Method and apparatus in the calendering of a web

Abstract

Method and apparatus in the calendering of a web in a calender comprising a calender stack including at least two calender rolls situated substantially one over the other defining at least one calendering nip between them in which the web to be calendered is pressed at a suitable linear load, and wherein the outer rolls of the stack are provided with internal apparatus for varying or adjusting the roll crowns. The mantle of one or both of the calender rolls defining a calendering nip is heated to produce in the web passing through the nip a significant temperature differential in the thickness direction of the web between its interior portion and its surface layers and/or between its opposite surface layers. In this manner, the mechanical calendering work normally a function of the linear loading of the calender rolls is compensated for by the temperature gradient produced by the temperature differential which acts on the plastic properties of the web. The heating of the calender roll mantles is accomplished by external heating devices which at the same time adjust the axial profile of the calendering nip and the transverse thickness profile of the web by changing the radius of the roll through the variations in the temperature thereof.