EP2430208B1 - Method for producing a coated metal strip with an improved appearance - Google Patents

Description

The invention relates to a method for manufacturing a metal strip having an improved appearance, more particularly intended to be used for the manufacture of skin parts for motorized land vehicles, without being limited thereto.

Steel sheets for the manufacture of parts for land motor vehicles are generally coated with a zinc-based, corrosion-resistant metallic layer deposited either by hot dipping in a zinc-based liquid bath or by electroplating in an electrolytic bath comprising zinc ions.

The galvanized sheets for the manufacture of skin parts are then shaped and assembled to form a blank body, which is then coated with at least one layer of paint, which provides increased protection against corrosion and good surface appearance.

For this purpose, conventionally, automakers first apply on the white box a layer of cataphoresis, then a layer of primer paint, a base coat of paint, and possibly a layer of varnish. To obtain a satisfactory painted surface appearance, it is generally applied a total paint thickness of between 90 and 120 μm, consisting of a layer of cataphoresis 20 to 30 μm thick, a layer of primer paint from 40 to 50 μm, and a base coat of 30 to 40 μm, for example.

In order to limit the thickness of paint systems to less than 90 μm, some car manufacturers have proposed either to avoid the cataphoresis step, or to limit the number of paint layers to increase productivity. However, to date, this reduction in thickness of the paint system is always carried out to the detriment of the final painted surface appearance of the part and is not implemented industrially.

Indeed, the base-based zinc-based coatings have what is called a corrugation of their surface, which can currently be compensated for only by significant layers of paint on pain of having an appearance called "skin" orange "unacceptable for body parts.

The corrugation W (waviness in English) of the surface is a geometric irregular softness, pseudoperiodic, of rather long wavelength (0.8 to 10 mm) that one distinguishes from the roughness R which corresponds to the geometrical irregularities low wavelengths (<0.8mm).

In the present invention, the arithmetic average Wa of the corrugation profile, expressed in μm, has been retained to characterize the corrugation of the surface of the sheet, and the corrugation measurements have been carried out with a cut-off threshold of 0 , 8 mm and denoted Wa _0.8 .

The object of the invention is therefore to provide a method of manufacturing a metal strip coated with an anticorrosive coating, the waving Wa _{0.8 of which} is reduced compared with the strips of the prior art, thus allowing to produce painted metal parts requiring a reduced total paint thickness compared to the parts of the prior art. Another object of the invention is to provide an installation for implementing such a method.

• faire passer la bande métallique dans un bain de métal en fusion, puis
• essorer la bande métallique revêtue au moyen de buses projetant un gaz de part et d'autre de la bande, ledit gaz présentant un pouvoir oxydant inférieur à celui d'une atmosphère constituée de 4% en volume d'oxygène et 96% en volume d'azote, puis
• à faire passer la bande dans une zone de confinement délimitée :
  • ■ en partie basse par la ligne d'essorage et les faces supérieures desdites buses d'essorage,
  • ■ en partie haute par la partie supérieure de deux caissons de confinement placés de part et d'autre de la bande, juste au-dessus desdites buses, et présentant une hauteur d'au moins 10 cm par rapport à la ligne d'essorage, et
  • ■ sur les côtés, par les parties latérales desdits caissons de confinement,

l'atmosphère régnant dans ladite zone de confinement présentant un pouvoir oxydant inférieur à celui d'une atmosphère constituée de 4% en volume d'oxygène et 96% en volume d'azote et supérieur à celui d'une atmosphère constituée de 0,15% en volume d'oxygène et 99,85% en volume d'azote.For this purpose, a first object of the invention is constituted by a method of manufacturing a metal strip having a corrosion protection metal coating, comprising the steps of:

• pass the metal strip through a bath of molten metal, then
• squeezing the coated metal strip by means of nozzles throwing a gas on either side of the strip, said gas having an oxidizing power lower than that of an atmosphere consisting of 4% by volume of oxygen and 96% by volume of nitrogen, then
• to pass the band in a defined containment zone:
  • ■ in the lower part by the spin line and the upper faces of said spin nozzles,
  • ■ in the upper part by the upper part of two containment boxes placed on either side of the strip, just above said nozzles, and having a height of at least 10 cm with respect to the spin line, and
  • ■ on the sides, by the lateral parts of said containment boxes,

the atmosphere prevailing in said confinement zone having an oxidizing power lower than that of an atmosphere composed of 4% by volume of oxygen and 96% by volume of nitrogen and greater than that of an atmosphere consisting of 0.15 % by volume of oxygen and 99.85% by volume of nitrogen.

