DEVICE AND METHOD FOR IMPROVED EXTRACTION OF METAL VAPOR

Abstract

A device minimizes or eliminates surface flaws caused by metal dust on a metal strip to be coated in a continuous hot-dip coating process, where at least some segments of the metal strip to be coated are conveyed through the device in an axial direction. The device may comprise a blowing/sucking unit with blow-in openings for applying protective gas to the metal strip, which blow-in openings are positionable on first and second sides of the metal strip. The blowing/sucking unit may further include suction openings for extracting protective gas laden with metal vapor and/or metal dust, which suction openings are positionable on the first and second sides of the metal strip. The blowing/sucking unit may have a blow-in region in which the blow-in openings are arranged, and a suction region downstream of the blow-in region in which the suction openings are arranged.

Claims

1.-16. (canceled)

17. A device that minimizes or eliminates surface flaws caused by metal dust on a metal strip to be coated in a continuous hot-dip coating process, wherein at least some segments of the metal strip to be coated are configured to be conveyed through the device in an axial direction, the device comprising a blowing/sucking unit that comprises: a blow-in region that includes a plurality of blow-in openings for applying protective gas to the metal strip, wherein some of the plurality of blow-in openings are positionable on a first side of the metal strip and some of the plurality of blow-in openings are positionable on a second side of the metal strip; and a suction region that includes a plurality of suction openings for extracting the protective gas, which is laden with at least one of metal vapor or metal dust, wherein some of the plurality of suction openings are positionable on the first side of the metal strip and some of the plurality of suction openings are positionable on the second side of the metal strip, wherein the suction region is positioned downstream of the blow-in region with respect to the axial direction.

18. The device of claim 17 wherein the plurality of blow-in openings and the plurality of suction openings are disposed such that the protective gas blown in through the plurality of blow-in openings of the blow-in region is entrained with the metal strip conveyed through the device in the axial direction and flows in the axial direction, after which the protective gas flows contrary to the axial direction to the plurality of suction openings of the suction region.

19. The device of claim 17 wherein the blow-in region and the suction region are disposed at mutually exclusive locations of the blowing/sucking unit.

20. The device of claim 17 wherein at least one of the plurality of blow-in openings or the plurality of suction openings are at least partially disposed in a pattern.

21. The device of claim 20 wherein the openings in the pattern are spaced at least 40 mm apart.

22. The device of claim 17 wherein at least some of the plurality of suction openings are larger than the plurality of blow-in openings.

23. The device of claim 17 wherein at least some of the plurality of blow-in openings are disposed such that the protective gas flows substantially transversely to the axial direction from the plurality of blow-in openings in a direction of a respective side of the metal strip.

24. The device of claim 17 wherein the blowing/sucking unit further comprises: a first blowing/suction box that is positionable on the first side of the metal strip; and a second blowing/suction box that is positionable on the second side of the metal strip.

25. The device of claim 24 wherein the first and second blowing/suction boxes each include a blowing box for providing the blow-in region and a suction box for providing the suction region.

26. The device of claim 17 further comprising a furnace trunk for connection of a continuous furnace to a metal bath, wherein the blowing/sucking unit is disposed at least partly in the furnace trunk.

27. The device of claim 17 further comprising at least one of: a continuous furnace disposed upstream of the blowing/sucking unit for heating the metal strip; a metal bath disposed downstream of the blowing/sucking unit for coating the metal strip; a separating device for cleaning the protective gas extracted through the plurality of suction openings; or a heating device for heating the protective gas fed through the plurality of blow-in openings.

28. A method for minimizing or eliminating surface flaws caused by metal dust on a metal strip to be coated in a continuous hot-dip coating process, the method comprising: conveying at least some segments of the metal strip to be coated in an axial direction through a device that includes a blowing/sucking unit; applying protective gas to the metal strip through a plurality of blow-in openings in a blow-in region of the blowing/sucking unit, wherein some of the plurality of blow-in openings are disposed on a first side of the metal strip and some of the plurality of blow-in openings are disposed on a second side of the metal strip; and extracting the protective gas, which is laden with at least one of metal vapor or metal dust, through a plurality of suction openings in a suction region of the blowing/sucking unit located downstream of the blow-in region with respect to the axial direction, wherein some of the plurality of suction openings are disposed on the first side of the metal strip and some of the plurality of suction openings are disposed on the second side of the metal strip.

29. The method of claim 28 wherein applying the protective gas to the metal strip comprises entraining the protective gas with the metal strip that is conveyed through the device in the axial direction such that the protective gas initially flows in the axial direction and then subsequently flows contrary to the axial direction to the plurality of suction openings in the suction region.

