EP2480717A1

EP2480717A1 - Roller covering

Info

Publication number: EP2480717A1
Application number: EP10740615A
Authority: EP
Inventors: Franz Grohmann
Original assignee: Voith Patent GmbH
Current assignee: Voith Patent GmbH
Priority date: 2009-09-23
Filing date: 2010-08-03
Publication date: 2012-08-01
Also published as: DE102009029695A1; CN102648316B; CN102648316A; WO2011035969A1

Abstract

The invention relates to a roller covering, particularly for a mating roller for use in a calender section (100) of a paper machine, wherein the mating roller comprises a first functional layer (34), which has a first surface forming the outer lateral surface of the roller covering and a second surface arranged opposite of the first surface, and wherein the mating roller comprises a second functional layer (33), the outer lateral surface of which adjoints the second surface of the first functional layer (34), and wherein the material of the first functional layer (34) has a more homogeneous composition as compared to the material of the second functional layer (33).

Description

roll cover

The invention relates to roll covers in particular for calender rolls for machines for producing and / or finishing fibrous webs such as paper webs.

The generation of smoothness and gloss on the surface of a paper web takes place in the calender section of a paper machine. In the calender section, the paper web is guided under high pressure and usually also at high temperatures via so-called hard calender rolls, the surface of which is not only very hard but also has a low roughness corresponding to the paper surface to be achieved. The pressure is generated with a counter roll which presses the paper web against the hard calender roll. The roll cover of the counter roll is elastic, to press the paper web flat against the hard calender roll.

In the first section of the calender section, first the first of the two surfaces of the paper web is smoothed or calendered. In this area, the counter roll presses on the still unsmoothed and thus rough side of the paper web, whereby the roll reference surface is exposed to a high mechanical stress. In order to ensure a high availability and service life of the roll surface with regard to economical operation of the paper machine, the cover of a counter roll used in this section of the calender section must be optimized for high mechanical resistance and provided with a correspondingly abrasion-resistant surface. A corresponding mechanical resistance and abrasion resistance is achieved by adding fillers and / or fibers to the plastic material used for the manufacture of the functional coating of the roll cover. By functional layer or functional layers are meant the layers of a roller which are substantially responsible for the formation of the nip and the surface properties of the roller in the nip area.

In the subsequent second section of the calender section, the second of the two surfaces of the paper web is then smoothed. In this area the reference expresses the counter roll against the previously smoothed side of the paper web. In order not to impair the surface quality of this already smoothed paper web page, the roll cover of a counter roll used in this section of the calender section is optimized for the most homogeneous and smooth surface properties possible. For this purpose, the functional layer of the cover is made, for example, of a plastic material with isotropic properties, ie without admixture of fillers and fibers or with admixture of lesser amounts and / or finer fillers and / or fibers. However, the missing or smaller amount of filler has a negative effect on the mechanical resistance of the covers and in particular their abrasion resistance. Furthermore, these roll covers are sensitive to cracking due to local overloads, such as those caused by deposits on the roll surface or edge overloads. Due to the small amount of filler, resulting cracks also tend to spread in all directions. In addition, local damage to the datum surface leads to a local increase in temperature at the point of damage, which further increases the damage and eventually leads to spalling of cover material. In order to maintain an economical operation of the paper machine, therefore, when using roll covers with different reference qualities as described above, more spare rolls must be kept available than when using only one reference quality. On the basis of what has been said, it is therefore desirable for counter rolls, which are intended for use in the second section of the calender section of a paper machine, to specify a roll cover which has better mechanical resistance than the counter roll covers conventionally used in this calender section.

According to one embodiment, the roll cover for a mating roll for use in a cal alternation of a paper machine comprises a first one Functional layer layer and a second functional layer layer. The first functional layer layer has a first surface, which forms the outer lateral surface of the roll cover, and a second surface arranged opposite the first surface, and the second functional layer layer has an outer lateral surface, which adjoins the second surface of the first functional layer layer. Here, the material of the first functional layer layer has a relation to the material of the second functional layer layer more homogeneous composition.

