WO1991013204A1

WO1991013204A1 - Press roll for paper machine

Info

Publication number: WO1991013204A1
Application number: PCT/FI1991/000056
Authority: WO
Inventors: Jukka Kinnunen; Pekka Siitonen; Erkki Kiiski; Pentti Kettunen; Olli-Pekka Sorma; Keijo Ruonala
Original assignee: Tampella Papertech Oy
Priority date: 1990-02-22
Filing date: 1991-02-21
Publication date: 1991-09-05
Also published as: FI84506B; FI900898A0; FI900898A

Abstract

Press roll (1) in a paper machine, comprising a metallic cylinder body (2), a ceramic surface layer (3) and an intermediate layer (4) between the cylinder body (2) and the surface layer (3). The intermediate layer is made of a mixture containing metal or a mixture of metals and ceramic components. The mixing ratio of the components of the intermediate layer (4) changes either continuously or in a steplike manner in the radial direction of the roll in such a way that the proportion of metal in the intermediate layer (4) is at greatest close to the cylinder body (2) and decreases therefrom in a radial direction outwards. The purpose of the intermediate layer (4) is that the thermal expansion coefficient changes smoothly from the basic material so that it corresponds to the ceramic surface material.

Description

Press roll for paper machine

The invention relates to a press roll in a paper machine, comprising a metallic cylinder body, a ceramic surface layer and an intermediate layer between the cylinder body and the surface layer, said intermediate layer being of a composite material of a metal and a ceramic material.

In the press section of a paper machine, which, as used in this patent application, refers to a paper machine, a paperboard machine or other similar machine, the roll used in a two- or three-nip roll press is generally made of granite. Granite is used as roll material due to its surface properties, as the paper web can be detached from its surface in a very controlled manner, which results in good runnability and keeps the number of breaks on a low level. The granite roll can be ground and polished extremely fine and smooth, which is of importance for fine paper and printing paper in particular. In addition, granite resists well the wear effect caused by scraping, which involves long service and main¬ tenance intervals.

The use of granite is, however, restricted by a number of factors. The running speeds of paper machines have increased and still keep increasing. Similarly, the compression pressures and temperatures are higher than previously, so that the mechanical and thermal strains imposed on the roll are greater. Being a natural material, granite is non-homogenous, so that its material properties and surface prop¬ erties are unevenly distributed, on account of which the availability of suitable stone material has be¬ come problematic as the roll sizes have increased, with a resultant rise in costs. Due to the strength requirements, the weight of the roll has also in¬ creased close to its extremity in view of the treat¬ ment and installation of the roll, which has also increased the weight of the frame constructions, which, in turn, involves an increase in the vibration sensitivity of the entire press section.

To replace granite rolls, synthetic roll sur¬ face materials to be fastened upon a metallic body have been developed. Such materials include polymer- and elastomer-base compositions containing granite, silica sand, or some other inorganic materials. It is also known to form the surface of the roll by means of thermally sprayed metals, ceramic materials, or their combinations. FI Patent 70273 and FI Patent Application 853544 suggest that the press roll should be coated with metals and combinations of a metal and a ceramic material. FI Patent Application 861803, in turn, teaches a press roll structure in which a metallic binding layer is attached to the surface of a metallic body, the coefficient of thermal expansion of the binding layer being smaller than that of the metal body; further, a ceramic surface layer is fastened upon the binding layer. This arrangement, however, has proved to have certain disadvantages. In practice, polymer- and elastomer-base coatings have proved inferior to granite, as only a few coatings operate satis¬ factorily and only with a limited number of paper grades. For the time being, concerning thermally sprayed coatings, paper detaching properties similar to those of granite have been achieved with ceramic coatings only. However, the adherence of ceramic materials to the basic material and the durability of the coating in long-term use have been problematic. Since the coefficients of thermal expansion of ceramic materials and the basic material differ from each other, a concentration of strains remains at the interface between the materials after the coating, and this concentration is further increased by temperature variations occurring during operation. As a consequence, the coating is damaged and may be com¬ pletely loosened during operation in the long run. The thin metallic intermediate layer provided between the basic material and the proper surface layer com¬ pensates for strains caused by the different coeffi¬ cients of thermal expansion of the body and the ceramic surface layer to some extent; in practice, however, not sufficiently. Still another problem with rolls coated with a ceramic material is the corrosion resistance. Being porous, ceramic materials allow the penetration of moisture so that it reaches the metal, thus causing corrosion, which further deteriorates the adherence of the ceramic coating. The object of the present invention is to provide a paper machine roll in which the strains caused between the ceramic coating and the body due to their unequal coefficients of thermal expansion are compensated for more efficiently than previously, thus avoiding the above-described problems. Another object of the invention is to improve the corrosion resistance of a roll provided with a ceramic surface layer. A paper machine roll of the invention is characterized in that the intermediate layer is of a composite material formed by a metal and a ceramic material, the mixing ratio of the components of the composite material being different in different por¬ tions of the intermediate layer in the radial direction of the roll. The invention will be described in the attached drawings, wherein

