AU2003236679B2

AU2003236679B2 - Method for the galvanic coating of a continuous casting mould

Info

Publication number: AU2003236679B2
Application number: AU2003236679A
Authority: AU
Inventors: Adrian Stilli
Original assignee: Concast AG
Current assignee: SMS Concast AG
Priority date: 2002-05-27
Filing date: 2003-05-19
Publication date: 2008-08-28
Anticipated expiration: 2023-05-19
Also published as: BR0311374B1; CA2504369A1; WO2003099490A1; JP5008111B2; AU2003236679A1; ES2452727T3; JP2005527705A; KR20050004877A; CN1655893A; PL371684A1; PL206254B1; BR0311374A; MXPA04011734A; EP1507612A1; RU2318631C2; CA2504369C; EP1507612B1; RU2004138096A; KR101082896B1; ZA200408991B

Description

WO 03/099490 PCT/EPO3/05238 Process for electrolytic coating of a strand casting mould The invention relates to a process for electrolytic coating of a strand casting mould according to the precharacterizing clause of claim 1.

Strand casting moulds are subject to a constant abrasive wear during casting, so that the mould cavity and therefore also the cross-section dimensions of the cast strands become ever larger. After a certain number of working cycles, the particular strand casting mould must therefore be replaced by a new one or reworked.

Various methods for reworking the moulds for the purpose or re-establishing the original geometry of the mould cavity or the intended dimensions of the mould cavity are known.

Reworking can be carried out, for example, by explosion forming of the mould on a mandrel. Not only is this method relatively complicated, expensive and environmentpolluting, it also means a deformation of the external shape of the mould, which in turn involves an enlargement of a water gap present on the periphery of the mould and as a result an adverse influence on the cooling of the mould.

Other known pressing processes for reshaping the moulds in which the mould is first compressed from the outside and the mould cavity is then brought to the original internal dimensions by internal grinding or internal milling also have the latter disadvantage.

Finally, it is known from EP-A-0 282 759 to bring the mould cavity of a strand casting mould back to the intended dimensions by electrolytic coating of the internal surfaces which demarcate the mould cavity. In this generic process, 00 the mould, which serves as the cathode, is immersed in an electrolyte bath (Cu sulfate bath) together with a perforated anode basket which is positioned in the mould cavity and is filled with soluble copper pieces (cubes, balls, discs). When a direct current is connected, the copper is separated out of the electrolyte bath and deposited on the mould surfaces, the copper separated out of the electrolyte bath being replaced by ID the dissolved anode copper. A relatively low current density, CR for example of about 15 A/dm 2 is achieved in this dipping electrolytic process. From experience, in the case of Cl electrolytic dip-coating of mould cavities which are usually polygonal in cross-section there is the risk that the layer is of insufficient thickness in the corner regions, that is to say the layer thickness is only about 1/4 to 1/10 of that in the other regions. This non-uniform layer build-up can be only partly remedied with special anode geometries. This means a further mechanical reworking is necessary.

With the production of thick layers there is furthermore the risk that corner bridges with enclosed cavities are formed, as a result of which the mould becomes unusable. A further disadvantage of electrolytic dip-coating is that the external surfaces of the mould must be covered with a material which is inert towards the electrolytic treatment.

According to the invention, there is provided a process for electrolytic coating of a strand casting mould in which the internal surfaces of the strand casting mould which demarcate a mould cavity are coated with a coating material for the purpose of achieving or re-achieving intended mould cavity dimensions, the strand casting mould, as the cathode, an anode positioned in the mould cavity and an electrolyte which contains the coating material being used, the process comprising: 00 positioning an insoluble anode having the same crosssection shape as the cross-section shape of the mould ;cavity in the mould cavity; sealing off the mould cavity with a head and a base piece with sealing elements for both front faces of the mould, whereby the head piece and the base piece each have at least one opening forming an intake or a discharge opening ID for introducing and discharging the electrolyte; CI pumping the electrolyte, serving as the carrier of the coating material through the mould cavity of the mould, in C1 a controlled manner; changing the current direction periodically by means of a rectifier device or the like with a pole changing function; and coating the mould cavity over its whole mould length with a uniform thickness by a corresponding choice of this periodic change.

Embodiments of the present invention provide a process of the abovementioned type with which the intended dimensions of the mould cavity can be achieved or re-achieved as simply as possible even in strand casting moulds having a mould cavity of polygonal cross-section, without problem zones arising in the corner regions of the mould cavity. Furthermore, the strand casting moulds to be coated may as far as possible remain unchanged in their external dimensions.

