Machine Clothing: How Can It Get Better?
September 1, 2003 By Pulp & Paper Canada
VOITHWhen vitality follows change”Short-term cost reduction and long-term development of value-added products and services are our challenges,” according to Bob Gallo, who leads the Voith Fabrics team…
When vitality follows change
“Short-term cost reduction and long-term development of value-added products and services are our challenges,” according to Bob Gallo, who leads the Voith Fabrics team for North and South America. “Globalization has changed the fundamentals of our industry and, for those papermakers and suppliers who are willing to think and act in new ways, the potential is great. It all depends on better serving our customers: printers, converters and consumers.”
First step, the basics
Gallo points out that the industry has been successful in the reduction of the specific consumption of clothing relative to the tons of paper and board produced. In many cases, fabric life has increased even when challenged with faster machine speeds, more recycled fibre, higher filler content, heavier press loadings and increased steam pressure.
The paper industry has also been successful in consolidating to improve its financial position by better managing its production capacity, product inventories and leveraging its greater purchasing power to negotiate better pricing from suppliers, typically from a reduced number of vendors.
In addition to strictly managing cost, the focus on improved product quality and consistency, especially when single sourcing is practiced, helps customers manage their clothing inventory. Much importance is being placed on improving fabric application expertise, fabric quality and repeatability because both supplier and customer gain as waste is eliminated. Says Gallo, “Following our successful growth in tissue, we launched business development teams for the graphics and board and packaging segments to improve our external focus on fabric applications for these markets. As part of this initiative, we have a constant dialogue with our customers. We listen to and act upon their input as to how we can provide added value. Our goal is to work closely with our customers so they can satisfy their customers.”
On the product front, the increasing knowledge of papermaking on a nanotechnology level is helping to develop innovative products that will completely redefine paper machine clothing. The use of new weaves, non-woven components, as well as advanced polymer chemistry, is essential to meet the new challenges of the paper industry. These challenges include answering the needs of the customers’ customer: printers, converters and consumers.
Eric Arseneault, a member of Voith Fabrics’ business development team for the press section, says that Voith’s Vector press fabric provides added value. Performance results show that this design enhances printability, saves energy and even reduces fibre requirements. Arseneault comments that solutions usually begin with focus on specific machine problems. He believes that matching a given machine’s requirements with the proper clothing system is the key to success.
Voith has other new products close to launching such as PrintFlex, the second level of a four-stage platform for the press section. “Hassle-free performance during papermaking and fewer problems for printers and converters are our goal,” states Arseneault. Voith Fabrics is also working diligently on new approaches for enhancing forming and dryer products.
Says Gallo, “We are well into the testing process of our new forming fabrics, press fabrics, process belts and sleeves, and dryer fabrics on our pilot paper machines. We have recently invested in new state-of-the-art pilot fabric making equipment, which will accelerate our rate of new fabric development, such as a weaving loom for forming fabrics and TAD fabrics and a pilot needle loom.”
Service with more than a smile
Gallo observes that two other key drivers provide greater value to the paper and board industry — process service and process system innovation. The idea here is that process service is more than the typical support included in the fabric price.
“We have introduced Voith Process Solutions to North America as a fee-for-value-added process service business. We have staffed this team with a collection of experienced papermakers, technical service engineers and product application specialists from Voith Paper, Voith Paper Service and Voith Fabrics,” states Gallo.
In fact, Voith Paper Technology now combines all of the resources of Voith Paper Capital Machinery, Fiber Systems, Finishing Systems, Threading, Automation, Roll Covers, Service and Paper Machine Clothing.
Complete understanding as a competitive edge
Gallo expresses his views of the future in this way, “Innovation of truly value-added paper machine clothing will be achieved when the papermaking process is better understood as a complete process system. With Voith Paper Technology’s fibre-to-finishing resources, we are on our way to achieving this.”
