EP2592171B1 - Method and apparatus for hot-dip coating a metal strip with a metallic coating - Google Patents

Description

The invention relates to a process for hot dip coating a metal strip with a metallic coating, in which the metal strip is passed in a continuous pass through a melt bath in which the thickness of the metallic coating present on its exit from the melt bath is adjusted by means of a scraping device, and wherein the slag present on the melt bath is expelled by means of a gas flow from the metal strip emerging from the melt bath. Typically, the metal strips coated in this manner are hot or cold rolled steel strips.

The invention also relates to a device for hot dip coating a metal strip with a metallic coating, said device comprising a melt bath, a conveyor for continuously passing the metal strip through the melt bath, a stripping device for adjusting the thickness of the metal present on its exit from the molten bath on the metal strip Coating and at least one nozzle for discharging a gas stream, which expels existing slag on the melt bath of the emerging from the melt bath metal strip.

The continuous hot dipping refinement of the type specified initially represents an industrially established, economically and ecologically sensible process principle with which metallic flat products can be coated with a metallic coating, for example for the purpose of corrosion protection. Thus, the hot dip finishing of a previously in-line recrystallization annealed metal strip with a Zn (hot dip galvanizing) or Al alloy coating (fire aluminizing) has a high importance for the production of starting material for sheet metal applications in the automotive, household appliance and mechanical engineering.

In the continuous hot dipping refinement, the annealed metal strip is passed through a melt bath consisting of a melt of the metal forming the respective coating or metal alloy forming the respective coating, and then deflected at least once within the melt bath via a roller system while being stabilized in its barrel until it comes out of the melt bath. Excess, still molten coating material is stripped off after leaving the coating of wiping nozzles. The stripping is usually done by blowing off by means of a gas stream. However, purely mechanical stripping systems are also in use.

During the dipping phase in the coating bath, something inevitably always dissolves from the steel material of the steel strip in the coating bath. At the same time, the molten coating bath is permanently in direct contact with the ambient air. Both do not lead to one avoidable slag formation in the melt bath. This slag floats on the melt bath as so-called "upper slag".

If top slag is entrained by the metal strip emerging from the coating bath, the coating quality can be permanently impaired by the resulting imperfections. For example, so-called "smear" or the tape is damaged by indentations when the entrained slag adheres to subsequent roles and cakes. This sometimes creates significant costs due to rework and devaluation of the coated metal strip. The discharge of larger lumps of top slag, so-called "bats", can even lead to cost-intensive roller damage to the usually in-line downstream skin pass mill.

The plant operator is thus faced with the constant challenge of avoiding the entrainment of upper slag by the coated metal strip as far as possible.

There are various known ways to avoid entrainment of slag by the metal strip emerging from the melt bath.

In the first place, here are manual-mechanical methods. In practice, the upper slag is removed from the coating bath at short intervals by employees with the aid of pull-off tools. This procedure has the disadvantage that the upper slag removal is discontinuous, thus always - albeit short - time windows exist in which upper slag can freely come into contact with the exiting metal strip. When manually removing the top slag from the immediate vicinity of emerging from the molten metal strip, the coating quality can be further affected by excessive swirling of the coating and by touching the metal strip with the stripping tool.

Likewise, so-called Abschlackeroboter are known, the motor-driven slag automatically deduct from the respective melt bath. Such Abschlackeroboter form the manual stripping and can not be placed on any hot dip coating plant due to the structural conditions.

Furthermore, so-called mirror rollers are used in practice, which are positioned parallel to the width axis of the exiting metal strip and remove the slag coming into contact with them, which adheres to its surface, from the melt bath. To this state of the art also belongs in the DE 10 2006 030 914 A1 described device in which a motor-driven working material strips the top slag at a uniform speed of the coating surface. The use of motorized mirror rollers or motorized scrapers allows a continuous operation. However, moving parts are in permanent contact with the coating bath. The industrial everyday life shows here that the aggressiveness of the molten coating bath a considerable Wear generated on such moving components. This applies to the coating of a steel strip with an Albasierten coating ("Feueralumierung").