• les caissons de confinement présentent une hauteur d'au moins 15 cm, de préférence 20 cm, voire 30 cm, par rapport à la ligne d'essorage ;
• les caissons de confinement sont alimentés en gaz présentant un pouvoir oxydant inférieur à celui d'une atmosphère constituée de 4% en volume d'oxygène et 96% en volume d'azote, et de préférence supérieur à celui d'une atmosphère constituée de 0,15% en volume d'oxygène et 99,85% en volume d'azote.
• le gaz d'essorage est constitué d'azote,
• la bande métallique est une bande d'acier.

In preferred embodiments, the method according to the invention may further comprise the following features, taken alone or in combination:

• the containment boxes have a height of at least 15 cm, preferably 20 cm or 30 cm, with respect to the spin line;
• the containment boxes are supplied with gas having an oxidizing power lower than that of an atmosphere consisting of 4% by volume of oxygen and 96% by volume of nitrogen, and preferably greater than that of an atmosphere consisting of 0 15% by volume of oxygen and 99.85% by volume of nitrogen.
• the spin gas consists of nitrogen,
• the metal strip is a steel strip.

• des moyens de défilement d'une bande métallique,
• un creuset contenant un bain de métal en fusion, et
• un dispositif d'essorage confiné constitué d'au moins deux buses
  d'essorage placées de part et d'autre du trajet de la bande après sa sortie du bain de métal en fusion, chaque buse étant munie d'au moins un orifice de sortie de gaz et comprenant une face supérieure, laquelle est surmontée d'un caisson de confinement ouvert sur une face située en regard de la bande, chaque caisson comprenant au moins une partie supérieure et deux parties latérales, la hauteur H des caissons de confinement par rapport à la ligne d'essorage étant supérieure ou égale à 10 cm.

The invention also relates to an installation for continuous coating of metal strips by hot dipping, comprising:

• means for scrolling a metal strip,
• a crucible containing a bath of molten metal, and
• a confined spinning device consisting of at least two nozzles
  on both sides of the path of the strip after outlet of the bath of molten metal, each nozzle being provided with at least one gas outlet orifice and comprising an upper face, which is surmounted by a containment box open on a face facing the strip, each box comprising at least one upper part and two lateral parts, the height H of the containment boxes with respect to the spin line being greater than or equal to 10 cm.

• les parties supérieures des caissons de confinement sont constituées d'une plaque de fond et d'une plaque supérieure ;
• chacun des caissons de confinement est compartimenté par une série de lames verticales s'étendant de la face supérieure de la buse jusqu'à la partie supérieure des caissons de confinement ;
• la distance D entre l'extrémité des parties latérales des caissons de confinement et la bande est comprise entre 5 et 100 mm et de préférence entre 10 et 100 mm ;
• les dispositifs d'essorage confinés comprennent en outre des plaques antibruit de chaque côté de la bande, en regard d'une partie de l'orifice de sortie des buses d'essorage ;
• les caissons de confinement comprennent en outre des pièces de confinement de rives placées entre les caissons de confinement, au-dessus des plaques antibruit, en face des rives de la bande ;
• les pièces de confinement de rives peuvent être déplacées horizontalement et verticalement ;
• chacune des pièces de confinement de rives est constituée de deux plaques rectangulaires parallèles à la bande, reliées par une plaque latérale placée face aux rives de la bande ;
• chacune des pièces de confinement de rives est constituée de deux plaques rectangulaires inclinées par rapport au plan de défilement de la bande et raccordées le long de leur arête verticale placée face aux rives de la bande;
• les pièces de confinement de rives comprennent en outre un moyen de rappel reliant les plaques rectangulaires, les plaques rectangulaires étant suffisamment inclinées par rapport au plan de défilement de la bande pour être en contact avec les parties latérales des caissons de confinement ;
• l'installation comprend des pièces de confinement de rives placées entre les caissons de confinement, en face des rives de la bande et se prolongeant en regard d'une partie de l'orifice de sortie des buses d'essorage ;
• les buses d'essorage sont munies d'un orifice de sortie unique en forme de fente longitudinale dont la largeur est au moins égale à celle de la bande à revêtir.

