid a trend toward charging for advanced diagnostic services?
• Where have seamed wires been a success and what grades and former types might see this in the future?
• Impingement drying is taking many shapes, including designs that go over a top dryer of a single tier, having to dry through the felt. What kind of designs and materials may work best?
• Equipment vendors are offering continuous dryer felt cleaners using water and air. Is there evidence that these units increase or decrease the life of dryer felts?
• Is there any evidence that increasing dryer felt permeabilities on single tier machines significantly improves drying?
• What do you see as the most cutting edge technology/materials being introduced, or have we reached a plateau in clothing design?
• Machine clothing is typically rated according to air permeability, Beran's fiber support index, drainage index, weight, open area, and caliper. Since these do not always predict product performance, do you see a need to better quantify clothing properties and/or a need for suppliers to do more homework using customer furnish in the lab or on pilot machines?
• Do you think paper machine clothing will ever become a "storeroom item" that customers simply order from a catalog?
• With recent mergers between both clothing suppliers and paper companies resulting a few "big players", do you see smaller accounts and specialty applications being neglected?
• With numerous paper machines running specialty grades in numerous quantities, how can a mill reduce its cost for machine clothing by 50%?
• Are there any computer models that can address total machine clothing design for a specific machine, for a specific type of paper, and for different types of fiber?
• Are there any theories relating to clothing on the grooved sleeves of a high-load press, i.e., shape of the groove, etc.?
• Other than nylon, are there any other materials that will improve wear life for forming fabrics?
• What technology is predicted for use in the near future to extend clothing life with no compromise in performance? What would this be for recycled systems?
• With all of the recent supplier consolidation, what is the general trend relative to single-source or multi-source supply?
• When mergers occur, how much product quality is lost or changed by the overtaken supplier?
• I've heard that some mills in Europe are getting 150 to 180 days of wet felt life. Is this true, and, if so, how is it being accomplished? |
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