EP0425354A1 - Process and apparatus for electroplating a metallic strip - Google Patents

Abstract

The apparatus comprises a set of cells (25a, 25b) of radial type. The electrical supply to the strip (16) to be coated forming the cathode is ensured by means of two electrically conductive diverting rollers (20) mounted so that each rotates around an axis parallel to the axis of the drum (8) of the electrolysis cell. The diverting rollers (20) are arranged at these partially below the upper level of the drum (8), near its outer surface. Two supporting rollers (21a, 21b) associated with each of the diverting rollers ensure that the strip is supported against the diverting roller over a substantial part of its periphery and as far as a region close to the part of the outer surface of the drum (8) which is immersed in the electrolyte liquid (2). The invention applies in particular to the zinc electroplating of a steel sheet. <IMAGE>

Description

The invention relates to an installation for electroplating a metal strip and in particular an installation for electrogalvanizing a steel strip.

The invention also relates to a coating process implemented in this installation, in particular for electro-galvanizing a steel strip.

Methods and devices are known for producing the electrolytic coating of a steel strip continuously, this strip being circulated so as to pass through one or preferably several successive electrolytic cells in which the coating metal is deposited on the two sides of the strip simultaneously or on only one of the two sides.

In particular, such methods have been applied for depositing a metal such as zinc or a zinc-based metal alloy containing nickel or iron on one or both sides of a steel strip.

The requirements of the customers, as regards the quality of the coated sheets or strips and the diversity of the products both as regards their dimensional characteristics and their compositions have led the producers of coated sheets and in particular the producers of galvanized sheets to seek processes and installations guaranteeing high product quality and offering great flexibility of use.

In particular, the installations and processes used in the future should make it possible to produce sheets comprising a single-sided coating or a very high-quality double-sided coating consisting either of pure zinc or of a zinc alloy containing nickel or iron. These sheets must have very good dimensional tolerances, edges of very good quality and the coating must have a perfectly defined and perfectly regular thickness in all parts of the sheet produced. In addition, this coating must not have any longitudinal marks liable to affect the appearance and quality of the product.

Finally, it is desirable to obtain improved mechanical characteristics for the coated sheets and in particular to be able to guarantee an elastic limit of the sheet at a required level.

In certain particular cases, it may also be necessary to produce sheets coated with alloys of different natures on each of their faces.

The processes and installations currently known do not make it possible to meet all of the requirements formulated by the customers.

The known methods and devices which are extremely varied use fixed electrodes brought to an anode potential with respect to the strip which constitutes a mobile cathode circulating, on a part of its course, in the vicinity of the active surface of the anodes. The anodes and the strip to be coated are therefore electrically connected to the corresponding terminals of a source of direct electric current capable of passing an electrolysis current of very high intensity through a layer of electrolytic liquid interposed between the anodes and the surface of the strip to be coated, this liquid being generally circulated, so as to improve its contact with the active surfaces and to ensure its renewal.

The electrolytic liquid is contained in a tank inside which the strip is brought to circulate near the active surfaces of the anodes which are completely immersed in the electrolytic liquid.

The different known methods and devices differ from each other mainly by the shape and position of the anodes, by the means for guiding the strip inside the tank filled with electrolytic liquid, by the means for supplying the cathode current strip, by the use of soluble anodes or, on the contrary, insoluble anodes and by the nature of the electrolyte used.

In the case where soluble anodes are used, the coating metal is transported in the electrolyte by the electrolysis current between the anode and the strip brought to a cathodic potential whereas in the case of insoluble anodes, the coating metal comes from the electrolytic bath itself which must be continuously regenerated.

Certain coating installations comprise anodes having planar active surfaces between which the sheet metal to be coated passes. These anodes can be arranged either vertically or horizontally and the corresponding electrolysis cells are designated as vertical cells or horizontal cells.

In most cases, the coating is carried out on both sides of the strip simultaneously.

Another type of installation is known comprising soluble anodes in the form of ring portions. The electrolysis cells designated as radial cells each consist of a tank containing an electrolytic liquid in which the anodes are immersed, delimiting an active internal surface in the form of a portion of a cylinder opposite which one face of the strip to be coated, the width of the interval between the internal face of the anodes and the surface to be coated being substantially constant. A drum mounted to rotate about a horizontal axis and substantially coaxial with the interior surface of the anodes is disposed inside the tank, so as to be partially immersed in the electrolytic liquid. This drum moves the strip inside the electrolytic cell. The electrolysis current flows through the space of annular shape and constant width between the interior surface of the anodes and the surface of the strip to be coated, in the radial direction of the drum which defines the cylindrical winding surface of the strip.

