Tensile Threshold
Papermaking physics defines the critical tensile stress limit at which an open, partially dewatered fiber network begins plastic deformation prior to thermal drying. At solids contents between forty and sixty percent, surface tension forces between wet fibers govern structural cohesion. The wet web yield strength determines the maximum web tension a paper machine wet press section can apply without triggering sheet breaks.
Papermakers monitor this value to optimize press draw settings and chemical strength additive additions. The threshold stops holding when sheet solids content increases past sixty percent and inter-fiber hydrogen bonding dominates.
Press Runnability
Sheet breaks in open draws between the press section and dryer section reduce paper machine efficiency. High web speed increases hydrodynamic drag and gravitational forces acting on the unsupported wet sheet. Sufficient wet web yield strength prevents catastrophic tensile failure when the wet paper web peels away from press roll surfaces.
Refined chemical pulp fractions and longer softwood fibers increase wet web cohesion at low solids levels. Chemical additives like cationic starch or wet-end polymers enhance fiber-to-fiber friction in the wet state.
Dewatering Limit
Dewatering efficiency in vacuum suction boxes raises solids content and elevates sheet cohesion. Higher solids content at the first press draw dramatically improves wet web stress resistance.
