Calender roll system

Details Calender roll system Calender roll system

1999-01-28

2001-05-22

Vo, Peter (Department: 3721)

Presses

Concurrent pressing and conveying

Roll type

C100S16200R, C100S172000

Reexamination Certificate

active

06234075

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 198 03 323.0, filed on Jan. 29, 1998, the disclosure of which is expressly incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a calender roll system and a method of operating the calender roll system. The calender roll system includes a roll stack having at least one center roll between two end rolls, and a drive mechanism for each of the end and center rolls. The rolls can be loaded in the stacking direction.
2. Discussion of Background Information
German Patent Disclosure DE 295 18 424 discloses a known calender roll system of the type generally discussed above, in which five and more rolls, preferably eight rolls, are arranged one above the other. The rolls form a number of working nips or gaps, which are defined by one hard roll and one elastic roll, and one varying nip, which is defined by two elastic rolls. Each roll is provided with its own drive mechanism. Auxiliary drive mechanisms are additionally provided to bring the circumferential speed of the applicable roll to the web speed, so that the roll system can be operated at the paper infeeding speed.
SUMMARY OF THE INVENTION
The present invention provides a novel variation of the calender roll system generally discussed above.
The present invention provides a method in which at least one center roll associated with at least one working nip is bent out of the plane of the roll stack, and the reaction forces required for the bending are generated by corresponding adjustment of the drive moments of the drive mechanisms.
Thus, by purposefully deflecting one, several, or all of the rolls crosswise to the center plane of the roll stack, a transverse compressive strain profile (crosswise pressure profile) can be varied. Within a wide allowable range, lesser to greater corrections may be attained, depending on the degree of sagging. In particular, the deflection of one roll may be adapted to a deflection of the neighboring roll, which results in a high degree of uniformity. This may be applicable particularly to the first and last working nips, because the end rolls are engaged by a reaction force that cannot be undershot, which leads to a deflection that is dependent only on the rigidity of the roll.
In accordance with the present invention, the feature of varying the compressive strain in the at least one working nip by increasing the difference in deflection of the rolls defining the working nip is based on a novel discovery that, if the bending lines of adjacent rolls spread apart, relief occurs not in the center of the web, for instance, but rather in peripheral regions of the web. To relieve the compressive strain in a peripheral region, the drive mechanism is utilized to transfer the drive moment, while to load the peripheral region, the drive moments are distributed more uniformly. In this manner, the drive mechanisms can be triggered to achieve relief or loading of the peripheral region in a simple way.
By closed-loop control of the transverse compressive strain profile, control of one web parameter pertaining to the web width may be monitored, and, upon a control deviation, at least some of the correction is accomplished by varying the drive moments. In this regard, the drive mechanisms are part of the control loop.
It may be preferred to select the drive moments so that reaction forces of adjacent rolls and, thus, their deflection are not equal to zero. This feature offers the advantageous possibility that the shear forces in the web may be virtually zero. However, this is on the precondition that deflection of the rolls is present. It has been found that paper produced in this way has greater tear strength.
It may be advantageous to keep the least value of the reaction forces unequal to zero so that the bearings for the rolls, embodied as rolling-contact bearings, have a longer service life because they are constantly under load.
It may also be advantageous that a center roll adjacent to one of the end rolls is bent out of the plane of the stack in a same direction as the end roll so as to lead to a very uniform transverse compressive strain profile.
Moreover, the calender roll system of the present invention includes at least one center roll having a slenderness ratio greater than approximately 10 and an open-loop control device for supplying drive moments. In this manner, the reaction forces F
R
at the at least one center roll and, thus, a deflection of the at least one center roll out of the center plane of the stack may be within an allowable range. In this regard, center rolls with a slenderness ratio over approximately 10 are very easily bendable and, therefore, will exceed the boundary of the allowable range unless contrary control by the drive moments is provided. For example, the allowable range is exceeded if the bending lines of adjacent rolls are spread so far apart that the ends of the rolls lift away from one another. The slenderness ratio is defined as a ratio of the length of a roll to its diameter. Such slender rolls are of great advantage, because due to their greater curvature they lead to a higher compressive strain in the nip, and because they have a lower weight.
It may be preferable for the rolls to have a slenderness ratio between approximately 12 and 16, and, most preferably approximately 14.
The two end rolls may have a lower slenderness ratio than the center rolls. In this manner, unavoidable deflection of the end rolls may be reduced so that even the adaptation of the next roll to the sagging of the end roll requires only slight deflection.
The calender roll system can also be arranged off-line. In this manner, a calender roll system, which operates independently of the papermaking machine, runs at a considerably lower speed than an in-line calender roll system coupled to a paper-making machine. For this kind of off-line calender roll system, a single drive mechanism on a roll that drags all the other rolls along by friction was thought in the prior art to be sufficient, however, this precluded utilizing the effects of the single drive mechanism.
The diameter of at least one center roll is preferably at most approximately 100 cm, and this upper limit value corresponds with a calender roll system having a width of approximately 10 meters and more.
Accordingly, the present invention is directed to a method for operating a calender roll system for a web material. The calender roll system includes a roll stack having at least one center roll positioned between two end rolls, in which each of the at least one center roll and the two end rolls have a drive mechanism, and in which the rolls can be loaded in a stacking direction. The method includes loading the rolls to form at least one working nip with at least one center roll, and, in the at least one working gap, bending the at least one center roll out of the plane of the roll stack. Reaction forces required to bend the at least one center roll are generated by corresponding adjustment of drive moments of the at least one center roll.
In accordance with another feature of the present invention, the method further includes changing a difference in deflection of the at least one center roll and an adjacent roll forming the at least one working nip. In this way, at least one of the compressive strain in the peripheral regions of the web may be reduced and the compressive strain in the center of the web may be increased.
In accordance with still another feature of the present invention, the method further includes at least one of transferring the drive moments of the at least one center roll from the drive mechanism, such that the compressive strain in a peripheral region may be relieved, and more uniformly distributing the drive moments, such that the peripheral region may be loaded.
In accordance with a further feature of the present invention, the calender roll system further includes a closed-loop control, and the method

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