This process has advantages in that the space between the electrodes in which the electrolyte is circulated can be maintained at a substantially constant value and practically independent of the flatness and the tension state of the strip which is pressed against the drum.

In addition, this type of radial cell installation is particularly well suited to the production of a coating on one side of the strip or to the production of coverings of different natures on each of the sides of the strip.

In fact, it is possible to ensure perfectly sealed contact between the face of the strip opposite its face to be coated and the lateral surface of the drum, at least in the lateral end portions of the strip. For this purpose, the drum is coated, at least in its end parts, with a layer of flexible material such as an elastomer. The lateral parts of the strip adjacent to its two edges are brought into contact with the parts of the drum coated with flexible and impermeable material, with a contact pressure sufficient to ensure a perfect seal. This avoids any infiltration of electrolytic liquid between the drum and the metal strip.

In order to supply the strip with electric current and to maintain it at a cathode potential with respect to the soluble anodes which are connected to the positive terminal of a direct current source, it is necessary to ensure the contacting of the strip with an electrically conductive element which is itself electrically connected to the negative terminal of the direct current electrolysis source.

The electrical contacting of the strip with the negative terminal of the current source is generally effected by means of the strip displacement drum immersed in the cell of the electrolysis cell. For this, the drum has on its lateral surface a ferrule of a metallic alloy, placed in a central position on the drum between its end parts coated with the flexible material of the elastomer type which is an electrical insulator.

In order to ensure a tight contact between the strip and the surface of the drum in its end parts, the lateral layers of elastomer are slightly projecting with respect to the central ferrule ensuring the electrical contact of the strip. It is therefore necessary, to bring the strip into electrical contact with the central ferrule of the drum, to exert sufficient pressure on the lateral end portions of elastomer to compress them so that the surface of the strip is in contact with the conductive ferrule over the entire surface of this ferrule.

It is therefore necessary to exert on the strip, on either side of the drum, tensile forces in opposite directions, the amplitude of which may be significant. These efforts are exerted by means of rollers guide and tension located above the liquid level in the cell of the electrolysis cell achieving a certain deflection of the strip on either side of the drum. These rollers also hold the strip on the drum, following a determined winding arc.

The traction exerted on the strip on either side of the drum generates significant mechanical stresses in the mass of the sheet, so that the mechanical characteristics of this sheet are sometimes deteriorated.

In addition, the distribution of the electric field along the width of the conductive shell is not perfectly uniform and in particular, certain anomalies appear in the vicinity of the edges of the shell where the electric field increases significantly.

In the case of electrolysis cells with vertical arrangement of the anodes, it is known to bring the electric current to the strip by means of deflection rollers arranged above the level of the liquid in the cell of the cell. However, such installations, in addition to the drawbacks linked to the vertical arrangement of the anodes and of the strip in its part on which the coating is carried out, are very uneconomical in terms of the consumption of electric current. This high consumption of electric current is partly due to the fact that the current is brought to the strip by the deflecting rollers in an area substantially distant from the anodes.

An installation is also known comprising cells of the radial type in which the electric current is supplied to the strip by means of rollers arranged on either side of the drum, these current supply rollers associated with rollers support being placed at a relatively small distance above the level of the liquid in the cell of the electrolysis cell and the ends of the anodes. However, the cathode current supply rollers to the strip are of very small diameter and come into contact with the strip in an area practically limited to a generator of the current supply roller. It is therefore only possible to pass a relatively low intensity current through the strip, which limits the possibilities of the installation as regards its productivity and the production of thick coating layers.

In addition, the electrolysis cell, although of the radial type, uses insoluble anodes which require continuous regeneration of the electrolyte during the coating process.

In the case of a radial type electrolysis cell with soluble anodes, it has been proposed to use a drum coated with insulating material such as an elastomer over its entire lateral surface and to bring the current to the strip coming in. sealed contact with the drum, by means of the two guide rollers arranged above the level of the electrolytic liquid in the cell ensuring the tensioning of the strip and the maintenance of the arc of winding of this strip on the drum.

In this arrangement, the strip is pinched, before entering the electrolytic liquid bath and at its exit, between the corresponding guide roller and the drum.

The guide and tension rollers ensuring the supply of electric current to the strip are of small diameter compared to the diameter of the drum and must exert a relatively large traction on the strip to ensure a tight contact of the strip. with the drum and a passage of electric current from the guide rollers to the strip without arcing.