The base material of the first and the second functional layer layer is formed in another embodiment of a polymer matrix, which is in particular selected from epoxide, polyurethane, polyether, polycarbonate and polyetheretherketone, whereby the properties of a roll surface can be adjusted within a wide range. For unrolling on paper web surfaces having a high degree of smoothness and gloss, the first functional layer layer according to a further embodiment contains no fillers.

In order to form a functional layer with higher wear resistance, the first functional layer layer according to a further embodiment contains fillers whose mean particle size is smaller than the average particle size of the fillers contained in the second functional layer layer.

In a further embodiment, the first functional layer layer has a smaller amount of fillers than the second functional layer layer, in order not to impair the gloss and smoothness of a paper web surface during unrolling.

In a further embodiment, the first functional layer layer and the second functional layer layer each have fibers, the proportion of the fibers in the first functional layer layer being less than the fraction of the fibers in the second Functional layer layer, to avoid that unevenness forms on the roll surface.

In a further embodiment, the thickness of the first functional layer layer is less than the layer thickness of the second functional layer layer, whereby forces and deformations acting on the first functional layer layer can be effectively absorbed by the second functional layer layer and thus an overload of the first functional layer layer with the risk of spalling of material is prevented.

According to a further embodiment, the composition of the material of the second functional layer layer in the direction of the second surface of the first functional layer layer has an increasingly homogeneous consistency, which corresponds essentially to the consistency of the first functional layer layer on its second surface at the interface to the second surface of the first functional layer layer. In this way, a gradient of the fiber and filler portions is created in the second or between the second and first functional layer layer, which ensures a steady and thus gentle transition of the introduction of force and the deformations in the second functional layer layer.

In order to improve the adhesion of the multilayer functional layer on the roller, in a further embodiment a carrier layer is arranged between the second functional layer layer and the roller core. According to one embodiment, a calender roll having a roll cover as specified above is used in a calender section of a paper machine, the calender roll being used after the first functional layer layer has been removed in the first section of the calender section by pressing the roll against the still unsmoothed surface of the paper web.

Another embodiment relates to a method of making a roll cover for a backing roll for use in a calender section of a Paper machine with steps for impregnating a fibrous web with a polymer, the fillers are added, winding the resin-impregnated fibrous web around the base layer, which encloses the roll body, curing the applied layer to the base layer for finishing the second functional layer layer and applying the first functional layer layer. The polymer possibly containing fibers and / or fillers for forming the first functional layer layer is thereby applied to the second functional layer layer in a casting process or a coating process, if the amount of the fibers in the polymer is less than 5% by volume.

Incidentally, the application of the first functional layer layer comprises steps for impregnating a fibrous web with a polymer to which fillers have been added, winding the resin-impregnated fibrous web around the second functional layer layer and curing the layer applied to the second functional layer to complete the first functional layer layer.

Further features of the invention will become apparent from the following description of exemplary embodiments in conjunction with the claims and the figures. The individual features can be realized in one embodiment according to the invention depending on one or more. In the following explanation of some embodiments of the invention reference is made to the accompanying figures, of which

Figure 1 is a schematic representation of a calender section for a

Paper machine in a side view and shows

Figure 2 shows the structure of an elastic calender roll in a schematic

Partial cross section through the surface region of the roller illustrated. Figure 1 illustrates a multinip calender 100 for smoothing the paper web surfaces toward the end of the papermaking process. The calender 100 has two sections 101 and 102, which in the example shown are arranged one above the other. In the first section 101 located at the top, the first surface 11 of the paper web 10 is smoothed; in the second section 101 located at the bottom, the second surface 12 of the paper web 10 is smoothed. The smoothing surface or side of a paper web 10 abuts the surface of the hard calender roll 20 when passing through a nip formed between a hard calender roll 20 and an elastic calender roll 30 (that is the gap between the two rolls).

The hard calender roll usually has a reference formed by a metal alloy in which hard grains are embedded for increasing the surface hardness. The surface roughness of this calender roll cover is one of the factors that determine the paper finish achieved in the calender 100. Of further critical importance is the formation of the nip between hard and elastic calender rolls, i. the shape of the nip area and the pressure distribution within the nip area. These are essentially determined by the reference of the counter roll 30.