Figure 1 is a schematic axial view of a roll of the invention;

Figure 2 is a schematic enlarged view of a specific structure of a surface layer and an intermediate layer of the roll of the invention, and the attachment of these layers to the metal body of the roll; and

Figure 3 is a schematic enlarged view of another specific structure of the surface layer and the intermediate layer of the roll of the invention, and the attachment of these layers to the metal body of the roll.

Figure 1 shows a roll 1 comprising a metallic cylinder body 2 formed in a manner known per se. The structure and manufacture of the cylinder body are obvious to one skilled in the art and will not be described more closed herein. The cylinder body 2 is surrounded with a surface layer 3 of a suitable ceramic material known per se, such as alumina (AI3O2), titania (Ti0₂), mullite (3A1₂0₃ x 2Si0₂) or their mixture or other similar ceramic oxides.

An intermediate layer 4 compensating for thermal expansions is provided between the surface layer 3 and the cylinder body 2, which layer is made of a mixture of a ceramic material and a metal. The ceramic material may be the same material as that used in the surface layer or a different material, and besides the materials mentioned above, suitable materials include zirconia (Zr0 ), tungsten carbide (WC), chrome carbide (Cr₂C3) or some other carbide ceramics or their mixture. The metal may be an iron-, chrome-, nickel-, copper-, cobalt- or aluminium-base mixture, such as stainless steel, a nickel/aluminium mixture, or a copper/nickel mixture. The ratio of the metal component to the ceramic component in the intermediate layer 4 is such that the amount of metal is at greatest close to the cylinder body 2 and its proportional amount decreases towards the surface layer 3 while the proportional amount of the ceramic component increases. This can be accomplished either by forming the whole intermediate layer so that its mixing ratio changes continuously, or by forming the intermediate layer of several sublayers having different mixing ratios changing according to the above-mentioned principle.

Figure 2 shows schematically on an enlarged scale one specific structure of the surface layer and the intermediate layer of the roll of the invention, and the attachment of these layers to the cylinder body. The intermediate layer 4 formed upon the cylin¬ der body 2 is a single integral layer formed by simultaneous feeding of the ceramic and the metal component, e.g., by spraying them thermally on to the surface of the cylinder body 2. During the spraying the feed ratio of the components is changed as the layer thickness increases, so that the proportion of metal decreases while the proportion of the ceramic material, shown schematically by black dots, in- creases, until the thickness of the intermediate layer 4 and the ratio of the metal to the ceramic material are suitable for the adherence of the ceramic surface layer 3.

Figure 3 shows schematically on an enlarged scale another specific structure of the surface layer and the intermediate layer of the roll of the inven¬ tion, and the attachment of these layers to the cylinder body. In the figure, the intermediate layer 4 comprises three separate sublayers 4a, 4b, and 4c. These are formed, e.g., by simultaneously spraying the metal and the ceramic component by a thermal spraying technique on to the surface of the cylinder body 2, whereby the first sublayer 4a is formed with one specific mixing ratio. Thereafter the mixing ratio of the feed materials and possibly also the materials are changed so that the coefficient of thermal expansion changes in a desired direction. Then the layer 4b is sprayed similarly on the surface of the layer 4a, whereafter the mixing ratio and/or the materials are again changed for spraying the . layer 4c. Finally, the roll is coated with the ceramic surface layer 3.