In addition, the metal strip reaches the guide rollers of the electrolysis cell and leaves this electrolysis cell in a substantially horizontal direction, which is not favorable in the case where several cells are arranged one after the other. others to constitute a coating installation by depositing successive layers on the strip.

Among the electrolytes most commonly used in the case of metallic coatings and in particular in the case of electrogalvanizing, there are chloride baths and sulfate baths which have essentially different electrical and chemical properties.

Chloride electrolytes have a much lower electrical resistivity than sulfate electrolytes, which generally results in less current consumption when used in an electrolytic coating installation. On the other hand, chlorides are generally more corrosive and cause faster wear of the cell structures coming into contact with the electrolyte.

Until now, the advantages of using a chloride-based electrolyte have never been combined with those of a radial cell installation in which the strip to be coated is supplied with electric current by cylinders located at the outside of the electrolyte bath.

The object of the invention is therefore to propose an installation for electrolytic coating of a metal strip and in particular an installation for electrogalvanizing a steel strip comprising at least one cell consisting of a tank containing electrolytic liquid, a rotating drum with a horizontal axis entirely coated on its external cylindrical lateral surface with an electrically insulating material and partially immersed in the electrolytic liquid, a set of soluble anodes in coating metal, in form of portions of rings arranged facing the external cylindrical surface of the drum in its submerged part with which the metal strip to be coated is kept in contact, means for supplying the anodes with electric current, means for injection of electrolytic liquid between the anodes and the metal strip in contact with the drum, against the current with respect to the direction of circulation of the strip and of the sets of electrically conductive rollers in contact with the strip in an area situated above of the upper level of the electrolytic liquid in the tank electrically connected to means ensuring a circulation ion of the electric current in the metal strip and a cathodic potential of this strip with respect to the soluble anodes, this installation makes it possible, both to avoid exerting tensile forces of high amplitude on the strip at the level of the cells electrolysis and the formation of longitudinal traces on this strip due to the presence of a conductive ferrule on the external surface of the drum.

For this purpose, the sets of electrically conductive rollers are constituted, for each of the cells, by two electrically conductive deflecting rollers over which the strip to be coated passes, rotatably mounted each around an axis parallel to the axis of the drum. , on either side of the drum and arranged at least partially below the upper level of the drum, near its external surface and two support rollers associated with each of the deflec rollers teurs ensuring the maintenance of the strip against the deflecting roller over a substantial part of its periphery and up to an area close to the part of the external surface of the drum immersed in the electrolytic liquid.

The invention also relates to an electrolytic coating process using an installation according to the invention and using a chloride solution as the electrolytic liquid.

• La figure 1 est une vue schématique en éléva­tion d'une cellule d'une installation d'électrozingage suivant l'invention.
• La figure 2 est une vue en élévation et en coupe partielle de la partie d'entrée d'une installation d'électrozingage suivant l'invention montrant deux cel­lules d'électrolyse successives.
• La figure 3 est une vue agrandie d'une partie de la figure 2 montrant en particulier un rouleau dé­flecteur et conducteur associé à deux cellules succes­sives de l'installation représentée sur la figure 2.
• La figure 4 est une vue de côté en élévation suivant 4 de la figure 3.
• La figure 5 est une vue de côté en élévation suivant 5 de la figure 3.

In order to clearly understand the invention, we will now describe, by way of nonlimiting example, with reference to the attached figures, an embodiment of an installation according to the invention and its use for the production of sheets coated with at least one layer of zinc or a zinc alloy.

• Figure 1 is a schematic elevational view of a cell of an electrogalvanizing installation according to the invention.
• Figure 2 is an elevational view in partial section of the inlet portion of an electrogalvanizing installation according to the invention showing two successive electrolysis cells.
• FIG. 3 is an enlarged view of a part of FIG. 2 showing in particular a deflector and conductive roller associated with two successive cells of the installation shown in FIG. 2.
• FIG. 4 is a side view in elevation along line 4 in FIG. 3.
• FIG. 5 is a side view in elevation along line 5 in FIG. 3.

In Figure 1, there is shown, schematically, an electrolysis cell of an electrogalvanizing installation according to the invention.

The cell comprises a tank 1 of which only part of the side wall has been shown.

The tank 1 contains an electrolytic liquid 2 of the chloride type containing Cl- ions in which are immersed soluble anodes 3 of zinc or other metal.

