Method and arrangement for preventing vibrations in a multi-nip calender or calender array

An arrangement for preventing vibrations in a multi-nip calender or an array of multi-nip calenders, each multi-nip calender comprising a lower roll, an upper roll and one or more intermediate rolls between the lower roll and the upper roll, wherein a plane is defined passing through the upper roll, the lower roll, and the intermediate rolls, a direction being defined lying in said plane, a fiber web being conveyable through two or more roll nips of the multi-nip calender with the roll nips closed, the intermediate rolls being equipped with load-relieving means and the upper roll and the lower roll being equipped with first loading means within said upper roll and lower roll and second loading means being connected to the lower roll and/or upper roll, respectively, for loading the rolls towards the intermediate rolls in the direction of the plane of the calender, wherein running parameters are applied to each of said two or more closed roll nips to apply a calendering impulse to the web, and wherein the entire multi-nip calender or array of multi-nip calenders applies an overall calendering impulse to the web to produce a web which leaves the multi-nip calender or array of multi-nip calenders with certain quality variables;

• the arrangement comprising:
• a measurement system;
• a control system, which comprises a calculation unit which issues control commands and a regulation unit, the regulation unit allowing continuous or intermittent changes of running parameters acting on the calendering impulse of one or more roll nips of said two or more closed roll nips on the basis of the control commands from the calculation unit, so that the overall calendering impulse of the calender or calender array and/or the quality variables of the fiber web remain substantially constant or within predetermined limits.

A method for preventing vibrations in a calendering apparatus having at least one multi-nip calender, each multi-nip calender having:

• a lower roll,
• an upper roll,
• two or more intermediate rolls between the lower roll and the upper roll, wherein a plane is defined passing through the upper roll, the lower roll, and the intermediate rolls, a direction being defined lying in said plane, and wherein a plurality of closed roll nips are defined between the rolls, and wherein the intermediate rolls have load-relieving means, and the upper roll and the lower roll have loading means for loading said rolls towards the intermediate rolls in the direction of the plane of the calender,
• the method comprising:
• passing a web through each of the plurality of closed roll nips of the calendering apparatus to calender the web;
• applying running parameters to each of the plurality of closed roll nips to apply a calendering impulse to the web, and wherein the calendering apparatus applies an overall calendering impulse to the web to produce a web which leaves the calendering apparatus with certain quality variables;
• and
• continuously or intermittently changing the running parameters acting on the calendering impulse of one or more selected roll nips of the plurality of roll nips so that the overall calendering impulse of the calender or calender array and/or the quality variables of the fiber web remain substantially constant and/or within predetermined limits.

A method for preventing vibrations in a calendering apparatus having at least one multi-nip calender, each multi-nip calender having:

• a lower roll,
• an upper roll,
• two or more intermediate rolls between the lower roll and the upper roll, wherein a plane is defined passing through the upper roll, the lower roll, and the intermediate rolls, and wherein a plurality of closed nips are defined between the rolls, and wherein the intermediate rolls have load-relieving means, and the upper roll and the lower roll have loading means for loading said rolls towards the intermediate rolls in the plane of the calender,
• the method comprising:
• passing a web through each of the plurality of closed nips of the calendering apparatus to calender the web, the calendered web leaving the calendering apparatus at a position downstream of the calendering apparatus, all positions on the web downstream of the calendering apparatus being after the calendering apparatus;
• applying running parameters to each of the plurality of closed nips to apply a calendering impulse to the web, and wherein the calendering apparatus applies an overall calendering impulse to the web to produce a web which leaves the calendering apparatus with certain quality variables;
• and
• intermittently or continuously changing first running parameters of first roll nips of said plurality of closed roll nips to change the calendering impulse received by the web in the first roll nips and thus reduce the vibration susceptibility of the calender;
• after or simultaneously with changing said first running parameters, calculating changes of second running parameters to compensate for the changes of the first running parameters, and changing the running parameters of second roll nips of said plurality of closed roll nips to be the second running parameters;
• and
• measuring the quality variables of the web after the calendering apparatus, checking the accuracy of the changes of the running parameters through a calculation unit, and making additional changes to the first and/or second running parameters.