Paper360 - November/December 2012 - (Page 24)

TISSUE CLOTHING AND COVERS New Tissue Fabric, Felt, and Roll Cover Technology Improved products help tissue machines run faster, with better quality and reduced energy OLIVER BAUMANN, STEPHAN ERNST, ARTHUR BULLERWELL, CHRISTIAN KUBERL, GARY KILBOURNE, and STEVE COLE MILL WISE O n modern tissue machines, the barrier to increased production and improved sheet quality is often the forming zone; its ability to rapidly drain water while simultaneously controlling fiber orientation and fiber distribution in the tissue sheet, can dictate the amount and quality of tons produced. A critical component of the tissue forming zone is the forming fabric which has three major requirements: High fiber support (FSI) and uniform Cross Machine Direction (CMD) oriented paper side. Very low basis weights and higher operating speeds require high fiber retention, uniform fiber distribution and improved sheet transfer. To achieve these objectives, the forming fabric surface must have a fine CMD oriented surface to support—and form—the mainly MD-oriented fibers. Straight-through drainage for rapid water removal and no water carry. As production rates increase, drainage times decrease. The sheet side of the forming fabric should determine the amount and the orientation of drainage resistance, while the machine side should be open to allow water to exit easily during sheet formation, and to minimize shower water flow resistance on the return run. Structural stability and wear resistance. Although the paper side of a tissue forming fabric contributes to the structural stability, the machine side of the fabric is primarily responsible for fabric stability and useful life. The goal is to deliver the abovementioned properties, while increasing the forming fabric’s economic life. Forming fabric design must balance the need for fiber retention, drainage and life which inspired Xerium developers to create Formsoft, a new concept tissue forming fabric specifically engineered to provide high-speed drainage over a short forming length, while retaining exceptionally high fiber support. It features a symmetrically woven design that ensures dimensional stability and uniformity for the life of the fabric. The top side improves tensile strength, formation and hand feel, while the bottom structure provides extended life capacity (Figure 1). Compared to existing triple layer designs, Formsoft provides significantly higher FSI (+6 percent @ the same Perm), and up to 10 percent lower fabric caliper. It also provides measurable improvements in production rates, CD basis weight profile, tensile strength (MD and CMD), soft ness, and formation. After installation, one customer reported a savings of $320,000. TISSUE FELT TECHNOLOGY Due to the rapid adoption of Crescent-former machines in recent years (where the tissue sheet is formed between the forming fabric and the tissue felt), demands on tissue felt technology have increased significantly. Modern tissue felts require very high fiber anchorage with uniform surface characteristics. In addition, the modern tissue felt can play an enormous role in overall machine productivity and energy consumption. Impact TS (Figure 2) meets the demands of the latest machine concepts by utilizing a highly hydrophilic yarn technology providing immediate felt saturation. In order to reach maximum dewatering performance in “flow controlled” tissue press nips, it is necessary to reach full saturation in the press zone such that the water flow from the tissue sheet flows through the felt to the open void volume in the press roll cover. The heart of the tissue machine is the suction press (Figure 3) where machine performance is crucial. Low-vacuum suction zones in the suction press before the highvacuum press zones, are required in order to introduce a proper sheet transfer to the press nip between the Yankee and suction press roll. A so-called “pre dewatering” in that suction zone is beneficial but can also be a downside if too much water is removed Figure 1. Formsoft’s symmetrically woven design ensures dimensional stability and uniformity. Figure 2. Impact TS utilizes a highly hydrophilic yarn technology providing immediate felt saturation. 24 Paper360º NOVEMBER/DECEMBER 2012

Table of Contents for the Digital Edition of Paper360 - November/December 2012

Over the Wire
Achieving Zero Landfill of Fiber
Creating a Monument to Safety
Keeping the Paper Flowing
Transforming an Industry
Supporting the Community
David Paterson Takes the Reins at Verso
New Tissue Fabric, Felt, and Roll Cover Technology
Protecting Your Mill Against Cyber Threats
Association News
TAPPISafe Takes a Page from Other Industries
Paper360° Online Exclusives

Paper360 - November/December 2012