Grammage Distribution
Structural distribution of dry fibre mass across the individual plies of a multi-ply paperboard represents a primary design method for maximizing sheet bending stiffness per unit of total material used. Through basis weight allocation, mill operators assign specific grammage targets to each headbox in a multi-ply forming section. This process optimizes the distribution to place dense refined softwood fibres in the outer liners and bulky mechanical fibres in the core.
The balance directly determines the caliper and compression resistance of the corrugated linerboard.
Thickness Optimization
Placing the heaviest ply in the center or dividing the stock equally among the outer plies depends on the mechanical demands of the converted packaging. Adjustments to the basis weight allocation shift the neutral axis of the sheet, which dictates how the board handles tensile and compressive stresses during die-cutting and folding.
Production Control
Modern multi-ply paper machines use scanner arrays to monitor the wet sheet after each forming section to maintain uniform basis weight allocation across the machine profile. Advanced multivariable control algorithms adjust the headbox slice openings and stock pump speeds continuously to maintain the desired distribution. If the stock flow to one headbox drifts, the machine profile exhibits localized variations in density and thickness that disrupt subsequent coating and converting operations.
Calendering steps cannot fully correct these variations, meaning that precise initial partitioning remains the primary means of ensuring flat, uniform board.