A third way of preventing the slag from the metal strip emerging from the melt bath is by continuously circulating the coating bath and by establishing cooling zones, by means of which slag formation can be deliberately laid in surface areas of the melt bath which are remote from the strip run. The effectiveness of these measures can thereby be increased by directing the flows within the coating bath so that they act counter to the strip run. As a result, dissolved metal strip components are transported away from the metal strip. Procedures of this kind are in each case in the WO 2009/098362 A1 , of the WO 2009/098363 A1 , of the US 5,084,094 A1 , of the US Pat. No. 6,426,122 B1 and the US 6,177,140 B1 described. A problem with these methods is that they sometimes require very complex and expensive equipment, which in many cases can not be retrofitted to any existing hot-dip coating equipment. Furthermore, it shows that the required bath flow in industrial everyday life is very difficult to maintain permanently. Moreover, in the apparatus required to carry out these methods, many mechanical components come into direct contact with the molten plating bath and are accordingly subject to high wear.

When stripping superfluous coating material from the metal strip by means of Abreifdüsen, immediately above are positioned at the coating bath surface, results at high gas pressures and correspondingly high flow rates of the gas stream as a positive side effect that a deflected to the coating surface of the partial gas flow supersize upper slag from the exiting metal strip. Wiping nozzles that do this are, for example, in the DE 43 00 868 Cl and the DE 42 23 343 Cl described. However, here the expulsion of the slag takes place from the emerging from the melt bath metal strip in each case in an uncontrolled, rather random manner. At low gas pressures, such as those set at low belt speeds or in the case of high coating thicknesses, the side effect "pushing the slag away from the metal strip emerging from the melt bath" does not occur.

From the JP 07-145460 Finally, it is known to arrange a nozzle carrier transversely to the metal strip emerging from the melt bath and parallel to the surface of the melt bath in such a way that the gas flowing out of it deposits the slag present on the melt bath through parallel to the strip and tangentially to the surface of the melt bath the roof surfaces of a pointed gable roof are driven laterally away from each other facing gas flows to the respective outer edge of the melt bath. The damming up there slag can then be mechanically removed. However, a disadvantage of this procedure, which is closest to the invention, is the dead space which inevitably arises in the area below the nozzle carrier. In this dead space slag can collect, which comes into contact with the emerging from the melt bath Band comes there and leads to significant surface defects in the bandwidth center. Another disadvantage of this approach is the fact that the gas streams of the nozzle beam, are arranged for the most part at a great distance from the metal strip and thus slag is driven at one point from the surface of the melt bath, at the no risk of penetration of the metal strip with Slag exists. This leads to unnecessary gas consumption.

Against the background of the prior art described above, the object of the invention was to provide a method and an apparatus for hot dip coating of metal strips, which allow with simple and inexpensive means to avoid the contact of slag with the emerging from the melt bath metal strip and to ensure an optimal surface quality.

With regard to the method, this object has been achieved according to the invention in that such a method comprises the measures specified in claim 1.

With regard to the device, this object has been achieved according to the invention in that such a device has the features specified in claim 10.

Advantageous embodiments of the invention are specified in the dependent claims and are explained below as the general inventive concept in detail.

Accordingly, in a method according to the invention for hot dip coating a metal strip with a metallic coating, in accordance with the prior art described above, the metal strip is passed continuously through a melt bath, then the thickness of the metallic coating present on the metal strip as it emerges from the melt bath set a scraper and thereby driven away on the melt bath slag by means of a gas stream of the emerging from the melt bath metal strip.

According to the invention, a gas stream flowing along the metal strip is directed along the surface of the melt bath and transversely to the conveying direction of the metal strip by means of at least one nozzle arranged laterally on one of the longitudinal edges of the metal strip emerging from the melt bath.

Similarly, an apparatus according to the invention for hot dip coating a metal strip with a metallic coating comprises a melt bath, a conveyor for continuously passing the metal strip through the melt bath, stripping means for adjusting the thickness of the metallic coating present on the metal strip as it emerges from the melt bath, and at least a nozzle for discharging a gas stream expelling slag present on the melt bath from the metal strip emerging from the melt bath.

According to the invention, the nozzle for discharging the gas stream is now arranged laterally of the conveying path of the metal strip emerging from the melt bath and oriented such that the gas stream discharged by it flows along the surface of the melt bath and aligned transversely to the conveying direction of the metal strip, along the metal strip.

