Process for manufacturing a coated metal strip of improved appearance

Abstract

An installation for continuous hot-dip coating of a metal strip is provided. The installation includes a tank containing a bath of molten metal, a metal strip running through the bath and a confined wiping device. The confined wiping device includes at least two wiping nozzles placed on each side of a path of the strip after the strip has left the bath of molten metal. Each nozzle has at least one gas outlet orifice and an upper face. The confined wiping device also includes a confinement box adjacent each upper face. The confinement boxes are open on a face which faces the strip. Each box includes at least one upper part and two lateral parts.

Claims

1. An installation for the continuous hot-dip coating of metal strip, comprising: a tank containing a bath of molten metal; a metal strip running through the bath; and a confined wiping device comprising: a respective wiping nozzle placed on each side of a path of the strip after the strip has left the bath of molten metal, each wiping nozzle having at least one gas outlet orifice and an upper face; and a respective confinement box located adjacent the upper face of each wiping nozzle, wherein the confinement boxes open on a face which faces the strip, each confinement box including an upper part including a vertical plate and a horizontal plate, each confinement box further including two lateral parts, wherein each confinement box further includes a plurality of vertical blades extending from the upper face of the adjacent wiping nozzle up to the horizontal plate of the upper part of said each confinement box, said plurality of vertical blades located between the two lateral parts of said each confinement box, the vertical and horizontal plates extending continuously between the two lateral parts, wherein each confinement box consists of the vertical plate, the horizontal plate, the two lateral parts, and the plurality of vertical blades.

2. The installation as recited in claim 1, wherein, in each confinement box, a width of the horizontal plate is equal to a width of each lateral part.

3. The installation as recited in claim 2, wherein the width of the horizontal plate and the width of each lateral part is less than or equal to a depth of the wiping nozzles.

4. The installation as recited in claim 2, wherein a height H of the confinement boxes in relation to a wiping line is greater than or equal to 10 cm.

5. The installation as recited in claim 1, wherein each of the wiping nozzles has a triangular general shape defined by two longitudinal plates fixed together by two triangular end plates.

6. The installation as recited in claim 1, wherein a distance D between an end of the lateral parts of the confinement boxes and the strip is from 10 to 100 mm.

7. The installation as recited in claim 1, wherein a height H of the confinement boxes in relation to a wiping line is greater than or equal to 10 cm.

8. The installation as recited in claim 1, wherein the confined wiping devices further include anti-noise plates on each side of the strip, facing part of the outlet orifice of the wiping nozzles.

9. The installation as recited in claim 8, further comprising edge confinement pieces placed between the confinement boxes above the anti-noise plates, facing edges of the strip.

10. The installation as recited in claim 9, wherein the edge confinement pieces may be moved horizontally and vertically.

11. The installation as recited in claim 9, wherein each of the edge confinement pieces includes two rectangular plates parallel to the strip and are connected by a lateral plate placed facing the edges of the strip.

12. The installation as recited in claim 9, wherein each of the edge confinement pieces includes two rectangular plates inclined to a plane in which the strip runs and joined together along a vertical edge, the vertical edges placed facing the edges of the strip.

13. The installation as recited in claim 1, further comprising a supply of wiping gas connected to the gas outlet orifice of each nozzle, wherein said wiping gas has an oxidizing power lower than that of an atmosphere consisting of 4% oxygen by volume and 96% nitrogen by volume and wherein the confinement box has an atmosphere with an oxidizing power lower than that of an atmosphere consisting of 4% oxygen by volume and 96% nitrogen by volume and higher than that of an atmosphere consisting of 0.15% oxygen by volume and 99.85% nitrogen by volume.

14. The installation as recited in claim 1, wherein the wiping nozzles include a single outlet orifice in a form of a longitudinal slot with a width at least equal to that of the strip to be coated.

15. The installation as recited in claim 1, wherein gas supplied to the confinement box is supplied only from the gas outlet orifice.

16. The installation as recited in claim 1, wherein the vertical blades define vertical passages extending from the upper face of the wiping nozzle up to the horizontal plate.

