The final finishing operation in most paper machines
is the calendering operation. The paper sheet passes between a series of
four to eight vertically stacked rolls called the calender stack. The paper is
compressed or calendered as it passes between the rolls, obtaining the desired
thickness and gloss characteristics. Self excited vibration of the calender
stack and regenerative wear of the calender rolls is a chronic problem
experienced by many paper mills. These phenomena are collectively known as
calender barring.
Variation in paper thickness and gloss and premature wear of
calender rolls are costly symptoms of calender barring. While much
work has been done to understand calender barring it remains a baffling and
costly problem. SDL worked with Abitibi-Price, Inc., and LSZ Paper Tech, Inc., to develop a meaningful computer
model of calender barring which incorporates both the paper sheet feedback and
regenerative wear mechanisms and the interaction between them.
The model is
based on vibration testing of an operating calender stack, recent PAPRICAN
research on paper properties and SDL's expertise in self-excited dynamic
systems. The computer model can be tuned to specific paper machines and used to guide
selection of calender stack setup parameters and paper machine operating
conditions to avoid barring. An on-line barring monitor was also developed
which measures whether the machine is operating in a stable or unstable barring
mode.
Solution:
Experimental testing of an operating calender stack and analytical modeling was conducted to develop a meaningful computer model of the calender barring process. The model guides choice of calender stack setup and machine operating parameters to avoid barring.