A particularly effective shielding of the emerging from the molten metal strip occurs when each side of each of the longitudinal edges of the emerging from the molten metal strip by means of at least one nozzle along the surface of the melt bath and transversely to the conveying direction of the metal strip aligned, flowing along the metal strip gas flow to Expelled driving the slag is discharged from the metal strip. In this embodiment of the invention, at least one nozzle is accordingly arranged on each of the longitudinal sides of the conveying path, wherein the gas flows emerging from opposite nozzles are directed against one another.

Surprisingly, it has been shown that by means of a directed surface strip, which in each case flows out of the melt bath and flows sideways onto the surface of the coating bath so as to be directed along its direction of flow along the coating gas surface, can be kept away from the escaping metal strip. The gas flow can be easily controlled and regulated. In particular, the pressure and Einblaswinkel the gas flow to the coating bath, the desired coating thickness and the Adjusted belt speed and always be chosen so that the gas flow acts directly on the coating. As a result, the risk of surface defects due to contact of the coating with slag present on the molten bath is effectively minimized by simple means and in a particularly reliable manner.

As a result of the procedure according to the invention and the special design of a device according to the invention, a particularly low wear and also a low susceptibility to interference results. This results in a high level of maintenance and user-friendliness with minimized operating costs.

Another advantage of the invention is that existing hot dip coating systems can be retrofitted with a device according to the invention with little effort and can be operated in accordance with the invention. In this case, the invention can be used independently of the composition of the respective processed melt bath.

In principle, according to the invention, the position and blowing direction of the respective nozzles used should be selected such that the gas flow applied in each case flows between wiping nozzles and coating bath surface along the metal strip and displaces the slag on the melt bath surface over the entire width of the metal strip emerging from the melt bath. The gas flow should be directed directly to the coating surface to a to ensure the most effective expelling of the slag reaching there.

The horizontal angle of injection, at which the central axis of the gas flow impinges on the surface of the melt bath, should be in the range of 10 ° - 30 °. At shallower injection angles, there is a risk that the portion of the gas flow passing over the coating bath surface without inducing a driving action on the top slag becomes too large and the remaining gas flow carries too little a pulse to safely drive the top slag over the entire metal strip width , By contrast, with blowing angles in excess of 30 °, it can happen that the gas flow only exerts its effect on an area which is too narrow in area. The gas flow then acts only selectively, which can cause not only insufficient gas flows at portions of the metal strip surface more distant from the nozzle, but also troublesome bath surfaces or turbulences on the melt bath surface, which degrade the coating result.

Advantageously, the gas flows are aligned so that a direct flow of the respective surface of the metal strip is avoided. By a direct flow, the band position of the metal strip could be destabilized in the Abstreifdüse. Therefore, the gas flow is optimally aligned in each case in such a way that it flows as far as possible parallel to the belt surface and, as far as possible, does not face the surfaces of the metal belt aligned transversely to the conveying direction of the metal belt directed impulse causes. For this purpose, the central axis of the gas flow emerging from the nozzle associated with the one longitudinal edge may lie in a common plane with the central axis of the gas flow emerging from the other longitudinal edge, the nozzles being optimally oriented in this case so that the central axes of the gas flows lie in the same plane, in which the middle layer of the metal strip as it exits the melt bath.

According to a further variant of the invention, the gas stream discharged from the respective nozzles is aligned so that the central axis of the respective gas stream lies in the plane in which the middle layer of the metal strip lies on its exit from the melt bath. In this orientation, the gas flow strikes the edge of the metal strip emerging from the melt bath and is split into two sub-streams, one of which flows along one surface and the other along the other surface of the metal strip. This proves to be particularly advantageous when the metal strip is at each of its two longitudinal edges flowing against a gas stream and the gas streams are aligned with each other so that their central axes lie in a common plane in which the center layer of the metal strip is located. By "center layer of the metal strip" is meant the layer which is arranged centrally between the two outer surfaces of the metal strip.