Preferred features of the invention form the subject matter of the dependent claims.

With the process according to a preferred embodiment of the invention, in which the electrolyte flows in a hydrodynamically 0D 0

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controllable manner through the mould cavity of the strand casting mould which forms the cathode, using an insoluble anode, the electrolyte alone supplying the coating material, it is possible to apply both a thin layer of the wear-resistant material with dimensional accuracy, without reworking being necessary, and a thick layer (with which at most minimal reworking arises), since the layer build-up is uniform without corner weaknesses. It is a considerable advantage of the process according to the preferred embodiment of the invention that during the electrolytic coating only the internal surfaces of the mould cavity come into contact with the electrolyte and the external surfaces of the strand casting mould therefore do not have to be covered. Furthermore, intermittent anode/cathode pole reversal is also possible, with which a pulsed deposition of the coating material can be achieved and the coating influenced.

It is to be emphasized as a particular advantage that the mechanical properties, such as, for example, the hardness, WO 03/099490 PCT/EP03/05238 4 and in particular also the structural formation of the coating can be kept largely uniform over the entire region.

The coating can be achieved more rapidly than with the conventional processes. Gristle formation on the coated surfaces can also be largely prevented.

The invention is explained in more detail in the following with the aid of the drawing.

In the drawing: Fig. 1 shows a schematic diagram of the process according to the invention.

Fig. 1 shows, in purely schematic form, a device 1 which is envisaged for electrolytic coating of internal surfaces 4 which demarcate a mould cavity 3 of a strand casting installation 2 with a wear-resistant coating material for the purpose of achieving or re-achieving intended mould cavity dimensions. The mould cavity 3 can have, for example, a rectangular or square cross-section and can thus be demarcated by 4 internal surfaces. However, the mould could also be a mould having another mould cavity crosssection circular, polygonal, longitudinally angled) or a so-called dog bone mould.

A head piece and a base piece 5, 6 which are joined to one another via an anode 7 which extends through the mould cavity 3 are assigned to the faces of the strand casting mould 2. Sealing elements 8, 9 on the faces of the strand casting mould 2 seal off the mould cavity 3. The anode 7 is also inserted in a sealing manner in the head piece and base piece 5, 6, cf. seals 13, 14. Both the base piece 6 WO 03/099490 PCT/EP03/05238 and the head piece 5 are provided with at least in each case one, preferably with a number of openings 11 and 12 respectively (in fig. 1 in each case one opening 11, 12 is indicated), which form intake and discharge openings for introducing and discharging an electrolyte 25 envisaged for the electrolytic coating into and out of the otherwise tightly closed mould cavity 3, which forms a reactor space.

This is pumped from a reservoir container 15 with the aid of a pump 16 in a hydrodynamically controllable manner into the reactor space from the bottom through the base piece 6 and is fed with an overflow (without pressure) on the head piece 5 back to the reservoir container 15 and to the pump 16. The coating material is metered into the electrolyte as oxide from a container 18.

For the electrolytic coating, the strand casting mould 2, as the cathode, and the anode 7 with the wings 7' indicated 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 simultaneously have an electrically insulating action. The anode matches in its cross-section shape the cross-section shape of the mould cavity 3. For polygonal mould cavities, corresponding prismatic anodes are used. The anode is made in particular from a platinum- or mixed ceramic-coated titanium material or from lead. It can also be constructed as a multiple anode. In principle, however, the coating material, such as, for example, copper, nickel or chromium, can also be contained in the anode, in which case it would be provided in a solid or piece form.

WO 03/099490 PCT/EP03/05238 6 The process according to the invention is suitable for application of, for example, layers of copper, nickel or chromium. The coating material is supplied by the electrolyte 25 alone. The anode in itself is insoluble.

The anodes can be, for example, platinum-coated anodes of titanium, anodes of Pb sheet, coated mixed ceramic and other materials. Methanesulfonic acid, cyanide or sulfuric acid electrolyte types can be used as the electrolytes.

Using these high-speed electrolytes, with intensive agitation of the electrolyte a current density of 20 to A/dm 2 can be achieved. With an efficient hydrodynamic control of the flow of the electrolyte through the reactor space, it is possible to apply both a thin layer of the wear-resistant material with dimensional accuracy, without reworking being necessary, and a thick layer (with which at most minimal reworking arises), since the layer build-up takes place uniformly and without corner weaknesses. The process according to the invention brings considerable advantages in particular in coating with chromium, since precisely in the case of chromium particularly severe corner problems arise during conventional electrolytic coating (layer 5 to 10 times thinner than on the surfaces) and the chromium can be reworked only with grinding.