17. The installation as recited in claim 1, wherein each confinement box is supplied with an inert gas.

18. A confined wiping device comprising: a respective wiping nozzle placed on each side of a path of a strip after the strip has left a bath of molten metal, each wiping nozzle having at least one gas outlet orifice and an upper face; and a respective confinement box located adjacent the upper face of each wiping nozzle, the confinement boxes open on a face which faces the strip, each confinement box including an upper part including a vertical plate and a horizontal plate, each confinement box further including two lateral parts, wherein each of the confinement boxes further includes a plurality of vertical blades extending from the upper face of the adjacent wiping nozzle up to the horizontal plate of the upper part of said each confinement box, said plurality of vertical blades located between the two lateral parts of said each confinement box, the vertical and horizontal plates extending continuously between the two lateral parts, wherein each confinement box consists of the vertical plate, the horizontal plate, the two lateral parts, and the plurality of vertical blades.

19. The device as recited in claim 18, wherein, in each confinement box, a width of the horizontal plate is equal to a width of each lateral part.

20. The device as recited in claim 19, wherein the width of the horizontal plate and the width of each lateral part is less than or equal to a depth of the wiping nozzles.

21. The device as recited in claim 18, wherein each of the wiping nozzles has a triangular general shape defined by two longitudinal plates fixed together by two triangular end plates.

22. The device as recited in claim 18, wherein a distance D between an end of the lateral parts of the confinement boxes and the strip is from 10 to 100 mm.

23. The device as recited in claim 18, further comprising a supply of wiping gas connected to the gas outlet orifice of each nozzle, wherein said wiping gas has an oxidizing power lower than that of an atmosphere consisting of 4% oxygen by volume and 96% nitrogen by volume and wherein the confinement box has an atmosphere with an oxidizing power lower than that of an atmosphere consisting of 4% oxygen by volume and 96% nitrogen by volume and higher than that of an atmosphere consisting of 0.15% oxygen by volume and 99.85% nitrogen by volume.

24. The device as recited in claim 18, wherein gas supplied to the confinement box is supplied only from the gas outlet orifice.

25. The device as recited in claim 18, wherein the vertical blades define vertical passages extending from the upper face of the wiping nozzle up to the horizontal plate.

26. The device as recited in claim 18, wherein each confinement box is supplied with an inert gas.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Preferred embodiments of the present invention will be elucidated with reference to the drawings, in which:

(2) FIG. 1 shows an embodiment of a confined wiping device according to the invention.

(3) FIG. 2 is a perspective view of an embodiment of a confined wiping device according to the invention.

(4) FIG. 3 is a perspective view of an embodiment of a confined wiping device according to the invention.

(5) FIG. 4 is a sectional view of the device of FIG. 3.

(6) FIG. 5 is a perspective view of an embodiment of a confined wiping device according to the invention.

(7) FIG. 6 is a perspective view of an embodiment of a confined wiping device according to the invention.

(8) FIG. 7 is a sectional view of the device of FIG. 6.

(9) FIG. 8 is a top view of the device of FIG. 6.

(10) FIG. 9 is a bottom view of an embodiment of a confined wiping device according to the invention; and

(11) FIG. 10 is a top view of an embodiment of a confined wiping device according to the invention.

DETAILED DESCRIPTION

(12) Referring firstly to FIG. 3, this shows a first embodiment of a confined wiping device 20 according to the invention, which comprises two identical wiping nozzles 3 placed at the same level on each side of the strip B. These wiping nozzles 3 have a triangular general shape and each consist of two longitudinal metal plates 4 and 4′ (not visible) that are fixed together by means of two lateral triangular plates 5 and 5′ (not depicted). The longitudinal metal plates 4 and 4′ are joined together in such a way that thin slots remain between them, so as to allow the pressurized wiping gas, conveyed by means that are not depicted, to pass through it.

(13) The confined wiping device 20 also includes two confinement boxes 21 and 22 which are each placed on the upper external faces of each nozzle 3, said spaces being formed from upper metal plates 4, and are welded to said plates. The box 22 consists of the assembly of two lateral plates 24 and an upper part consisting of a horizontal plate 25 and a vertical plate 23. The plates 24 and 25 preferably have the same width, which may be equal to or smaller than the depth of the nozzle 3.

(14) The box 21 is identical in all points to the box 22.

(15) Finally, the confined wiping device 20 includes two metal plates 6, called “antinoise baffles”, the function of which is to prevent the wiping gas streams emanating from each nozzle 3 meeting one another in the lateral zones where the strip B is not present. In this way, strips of variable width can run through the same coating installation, and the interposition of such plates 6 is useful, especially for preventing sound vibrations of very large amplitude from being generated.