According to Gallo, “We are also investing in our future by creating a VPT Papermaking Process Research Center in Pfullingen, Germany, to further advance our understanding of the process and how we can best optimize system performance for our customers. The product development cycle for clothing includes its testing on one of our pilot machines. This will accelerate our fabric application learning curve and reduce risks for our customers.”
Gallo concludes by saying, “A supplier’s greatest competitive advantage is to first completely understand all of their customer’s needs, and those of its customer, and then to possess the ability to provide value-added solutions by combining technologies. Voith’s increasing ability to view paper machinery and paper machine clothing as a single system is the ticket to the future.”
Press felt technology
In today’s market, 52% of the US press felt business is in seam felts. The conventional seam felt is made up of single monofilament yarns in both the machine direction and the cross-machine direction. The market continues to grow even though seam felts tend to start up very slow due to their high caliper, high void volume, and the rewet that comes from uhle box dewatering.
The Seamexx TX is the first of the next generation in seam felt technology exclusive to Weavexx. The base fabric consists of a special patented duplex TX-weave incorporating both plied and single monofilaments. The design is very stable with a zero gap setting in the seam resulting in a mark-free and abrasion resistant seam.
Among the differences between this product and conventional seam felts are the plied monofilaments in the cross-machine direction and the patented low caliper TX-weave. This combination provides a compressible structure ideal for high nip dewatering to maximize sheet dryness by reducing sheet rewetting. The Seamexx TX combines all of the benefits of a seam felt (easy and quick installation, minimized risk of accidents) with the performance of an endless felt (improved batt anchorage, high nip dewatering, fast start up).
The Seamexx TX is targeted for demanding, abrasion prone positions with high nip dewatering on light to medium weight paper grades (printing and writing grades) where fast start up with nip dewatering is a requirement. It is also ideal for mid-loaded last presses and for tissue.
Papermaking press felts made with the patented Huyperpunch-D technology are producing unprecedented process and quality improvements on today’s most demanding paper machines. Unlike conventional needling, this technology utilizes elliptical beam movement synchronous with the felt during the process while providing for simultaneous angular needling and is now available for seam felts. The resulting improvement in felt surface quality ensures increased sheet smoothness and pressure uniformity while enhancing dryness potential and improved batt anchorage for extending life
The development of new press felt designs has been concentrated on eliminating the “missing dots” and the improvement of the surface. The “missing dots” sometimes result from irregular dewatering of the top and the bottom side of the sheet. More frequently, the poor printing quality can be attributed to mechani
cal markings on the paper surface, resulting from bundles of fibre ends in the press felt.
Two years of research and development resulted in Huyperm, the improved dewatering belt.
The technology combines the advantages of an impermeable transfer belt for high smoothness and stable sheet transfer with the dewatering performance of a high-performance press felt. Polymeric systems proven in the belt technology are condensed in a special cross-linking process to build a monoplane surface with flow-controlled and pressure-resistant dewatering channels. The high wear resistance of the cross-linked surface guarantees constant runnability and dewatering characteristics during a long life. The optimum fibre anchorage of the fibre material in the cross-linked structure guarantees the absolute absence of fibres. The hydrophilic/hydrophobic surface provides the contamination resistance and enables easier conditioning.
Currently, the Huyperm belt has predominantly been installed on last press positions in order to reduce the two-sidedness and to calender the sheet. However, the potential for improved sheet quality is even higher at earlier presses where the moist sheet is significantly more sensitive to marking. It is available in both endless and seamed versions. As the demands on paper quality increase, Weavexx will continue to provide new and innovative technology to meet or surpass those demands.
New forming fabric technology
The paper industry, today more than ever, continues to push for products that will yield quality improvements through cost effective products while trying to maintain, if not to improve, sheet properties. Consequently, speeds are increasing and cycle time for forming fabrics, particularly short fabrics on many gap formers, is decreasing. As paper makers move to triple layer designs for sheet retention, smoothness, and other quality reasons, the need for reduced caliper triple became apparent to address the rapid elimination of water in the short runs. The Huytexx Synergie was created to meet this challenge.
