Clogged mesh and backing fabrics: the most easily overlooked silent killers.

When clogging occurs on forming fabrics or press felts during papermaking, the immediate reaction is often to blame the pulp (too dirty or high in stickies), excessive filler deposition, the need for a felt replacement, or insufficient cleaning agent dosage. While these are indeed common causes, there is another critical-yet frequently overlooked-variable: the spray water system itself. Normal pressure gauge readings do not guarantee that the fabric is actually clean. Clogged nozzles, misaligned spray angles, improper water temperatures, incomplete coverage, or even high levels of micro-bubbles in the water can severely compromise cleaning efficiency, trapping fabrics and felts in a vicious cycle of progressive clogging. How many of these typical symptoms do you recognize? Continuous decline in forming fabric dewatering capacity and a receding water line; reduced water removal despite constant vacuum box levels; gradually decreasing felt permeability and lower dryness at the press exit; uneven moisture across the sheet and cross-direction moisture fluctuations; a spray system that appears "normal" yet delivers increasingly poor cleaning results; or a situation where performance improves briefly after a fabric or felt change, only to deteriorate again after a few days of operation.

Relying solely on increasing the dosage of cleaning agents often provides only temporary relief; it treats the symptoms rather than the root cause. I. Why does spray water determine the "life or death" of forming fabrics and press felts? During operation, forming fabrics and press felts are in constant contact with pulp, fines, fillers, stickies, resins, sizing agents, and other substances. While some of these materials are discharged with the white water, others remain lodged within the mesh openings and felt pores.
The function of spray water goes far beyond merely "rinsing the surface." It must effectively wash away surface deposits, clear clogged mesh openings and pores, prevent contaminants from being forced into the fabric or felt structure, work in tandem with the vacuum system to remove dislodged debris, and maintain permeability to both water and air. If spray water pressure, flow rate, or coverage is inadequate, contaminants will gradually accumulate. A decrease in effective open area leads to slower dewatering, higher white water concentration, and increased contaminant deposition-ultimately creating a vicious cycle of progressive clogging.