Coated roller

Description

[0001] The invention relates to a heatable roller with a coating providing a web contact side, which is suitable for a machine for producing and / or finishing a material web, in particular a fibrous web such as a paper, cardboard or tissue web. The invention also relates to a method for coating such a roller. Heated rollers, such as drying cylinders or calender rollers, usually come into direct contact with the fibrous web to be dried and / or smoothed. In this case, a high heat transfer from the cylindrical roller shell of the heated roller to the fibrous web must be ensured. For this reason, the roller shell of such rollers is usually made of a metallic material such as cast iron or steel. To increase abrasion resistance, it was proposed in the past to coat the radially outer side of the roller shell, i.e.The side that provides the web contact side is provided with an abrasion-resistant coating. Such coatings, such as those known from EP0383466, contain a high proportion of nitrides or carbides and are therefore highly abrasion-resistant, but have the disadvantage of low thermal conductivity. WO 96 / 41918 describes a heatable roller with a coating according to the preamble of claim 1.

[0002] The object of the present invention is to propose a heated roller with a coating of the roller shell, in which the coating has an improved thermal conductivity compared to the prior art combined with sufficient abrasion resistance.

[0003] The object is achieved by a heatable roller which is suitable for a machine for producing and / or finishing a material web, in particular a fibrous web such as a paper, cardboard or tissue web, and which comprises a base body with a metallic and cylindrical roller shell which can be heated by suitable means and on whose radially outer shell surface a coating is arranged at least in sections, which, when the roller is used as intended, provides a web contact side which can be brought into contact with the material web.The heatable roller according to the invention is characterized in that the coating comprises or is formed from at least one metallic or metal-carbide layer, wherein the at least one metallic or metal-carbide layer comprises or is formed from a first layer component providing a matrix and a second layer component distributed in the matrix, and the first layer component has a higher abrasion resistance than the second layer component and the second layer component has a higher thermal conductivity than the first layer component.

[0004] Suitable means for heating the roll shell are generally known and include means in which the roll is heated with steam and / or oil and / or hot water and / or by radiation and / or induction.

[0005] The coating provides at least one layer with a first and a second layer component, wherein the first layer component forms the matrix in which the second layer component is distributed, i.e. the two layer components are present separately from one another in the at least one layer and in particular do not form an alloy with one another. However, separate does not necessarily mean that these two layer components actually have to form two separate layers, e.g. layers lying one above the other. Rather, in the context of the present invention, it is meant that the two layer components each form a phase in their own right, so that the coating has (exactly) two different phases. The phases can therefore be dissolved in one another, penetrate one another, or surround one another.By providing a layer with two separate layer components, of which the first layer component has a higher abrasion resistance than the second layer component and the second layer component has a higher thermal conductivity than the first layer component, an optimal layer component is provided for each of the two functions, namely high thermal conductivity and high abrasion resistance, without having to make compromises, as is the case, for example, with layers with only one layer component that must meet both requirements equally.

[0006] A metallic layer is a layer that essentially contains metallic components or only metallic components. A metal-carbide layer is a layer that essentially contains metallic and carbide components or only metallic and carbide components.

[0007] Unless otherwise stated, the term that a layer or coating essentially has a particular component means that this component is present in more than 50% by weight of the layer or coating.

[0008] Advantageous embodiments and further developments of the invention are specified in the subclaims.

[0009] Preferably, the coating is a metallic or metal-carbide coating, ie all layers of the coating contain essentially or only metallic components or essentially or only metallic and carbide components.

[0010] Various possibilities for the construction of the second layer component are conceivable. For example, it is conceivable that the second layer component is formed essentially, in particular entirely, by a plurality of discrete regions. In this context, "essentially" means at least 75% by weight, preferably at least 85% by weight. The discrete regions of the second layer component have a size in the range of 5 to 50 µm. Adjacent regions form grain boundaries between them.

[0011] The second layer component can also at least partially form a 3-dimensional network. The formation of a 3-dimensional network significantly increases the thermal conduction in at least one layer.