In preferred embodiments, the installation according to the invention may further comprise the following features, taken alone or in combination:

• the upper parts of the containment boxes consist of a bottom plate and an upper plate;
• each of the containment boxes is compartmentalized by a series of vertical blades extending from the upper face of the nozzle to the upper part of the containment boxes;
• the distance D between the end of the lateral parts of the containment boxes and the band is between 5 and 100 mm and preferably between 10 and 100 mm;
• the confined wiping devices further comprise noise canceling plates on each side of the strip, facing a portion of the wiper nozzle outlet orifice;
• the containment caissons further comprise edge containment pieces placed between the containment boxes, above the noise barriers, opposite the banks of the strip;
• the bank containment rooms can be moved horizontally and vertically;
• each of the bank confinement pieces consists of two rectangular plates parallel to the strip, connected by a side plate placed facing the banks of the strip;
• each of the bank confinement pieces consists of two rectangular plates inclined with respect to the scroll plane of the band and connected along their vertical edge placed facing the banks of the band;
• the bank confinement rooms further comprise a return means connecting the rectangular plates, the rectangular plates being sufficiently inclined relative to the strip travel plane to be in contact with the lateral parts of the containment boxes;
• the installation comprises edge containment pieces placed between the containment boxes, facing the edges of the strip and extending opposite a portion of the outlet orifice of the spinning nozzles;
• the spin nozzles are provided with a single outlet orifice in the form of a longitudinal slot whose width is at least equal to that of the band to be coated.

The invention further relates to a confined wiper device as defined above.

The features and advantages of the present invention will appear better in the following description given by way of non-limiting example.

With reference to the figure 1 the first step of the process according to the invention consists of continuously passing a metal strip B, such as a steel strip, in a coating bath 1 containing molten metal, contained in a crucible 2. Being immersed in this bath 1, the band B is generally annealed in an oven which makes it possible in particular to prepare the surface.

The running speed of the strip on the industrial lines is generally between 40m / min and 200m / min, for example, and is preferably greater than 120 m / min, or even greater than 150 m / min.

The composition of the coating bath to be used in the process according to the invention may in particular be based on zinc or zinc alloy, but also based on aluminum or aluminum alloy. These elements both protect the band against corrosion.

The composition of the bath may also contain up to 0.3% by weight of optional addition elements such as Si, Sb, Pb, Ti, Ca, Mn, Sn, La, Ce, Cr, Ni, Zr or Bi . These various elements may allow, among other things, to improve the corrosion resistance of the coating or its fragility or adhesion, for example. Those skilled in the art who know their effects on the characteristics of the coating will know how to use them according to the complementary aim sought. It has also been verified that these elements do not interfere with the control of the corrugation obtained by the process according to the invention. In certain circumstances, however, it will be preferred to limit the titanium content to less than 0.01%, or even less than 0.005% because this element can generate pollution problems of degreasing and phosphating baths of automobile manufacturers.

Finally, the bath may contain unavoidable impurities from the crucible feed ingots or even the passage of the strip in the bath. It will be possible to mention, in particular, iron, etc.,

The bath is maintained at a temperature between liquidus + 10 ° C and 750 ° C, the liquidus temperature varies depending on its composition. For the range of coatings used in the present invention, this temperature will therefore be between 350 and 750 ° C. It will be recalled that the liquidus is the temperature beyond which an alloy is in the fully fused state.

After passing through the crucible 2, the metal strip B coated on its two faces is then subjected to spinning by means of nozzles 3 placed on either side of the band B, nozzles which project a spin gas towards the surface This conventional operation, well known to those skilled in the art, allows to adjust the thickness of the coating accurately, while it is not yet solidified.

One of the essential characteristics of the process according to the invention consists in choosing a dewatering gas having an oxidizing power lower than that of an atmosphere consisting of 4% by volume of oxygen and 96% by volume of nitrogen. In particular, it will be possible to use pure nitrogen or argon or still more mixtures of nitrogen or argon and oxidizing gases such as, for example, oxygen, mixtures of CO and CO ₂ or mixtures of H ₂ and H ₂ O. It is also possible to use mixtures of CO and CO ₂ or mixtures of H ₂ and H ₂ O without addition of inert gas.

• en partie basse par la ligne d'essorage L et les faces externes supérieures des buses d'essorage 3,
• en partie haute par la partie supérieure de deux caissons de confinement C placés de part et d'autre de la bande, juste au-dessus des buses 3, et présentant une hauteur d'au moins 10 cm par rapport à la ligne d'essorage I, et
• sur les côtés, par les parties latérales des caissons de confinement C, l'atmosphère régnant dans la zone de confinement présentant un pouvoir oxydant inférieur à celui d'une atmosphère constituée de 4% en volume d'oxygène et 96% en volume d'azote et supérieur à celui d'une atmosphère constituée de 0,15% en volume d'oxygène et 99,85% en volume d'azote.

At the end of the spinning, the other essential characteristic of the process according to the invention is the passage in a delimited confinement zone:

• in the lower part by the spin line L and the upper outer faces of the spin nozzles 3,
• in the upper part by the upper part of two containment boxes C placed on either side of the band, just above the nozzles 3, and having a height of at least 10 cm from the spinning line I, and
• on the sides, by the lateral parts of the confinement caissons C, the atmosphere prevailing in the confinement zone having an oxidizing power lower than that of an atmosphere consisting of 4% by volume of oxygen and 96% by volume of nitrogen and greater than that of an atmosphere consisting of 0.15% by volume of oxygen and 99.85% by volume of nitrogen.

