Porosity Loss
Mechanical compaction and contaminant deposition reduce the void volume of press fabrics during continuous paper machine operation. Deposits of pitch, microstickies, filler clay and fine fibres lodge inside the woven structure, causing press felt blinding that severely impairs water removal capability. Dewatering capacity drops rapidly as fluid flow channels within the synthetic batt become occluded.
Papermakers monitor vacuum suction pressures across the couch and press boxes to detect early stages of fabric clogging. High hydraulic resistance in the press nip forces water back into the incoming paper web, causing wet end defects. Void fraction loss accelerates when wet strength resins and sizing agents coagulate within the inner woven base fabric.
Operational Effect
Reduced void fraction elevates hydraulic pressure within the nip, inducing sheet crushing and localized web breaks. Dewatering shifts from uniform displacement to forced hydraulic flow, damaging the wet paper structure before entering the dryer section. Steam consumption rises sharply in downstream drying cylinders to compensate for lower sheet dryness exiting the press section.
Production speed reductions become mandatory when thermal drying capacity reaches its upper limit.
Chemical Cleaning
Targeted chemical washing regimes restore fluid permeability by dissolving organic resins and inorganic salts. Acidic showers break down calcium carbonate scales, while alkaline detergent solutions dislodge hydrophobic tackies. Continuous high-pressure water showers operating at 20 to 30 bar remove loose particulate matter during fabric rotation.
Periodic off-line chemical boils extend total fabric service life, maintaining consistent sheet dryness until mechanical wear requires full felt replacement.
