EP1507612B1 - Method for the galvanic coating of a continuous casting mould - Google Patents

Description

The invention relates to a process for the galvanic coating of a continuous casting mold according to the preamble of claim 1.

Continuous casting molds are subject to continuous abrasive wear during casting operation, so that the mold cavity and thus also the cross-sectional dimensions of the cast strands become larger and larger. After a certain number of working cycles, therefore, the respective continuous casting mold must be replaced by a new or reworked.

There are various methods for the post-processing of the molds for the purpose of restoring the original geometry of the mold cavity or of the desired mold cavity. The post-processing can be done, for example, by an explosion deformation of the mold on a mandrel. This method is not only relatively complicated, expensive and polluting, but also means a deformation of Kokillenaussenform, which in turn brings an enlargement of existing at Kokillenumfang water gap and thus a negative impact on the Kokillenkühlung with it. The latter disadvantage also has other known pressing method for recovering the molds, in which first the mold is compressed from the outside and then the mold cavity is brought to the original internal dimensions by internal grinding or internal milling.

Finally is from the EP-A-0 282 759 It is known to restore the mold cavity of a continuous casting mold to the desired dimension by electroplating the inner surfaces delimiting the mold cavity. In this generic process, the mold serving as a cathode is immersed in an electrolyte bath (Cu sulphate bath) together with a perforated anode basket filled with soluble copper pieces (cubes, spheres, disks) and arranged in the mold cavity. In a DC connection, a deposition of the copper from the electrolyte bath and deposition of the same takes place on the Kokillenflächen, wherein the deposited from the electrolyte bath copper is replaced by the dissolved anode copper. In this Tauchvanvanik process is a relatively low current density, for example, of about 15 A / dm ² , achieved. In the dipping electroplating of mostly polygonal cross-sectional mold cavities experience has shown that the risk that in the corner regions, the layer is insufficiently thick, that is, the layer thickness is only about 1/4 to 1/10 of that in the other areas. This uneven layer structure can be remedied only partially with special anode geometries. This means that further mechanical post-processing is necessary.

When making thick layers there is also the danger that corner bridges form with enclosed cavities, whereby the mold is unusable. A further disadvantage of the immersion electroplating coating is that the outer surfaces of the mold have to be covered with a material that is inert to the electrolytic treatment.

The present invention has for its object to provide a method of the type mentioned, with which the desired mold cavity can be achieved as easy as possible or even re-achieved in Stranggiesskokillen with polygonal polygonal mold cavity without problem areas in the corner regions of the mold cavity arise. Furthermore, it should be ensured that the continuous casting molds to be coated remain as unchanged as possible in their external dimensions.

This object is achieved according to the invention by a method having the features of claim 1.

Preferred embodiments of the invention form the subject of the dependent claims.

With the method according to the invention, in which the mold cavity of the cathode-forming continuous casting mold is flowed through hydrodynamically controllable by the electrolyte using an insoluble anode, wherein the electrolyte alone supplies the coating material, both a thin layer of the wear-resistant material can be dimensionally accurate, without any need for reworking is, as well as a thick film (in which at best minimal rework occurs) are applied, since the layer structure evenly, without corner weaknesses occurs. A significant advantage of the inventive method is that in the galvanic coating, only the inner surfaces of the mold cavity come into contact with the electrolyte and therefore the outer surfaces of the continuous casting mold need not be covered. In addition, an intermittent pole reversal anode / cathode is possible with which a pulsating deposition of the coating material can be achieved and the coating can be influenced.

A particular advantage should be emphasized that the mechanical properties, such as hardness, and in particular the microstructure of the coating over the entire area can be kept substantially uniform. The coating can be achieved faster than with the conventional methods. A cartilage formation on the coated surfaces can be largely prevented.

The invention will be explained in more detail with reference to the drawing.

• Fig. 1 ein Prinzipschema des erfindungsgemässen Verfahrens.

It shows:

• Fig. 1 a schematic diagram of the inventive method.