To determine the oxidizing power of the atmosphere surrounding the band, one will proceed to the evaluation of its oxygen equivalent partial pressure at equilibrium.

When the only oxidizing gas present is O ₂ , mixed with an inert gas (nitrogen, argon), this pressure is then equal to the volume content of O ₂ that can be measured in real time by means of a suitable sensor.

When other oxidizing gases, such as H ₂ O or CO _2, are present in a mixture with a reducing gas such as H ₂ or CO, for example, the equivalent oxygen partial pressure is calculated by the mass action law. at the gas temperature considered.

For example, for the couple H ₂ / H ₂ O, the reaction is written as follows:

H ₂ +1/2 O ₂ ↔ H ₂ O

avec R la constante des gaz parfaits, T la température des gaz en Kelvin, et ΔG la variation d'énergie libre associée à la réaction, que l'on trouve dans les tables de thermodynamique, en calories par mole ou en Joules par mole selon la valeur prise pour la constante R.At thermodynamic equilibrium, the partial pressures of the gases obey the following relation: $$\frac{{\mathrm{<figure-callout\; id="2"\; label="pH"\; filenames="imgf0001.png"\; state="\{\{state\}\}">pH</figure-callout>}}_{\mathrm{2}}\mathrm{<figure-callout\; id="2"\; label="O\; pH"\; filenames="imgf0001.png"\; state="\{\{state\}\}">O\; </figure-callout>}}{{\mathrm{pH}}_{}}={\mathrm{e}}^{-\frac{\mathrm{.DELTA.G}}{\mathrm{RT}}}$$

with R the constant of the perfect gases, T the temperature of the gases in Kelvin, and ΔG the variation of free energy associated with the reaction, which is found in the thermodynamic tables, in calories per mole or in Joules per mole according to the value taken for the constant R.

From this relationship, the value of pO ₂ equilibrium oxygen partial pressure is extracted for the gas mixture under consideration.

In the context of the invention, pO _{2 must} be between 0.0015 and 0.04 in the confinement atmosphere.

The present inventors have indeed found that by using a dewatering gas according to the invention and by passing the strip in such a confinement zone, surprisingly a coating having a smaller corrugation than that of the coated strips was obtained. of the prior art.

In the context of the present application, the term "spinning line" means the shortest segment connecting the nozzle and the sheet, corresponding to the minimum path carried out by the dewatering gas, as designated by the letter L on the figure 1 .

The containment boxes used in the process according to the invention may be fed with low oxidizing gas, see inert or may simply be fed by the flow of spin gas escaping from the nozzles.

The oxidizing power of the dewatering gas is limited to that presented by a mixture consisting of 4% by volume of oxygen in 96% by volume of nitrogen, since, beyond this degree of oxidation, the undulation of the coating is not improved over the prior art.

On the contrary, a low limit is imposed for the oxidizing power of the confinement atmosphere; fixed to the oxidizing power of a mixture consisting of 0.15% by volume of oxygen in 99.85% by volume of nitrogen, because if this confining atmosphere is not sufficiently oxidizing, its use will promote the vaporization of zinc from the coating not yet solidified, vapors which can then come foul the containment box and / or redeposit on the band thus creating defects of crippling aspects.

Although all kinds of spin nozzles can be used for the implementation of the method according to the invention, it is more particularly preferred to choose nozzles whose outlet orifice is in the form of a blade whose width exceeds that of the tape to be coated. This type of nozzle makes it possible to achieve good confinement of the lower part of the spinning zone. In particular, it is possible to advantageously use triangular section nozzles as schematically represented in FIG. figure 1 , especially. These nozzles are generally 30 or 40 cm from the surface of the bath.

In compliance with these instructions, there is indeed a surprising and significant improvement in the undulation of the coatings in question, as shown by the tests presented below.

When the coated sheet is completely cooled, it can undergo a skin-pass operation that gives it a texture to facilitate its subsequent shaping. Indeed, the operation of the skin-pass makes it possible to transfer to the surface of the sheet a sufficient roughness so that its shaping is carried out under good conditions, by favoring a good retention of the oil applied on the front plate its formatting.

This skin-pass operation is generally performed for metal sheets intended for the manufacture of body parts for land motor vehicles. When the metal sheets according to the invention are intended for the manufacture of household appliances, for example, this additional operation is not carried out.