(16) Turning now to FIG. 4, this shows a sectional view of the device of FIG. 3, in which the two wiping nozzles 3 are depicted, an arrow indicating the stream of wiping gas on each side of the strip. The height of the confinement boxes 21 and 22, depicted by the letter H, is measured between the wiping line and the upper part of the boxes. In the process according to the invention, this height has to be at least 10 cm in order to obtain satisfactory results in terms of waviness.

(17) The distance D separating the boxes 21 and 22 from the strip B varies according to the width of the lateral and upper plates 24 and 25. On completing the various trials, the present inventors have demonstrated that a distance D between 10 and 100 mm allows the wiping gas to be satisfactorily extracted, while still remaining sufficiently far from the path of the strip B in order to avoid any contact therewith.

(18) The distance Z between the end of the nozzles 3 and the strip B is preferably between 3 and 25 mm, as is conventional.

(19) Turning now to FIG. 2, this shows another embodiment of a confined wiping device 10 according to the invention. As previously, this device includes wiping nozzles 3 identical to those described in the case of FIG. 3 and antinoise plates 6.

(20) It further includes two confinement boxes 11 and 12 placed on and fixed to the upper face 4 of the wiping nozzles 3. The box 12 comprises an inclined upper plate 13 joined to two triangular lateral plates 14. The box 11 is identical to the box 12.

(21) As for the boxes in FIG. 3, the boxes 11 and 12 have a width which may in the maximum case be equal to the depth of the nozzles 3.

(22) In this embodiment, the height H of the confinement boxes 11 and 12 is measured between the wiping line and the upper edge of the plates 13.

(23) This embodiment has in particular the advantage of enclosing a smaller volume than that in FIG. 3, thereby making it easier to control the confinement atmosphere and enabling a smaller amount of inerting gas to be consumed when it is necessary to supply such a gas.

(24) Referring now to FIG. 5, this shows another embodiment of a confined wiping device 30 according to the invention. It is overall identical to the device 20 of FIG. 3 and in particular comprises two confinement boxes 31 and 32 comprising an upper part consisting of vertical plates 33 joined to horizontal plates 35, and lateral parts 34. Each of the boxes 31 and 32 is also compartmentalized by a series of vertical blades 36 extending from the upper face of the wiping nozzle 3 up to the upper part 35 of the confinement boxes 31 and 32.

(25) This particular arrangement has the advantage of limiting the ingress of oxygen into the confinement boxes 31 and 32.

(26) FIG. 6 shows another embodiment of a confinement device according to the invention similar to that shown in FIG. 3, but further including edge confinement pieces 26 placed between the confinement boxes 21 and 22, above the antinoise plates 6 and facing the edges of the strip B. As their name indicates, these pieces have the function of further confining the atmosphere surrounding the strip B along its edges.

(27) In a preferred embodiment, these edge confinement pieces may be moved horizontally and vertically in order to adapt to the various formats of strip to be coated.

(28) In the embodiment shown in FIG. 6, the edge confinement piece 26 consists of two rectangular plates parallel to the strip B and joined by a lateral plate placed facing the edges of the strip B.

(29) FIG. 7 shows the relative position of the confinement piece 26 above the antinoise plate 6.

(30) As illustrated in FIG. 8, the width C of the lateral plate can vary depending on the extent of edge confinement desired.

(31) FIG. 9 shows another embodiment of the confinement pieces according to the invention. The piece 27 consists of two rectangular plates inclined to the plane in which the strip B runs and joined along their vertical edge facing the edges of the strip B.

(32) This embodiment has the advantage of limiting the ingress of oxygen even more than the design shown in FIG. 6. The inclined positioning of the two rectangular plates promotes gas flow from the inside of the box toward the outside and discourages gas flow from the outside toward the interior of the box.

(33) FIG. 10 shows another embodiment of the confinement pieces according to the invention in which the confinement piece 28 further includes a return means 29, here taking the form of a spring, joining the inclined rectangular plates together. These plates are inclined to the plane in which the strip B runs so as to be in contact with the lateral parts of the confinement boxes 21 and 22.

(34) The edge confinement pieces described above are placed on top of the antinoise plates 6. However, it is possible to extend them as far as the outlet orifices of the wiping nozzles in order to give them an antinoise plate function, making the use of such plates pointless.