ROLLER FOR DEFLECTING OR GUIDING A METAL STRIP, WHICH IS TO BE COATED, IN A METAL MELT BATH

Abstract

A roller for deflecting or guiding a metal strip to be coated in a metal melt bath may include bearing journals disposed coaxially with one another for rotationally supporting the roller. To obtain a high coating quality while hot-dip coating the metal strip, in particular steel strip, and to increase the service life of such a roller, each bearing journal may comprise a plurality of axially spaced annular elevations that have or are formed from a plain-bearing coating. The roller may comprise a steel roller shell, and each bearing journal may include a substantially cylindrical or circular-disk-shaped connecting steel portion that extends radially in the direction of the roller shell. At least one of the connecting portions may comprise a passage opening at an end face of the roller shell. The passage may be closed by means of a gas-permeable plug element comprised of ceramic material.”

Claims

1.-11. (canceled)

12. A roller for deflecting or guiding a metal strip to be coated in a metal melt bath, the roller comprising bearing journals that provide rotational support for the roller and are positioned coaxially with one another, wherein each of the bearing journals comprises axially-spaced annular elevations that either have or are formed from a plain-bearing coating, wherein the plain-bearing coating in an area of the axially-spaced annular elevations is radially raised relative to a circumferential surface of each of the bearing journals.

13. The roller of claim 12 wherein the plain-bearing coating is at least one of molybdenum-based, tungsten-based, or chromium-based.

14. The roller of claim 12 wherein the plain-bearing coating in the area of the axially-spaced annular elevations is radially raised to the circumferential surface by 0.1 mm to 1.0 mm.

15. The roller of claim 12 wherein the plain-bearing coating in the area of the axially-spaced annular elevations is radially raised to the circumferential surface by 0.1 mm to 0.5 mm.

16. The roller of claim 12 wherein the plain-bearing coating is disposed in annular grooves of each of the bearing journals, wherein the annular grooves are disposed between the axially-spaced annular elevations, wherein the plain-bearing coating in the area of the annular grooves comprises annular depressions that are radially spaced relative to the axially-spaced annular elevations.

17. The roller of claim 16 wherein each of the annular grooves has a depth of 0.05 mm to 0.4 mm.

18. The roller of claim 12 further comprising a steel roller shell, wherein each of the bearing journals comprises a steel connecting portion that is substantially cylindrical or circular-disk-shaped and extends radially in a direction of the steel roller shell, wherein at least one of the steel connecting portions comprises a passage opening at an end face of the steel roller shell, the passage being closed by a gas-permeable plug element comprised of ceramic material.

19. The roller of claim 18 wherein the gas-permeable plug element has a composition such that the gas-permeable plug element cannot be wetted by an aluminum-based molten metal or by a zinc-based molten metal.

20. The roller of claim 18 wherein the passage narrows from an inside outwards, wherein the gas-permeable plug element corresponds to and is axially fixed in the passage.

21. The roller of claim 18 further comprising a filler element of ceramic material disposed on a space defined by the steel roller shell.

22. The roller of claim 18 wherein an outer end face of each of the steel connecting portions includes a protective coating.

23. The roller of claim 12 having an overall density of 0.8 to 1.2 times a density of a molten metal of the metal melt bath.

24. The roller of claim 12 having an overall density of 1.0 to 1.1 times a density of a molten metal of the metal melt bath.

Description

[0024] The invention is explained in more detail below, referring to a drawing representing a plurality of exemplary embodiments. In the drawing:

[0025] FIG. 1 shows a schematic representation of a hot-dip coating facility;

[0026] FIG. 2 shows an axial section through a roller for arrangement in a melt bath of a hot-dip coating unit;

[0027] FIG. 3 shows a bearing journal of the roller in FIG. 2 in an axial representation with a portion partially cut away;

[0028] FIG. 4 shows an end face view of the bearing journal in FIG. 3; and

[0029] FIG. 5 shows an axial sectional view of a bearing journal of a roller according to the invention.

[0030] The hot-dip coating facility represented schematically in FIG. 1 comprises a melt bath vessel 1, which is filled with a molten metal 2, for example an aluminum or zinc-based molten metal. A steel strip 4 to be coated is fed into the molten metal 2 via a funnel 3 immersed into the molten metal 2. A deflection roller (so-called immersion or pot roller) 5, which serves to deflect the steel strip 4 out of the running direction directed obliquely downwards into an upwardly directed, preferably substantially vertical running direction, is arranged in the melt bath vessel 1. Also arranged in the melt bath vessel 1 are one or two guide rollers (so-called stabilizer rollers or “stabirollers”) 6, which serve to suppress oscillations of the steel strip 4 and thereby ensure the most accurate possible running of the strip 4 in relation to a wiper device 7. The wiper device removes excess coating material from the surface of the coated steel strip 4 and for this purpose comprises wiper nozzles 7 in the form of flat-spray nozzles, typically operated with compressed air or inert gas.

[0031] The deflection roller 5 and/or at least one guide roller 6 are of a construction which is represented by way of example in FIGS. 2 to 4. The roller 5 or 6 comprises a roller shell 8 composed of steel, for example chromium-molybdenum steel. The roller shell 8 is of tubular design. The circumferential surface 8.1 of the roller here may be of cambered design, so that the outside diameter of the roller 5 or 6 diminishes from the center towards the ends of the roller.