In the event that at least one nozzle is assigned to each longitudinal edge of the metal strip or conveying path, it may be expedient to arrange the nozzles in such a way that the nozzle is oriented in the manner explained above on the edges of the metal strip emerging from the melt bath from the one longitudinal edge associated nozzle discharged gas flow along one surface and the emerging from the other longitudinal edge associated nozzle gas stream flows along the other surface of the metal strip. In this way, large volume flows can be blown along the respective surface, without causing a mutual obstruction.

In practice, the respective gas stream may be air, a gas inert with respect to the melt bath, or a gas mixture formed from air and a gas inert to the melt bath. It has been found that pressurization of the gas flow supplied to the nozzles in the range of 1 to 15 bar leads to good results under the conditions prevailing in practice. A gas supply with pressures of less than 1 bar results in a poor coating result because the momentum of the gas flow is too low to effectively drive the top slag off the surface of the metal strip exiting the melt bath. A gas supply with pressures greater than 15 bar leads to a poor coating result, because the strong momentum of the gas stream in the coating bath surface in unwanted vibrations added or even stirred up. The regulation and control of the gas flow can be done by the operator via adjustment of the horizontal, vertical and possibly axial alignment of the device according to the invention and the gas pressure take place.

The "blown" upper slag can be skimmed off in a conventional manner at a sufficient distance from the exiting metal strip mechanically from the coating.

Experimental observations have shown that a particularly positive effect of the method according to the invention is achieved when N ₂ or another gas inert with respect to the metallic coating and the melt bath is used for the gas flow. This results from the fact that when using nitrogen or a comparably inert gas in addition to the pure driving away of the upper slag and the formation of new upper slag in the area swept by the gas stream is markedly reduced.

The metal strips processed in accordance with the invention are typically cold-rolled or hot-rolled steel strips.

For the melt baths, all of the metallic melts that can be applied by hot dip coating can be used. These include, for example, zinc or zinc alloy melts as well as aluminum or aluminum alloy melts.

Fig. 1

eine Vorrichtung zum Schmelztauchbeschichten eines Stahlbands in seitlicher Ansicht;

Fig. 2

die Vorrichtung gemäß Fig. 1 in einem Schnitt entlang der in Fig. 1 eingezeichneten Schnittlinie X-X;

Fig. 3

die Vorrichtung gemäß Fig. 1 mit einer variierten Anordnung der in ihr vorgesehenen Düsen in einer der Fig. 2 entsprechenden Ansicht;

Fig. 4

eine weitere Vorrichtung zum Schmelztauchbeschichten eines Stahlbands in einer den Figuren 2 und 3 entsprechenden Ansicht;

Fig. 5

die Vorrichtung gemäß Fig. 4 in einer seitlichen Ansicht.

The invention will be explained in more detail by means of exemplary embodiments. Each show schematically:

Fig. 1

a device for hot dip coating a steel strip in a side view;

Fig. 2

the device according to Fig. 1 in a section along the in Fig. 1 drawn section line XX;

Fig. 3

the device according to Fig. 1 with a varied arrangement of the nozzles provided in it in one of Fig. 2 corresponding view;

Fig. 4

another device for hot dip coating a steel strip in a FIGS. 2 and 3 corresponding view;

Fig. 5

the device according to Fig. 4 in a side view.

A device 1 for the hot dip coating of a metal strip M, which is, for example, cold-rolled steel strip made of a corrosion-sensitive steel, comprises a melt bath 3 filled in a vessel 2 into which the coating to be coated, previously in a known manner, has a sufficient immersion temperature brought metal strip M is passed over a trunk 4.

In the hot-dip bath 3, the metal strip M is deflected at a deflection roller 5 in such a way that it leaves the melt bath 3 in a vertically oriented conveying direction F. exit. In this case, the metal strip M emerging from the melt bath 3 passes through a stripping device 7 arranged at a specific distance above the surface 6 of the melt bath 3. This comprises two stripping nozzles 8,9 formed as slit nozzles, one of which comprises a stripping gas stream AG1 on the one surface O1 of the metal strip M extending on one side between the longitudinal edges L1 and L2 of the metal strip M, and the other of which directs a Abstreifgasstrom AG2 on the present on the opposite side of the metal strip M surface 02.

