Principal Factors Controlling Press Room Breaks, 1999 International Paper Physics Conference Proceedings

T. Uesaka, M. Ferahi

A probabilistic model has been developed to identify principal factors controlling press room breaks. The factors considered are the local strength distribution and the distribution of macro-defects, as represented by cracks. Model parameters related to the strength distribution and crack length dependence of failure tension were determined experimentally. The model predicted reasonably well the data obtained from published pilot-scale runnability studies. A parametric study revealed that 1) break frequency is extremely sensitive to applied tension; 2) within the normal range of press room tension (10-20 kgf/m or 98-196 N/m), there is virtually no break due to strength non-uniformity; and 3) even with a very large intensive defect (a horizontal centre crack of 40 mm length) embedded in every roll, the rolls can still run with a modest increase in break frequency, as long as the press room tension is kept in the normal range. These results suggest that most press room breaks occur due to tension variations rather than weakness or small defects in paper. A simple dimensional analysis of tension variations indicates that under varying tension conditions the ratio of tensile strength to elastic modulus in the machine direction is an important paper factor controlling breaks.