With higher machine speed, through the dryer section liquidity has become an important issue. The transition from double-tier dryer sections to single-felted unirun provided for improved sheet support through the dryer section, allowing higher speeds. However, as machine speeds continue to rise, dryer section runnability issues persist. One major factor is the dryer fabric screen and the amount of air entrained in the boundary layer, and the interaction with entrained air and the machine configuration, especially in the converging nip section of single-felted machines. This has been and continues to be a bottleneck area, and has led to the development of blow box devices to deal with these entrained airflows and ensure sheet stability.

A relatively small number of researchers have reported on air flows over dryer fabric screen. Siquet and Stoppelman carried out air flow measurements on dryer fabric screen in an open jet wind tunnel. Air permeability was identified as being the main factor in determining air carrying, with dryer fabric screen materials playing a secondary role, and surface roughness a distant third. 

Previous work in this field has, for the most part, been limited to air flow measurements over bare fabrics. In reality, the boundary conditions at the paper making fabric surface vary along the fabric run. In a typical dryer run section, the paper making fabric will be uncovered in the return run (between transfer points), otherwise it will be carrying a sheet and tensioned against an impermeable dryer can surface (or turning roll) or supporting a paper web (a largely impermeable surface).

The goal of this work was, therefore, to determine the influence of fabric design and boundary conditions on air flow over dryer fabric screen. This was expanded to include flow measurements along the edge of the dryer fabric screen so as to observe edge effects. 

Anna
Sales Department
Hebei Defeng Polyester Fiber Co., Ltd
Add: Jingjiu Railway west, wugong town, Raoyang County
TEL: 86-311-67699480
FAX: 86-311-67699480
Website: www.china-polyestermesh.com.
E-mail:anna@china-polyestermesh.com

 

Tag: dryer fabric screen, paper making fabric