In Fig. 1 is purely schematically a device 1 is shown, which is provided for the galvanic coating of a mold cavity 3 of a continuous casting 2 limiting inner surfaces 4 with a wear-resistant coating material in order to achieve or re-reaching a desired mold cavity. The mold cavity 3 may for example have a rectangular or square cross-section and thus be limited by four inner surfaces 4. But it could also be a mold with a different mold cavity cross section (eg, round, polygonal, langckförmig) or a so-called dogbone mold.

The Stranggiesskokille 2 are the front side of a head and a bottom piece 5, 6 associated with each other, the projecting through a cavity 3 anode 7 with each other are connected. Sealing elements 8, 9 at the end faces of the continuous casting mold 2 seal the mold cavity 3 from. Also, the anode 7 is in the top and bottom piece 5, 6 sealingly inserted, see. Seals 13, 14. Both the bottom piece 6 and the head piece 5 are provided with at least one each, preferably with a number of openings 11 and 12 (in Fig. 1 each one opening 11, 12 indicated), the inlet or outlet openings for insertion or outlet of an electrode provided for the galvanic coating 25 into or form the otherwise sealed, forming a reactor space mold cavity 3. This is pumped hydrodynamically controllable from a storage tank 15 by means of a pump 16 from below through the bottom piece 6 into the reactor chamber and passed with overflow (without pressure) on the head piece 5 back to the feed tank 15 and the pump 16. The electrolyte 25, the coating material is metered as oxide from a container 18.

For the galvanic coating, the continuous casting mold 2 as the cathode and the anode 7 with indicated wings 7 'can be connected to a direct current source 20 and thereby form a direct current circuit. Either the sealing elements 8, 9 or the seals 13, 14 act simultaneously electrically insulating. The anode is adapted in its cross-sectional shape of the cross-sectional shape of the mold cavity 3. For polygonal mold cavities corresponding prismatic anodes are used. The anode consists in particular of a platinum or mixed ceramic-coated titanium material or of lead. It can also be designed as a multiple anode. In principle, however, the coating material, such as copper, nickel or chromium may be contained in the anode, where it would be provided in solid or piece form.

The inventive method is suitable for applying, for example, copper, nickel or chromium layers. The coating material is supplied by the electrolyte 25 alone. The anode itself is insoluble. For example, platinum coated titanium anodes, Pb sheet metal anodes, coated mixed ceramic, and other materials may be used. In the case of the electrolytes, it is possible to use methanesulfonic acid, cyanide or sulfuric acid electrolyte types. With these high-speed electrolytes, a current density of 20 to 40 A / dm ² can be achieved during intensive electrolytic movement. With an efficient hydrodynamic control of the electrolyte flow through the reactor space, both a thin layer of the wear-resistant material can be mass-accurately applied without the need for reworking, as well as a thick layer (which requires minimal reworking if necessary), since the layer build-up is uniform and without corner weaknesses. The process according to the invention brings significant advantages, in particular in the case of chromium plating, since particularly corner problems arise particularly with chromium in the conventional galvanic coating (layer 5 to 10 times smaller than on the surfaces), and the chromium can only be refinished with grinding.

With the method according to the invention, in which the electrolyte 25 alone provides the coating material, it is also possible to achieve pulsating deposition of the coating material, since in addition to the hydrodynamic control, an intermittent pole reversal anode / cathode is also possible and can influence the coating.

A significant advantage of the inventive method is that in the galvanic coating, only the inner surfaces of the mold cavity come into contact with the electrolyte 25 and therefore the outer surfaces of the continuous casting mold do not need to be covered.

The anode and / or the continuous casting mold could in principle be designed to be rotatable about its longitudinal axis, so that a rotation during the coating and thus an improved coating could be made possible.

The continuous casting mold 2 is cleaned before coating by a rinsing process, in particular a cascade rinse, which is not explained in detail. It is involved here for the coating and preferably for this rinse in a closed system.

The continuous casting mold consists of a metallic material or material composite, such as copper, aluminum, nickel, of a plastic or composite plastic or of a ceramic material or other materials.

