EP0298887A1 - Conductor roll for continuously electroplating a metal or other conductive strip - Google Patents

Abstract

A rotary conductor roll intended to be partially immersed in an electrolyte in a manufacturing line for continuously electroplating a strip (2), the roll includes, on its periphery, at least one electrically conductive active zone (3) and at least one coated zone (41) coated with a flexible material which may optionally be associated with an adhesive and which serves to seal the contact between the strip (2) and the conductive active zone (3) from the electrolyte. At least one intermediate ring (42) is interposed between said conductive active zone (3) and said coated zone (41), said intermediate ring being made of a polymer for which at least one of the following coefficients is intermediate in value between the corresponding coefficients of the material constituting the conductive active zone (3) and of the material constituting said coated zone (41), said coefficients being: coefficient of expansion, flexibility, and swelling due to contact with the electrolyte, e.g. by absorption or by chemical combination.

Description

The present invention is in the field of surface coating of metallurgical products or semi-finished products in strips and is aimed in particular at coatings applied to electrically conductive strips by electrolytic deposition, such as steel sheets for example.

The invention is in particular intended for the metallurgical industry and more precisely for circular apparatuses, included in electrodeposition lines of the type for example "continuous electrogalvanizing", called conductive rollers, and known for example from documents US-P- 3,483,113 (in particular Figures 7,8,9) US-P-3,634,223 or EP-A 0089790.

These conductive rollers, which play a cathode role, most often consist of at least one cylindrical conductive ferrule, generally made of stainless steel, mounted on a carbon steel body wider than the active area or areas of the at least one ferrules and through which the electric current passes. This steel body is covered with a flexible polymeric substance, both elastic and insulating, on each side of the active zone or zones, this substance playing a role of eventual entrainment, sealing, electrical insulation and protection of the body against corrosion. These rollers are partially immersed in an electrolyte, the temperature of which is generally substantially higher than ambient temperature.

The strip is partially wrapped around a conductive roller, the internal face which will not be coated being in contact on the one hand with the active area of the conductive shell in order to establish the electrical contact, and on the other hand with the elastic insulating substance in order to ensure the tightness of the contact device.

It is easily understood that if one wants uniformity of deposit on the strip during its passage through the electrolyte, the quality and uniformity of the contact between the ferrule and the strip as well as the quality and uniformity of the lateral sealing as well as the uniformity of the current densities are essential.

The improvements which are the subject of the aforementioned American patents relating to these conductive rollers for electrodeposition are most often oriented towards the quality and uniformity of this electrical contact as well as towards the distribution of the current densities which are very important factors. For sealing, provision is generally made for covering the body of the conductive rollers in rubber, neoprene or similar material, or in polyurethane, and the need is also stressed for the use of suitable adhesives for these sealing strips. elastic given the essential role they also play in this process.

Special geometrical arrangements at the ends of the conductive shell (s) in "hollow", "protuberance", "sawtooth" or bevel shape are sometimes provided in an attempt to increase the reliability of this seal (see fig. 4 of US-P-3634223 or fig. 2 of EP-A-0089790 already cited).

Furthermore, to be sure of combining the functions of sealing and electrical insulation, the sealing rings are sometimes mounted on a hard insulating bandage (see fig. 7 of document US-p-3,483,113).

However, all of these provisions do not fully guarantee the regularity of the contact and the diffusion of the electric current between the strip and the conductive ferrule, nor the seal. In fact, in all of the above arrangements, the elastic sealing bandage comes directly (with the exception of a thin interface formed by the adhesive) into contact with the lateral faces of the active area of the conductive ferrule. This has certain drawbacks.
. Under the effect of temperature and taking into account the fact that elastomers expand much more than steel, the elastic bandage sees its (radial) thickness increase much faster than that of steel, which tends to deteriorate the quality and the uniformity of the physical and electrical contact of the strip on the active area of the conductive shell despite the tensile force exerted on the strip.
. Under the effect of time, the elastic elastomer bandage, due to its immersion in an electrolyte, also sees its thickness increase due to the phenomena of absorption and chemical combination with the electrolyte (phenomenon well known in the profession of elastomers ), which again contributes to the deterioration of the quality and uniformity of the physical and electrical contact between the strip and the ferrule.