In the first section 1 01 of the calender section 1 00 of a (not shown in the figures) paper machine always the same page 1 1 of the paper web 10 is guided over the outer surfaces of the hard calender rolls 20 and thus smoothed. Under lateral surface in this application, in accordance with the common technical language use, the surface of a volume, which results from rotation of a graph of fun ction about a coordinate axis, wherein the end faces are not to be counted to the lateral surface. The deflection of the paper web 10 is effected by means of deflection rollers or rollers 40, which are also used to guide the paper web in and out of the calender section.

In order to be able to glaze the second side 12 of the two paper surfaces in the second calender section 102, the paper web 10 is guided between the two calender sections 101 and 102 through a change nip formed by two elastic calender rolls, so that in the following nip this second paper web surface 12 over the outer surfaces of the hard calender rolls to be led. In this calender section 102, the surface of the cover of the elastic mating rollers 30 now presses against the previously smoothed side 11 of the paper web 10 and, in order not to worsen the already completed smoothing of this page, must be provided with a smooth and homogeneous surface. Because rough as well as inhomogeneous roll surfaces lead to small-scale pressure changes in the nip area, which provided the already smoothed paper surface 1 1 with an embossed pattern.

Therefore, the covers of these elastic calender rolls used in the second section 102 of a calender 100 are provided with an outer functional layer 34 as illustrated in FIG. 2, which has as homogeneous a material composition as possible and a smoothly ground surface of low roughness. The surface of these functional layers 34 preferably has an average roughness of less than Ra = 0.3 μιτι on.

In particular, polymers such as, for example, epoxy resins, polyurethanes, polyethers, polycarbonates and polyetheretherketones are used for this purpose. The advantage of cast covers lies in the isotropy of the material and the resulting very smooth and homogeneous reference surface. However, the mechanical and dynamic strength of these functional layers is limited and cracks developed in the layer tend to spread rapidly and widely because there are little or no crack stops in the form of fibers or coarse fillers.

For improvement, therefore, fillers are embedded in the polymer matrix of the functional layer, which give it a higher elasticity and also mechanical resistance. Oxides, carbides or nitrides such as silica, alumina, titanium dioxide, titanium carbide or titanium carbonitride can be used as fillers, functional fillers 34 for the second calender section 102 preferably containing fine fillers, ie smaller fillers than functional layers 33 for the first calender section 101, for example based on of silicon oxide and / or titanium oxide. The particle sizes or particle sizes of the fillers for the functional layer 34 are preferably in the range of 20 nm to 1 2 μιτι, wherein the Fül Istoffpartikel also very homogeneously distributed in the polymer matrix, so that none of the smoothing of the paper web surface 1 1 impairing Form material inhomogeneities between fillers and polymer matrix. In contrast, for the formation of a functional layer 33 for use in the first calender section 101 fillers with dimensions up to 10 m are used. The filler content of the functional layer 34 is usually less than the filler content of a functional layer 33 which is designed for contact with a still unsmoothed paper web surface. It usually depends on the type of paper to be produced, for example for coated or magazine paper, and is generally between 2 and 20 percent by volume. Furthermore, the mechanical resistance can also be improved, or in addition, by the addition of fibrous materials, for example aramid and / or glass fibers, which prevent an intensification of small damages in the covering layer. In the functional layer 34, the pulp fraction with values of 1 to 5 percent by volume can be chosen substantially lower than in the functional layers 33 for the first section 101 of the calender 100.

To ensure the adhesion of the functional layers 34 and 33 on the calender roll 30, the elastic roll cover 10 has a base layer 32, referred to in the technical language baselayer, which rests on the core 31 of the calender roll 30 and a dynamically fixed connection between roll core and functional layer manufactures. The base layer 31 consists essentially of a fiber-reinforced resin impregnation with fillers, which is wound on the roll core, cured and then ground in shape. Usually, glass fabric is used to make the base layer 32.

