Optimizing Chemi-Thermomechanical Pulp Core Fractions for Lightweight Board
Balancing middle ply mechanical pulp freeness preserves sheet caliper and bending resistance while controlling delamination under high-speed scoring.
Couch Vacuum Level
Dewatering Force
Operational parameter representing the pressure differential applied across the paper web at the wet end of a paper machine to remove water. A precise couch vacuum level ensures that the sheet reaches the correct dryness before it transfers to the press section. Applied pressure helps compact the fiber mat and increases the initial wet web strength.
Drainage Efficiency
Suction boxes located under the forming wire utilize air pressure to pull moisture from the slurry. Adjusting the couch vacuum level allows operators to control the solids content of the paper as it leaves the forming section. High vacuum settings can lead to wire marking or excessive drag on the machine drive.
Conversely, low levels result in a sheet that is too wet to support its own weight during the transfer to the first press nip. Maintaining a stable airflow prevents fluctuations in the moisture profile of the finished board. Proper seal strips must be maintained to avoid air leakage which would compromise the efficiency of the pump system.
Production Constraint
Fiber orientation and drainage speed dictate the maximum effective pressure. The couch vacuum level reaches a point of diminishing returns where additional suction fails to remove more water. Excessive vacuum at this stage can also pull fine particles through the wire into the white water system.