The anodes 3 have the shape of portions of circular rings constituting an arc of an angular amplitude a little less than 90 °.

The anodes 3 are arranged two by two one after the other, with a slight spacing, so as to present an active inner surface having an enveloping arc a little less than 180 °. In a horizontal axial direction, the anodes 3 constitute a continuous active surface of cylindrical shape whose width is at least equal to the width of the strip to be coated.

The soluble anodes 3 rest on two support elements 5 made of a material which is good conductor of electricity which are connected to the positive terminal of a direct current source 6, so as to bring the conductive elements 5 and the soluble anodes 3 into electrical contact with these elements, at an anode potential and passing the electrolysis current through the soluble anodes 3.

A drum 8 whose diameter is slightly less than the diameter of the active cylindrical surface of the anodes 3 is rotatably mounted on the cell 1, via a horizontal axis 9. The drum 8 is arranged so that the level 10 of the electrolytic liquid 2 in the tank 1 is located slightly below the diametrical plane of the drum 8.

The lateral surface of the drum 8 is entirely coated with an insulating material which may preferably consist of an elastomer. The strip to be coated 16, for example a strip of sheet metal or of steel strip, is brought into contact with the insulating lateral surface of the drum 8 whose rotation in the direction of the arrow 13 allows the movement of the strip inside the electrolyte bath 2, opposite the active surface of the anodes 3.

A first ramp 14 for injecting electrolytic liquid is placed in the vicinity of the outlet end of the anode portions 3 and comprises a set of injectors 14 ′ for injecting electrolytic liquid into the space formed between the portion anode 3 and the outer surface of the drum 8 over which the strip to be coated 16 passes.

A second injection ramp 15 is placed at the lower part of the drum, in the zone situated between the lower end parts of the anode portions 3. The ramp 15 is a double ramp comprising injectors 15 at each of the portions of anodes 3 directed in opposite directions for each of the parts of the double ramp 15.

In the case where the drum rotates in the direction of arrow 13, which corresponds to the direction of travel 12 of the strip, the injectors 15 ′ connected to the ramp 15 located on the left in FIG. 1 are put into operation. In this way, the electrolytic liquid circulates against the current with respect to the direction of circulation of the strip, throughout the annular space situated between the anodes 3 and the drum.

The level 10 of the electrolytic liquid in the tank 1 of the electrolysis cell corresponds to a level of overflow of this liquid in a space 17 (arrow 18) in which the electrolytic liquid is collected to be reinjected by the ramps 14 and 15.

The path of the strip 16, on either side of the drum 8 is defined by deflector rollers 20 and 20 ′ also ensuring that the strip 16 comes into contact with the surface of the drum 8, with a certain bearing pressure .

Two support rollers 21a and 21b maintain the strip 16 on the deflector roller 20, along a certain winding arc. Similarly, two support rollers 21′a and 21′b maintain the strip 16 on the deflector roller 20 ′, at the outlet of the electrolysis cell.

According to one of the characteristics of the invention, the deflection rollers 20 and 20 ′ are each connected to the negative terminal of one of the direct current sources 6, in order to bring the strip to a cathodic potential and to pass the electrolysis current in the strip 16, the rollers 20 and 20 ′ being made entirely of a conductive material.

A wringing roller 22 disposed on the path of the strip 16 at the outlet of the electrolysis cell makes it possible to avoid the electrolyte entrainment by the strip 16 at its outlet from the electrolyte bath 2.

Figures 2 to 5 show an electrolytic coating installation according to the invention which can be used to coat a steel strip with a layer of zinc or zinc alloy on one of its faces or on its two sides.

This installation comprises successive electrolysis cells whose general structure is identical to the structure which has been described and which is shown in FIG. 1. The corresponding elements in FIG. 1 and in FIGS. 2 to 5 bear the same references.

In FIG. 2, the inlet part of the installation comprising the first two electrolysis cells is shown, in the direction of movement of the strip symbolized by the arrow 24.

The tanks 1a and 1b of the two successive electrolysis cells 25a and 25b rest on a struc common structure 26 constituting the support for the installation for coating the strip.

The tanks 1a and 1b of two successive cells have vertical end walls 27, the upper level of which determines the level of overflow of the electrolytic liquid 2 in a space 17 delimited by a wall 28 fixed on the external surface of the wall 27.

A pipe 29 for recovering electrolytic liquid is disposed at the lower part of each of the spaces 17 delimited by a wall 28.

The electrolytic liquid recovered by the lines 29 can be returned by pumps to the injection manifolds 14 and 15 which operate in the manner which has been described above.