To further improve the mechanical resistance of the functional layer of a suitable for the second portion 102 of a calender 100 elastic Roller 30, the functional layer is performed in multiple layers according to an embodiment. FIG. 2 shows an elastic calender roll 30 with such a multilayer functional layer. In the illustrated example, the invention is essentially independent of a first functional layer layer 34 and a second functional layer layer 33 arranged thereunder.

The first functional layer layer 34 has two mutually opposite lateral surfaces, of which the outer simultaneously forms the outer peripheral surface of the elastic calender roll 30. The other lateral surface adjoins the outer lateral surface of the second functional layer layer 33, and is adhesively bonded thereto. The second functional layer 33 is applied to the base layer 32, which ensures the adhesion of the functional layer to the roll core 31. The structure and composition of the second functional layer layer 33 correspond to that of a functional layer for use in the first section 101 of a calender 100. This second functional layer layer is optimized in particular for abrasion resistance and mechanical resistance, in particular with regard to a resistance to local overloads, so that the size of the damage is limited in the event of damage and there is only a low probability of consequential damage from broken parts. For the formation of the second functional layer layer 33, it is possible, for example, to use crosslinked epoxy resins which are reinforced with fine and / or coarse fillers and short fibers. The proportion of fillers is preferably selected in the range of 10 to 30% by volume, that of the short fibers in the range of 5 to 15% by volume.

Aramid fibers are preferably used as short fibers. The first functional layer layer 34 is optimized for use in the second section 102 of a calender 100, ie. Achieving and maintaining a very smooth and homogeneous surface. For the formation of the first functional layer layer, for example, crosslinked epoxy resins can be used, embedded in the fine fillers with dimensions of preferably less than 1 μιτι and short fibers become . The adhesive filler in the first functional layer layer 34 preferably has values in the range from 2 to 20% by volume, that of the short fibers values from the range from 0.5 to 12% by volume. The short fibers are preferably formed by aramid fibers.

Furthermore, if the proportion of the fillers exceeds 13% by volume, the proportion of short fibers is preferably less than 8% by volume. Similarly, if the proportion of short fibers exceeds 8 volume percent, the proportion of the fillers is preferably less than 13 percent.

By applying the first functional layer layer 34 optimized for the second calender section 102 to a second functional layer layer 33 optimized for the first calender section 101, the mechanical and thermal stresses acting on the first functional layer layer 34 are transferred to the second, more stable functional layer layer, thereby increasing the mechanical resistance of the functional layer improved first functional layer 34. Because of the resulting better resistance to local overloads, the described multiple structure of the expansion layer of an elastic roll cover reduces the likelihood of flaking and consequential damage from broken parts.

In a further embodiment, filler content and particle sizes of the fillers in the second functional layer layer 33, as well as possibly also their fiber content in the outer edge region, increasingly decrease relative to the first functional layer 34. Such a gradual transition to the first functional layer layer minimizes stresses between the first and second functional layers and additionally increases the mechanical resistance of the first functional layer. The gradual transition can be regarded as an independent intermediate layer or can also be designed as such, which is arranged between the first and second functional layer layers. However, the gradual transition can also extend over a large part or the entire second functional layer layer 33, since this functional layer layer layer, as will be explained below, does not coincide with the smooth one Side of a paper web comes into contact, but possibly only with the unsmoothed. A negative influence on the final smoothing result by a gradually changing filler and fiber binding is not to be feared in these applications.

Usually, the functional layer of an elastic calender roll cover has a thickness of about 5 b m s 1 5 m. In the case of a two-layer functional layer, in one embodiment, the layer thickness of the first functional layer 34 is less than that of the second functional layer. For example, the first functional layer has a layer thickness of about 1 to 3 mm, while the second functional layer has a layer thickness of about 4 to 12 mm.

In addition to a higher mechanical resistance in comparison to conventional roller covers for the second section 102 of a calender 100, a functional layer having multiple layers as described has the further advantage that the roller can continue to be used in the first section 101 of a calender after wear of the first functional layer, in that the roll surface moves against the still unsmoothed side of the paper web. You can reduce the number of replacement rollers needed to maintain calendering. Of course, the first functional layer can alternatively be renewed after wear on the second functional layer again.