Pulsed deposition of the coating material can also be achieved with the process according to the invention, in which the electrolyte 25 alone supplies the coating material, since in addition to the hydrodynamic control, an intermittent anode/cathode pole reversal is possible and can influence the coating.

WO 03/099490 PCT/EP03/05238 7 A considerable advantage of the process according to the invention is that during the electrolytic coating only the internal surfaces of the mould cavity come into contact with the electrolyte 25 and the external surfaces of the strand casting mould therefore do not have to be covered.

The anode and/or the strand casting mould could in principle be constructed rotatably about their longitudinal axis, so that rotation during the coating and therefore an improved coating could be rendered possible.

Before the coating, the strand casting mould 2 is cleaned by a rinsing process, in particular a cascade rinsing, which is not explained in more detail. It is integrated in a closed system here for the coating and preferably for this rinsing.

The strand casting mould is made from a metallic material or composite material, such as copper, aluminium or nickel, from a plastic or composite plastic or from a ceramic material or other materials.

A rectifier device can furthermore be provided, by means of which the current direction can be reversed for the purpose of achieving a uniform layer application.

If copper is used as the coating material, a commercially available copper oxide, in which the too high chlorine content is reduced by means of a washing/dissolving process, is furthermore used beforehand.

00 O Alternatively, the strand casting mould 2 can be coated only in certain regions or more thickly, i.e. with a larger layer ;thickness, in these regions where a relatively higher degree of M wear occurs during operation, for example in the region of the bath surface, where an additional wear occurs in particular due to the covering material. An efficient coating is thus N achieved. Such a partial coating can be achieved by partial

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Scovering of the anode or by insertion of non-conducting screens Sor by similar measures.

During the coating operation, electromagnetic fields can be generated by magnets, which are not shown in more detail, through which the particles of the coating material can be conducted and led such that a layer of the same thickness as in the other regions is deposited in certain regions, preferably in the edge regions of the strand casting mould.

While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not by way of limitation.

It will be apparent to a person skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention.

Thus, the present invention should not be limited by any of the above described exemplary embodiments.

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of 00 the common general knowledge in the field of endeavour to which this specification relates.

SThroughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be IND understood to imply the inclusion of a stated integer or step

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M or group of integers or steps but not the exclusion of any Sother integer or step or group of integers or steps.

The reference numerals in the following claims do not in any way limit the scope of the respective claims.

Claims

2. Process according to claim 1, whereby the mould cavity (3) has a polygonal cross-section and the anode has the same polygonal cross-section shape as the mould cavity. I 00
3. Process according to claim 1 or 2, wherein copper, nickel or chromium is used as the coating material and is in each case ;metered into the electrolyte (25) as oxide.
4. Process according to any one of the preceding claims, wherein an electrolyte (25) containing methanesulfonic acid, IND cyanide or sulfuric acid is used. \O IcN Process according to any one of the preceding claims, wherein the anode 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.
6. Process according to any one of the preceding claims, wherein the electrolyte (25) is pumped by means of a pump (16) into a reactor space which is surrounded by the internal surfaces of the mould cavity and is closed off at the faces by a base piece and a head piece and is fed from this back to the pump (16)
7. Process according to any one of the preceding claims, wherein the anode and/or the strand casting mould are constructed rotatably around their longitudinal axis, so that rotation during the coating is rendered possible.
8. Process according to any one of the preceding claims, wherein the strand casting mould is cleaned by a rinsing process, in particular a cascade rinsing, before the coating.
9. Process according to any one of the preceding claims, wherein the strand casting mould is integrated in a closed system for the coating and preferably for the rinsing. 00 Process according to any one of the preceding claims, O wherein the strand casting mould is made from a metallic material or composite material, such as copper, aluminium or M nickel, from a plastic or composite plastic or from a ceramic material or other materials. ND 11. Process according to any one of the preceding claims, \O Swherein a rectifier device is provided, by means of which the M current direction can be reversed periodically for the purpose of achieving a uniform layer application.
12. Process according to claim i, wherein the coating material, such as, for example, copper, nickel or chromium, is employed as the anode.
13. Process according to any one of the preceding claims, wherein 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.
14. Process for electrolytic coating of a strand casting mould substantially as hereinbefore described with reference to the drawings and/or Examples.