The use of modern press fabrics on a paper machine requires that these fabrics be properly conditioned. Fabric conditioning is done for two main reasons -- runnability and longevity -- as well as for product (paper) consistency. To properly clean a fabric, it is necessary that any dirt, such as fines and fillers contained within the fabric structure and sheet side surface contaminants (stickies, a generic term for pitch, latexes, adhesives and inks), be dislodged from the fabric fibers and structure and removed from the system.
Dislodging these contaminants is normally accomplished by using a high pressure oscillating needle jet shower. The contaminants are removed from the fabric by a uhle/felt suction box. High pressure oscillating showers should be located on the face (sheet side) of the fabric run, near a supporting roll. High pressure showers on the inside are of little to no value and often cause excessive damage because of the excessively high pressure required to penetrate the fabric. High pressure showers are effective in keeping contaminants from adhering to the fabric fibers. The contaminants are easily removed by uhle/felt suction boxes as long as they are suspended in water. High pressure showers slow the process of compaction and restore permeability, requiring the sheet side location and continuous use from the "new fabric" start-up. Lubricating showers are located immediately ahead of the felt suction box on the face side of the fabric.
Correct application and operation of these showers is critical for proper fabric conditioning. Water applied by this shower must be completely even in the cross direction to eliminate marking, both fabric and sheet, and to optimize felt suction box dewatering and subsequent fabric dryness into the press nip.
