Solid Bleached Sulfate Board Bending Stiffness Evaluation Methods
SBS bending stiffness scales with the third power of caliper and dictates carton bulking resistance, requiring verification via ISO 2493 load-cell testing.
Outer Ply Compression
Structural Resistance
Physical load capacity determines the limit of vertical force a substrate withstands before surface collapse occurs during high speed converting or palletized storage. Outer ply compression measures the force required to buckle the exterior layer of a corrugated board structure when subjected to flat crush conditions. Engineers use this metric to specify board grades for automated packaging lines where vertical stacking imposes consistent force on the bottom container.
Loading Mechanics
High stress concentrations develop at the nip points of converting machinery where rollers apply force across the width of the sheet. Variations in the moisture content of the liners change the bonding strength between the fibre network and the adhesive, which directly alters the force required to induce failure. Dense coatings applied to the exterior surface modify the stiffness of the outer sheet and force the underlying fluting to support a higher proportion of the total load.
Uniformity in the forming section of the board machine dictates the consistency of this property across the entire run of production.
Analytical Boundary
Laboratory testing for this property uses a circular platen to compress a small sample of board at a controlled rate until the peak force registers on the load cell. Equipment settings follow standard force application protocols to ensure the results compare accurately across different board mills. Technicians define the boundary of this measure at the moment the outer liner begins to show localized micro-buckling or separation from the corrugated medium.
Values derived from these tests remain valid only for the specific moisture and temperature environment recorded during the trial. Structural failure of the outer liner precedes the total collapse of the combined board structure under steady compressive loads.