It is easy to understand that the deteriorations in quality and uniformity of contact are especially sensitive to the lateral edges of the conductive shell since the elastomer (which expands and swells) arrives close to these edges, and that the metal, comparatively, changes very little: however it is precisely in these areas that the diffusion of electric current is most delicate, since the width of the strip to be coated is greater than that of the conductive ferrule and that a current density is sought in the strip as uniform as possible.

These detachment tendencies, even minute, are immediately very important from the point of view of the variation of electrical resistance, therefore from the point of view of the uniformity of the deposit and the efficiency of the installation. Profile retouching is therefore commonly practiced on these elastic bandages, which requires stopping and dismantling the installation.

Furthermore, these relative movements between the elastomer and the metal end up degrading the elastomer-metal adhesion and thus allowing the electrolyte to pass, which then infiltrates between the two constituents, further deteriorating the uniformity of the diffusion of the electric current, but also and especially corroding the body of the conducting roller.

The purpose of the present invention is to significantly reduce these drawbacks while ensuring the vital functions of sealing, electrical insulation, protection of the roller body against corrosion and possible entrainment. The invention also aims to improve the coatings applied to the strips, as well as the energy efficiency of the installation, and to reduce the maintenance costs and the frequency of plant shutdowns.

This object is achieved in that, according to the invention, at least one intermediate ring is interposed between the active conductive area constituted by the ferrule and the area coated with the elastic and insulating substance, this ring being made of a polymer whose coefficient of dilation, flexibility or changes by swelling following absorption or chemical combination with the electrolyte, have values intermediate between those of the material constituting the conductive active area and those of the material of said coated area.

Thus, according to the invention, the flexible or sealing elastomer or polymer coating as well as its optional adhesive, are not in direct contact with the lateral edges of the active zone (s) of the conductive shell (s), but it is provided to insert between the elastomer or the flexible or sealing polymer and the lateral edges of the active area (s) of the conductive shell (s) one or more polymers, which will be called in the remainder of this text: "intermediate polymers" , put in the form of juxtaposed rings with or without partial superposition, whose expansion coefficients, flexibility or the risks of swelling by absorption or by chemical combination with the electrolyte, or two or three of these parameters at the same time, are intermediate between those, very weak, of stainless steel (generally used for the shell) and those of the elastomer or of the flexible or sealing polymer.

We can for example choose to do this intermediate polymers of the sulfur rubber type (natural or nitrile) hardened commonly called ebonite in the profession, or epoxy resins, or any other polymer with relatively closed crosslinking system, resistant to acids and low coefficient of expansion, high hardness of this or these intermediate polymers not being a handicap taking into account the particular geometry of the coating provided for in the invention.

In a particular embodiment of the invention, there is provided in the intermediate polymer or polymers a fiber reinforcement (which may for example be: metallic, glass, textile, or synthetic) which radially blocks the intermediate polymer or polymers and limits the variations radial dimension of this part of the intermediate polymer coating, and which can play, in the case of conductive fibers, a possible advantageous role of degressive conduction of electricity from the edge of the active conductive area of the ferrule concerned.

• Les figures 1 et 2 sont des vues de côté et de dessus d'un rouleau de l'art antérieur, la figure 3 étant une vue en coupe transversale partielle III-III du rouleau de la figure 1.
• La figure 4 est une vue en coupe transversale partielle du rouleau conducteur, d'une virole conductrice et du revêtement isolant selon une première forme de réalisation.
• Les figures 5 à 7 sont des vues similaires à figure 2 illustrant trois autres formes de réalisation du revêtement isolant.
• Les figures 8 et 9 sont des vues en coupe similaires aux précédentes mais illustrant des modes de réalisation de revêtement isolant comportant plusieurs polymères intermédiaires.
• La figure 10 est une vue en coupe similaire à la figure 4, avec un polymère intermédiaire à armature de fibres.
• Les figures 11 à 14 sont des vues en coupe similaires aux précédentes dans lesquelles la virole conductrice comporte des bords à profil dégressif, comme décrit dans le document US-A-3 634 223.

The invention will be better understood and other characteristics will be highlighted with the aid of the description which follows, with reference to the appended schematic drawings illustrating by way of nonlimiting examples several embodiments of the insulating coating according to the invention .

