Method and apparatus in the calendering of a web

A method 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, said stack of calender rolls including outer rolls provided with internal means for variably adjusting the crowns thereof, comprising the steps of:

• providing means for heating the mantle of at least one of said calender rolls defining a calendering nip, said heating means being situated externally of said calender rolls heated thereby;
• heating the mantle of said at least one of said calender rolls defining a calendering nip by said heating means to produce in the web passing through said nip a significant temperature differential in the thickness direction of said web between its interior portion and its surface layers and/or between its opposite surface layers to produce a temperature gradient over the thickness of the web;
• acting on the plastic properties of said web to be calendered by means of said temperature gradient in said web based on said temperature differential to compensate for mechanical calendering work based on linear loading of said calender rolls;
• and
• adjusting the axial profile of said calendering nip and the transverse thickness profile of said web by changing the radius of said at least one of said calender rolls by varying its temperature utilizing said heating means.