Equipment & Systems
FOCUS: High tech in paper machine clothing
While the results of the proliferation of the Internet, communications and modern control systems is obvious from the business cycle and production processes point of view, the application of advanced...
February 1, 2002 By Pulp & Paper Canada
While the results of the proliferation of the Internet, communications and modern control systems is obvious from the business cycle and production processes point of view, the application of advanced computer simulation and modeling techniques in conjunction with advanced fabrics are pivotal components allowing the state-of-the-art cloth design to be custom-tailored to the given application and the particular client installation.
We have contacted a few leading PMC suppliers to get their “inside” view and to find out how current technology was used to satisfy and advance the higher performance requirements for their products.
Specifically: How is high tech impacting the development of machine clothing fabrics and helping companies fulfill the ever-changing operating parameters?
Today, when one speaks of “high-tech”, the usual connotation involves new communication and information systems that are now available, since like to any other industry, the speed of communication in a global market is critically important.
However, the vital examples of “high-tech” that are used to keep pace with the ever-increasing demands of the papermaker for higher speeds and more efficient operation concentrate in the development of today’s forming, pressing, and dryer clothing. This process is aided in large part by sophisticated modeling programs such as Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA). These programs simulate the separation processes performed by the clothing, as well as the stresses encountered in performance. Aerodynamic modeling of dryer fabrics is used to optimize sheet-handling behavior for high speed machines.
Advanced measurement and sensor technologies provide greater knowledge about the paper sheet /clothing surface interface. Today, the uniformity of applied pressure transmitted through a press fabric can be measured in dimensions smaller than a pulp fiber, thus providing new design targets for optimized dewatering. In addition, these technologies are used in the scanning and measurement of the fabrics during manufacture to assure uniformity at the macro-level.
New developments in polymeric materials used as filaments and films in PMC are now available that provide greatly increased levels of chemical, thermal and mechanical stress resistance. This results in more consistent performance of the clothing over time.
Ever increasing machine speeds can decrease clothing life over the same number of machine cycles. Correspondingly, water drainage rates must increase in the forming and press sections, while drying rates must increase in the dryer section.
Accommodating greater drainage in the former with good retention of fines and fillers while minimizing wire mark requires utilization of finer mesh fabrics with smaller diameter yarns in the papermaking surface. Clothing suppliers are responding to this challenge by developing triple layer fabrics that pair a fine mesh top layer for papermaking with a coarse and durable bottom layer to fulfill mechanical stability requirements and enhance fabric life.
However, with fine mesh yarn diameters approaching 0.1mm, the result is yarn not much larger than a coarse press felt batt fiber (approximately 0.08mm). Revolutionary intrinsic binder triple layer fabric designs have been developed to facilitate the use of these smaller yarns. Yarn suppliers are utilizing state-of-the-art processing and blending technology to produce the small yarns, while maintaining extraordinarily demanding dimensional tolerances. Weaving loom and automatic seaming machine builders have been hard at work to develop faster equipment capable of handling the small yarns and finer meshes.
In the press section, shaped batt fibers as well as improvements by suppliers in yarn toughness have helped combat the accelerated wear and compaction caused by increased speeds. Additionally, revolutionary multi-axial base cloth laminating technology has permitted the development of compaction resistant base fabric designs that were not possible with conventional endless woven designs.
Dryer section drying rates can be improved by increasing section temperatures and fabric tension. Yarn suppliers have developed mid and high temperature yarns. Clothing suppliers have developed specialized designs that can economically employ these yarns and at the same time withstand higher operating tensions. To take full advantage of very high temperature technology, such as high intensity drying, a move away from thermoplastic polymers will be necessary.
Clothing suppliers will continue to expand use of nontraditional materials, such as non-wovens, to develop engineered structures better suited to meet performance demands of modern high speed paper machines. Without the innovations in filaments, the investment in advanced clothing manufacturing processes, unique new clothing designs, and the incorporation of a broad array of new material components, the papermaker’s quest for increased paper machine operating rates would be stymied.
High tech impacts on the development of machine clothing concentrate in two areas: facilitating the paper machine speed increases and controlling the cloth production process to yield the desirable results and consistently high quality products.
Speed increases are for the most part inevitable and desirable with increased volume, although not always increased quality in the final product. To cope with the additional stresses and demands on a wire or fabric running at higher speeds it is necessary to work very closely with wire and yarn suppliers. Manufacturing of high tech products, with specific chemical and mechanical characteristics, requires applying the custom solutions to fit the particular application: “one size, or design, does not fit all”. These high tech wires and yarns are the major factors in the ability of the woven product to run at high speed.
