Roller cover for a machine for the production or finishing of a fibrous web

Abstract

Roller covering (8) for a press device of a machine (1) for the production or finishing of a fibrous web (2), such as paper, tissue, or cardboard web, with a plurality of individual structures (11) spaced apart from one another over the circumference of the roller covering (6), wherein each individual structure (11) comprises or consists of a groove and / or a series of bores (10) and wherein the spacing and / or depth of adjacent individual structures (11) changes in the circumferential direction of the roller covering (8).

Description

[0001] The invention relates to a roll cover and a roll for a machine for producing or finishing a fibrous web, such as a paper, cardboard or tissue web, the use of such a roll, a pressing device and a machine comprising such a roll, in detail according to the features of the independent claims.

[0002] Such rollers are available in a variety of positions and with a variety of functions in the machine mentioned above. Rollers with comparatively soft covering layers are suitable for pressing and dewatering the fibrous web, while rollers with comparatively hard surfaces, especially those with a heating device, are primarily used for smoothing and drying the fibrous web.

[0003] Suction press rolls, for example, are used to dewater the fibrous web. These comprise a roll cover arranged on a roll core. The roll core and roll cover have through-holes connected to a corresponding suction device to drain water from the fibrous web through the through-holes. For this purpose, the suction press rolls form a press nip with a corresponding press roll, through which the fibrous web is guided for dewatering.

[0004] The present invention relates, among other things, to suction press rolls of this type, but also to other rolls that can be used in a paper machine. Such rolls are described, for example, in DE 197 04 682 A1, DE 10 2011 084 980 A1, EP 241 389 A1, or DE 11 2007 001 328 T5.

[0005] Vibrations are unavoidable in the operation of such machines. These have a detrimental effect when different vibrations overlap. This leads to interference, which can be transmitted from the machine to the rollers and ultimately to the fiber web being produced. This can result in mass fluctuations in the longitudinal direction, i.e., in the production direction of the fiber web. These mass fluctuations can manifest as bands in the width direction, which are not noticeable during or after the production of the fiber web and only become apparent during printing.

[0006] Accordingly, the object of the invention is to provide a roll cover, a roll, its use, a pressing device, and a machine comprising such a roll that are improved over the prior art. In particular, the formation of mass fluctuations in the longitudinal direction of the fibrous web to be produced or finished is to be minimized.

[0007] The object is achieved by a roll cover, a roll, its use, a pressing device, and a machine having the features of the independent claims. Further advantageous features of the inventive embodiment are found in the subclaims.

[0008] The inventor has recognized that the disadvantages mentioned above can be avoided by providing a roll covering whose grooves and / or blind bores are specially designed. According to a first alternative of the invention, the grooves and / or blind bores are not distributed symmetrically around the circumference of the roll covering, as has been usual up to now, nor do they form a regular pattern, as has previously been the case. However, the grooves and / or blind bores are also not arranged chaotically or randomly around the circumference. Rather, they are arranged in such a way that individual structures of grooves and / or blind bores result, and the distances between individual structures of grooves and / or blind bores vary from individual structure to individual structure around the circumference. The individual structures can all have the same width when viewed in the circumferential direction, i.e. in the width direction.This means that there is no regularly repeating overall pattern around the circumference of the roll covering, even though the individual structures themselves can be identical to one another. It would also be conceivable for the distances between the individual structures to be the same, but for their widths to vary from individual structure to individual structure in the circumferential direction. According to the second alternative, the depths of the grooves and / or blind holes can vary from individual structure to individual structure. This means, for example, that the hole or groove depth of two directly adjacent individual structures - viewed in the circumferential direction of the roll covering - is not the same, but different. The grooves and / or blind holes can, as previously known, also be arranged symmetrically around the circumference of the roll covering and form a regular pattern.One could also say that the individual structures are evenly spaced from each other in the circumferential direction of the roll cover, but the depths of the holes and / or grooves change in the radial direction.

[0009] Although the effect has not yet been conclusively clarified, such a roller cover according to the invention does not result in constructive interference, but rather in destructive interference with various vibrations that occur during machine operation. This means that certain frequencies that generate harmful vibrations can be reduced. The inventive design of the roller cover now allows mass changes in the longitudinal direction of the fibrous web being produced, which corresponds to the circumferential direction of the roller cover, to be minimized.

[0010] An individual structure within the meaning of the invention is understood to be a spatially interconnected group of several grooves and / or bores. Such a group can be formed by an envelope, i.e. an outer contour that connects all such interconnected grooves and / or bores. The envelope, i.e. the individual structure, can be in the form of geometric figures, such as straight lines or circles. This refers to figures composed of simple elements such as straight lines and circles. Individual structures are thus groups of recesses (grooves and / or bores) interrupted by zones that are free of recesses. Viewed in the circumferential direction of the roll cover, individual structures alternate with zones that are free of such individual structures.