[0012] If the second layer component is constructed at least partially from discrete regions, a plurality, in particular a majority, of these discrete regions can form at least a large part of the 3-dimensional network or the 3-dimensional network, touching one another. If the second layer component is constructed at least partially in one piece, i.e., without grain boundaries, this one-piece section can form at least a large part of the 3-dimensional network or the 3-dimensional network. The majority of the 3-dimensional network is understood to mean more than 50%, in particular more than 70%, of the spatial extent of the 3-dimensional network.

[0013] It is conceivable that the first layer component comprises an iron-based alloy and / or a cermet, in particular is formed therefrom. Furthermore, the iron-based alloy can comprise, in addition to iron, chromium and / or niobium and / or tantalum and / or molybdenum and / or silicon and / or boron and / or tungsten as further component(s). An iron-based alloy is understood to be an iron alloy that consists of more than 50% iron by weight. The iron-based alloy is preferably a high-alloy iron-based alloy. A high-alloy iron-based alloy is characterized in particular by high abrasion resistance. The iron-based alloy is considered to be high-alloyed if the mass fraction of one of its alloying elements is more than 5% by weight. In this context, it is particularly conceivable that the iron-based alloy contains 3-5% tantalum by weight, 3-6% niobium by weight, 19-22% chromium by weight, and the remainder iron.

[0014] The second layer component comprises, in particular, copper or a copper-based alloy, or is in particular formed therefrom. A copper-based alloy is understood to be a copper alloy that consists of more than 50% copper by weight. The ductile behavior of copper can improve the adhesion of the at least one layer, in particular the coating, to the outer surface of the heated roller, thereby improving the heat transfer between the coating and the roller shell.

[0015] It is further preferred that the at least one layer be formed by 60% or more by weight, preferably more than 75%, of the first layer component and by a maximum of 40% by weight, preferably 5-25% by weight, particularly preferably 10-15% by weight, of the second layer component. Such a distribution between the first and second layer components ensures optimal adjustment of high abrasion resistance and high thermal conductivity of the at least one layer.

[0016] Preferably, the coating is formed by the at least one metallic or metal-carbide layer, in particular the coating is formed by a single one of the at least one metallic or metal-carbide layer.

[0017] Furthermore, the at least one layer, in particular the coating, has a specific thermal conductivity of 15 W / mK or more, preferably in the range of 15 W / mK to 250 W / mK, particularly preferably in the range of 15 W / mK to 175 W / mK. The specific thermal conductivity can be measured, for example, with a laser flash device marketed by NETSCH-Gerätebau GmbH, D95100 Selb, Germany, under the designation "LFA 457 MicroFlash."

[0018] Furthermore, the at least one layer, preferably the layer providing the web contact side, has an abrasion resistance of less than 0.5g, preferably less than 0.2g, measured according to ASTM G65-04.

[0019] Specifically, the roll can be a drying cylinder, in particular a drying cylinder for a single-row or double-row cylinder drying group, or a Yankee drying cylinder. It is also conceivable that the heated roll is a heated calender roll.

[0020] Tests conducted by the applicant have shown that sufficient coating stability coupled with good heat transfer is ensured when the coating has a thickness in the range of 50 µm to 1500 µm, preferably 100 µm to 1000 µm, and particularly preferably a maximum of 800 µm. Specifically, the coating thickness can be a maximum of 800 µm for a Yankee drying cylinder, in the range of 150-200 µm for a heated calender roll, and between 200 and 350 µm for a drying cylinder for a single- or double-row cylinder drying group.

[0021] According to a second aspect of the invention, a method for coating a heatable roller having a base body with a metallic and cylindrical roller shell and which can be heated by suitable means is proposed, the method comprising the following steps: a. Providing the radially outer side of the roll shell and b. Applying a coating which comprises or is formed from at least one metallic or metal-carbide layer, wherein the at least one metallic or metal-carbide layer is applied in such a way that it comprises or is formed from a first layer component providing a matrix and a second layer component distributed in the matrix, and the first layer component has a higher abrasion resistance than the second layer component and the second layer component has a greater thermal conductivity than the first layer component.

[0022] The method according to the invention can be used in particular for the recoating of drying cylinders, which is necessary at regular intervals due to the regular wear on the web contact side of such drying cylinders. However, it is generally applicable to other components of the aforementioned machine, especially those subject to highly abrasive stress.