• FIGS. 1 and 2 are side and top views of a roller of the prior art, FIG. 3 being a view in partial cross-section III-III of the roller of FIG. 1.
• Figure 4 is a partial cross-sectional view of the conductive roller, a conductive ferrule and the insulating coating according to a first embodiment.
• Figures 5 to 7 are views similar to Figure 2 illustrating three other embodiments of the insulating coating.
• Figures 8 and 9 are sectional views similar to the preceding but illustrating embodiments of insulating coating comprising several intermediate polymers.
• Figure 10 is a sectional view similar to Figure 4, with an intermediate fiber-reinforced polymer.
• FIGS. 11 to 14 are sectional views similar to the previous ones in which the conductive ferrule has edges with a decreasing profile, as described in document US-A-3,634,223.

Figure 1 shows the rotary roller 1 of electrodeposi tion, partially immersed in an electrolyte 5. Figure 2 highlights the active area 3 of the conductive shell, surrounded by the area 4 coated with an elastic and insulating substance.

As shown in Figures 1 to 3, the strip 2 is partially wrapped around the conductive roller 1, the face that one does not want to cover during this passage being brought into contact with the active area 3 of the shell conductive in order to establish electrical contact, and also being brought into contact with the elastic and insulating substance 4 in order to ensure the tightness of the contact device.

As shown in Figure 4, the elastic and insulating coating according to the invention consists of two different polymers, although in intimate or sealed lateral contact with each other. The polymer 41 fulfills the functions of sealing, elasticity, entrainment, and electrical insulation whereas the polymer 42, called here intermediate polymer, must only fulfill the functions of sealing and electrical insulation. This therefore allows the choice of harder polymers, with a more closed reticular structure and whose expansion or swelling characteristics are much more acceptable with regard to steel than are those of the types of polymers which one can choose as polymer 41.

This intermediate polymer 42 must be adhered perfectly with the lateral end face 3a of the active area 3 of the conductive ferrule and must of course be adhered correctly with the body 1 and with the polymer 41.

We have already defined what we can choose as intermediate polymer 42; as regards polymer 41, one can choose either a polyurethane, or a Hypalon (from Du Pont de Nemours), or even more advantageously, the compound VARIOLASTIC (from the company SW INDUSTRIES, located at Southborough Technology Park, 333 Turnpike Road , SOUTHBOROUGH, MA 01772, USA).

It is easy to understand that, thanks to this intermediate polymer, the movements or variations in dimensions of the polymer 41 will affect the quality and uniformity much less. of the electrical contact of the strip 2 on the active face of the conductive ferrule 3 and that the seal, therefore again the uniformity of the electrical diffusion at the end of the conductive ferrule 3 as well as the protection of the body 1 against corrosion will be largely increased. Full-scale tests have proven the effectiveness of the invention compared to conventional solutions, by very significantly improving the overall yield of the installation as well as the quality and uniformity of the deposit and multiplying by a factor greater than three the working time of the conductive roller between two retouching of the profile by rectification, thus reducing in the same proportions the frequency of necessary stops.

Good results are already obtained with an intermediate polymer width 42 greater than 10 mm, the optimum being, of course, depending on the strip widths to be worked, between 10 and 40 mm.

FIG. 5 represents another arrangement of the invention according to which the polymer 42 is also used as a sub-layer 42a of the polymer 41 which makes it possible to increase the seal of the assembly.

FIG. 6 shows a particular geometry of the polymer coatings 43 and 41 in that their connecting face is inclined in order to make the passage from one zone to the other even more gradual in terms of expansion or swelling.

In FIG. 7, as in FIG. 5, the intermediate polymer 43, here in inclined connection with the polymer 41, also serves as an underlayer 43a.

In FIG. 8, two intermediate polymers 42 and 44 are seen, chosen so that their physicochemical characteristics ensure good progressiveness between the characteristics of the stainless steel used for the conductive shell and those of the elastic and insulating polymer. 41.

In a variant of the invention, these polymers 42 and 44, by their nature relatively insulating, are doped with conductive elements, such as conductive particles of the powder or metallic or carbon fibers in order to ensure the progressiveness of the diffusion of the electric current in the strip from the edge 3a of the conductive ferrule, which avoids resorting to very delicate machining of the edges of conductive ferrules and which makes it possible to 'be perfectly master of the diffusion of electric current. In some cases the flexible or sealing polymer may itself be partially doped with electrically conductive elements.

In FIG. 9, the second intermediate polymer 45 serves as a partial sublayer 45a to the polymer 41.