It should be noted that two ramps 14 are associated with each of the electrolysis cells 25 and arranged on either side of the drum 8 so that the injectors 14 ′ are directed towards the inside of the corresponding end parts of the anodes 3. On the other hand, the injection ramp 15 is a double ramp comprising injectors 15 ′ directed in different directions and capable of injecting electrolytic liquid into the space existing between the strip 16 and the active surface of the corresponding portion of anode, in different directions.

This arrangement of the injection ramps 14 and 15 makes it possible to use the installation both in the direction of movement of the strip represented by the arrow 24 and in the opposite direction.

Whatever the direction of circulation of the strip 16, it will be possible to ensure the circulation of an electrolyte current in the opposite direction to the direction of circulation of the strip by using one or the other of the injection ramps arranged on either side of the drum and the ramp 15 whose injectors 15 ′ are directed in the corresponding direction. In the case where the installation operates so that the strip circulates in the opposite direction to the arrow 24, the end of the installation shown in FIG. 3 corresponds to its outlet end and the drum 8 driving the strip 16 is rotated in the direction of arrow 13 ′.

On either side of each of the electrolytic cells 25, the deflector rollers 20 and 20 ′ of the strip are rotatably mounted about a horizontal axis parallel to the axis 9 of the drum 8, on a support 30 integral with the structure support 26 of the installation.

The deflection rollers 20, 20 ′ are preferably motorized, so as to facilitate the circulation of the strip 16 and to avoid sliding of this strip on the deflection roller.

The deflector rollers 20 and 20 ′, generally made of steel, are electrically connected, as explained with reference to, FIG. 1, to the negative terminal of a high power direct current source capable of supplying a very high intensity at a voltage determined by the optimal conditions for carrying out the electrolysis carried out inside the cell.

As can be seen in FIG. 2, the deflection rollers 20 and 20 ′ have a large diameter, this diameter being, in the case of the installation described, slightly greater than the radius of the drum 8 of the electrolysis cell.

The deflection rollers 20 and 20 ′ are on the other hand placed so that at least part of the roller, and preferably a substantial part, is situated at a level below the upper level of the drum 8. However, the deflecting rollers 20 and 20 ′ are arranged above the upper end of the walls 27 of the tank 1 and therefore entirely above the level 10 of the electrolyte in the corresponding tank 1.

Each of the successive deflector rollers 20 and 20 ′, with the exception of the initial roller 20a (and the roller placed at the outlet of the installation not visible in FIG. 2), constitutes both the input roller of a cell electrolytic and the output roller of the previous electrolytic cell. For example, the roller 20 shown in FIG. 3 constitutes the inlet roller of the electrolytic cell 25b and the outlet roller of the electrolytic cell 25a.

The sheet metal strip 16 is returned substantially at 180 ° by the successive deflection rollers 20 and 20 ′ 20′ with the exception of the initial roller 20a which returns the strip 16 to 90 °.

The support rollers 21a and 21b placed on either side of the deflector roller 20 ensure that the strip 16 is pressed onto the roller 20 in an arc at least equal to 190 °. A large contact surface is thus obtained between the strip 16 and the roller 20 by the fact that this roller has a large diameter and a large amplitude winding arc. It is therefore possible to pass a very high intensity of cathode current through the strip.

Referring to Figure 3, there is shown a deflector roller 20 constituting the output roller of a first electrolysis cell 25 and the input roller of the next electrolysis cell 25 ′. The deflector roller 20, the diameter of which is slightly greater than half the diameter of the drums 8 and 8 ′ of the cells 25 and 25 ′ is placed on its support 30, so that a substantial part of the roller 20 is disposed at a level below the upper level of the drums 8 and 8 ′. The deflector roller 20 is interposed between the drums 8 and 8 ′ such that part of its lateral surface is close to the lateral surface of the drum 8 and another part of its surface is close to the outer surface of the drum 8 ′. The axis of rotation of the deflector roller 20 is in a vertical plane equidistant from the end walls 27 of the successive cells 25 and 25 ′.

In addition, the support rollers 21a and 21b which have been shown in Figure 3 in solid lines in their operating position ensure, in this position, the contact of the strip 16 with the lateral surface of the deflector roller 20, in two generators located below the horizontal diametral plane of the deflector roller 20. In this way, the strip 16 is kept in contact with the deflector roller 20 of large diameter, over an arc length greater than 180 ° and generally close to or a little more than 190 °.