[0011] The distance between two adjacent or consecutive individual structures refers to the smallest occurring length of a perpendicular that lies on the envelope of two adjacent or consecutive individual structures. If the distance varies from individual structure to individual structure across the circumference of the roll covering, then for each individual structure, the distance to one direct neighbor is different from that to the other direct neighbor, viewed circumferentially. This applies whenever three individual structures that are directly adjacent in the circumferential direction are considered. Starting from the middle individual structure, its two neighbors are spaced differently from the middle individual structure in the circumferential direction.

[0012] The holes can be designed as through holes or blind holes. Through holes extend across the entire thickness of the roll cover, viewed in the radial direction relative to its rotational axis. Through holes can be provided for suction rolls. Blind holes, on the other hand, do not extend across the entire thickness of the roll cover. They can be provided for conventional press rolls.

[0013] Grooves can run longitudinally, i.e., parallel to the rotational axis of the roll cover or roll, or circumferentially. Combinations in which the grooves run in both directions, i.e., at an angle to the longitudinal direction, are conceivable.

[0014] According to the invention, the term "functional layer" refers to the surface facing the fibrous web, i.e., the outer surface (radially outermost surface) of the roll cover or roll. This is the surface that comes into at least indirect contact with the fibrous web during normal operation.

[0015] The grooves and / or holes are made in the outer surface, i.e. in the functional layer of the roll cover.

[0016] In principle, the roller cover or roller according to the invention is suitable for any application in the machine mentioned above.

[0017] A fibrous web, as defined by the invention, is understood to be a woven or interlaced web of fibers, such as wood fibers, plastic fibers, glass fibers, carbon fibers, additives, or the like. For example, the fibrous web can be a paper, cardboard, or tissue web. It can essentially comprise wood fibers, although small amounts of other fibers or additives may also be present. This is left to the expert's discretion, depending on the specific application.

[0018] The longitudinal direction refers to the direction parallel to the longitudinal axis of the roll or roll cover. The longitudinal axis also corresponds to the roll's axis of symmetry or rotation. The circumferential direction of the roll cover runs around its radial boundary, around the longitudinal axis.

[0019] The invention also relates to a roller comprising the roller cover according to the invention, which is then arranged on a roller core. The roller cover can be designed such that it cannot be removed from the roller core without destroying the core. The roller can be designed as a suction press roller, in which case it has through holes, or as a press roller, in which case it has blind holes.

[0020] Furthermore, the invention relates to a pressing device for mechanically dewatering a fibrous web, such as a paper, cardboard or tissue web, comprising at least one such roller according to the invention.

[0021] The invention also relates to a machine for producing or finishing a fibrous web, such as a paper, cardboard or tissue web, comprising a pressing device according to the invention.

[0022] Finally, the invention relates to a use of a roller according to the invention in a machine according to the invention.

[0023] Further advantageous embodiments of the invention are explained using exemplary embodiments with reference to the drawings. The features mentioned can be advantageously implemented not only in the illustrated combination, but also individually combined with one another. The figures show in detail: Fig. 1 a partial, schematic representation of a paper machine according to the invention according to a possible embodiment; Fig. 2 shows a schematic, not to scale, cross-section through the longitudinal axis of a roller according to the invention according to a possible embodiment; Fig. 3 a development of the lateral surface of a roll cover according to a first alternative of the invention; Fig. 4 a development of the lateral surface of a roll cover according to a second alternative of the invention;

[0024] In Fig. Figure 1 shows a partial, schematic representation of a possible embodiment of a machine 1 according to the invention, designed here as a tissue paper machine. The fibrous web 2 to be dried and creped, in this case the tissue web, is transported on a fabric from the bottom right and transferred to a heated or heatable drying cylinder 3, such as a Yankee cylinder. The transfer takes place via a roller 6, designed here as a suction press roller. For this purpose, the roller 6 is placed with its radially outermost surface against the radially outermost surface of the drying cylinder 3. As a result, the two elements form a press nip 5 together. The suction press roller 6 is suctioned via a suction device (not shown) to generate a vacuum in order to dewater the fibrous web 2 in the press nip 5.

[0025] After being transferred, the tissue web 2 is dried on the drying cylinder 3 and then detached from the surface of the drying cylinder 3 by creping using a creping doctor 4.

[0026] In Fig. 2 is a schematic, not to scale, cross-section through the longitudinal axis 6.1 of the roller 6, as used in a machine of the Fig. 1 could be used.

[0027] The roller 6 comprises a roller core 7 and a roller cover 8 applied to the radially outer surface of the roller core 7. The roller core 7 and the roller cover 8 have a plurality of communicating bores 10—illustrated here in an exaggerated manner. The bores 10 are distributed around the circumference of the roller 6 and, in this case, are designed as through-bores.

