Method and device changing the vapor pressure inside the paper web in calendering

A device for calendering a paper or board web comprising:

• a first roll;
• a second roll spaced a first distance from the first roll;
• a third roll defining a first roll pair with the first roll;
• a fourth roll spaced the first distance from the third roll, and forming a second roll pair with the second roll;
• a first belt which rotates about the first roll and the second roll, the first belt defining a first smooth moisture impermeable counter surface having a first temperature of at least 100° C.;
• a second belt which rotates about die third roll and the fourth roll, the second belt defining a second smooth moisture impermeable counter surface having a second temperature which is at least 160° C. and higher than the first temperature, the second counter surface forming with the first counter surface a long nip through which the web travels under a slight external pressing pressure, wherein at least one of the first counter surface and the second counter surface is heated, and wherein a first surface of the web is in contact with the first counter surface and a second surface of the web is in contact with the second counter surface, such that the second surface of the web is calendered during travel between the counter surfaces by the contact with the second counter surface and the web has an inner vapour pressure which is increased due to the heating of the web mid the restriction of the evaporation of moisture from the web by the counter surfaces, said inner vapour pressure resisting the slight pressing pressure between the smooth counter surfaces thus counteracting reduction of the thickness of the web during calendering.