The skin-shaped sheet or not is then shaped, for example by stamping, bending or profiling, and preferably by stamping, to form a part that can then be painted. In the case of parts for household appliances, it may also optionally subject this layer of paint to an annealing by physical and / or chemical means, known in themselves. For this purpose, the painted piece can be through a hot air or induction furnace, or under UV lamps or under a device beam scattering electron.

For the production of parts for the automobile, it is soaked in a cataphoresis bath, and applied successively, a primer coat, a base coat of paint, and optionally a layer of finishing varnish.

Before applying the cataphoresis layer on the part, it is previously degreased and phosphated to ensure the adhesion of cataphoresis. The cataphoresis layer provides the part with additional protection against corrosion. The primer coat, usually applied by spray, prepares the final appearance of the part and protects it from gravel and UV. The base coat of paint gives the piece its color and its final appearance. The varnish layer gives the surface of the part a good mechanical resistance, a resistance against aggressive chemical agents and a good surface appearance.

The layer of paint (or paint system) used to protect and guarantee an optimal surface appearance to galvanized parts, for example, has a cataphoresis layer 10 to 20 μm thick, a primer coat of less than 30 μm, and a base coat of less than 40 microns.

• couche de cataphorèse : inférieure à 10 à 20 µm,
• couche de peinture d'apprêt : inférieure à 20 µm,
• couche de peinture de base : inférieure à 20 µm et avantageusement inférieure à 10 µm, et
• couche de vernis : de préférence inférieure à inférieure à 30 µm.

In cases where the paint system further comprises a layer of varnish, the thicknesses of the different layers of paint are generally as follows:

• cataphoresis layer: less than 10 to 20 μm,
• primer coat: less than 20 μm,
• base coat: less than 20 μm and advantageously less than 10 μm, and
• varnish layer: preferably less than less than 30 microns.

The paint system may also not include a cataphoresis layer, and include only one layer of primer paint and a base coat of paint and possibly a layer of varnish.

testing

The tests are carried out from a cold-rolled steel sheet of the IF-Ti type, which is passed through a crucible containing a bath of variable composition. It is maintained at a temperature of 70 ° C. beyond the liquidus of the composition.

At the outlet of the bath, the coating obtained is wrung with nitrogen, by means of two conventional nozzles so as to obtain a coating thickness of about 7 .mu.m.

• une zone 1 allant de la sortie du bain jusqu'à une distance de 10cm sous la ligne d'essorage,
• une zone 2 allant de la fin de la zone 1 jusqu'à la ligne d'essorage,
• une zone 3 allant de la fin de la zone 2 jusqu'à une distance de 10cm au dessus de la ligne d'essorage et
• une zone 4 allant de la fin de la zone 3 jusqu'à la solidification du revêtement métallique.

The path of the steel strip between the coating bath outlet and the post-spin zone is subdivided into four zones:

• an area 1 from the bath outlet to a distance of 10cm below the spin line,
• an area 2 from the end of zone 1 to the spin line,
• a zone 3 going from the end of zone 2 to a distance of 10cm above the spin line and
• an area 4 from the end of zone 3 to the solidification of the metal coating.

At each of these zones, containment boxes are set up with various nitrogen-based atmospheres comprising a volume fraction of oxygen as indicated in the following table, or constituted by air. Specific sensors make it possible to check the oxygen content in the caissons.

Once the sheet is coated, three sets of samples are taken. The first series does not undergo other modifications, the second series is stamped according to a mode of equibiaxial deformation to 3.5% (Marciniak), the third series is first subjected to a skin-pass operation with a rate 1.5% elongation, then swaged as the second.

