Wave Corrugation
Central undulating paper layers bonded between flat facing liners form the internal arch matrix of corrugated board structures. The application of fluting media creates structural separation between facing liners to maximize bending stiffness and shock absorption. High heat, steam, and pressure soften starch bonds and fiber networks as the paper passes through heated corrugating rolls.
Semi-chemical hardwood pulps yield superior crush resistance due to high residual lignin content. Neutral sulfite semi-chemical pulps or recycled old corrugated container fibers supply the bulk of raw material for this application. The term does not apply to flat linerboard facings or solid uncorrugated folding boxboard.
Forming Mechanism
Steam showers precondition the sheet to increase fiber elasticity before profile formation. Heated corrugating rolls press the paper sheet into specific flute geometries ranging from coarse A-flute to ultra-thin microflutes. Starch adhesive applied to the flute tips bonds fluting media to the single-facer linerboard.
Speed matching between corrugating rolls and paper web tension prevents web breaks.
Crush Threshold
Flat crush resistance depends directly on the stiffness of internal wave arches under perpendicular loads. Measuring fluting media with concora medium testing evaluates crush strength prior to corrugator converting. Low ring crush resistance in raw fluting stock leads to crushed flutes during board combining and reduced box stacking strength.
Moisture absorption weakens hydrogen bonds between fibers, lowering flat crush resistance in humid storage environments. Starch addition at the wet end of the paper machine raises structural stiffness in recycled fluting media.
