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TECHNICAL

Innovative Paper Machine Clothing Improves Machine Efficiency

Bruce Janda, Forming Product Business Leader
AstenJohnson
6480 W. College Ave.
PO Box 8005
Appleton, WI 54912-8005

Jim Heaton, Dryer Product Manager
AstenJohnson

ABSTRACT
This paper describes two approaches to the design of paper machine clothing to create a “smart surface” that can improve machine efficiency by reducing the tendency of contaminants to adhere or improving the cleaning process. The technology employed in both examples is very different. Dryer fabrics produced from micro grooved yarns are described which create a structured surface making cleaning more effective. Forming and TAD fabrics coated with nanotechnology creating yarns with structured surface on a much smaller scale that both improves showering effectiveness and reduces the tendency of water to carry in the interstices of the fabrics. Although the technical approaches are quite different, the principles employed to create a “smart surface” are very similar. They offer the papermaker increased opportunities for improving machine efficiency.

INTRODUCTION
Paper machine clothing performance that helps keep the machine running efficiently adds to the bottom line. Not only must clothing be engineered correctly for the application, it must maintain its design properties over a sufficient lifetime to be cost effective and produce a high quality sheet.

Fabrics are designed and manufactured with optimum openness for the application. With the increased amount of recycled material being used today, the ability of clothing to remain open or clean has become increasingly critical. Machine performance is negatively impacted when fabrics experience plugging or contamination build up. Maintenance of the fabric’s openness is required to achieve product performance and extend useful fabric life. This can be addressed by properly positioned and maintained shower systems as well as by fabric design and material selection.

This paper will discuss two new approaches to fabric design that provide a higher level of effectiveness in maintaining fabric openness. Even though different technologies are applied in forming and dryer sections, the common principle of creating a “Smart Surface” is employed in both to make cleaning and maintenance of the papermaking surface more effective. In some cases the improved fabric cleanability properties can also result in energy savings as well as efficiency.

NANOTECHNOLOGY CREATES A SMART SURFACE
Fibers, stickies, and other contaminants tend to build up on papermaking fabric surfaces and in the interior drainage paths in the forming section. This blocks water drainage through the fabric and creates light spots and pin holes in the sheet. Successful Forming or Through Air Drying, (TAD Tissue and Towel grades), fabric operation requires a significant investment in investment in cleaning systems to keep the fabrics open and running efficiently for maximum productivity at a given energy consumption. The cleaning systems, in turn, consume energy in the form of high pressure showers, as well as vacuum in the case of TAD fabric runs. A yarn surface treatment coating was developed using nanotechnology that creates a tightly bonded hydrophobic and oleophobic “Smart Surface” resulting in opportunities for more efficient machine operation.

Nanotechnology has been defined as manipulation and control of matter at the nano scale with nano being a billionth of a meter . Nanotechnology offers opportunities to create products with unique properties. It has been identified for application to paper and board for improved packaging materials. Fabric materials treated with nanotechnology have been shown to repel liquids, resist wrinkling, and dry fast and breathe. AstenJohnson has been developing a yarn surface treatment called ArmorTec™ that uses a nanochemical coating that is cured onto the fabric. The unique properties of the nano-scale material create a surface tightly bonded to the fabric yarns. The thickness of this coating is only several molecules and, therefore, does not measurably reduce the air permeability of the fabric. The result is a surface that has a very large number of very small contact points. This creates a self-cleaning “Lotus-Leaf” surface effect that is both hydrophobic and oleophobic as the contact angle of the surface is greatly increased. “Water drops on a lotus leaf touch the surface at only a few points, resting on microscopic ‘bumps.’ A slight tilt of the surface enables the water droplets to roll off under their own weight.”

The photos shown below demonstrate this effect. A measured drop of water placed on an uncoated fabric (left) spreads out and wets all the yarns, especially the interstices. The photo on the right shows the result of the same procedure on a coated fabric. The water drop beads up on the surface and does not wet the yarns on the interior of the fabric. However, when a driving pressure like a vacuum box or pressure pulse in the forming zone is applied, the water drop moves completely through the fabric leaving the interior surfaces dry.

Water on uncoated fabric
Water on coated fabric
Water on uncoated fabric Water on coated fabric
The next two photos show a similar result from applying a drop of oil to both a treated and untreated fabric. This oleophobic property presents the opportunity to reduce the propensity of some stickies to attach to the fabric surface.

Oil on uncoated fabric
Oil on coated fabric
Oil on uncoated fabric Oil on coated fabricc

In practice, the fabric coating has been shown to maintain its effectiveness over the fabric's life even as the machine and the sheet side contact areas wear. This is because the overall yarn surface is treated, even in the interior of the fabric where contaminants tend to lodge and excess water is carried. This effect in the interior is not significantly diminished by surface wear on the sheet or machine side planes of the fabric. The coated fabric becomes easier to clean, carry less water, and reduces or eliminates the need for application of additional protective coatings during a run.

TAD TISSUE DYER FABRIC APPLICATIONS
The TAD process produces tissue and toweling with superior softness, bulk and absorbency. However, it is a very energy intensive process subject to recent surges in energy prices. Recent work on the Metso pilot tissue line has shown that 16% of the energy consumed in a Tissue or Towel TAD (Though Air Dryer) section can be attributed to the residual shower water carried back from the fabric cleaning station. Application of smart surface technology represents an opportunity to significantly reduce energy consumption in the TAD section.

Lab scale work was carried out on laboratory dewatering and drying apparatus at the Institute of Paper Science and Technology (IPST) in Atlanta, GA. and Karlstad University in Karlstad Sweden to define the scope of the opportunity. Trials were carried out to simulate the TAD fabric conditioning process to determine the potential for water carrying by the TAD fabric into the molding and drying stage. In addition the molding phase was simulated to determine the residual water carry by the web as well as the TAD fabric. Both conventional and treated fabrics were tested using a standard M weave 44 mesh single layer TAD fabric.

The graph below shows the results of the studies. The application of the coating resulted in reductions in both the water carried by the fabric and the sheet. Energy savings in excess of 10% were indicated by both studies.

Graph

The energy savings were confirmed in a joint pilot study with Metso on their pilot TAD paper machine. Total energy use by TAD 1 and TAD 2 was reduced by 4.1% for toweling grade runs and 5.6 % for the tissue runs . At current North American industrial natural gas prices, these results represent potential savings of over $500,000 per year on a 200 inch wide TAD machine.

Commercial trials of coated TADS fabrics have yielded similar results. Energy savings of this magnitude are very significant, but difficult to measure in day to day practice as grade schedules change. A North American TAD machine overcame this by alternating coated and uncoated fabrics, measuring energy consumption per day over the life of the individual fabrics. Repeating the trial runs resulted in an average energy savings of 6% for the coated fabrics over their approximately 80 day fabric life. Results at other sites include reduced downtime for batch washing of TAD fabrics as well as reduction in conditioning shower water fibre solids.

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