FIG. 10 represents an intermediate polymer 42 of the type of that shown in FIG. 2 but comprising a frame 7 of natural or synthetic fibers.

In one embodiment of the invention, we have chosen insulating fibers, but in another embodiment of the invention, we have chosen electrically conductive fibers in order to create a certain electrical conductivity in this area to better control the diffusion. electric in the strip.

This armature then plays the very interesting role of a mechanical clamping on the one hand, which limits the dimensional radial variations and the no less interesting role, if it is conductive, of vector of progressive electric diffusion on the other hand.

The reinforced intermediate polymer can also serve as a sub-layer and be the subject of variants of FIGS. 5 to 7.

According to a variant of the invention, all or part of an intermediate ring is housed under an edge flange of the conductive active area.

In FIG. 11, the conductive ferrule 3 has an edge 3b with a progressive profile as described in document US-P-3,634,223, and the intermediate polymer 42 comes to fill the entire "hollowed out" part of this ferrule end. The advantage of this harder, more inert intermediate polymer 42 than polymer 41 is even more evident here because in conventional solutions, the slightest swelling of the elastomer causes this wing to lift. edge immediately deteriorating the quality of the strip electrical contact on the conductive ferrule.

The invention described here makes it possible to guarantee the straightness of the entire external generator of the active surface of the conductive ferrule 3 by producing, thanks to the intermediate polymer 42, a real blocking of the end wing of the conductive ferrule.

Variants of the invention appear in FIGS. 12 to 15 with an undercoat for the polymer 41 and / or therefore progressive inclined contact between the polymers 42 and 41.

It goes without saying that the present invention is not limited to the sole exemplary embodiments shown above by way of nonlimiting examples, but on the contrary embraces all of the embodiments employing similar or equivalent means. .

Thus, for example, any width can be given to the areas filled with the intermediate polymers as long as the contact of the strip on the polymer 41 remains sufficient to ensure the functions of sealing, insulation, d elasticity and possible entrainment by adhesion. Similarly, the number of intermediate polymers is not limiting.

Furthermore, the various embodiments shown above can be combined together without departing from the scope of the present invention.

Finally, this invention applies particularly well to the continuous electrogalvanizing industry, but it is obvious that it can be applied wherever it is desired to carry out a continuous coating by electrodeposition.

Claims (10)

1. Rotating conductive roller, intended to be partially immersed in an electrolyte (5) in a continuous plating line on strip (2), of the type comprising at its periphery at least one median active area (3) conducting the electric current and at least one end zone (41) at each end coated with a flexible material and intended to seal against the electrolyte the contact surface between the strip (2) and the zone active conductive (3), roller characterized in that at least one intermediate ring (42,43, 44,45) is interposed between said active conductive zone (3) and said coated zone (41), this ring being made of a polymer whose coefficient of expansion, flexibility or changes by swelling following absorption or chemical combination with the electrolyte, have intermediate values between those of the material constituting the active conductive area (3) and those of the material of said area coated (41). 2. Roller according to claim 1 characterized in that the polymer used to form the intermediate ring (42) is reinforced with natural or synthetic fibers of insulating nature. 3. Roller according to claim 1 characterized in that the polymer used to form the intermediate ring (42) is reinforced with natural or synthetic fibers of an electrically conductive nature. 4. Roller according to claim 1, 2 or 3, characterized in that the polymer used to form the intermediate ring are doped with conductive elements. 5. Roller according to claim 1, characterized in that the flexible material of the coated area (41) is partially doped with conductive elements. 6. Roller according to claim 1 or 5, characterized in that the intermediate ring (42,43,45) forms a sub-layer (42a, 43a, 45a) for the material of the coated area (41). 7. Roller according to claim 1, characterized in that the intermediate ring (42,43) is housed at least partially under an edge flange (3b) of the active conductive area (3). 8. Roller according to claim 1, characterized in that the intermediate ring (42-43) has a connecting surface inclined relative to a plane perpendicular to the axis of rotation of the conductive roller (1). 9. Roller according to claim 1, characterized in that it comprises two juxtaposed intermediate rings (42,44) made of polymers of different physicochemical properties, the characteristics of expansion or flexibility or swelling by absorption or chemical combination with l electrolyte of these different polymers having progressive values ring by ring to pass from those of the active conductive area (3) to that of the coated area (41). 10. Roller according to claim 1 characterized in that the flexible material of the end zone (41) is coated with an adhesive.

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