Calender

Details Calender Calender

2001-03-02

2003-08-19

Bray, W. Donald (Department: 3721)

Presses

Methods

C100S047000, C100S16300R, C091S448000

Reexamination Certificate

active

06606940

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 100 10 772.9, filed on Mar. 4, 2000, 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 stand, an upper roll, a lower roll, and two center rolls located between the upper and lower rolls. The two center rolls are supported on the stand by way of cylinders.
2. Discussion of Background Information
A calender similar in general to that discussed above is known from DE 37 02 245 A1. Further, U.S. Pat. Nos. 4,736,678 and 5,806,415 disclose similar type calenders as well.
Cylinders, which can also be referred to as, e.g., compensation cylinders, are either directly or indirectly supported on the stand or frame of the calender. Further, the cylinders are utilized for different purposes, e.g., during operation, when a material web is glazed, the cylinders compensate for overhanging loads on the roll, e.g., guide rolls or scrapers, or a part of the roll load itself. In a calender according to, e.g., U.S. Pat. No. 5,806,415, even the entire roll weight is compensated by these cylinders. The advantages resulting from this operational mode are more even line loads across the width and higher line loads being possible in the upper nips while maintaining even line loads in the lower nip.
A second purpose of the cylinder is to allow a quick separation of the rolls, i.e., opening the nips as abruptly as possible. Such an opening is necessary in certain situations of malfunctions, e.g., a web break, to avoid damage to the rolls.
Such quick separations are known per se. For this purpose, the lower roll is dropped and the cylinders of the center rolls are relaxed. In order to avoid a hard impact of the rolls, dampening is provided for the final position, i.e., at the end of the piston motion of the cylinders, the cross section for the hydraulic fluid to discharge is reduced so that the roll is slowed more gently to some extent at the end of its motion.
SUMMARY OF THE INVENTION
The present invention is directed to improving the quick separation capabilities of the calender.
According to the invention, a calender of the type mentioned at the outset is provided with a discharge path controlled over more than ¾ of a piston stroke necessary for lowering the center roll.
Further, it is noted that the instant invention is described, by way of example, as a calender in which the center rolls are positioned on the stand by way of levers. However, it is noted that this is purely for the purpose of explanation and illustration, and that other arrangements are likewise contemplated, e.g., positioning the rolls in linear guides.
In accordance with the features of the instant invention, the abilities of control are no longer limited to braking the roll at the end of its motion, which ultimately has the effect of avoiding an abrupt contact of the roll and the shock connected therewith. Moreover, it is possible to control the roll throughout the longest part of its motion. Thus, it is now possible to increase the speed of lowering the rolls and opening the nips. Relatively high motion speeds can be permitted, especially at the beginning of the motion. Additionally, it is now possible to adjust the motion of neighboring rolls to one another so that, during the opening motion, a collision of neighboring rolls can virtually be excluded.
Preferably, the discharge path is controlled by a motion of the piston in relation to the cylinder housing. This results in the control by the motion of the roll itself. External measures are not necessary, so additional control mechanisms can be omitted.
Preferably, the resistance of the discharge path increases the farther the piston is inserted into the cylinder housing. This applies for the usual procedure in which the nips are closed when the piston is extended. In cases in which the nips are closed by a cylinder operating in reverse, the resistance of the discharge path increases accordingly. With such a design, the motion speed of the center roll can be controlled so that the opening motion can be introduced very quickly, but can then be decelerated increasingly. Thus, the entire opening motion requires the same amount of time as in known cases. However, the increase of the nip opening at the beginning of the motion occurs more quickly.
Preferably, the cylinders of different center rolls are provided with different resistances of discharge paths in the case of closed nips, with the resistance increasing from the bottom to the top. This takes into account the fact that the uppermost center roll must travel a shorter total distance than the lowermost center roll. Essentially, the uppermost center roll has to travel only the distance that corresponds to the desired nip opening. The subsequent center roll must already travel a distance twice as long, i.e., the distance necessary for opening the nip between the uppermost and the subsequent center roll by the predetermined amount plus the opening width of the uppermost roll. In order to avoid a collision of the “falling” rolls the resistance of the discharge path is selected such that the uppermost roll falls more slowly and the initial speeds of the rolls during opening increases from the top to the bottom. This can be performed easily by already providing different resistances in the discharge paths before the beginning of the motion of the rolls. The roll with the lowest resistance in the discharge path can remove the hydraulic fluid from the piston the fastest and, therefore, travel a longer distance during the same time.
Preferably, the pistons are embodied identically to one another, but the pistons are extended to different lengths when the nips are closed. When the distance in the discharge paths is dependent on the position of the piston, the relatively simple possibility results of providing different flow resistances for different roll positions in spite of identical pistons. When the piston is inserted farther, the discharge path already has a greater resistance. Such a piston inserted farther can be found in a roll positioned further up. The lowermost center roll has the piston that is pulled out the farthest and, thus, the lowest discharge resistance in the discharge path.
Advantageously, a pipe is provided in the cylinder housing, having openings in its wall and protruding into a bore of the piston. This pipe forms the variable resistances in the discharge path of the cylinder. The more free openings in the wall of the pipe, the smaller the resistance in the discharge path. When the piston is being driven in, more and more openings in the wall of the pipe are covered and, thus, the resistance in the discharge path is automatically increased.
Preferably, the pipe extends into the piston over the entire piston stroke. This allows a speed control over the entire piston stroke. The pipe is guided over the entire piston stroke in the piston and, thus, fixed so that possibility of error remains small.
Preferably, a seal is provided between the piston and the pipe. This creates clearly defined flow relations. Moreover, hydraulic fluid is prevented from seeping through a gap between the piston and the pipe and, thus, from resulting in uncontrolled flow relations.
Preferably, the pipe is open at its face. This is of lesser importance for the lowering motion, i.e., the opening of the nips. However, this opening can be advantageous during closing, i.e., the hydraulic fluid in the interior of the piston can act in a supporting manner so that the piston can be driven out faster.
Advantageously, the pipe is centrally positioned in the cylinder housing and centrally in relation to the piston. In this way, unsymmetrical stress can be omitted.
In one embodiment it may be preferred for the openings to be evenly distributed over the length of the pipe. This can be achieved, e.g., by sizing all openings equally and by positioning them in the longitudinal dir

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