[0032] Bearing journals 9 arranged coaxially with one another, which are likewise made of steel, for example chromium molybdenum steel, are arranged at the ends of the roller shell 8. Each bearing journal 9 comprises a substantially cylindrical or circular-disk-shaped connecting portion 9.1. The connecting portion 9.1 is preferably integrally formed with the journal part 9.2 projecting axially at the end face of the roller shell 8. The connecting portion 9.1 extends radially from the journal part 9.2 or the axis of rotation of the roller 5 or 6 in the direction of the roller shell 8. At its ends the roller shell 8 has inner faces 8.2 of wider diameter, which each define a circumferential internal step 8.3. The connecting portions 9.1 of the bearing journals 9 are pushed into the wider-diameter internal portions of the roller shell 8, forming a positive inlock, and are fixedly connected thereto by annular weld seams 15.

[0033] The outside diameter of the journal part 9.2 of the bearing journal 9 is smaller than the outside diameter of the roller shell 8 by a factor ranging from 3.0 to 7.0, preferably 4.0 to 5.0. The use of a bearing journal 9 having a correspondingly small journal diameter (diameter of the journal part 9.2) is preferred, since the journal part 9.2 then forms less resistance to rotation and the roller 5 or 6 is therefore easier to turn.

[0034] The connecting portion 9.1 of each bearing journal 9 has at least one or—as can be seen from FIGS. 2 to 4—more passages 9.3, which open out at the end face of the roller shell 8 and on the inner side of the connecting portion 9.1 or the bearing journal 9. In the exemplary embodiment shown, for example, four passages 9.3, which run substantially parallel to one another and are arranged uniformly spaced on a common graduated circle, are provided in each connecting portion 9.1 or bearing journal 9. As a modification to this exemplary embodiment, the connecting portion 9.1 or bearing journal 9 may also have fewer or more than four passages 9.3. According to the invention each passage 9.3 is closed by a gas-permeable plug element (insert) 10 composed of ceramic material.

[0035] The plug element 10 is produced on a calcium-silicate base, for example, preferably from a fine-pored calcium silicate ceramic. Calcium-silicate ceramic can be wetted only slightly, if at all, by non-ferrous molten metals such as AlSi molten metals or zinc-based molten metals. To increase its strength, the ceramic material of the plug element 10 may contain reinforcing fibers, for example carbon fibers.

[0036] Each passage 9.3 is preferably formed as a bored hole. In each case it has a step 9.31, so that it narrows from the inside outwards. The bolt-shaped plug element 10 is correspondingly formed and therefore likewise has a step 10.1 and can therefore be axially fixed in the passage 9.3. In the assembled state the plug element 10 terminates substantially flush with the outer end face 9.11 of the connecting portion 9.1 of the bearing journal 9 (cf. FIGS. 2 and 3).

[0037] The end face 9.11 of each connecting portion 9.1 may be provided with a protective coating, for example an aluminum-zirconium oxide-based protective coating.

[0038] The cavity of the roller 5 or 6 defined by the roller shell 8 and connecting portions 9.1 of the bearing journals 9 is preferably filled with one or more filler elements 11 composed of ceramic material. In the exemplary embodiment represented in FIG. 2 a plurality of circular disk-shaped filler elements 11 are arranged in series in the roller shell 8. The filler elements 11, for example, are made from the same material as the plug elements (ceramic inserts) 10. The cavity of the roller 5 or 6 between the connecting portions 9.1 is preferably filled substantially in its entirety with the disk-shaped filler elements 11. The ratio between the outside diameter and the inside diameter of the roller shell 8 ranges from 1.2 to 2.0, for example, preferably lying in the range from 1.4 to 1.6. The overall density of the roller 5 or 6 ranges, for example from 0.8 times to 1.2 times, preferably 1.0 times to 1.1 times the density of the molten metal 2 used, which in particular may be an aluminum or zinc-based molten metal.

[0039] The axially projecting journal part 9.2 of the bearing journal 9 is provided with a plain-bearing coating 12. The plain-bearing coating 12 is preferably made from molybdenum. In addition or alternatively it may also contain tungsten and/or chromium.

[0040] The plain-bearing coating 12 is of banded formation. It comprises a plurality of axially spaced annular elevations (bands) 12.1. For this purpose the material of the plain-bearing coating 12 is introduced into correspondingly spaced annular grooves 9.4 of the bearing journal 9 and/or applied to annular elevations 9.5 of the bearing journal 9. The grooves 9.4, for example, have a depth ranging from 0.05 mm to 0.4 mm. The layer thickness of the plain-bearing coating 12 is formed substantially uniformly over its axial extent. Accordingly, the surface structure of the bearing part 9.2 defined by the annular grooves 9.4 stands out in the circumferential surface of the plain-bearing coating 12. Molten metal may collect and form a sliding film in the depressions 12.2 of the plain-bearing coating 12 situated between the annular elevations 12.1.

[0041] The embodiment of the invention is not limited to the exemplary embodiments represented in the drawing. Rather, further variants are feasible which, with due modification, also make use of the invention specified in the claims. Thus, for example, the plain-bearing coating 12, slightly raised relative to the circumferential surface of the bearing journal 9, may also take the form of annular, axially spaced elevations 12.1, which are formed on a substantially cylindrical bearing journal having no grooves 9.4. Alternatively, the plain-bearing coating 12 may also be introduced only into the annular grooves 9.4 and at the same time be radially slightly raised relative to the annular elevations 9.5 of the bearing journal 9.