Calculating Substrate Compression Ratios in Embossing Operations
Substrate compression ratio measures z-axis compaction, balancing tool impression depth against fiber strain limits to maximize embossing height without shearing.
Grammage Variability
Weight Distribution
Fluctuation in the mass per unit area of paperboard across different regions of a single reel or between separate production runs affects both the mechanical strength and the feeding performance of the substrate. In industrial papermaking, grammage variability is monitored continuously using online scanning sensors that measure basis weight with beta-ray attenuation. This variation is calculated as a standard deviation or a coefficient of variation.
Manufacturers set strict tolerance limits to prevent issues in downstream converting.
Runnability Outcome
Uneven weight distribution across the web alters the tension profiles during high-speed unwinding, which can cause web breaks or registration errors. When grammage variability is high, the sheets fed into a folding carton gluer do not bend uniformly, causing jams in the folding section. Heavy sections require more force to crease, while light sections may warp or tear.
Consistently flat and uniform board is essential for high-yield automatic packaging machines.
Print Consistency
Absorption of inks and coatings changes when the density of the board is inconsistent. Localised patches of high or low weight can cause uneven ink transfer, which results in mottled solid prints. This variation is especially problematic in multi-colour offset lithography, where dot gain must remain uniform to preserve colour accuracy.