Under optimum operating conditions, the metal strip M emerging from the melt bath 3 is aligned such that its center layer ML aligned centrally between the surfaces 01, 02 lies in a vertically oriented plane H.

When in the FIGS. 1 to 3 In the embodiment shown, two lance-like nozzles 10, 11 are arranged between the wiping nozzles 8, 9 of the wiping device 7 and the surface 6 of the melt bath 3, of which one is arranged laterally of one longitudinal edge L1 and the other laterally of the other longitudinal edge L2 of the metal strip M.

The lance-like nozzles 10,11, for example, consist of tubes with a tube diameter of 20 mm, which are connected via hand-operated cone valves to a gas supply, not shown here for clarity. The gas supply may be, for example, a nitrogen house line, the is provided as standard in the building in which the device 1 is located. The gas supply and pressure control takes place separately for each of the lance nozzles 10,11. The pressure of the gas was varied within a pressure range of 1 - 15 bar, and also for each of the nozzles 10,11 individually.

The nozzles 10,11 each bring a gas flow G1, G2, which is formed for example by nitrogen gas.

When in Fig. 3 In the embodiment illustrated, the nozzle openings of the nozzles 10, 11 are aligned such that the central axes Ga1, Ga2 of the gas streams G1, G2 flowing towards each other lie in the plane H of the center layer ML of the metal strip M and, accordingly, the respective edges associated therewith at the respective longitudinal edge L1 , L2 meet. In this way, the gas streams G1, G2 are divided at the longitudinal edges L1, L2 into two partial streams G11, G12 and G21, G22. In this case, the partial flows G11, G21 flow toward each other along the one surface O1, while the other partial flows G12, G22 flow along the opposite surface 02 of the metal strip M. The partial flows G11, G21 or G12, G22 assigned to the respective surfaces 01, 02 each meet in the area of the strip center MB, so that there arises a gas flow G ', G "directed away from the respective surface 01, 02 of the metal strip M. forces possibly acting on the metal strip M cancel each other out as they occur in the same way on both sides of the metal strip M.

The gas streams G1, G2, the partial gas streams G11-G22 formed therefrom, and the gas streams G ', G "flowing from the metal strip M and formed from the partial gas streams G11-G22 produce or form new slag on the surface 6 of the melt bath 3 S driven away from the metal strip M, so that the surface 6 of the melt bath 3 in the region A of the exit of the metal strip M from the melt bath 3 is kept largely free of slag and prevents contamination of existing on the surfaces 01,02 of the metal strip M metallic coating with slag becomes.

When in Fig. 2 the embodiment shown are the nozzles 10,11, as well as in Fig. 1 indicated, offset in the horizontal direction H offset from one another so that only the effluent from the one nozzle 10 gas flow G1 flows along one surface 01 of the metal strip M, while emerging from the other nozzle 11 gas flow G2 along the other surface 02 of the metal strip M flows. In this case, the gas streams G1, G2 drive away the slag S passing into the region A of the outlet of the metal strip M in the lateral direction, so that they move laterally in the region A to the opposite side Ranges of the melt bath 3 adjacent areas B1, B2 collects and there mechanically, that can be removed manually or by means of a suitable, motor-driven device from the surface 6 of the melt bath 3.

When in Fig. 4 shown embodiment, only a single nozzle 10 laterally of the conveying path or the one longitudinal edge L1 of the metal strip M is aligned so that the central axis Ga1 of the gas stream G1 discharged by it as in the Fig. 1 and 2 illustrated embodiment in the plane H of the center layer ML of the metal strip M is located. The accordingly also at the longitudinal edge L1 and there existing edge of the metal strip M from the gas flow G1 divided streams G11 and G12 flow along their respective associated surface 01,02 of the metal strip M, thereby driving the slag reaching there in the direction of the at opposite edge adjacent region B2 of the slag bath 3, from where the slag can be removed mechanically again.

The horizontal orientation of the nozzles 10,11 is selected so that the gas flows G1, G2 meet with their respective central axis Ga1, Ga2 each at an injection angle ß on the surface 6 of the melt bath 3, which is in the range of 10 ° - 30 ° , The injection angle β is related to a parallel to the mirror of the surface 6 of the melt bath 3 oriented horizontal ( Fig. 5 ).

