Method for controlling one or more surface quality variables of a fiber web in a shoe calender
AssigneeMetso Paper, Inc.
InventorsTapio Mäenpää, Kalle Hasu, Matti Lares, Pekka Koivukunnas
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Abstract
The invention relates to a method for controlling a surface quality variable (300) in one or more fiber webs (3) in a shoe calender (1) comprising one or more calender nips. In each calender nip of the shoe calender, the overall loading pressure of the shoe element (8) and the loading pressure difference between the leading edge (8′) and the trailing edge (8″) of the shoe element are controlled so as to achieve minimum difference between the determined values (300″) for the surface quality variables of the fiber web and the set values (300′) for the same quality variables after the shoe calender.
Claims18
A method for controlling at least one surface quality variable in a fiber web in a shoe calender having at least one calender nip, comprising the steps of:
- (a) providing a shoe element in each calendar nip;
- and
- (b) controlling, in each calender nip of the shoe calender, overall loading pressure of the shoe element and loading pressure difference between a leading edge and a trailing edge of the shoe element to achieve minimum difference between each determined value for the at least one surface quality variable of the fiber web and each set value for the at least one surface quality variable after the shoe calender, the controlling step being conducted based on the effect of the loading pressure difference between the leading edge and the trailing edge of the shoe element on the at least one surface quality variable as known through a control algorithm chosen from the group consisting of a response model, a table and a curve, whereby, when web rate V is substantially changed from a first fiber web rate V1 to a second fiber web rate V2, controlling is carried out by changing mentioned set value for at least one surface quality variable in a staggered way over consecutive set values based on predicting control algorithm.
Dependencies are inferred from the claim text.