Synergie is a triple layer based on proven Huytexx technology and possesses a fine, plain weave surface with integral SSB (support shute binder) stitching. The plain weave delivers very high fibre support, improved drainage and low caliper and void volume. SSB binding significantly increases the number of binding points, a key feature as it virtually eliminates the risk for delamination.
Plain weave surfaces offer improved surface uniformity through elimination of objectionable twill pattern, and improved fabric surface smoothness. The symmetrical plain weave structure of Huytexx Synergie provides higher fibre support index (FSI) compared with all other fabric designs which results in improved mechanical retention. This means chemical usage can be reduced and sheet quality is improved through reduced flocking and/or better filler retention and significant dollar savings can be achieved as a result.
High FSI also translates into better fabric cleaning and conditioning. With more points of contact on the surface of the fabric, the fibres will staple less into the fabric structure, resulting in easier cleaning through showering. This has been proven in many mills. Additionally, increased FSI can lead to easier sheet release to the pick-up.
The use of large diameter roll-side cross-machine direction yarns in many triple layer designs results in relatively thick products. The added caliper creates a potential for water spray on short loop, high-speed applications as well as a condition favourable for excessive water carry down the Fourdrinier on position with limited vacuum.
Synergie offers low caliper yarns in both MD and CMD mean that caliper and void volume are minimized and are comparable to that of fine duplex. By this means, water carry/spray can be eliminated. Caliper and void volume are lower than all other SSB fabrics.
Synergie offers an avenue to higher permeability at any given fibre support. Combining high CFM with high fibre support, it provides a very high drainage capacity. Moreover, lower caliper can reduce the dewatering dwell time through the fabric, which improves water removal over suction elements, leading to a dryer sheet. This product has proven to give higher couch dryness and reduced water carry, even on demanding high-speed gap formers.
Huytexx Synergie is engineered to provide high fibre support, a smooth surface, superior drainage in a specially woven, thin structure that reduces water carry-back, spray, rewet, and can improve off-couch dryness. Synergie answers today’s machine requirements for runnability, sheet quality and chemical usage, and it provides an avenue for meeting future paper machine requirements.
from Pierre Brune (application specialist-newsprint) and Luc Farly (application specialist-fine papers) with credit Andrew White (application engineer, Huyck Europe).
Engineered to make the grade
Global pressures on the pulp and paper industry are driving paper machine clothing suppliers to provide greater value to their customers. This value is often achieved as a result of new clothing technology, with clearly documented quality enhancements and reduced machine operating costs (lower fibre usage, less chemical usage, speed increases or machine efficiency improvements). AstenJohnson remains strongly committed to research and to development of new technology, not just incremental product development or repackaging of older technology. InTegra, the intrinsic weft triple layer forming fabric, was introduced in 1996 to newsprint applications and quickly followed into fine papers. The flexibility of the unique intrinsic weft concept has allowed its use to be extended across the full paper product range. It has been applied to both positions on all the modern high speed twin wire formers as well as standard Fourdriniers and multiply boxboard and linerboard positions. Its flexibility of design has given the ability to “Engineer to Make the Grade” for individual paper machines, mill or grade specific fibre lengths, and specific end user requirements.
Paper machine efficiency, machine speeds and fabric return run cleanliness have all been positively affected by providing the maximum fibre support to match the individual fibre lengths and, at the same time, design into the fabric the required drainage characteristics to match the requirements of that individual position. Consequently the sheet is formed on top of the fabric and not embedded within the fabric, resulting in high, more uniform drainage and a much easier sheet release.
The intrinsic weft yarns provide not only extra support but also create an integrated top and bottom surface to the fabric. This combination produces a very stable fabric having long life potential due to the increase in wear volume on the machine side. The increased stability has led to improvements in 2 sigma CMD basis weight profiles on grades from tissue to linerboard. It has also resulted in a more uniform, stable return run, particularly noticeable on the very high drag linerboard machines.