30. The method of claim 28 wherein the protective gas flows substantially transversely to the axial direction from the plurality of blow-in openings in a direction of a respective side of the metal strip.

31. The method of claim 28 wherein the application and the extraction are performed at least partly in a furnace trunk for connection of a continuous furnace to a metal bath.

32. The method of claim 28 further comprising supplying a barrier gas to the device upstream of the blowing/sucking unit with respect to the axial direction.

33. The method of claim 28 further comprising at least one of: heating the metal strip to be coated in a continuous furnace upstream of the blowing/sucking unit with respect to the axial direction; coating the metal strip in a metal bath disposed downstream of the blowing/sucking unit with respect to the axial direction; cleaning the protective gas extracted through the plurality of suction openings in a separating device; or heating the protective gas fed through the plurality of blow-in openings in a heating device.

Description

[0049] The invention shall be explained more closely below with the aid of the drawing. Further preferred embodiments and advantages of the invention can be found in the drawing and the description of the exemplary embodiment shown in the drawing. The drawing shows:

[0050] FIG. 1 a longitudinal sectional view of an exemplary embodiment of a device according to the invention for carrying out an exemplary embodiment of a method according to the invention;

[0051] FIG. 2 a perspective representation of the furnace trunk from FIG. 1;

[0052] FIG. 3 a longitudinal sectional view of the furnace trunk from FIG. 1;

[0053] FIG. 4 a top view of the blow-in region and the suction region of the blowing/suction box of FIG. 1.

[0054] FIG. 1 shows a longitudinal sectional view of an exemplary embodiment of a device 1 according to the invention in the form of a continuous hot-dip galvanization layout for carrying out an exemplary embodiment of a method according to the invention. The device 1 comprises in particular a furnace trunk 2. A metal strip 4 to be galvanized, such as a steel strip, is annealed in a continuous furnace (not shown) and supplied under protective gas (HNX) to a zinc bath 6. The strip 4 dips down at a slant into the zinc bath 6 and is deflected upward by a roller 8 arranged in the zinc bath 6. The bath temperature is typically in the range of around 440 C. to 470 C. Upon emerging from the bath 6, the strip 4 entrains a quantity of liquid zinc, which may lie significantly above the desired coating thickness. The still liquid excess coating material is stripped off from the first side and the second side (that is, the top and bottom or front and back side) of the now coated strip 4 by flat air jet nozzles 10 extending across the width of the strip.

[0055] In order to avoid too intense a cooldown (especially below the dew point or resublimation temperature of the protective gas/zinc vapor mixture) of the furnace trunk 2 in the region near the zinc bath 6, insulating elements 12 (such as mineral wool and/or ceramic tiles) may be provided optionally.

[0056] The furnace trunk 2 among other things is meant to prevent the annealed strip 4 from being oxidized before the galvanization, which would impair the adherence of the zinc layer. Therefore, the strip 4 is subjected to protective gas. At the same time, the protective gas should serve to prevent the dispersion of zinc vapor. For this reason, the furnace trunk 2 is outfitted with a special blowing/sucking unit 14, which applies protective gas to the metal strip 4 and extracts the protective gas laden with zinc vapor and/or zinc dust.

[0057] FIG. 2 shows a perspective representation of the furnace trunk 2 from FIG. 1 and FIG. 3 shows a longitudinal sectional view of the furnace trunk 2 from FIG. 1.

[0058] The metal strip 4 to be coated is conveyed in this section along an axial direction 16 through the furnace trunk 2 and through the blowing/sucking unit 14 of the device 1. The blowing/sucking unit 14 has a plurality of blow-in openings 18 for applying protective gas to the metal strip 4. A plurality of blow-in openings 18 are arranged on a first side of the metal strip and a plurality of blow-in openings 18 on a second side of the metal strip, so that the metal strip 4 can be subjected to the protective gas on both sides. The blow-in openings 18 form a blow-in region 20. Furthermore, the blowing/sucking unit 14 has a plurality of suction openings 22 for extracting protective gas laden with metal vapor and/or metal dust. A plurality of suction openings 22 are arranged on the first side of the metal strip 4 and a plurality of suction openings 22 are arranged on the second side of the metal strip 4. The suction openings 22 form a suction region 24.

[0059] The blow-in region 20, in which the blow-in openings 18 are arranged, is arranged behind the suction region 24, in which the suction openings 22 are arranged, looking in the axial direction 16. The blow-in region 20 and the suction region 24 are arranged free of overlap.

