Moisture Evaporation
Mechanical dryer assemblies positioned after the press section remove residual water from the continuous paper web through direct contact with steam-heated iron drums. Paper machines route the moist web through a cylinder drying section comprising dozens of rotating cast iron cylinders arranged in upper and lower tiers. Moisture content drops from roughly sixty percent to final target levels around five percent during passage.
Thermal Transfer
Heat transfers from internal steam condensation through the cylinder wall directly into the damp paper web pressed tightly against the metal surface by synthetic dryer fabrics. As water evaporates from the paper sheet, pocket ventilation systems purge moisture-laden air to maintain high evaporative driving forces between adjacent cylinders. Steam pressure inside individual cylinder groups increases progressively down the drying line to manage temperature profiles and prevent sheet blistering.
Condensation siphon pipes remove condensate from cylinder interiors to prevent thermal insulation buildup that disrupts heat transfer efficiency. Modern paper machines partition the dryer group into separate drive zones to control web draw and shrinkage.
Web Tension
Controlled web restraint prevents sheet cockling and width contraction as fibers lose moisture and shrink. Synthetic dryer felts apply uniform mechanical pressing forces across the cylinder contact surface. Differential speed control between cylinder banks compensates for web shrinkage during drying.