[0023] The method according to the invention therefore preferably comprises the step of surface-treating the radially outer side of the roll shell and / or any existing coating prior to application of the coating, in particular by partially or completely grinding it off. This measure allows grooves to be removed from the web contact side and the roundness of the heated roll, such as the drying cylinder, to be restored.

[0024] To produce the at least one layer, in particular the coating, a thermal spraying process, in particular a high-velocity flame spraying process (also called HVOF), can be used. In this case, for example, a powder mixture comprising the starting materials for the first and second layer components can be used as the starting material for producing the at least one layer. Specifically, for example, a powder mixture can be used which comprises a highly alloyed iron-based powder and a pure copper powder, or which consists of these powders. As an alternative to thermal spraying, the at least one layer, in particular the coating, can be produced using the so-called laser cladding process.

[0025] To increase the smoothness of the web contact side and thus to reduce abrasion and to increase the heat transfer between the web material and the heated roller, it is advisable to grind the metallic or metal-carbide layer providing the web contact side after thermal spraying.

[0026] Comparative tests have now shown that, surprisingly, the invention can achieve reduced wear on scraper blades that are in contact with the coating during roller operation to scrape the roller. This effect is particularly remarkable when copper is used as the second layer component. Although the mechanism of action is not fully understood, it is assumed that the second layer component, bound in the layer component serving as a matrix in the manner of a phase, also acts as a dry lubricant or solid lubricant. During operation, the scraper blade successively removes the matrix, whereby the second layer component is exposed as a result of the abrasion of the coating by the scraper blade and comes to the surface of the scraper blade. The second layer component embedded in the matrix thus "lubricates" the gap defined by the scraper blade and the radially outermost surface of the roller.

[0027] Particularly preferably, the second layer component comprises a soft metal such as copper, brass, gunmetal, aluminum, or lead—particularly acting as a solid lubricant—or a mixture of these or corresponding alloys, or is (fully) made of such a metal. Other materials suitable for the intended use, particularly non-metallic materials such as graphite, are also conceivable. It can be advantageous for use in both heated or heatable rollers and non-heated rollers if the soft metal has a comparatively high thermal conductivity.

[0028] The present invention is therefore fundamentally also applicable to unheated or non-heatable rollers or, generally, to components subject to high levels of abrasion of a machine mentioned above for producing and / or finishing a material web. The same applies analogously to the method for producing a coating, particularly when the second layer component is selected such that, as a solid lubricant, it provides emergency running properties. Particularly preferably, in such a case, the second layer component can be selected such that it has a relatively high thermal conductivity, so that, in the event of emergency running, it can additionally dissipate heat induced by abrasion from the surface of the coating.

[0029] The present invention also relates to a coating according to the invention for a component of such a machine, such as a (non-heated) roller or doctor blade, as well as to a method for producing such a coating. Furthermore, the present invention also relates to a machine as mentioned above for producing and / or finishing a material web, comprising at least one component with a coating according to the invention, such as a roller.

[0030] The invention is explained in more detail below using an embodiment, see Table 1 and Figure 1 as well as Figures 2 and 3 .

[0031] The present embodiment is a coating formed by only one metallic layer, which is applied to the radially outer side of the surface of a Yankee drying cylinder and has the following properties and composition:

[0032] It can be seen that the solution according to the invention provides a significantly higher thermal conductivity than known from the prior art, with comparable abrasion resistance:

[0033] Figure 1 shows a sectional and not to scale representation of a roll shell 1 of a Yankee drying cylinder with the coating 2 according to the invention according to Table 1. The coating 2 is formed by a metallic layer, which in turn is formed by a first layer component 3 providing a matrix and a second layer component 4 distributed in the matrix 3 (shown hatched).

[0034] In the present case, the second layer component 4 is pure copper (99.9 wt%) and is formed entirely by a plurality of discrete regions that are arranged adjacent to one another, at least partially. The discrete regions of the second layer component 4 have a size in the range of 5 to 50 µm. Furthermore, the second layer component 4 at least partially forms a 3-dimensional network, with a plurality of the discrete regions of the second layer component 4 being adjacent to one another and touching one another, forming the 3-dimensional network.

