EP1559831A1 - Extended nip calender - Google Patents

Abstract

The wide nip (4) at a calender to polish paper and cardboard webs (5), with a shoe roller and a counter roller, is structured so that at a given pressure between the shoe roller (2) and the counter roller (3) at least 70% of the press length while the roller mantle (10) is in contact with the web is after the plane (16) through the roller axes in the direction (6) of web travel. The press shoe (11) has a bump (17) at the entry side which lower than the bump (18) at the exit side.

Description

The invention relates to a wide-nip calender with a Shoe roll and a counter roll, which is between them form a broad nip, wherein the shoe roll has a circumferential Jacket has, by a pressure shoe with approximately concave contact surface in the direction of the Counter roller is pressurizable, and the pressure shoe is arranged asymmetrically to a plane in which the Shafts of shoe roll and counter roll lie.

Such a broad-nip calender is known from DE 43 44 165 A1 known. By the displacement of the pressure shoe to leaking side of the nip and relative to the plane, in which the axes of shoe roll and counter roll lie, you can use a pressure curve to an optimal Optimize smoothing result.

The smoothing of a web, in particular a paper web or cardboard sheet, in a wide-nip calender has the Advantage of being compared to smoothing in one Calender, which is formed by two rollers, a relative long treatment time of the web reached in the nip. This longer treatment time allows to reduce the pressure without deteriorating Smoothing result receives. In addition, the satin finish in a wide-nip calender the advantage that the volume of the web is spared, i. the train becomes not as strongly compressed as when satinizing between two rollers.

The counter-roller is usually heated. The surface temperature can be up to 300 ° C. For this Reason is the pressure shoe from the at rest cylindrical Outline of the coat moved out to outside the work area where the shoe roll and the mating roll through the wide nip passing Railway are separated, a contact between in the Usually heat-sensitive coat and the counter roll to avoid.

The calendering in a wide-nip calender has proven itself many webs, in particular webs of paper or cardboard, proven. In some cases, however, in particular observe in the calendering of paper webs, that wrinkles form in the web.

The invention is based on the object, wrinkling to avoid.

This task is at a wide-nip calender of the beginning mentioned type achieved in that at a predetermined Contact pressure between shoe roll and counter roll at least 70% of a contact length in which one the broad nip continuous web contact with the mantle has, lie in web running direction behind the plane, the Defined by the axes of shoe roll and counter roll is.

It is believed that wrinkling in the web by a stretching and shrinking process of the jacket is produced in the nip. The contact shoe has, due to its nearly concave shape, a inlet side "hump" and an outlet side "Hump" and in between a valley. This embodiment is necessary for the web to be satin over the Anpreßlänge with a predetermined pressure at the Counter roll can rest. This pressure must indeed over The contact length should not be constant. Nevertheless, should be in usually the contour of the pressure shoe at least substantially the outer contour of the counter roll correspond. If you change the conditions over the entire contact length would like to keep constant, then the contact surface of the Anpreßschuhs a curvature with a radius approaching the radius of the backing roll plus the thickness of the shell plus the thickness of the wide nip passing through Railway corresponds. This has the consequence that the coat on the inlet and outlet side humps of the pressure shoe is stretched. In the intervening, concave zone the coat can contract again. By this shrinkage, which is pressed on the in the nip Railway transfers, wrinkles can arise in the web. The train would be with it committee. If you now the pressure shoe asymmetric builds or orders, then is the inlet-side contour of the pressure shoe shallower. Accordingly The coat is when entering the nip not stretched as much as before. Accordingly also results in a reduced shrinkage in the concave contact surface. This reduced shrinkage is then no longer sufficient to cause wrinkling to lead, if 70% of the contact length behind the plane lie the axes of mating roll and shoe roll connects with each other. At the outlet side of the pressure shoe then results in a stronger strain. This is largely uncritical. If the strain transferred to the railway, this has no disadvantage Consequences. The subsequent shrinkage of the shell takes place then in an area where the coat is not Contact more by train.

Preferably, at least 80%, in particular at least 95%, the contact length behind the plane. The bigger the area of the Anpreßlänge is behind the plane lies, the lower the risk that the coat shrinks in contact with the railway. Exclude You can certainly do this if 100% of the Anpreßlänge lie behind the plane. At the contact pressure can it is the operating pressure that comes with the satin finish the railway is chosen. One can also be arbitrary Specify selected minimum pressure of, for example 0.1 MPa.

