Paper Quality Improvements Through Supercalendering With Rolls of High Surface Finish, 1997 Finishing and Converting Conference Proceedings

Melanie Whyte, Alan T. Young <>

Caledonian Paper Co.

J. David Pfeiffer

JDP Innovations Inc.

Richard D. Lampman

Praxair Surface Technologies

Tungsten carbide flame-sprayed coatings applied to chilled iron rolls not only resist wear but also allow grinding and polishing the rolls to mirror-like surfaces of 0.05 µm Ra (2.0 µin Ra) or better. When these rolls are used in conjunction with synthetic polymer-filled rolls in supercalender stacks it provides ideal conditions for replication of the smooth surfaces onto the paper. The wear resistance of the coating ensures that the finish and dimensional tolerances are maintained for extended periods. Paper smoothness tests have indicated that more consistent finishing has resulted, even though the highly polished roll surfaces are present at only 2 of the 11 nips. The experiences of one mill in using these rolls in one of their calender stacks are related. The two supercalenders at Caledonian Paper PLC in Irvine, Scotland produce medium weight publication paper ranging from 42 g/m 2 to 90 g/m 2 at 800 m/min. speed. Both supercalenders are equipped with flying pasters, so no rethreading of the stack is necessary between sets. As shown in Fig. 1, these are twelve-roll stacks, 8.7 meters wide. The top, or queen roll in each stack is an adjustable crown roll of 860 mm diameter, while the king rolls (#l position) are also anti-deflection rolls of 1050 mm dia-meter. The driven roll in each stack is a chilled iron roll in the number 3 position. These rolls have a nominal dia-meter of 560 mm, similar to other chilled iron rolls in positions 5, 8, and 10. Conventional filled rolls made of a cotton-wool blend are used in positions 11, 9, and run against each other in the reversing nip at 6 and 7. These rolls have a diameter of 790 mm...