In accordance with one embodiment, in order to form the second functional layer 33, a fibrous web is impregnated with a polymer, for example a resin or a resin mixture, to which the fillers have been added. The polymer-impregnated fibrous web is then wound around the base body surrounding the roll body. Subsequently, the polymer is cured by means of heat and / or radiation. If the proportion of the fibers in the first functional layer layer 34 is less than about 5 percent by volume, this is applied in an analogous manner to the production of the second functional layer layer, depending on Embodiment different Füllstoffarten or amounts and polymer systems can be used. This layer is also cured by the action of heat and / or radiation. If the first functional layer layer has a proportion of fibrous materials of significantly less than 5% by volume, the first functional layer layer 34 is preferably applied to the second functional layer layer 33 in a casting process or in a coating process. Of course, first and second functional layer layer can also be cured together in a common step.

Claims

Claims 1. Roll cover for a counter roll (30), in particular for use in a calender section (100) of a paper machine, comprising:

- A first functional layer layer (34) having a first surface, which forms the outer surface of the roll cover, and with a relation to the first surface arranged second surface, and

- A second functional layer layer (33) whose outer lateral surface adjoins the second surface of the first functional layer (34), wherein the material of the first functional layer layer (34) has a relation to the material of the second functional layer layer (33) more homogeneous composition.

2. Roll cover according to claim 1, wherein the base material of the first and the second functional layer layer is formed by a polymer matrix, which is in particular selected from epoxide, polyurethane, polyether, polycarbonate and polyetheretherketone.

3. roll cover according to claim 1 or 2, wherein the first functional layer layer (34) contains no fillers.

4. roll cover according to claim 1 or 2, wherein the first functional layer layer (34) contains fillers whose average particle size kl e i n e r i sta l s d i e m ittl with more particle size of the fillers contained in the second functional layer layer (33).

5. roll cover according to claim 1, 2 or 4, wherein the first functional layer layer (34) has a smaller amount of fillers than the second functional layer layer (33).

A roll cover according to any one of claims 1, 2, 4 or 5, wherein the first functional layer layer (34) and the second functional layer layer (33) each comprise fibers, and wherein the proportion of the fibers in the first functional layer layer (34) is less than that Proportion of the fibers in the second functional layer layer (33).

7. roll cover according to one of the preceding claims, wherein the layer thickness of the first functional layer layer (34) is smaller than the layer thickness of the second functional layer layer (33).

A roll cover according to any one of the preceding claims, wherein the composition of the material of the second functional layer layer (33) towards the second surface of the first functional layer layer (34) has an increasingly homogeneous consistency which is at the interface with the second surface of the first functional layer layer in the

Substantially corresponds to the consistency of the first functional layer layer (34) on the second surface.

9. roll cover according to one of the preceding claims, wherein a carrier layer (32) between the second functional layer layer (33) and

Roller core (31) is arranged.

Use of a calender roll having a cover according to one of the preceding claims in a calender section (100) of a paper machine, the calender roll (30) being used after the removal of the first functional layer layer (34) in the first section (101) of the calender section (100) in that the roller (30) presses against the still unsmoothed surface of the paper web (10).

1 1. A method of making a roll cover for a backing roll for use in a calender section (100) of a paper machine comprising steps of soaking a fibrous web with a polymer, the Fillers are mixed, winding the resin-impregnated fibrous web to the base layer, which encloses the roll body, curing the applied to the base layer layer to complete the second functional layer layer (33) and applying the first functional layer layer (34), which may contain fibers and / or fillers Polymer for forming the first functional layer layer (34) in a casting process or a coating process on the second functional layer layer (33) is applied, if the proportion of fibers in the polymer is less than 5 percent by volume.

12. The method of claim 1 1 comprising steps for impregnating a fibrous web with a polymer, the fillers are added, winding the resin-impregnated fibrous web to the second functional layer layer (33) and curing of the second functional layer layer (33) applied layer for finishing the first 35th Functional layer layer (34) if the proportion of fibers in the polymer is more than 5% by volume.