Calender

Details Calender Calender

2000-09-14

2004-03-09

Ostrager, Allen (Department: 3725)

Presses

Concurrent pressing and conveying

Roll type

C100S035000, C100S047000, C100S170000, C100S171000

Reexamination Certificate

active

06701833

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 199 45 780.8, filed on Sep. 24, 1999, 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 with a frame (seating), an upper roll that is embodied as a sag (deflection) compensation roll, a lower roll that is embodied as a sag compensation roll, and an intermediate roll arrangement with an intermediate roll that is fixed in the frame.
2. Discussion of Background Information
Such a calender is known from, e.g., published German Patent Application No. 198 32 067. In this calender, a roll stack is provided in which the upper roll and lower roll are embodied as sag compensation rolls. This possibility is not present for the rolls in the intermediate roll arrangement. However, one of the intermediate rolls is fixed in the frame so that the compressive strain conditions in the nips above the fixed intermediate roll and below the fixed intermediate roll can be freely adjusted to a large extent.
When using bending compensation rolls or sag compensation rolls in a roll stack, a differentiation is made between roll jackets that are mounted in a fixed manner, which are also known under the name “NIPCO K,” and radially moveable roll jackets, also known as “NIPCO F.” In the past, a combination of these roll types was used as the upper and lower roll in order to achieve a position-stable roll mounting. The use of two bending compensation rolls with roll jackets that are mounted in a stationary fashion was usually avoided because, in this case, the load coordination of the pressure transduction inside and outside the rolls is problematic because of the calender hydraulics. However, the combination of two radially moveable roll jackets requires a complicated regulation of the bearings of the roll stack, which should be prevented if possible. The simultaneous use of two bending compensation rolls with radially moveable roll jackets is advantageous, however, since only one roll type is being used in this case. Therefore, it is substantially easier to keep replacements on hand. Furthermore, calender hydraulics can be eliminated. This can be realized, among other things, in that the designated intermediate roll is mounted in its frame in a fixed manner in order to attain a geometric fixed point there.
SUMMARY OF THE INVENTION
The present invention improves the possibilities for affecting a material web. In particular, the instant invention is directed to a calender of the type mentioned at the outset in which the intermediate roll is provided with a load limiting device (over force safety device).
It is possible to introduce the treatment of the paper web in the individual nips up to the limits of the load capacity of the fixed intermediate roll. In general, the intermediate rolls of the intermediate roll arrangement, and therefore the fixed intermediate roll as well, are only dimensioned for a symmetrical load from two sides. Only in a limited range compared to the total load is a middle roll, and in particular the fixed intermediate roll, structured for flexural loading. This flexural loading especially occurs when only one sag compensation roll is used in the assigned nip for producing compressive strain. But even in the case of strongly differing pressures in the upper and lower sag compensation roll, the danger exists of the intermediate roll being overloaded, which can lead to destruction. In any case, because such an error can be detected so quickly, it is fundamentally controllable. However, damages that do not become immediately apparent are critical. In this case, a section of material web that is treated after the damage can have a sharply decreased quality. If a load limiting device is used, the compressive strain in the nips can be brought as high as the intermediate roll can stand, if desired. Therefore, it is not necessary to maintain a large safe distance from the load limit, which increases the possibilities for treating material webs. There is also no risk of damaging the roll, which makes operation more reliable.
More preferably, the load limiting device has a release device that acts in a force-dependent manner which, if a predetermined threshold value is exceeded, causes a decrease in the force acting upon the intermediate roll. Therefore, the load limiting device not only indicates overloading, it acts to prevent an overloading of the fixed intermediate roll. If such a loading situation develops, the force oil the intermediate roll is decreased in a timely fashion.
Here, it is preferred for the intermediate roll to be mounted in levers and for the load limiting device to be arranged between at least one lever and the frame. The mounting of the intermediate rolls in levers is known from many calenders, i.e., so-called “lever calenders.” If the load limiting device is arranged between the lever and the frame, the advantage of a lever translation can be used. In this case, the sensitivity of the load limiting device can be significantly improved.
Preferably, the load limiting device is arranged at both axial ends of the intermediate roll. The load limiting device then determines the forces at both axial ends of the intermediate roll. This device can not only determine an overloading, but also an asymmetric distribution of forces, which could cause a tilt or a skewed loading. This also facilitates the adjustment of the calender and/or its hydraulics or the hydraulics in the sag compensation roll at start-up or readjustment.
Preferably, the load limiting device also has a force indicator device. In this case, the forces acting on the individual mounting points of the intermediate roll can be transmitted to an operator or a monitoring program so that information about the loading of the individual mounting points is constantly kept ready. Besides the possibilities for documentation, this especially has the advantage that, at least in the case of the intermediate roll, i.e., in the middle of the calender, the information can be collected at all.
Preferably, the load limiting device also has a hydraulic support that acts on the intermediate roll or a mounting attached thereto from opposite sides essentially parallel to the press direction, with a comparison device being provided for the hydraulic pressure on both sides. With this type of support, a pressure difference measurement can be performed, so to speak, in order to determine exactly the force with which the roll or its mounting, e.g., the lever, is being loaded. Besides the simple load limiting device, it is possible using this embodiment to mechanically record the actual force acting on each mounting side of the fixed roll according to size and direction at every point in operation. This facilitates that adjustment of the correct load coordination in the upper and lower part of the roll stack. As mentioned above, an imbalance of forces or a tilt can thus be detected immediately.
Here, it is especially preferred for the comparison device to have a differential pressure valve that controls a quick unloading function, at least for one sag compensation roll. If a differential valve is used, it is not necessary to have a measured data conversion, i.e., converting hydraulic pressure into an electric control signal by way of a control device, e.g., SPS. The release of the lowering of the sag compensation roll, preferably the lower sag compensation roll, occurs automatically in the case of a predetermined differential pressure being exceeded. This guarantees a relatively secure flow of signals.
The hydraulic support is preferably embodied in a hydrostatic manner. This achieves the further advantage of greatly dampening the roll vibrations.
As an alternative, the hydraulic support can have two prestressed hydraulic cylinders. When force is exerted on the roll, the pressure must increase in one cylinder and decrease in the other. This can be achieved independently in that t

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