Presses – Methods – Forcing through constricted passage
Reexamination Certificate
2001-02-06
2004-03-02
Ostrager, Allen (Department: 3725)
Presses
Methods
Forcing through constricted passage
C100S161000, C100S168000, C100S176000
Reexamination Certificate
active
06698341
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. § 119 of German Patent Application No. 100 06 299.7, filed on Feb. 12, 2000, the disclosure of which is expressly incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is related to a process for operating a calender roll that cooperates in a rotating manner with at least one other calender roll of a roll stack, with at least one of the calender rolls of the roll stack being provided with an elastic surface. The invention also relates to a calender roll with a roll jacket and a supply connection arrangement.
2. Discussion of Background Information
Such calender rolls are frequently used as the center rolls in a calender; thus, they form a part of a roll stack. Here, neighboring rolls form nips through which a material web is guided in order to be subjected to an increased pressure and perhaps an increased temperature.
Such rolls are broadly used in the processing of a paper web which is used in the following as an example for describing the invention. However, the same problems arise in other material webs as well.
In such calenders so-called “soft” rolls generally cooperate with “hard” rolls. Sometimes two “soft” rolls can also work together. Here, the soft rolls are covered with a plastic cover. It has been observed that, after a certain period of operation, a so-called barring can be observed. This barring appearance, on the one hand, causes an undesired stripe-shaped pattern on the paper web. However, these stripes can also be detected as stripe-shaped markings on the elastic rolls with the plastic covers. The soft rolls become multi-angled, so to speak. At a certain depth or intensity, these bar rings lead to rejections in the material web. Then, the correlating roll or the correlating rolls must be reworked in order to remove the deformation of the plastic cover. This is generally performed by turning the roll on a lathe.
SUMMARY OF THE INVENTION
The invention is based on the aspect of reducing the appearance of barring. This aspect is attained in a process of the type mentioned at the outset by changing the mass of the calender roll during operation. This is based on the following:
A roll stack made up of several rolls has a multitude of frequencies of its own. Among these frequencies there are, e.g., autonomous bending frequencies which are of lesser importance in this case and autonomous oscillation forms that result from the vibrating roll masses on the spring and damper systems which are formed by the plastic covers positioned between the rolls and also by the roll bearings. An operating calender creates exciting forces whose frequencies are connected with the roll rotations and which are equivalent each to a multiple of the roll rotations in a first approximate calculation. These exciting forces can have many sources, e.g., inhomogeneities, anisotropies, or geometric faults. Variations of the thickness of the paper web traveling through the calender can also excite the roll stack. When one of these exciter frequencies meets one of the autonomous frequencies, the oscillation system responds with enlarged oscillations. Due to the multitude of possible exciters and the multitude of possible forms of autonomous oscillations, these points of resonance can virtually not be avoided. In general, the system of oscillations is dampened so much and the exciter forces so small that the resulting oscillation does not disturb immediately. However, over a shorter or longer duration these vibration motions imprint into the plastic surfaces of the elastic roll. It can frequently be observed that the closest integral multiple of the oscillation frequency is imprinted into the rolls as a pattern. This, however, results in a regeneration of the oscillation. The oscillations amplitudes increase exponentially. They result, on the one hand, in an increased sound level [up to more than 115 dB (a)] and, on the other hand, in periodic thickness fluctuations of the passing paper web that leads, as mentioned above, to rejections.
According to the invention, the originating mechanism of the periodic surface waviness is disturbed for avoiding the above-mentioned regenerating effect. In order to avoid a constant integral pattern with a frequency close to the internal frequency of the system being imprinted into the rolls, the oscillation system is modified by changing the mass of the calender roll and changing the correlating internal frequencies. By changing the internal frequencies, it is achieved that the oscillating system cannot be operated with a regenerating frequency over a longer period of time which again can have negative effects, in particular concerning the formation of bar rings. In most cases, in order to change the mass of the calender roll, mass is actually introduced or removed. In some cases, however, it will be sufficient if the mass distribution inside of the calender roll is changed, i.e., shifting, for instance, mass from the radial inside to the radial outside. Such a change affects the inertial momentum, among other things.
Preferably, the mass is changed continuously during operation. It is therefore provided that the mass of the calender roll is continuously increasing or decreasing during operation. Thus, the frequency of resonance is changed continuously so that the formation of a stationary frequency of resonance, which leads to an undesired formation of barring, can be avoided with a relatively high degree of security.
Advantageously, the mass of the calender roll is increased by 10 to 15% of its basic mass. The basic mass is the “empty weight” of the calender, so to speak. It has been discovered that a change of mass of about 10 to 15% of the roll mass can result in a change of the internal frequency of the calender roll in the amount of 4 to 7%. This change is sufficient to avoid the formation of bar rings.
Preferably, a predetermined amount of fluid is introduced during operation and this amount of fluid is then removed again. The change of the mass of a calender roll can be easily achieved with the aid of a fluid. The fluid has the advantage that it spreads relatively quickly over the entire axial length of the calender roll due to the centrifugal force that is present in the interior of the calender roll during operation, so that no localized unbalanced states can occur by introduction or removal of a fluid. The introduction and removal of fluids is known per se, for instance, for heating and cooling. However, in the known cases, it is desired to keep the mass of the fluid that is pumped through constant. According to the invention, it is desired to achieve a change of the mass of the calender roll with the aid of the fluid.
Preferably, the fluid is in contact with the inner wall of the roll jacket. Therefore, the fluid is guided such that it connects vibrationally with the calender roll without creating an air pocket, if possible. This ensures that the fluid mass participates in the oscillating motion. If air were to remain between the fluid and the calender roll, it could oscillate differently than the calender roll itself in a springlike manner due to its compressibility.
Preferably, the fluid is to rotate with the roll. Here, it is perhaps necessary to provide carriers for the fluid in the roll. Thus, the fluid becomes a “part” of the roll in relation to the rotational motion of the roll and thus can be considered as belonging to its mass in any possible way.
Preferably, the fluid is blown out of the roll with the aid of compressed air. Instead of compressed air, however, any other compressed gas can certainly be used. Compressed air is advantageous for reasons of expense, however. This omits the expensive pumping mechanism that either pumps the fluid out of the interior of the calender roll or suctions it out. With the aid of pressed air, it can be provided that, even when the calender roll is being emptied, i.e., during removal of the fluid, the contact between the fluid and the calende
Greenblum & Bernstein P.L.C.
Ostrager Allen
Self Shelley
Voith Paper Patent GmbH
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