Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D1/00—Electroforming
  • C25D1/04—Wires; Strips; Foils

Definitions

• the invention relates to the continuous casting of metals. More specifically, it relates to the conditioning of the external surface of the cylinder or cylinders which constitute the movable wall or walls of the molds for continuous casting of thin strips of metals such as steel.
• the ingot molds for continuous casting machines of steel strips a few mm thick between two cylinders directly from liquid metal have a casting space defined by the lateral surfaces of two cylinders rotating in opposite directions around their axes kept horizontal and by two refractory side plates pressed against the edges of the cylinders.
• These cylinders have a diameter of up to 1500 mm and a width which, on current experimental installations, is approximately 600 to 800 mm. But, in the long term, this width will have to reach 1300 to 1500 mm to meet the productivity requirements of an industrial installation.
• These cylinders are most often formed by a steel core around which is fixed a ferrule made of copper or copper alloy, cooled by a circulation of water between the core and the ferrule or internal to the ferrule.
• the surface of the shell which is intended to come into contact with the liquid metal can be coated with a metallic layer, most often nickel, of which l thickness generally reaches 1 to 2 mm.
• This layer of nickel makes it possible to adjust the heat transfer coefficient of the shell to an optimal value (lower than if the metal was brought directly into contact with copper) so that the solidification of the metal takes place under good metallurgical conditions: too rapid solidification would cause defects on the surface of the product.
• This adjustment is made by varying the thickness and the structure of the nickel layer.
• the nickel deposition is preferably carried out by an electrolytic route, as follows.
• the new ferrule (or previously partially or totally nickel-free), which is generally in the form of a hollow cylinder made of copper or copper alloy such as a copper - chromium (1%) - zirconium (0, 1%) alloy , went up on a tree, thanks to which it can easily be transported from one treatment station to another in the nickel-plating / nickel-plating workshop.
• the ferrule After having undergone various preparatory surface treatments (polishing, degreasing, acid pickling, etc.) aimed at improving the adhesion of nickel to copper, the ferrule is brought to the electrolytic nickel-plating station.
• This station consists of a tank containing the nickel-plating solution, above which the tree can be placed in a horizontal position and rotated around its axis. The lower part of the ferrule is thus soaked in the tank, and the rotation of the shaft-ferrule assembly at a speed of approximately 10 rpm, for example, makes it possible to carry out the treatment of the entire the ferrule.
• the ferrule constitutes the cathode
• the anode can be constituted by one or more anode titanium baskets immersed in the tank, closed by thin membranes, facing the surface of the ferrule and containing nickel beads. If you also want to coat with nickel a large fraction of the edges of the shell (which, during casting, will rub against the side plates in refractory and are therefore likely to wear), there are other anodic baskets facing these chants. Other types of anodes (soluble or insoluble) can also be used.
• the shell As a variant, it is possible to provide for the shell to remain fixed and for the electrolyte to pass past it. The main thing is therefore to create a relative movement between the shell and the electrolyte which ensures the continuous renewal of their interface.
• the nickel deposit is subjected to intense stresses, both mechanical and thermal. And we often see after just a few flows the appearance, near the edges of the cylinders, of cracks in the nickel deposit. These cracks relate to areas a few cm wide from the edges of the shell. They can lead to the formation of defects on the surface of the cast product, since they make its cooling heterogeneous. Above all, they constitute weak points from which very rapid degradation of the entire nickel deposit can begin.
• the object of the invention is to improve the performance of resistance to thermo-mechanical stresses of the metallic coating of the shell, by delaying as much as possible, or even by suppressing the appearance of cracks on the edges, so as to extend the average duration of use of the ferrule between two repairs to its coating.
• the subject of the invention is a method of electrolytic coating with a metal layer of the casting surface of a cylinder for the continuous casting of thin metal strips between two cylinders or on a single cylinder, according to which said surface is at least partially immersed.
• the invention also relates to an installation for electrolytic coating with a metal layer on the casting surface of a cylinder for the continuous casting of thin metal strips between two cylinders or on a single cylinder, of the type comprising a tank containing an electrolyte containing a salt of the metal to be deposited, means for at least partially immersing said casting surface in said tank and for creating a relative movement between said casting surface and said electrolyte, at least one anode disposed in the tank facing said surface casting, and means for bringing said casting surface to a cathodic potential, characterized in that it comprises masks of an insulating material interposed between the edges of said casting surface and said one or said anodes, said masks avoiding a concentration of streamlines on said edges.
• said masks have a general shape in an arc of a circle whose center of curvature is the same as that of the edge of the casting surface to which they face, and have two parallel edges each placed in the extension of said edge at the same distance "d" from it and connected by a wedge-shaped notch whose sides are perpendicular to each other.
• the invention consists in carrying out the electrolytic deposition of the metal coating by placing insulating masks in the vicinity of the edges of the ferrules. These masks, a preferred example of which is described, aim to obtain a regular distribution of the current lines in the edge areas of the ferrule. This gives the deposit a uniform thickness in these areas, in accordance with the desired nominal thickness.
• the inventors have found that there is a correlation between the speed of the appearance of cracks in the nickel coating at the edges of the shell and the regularity of the thickness of this deposit in these same areas, in particular on the right edges.