[0060] The blowing/sucking unit 14 comprises a first blowing/suction box 14a, which is arranged on the first side of the metal strip 4 to be coated, and a second blowing/suction box 14b, which is arranged on the second side of the metal strip 4 to be coated. The blowing/suction boxes 14a, 14b each have two blowing boxes 26a and 26b for providing the blow-in region 20 and two suction boxes 28a and 28b for providing the suction region 24. The blowing boxes 26a (or 26b) are separated from each other in each case by a partition wall 42a (or 42b). The suction boxes 28a (or 28b) are also separated from each other by a partition wall 44a (or 44b). The blowing box 26a (or 26b) and the suction box 28a (or 28b) are likewise separated from each other by a partition wall 46a (or 46b).

[0061] The individual blowing boxes 26a, 26b each have separate ports 30a, 30b for the supply of protective gas. The standard volume flow for the blowing in through the ports 30a is around 150 Nm.sup.3/h. The standard volume flow for the blowing in through the ports 30b is likewise around 150 Nm.sup.3/h. The standard volume flow for the extraction through the ports 32a is around 200 Nm.sup.3/h. The standard volume flow for the extraction through the ports 32b is likewise around 200 Nm.sup.3/h.

[0062] At the same time, barrier gas can be fed to the device 1 by means of the barrier gas feed line 3 (see FIG. 1). The barrier gas here is identical to the protective gas and it is blown in at 300 Nm.sup.3/h through the barrier gas feed line 3, as is also illustrated by the arrows 33 in FIG. 3. The barrier gas is advantageously fed in between two sealing flaps (see FIG. 1). The barrier gas shields the gas flow in the furnace trunk 2 against a furnace located upstream, so that an entrainment of zinc vapor into the furnace is prevented. For example, the pressure drops off from the region of the protective gas feed line 3 via the region of the blowing boxes 26a and 26b to the region of the suction boxes 28a and 28b.

[0063] As is especially evident in FIG. 3, the blow-in openings 18 are provided such that the protective gas flows substantially transversely to the axial direction 16 from the blow-in openings in the direction of the respective side of the metal strip 4. The protective gas in this case is blown through the blow-in openings 18 perpendicularly in the direction of the respective side of the metal strip 4. The direction of flow of the protective gas is illustrated by the arrows 34. The protective gas blown in through the blow-in openings 18 of the blow-in region 20 is at first deliberately entrained with the metal strip 4 being conveyed through the device 1 in the axial direction 16 and flows in the axial direction 16. The protective gas flows along the surface of the metal strip 4. After this, the protective gas mixed with zinc vapor and zinc dust flows along the wall of the furnace trunk 2 contrary to the axial direction 16 toward the suction openings 22 of the suction region 24.

[0064] The dots 36 illustrate the distribution and the concentration of the zinc vapor and zinc dust. The concentration of the zinc dust and zinc vapor decreases evidently opposite the axial direction 16. The blowing/sucking unit 14 enables an effective barrier for the zinc vapor and the zinc dust and an effective extraction of the zinc vapor and zinc dust.

[0065] For example, if one assumes a zinc vapor input of around 34 g/h by the zinc bath 6, simulations reveal a zinc vapor concentration of around 510.sup.5 kg/m.sup.3 in the vicinity of the zinc bath 6 in the lower region of the furnace trunk. In the suction region 24 there is still present a zinc vapor concentration of around 310.sup.5 kg/m.sup.3 to around 710.sup.6 kg/m.sup.3. In the blow-in region 20, the zinc vapor concentration is already less than 710.sup.6 kg/m.sup.3.

[0066] For a larger zinc vapor input of 340 g/h, one still gets zinc vapor concentrations of up to 510.sup.5 kg/m.sup.3 in the suction region 24. However, they drop off in the blow-in region 20 to less than 110.sup.5 kg/m.sup.3, in part also to below 710.sup.6 kg/m.sup.3. Thus, the device and the method are also suitable for such high zinc vapor inputs.

[0067] FIG. 4 finally shows as an example a top view of the blow-in region 20 and the suction region 24 of the blowing/suction box 14a from FIG. 1. The blow-in openings 18 of the blow-in region 20 and the suction openings 22 of the suction region 24 are arranged in a regular pattern. The shortest spacing of neighboring openings 18, 22 in the axial direction 16 is greater than that transversely to the axial direction 16. The shortest spacing 38 of the blow-in openings 18 or the suction openings 22 in the axial direction amounts to around 100 mm here. The shortest spacing 40 of the blow-in openings 18 or the suction openings 22 transversely to the axial direction 16 amounts to around 60 mm. The blow-in openings 18 are configured smaller than the suction openings 22. The diameter of the blow-in openings 18 is around 8 mm. The diameter of the suction openings 22 is around 10 mm.