Metal founding – Means to shape metallic material – Continuous or semicontinuous casting
Reexamination Certificate
2000-02-07
2001-11-20
Dunn, Tom (Department: 1725)
Metal founding
Means to shape metallic material
Continuous or semicontinuous casting
C164S487000
Reexamination Certificate
active
06318449
ABSTRACT:
The invention relates to the hot-top continuous casting of metals, especially steel. It relates more specifically to the hot-top casting of products of elongate cross section, especially of broad cross section, such as slabs, more commonly called “flat products”.
In its current state of development, hot-top continuous casting may be regarded as an extension of the conventional continuous casting process, which aims to shift vertically in the mould the point where the cast metal starts to solidify by contact with the internal face of the cooled copper wall, from the point, located above, where the free surface (the “meniscus”) of the cast liquid metal lies. It is known that the first solidification takes place by a very sensitive physical mechanism, and at the same time it constitutes an essential factor in the quality of the product obtained. By virtue of the separation in the levels of the above two points, specific to hot-top continuous casting, this solidification takes place at a point which is hydrodynamically calm, far from the permanently disturbed zone formed by the meniscus region. Schematically, this separation of the two levels is produced by sitting on top of the cooled copper body of the mould an uncooled added feed head made of a refractory material having good thermal insulation properties (as it were, a feeder head) which is internally well aligned with the mould and within which the caster will place and maintain the meniscus of cast steel poured from a tundish positioned above it.
Hot-top continuous casting of this type, known for a long time according to these principles, and described for example in FR-2,009,365, has never hitherto been obtained on an industrial scale to the knowledge of the applicants. Their own studies carried out more recently on the subject (see, for example, French Patent Applications Nos. 96/04304 and 96/04305) have shown the great advantage of providing, between the insulating feed head made of refractory and the cooled copper mould which supports it, an insert which is also made of refractory but one which is dense and therefore mechanically stronger than the usual insulating refractories, which are generally fibrous. This inserted piece must in fact be both quite a good thermal insulator in order to keep the molten steel that it will contain in the liquid state in the manner of the feed head, and have good mechanical strength properties in order to preserve for as long as possible the geometry of the upper edge of the copper wall on which it rests, precisely at the point where the cast metal starts to solidify. It is known that a material such as SiAlON® satisfies such conflicting requirements quite well.
However, this type of material is expensive, particularly when it has to be shaped into a ring matching the internal perimeter of the mould. Its cost may even become prohibitive for long inserts, as is the case with moulds having a long solidification perimeter that moulds for casting products with a large cross section, such as slabs, necessarily have. Moreover, and as the studies by the Applicants have also confirmed, it is important for the success of the casting operation to keep the SiAlON in alignment with the mould within very tight tolerance margins (at most 0.1 mm). Such a requirement is all the harder to meet in this case, since the inevitable phenomena of hot differential expansion of the various parts when in contact with the molten metal are a major cause of misalignment. In addition, it should be noted that such phenomena are all the more important the more elongate the mould, which is particularly the case of the casting of steel slabs (whose width may conventionally reach or even exceed 1800 mm).
The object of the present invention is to provide a simple, reliable and inexpensive solution to the aforementioned difficulties encountered with the casting of products of broad cross section.
For this purpose, the subject of the invention is a mould head for the vertical hot-top continuous casting of metals, particularly steel, comprising a feed head made of thermally insulating refractory, which sits on top of the cooled metal crystallizer of the mould (generally made of copper or copper alloy) which is internally aligned with it and includes, between the feed head and the crystallizer, an insert made of dense refractory having mechanical strength properties (for example SiAlON) and shaped in the form of a ring so as to be able to match the internal periphery of the mould, characterized in that the said insert consists of bars, each bar being formed from a rigid assembly of juxtaposed and aligned contiguous elements which are kept clamped against each other by a clamping means incorporated into the said bar, and in that means for aligning the said bar with the body of the mould are provided and consist of a pusher associated with a positioning stop made on the cooled copper body, against which stop is pressed the said assembly subjected for this purpose to the action of the pusher which tends to continuously push it back towards the inside of the mould.
Several assemblies of this type, butted together one after the other with suitable connecting corners (generally right-angled corners since the continuous cast products are ordinarily of rectangular cross section), will form an insert in its desired final geometry for matching the perimeter of the mould.
In a preferred embodiment of the invention, the integrated clamping means consists of a threaded cross-tie in the long direction and associated with clamping nuts (more generally clamping pads) which are provided at least so as to bear on the free front face of the elements located at each end of the assembly. Advantageously, the cross-tie is placed in an offset position near the “cold” face of the assembly, that is to say its rear face on the opposite side from the front “hot” face intended to be brought into contact with the molten metal to be cast.
Also preferably, intermediate clamping nuts are also provided so as to bear against the internal front faces of the various elements so as to put each of the elements in mechanical compression in the long direction.
According to another advantageous embodiment of the invention, the assembly of constituent elements of the insert is provided, apart from the aforementioned overall clamping means, with means for mechanically stiffening the “cold” face.
As will doubtlessly have already been understood, the invention consists, in its essential characteristics, in constructing a long straight bar of compact refractory (which it will be assumed hereafter to be of SiAlON in order to be specific) from elements which are possibly identical, in all cases dressed as required in order to allow, of course, the joints between them to be sealed, and butted together one after the other over a distance corresponding to the desired length of the bar, and then joined together into a whole made rigid with the aid of intrinsic clamping means designed also to ensure that the assembly is mechanically strengthened. Thus, a SiAlON bar of a desired length is produced which is much less expensive and much stronger than an equivalent monolithic bar that might be available commercially. Consequently, this increased strength makes it possible to adopt alignment solutions which are unsophisticated but nevertheless precise and reliable, of the “stop+ pusher” type, which could not be applied to fragile or brittle members.
REFERENCES:
patent: 5176197 (1993-01-01), Hamaguchi et al.
patent: 6050324 (2000-04-01), Jolivet et al.
patent: 6135197 (2000-10-01), Jolivet et al.
patent: 0 620 062 (1994-10-01), None
patent: 1 253 787 (1961-05-01), None
patent: 1 358 802 (1964-07-01), None
patent: 2 690 099 (1993-10-01), None
Jolivet Jean-Marc
Perrin Eric
Salaris Cosimo
Spiquel Jacques
Cole Thomas W.
Dunn Tom
Nixon & Peabody LLP
Sollac
Tran Len
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