As and when the tests progress, the rms values Wa _0.8 are measured. This measurement consists in acquiring by mechanical palpation, without pad, a profile of the sheet of a length of 50 mm, measured at 45 ° of the rolling direction. We deduct from the signal obtained the approximation of its general form by a polynomial of degree at least 5. The wavulation Wa is then isolated from the roughness Ra by a Gaussian filter with a cut-off of 0.8mm. The results obtained are summarized in the following table: Trial Composition of coating (% by weight) Zone 1 (% vol.) Zone 2 (% vol.) Zone 3 (% vol.) Zone 4 (% vol.) Wa _0.8 (μm) ripple Zn al mg Yes Without skin-pass or deformation Without skin-pass and after deformation With skin-pass and before deformation With skin-pass and after deformation 1 92 8 0 0 Air Air Air Air 0.68 0.61 0.39 0.67 2 * 92 8 0 0 Air Air 3% O ₂ Air 0.55 0.5 0.48 0.53 3 98 2 0 0 Air Air Air Air 0.69 0.62 0.47 0.66 4 * 98 2 0 0 Air Air 3% Air 0.6 0.57 0.47 0.58 5 85.5 11.5 3 0 Air Air Air Air 0.89 0.82 0.5 0.84 6 * 85.5 11.5 3 0 Air Air 3% O ₂ Air 0.71 0.65 0.46 0.69 7 45 55 0 0 Air Air Air Air 0.91 0.84 0.48 0.87 8 45 55 0 0 Air Air 6% O ₂ Air 0.89 0.87 0.46 0.89 9 * 45 55 0 0 Air Air 3% O ₂ Air 0.74 0.68 0.44 0.63 10 45 55 0 0 0.1 O ₂ 0.1 O ₂ 0.1 O ₂ Air born born born born 11 0 80 0 20 Air Air Air Air 0.83 0.73 0.47 0.77 * 12 0 80 0 20 Air Air 3% O ₂ Air 0.65 0.59 0.49 0.61 13 99.7 0.3 0 0 Air Air Air Air 0.72 0.62 0.41 0.63 14 99.7 0.3 0 0 Air Air 6% O ₂ Air 0.75 0.67 0.44 0.72 * 15 99.7 0.3 0 0 Air Air 3% Air 0.53 0.48 0.37 0.45 16 99.7 0.3 0 0 0.1 O ₂ 0.1 O ₂ 0.1 O ₂ Air born born born born 17 95 5 0 0 Air Air Air Air 1.37 1.14 0.46 0.93 * 18 95 5 0 0 Air Air 3% O ₂ Air 0.87 0.79 0.42 0.84 not: not evaluated, *: according to the invention

On reading the test results, it is clear that the method is applicable to many types of coatings.

Moreover, its influence on the level of waviness of the coatings obtained is also noted. In particular, tests 1, 3, 5, 7, 11, 13 and 17 show that by not controlling the spin atmosphere, the corrugation is not at a satisfactory level.

Tests 8 and 14 show that a spinning atmosphere with too high oxygen content and thus with too much oxidizing power also does not achieve satisfactory levels, although they are slightly improved compared to prior art.

Tests 10 and 16 further demonstrate the need to maintain a minimum of oxidizing power in the containment atmosphere and the need not to confine the strip from the coating bath to avoid zinc vaporization which generates defects in the atmosphere. unacceptable aspects.

• Fig. 2: une vue en perspective d'un mode de réalisation d'un dispositif d'essorage confiné selon l'invention,
• Fig. 3: une vue en perspective d'un mode de réalisation d'un dispositif d'essorage confiné selon l'invention,
• Fig. 4 : une vue en coupe du dispositif de la figure 3,
• Fig.5: une vue en perspective d'un mode de réalisation d'un dispositif d'essorage confiné selon l'invention,
• Fig. 6 : une vue en perspective d'un mode de réalisation d'un dispositif d'essorage confiné selon l'invention,
• Fig. 7: une vue en coupe du dispositif de la figure 6,
• Fig. 8: une vue de dessus du dispositif de la figure 6,
• Fig. 9: une vue de dessus d'un mode de réalisation d'un dispositif d'essorage confiné selon l'invention,
• Fig. 10 : une vue de dessus d'un mode de réalisation d'un dispositif d'essorage confiné selon l'invention.

In order to implement the process according to the invention, the present inventors have developed various confined wiping devices which will be described as indicative and nonlimiting with reference to the appended figures 2 to 10 which represent:

• Fig. 2 : a perspective view of an embodiment of a confined wiper device according to the invention,
• Fig. 3 : a perspective view of an embodiment of a confined wiper device according to the invention,
• Fig. 4 : a sectional view of the device of the figure 3 ,
• Fig.5 : a perspective view of an embodiment of a confined wiper device according to the invention,
• Fig. 6 : a perspective view of an embodiment of a confined wiper device according to the invention,
• Fig. 7 : a sectional view of the device of the figure 6 ,
• Fig. 8 : a top view of the device of the figure 6 ,
• Fig. 9 : a top view of an embodiment of a confined wiper device according to the invention,
• Fig. 10 : a top view of an embodiment of a confined wiper device according to the invention.

Referring first to the figure 3 it can be seen a first embodiment of a confined wiper device 20 according to the invention which comprises two identical spin nozzles 3, placed at the same level, on either side of the band B. Spin nozzles 3 have a generally triangular shape and each consist of two longitudinal metal plates 4 and 4 '(not visible) fixed together by means of two lateral triangular plates 5 and 5' (not shown). The longitudinal metal plates 4 and 4 'are assembled so that a thin slot remains between them to allow the passage under pressure of the spin gas, conveyed by means not shown.