Furthermore, a rectifier device can be provided, by means of which the current direction can be reversed in order to achieve a uniform layer application.

Furthermore, when using copper as the coating material, a commercially available copper oxide is previously taken, in which the excessively high chlorine content is reduced by means of a washing / dissolving process.

The continuous casting mold 2 may alternatively be reinforced only in certain areas or areas, i. coated with a greater layer thickness, in which a relatively higher wear occurs during operation, for example in the region of the bath surface, in which an additional wear occurs in particular by the covering material. This achieves an efficient coating. Such partial coating can be achieved by partially covering the anode or by inserting non-conductive diaphragms or by similar means.

During the coating process, electromagnetic fields can be generated by magnets not shown in detail by which the particles of the coating material are conducted or guided such that in certain areas, preferably in the edge regions of the continuous casting mold, an equally thick layer deposits as in the other areas.

The invention is sufficiently demonstrated with the above statements. It could of course be illustrated in other variants.

Claims (13)

1. Process for electrolytic coating of a strand casting mould (2), in which the internal surfaces (4) of the strand casting mould (2), which demarcate a mould cavity (3), are coated with a coating material for the purpose of achieving or re-achieving intended mould cavity dimensions, the strand casting mould (2), as the cathode, an anode (7) positioned in the mould cavity (3) and an electrolyte (25) which contains the coating material being used, characterized in that an insoluble anode (7) having a cross sectional shape, which is adapted to the cross sectional shape of mold cavity (3), is introduced into the mold cavity (3), the mold cavity (3) is sealed at the face side with sealing elements (8, 9) and with a head - (5) and a bottom piece (6) and will be controlled flowed through by the electrolyte serving as carrier of the coating material, and that the current direction is changed periodically by means of a rectifier device or the like with pole-changing function, and by a corresponding choice of this periodic change a uniform layer application is achieved by this means.
2. Process according to claim 1, characterized in that copper, nickel or chromium is used as the coating material and each is metered into the electrolyte (25) as oxide.
3. Process according to claim 1 or 2, characterized in that an electrolyte (25) containing methanesulfonic acid, cyanide or sulfuric acid is used.
4. Process according to any one of claims 1 to 3, characterized in that the anode (7) used in insoluble form, which can be also constructed as a multiple anode, is constructed from a platinum- or mixed ceramic-coated titanium material or from lead.
5. Process according to any one of the claims 1 to 4, characterized in that the electrolyte (25) is pumped by means of a pump (16) into a reactor space which is surrounded by the internal surfaces (4) of the mould cavity (3) and is closed off at the faces by a base - and a head piece (6, 5), and is fed from this back to the pump (16).
6. Process according to any one of the claims 1 to 5, characterized in that the anode (7) and/or the strand casting mould (2) are constructed rotatably around their longitudinal axis, so that rotation during the coating is rendered possible.
7. Process according to any one of the claims 1 to 6, characterized in that the strand casting mould (2) is cleaned by a rinsing process, in particular a cascade rinsing, before the coating.
8. Process according to any one of the claims 1 to 7, characterized in that the strand casting mould (2) is integrated in a closed system for the coating and preferably for the rinsing.
9. Process according to any one of the claims 1 to 8, characterized in that the strand casting mould (2) is made from a metallic material or composite material, such as copper, aluminum, nickel, from a plastic or composite plastic or from a ceramic material or other materials.
10. Process according to claim 1, characterized in that if copper is used, a commercially available copper oxide is used beforehand, in which the too high chlorine content is reduced by means of a washing-/dissolving process.
11. Process according to any one of the claims 1 to 10, characterized in that the inner surfaces of a polygonal rectangular mold cavity cross section will be coated.
12. Process according to claim 1, characterized in that the coating material, such as for example, copper, nickel or chromium, is employed as the anode.
13. Process according to any one of the claims 1 to 12, characterized in that during the coating operation the particles of the coating material are conducted by electromagnetic fields such that in certain regions, in particular in the edge regions of the strand casting mould, a layer of the same thickness as in the other regions is deposited.

Images