Presses – Methods
Reexamination Certificate
1999-04-05
2001-03-13
Gerrity, Stephen F. (Department: 3721)
Presses
Methods
C072S010200, C072S249000, C100S047000, C100S172000, C226S042000, C226S157000
Reexamination Certificate
active
06199476
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a roll machine for manufacturing or treating a material web. More specifically, the present invention is directed to a roll machine with a number of rolls that are disposed in a stack and form a number of nips therebetween for treating or manufacturing a material web, where at least two of the rolls are driven. The present invention also relates to a process for operating such a roll machine.
2. Discussion of the Background Information
DE 295 18 424 U1 discloses a roll machine, particularly a calender. The drive devices of the rolls control the individual rolls to match the speed of the web traveling through before the nips are closed. This matching of speed prevents a speed differential when the nips are closed on the web that might otherwise stress or tear the web.
Such a roll machine can be used both as a calender and as a calender stack, preferably for the treatment or manufacture of a paper web. The paper web is subjected to a certain pressure in the nips between adjacent rolls for several purposes, including evening out irregularities in the surface of the paper web, compressing the paper web, and providing the surface of the paper web with a desired smoothness and/or a desired gloss.
Other material webs, for example made of plastic or aluminum, can also be treated in a similar manner in calenders or calender stacks.
In any case, a drawback of this prior art roll machine is that, after a certain operating time, lateral stripes of varying gloss form on the material web. Material webs with such lateral strips, known in the industry as “barring,” cannot be used and are discarded. The corresponding roll must also be replaced or refinished.
The cause of barring has not yet been conclusively identified. One possible cause is initial defects, such as thickness fluctuations in the material web resulting from a periodically fluctuating headbox, cause the rolls and/or their jackets to oscillate at their natural frequency. This can consequently form markings in the surface of one or more rolls, and gradually cause a roll to become polygonal rather than cylindrical. This leads to a corresponding repercussion in the material web so that the polygon shape becomes even more pronounced over time. The lateral strips then become visible after a certain point.
In addition, a polygonal roll produces oscillations that propagate through the entire roll machine, causing malfunctions in other nips. Such oscillations are investigated, for example, in “Barringbildung am Glättkalander einer Papiermaschine” (Barring Formation in the Calender Stack of a Paper Making Machine) by M. Hermanski, Das Papier, Vol. 9, 1995, pp. 581-590. A solution of using more wear resistant surfaces of the roll covers of the soft rolls has been proposed. In “Vermeidung von Glättwerkmarkierungen im Papier mit Escher Wyss Nipco-Walzen” (Preventing Calender Stack Markings in Paper with Escher Wyss Nipco Rolls), Technische Rundschau Sulzer February 1977, pp. 83-89, the authors ascribe the formation of barring to oscillations of the roll machine and propose employing a particularly well-damped roll, namely the Nipco roll, to reduce oscillations.
Nevertheless, barring can be observed even with more wear resistant roll covers and with the use of deflection adjustment rolls with hydrostatically functioning support shoes.
SUMMARY OF THE INVENTION
Accordingly, the present invention overcomes the drawbacks of the prior art.
Further, the invention is directed to providing a roll machine and a corresponding method of operation of the roll machine to prevent or reduce the onset of barring.
According to the features of the present invention, a roll machine is provided having several rollers, some of which are driven. The driven rolls have a common drive control that varies the driving torque distribution of the driven rolls.
The conclusion that the present invention will prevent or reduce barring is derived from experience, which has shown that a barring formation only occurs after a certain service life of the rolls and roll machine. The formation of barring during the initial use of new or refinished rolls is extremely rare. It is therefore a logical conclusion that the onset of barring results from slowly occurring changes in the rolls. These changes are believed to arise due to a uniform operation of the device over a longer period of time. Such uniform operation is quite desirable in the production of continuous material webs.
A certain driving torque is required for the operation of a roll machine. This driving torque must, for example, overcome the friction of the rolls on the bearings. In the prior art, only one roll was driven in calenders or calender stacks, while the other rolls were carried along with it. It has been observed that rolls carried along, i.e., the rolls that do not have their own drive devices, deflect and “buckle out” from the roll stack.
The addition of at least another drive source reduces the tangential forces responsible for the bending the rolls, and can go as far as to reduce these forces to zero (or to even reverse their direction). Changing the driving torques of the driven rolls can therefore also reduce the “geometry” of the roll stack. If this change in torque occurs before the roll changes that cause barring become distinct, then these roll changes are transformed again. These roll changes do not necessarily have to cancel each other. However, another change is required before these transformations will lead to the barring formation.
In many cases, changing the driving torques of the individual rolls can also achieve a small, but perceptible, phase shift of the individual rolls in relation to one another. This also leads to an “interference” of the uniform operation, which “interferes” with long-term roll changes.
The variation of the driving torque is, of course, limited. For example, the sum of the driving torques applied to different rolls must be sufficient to operate the roll machine. The difference between the driving torques must not be so great that the material web tears. Otherwise, the distribution of the driving torques among the individual rolls is essentially arbitrary. This is also the case when more than two rolls are driven.
Advantageously, the drive control for the driven rolls includes a random generator. With the aid of the random generator, the distribution of driving torques between rolls can be varied without any periodic operation in this variation which could in turn lead to a barring formation. The random generator can either act directly on the driving torque distribution, or the control can evaluate functions with which the driving torque distribution is varied.
The drive control preferably has a limiter, which keeps the rate at which driving torque for any particular roll is changed below a predetermined value. Jumps in the driving torque of a roll (i.e., high rates of change in the driving torque) could tear or damage the material web.
The drive control also preferably connects to a sensor device that detects at least one property of the material web and/or at least one operating parameter of the machine, and changes the driving torque distribution between rolls as a function of at least one output signal of the sensor device. The barring formation can already be detected in its developing stages with appropriate sensors. For example, with suitable sensors, barring can be detected before they are visible to the naked eye. Another possibility is that oscillations of the roll machine are detected, which increase with the onset of barring. In each of these cases, the drive control can respond by changing the distribution of driving torques to the driven rolls before the barring formation actually becomes so noticeable that the material web is no longer usable.
Preferably, the drive control has a timer. Particular time blocks can be adjusted in which the driving torque distribution is constant. A change in the driving torque distribution can be carried out after the expiration of su
Gerrity Stephen F.
Greenblum & Bernstein P.L.C.
Voith Sulzer Papiertechnik Patent GmbH
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