Preferably, the pressure shoe has an inlet side and a discharge-side hump, wherein the inlet side bump lower than the outlet side Hump is. Together with the asymmetric arrangement the Anpreßlänge this leads to a further reduction the stretching of the sheath before contact with the train. Accordingly, the risk is one Shrinking the coat as long as he is still in contact with the train stands, lower.

Preferably, the jacket is fiber reinforced. This too is a measure to reduce the shrinkage of the shell small hold. A fiber reinforced mantle stretches across a non-fiber reinforced sheath that otherwise Equally trained, less strong. Accordingly the shrinkage is also lower.

Preferably, the jacket is at its trajectory in contact with a hard, smooth surface Surface layer provided. This surface layer then causes a reduced friction against the train. Should it in the coat to a shrinking process come, then this shrinking will not be complete or even not transferred to the train because of Coat can glide over the track something. Because the In addition, surface layer is hard, it provides additionally a mechanical resistance against Shrink.

Preferably, the surface layer is thermally conductive educated. This has the added benefit of being one via the surface layer, a quantity of heat in the web can register in order to smooth it out better. The smoothness The surface layer then has two tasks. she On the one hand leads to the above-mentioned friction reduction between the coat and the web. She takes care of others for improved smoothness of the jacket Surface of the railway. Since usually primary the side adjacent to the counter roll is smoothed, This results in an improved two-sided smoothing. It is particularly preferred that the surface layer is formed as a metal layer. A metal layer is a particularly simple embodiment. For example, you can vaporize a metal on the jacket or otherwise. One can under Circumstances also a metal band between the jacket and lead the train through the wide nip.

Preferably, the web abuts against the backing roll before she comes in contact with the coat. In this embodiment one is in the design of the stretching behavior of the coat freer.

It is particularly preferred that the jacket a Stretching zone having a maximum elongation, in Running direction is located in front of a position at which the coat comes in contact with the train. When the pressure shoe pushed out of the contour of the undeformed shell is, arises, as stated above, always an elongation of the coat. Now, if you stretch, or at least the maximum elongation to take place in one area leaves, where still no contact between the coat and the Course, then the coat can be up to contact with shrink the web. A transfer of shrinkage the train then no longer takes place or is strong reduced.

Fig. 1

eine schematische Darstellung eines Breitnip-Kalanders und

Fig. 2

eine vergrößerte Ausschnittsdarstellung nach Fig. 1.

The invention will be described below with reference to a preferred embodiment in conjunction with the drawings. Herein show:

Fig. 1

a schematic representation of a wide-nip calender and

Fig. 2

an enlarged sectional view of FIG. 1.

A wide-nip calender 1 has a shoe roll 2 and a Counter roller 3, which has a wide nip between them 4 form, through which a web 5 with a running direction. 6 is guided.

The counter roll 3 is a hard, heated roll. When Example of a heating possibility are several represented peripheral bores 7 through which a heat transfer medium, For example, hot oil to be passed can, to the surface 8 of the backing roll 3 on a Temperature up to 300 ° C to heat. The counter roll has an axis of rotation 9.

The shoe roll 2 has a circumferential jacket 10, with the help of a pressure shoe 11 in the direction of the Counter roll 3 is pressed. The pressure shoe 11 has a concave pressing surface 12, the concave shape the shape of the counter roll 3 is adapted. The contact surface thus has a credit to a radius, the radius of the backing roll 3 plus the thickness of the shell 10 plus the thickness of the web 5 corresponds. deviations of such a shape are possible.

The pressure shoe 11 is on a coat 10 passing through Carrier 13 via at least one pressure transducer 14th supported. By applying the pressure transducer 14 or the pressure transducer 14 can be in the extended nip 4 a predetermined Create pressure to act.

The jacket 10 is cylindrical in the unloaded state and runs in operation in the manner of a roller an axis 15 um. The two axes 9, 15 lie in one common level 16.

It can now be seen that the pressure shoe 11 is not is arranged symmetrically to this level 16, but asymmetrical to it. At least 70% of the length on which the web 5 in the nip 4 has contact with the jacket 10, lie in the web running direction 6 behind the level 16. Cheaper is it, if an even greater part in the direction of travel 6 is behind level 16, for example 80% or even 95%. In extreme cases, even 100% of these Contact length in the direction 6 behind the plane 16, as shown in Fig. 2.