National Wire Fabric incorporates the high tech products and custom weaves and finishes them to the customers needs for each specific application. The advanced production controls systems are applied throughout the manufacturing process, in particular in the finishing area where computer controlled heat setting, stretching and seaming is critical to maintain high quality and high throughput production. The further application of the high tech cameras, flow and support tests to ensures this custom fit requirement of the finished product.
With access to pilot machines located on three continents and more than a century of paper-making experience, Voith Fabrics applies its broad knowledge base to the development of new materials and production methods that anticipate and solve tomorrow’s problems. This includes leading-edge work in composite technology, innovative weave designs in both monofilament and batt fibre developments.
Technically-advanced paper machine clothing is an essential part of the future development of paper machines. Voith Fabrics works closely with Voith Paper developing forming, press, and dryer fabrics for current and the new generation of paper machines.
As technological advances are made in materials, Voith Fabrics updates its manufacturing methods. Some improvements have been accomplished in co-operation with equipment manufactures and some have been done in-house. Examples are: Hindle looms, auto seaming machines, spiral forming and joining machines, gripper shuttle designs, resin coating machines, application methods for edge sealants, automatic pirn changing equipment, pneumatic picking.
Voith Fabrics manufactures a complete product range of forming fabrics for the pulp and paper industry spanning from single-layer to complex composite designs.
New technology products include:
Spectra composite fabrics
Flow control membrane
Non-woven base cloths
Trilobal sheet side fabrics
Micromesh sheet side fabrics
Voith Fabrics maintains that its quest for ever higher paper quality and machine efficiency is continuous and that the products are consistently improving paper
machine runnability and speed while enhancing sheet properties.
Forming fabrics and their correct application are a key element of the papermaking process. In addition to satisfying the basic requirements, the ability to optimize forming fabric design has been shown to give the papermaker added value both in terms of increased productivity and improved quality.
Over the years there have been a number of attempts to simulate sheet formation and the effect of fabric topography on marking. Results have shown limited success due to a combination of lack of computing power, the two-dimensional nature of the models and limited input variables.
FibreStar and CyberFab are two revolutionary modern computer simulation programs bringing virtual reality environment to Forming Fabric design, manufacture and application. Both applications are a result of an ongoing project between Weavexx/Huyck, Ecole Francaise de Papeterie et des Industries Graphiques (EFPG), and Centre Technique du Papier (CTP) which brings together considerable theoretical knowledge and practical experiences gained over many years.
The programs are utilized to troubleshoot paper machines and to design and apply the proper fabrics and felts. The ability to simulate papermaking conditions, whilst applying different forming fabric structures, offers both fabric supplier and papermaker a unique opportunity to better understand and assess the impact on drainage, sheet formation and ultimately paper quality.
Simulations performed on a virtual sheet to vary forming conditions to evaluate the effects on sheet properties allow further optimization of the virtual papermaking conditions.
In order to quantify the effect of forming fabric design on the virtual paper properties generated by FibreStar the first step is to construct a model of the fabric in terms of weave pattern, yarn diameters and mesh count. CyberFab software generates a meticulous mathematical model for that specific purpose with outputs including calculation of FSI, open area, void volume, caliper, CdF, wear factor, hole size and orientation at levels throughout the fabric structure. The software can simulate single layer to triple layer designs. An important additional feature of CyberFab is its ability to include consideration of plane difference (burial) on both the paper and machine side. The simulation can then evaluate the impact of the fabric design on sheet surface qualities. Consequently, the effect of forming fabric structures on wiremark and therefore calendering and printability can be studied, and fabric application optimized. Benefits of the this technology include:
Improved understanding of forming fabric application resulting in increased chance of success. Risk of change and loss of production time is reduced as paper machine conditions can be adjusted ‘virtually’ and evaluated so that actual changes are made with minimum risk of disruption to valuable production time.
The ability to apply fabrics that add value to operation by focusing on improving quality, productivity and cost reduction.
The speed of development of new and innovative designs is enhanced as theoretical designs can be evaluated more efficiently without the time consuming process of trial weaving and process development and then can be fast tracked to field trial.
Information in this article has been provided by Ken Pulver (vice president, corporate communications, Albany International), Daniel Perron (product manager, Albany International), Graham Jackson (vice president, AstenJohnson), Mike Maguire (president, National Wire), Steve Cole (director of product management, Weavexx), Paul Keen (European product manager-Huyck) and the company websites.
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