In addition, as can be seen in FIGS. 4 and 5, the support rollers 21a and 21b are in contact with the deflector roller 20 over its entire length so that the contact surface between the strip 16 and the deflector roller 20 has a very important dimension. It is therefore possible to pass an electric current of very great intensity between the conductive roller 20 connected to the source of direct current and the steel strip 16 in circulation.

In addition, the support rollers 21a and 21b ensure perfect contact of the strip with the deflector roller, without it being necessary to exert significant traction on the strip. This reduces the possibility of arcing between the strip and the roller. In addition, the density of cathode current flowing from the roller to the strip can be reduced as long as the contact area is large.

On the other hand, the support rollers are arranged in a narrow width interval delimited by the surfaces facing the deflector roller and the corresponding drum. This arrangement close to the zone where the deflector roller is closest to the drum makes it possible to ensure effective contact between the strip and the deflector roller by which the strip is supplied with electric electrolysis current, in an area close to the part drum 8 or 8 ′ submerged under level 10 of the electrolyte bath in cells 25 and 25 ′. The electric current therefore travels a short length of the strip 16 before reaching the annular zone where the electrolysis takes place situated between the soluble anodes 3 and the corresponding drum 8 or 8 ′, this zone comprising an upper inlet part situated just below level 10 of the electrolyte bath. This avoids losses of electric current, so that the energy efficiency of the process remains very satisfactory despite a cathodic supply of the strip outside the electrolyte bath. This result is moreover obtained without having to exert significant traction on the strip, the electrical contact of the strip and of the deflector and conductive roller 20 being ensured by the support rollers.

In FIGS. 3, 4 and 5, it can be seen that the support rollers 21a and 21b are fixed at their longitudinal ends, on lever arms 31a and 31′a, as regards the support roller 21a and 31b and 31′b as regards the roller 21b, the lever arms themselves being articulated about a horizontal axis on a corresponding support 32 resting on the fixed frame 33 of the installation.

The end of each of the levers 31a, 31′a, 31b, 31′b opposite the end connected to the corresponding support rollers 21a or 21b is articulated, around a horizontal axis, to the rod 34 a cylinder 35.

By extraction or retraction of the rods 34 of the jacks 35 associated with a support roller 21a or 21b, this roller can be moved between its service position, shown in solid lines in FIG. 4 where the roller ensures the support of the strip 16 on the deflector roller 20, and an out of service position, shown in broken lines in FIG. 4 where the corresponding support roller is distant from the lateral surface of the deflector roller 20 and is no longer in contact with the strip of sheet 16.

The actuating cylinders 35 for the support rollers are mounted on the upper part of the support 32 resting on the frame 33 of the installation.

The bearings 36 in which the ends of the shaft of the deflection roller 20 are mounted also rest on the frame 33 of the installation, by means of a support 37 on which the support 32 of the support rollers is fixed.

As can be seen in FIGS. 3 and 4, an extractor roller 22 is rotatably mounted about a horizontal axis parallel to the axis of the deflector roller 20 and the drum 8 ′, between two end flanges 42 and 42 ′ secured an axis 43 parallel to the axis of the deflector roller 20, the ends of which are fixed to a lever arm 44 or 44 ′ connected in an articulated manner to the rod of an actuating cylinder 45 or 45 ′ fixed, by l 'through a support, on the fixed frame 33 of the installation.

The actuation of the cylinders 45 and 45 ′ makes it possible to rotate the axis 43 in one direction or the other so as to move the wringing roller 22 between its service position shown in solid lines in FIG. 3 in which the roller 22 is in contact with the sheet metal strip 16 and an out of service position in which the roller 22 is no longer in contact with the strip 16.

The dewatering roller comprises a tubular metal core rotatably mounted by means of bearings on the axis of the roller 22, the ends of which are fixed to the flanges 42 and 42 ′ and an external coating of flexible material coming into contact with the metal strip 16 , in the service position of the wringing roller.

In this position, the wringing roller comes into contact with the strip 16, in the part of this strip coming into contact with the drum 8, immediately above the level 10 of the electrolyte bath and the end of the soluble anodes 3 In this way, the strip 16 is pinched between the drain roller 22 and the drum 8, so that it is possible to exert a relatively strong spin pressure on the sheet, by means of the flexible external surface. of the wringer 22, thanks to the actuating cylinders 45 and 45 ′.

