The high-pressure contact zone where two rotating cylinders meet. On a paper machine, the web passes through multiple nips in the press section to squeeze out water, and in the calender stack to compress the fibers. The pressure and geometry of the nip directly control the final caliper, smoothness, and gloss of the sheet.
We're getting crushing in the second press nip, back off the loading by five kilonewtons.
Uneven nip pressure across the width of the machine is a primary cause of uneven gloss and caliper variations.
Related terms
Calender
Stack of hard rolls that presses a paper web to make it smoother, glossier and more even in thickness.
Supercalender
Off-machine stack of alternating steel and resilient filled rolls that gives paper high gloss and smoothness.
Caliper
Thickness of a single sheet of paper, measured under a set pressure and given in micrometers or thousandths of an inch.