In the solutions shown in Figures 2 and 3, the intermediate layer portion or the sublayer 4a closest to the cylinder body 2 is of almost pure metal so that it does not allow the penetration of moisture and thus prevents corrosion at the interface between the intermediate layer 4 and the cylinder body 2. For this reason, the layer or layer portion closest to the cylinder body has to be of corrosion resistant material, such as stainless steel. The corrosion resistance of the metal of the layers closer to the surface layer need not be equally good, and the metal can be chosen more freely to achieve a suitable co- efficient of thermal expansion.

The intermediate layer and the surface layer are preferably formed by thermal spraying methods, such as gas or liquid stabilized plasma spraying, flame spraying, hypersonic flame spraying or detonation spraying. The different layers or layer portions can be made by the same method or by dif¬ ferent methods.

The above description and the drawings describe the invention by way of example and the invention is not restricted to it. The metal component of the integral intermediate layer can be formed by one or more metals and the mixing ratio of the metals may change e.g. in proportion to the layer thickness in such a way that the proportional amount of one metal increases in the same proportion as the ceramic material or in a different proportion in accordance with the desired structure and thermal expansion properties of the intermediate layer. Corresponding¬ ly, the ceramic component may contain one or more ceramic materials and the ratio of the different materials to each other may be constant or it may vary. In the solution comprising superimposed sub¬ layers, the metals in the sublayers may be the same or different; similarly, the ceramic material may be any one of the above-mentioned alternative ceramic materials suited for the purpose. The sublayers can be formed similarly as the integral layer so that the mixing ratio changes with the thickness of the sub¬ layer in the radial direction of the roll^' to achieve better matching.

Claims

Claims :

1. Press roll in a paper machine, comprising a metallic cylinder body (2), a ceramic surface layer (3) and an intermediate layer (4) between the cyl¬ inder body (2) and the surface layer (3), c h a r¬ a c t e r i z e d in that the intermediate layer (4) is of a composite material formed by a metal and a ceramic material, the mixing ratio of the components of the composite material being different in dif¬ ferent portions of the intermediate layer (4) in the radial direction of the roll.

2. Press roll according to claim 1, c h a r ¬ a c t e r i z e d in that the ratio of the com- ponents of the composite material is such that the proportion of the metallic components is at greatest close to the cylinder body (2) and decreases in the radial direction as the distance from the cylinder body (2) increases, while the proportion of the ceramic components increases.

3. Press roll according to claim 1 or 2, c h a r a c t e r i z e d in that the intermediate layer (4) is formed by an integral composite material layer, the mixing ratio of the components changing substantially continuously in the radial direction of the roll (1),

4. Press roll according to claim 1 or 2, c h a r a c t e r i z e d in that the intermediate layer (4) comprises at least two sublayers (4a - 4c).

5. Press roll according to claim 4, c h a r ¬ a c t e r i z e d in that each sublayer (4a - 4c) comprises the same components, the sublayers (4a - 4c) having different component mixing ratios.

6. Press roll according to any of the preceding claims, c h a r a c t e r i z e d in that the thermal expansion coefficient of the entire inter¬ mediate layer (4) is smaller than that of the cylinder body (2).

7. Press roll according to any of the preceding claims, c h a r a c t e r i z e d in that the thermal expansion coefficient of the intermediate layer (4) is at greatest close to the cylinder body (2) and at smallest close to the surface layer (3) .

8. Press roll according to claim 4 or 5, c h a r a c t e r i z e d in that the component ratios of the sublayers (4a - 4c) are chosen so that the thermal expansion coefficient varies substantial¬ ly evenly from one sublayer (4a - 4c) to another from the cylinder body (2) towards the surface layer (3).

9. Press roll according to claim 8, c h a r ¬ a c t e r i z e d in that the sublayers (4a - 4c) have different thermal expansion coefficients.

10. Press roll according to claim 8 or 9, c h a r a c t e r i z e d in that the thermal expansion coefficient of each sublayer (4a - 4c) is smaller than that of the cylinder body (2), the thermal expansion coefficient being at greatest in the sublayer (4a) close to the cylinder body (2) and at smallest in the sublayer (4c) close to the surface layer (3).