Presses – Methods
Patent
1998-11-02
1999-12-21
Gerrity, Stephen F.
Presses
Methods
100 75, 100162R, 100166, 100172, 162205, D21G 100
Patent
active
060034408
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention concerns a method in calendering, in particular supercalendering, of a paper web or equivalent, in which method the paper web or equivalent is passed through the calendering nips formed by rolls for calendering of the paper web, in which method the rolls are placed in at least two stacks of rolls, in which method the paper web is passed from a corresponding calendering nip in each stack of rolls into a corresponding calendering nip in the next stack of rolls.
BACKGROUND OF THE INVENTION
As is well known, the set of rolls in a supercalender comprises a number of rolls, which have been arranged one above the other as a stack of rolls. The rolls placed one above the other are in nip contact with each other, and the paper web to be calendered is arranged to pass through the nips between the rolls. Supercalenders involve the drawback that in supercalenders the nips are loaded by the force of the weight of the set of rolls, in which case the distribution of the linear load from the upper nip to the lower nip is increasing in a substantially linear way. This has the consequence that the linear load present in the lower nip determines the loading capacity of the calender. Thus, the calender is dimensioned in compliance with the performance of the lowest rolls and, at the same time, some of the loading or calendering potential of the upper nips remains unused. Earlier, attempts have been made to solve this drawback related to the prior art so that attempts have been made to increase the deficient loading of the upper nips so that the supercalender is placed in the horizontal plane or that the stack of rolls in the calender is divided into two stacks of rolls. Such an embodiment has, however, also proved expensive, because a calender of two parts requires a higher number of adjustable-crown rolls. One embodiment in which the set of rolls in the calender has been divided into two stacks of rolls is described in the DE Utility Model Application No. 295 04 034.3. In this prior-art solution, in the calender divided in two stacks of rolls, the paper web is first passed through the calendering nips in one stack of rolls, and after that the paper web is passed into the other stack of rolls, in which the paper web is passed through its calendering nips.
In the way known from the prior art, in supercalenders, first one side, for example the top side, of the paper web has been calendered/glazed, and then the other side, for example the bottom side. In the prior-art solutions, a so-called reversing nip has determined where the side to be glazed is changed. In supercalenders, the glazing takes place most intensively in the first nips, in which case the glazing of the side that is glazed in the later nips to the same glaze level as is reached by the side glazed first requires, relatively speaking, higher linear loads, and this causes a higher loss of bulk in the web. Also, the difficult control of successive glazing often produces unequalsidedness in the paper glaze degree.
OBJECTS AND SUMMARY OF THE INVENTION
The object of the present invention is to provide a solution in which the problems related to unequalsidedness of glazing have been eliminated or at least minimnized.
In view of achieving the objectives stated above and those that will come out later, the method in accordance with the invention is mainly characterized in that, in the method, the paper web is passed from one stack of rolls into the next stack through a corresponding calendering nip in each stack of rolls until the web is passed from the last stack of rolls back through the following corresponding calendering nips from one stack of rolls into the next stack in the reversed sequence, and this is repeated until the paper web is passed from the last calendering nip to further processing.
According to the invention, the set of rolls in the supercalender has been divided into at least two stacks of rolls placed at a distance from one another, wherein the web runs from one stack of rolls into the next one until it is ret
REFERENCES:
patent: 2300994 (1942-11-01), Thiele et al.
patent: 2578594 (1951-12-01), Putnam
patent: 3270664 (1966-09-01), Veneman et al.
patent: 4332191 (1982-06-01), Kankaanpaa
patent: 4375188 (1983-03-01), Leivska
Partial Translation of Paperi Ja Puu--Paper and Timber vol. 77/No. 5/1995 Effect of the tension profile of paper on runnability, p. 280, col. 3, third paragraph--p. 281, col. 1, first paragraph.
Koskinen Jukka
Kyytsonen Markku
Nissinen Vilho
Gerrity Stephen F.
Valmet Corporation
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