The papermaker is under continuing pressure to improve the sheet or linerboard surface to enhance print quality. At the same time, because of the pressure to use recycled materials, he is required to produce lighter basis weights at higher speeds using shorter fibres. The intrinsic weft concept allows for designs to accommodate these challenging requirements.
The key, however, to obtaining the best print quality on any surface is to have a high fines content on or close to the surface to be printed, resulting in a fine, uniform surface allowing for consistent ink absorption which in turn produces high print quality. This is why the top grades of printing are coated or are highly supercalendered with short fibres.
ParaTec, multi-axial press felt technology, first appeared in the early to mid 1990’s and has been developed in endless form for all grades. Multi-axial fabrics address the most important needs of production and improved sheet quality. The key to their success is the unique construction. Multi-
axial fabrics are produced using dense, single-layer base modules that provide optimal transfer of the nip’s pressure. The fabric’s components are angled to one another, preventing structural collapse. The dense mesh, all monofilament modules create a true laminated base structure for the ultimate in void volume retention and pressure uniformity. Multi-axial products are produced without loom edges, which are major contributors to press bounce and vibration. Improved sheet smoothness, higher resistance to collapse/compaction, increased water removal, improved machine performance and longer felt life are some of the benefits being realized on the paper machines.
Only recently has the multi-axial technology been expanded to include a seamed version in the new ParaTec seamed felt. It combines all the benefits of the multi-axial product, as well as all the benefits of seamed products: faster installations, reduced downtime, increased safety factor, less crane time and fewer personnel for installation.
The further enhancement is “thermally fusing” of all layers of batt fibres for maximum fabric and seam flap wear resistance. The result is longer life and more consistent steady-state machine performance. Para-Tec is available in both 2 and 3-layer, with the 3rd layer consisting of AstenJohnson’s unique Stratus membrane technology.
MicroTier — AstenJohnson revolutionized dryer fabrics with flat monofilament yarn in the late 70’s, then again with stacked machine direction yarn technology in the early 90’s. Now MonoTier fabrics are the preferred choice for modern, high-speed dryer sections. However, dryer fabric contamination continues to be a problem on many machines. Once again AstenJohnson leads the way with Smart Surface Technology. Utilizing concepts employed by nature itself, AstenJohnson engineers the MonoTier yarn surface topography to be much more easily cleaned. Results from our Belgium operation, where the technology was developed, have been excellent with over 100 successful field trials in Europe and Asia. The technology is now available in North America as MicroTier. By having an easier-to-clean surface, MicroTier fabrics retain more original porosity, thereby reducing sheet breaks, maintaining better sheet contact and drying, and reducing energy consumption.
Even though these new products represent major technological breakthroughs, the innovation engine never rests while AstenJohnson strives to develop and introduce new added value technology to all stakeholders.
ALBANY INTERNATIONAL – PRESS FABRICS
Sheet printability: porous pressing media
Emphasis on paper quality considerations is an accelerating issue for containerboard and boxboard producers. In an industry focused on balancing supply and demand, many producers are examining all areas of the papermaking process in hopes of garnering a competitive advantage within existing markets or gaining access to other markets. The press section has proved to be fertile ground for utilizing new press fabric technologies developed as a result of the demand for improved pressing uniformity and sheet printability.
Finish vs. function
Attempting to emulate the pressing uniformity of a smooth press roll with any porous structure is no easy task. The undertaking would be a bit less daunting but for the numerous press fabric functions that must be considered for any application, such as per web consolidation/strength, paper web support / transfer, power transmission, pliability, dewatering capability, dimensional stability MD/CD, durability, cleanability and repeatability.
These requirements have presented the press fabric design engineer with the need to balance finish, drainage, and life.
Development of new press fabric materials, manufacturing technologies, and processes has allowed more freedom and latitude for the press fabric design engineer to maximize these properties. Yet one must remember that any press fabric remains a compromise of one or more of these characteristics.
