Calendering Moisture Profiles and Z-Direction Density Control in FBB Cores
Moisture-gradient calendering plasticizes outer chemical skins while keeping mechanical cores dry, maximizing FBB bending stiffness and yield.
Shoe Calender
Extended Contact
Calendering machinery using a flexible roll or belt pressed against a curved metal shoe applies uniform compression over an elongated contact area. The shoe calender increases the dwell time of the paperboard in the compaction zone compared to a conventional roll nip. This longer contact allows for efficient heat and pressure transfer at lower peak pressure levels.
Bulk Preservation
Mechanical densification of the web is minimized in the sheet core while being concentrated on the surface layers. A shoe calender achieves the desired surface smoothness and gloss without collapsing the internal bulk of the board. This preservation of bulk is crucial for maintaining the bending stiffness of multi-ply folding boxboards.
This process allows mills to use less raw fiber to achieve the same strength.
Paperboard Finishing
Uniform surface finish is produced across the width of the machine because the backing shoe can be adjusted to compensate for web profile variations. Utilizing a shoe calender prevents the formation of localized hard or soft spots in the sheet, which improves ink absorption and coating uniformity. This consistent surface is highly valued for high-speed gravure and offset printing.
The finished board runs without jamming on high-speed converting and gluing lines.