Calculating Crease Matrix Dimensions for Uncoated Folding Cartonboard
Calculate crease matrix width by multiplying uncoated cartonboard caliper by 1.5 and adding rule thickness, setting channel depth equal to board caliper.
Crease Matrix Width
Dimensional Clearance
Internal space between the walls of a creasing channel determines the volume available for board displacement during a fold. Selecting the correct crease matrix width prevents the outer liners of the cartonboard from rupturing under tension. The measurement usually equals the sum of the creasing rule thickness and the thickness of the board multiplied by a factor based on fiber direction.
If the channel is too narrow, the board will shear instead of folding.
Folding Calculation
Conversion standards for folding boxboard require specific formulas to match the tooling to the material grade. A standard crease matrix width calculation for board thicker than 300 microns often adds a fifty percent margin to the paper caliper. When the grain of the board runs parallel to the crease, a narrower channel might be necessary to maintain a crisp edge.
Conversely, cross-grain creases require more room for the compressed fibers to expand. Precision in this setting reduces the torque required by automatic filling machines. Improperly sized channels lead to unsightly bulges or cracked coating on the exterior of the package.
Process Boundary
Tolerance for error in channel sizing narrows as the speed of the folder-gluer increases. Matrix performance ends when the adhesive backing fails or the edges of the channel become rounded by repeated impact.