Press fabric component influences
Separating the press fabric into a two-component system of woven base and needled batt revolutionized press fabric design and proved to be a springboard for numerous recent material, process, and technological advancements.
As base fabric structures evolved and demands for further improvements in sheet quality accelerated, the need to consider more than the base component of the press fabric became apparent. With the demand for improved sheet printability as a driving force, design and development engineers have focused on opportunities within three basic areas of press fabric construction considered primary agents of influence on pressing-related sheet smoothness issues: base fabric, batt structure and needling technology.
Base fabric evolution
To keep pace with the demands of increasing speeds, press impulse levels, operating temperatures and a growing overall consciousness of sheet quality, laminated press fabrics were introduced and gained wide acceptance on long nip presses (LNP) and shoe presses by the early 1980s. These structures typically consist of a relatively coarse bottom base, engineered for void volume and load bearing properties, with a finer mesh top base to improve the pressure uniformity in the nip.
A relatively new concept, multiaxial press fabrics were introduced in the mid-1990s. This unique process incorporates “flat” weaving techniques and provides forming fabric quality, sheet support, and uniformity previously unavailable in laminated products using conventionally (endless) woven base fabrics. With yarn systems in four different directions, compaction resistance and openness of the base structure under load are also enhanced. These attributes provide the design engineer with even more latitude to consider finer batt structures to address sheet micro-surface characteristics while maintaining the required fabric cleanability and drainage characteristics.
On the leading edge of development efforts made possible through multiaxial manufacturing techniques is a new class of press fabric utilizing porous polymeric materials. These non-oriented thermoplastics offer outstanding thickness retention when subjected to cyclic compression. The engineered polymeric component includes an array of round holes (apertures) to maximize z-directional flow properties while providing planar land areas between the holes. From a pressure uniformity standpoint, the implications are significant due to the absence of textile weave knuckles and the associated pressure concentrations that impact negatively on sheet topography.
Batt structure influence
Press fabric structures have changed dramatically in just the last decade. While base structure applications for mark critical grades evolved from laminated to multiaxial to those containing porous polymeric components, smoothness and print quality expectations on these grades continued to escalate. In addition, computerized instrumentation developed to detect, analyze, and track surface characteristics that affect print quality has become commonplace.
The importance of considering batt fibre influence on the micro-surface characteristics of today’s highest quality containerboard and boxboard grades has never been clearer. A fundamental issue for improving the micro-surface characteristics of a sheet is minimizing the pressure concentrations caused by the individual batt fibres at the felt-paper interface. Fine denier fibre strength concerns on highly loaded last press positions has led to a resurgent interest in fibres with a flat cross-section.
Two primary issues of concern relating to needling techniques and the effects on surface smoothness and uniformity characteristics are fibre stratification and needle tracking patterns.
Press fabric drainage, cleanability, and life expectations often mandate relatively open (low surface area) batt fibre structures. This is typically accomplished by utilizing coarser fibres and/or reducing the amount of batt fibre in the structure. Neither of these two options is generally conducive
to optimum pressing uniformity on either a macro- or micro-scale. However, processes developed in recent years have greatly improved the ability to produce structures with enhanced batt fibre stratification. These techniques allow the design engineer increased flexibility to use coarser interior and roll-side fibres to maintain openness and cleanability while utilizing finer sheet-side surface deniers relatively free of coarse fibre contamination.
Porous pressing media has evolved dramatically in recent years due, in large part, to ever increasing expectations for sheet smoothness and printability coupled with escalating requirements for greater productivity. Available options in porous pressing media today address sheet smoothness issues from several fronts. Recent developments in base fabric, batt fibre, and needling technology have resulted in significant improvements in smoothness and sheet appearance documented by air leak smoothness tests, stylus profiling measurements, and low angle reflected light photographic analysis. The end result for many paperboard/packaging grade producers has been improved sheet quality, a more saleable product, and the resulting expanded potential customer base.
from Phillip R. Elkins
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