• the nominal thickness of the deposit is 2 mm over most of the surface of the shell, it can be seen that this thickness sometimes exceeds 7 mm in line with the edges.
• the inventors have found that the most reliable way to obtain a very homogeneous nickel deposit on the edges of the shell and in their immediate vicinity is to have insulating masks, preferably of a determined configuration, at a short distance from the edges, and that under these conditions, it was possible to suppress the early appearances of cracks in the coating of the edges of the ferrules.
• FIG. 1 which shows schematically a cross-sectional profile view along I-I an installation for coating a cylinder shell for casting between cylinders suitable for implementing the method according to the invention
• Figure 1 shows in cross section an installation according to the invention, the cutting plane being located inside the tank 1 containing the electrolyte solution 2 whose main component is a nickel salt, but in front of the shell made of copper 3 placed as a cathode and two anodes 4, 4 ′ arranged in the bottom of the tank 1.
• the ferrule 3, of cylindrical external shape and with an external diameter of 1500 mm, is mounted on a shaft 5 whose axis 6, during the electroplating operation, is rotated by means not shown. At least the lower part of the shell 3 is immersed in the electrolyte solution 2.
• the anodes 4, 4 ′ are soluble anodes formed by anodic baskets of titanium of curved shape, filled with nickel granules .
• the anodes 4, 4 ′ extend behind the cutting plane over a width greater than that of the ferrule 3. Facing the banks of the ferrule 3 are arranged masks 7, 7 ′ (7 being the only one visible in FIG. 1 ) an insulating material such as a polymer, the function of which is to prevent the current lines coming from the anodes 4, 4 ′ from reaching directly the edges and the edges of the ferrule 3, in order to avoid excess thicknesses of the deposit of nickel at their level.
• the positions of these masks 7, T with respect to the shell 3 can be adjusted by positioning means symbolized by movable rods 8.
• these masks 7, 7 ′ are in the form of tubes of substantially square or rectangular section, having the general shape of an arc of a circle, the center of curvature is the same as that of the edge of the ferrule 3 which they face.
• Their upper edge closest to the shore where their action is exerted has a notch 9, 9 'in the form of a corner, the two edges 10, 10' of which are perpendicular and of substantially equal lengths, for example of the order of 5 mm.
• the masks 7, 7 ' are arranged by means of the rods 8 so that the outer edges 1 1, 1 l 'of the notches 9, 9' are each placed substantially at the same distance "d" from the edge 12 of the ferrule 3 facing which they are arranged.
• This distance "d" is, initially, of the order of 5 mm when it is desired to deposit a nickel deposit 2 to 3 mm thick.
• the sides 13, 13 'of each mask 7, 7' which are pe ⁇ endicular to the ferrule 3 must in this example of implementation of the invention, have a minimum length of 50 mm. It is under these conditions that the masks 7, 7 ′ can deflect the current lines enough to homogenize their distribution as well as possible on the banks of the shell 3.
• the masks 7, 7 may be gradually removed 'of the ferrule 3 as the thickness of the nickel deposit increases. This removal can be carried out in successive stages or continuously. We can thus ensure that there will always be enough space between the mask and the deposit to allow the growth of the nickel deposit.
• the edges of the shell 3 will be coated in a homogeneous manner over a greater or lesser portion of their surface.
• the masks can be constituted differently from those which have just been given as an example, in so far as they make it possible to obtain the desired homogeneity for the thickness of the deposit.
• they instead of being constituted by tubes of square, rectangular or other section, they can consist of a plate or an assembly of plates, the surface of which facing the ferrule would preferably have the same configuration as that of the tubes of the 'example.
• this surface should preferably have two parallel edges each placed in the extension of the edge of the ferrule at the same distance "d" from the latter and connected by a wedge-shaped notch whose sides are pe ⁇ endicular the one to another.
• the invention does not exclude that, in order to further complete and refine the action of the masks, recourse is also had to thieves of current, integrated into the masks or independent of them, permanently or intermittently.
• the invention can be applied to the deposition of metals other than nickel on the shell.
• the cylinder thus coated can be used not only on a machine for continuously casting thin metal strips (of steel or another material) between two cylinders, but also on a machine for continuously casting thin bands where a rotating cylinder unique comes to lick the surface of a bath metallic (cast on a cylinder).
• it can also be applied to the coating of the casting surface of a massive cylinder where the ferrule and the core would constitute only one and the same part. It is also easy to transpose it to a case where the ferrule or the massive cylinder could be completely submerged in the electrolyte bath.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Engineering & Computer Science (AREA)
• Electroplating Methods And Accessories (AREA)
• Continuous Casting (AREA)
• Electrolytic Production Of Metals (AREA)
• Application Of Or Painting With Fluid Materials (AREA)
• Prevention Of Electric Corrosion (AREA)
• Other Surface Treatments For Metallic Materials (AREA)

Applications Claiming Priority (5)

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• 1996
  • 1996-12-31 FR FR9616255A patent/FR2750438B1/fr not_active Expired - Fee Related
• 1997
  • 1997-06-06 UA UA99010423A patent/UA54438C2/uk unknown
  • 1997-06-06 ES ES97927245T patent/ES2183183T3/es not_active Expired - Lifetime
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  • 1997-06-06 DK DK97927245T patent/DK0909346T3/da active
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  • 1997-06-06 US US09/147,205 patent/US6228242B1/en not_active Expired - Lifetime
  • 1997-06-06 CZ CZ19984002A patent/CZ295349B6/cs not_active IP Right Cessation
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  • 1997-06-06 EP EP97927245A patent/EP0909346B1/de not_active Expired - Lifetime
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  • 1997-06-06 AU AU31802/97A patent/AU715095B2/en not_active Ceased
  • 1997-06-06 WO PCT/FR1997/001000 patent/WO1997049843A1/fr active IP Right Grant
  • 1997-06-06 PL PL97330923A patent/PL187533B1/pl not_active IP Right Cessation

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