The confined wiper device 20 also comprises two containment boxes 21 and 22 each placed on the upper outer faces of each nozzle 3, formed of the upper metal plates 4 and welded thereto. The box 22 consists of the assembly of two side plates 24 and an upper part consisting of a horizontal plate 25 and a vertical plate 23. The plates 24 and 25 are preferably of the same width, which width may be equal to or less than the depth of the nozzle 3.

The box 21 is in all respects identical to the box 22.

Confined spinning device 20 finally comprises two metal plates 6 called "noise baffles" whose function is to prevent the flow of spin gas emanating from each nozzle 3 is encountered in the lateral areas where the band B n is not present. Indeed, the same coating plant can see scrolling strips having various width formats and the interposition of such plates 6 is useful, in particular to avoid generating very significant sound vibrations.

If we now consider the figure 4 , we can see a sectional view of the device of the figure 3 on which are represented the two wiping nozzles 3, an arrow materializing the flow of spin gas on either side of the band. The height of the containment boxes 21 and 22, represented by the letter H is measured between the spin line and the upper part of the boxes. In the process according to the invention, it has been seen that this height must be at least 10 cm to obtain satisfactory results in terms of undulation.

Depending on the value of the width of the side and top plates 24 and 25, the distance D separating the boxes 21 and 22 of the band B is greater or smaller. As a result of various tests, the present inventors have been able to observe that a distance D of between 5 and 100 mm makes it possible to extract the spin gas satisfactorily while remaining sufficiently far from the path of the strip B to avoid any contact.

The distance Z between the end of the nozzles 3 and the band B is preferably between 3 and 25 mm, in conventional manner.

If we now consider the figure 2 it is possible to see another variant embodiment of a confined wiper device 10 according to the invention. As before, this device comprises spin nozzles 3 identical to those described for the figure 3 and anti-noise plates 6.

It further comprises two containment boxes 11 and 12 placed and fixed on the upper face 4 of the spin nozzles 3. The box 12 here comprises an inclined top plate 13, connected to two triangular side plates 14. The box 11 is identical at the caisson 12.

As for the caissons of the figure 3 , the boxes 11 and 12 have a width that can be at most equal to the depth of the nozzles 3.

In this embodiment, the height H of the containment boxes 11 and 12 is measured between the spin line and the upper edge of the plates 13.

This embodiment has the particular advantage of including a smaller volume than that of the figure 3 , which facilitates the management of the confinement atmosphere and allows to consume a smaller amount of inerting gas when the supply thereof is necessary.

If we then consider the figure 5 there can be seen another embodiment of a confined wiper device 30 according to the invention. This is globally identical to the device 20 of the figure 3 and in particular comprises two containment boxes 31 and 32 comprising an upper part consisting of vertical plates 33 connected to horizontal plates 35, and side portions 34. Each of the boxes 31 and 32 is further compartmentalised by a series of vertical blades 36 extending from the upper face of the wiper nozzle 3 until at the upper part 35 of the containment boxes 31 and 32.

This particular arrangement has the advantage of limiting the oxygen inputs in the containment boxes 31 and 32.

The figure 6 presents another embodiment of a confinement device according to the invention similar to that shown in FIG. figure 3 but further comprising edge containment pieces 26, placed between the containment boxes 21 and 22, above the noise plates 6 and opposite the banks of the strip B. As the name suggests, these pieces have as a function of further confining the atmosphere surrounding Band B on its banks.

In a preferred embodiment, these bank confinement pieces can be moved horizontally and vertically to accommodate different tape formats to be coated.

In the embodiment shown at figure 6 , the edge containment piece 26 consists of two rectangular plates parallel to the band B connected by a side plate placed facing the banks of the band B.

The figure 7 shows the relative positioning of the containment piece 26 above the noise plate 6.

As illustrated in figure 8 , the side plate has a width C greater or less, depending on whether one wants to achieve a significant confinement or not in banks.

The figure 9 shows another embodiment of the containment parts according to the invention. The part 27 consists of two rectangular plates inclined with respect to the band B running plane and connected along their vertical edge placed facing the banks of the band B.

This embodiment has the advantage of limiting the oxygen inputs even more than the design of the figure 6 . The inclined positioning of the two rectangular plates promotes the flow of gas from inside the box outwards and disadvantages the flow of gas from the outside to the inside of the box.

The figure 10 presents another embodiment of the containment parts according to the invention wherein the confinement part 28 further comprises a return means 29 connecting the inclined rectangular plates and here taking the form of a spring. These plates are inclined relative to the running plane of the band B in order to be in contact with the lateral parts of the containment boxes 21 and 22.