For operational experiments, a N ₂ gas flow was blown by means of nozzle nozzles 10,11 trained nozzle lances between the melt bath and stripping nozzles on a large industrial hot dip coating plant during the fire aluminizing. The coating bath contained 9.5 wt .-% Si, 2.5 wt .-% Fe and the remainder A1 and traces of other elements and unavoidable impurities. The speed of the metal strip emerging from the melt bath was 38 m / min with a coating layer to be applied of min. 75 g / m ² per side of the metal strip M.

Blown-off top slag was manually-mechanically removed from the aluminum bath surface. Over a longer production period, surface defects due to entrained top slag could be effectively reduced or prevented.

Table 1 shows in accordance with the invention below the stripping nozzles each side of the longitudinal edges of the metal strip arranged nozzle lances that this Gießgebnis was not given if no gas flow was applied or the present invention given boundary conditions were left.

REFERENCE NUMBERS

1

Device for hot dip coating

2

boiler

3

melt bath

4

trunk

5

idler pulley

6

Surface of the melt bath 3

7

stripping

8.9

wiping

10.11

jet

A

Area of exit of the metal strip M from the melt bath third

AG1, AG2

Abstreifgasstrom

B1, B2

Portions of the surface 6 of the melt bath 3

F

conveying direction

G ', G "

gas flows

G1, G2

from the nozzles 10,11 discharged gas streams

G11-G22

divided from the gas flows G1, G2 partial gas streams

Ga1, Ga2

central axes of the gas flows G1, G2

H

vertically aligned plane of the middle layer ML

L1, L2

Longitudinal edges of the metal strip M

M

metal band

MB

Tape center of the metal band

ML

Middle layer of metal band M

O1, O2

Surfaces of the metal strip M

S

slag

ß

supply angle

Table 1 attempt arranged per longitudinal side nozzles Gas pressure [bar] Blowing angle [°] Surface defects? According to the invention? 1 none no gas flow often No 2 1 0.5 20 ° often No 3 1 10.0 5 ° often No 4 1 0.8 10 ° often No 5 1 2.0 10 ° isolated Yes 6 1 10.0 15 ° none Yes 7 1 10.0 20 ° none Yes 8th 1 15.0 25 ° none Yes 9 1 18.0 25 ° often No 10 1 12.0 30 ° none Yes 11 1 10.0 45 ° often No 12 2 10.0 5 ° often No 13 2 0.8 10 ° often No 14 2 2.0 10 ° none Yes 15 2 10.0 15 ° none Yes 16 2 10.0 20 ° none Yes 17 2 15.0 25 ° none Yes 18 2 18.0 25 ° often No 19 2 12.0 30 ° none Yes 20 2 10.0 45 ° often No

Claims (16)

1. Method for hot-dip coating a metal strip (M) with a metallic coating,

   - in which the metal strip (M) is conveyed through a molten bath (3) in a continuous pass,

   - in which the thickness of the metallic coating present on the metal strip (M) when it exits from the molten bath (3) is regulated by means of a skimming device (7), and

