Calibrating Artwork Scaling Factors for Heated Platen Brass Chases
Calibrating artwork scaling factors offsets brass thermal expansion and substrate heat shrinkage to achieve exact register alignment on hot platen presses.
Cross Machine Direction Contraction
Dimensional Shift
Paper fibres orient themselves along the production path while they settle on the forming fabric, creating an anisotropy that governs how sheets react to subsequent wetting and drying cycles. Cross machine direction contraction occurs when internal moisture loss triggers a reduction in width as the web exits the presses or dryers. This specific shrinkage magnitude depends on the restraint applied by the drying cylinders and the tension profiles held across the deckle.
Adjusting these forces remains the primary method for mill operators to limit edge curl and prevent register issues in high speed offset printing.
Fiber Tension
Managing lateral stress requires precise control over the draw between individual drying groups. Dryers pull the paper taut, which physically prevents the sheet from pulling inward toward the centerline. When vacuum transfer rolls maintain a consistent grip, the paper exhibits uniform lateral stability across the entire web width.
Irregular tension profiles lead to localized variation, where parts of the sheet shrink harder than others, resulting in baggy edges or localized puckering that ruins flat feeding in converting equipment.
Structural Impact
High lateral shrinkage values lead directly to misregistration in multi color print applications because the substrate changes size between passes. Measuring the difference between the width at the wet end and the finished reel provides a standard quality metric for industrial bond and coated stocks. Low contraction figures indicate a stable sheet with high resistance to humidity fluctuations, whereas excessive contraction suggests a high degree of internal strain that causes paper instability under varied environmental conditions.