In addition, the arrangement of a single wringing roller bearing on the drum 8 in an area located just above the level 10 of the electrolyte makes it possible to increase the efficiency of the wringing of the strip as it exits. the electrolysis cell while avoiding lengthening the length of the sheet metal strip 16 between the corresponding support roller 21a and the annular electrolysis zone.

This arrangement of the wringer eliminates the need for pinch and wringer rollers in a free part of the strip located between the deflector roller and the drum.

As can be seen in FIGS. 3 and 5, the installation further comprises a sanding assembly 48 of the lateral surface of the deflection roller 20 secured to an axis 49 rotatably mounted at its ends in supports 46 ′ similar to the supports 46 receiving the end parts of the axis 43 for supporting and positioning the wringing roller 22.

The sanding assembly 48 fixed on the axis 49 can be moved between an active position in contact with the corresponding deflector roller and an inactive position distant from the roller by means of jacks such as 50 connected to the ends of the axis 49 by the intermediate of articulated connecting rods.

The drain roller 22 and the sanding assembly 48 of the deflector roller 20 are placed on either side of the vertical plane of symmetry of the roller 20.

It should be noted that the supports 46 and 46 ′ have openings allowing mounting in these supports located on either side of the plane of symmetry of the deflector roller 20 or of the wringer assembly 43, 42, 22, or of the '' sanding set 48, 49.

When reversing the direction of circulation of the strip 16 through the installation, it is necessary to perform a permutation of the position of the wringer assembly and of the sander assembly associated with a deflector roller, which can be carried out easily and quickly by simple disassembly and reassembly of the axes 43 and 49 on the corresponding supports 46 and 46 ′.

It may be possible to use a slightly different mounting and use a single cylinder to move and position the wringer assembly and the sander assembly.

Figures 4 and 5 also show the injection assemblies 14 arranged at the inlet and outlet of the drums 8 and 8 'respectively. These injection assemblies include a very large number of small diameter injectors 14 ′ opening into the annular electrolysis space delimited by the corresponding drum and the sheet on the one hand and the internal active surface of the soluble anodes on the other. go.

As explained above, one of the assemblies 14 is put into operation, according to the direction of circulation of the strip 16 in the installation.

Advantageously, the installation according to the invention can be implemented using an electrolytic bath consisting of a chloride having good electrical conductivity. One can thus obtain a very good energy efficiency of the installation, insofar as the electrical losses coming from the supply of the strip outside the bath are limited to a relatively low value.

In addition, the implementation of the installation according to the invention has all the advantages of known methods with radial cells, in particular as regards the production of a high quality coating on one of the faces of the strip. In addition, the installation according to the invention makes it possible to avoid the drawbacks of known methods with radial cells using a conductive ferrule wound on the drum, that is to say the need to exert significant pulls on the strip and the formation of longitudinal traces corresponding to shell marks.

The installation according to the invention can comprise a large number of cells, which allows ac increase the speed of circulation of the strip and therefore the productivity of the installation.

This installation can also be very easily and quickly adapted to one direction of traffic or another of the strip to be coated.

The installation and the method according to the invention can be easily adapted to the production of a sheet coated on its two faces with identical or different layers constituted for example by zinc or zinc layers containing iron or nickel.

It is understood that the invention is not limited to the embodiment which has been described.

The size and arrangement of the deflection rollers and the support rollers associated with these deflection rollers can be different from those which have been described, the arc for winding the strip on the deflection rollers can have a variable value.

The dewatering rollers located at the outlet of the electrolysis cells can be produced in a different way from that which has been described and likewise, the circulation of the electrolyte in the annular zone situated between the drum and the soluble anodes can be performed in a manner different from that which has been described.

The installation according to the invention can be used with different electrolytes of chloride solutions and the electrical parameters for controlling the process can be determined in the usual way, depending on the operating conditions of the installation.

Finally, the installation and the method according to the invention can be used not only for the electrogalvanization of steel sheets but also in the case of the production of a metallic coating of any kind on a steel sheet or strip or on any other metallic support in the form of a strip of great length.

