Optimizing Score Line Geometry for Low-Fibre-Length Recycled Substrates
Low-fibre recycled board requires widening female matrix channels to 1.8 times caliper and reducing penetration depth to prevent top-liner rupture.
Bending Moment ISO 2493
Standard Metric
Paperboard stiffness evaluation relies on standardized force measurements over a specified deflecting arc and free span distance. The protocol governing bending moment ISO 2493 defines the torque required to deflect a rectangular test specimen through a designated angle of 15 degrees at a nominal free length of 10 millimetres or 50 millimetres. This empirical torque value characterizes the flexural rigidity of paperboard and solid fibreboard substrates under controlled laboratory atmospheres.
It governs material specifications for cartonboard grades destined for automated packaging operations. The boundary of this standard excludes corrugated board structures exceeding specific thickness limits where shear deformation dominates flexural behavior.
Testing Mechanism
Testing equipment clamps a prepared specimen at one end while applying a perpendicular force at a defined bending length. In bending moment ISO 2493, the load cell measures the force required to reach the target angular deflection, expressing the resulting resistance in millinewton metres. High-speed carton lines require consistent board resistance to prevent creasing failure or panel bulging during carton erection and glue flap tucking.
Machine direction orientation yields substantially higher resistance values than cross direction orientation due to the alignment of cellulose fibres during web formation on the paper machine. Variations in humidity alter the moisture equilibrium of the board, weakening hydrogen bonding within the fibre matrix and reducing resistance readings. Converting plants set incoming board tolerances against these values to ensure blank feeder stability and proper crease formation during high-speed folding operations.
Converting Limit
Deflections beyond the elastic limit induce permanent fiber rupture along the outer face of the board specimen. Measuring bending moment ISO 2493 past the initial yielding point alters the deformation mechanism from elastic bending to progressive failure. Creasing lines engineered into folding boxboard modify local flexural stiffness, requiring distinct test procedures for creased board samples.