   - in which dross (S) present on the molten bath (3) is driven away from the metal strip (M) exiting from the molten bath (3) by means of a gas flow (G1, G2),
   characterised in that in order to drive the dross (S) away from the metal strip (M) a gas flow (G1, G2), which is aligned along the surface (6) of the molten bath (3) and transverse to the conveying direction (F) of the metal strip (M) and which flows along the metal strip (M), is discharged by means of at least one nozzle (10, 11) arranged laterally in relation to one of the longitudinal edges (L1, L2) of the metal strip (M) exiting from the molten bath (3).
2. Method according to Claim 1, characterised in that laterally in relation to each of the longitudinal edges (L1, L2) of the metal strip (M) exiting from the molten bath (3) a gas flow (G1, G2), which is aligned along the surface (6) of the molten bath (3) and transverse to the conveying direction (F) of the metal strip (M) and which flows along the metal strip (M), is discharged by means of at least one nozzle (10, 11) in each case, in order to drive the dross (S) away from the metal strip (M).
3. Method according to Claim 2, characterised in that the central axis (Ga, Ga2) of the gas flow (G1, G2) issuing from the nozzle (10, 11) assigned to the one longitudinal edge (L1, L2) lies in a common plane (H) with the central axis (Ga2, Ga1) of the gas flow (G2, G1) issuing from the nozzle (11, 10) assigned to the other longitudinal edge (L1, L2).
4. Method according to any one of the preceding claims, characterised in that the central axis (Ga2, Ga1) of the respective gas flow (G1, G2) lies in the plane (H), in which the central position (ML) of the metal strip (M) runs when it exits from the molten bath (3).
5. Method according to Claim 2, characterised in that the nozzles (10, 11), which are in each case arranged laterally in relation to the longitudinal edges (L1, L2) of the metal strip (M) exiting from the molten bath (3), are arranged in such a way that the gas flow (G1) discharged from the nozzle (10) assigned to the one longitudinal edge (L1) flows along the one surface (O1) and the gas flow (G2) issuing from the nozzle (11) assigned to the other longitudinal edge (L2) flows along the other surface (02) of the metal strip (M).
6. Method according to any one of the preceding claims, characterised in that the respective gas flow (G1, G2) consists of air, of a gas which is inert in relation to the molten bath (3) or of a gas mixture formed from air and a gas which is inert in relation to the molten bath (3).
7. Method according to Claim 6, characterised in that the inert gas is nitrogen.
8. Method according to any one of the preceding claims, characterised in that the flow injection angle (ß), at which the central axis (Ga1, Ga2) of the gas flow (G1, G2) is directed onto the surface (6) of the molten bath (3), in relation to a horizontal is in the range from 10° - 30°.
9. Method according to any one of the preceding claims, characterised in that the respective gas flow (G1, G2) flows tangentially against the surface of the molten bath (3).
10. Method according to any one of the preceding claims, characterised in that the dross (S) driven away by means of the respective gas flow (G1, G2) is removed from the molten bath (3) by means of a mechanically powered device.
11. Apparatus for hot-dip coating a metal strip (M) with a metallic coating,

    - having a molten bath (3),

    - having a conveying device for continuously conducting the metal strip (M) through the molten bath(3),

    - having a skimming device (7) for regulating the thickness of the metallic coating present on the metal strip (M) when it exits from the molten bath (3)
    and

    - having at least one nozzle (10, 11) for discharging a gas flow (G1, G2) which drives away dross (S) present on the molten bath (3) from the metal strip (M) exiting from the molten bath (3),
    characterised in that the nozzle (10, 11) for discharging the gas flow (G1, G2) laterally in relation to the conveying path of the metal strip (M) exiting from the molten bath (3) is arranged and aligned in such a way that the gas flow (G1, G2) discharged by it and aligned along the surface (6) of the molten bath (3) and transverse to the conveying direction (F) of the metal strip (M) flows along the metal strip (M).
12. Apparatus according to Claim 11, characterised in that the nozzle (10, 11) seen in the conveying direction of the metal strip (M) exiting from the molten bath (3) is arranged between the skimming device (7) and the surface (6) of the molten bath (3).
13. Apparatus according to either of Claims 11 or 12, characterised in that at least one nozzle (10, 11) is respectively arranged laterally in relation to the opposing sides of the conveying path of the metal strip (M) exiting from the molten bath (3) and discharges a gas flow (G1, G2), which is aligned along the surface (6) of the molten bath (3) and transverse to the conveying direction (F) of the metal strip (M) and which flows along the metal strip (M), in order to drive the dross (S) away from the metal strip (M).
14. Apparatus according to Claim 13, characterised in that the central axes (Ga2, Ga1) of the gas flows (G1, G2) issuing from the nozzles (10, 11) arranged opposite one another lie in a common plane (H).
15. Apparatus according to Claim 14, characterised in that the central axes of the gas flows lie in the plane, in which the central position of the metal strip (M) lies when it exits from the molten bath (3).
16. Apparatus according to Claim 15, characterised in that the nozzles, which are in each case arranged laterally in relation to the conveying path of the metal strip (M) exiting from the molten bath (3), are arranged in such a way that the gas flow discharged from the one nozzle flows along the one surface and the gas flow issuing from the other nozzle flows along the other surface of the metal strip (M).

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