Excessive hydraulic pressure within the press nip damages the web structure by over-draining water, resulting in sheet crushing.
Inspect the felt tensioning and felt guiding devices.
Wash or replace dirty, clogged press felts; check felt design and wear conditions.
Check for blockages in felt Uhle boxes and/or raise vacuum level.
Test pulp freeness; lower beating degree or adjust fiber furnish to improve freeness.
Reduce press nip load to prevent rewetting between nips; inspect shower water and clean clogged spray nozzles.
Consider revising the felt design or lowering machine speed to extend dwell time in the press section.
Clean or replace suction press rolls; inspect Uhle box seals for air leakage; check pulp buildup on press roll surfaces, which may trigger crushing.
Verify camber and crown curvature of press rolls; replace rolls if necessary.
Excessively hard roll covers can cause sheet crushing.
Likewise, check vacuum level of suction press rolls.
Check and adjust load distribution evenly across the press felts from front to back side.
Check if pulp temperature is too low.
Inspect the operating status of felt shower water and avoid over-spraying; reduce water pressure if required.
Poor beating control, unstable basis weight or fluctuating ash retention may also lead to sheet crushing defects.
