Calendering apparatus using inductive heating for hot-calendering a paper web

DETAILED DESCRIPTION The present invention relates to a calendering apparatus and method for hot-calendering a paper web.
The apparatus includes a rotatable calendering roll which defines a smooth calendering surface and a backing roll rotatably cooperating with the calendering roll for defining therebetween a calendering nip for the passage therethrough of the web.
An induction heater is disposed in close proximity to the calendering surface for inducing eddy currents within the calendering roll such that the calendering roll is heated.
Air blowing means is disposed in close proximity to the calendering surface and between the heater and the nip.
The blowing means defines a plurality of compartments which are disposed in a cross-machine direction.
Each of the compartments selectively blows a current of cooling air against the calendering surface for controlling the temperature of the calendering surface so that the temperature of the calendering surface adjacent to the nip is controlled in a cross-machine direction.
In a more specific embodiment of the present invention, the calendering roll is a solid, hard metal roll.
In an alternative embodiment of the present invention, the calendering roll includes a core and an annular insulating layer surrounding the core.
A heatable annular shell surrounds the insulating layer with the shell defining the calendering surface.
The soft backing roll includes a soft outer cover and the induction heating means includes an electrical coil and a laminated core encompassing the coil.
The core is fabricated from steel or steel laminates or, in an alternative embodiment of the present invention, the core is of a ferrite ceramic.
More specifically, the core defines an air gap with the air gap being disposed between the core and the calendering surface.
The air gap progressively increases towards the side edges of the core such that less heat is supplied to the calendering roll adjacent to the axial edges thereof so that overheating of the lateral edges of the web is inhibited