Creasing Rule Selection for Coated Folding Boxboard Conversion
Selecting steel creasing rules and matrix channels for coated FBB requires matching board caliper and CTMP core shear limits to prevent surface cracking.
Blank Squareness
Sheet Geometry
Dimensional orthogonality describes the precise ninety-degree relationship between the lead edge and the side edge of a substrate during the guillotine process. Blank squareness quantifies the deviation from a perfect rectangle across a stack of cut paper. Mills maintain this alignment to ensure that feeding mechanisms on high speed presses or folding machines avoid skewed registration.
Excessive variance triggers jams in the delivery pile because the mechanical grippers fail to align with the irregular corners of the sheet.
Alignment Protocol
Converters verify this geometry by placing a calibrated square against the corner of a sample pulled from the top and bottom of a pallet. Workers shift the stack position if the measurement exceeds the standard tolerance defined by the print house. Friction between sheets during the cutting stroke often causes slight movement, which leads to the accumulation of drift across the pile.
Digital press software calculates compensation patterns when the input stock shows a consistent skew in the measured angle. Mechanical edge guides require a flat surface to maintain throughput speeds.
Tolerance Regulation
Technical specifications for commercial printing demand a maximum angular variance of less than one millimeter per meter of length for high quality four color work. Tight limits prevent misaligned ink traps that ruin the visual output of the finished product. Heavy substrates exhibit larger deviations during the cutting phase because the knife blade undergoes greater lateral deflection under pressure.
Printers reject entire lots if the deviation exceeds the mechanical threshold of the feeder system. Absolute flatness at the corners dictates the registration accuracy of the entire production run.