[0028] The water escaping from the fibrous web 2 in the press nip 5 can be drained off via the bores 10 by the suction device (not shown).

[0029] Although the roller cover 8 of the roller 6 in the Fig. While 2 is shown as a single layer, it could also be multi-layered. The roller cover could thus have more than the radially outermost functional layer 9.

[0030] In principle, it would be conceivable that grooves could also be provided instead of or in addition to the recesses shown in the form of bores 10.

[0031] The holes could also be blind holes, which means that they would not reach from the radially outermost surface to the roller core 7. This is indicated by the points in Fig. 2 indicated.

[0032] The representation of the Fig. Figure 3 shows a developed view of the radially outermost surface of the roll cover 8 according to a first alternative of the invention, not drawn to scale. As can be seen, the bores 10 are arranged in rows. These rows can be referred to as individual structures 11, of which three adjacent individual structures 11 are shown here as examples, shown in dashed lines.

[0033] The individual structures can vary in width (in the circumferential direction of the roll cover), ie, for example, three rows of holes 10 are combined to form a corresponding individual structure 11.

[0034] In order to achieve the advantages according to the invention, individual structures directly adjacent to one another in the circumferential direction - in Fig. 3 from left to right - either wider (here, three rows of holes 10 instead of one) or their spacing from one another varies from individual structure 11 to individual structure 11 around the circumference. This creates an irregular, i.e., non-repeating pattern of individual structures 11 and zones in between that are free of individual structures 11 over the entire surface or circumference of the roller 6.

[0035] This special arrangement of the holes 10 results in a special effect. Certain frequencies that generate harmful vibrations during machine operation can be reduced by means of such a roller 6. This allows mass changes in the longitudinal direction of the fibrous web 2 to be produced to be minimized.

[0036] According to the second alternative of the invention as described in Fig.4, all rows of bores 10 are evenly distributed around the circumference, i.e., always spaced at the same distance from one another. Here, too, three randomly selected, directly adjacent individual structures 11 are shown in dashed lines. It can be seen that the distance between them is the same for each individual structure 11 over the entire circumference of the roll cover 8. However, to achieve the same effect as in the first alternative, the depths of the bores 10 vary from adjacent individual structure 11 to adjacent individual structure 11. The same naturally also applies to the embodiment with grooves (not shown).

Claims

[1] Roller cover (8) for a pressing device of a machine (1) for producing or finishing a fibrous web (2), such as a paper, tissue or cardboard web, with a plurality of individual structures (11) arranged at a distance from one another over the circumference of the roller cover (6), wherein each individual structure (11) comprises or consists of a groove and / or a series of bores (10) and wherein the distance and / or the depth of adjacent individual structures (11) changes when viewed in the circumferential direction of the roller cover (8). [2] Roller cover (8) according to claim 1, characterized by that the individual structures (11) are identically formed. [3] Roller cover (8) according to at least one of the preceding claims, comprising a functional layer (9) which is made of a polymer, wherein the polymer comprises or is made of a rubber or polyurethane. [4] Roller cover (8) according to claim 3, characterized bythat the rubber is selected from the group consisting of crosslinked natural rubbers, crosslinked nitrile rubbers (NBR), crosslinked hydrogenated nitrile rubbers (HNBR), crosslinked carboxylated nitrile rubbers, styrene-butadiene rubbers (SBR), ethylene-propylene-diene rubbers (EPDM) and any mixtures of two or more of the aforementioned crosslinked rubbers. [5] Roller cover (1) according to claim 3, characterized by that the polyurethane is produced by reaction of a polyol with a diisocyanate and a crosslinker, wherein the polyol is preferably a polyether or polyester polyol or a mixture of the aforementioned polyols and preferably the diisocyanate comprises: methylenediphenyl isocyanate (MDI), naphthylene-1,5-diisocyanate (NDI), toluene-2,4-diisocyanate (TDI), 1,4-phenylene diisocyanate (PPDI), polycarbonates or polycarbonatediols (PCDL) or mixtures of the aforementioned diisocyanates. [6] Roller (6) for a pressing device of a machine (1) for producing or finishing a fibrous web (2), such as a paper, tissue or cardboard web, which is designed in particular as a press roller or suction press roller, comprising a roller core (7) and a roller cover (8) formed on the roller core (7) according to at least one of the preceding claims. [7] Pressing device for mechanically dewatering a fibrous web (2), such as a paper, tissue or cardboard web, comprising at least one roller according to claim 6. [8] Machine (1) for producing or finishing a fibrous web (2), such as a paper, tissue or cardboard web, comprising a pressing device according to claim 7. [9] Use of a roller (6) according to claim 6 for a machine (1) for producing or finishing a fibrous web (2), such as paper, tissue or cardboard web.

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