[0035] Layer 2, and thus the coating, has a specific thermal conductivity in the range of 32W / mK and an abrasion resistance in the range of 0.2g, measured according to ASTM G65-04. The thickness of coating 2 is 500µm.

Claims

1. Heatable roll suitable for a machine for the production and / or finishing of a material web, in particular a fibrous web such as, for example, paper, board or tissue web, having a base body which comprises a metallic and cylindrical roll shell which can be heated by suitable means and on the radially outer side of which a coating is applied at least in sections. Paper, board or tissue web, having a base body which comprises a metallic and cylindrical roll shell which can be heated by suitable means and on the radially outer side of which a coating is applied at least in sections which, when the roll is used as intended, provides a web contact side which can be brought into contact with the material web, the coating comprising at least one metallic or metal-carbide layer or being formed therefrom, characterized in that the at least one metallic or metal-carbide layer comprises or is formed from a first layer component providing a matrix and a second layer component distributed in the matrix, and the first layer component has a higher abrasion resistance than the second layer component and the second layer component has a higher thermal conductivity than the first layer component.

2. Heatable roller according to claim 1, characterized in that the second layer component is essentially, in particular completely, formed by a plurality of discrete regions3. Heatable roller according to claim 1 or 2, characterized in that the first layer component comprises an iron-based alloy and / or a cermet, in particular is formed therefrom.

4. Heatable roller according to claim 3, characterized in that the iron-based alloy comprises, in addition to iron, chromium and / or niobium and / or tantalum and / or molybdenum and / or silicon and / or boron and / or tungsten as further constituent(s).

5. Heatable roller according to one of claims 1 to 4, characterized in that the second layer component comprises copper or a copper-based alloy, in particular is formed therefrom.

6. Heatable roller according to one of the preceding claims, characterized in that the at least one layer is formed by 60% by weight or more, preferably more than 75%, of the first layer component and by a maximum of 40% by weight, preferably 5-25% by weight, particularly preferably 10-15% by weight, of the second layer component.

7. Heatable roller according to one of claims 2 to 6, characterized in that the discrete regions of the second layer component have a size in the range from 5 to 50 µm.

8. Heatable roller according to one of claims 1 to 7, characterized in that the second layer component at least partially forms a 3-dimensional network.

9. Heatable roller according to claim 1-8, characterized in that a plurality, in particular a plurality, of the discrete of the second layer component regions form a 3-dimensional network in contact with one another.

10. Heatable roller according to any one of claims 1 to 9, characterized in that the coating is formed by the at least one metallic or metal-carbide layer, in particular in that the coating is formed by a single one of the at least one metallic or metal-carbide layer.

11. Heatable roller according to one of claims 1 to 10, characterized in that the at least one layer, in particular the coating, has a specific thermal conductivity of 15 W / mK or more, preferably in the range from 15 W / mK to 250 W / mK, particularly preferably in the range from 15 W / mK to 175 W / mK12. Heatable roller according to one of claims 1 to 11, characterized in that the at least one layer, in particular the coating, has an abrasion resistance of less than 0.6g measured according to ASTM G65-04.

13. Heatable roller according to one of claims 1 to 12, characterized in that the coating has a thickness in the range from 50µm to 1500µm, preferably 100µm to 1000µm, particularly preferably a maximum of 800µm.

14. A method of coating a heatable roller having a base body with a metallic and cylindrical roller shell which is heatable by suitable means, the method comprising the following steps: a. Providing the radially outer side of the roller shell and b. Application of a coating which comprises or is formed from at least one metallic or metal-carbide layer, wherein the at least one metallic or metal-carbide layer is applied in such a way that it comprises or is formed from a first layer component providing a matrix and a second layer component arranged distributed in the matrix, and the first layer component has a higher abrasion resistance than the second layer component and the second layer component has a greater thermal conductivity than the first layer component.

15. Process for coating a heatable roller according to claim 14, wherein the radially outer side of the roller shell is surface-treated, in particular ground, before the coating is applied.

16. Method for coating a heatable roller according to claim 14 or 15, wherein the at least one layer, in particular the coating, is produced by means of thermal spraying, in particular by means of high-speed flame spraying.

17. Process for coating a heatable roller according to one of claims 14 to 16, wherein the metallic or metal-carbide layer providing the web contact side is ground after thermal spraying.