Claims (10)

1.- Installation of electrolytic coating of a metal strip (16) and in particular installation of electrogalvanizing of a steel strip comprising at least one cell (25) formed by a tank (1) containing electrolytic liquid (2 ), a drum (8, 8 ′) rotating with a horizontal axis entirely coated on its external lateral surface with an electrical insulating material and partially immersed in the electrolytic liquid (2), a set of soluble anodes (3) of metal coating in the form of portions of rings arranged facing the external cylindrical surface of the drum (8, 8 ′) in its submerged part with which the metal strip (16) to be coated is kept in contact, a means of supply (6) of the anodes (3) with electric current, means for injecting electrolytic liquid (14, 15) between the anodes (3) and the metal strip (16) in contact with the drum (8), against the current in relation to the direction of movement of the strip (16) and electrically conductive roller assemblies (20, 21) in contact with the strip (16) in an area above the upper level (10) of the electrolytic liquid (2) in the tank (1) electrically connected to a means (6) ensuring a circulation of the electric current in the metal strip (16) and a setting to a cathodic potential of this strip (16) relative to the soluble anodes (3), characterized in that the roller assemblies electrical conductors (20, 21) are constituted, for each of the cells (25), by two deflector rollers (20) electrical conductors rotatably mounted each around an axis parallel to the axis of the drum (8, 8 ′ ) on either side of the drum (8, 8 ′) and arranged at least partially below the upper level of the drum (8, 8 ′), near its external surface and two support rollers (21a, 21b) associated with each of the deflection rollers (20, 20 ′) ensuring the maintenance of the strip (16) against the deflection roller (20, 20 ′) over a substantial part of its periphery and up to an area close to the part of the external surface of the drum (8, 8 ′) immersed in the electrolytic liquid. 2.- Installation according to claim 1, characterized in that the support rollers (21a, 21b) are rotatably mounted at the end of lever arms (31a, 31′a, 31b, 31′b) articulated on a fixed frame (33) of the installation and connected at their ends opposite to the rollers (21a, 21b) to actuating cylinders (35) to move the support rollers between a service position in contact with the strip ( 16) and an out-of-service position remote from the strip (16) passing over the corresponding deflector roller (20). 3.- Installation according to one of claims 1 and 2, characterized in that a wringing roller (22) whose axis is parallel to the axis of the drum (8) is placed so as to come into contact with the face of the strip (16) on which the coating is produced, in an area where the strip (16) is in contact with the drum (8) situated above the upper level (10) of the electrolyte in the tank (1) of the cell (25) and below the support roller (21a) ensuring the maintenance of the strip (16) against the deflection roller (20), on the side of the drum (8) corresponding to the outlet of the electrolysis cell (25). 4.- Installation according to claim 3, characterized in that the squeezing roller (22) is rotatably mounted on an axis integral at its ends with flanges (42, 42 ′) fixed on a shaft (43) connected to cylinders d actuation (45, 45 ′) so as to move the roller (22) between a service position where the roller (22) is brought into contact with the strip (16) under a certain pressure and an inactive position where the roller (22) is moved away from the strip (16). 5.- Installation according to any one of claims 1 to 4, characterized in that the support rollers (21a, 21b) are arranged relative to the deflector rollers (20) corresponding so as to maintain the strip (16) on the deflector roller (20), following a winding arc of an amplitude greater than 180 °. 6.- Installation according to one of claims 1 to 5, characterized in that each of the deflector rollers (20) interposed between two drums (8) of two successive electrolysis cells (25a, 25b) imposes on the strip a return substantially 180 ° in the vertical direction. 7.- Installation according to any one of claims 1 to 6, characterized in that the conductive deflector rollers (20, 20 ′) have a diameter at least equal to half the diameter of the drum (8, 8 ′) corresponding . 8.- Installation according to any one of claims 1 to 7, characterized in that it comprises7 for each of the cells (25), a wringing assembly (22) and at least one means (14, 14 ′) injecting electrolytic liquid between the anodes (3) and the strip (16) adaptable so as to allow a change in the direction of circulation of the strip (16) in the installation comprising successive electrolysis cells (25). 9.- Process for electrolytic coating of a metal strip and in particular process for electrogalvanizing a steel strip in an installation comprising at least one cell of the radial type with soluble anodes, characterized by the fact that contact the strip (16), at the entry and exit of the cell (25) of radial type with the surface of a deflector roller, over a substantial part of the periphery of this deflector roller (20, 20 ′), up to an area of the deflector roller located near the upper level (10) of the electrolyte in the radial type cell, which the strip is made to circulate in the electrolyte in contact with the surface of a drum (8) coated with an insulating material, opposite the active surfaces of the soluble anodes (3) immersed in the electrolyte,
- that the strip is supplied with cathode current via the conductive deflector rollers (20, 20 ′), the electrolyte being constituted by a chloride. 10.- Method according to claim 9, characterized in that the strip is wrung (16) above the upper level (10) of the electrolyte bath, at its outlet from the cell (25), in contact with the drum (8).

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