In the direction 6 on the inlet side of the Clamping surface 12 is an inlet-side hump 17 and on the other side of the pressure surface 12 is an outlet side Bump 18 provided. Of course, extend the two bumps 17, 18 just like the pressure surface 12 over the entire working width of the wide-nip calender 1. The hump 17 is always smaller than the Hump 18 and may even be omitted altogether.

If now the coat 10, which in its "resting form" the Form of a circular cylinder has, by extending the Pressing shoe 11 is deformed, then the jacket 10th stretched when he over the inlet-side hump 17 running. To the center of the pressure surface 12 out lets the strain after and the jacket 10 shrinks. After that he will stretched again by the outlet-side hump 18. This has the consequence that wrinkles form in the web 5 can, when the shrinkage of the coat on the Lane 5 transmits.

To avoid this, designed the pressure shoe 11th so that the inlet-side contour is flatter. At the Embodiment of Fig. 1 is for example the inlet-side bumps 17 lower than the outlet side Höcker 18. Behind the level 16 (in running direction 6) creates a significantly greater pressure length and thus a much larger pressure surface than the inlet side.

At constant pressure profile is thus the pressure force no longer on the center line or axis 9 of the counter roll 3 directed, but generates a tilting moment to this line.

In the embodiment of FIG. 2, the pressure shoe 11 even offset so far that the contact surface 12 completely in the direction 6 of the web 5 behind the Level 16 is located. The inlet-side hump 17 is so small, that he is no longer visible. You can do it also completely omit. The web 5 is located on the counter roll 3, before contacting with the shell 10 of the shoe roll 2 comes into contact.

The jacket 10 is made of an elastic material and can be reinforced with fibers 19 to increase strength be. It can also be a surface layer 20 of a hard, smooth and thermally conductive material. The Surface layer 20 may be metallic, for example Layer be formed.

In the embodiment of Fig. 2, the web 5 touches the counter roll 3, before coming into contact with the jacket 10 comes. In addition, it is ensured that an elongation of the jacket 10 takes place before the jacket 10 and the web 5 come into contact. This arrangement can may be problematic because of the coat 10 on the outlet side bump 18 of the pressure shoe 11th is stretched very much, especially at very long Wide nip and / or counter-rollers 3 with a small diameter. Therefore, it may be cheaper to be a part of To press contact shoe 11 in front of the plane 16, like this can be seen from Fig. 1.

The length of the broad nip 4 and thus the effective length of the pressure shoe 11 of course varies with the pressure. To be able to make a clear definition here, will provided that the 70%, with the effective Anpreßlänge is behind level 16, either at the intended Operating pressure can be achieved or at a Pressure of 0.1 MPa.

To stay flexible, the wide-nip calender 1 also be designed so that the position of the Pressing shoe 11 by changing the corresponding parts (Contact shoe 11, pressure transducer 14) can still vary.

Claims (9)

Wide-nip calender with a shoe roll and a backing roll, which form a broad nip between them, wherein the shoe roll has a circumferential jacket which can be pressurized by a pressure shoe with an approximately concave contact surface in the direction of the backing roll, and the pressure shoe is arranged asymmetrically to a plane in which the axes of the shoe roll and counter roll lie, characterized in that at a predetermined contact pressure between shoe roll (2) and counter roll (3) at least 70% of a Anpreßlänge in which a broad nip (4) continuous web (5) contact with the jacket (10), in the web running direction (6) lie behind the plane (16) defined by the axes of the shoe roll and the counter roll. Calender according to Claim 1, characterized in that at least 80%, in particular at least 95%, of the pressing length lie behind the plane (16). Calender according to Claim 1 or 2, characterized in that the pressure shoe (11) has an inlet-side bump (17) and an outlet-side bump (18), wherein the inlet-side bump (17) is lower than the outlet-side bump (18). Calender according to one of claims 1 to 3, characterized in that the jacket (10) is fiber-reinforced. Calender according to one of Claims 1 to 4, characterized in that the casing (10) is provided with a hard, smooth surface layer (20) on its surface in contact with the web (5). Calender according to Claim 5, characterized in that the surface layer (20) is designed to conduct heat. Calender according to claim 5 or 6, characterized in that the surface layer (20) is formed as a metal layer. Calender according to one of Claims 1 to 7, characterized in that the web (5) bears against the counter-roller (3) before coming into contact with the jacket (10). Calender according to Claim 8, characterized in that the jacket (10) has a stretching zone with a maximum elongation which lies in the running direction (6) in front of a position at which the jacket (10) comes into contact with the web (5).

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