The edge containment pieces just described are placed above the noise plates 6. However, it is possible to extend them to the outlets of the spinning nozzles to give them a noise-canceling function, making them the use of such plates not applicable

Claims (18)

1. Method of producing a metal strip having a metal coating to protect against corrosion, comprising the steps consisting of:

   - passing the metal strip through a bath of molten metal, then

   - drying the coated metal strip by means of nozzles spraying a gas on either side of the strip, said gas having an oxidising power lower than that of an atmosphere made up of 4% by volume of oxygen and 96% by volume of nitrogen, then

   - passing the strip through a confinement zone, bounded:

   ■ at the bottom part by a drying line and the top faces of said drying nozzles,

   ■ at the top part by the top part of two confinement boxes positioned on either side of the strip, just above said nozzles and having a height of at least 10 cm relative to the drying line, and

   ■ at the sides by the side parts of said
   confinement boxes,
   the atmosphere prevailing in said confinement zone having an oxidising power lower than that of an atmosphere made up of 4% by volume of oxygen and 96% by volume of nitrogen and higher than that of an atmosphere made up of 0.15% by volume of oxygen and 99.85% by volume of nitrogen.
2. Method as claimed in claim 1, for which said confinement boxes have a height of at least 15 cm relative to the drying line.
3. Method as claimed in claim 1 or 2, for which said confinement boxes are supplied with gas having an oxidising power lower than that of an atmosphere made up of 4% by volume of oxygen and 96% by volume of nitrogen.
4. Method as claimed in any one of claims 1 to 3, for which the drying gas is nitrogen.
5. Method as claimed in any one of claims 1 to 4, for which the metal strip is a steel strip.
6. Installation for continuously coating metal strips by hot dipping, comprising:

   - means for feeding a metal strip,

   - a tank (2) containing a bath of molten metal (1), and

   - a confined drying device (10; 20; 30) made up of at least two drying nozzles (3) positioned on either side of the path of the strip after it has left the bath of molten metal (1), each nozzle (3) being provided with at least one gas outlet orifice and comprising a top face (4), on which is mounted a confinement box (11, 12; 21, 22; 31, 32) open at a face disposed facing the strip, each box (11, 12; 21, 22; 31, 32) comprising at least a top part (13; 23, 25; 33, 35) and two side parts (14; 24; 34), the height H of said confinement boxes (11, 12; 21, 22; 31, 32) relative to the drying line being greater than or equal to 10 cm.
7. Installation as claimed in claim 6, in which said top parts of the confinement boxes (21, 22; 31, 32) consist of a base plate (23; 33) and a top plate (25; 35).
8. Installation as claimed in claim 6 or 7, in which each of said confinement boxes (31, 32) is divided into compartments by a series of vertical blades (36) extending from the top face of the nozzle (3) as far as the top part (35) of said confinement boxes (31, 32).
9. Installation as claimed in any one of claims 6 to 8, in which the distance D between the end of the side parts (14; 24; 34) of said confinement boxes (11, 12; 21, 22; 31, 32) and the strip is between 5 and 100 mm.
10. Installation as claimed in any one of claims 6 to 9, in which said confined drying devices (10; 20; 30) further comprise anti-noise plates (6) on each side of the strip facing a part of the outlet orifice of said drying nozzles (3).
11. Installation as claimed in claim 10, in which said confinement boxes (11, 12; 21, 22; 31, 32) further comprise edge confinement pieces (26; 27; 28) positioned between said confinement boxes (11, 12; 21, 22; 31, 32) above said anti-noise plates (6), facing the edges of the strip.
12. Installation as claimed in claim 11, in which said edge confinement pieces (26; 27; 28) can be displaced horizontally and vertically.
13. Installation as claimed in claim 11 or 12, in which each of said edge confinement pieces (26) is made up of two rectangular plates parallel with the strip, connected by a side plate positioned facing the edges of the strip.
14. Installation as claimed in any one of claims 11 to 13, in which each of said edge confinement pieces (27; 28) is made up of two rectangular plates inclined relative to the plane in which the strip is fed and joined along their vertical edge positioned facing the edges of the strip.
15. Installation as claimed in claim 14, in which said edge confinement pieces (28) further comprise a return means (29) linking said rectangular plates, said rectangular plates being sufficiently inclined relative to the plane in which the strip is fed to be in contact with the side parts of said confinement boxes (21, 22).
16. Installation as claimed in any one of claims 6 to 9, comprising edge confinement pieces positioned between said confinement boxes (11, 12; 21, 22; 31, 32) facing the edges of the strip and extending so as to face a part of the outlet orifice of said drying nozzles (3).
17. Installation as claimed in any one of claims 6 to 16, in which said drying nozzles (3) are provided with a single outlet orifice in the shape of a longitudinal slit, the width of which is at least equal to that of the strip to be coated.
18. Confined drying device (10; 20; 30) as defined in any one of claims 6 to 17.

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