EXTRUSION DIE FOR LIQUID METALS, IN PARTICULAR FOR LIQUID

Abstract

An extrusion die (1) for the casting of liquid metals, in particular of liquid steel materials, has a heat flow density which is distributed non-homogenously over the die face. A homogenizing of the heat flow density can be obtained if the spacing between the hot side and the cooling duct base (=thickness (6) of the die wide side plate (2)) in the new state as a typical normal thickness (100%) is reduced by at least 20% to 80%, and a further reduction, obtained by means of reworking processes, of the thickness (6) which is initially reduced to 80% is restricted to 5 mm a final thickness (6a) by means of a final reworking process.

Description

The invention relates to a continuous-casting mold for molten metals, in particular, for molten steel, comprising mold side plates surrounded by water boxes for the circulation of coolant, the side plates defining a mold cavity with a straight and/or curved path, and mold end plates composed of copper, on the outer cold face of which a plurality of coolant passages are provided that generally at the upper melt surface have a minimum coolant-passage flow cross-section with a thickness reduction of the respective mold side plate.

Field measurements in thin-strand equipment have shown that the thermal load on the continuous-casting mold is distributed very unevenly over the mold surface. The load is particularly strong in the region approximately 70 mm below the upper melt surface. The heat flux densities measured at this point are an order of magnitude greater than the mean heat-flux density as measured over the entire mold. Along the upper melt surface in the width direction, the heat-flux density is also not distributed homogeneously. Values higher than at the center are reached at multiple sites in the outer regions of the mold side plates, this being attributable to the central location of an immersion lance.

Like this very uneven distribution of the heat-flux density, the temperature of the mold surface on the inner hot face, which is located in contact with the molten steel or the solidifying strand shell, is also extremely variable. In addition to negative consequences that cannot be excluded for the cast strands (for example, slab cross-sections or thin-strand cross-sections), the locally higher surface temperatures on the mold hot face also result in greater wear in these regions that can turn up in local distortion faults or cracking. As soon as the wear occurring on the inner hot face of the mold exceeds a certain level, the entire mold plate face, including the less-worn or still-usable surface portions must be resurfaced, a step that can only by effected by milling off or other machining techniques.

The continuous-casting mold identified above is known from DE 102 26 214 [U.S. Pat. No. 7,363,958]. The cassette-like inserts therein composed of copper alloy rest on steel insert plates and can be replaced. The thickness of the copper plates here between the coolant and the hot face of the copper plates varies over the width and/or the height of the mold. This thickness at the coolant-passage flow cross-section at the upper melt surface is designed with a minimum size, while in the lower regions this thickness is always larger, the thickness in the lower region of the copper plate also always being made larger. None of these measures is able to prevent the above-described wear of the copper plates after a number of casting cycles.

The fundamental problem to be solved by the invention is to reduce the varying thermal loads on the continuous-casting mold within the mold side plate, thereby reducing wear.

The problem posed is solved according to the invention by an approach wherein the spacing between the hot face and the coolant passage of the mold side plate (=thickness of the mold side plate (2)) in the new state as the typical normal thickness (100%) is reduced at least 20% to 80%, and a further reduction due to several resurfacings of the thickness that is initially reduced to 80% is limited to an approximately 5 mm final thickness by a final resurfacing. As a result, the surface temperatures of the mold hot face are reduced in regions that are subject to especially high thermal loads, and as a result both the mechanical load on the strand shell is reduced and also the service like of the continuous-casting mold is improved. This positive effect of a noticeable reduction in surface temperatures of the mold side plate occurs when the spacing between the coolant passages and the surface of the mold in the new state is reduced by at least 20%. The previous new state can be assumed to be 20 mm to approximately 40 mm plate thickness, depending on how the broad-side mold thickness is specified for the relevant casting strand thickness. The previously employed thickness values for the broad-side mold plates are thus assumed. Given the currently presumed conditions, this corresponds to a reduction in the spacing of 5 mm starting from the new thickness, which is thus reduced. In the end, the spacing should not be become less than 5 mm during the entire operation for reasons of safety.

By way of example: In conventional mold plates for thin slab equipment of constant thickness, the thickness in the new state typically measures 25 mm. This value is now reduced by 5 mm (20%) down to 20 mm.

Additional features are that the coolant-passage flow cross-section at the upper melt surface is reduced proportionally to the reduction in the thickness of the mold side plate.

In order not to prevent the flow resistance, and thus the loss of pressure, in this region from becoming excessive, another of the features provides that the coolant-passage flow cross-section is not reduced more than 80% of the new state of the initial coolant-passage flow cross-section.

In another embodiment, provision is made whereby both the reduction in the thickness of the mold side plate and the reduction in the coolant-passage flow cross-section are effected as a function of the dissimilar position of the given coolant passage in the width direction.

In addition, it is proposed that the mold side plates (2) be reduced in thickness (6) between 5 mm and 10 mm up to a maximum of 15 mm in 3-10 resurfacings, where a single resurfacing consists in a removal of copper material amounting to 0.3 mm to 1.5 mm, at maximum 3 mm.

In the additional embodiment, provision is made whereby the coolant-passage flow cross-section at the upper melt surface and up to the mold outlet is formed by one filler piece each attached to the outer face and composed of normal-temperature-resistant material.

It is furthermore advantageous here that the filler piece for reducing the coolant-passage flow cross-section is adjustable.

In an alternative embodiment of the casting space, provision is made whereby at least the mold side plates are designed as cassette plates that on the outer cold face rest on cooled adapter plates and are expandable.

A development based thereon is created by providing a separate displacement body on the adapter plate to form the minimum coolant-passage flow cross-section.

The displacement body can be designed having different shapes, stored, and attached in a replaceable manner.

Illustrated embodiments are illustrated in the drawing that are described in more detail below.

In the drawing:

FIG. 1 is a perspective view of a continuous-casting mold with the front mold side plate omitted to expose the view into the interior into which the immersion lance is lowered;

FIG. 2 is a planar vertical partial section through a mold side plate that shows the thickness(es) of the copper plate in connection with the proportions of the coolant passage over the height of the mold;

FIG. 3 illustrates a planar vertical partial section, as in FIG. 2 but with an adapter plate; and

FIG. 4 is a view toward the outer face of the mold side plate with its filler piece or adapter plate removed.

The continuous-casting mold 1 (FIG. 1) is formed by two wide mold side plates 2 defining a mold cavity 1b and by narrow plates 3 located at the ends, a coolant 1a (such as, for example, water) flowing through coolant passages 4 (FIGS. 2 through 4) under pressure. As shown, regions 5a and 5b of different heat-flux density are created by an immersion lance 12 in at a region adjacent the upper melt surface 5. The heat-flux density in the regions 5a is higher than in the region 5b. In addition, different heat flux densities are also created by the molten steel flowing out of the immersion lance 12, these occurring even in the case of a funnel-shaped upper widening 11 of the mold inlet. These varying heat flux densities must be compensated for by cooling. To this end, a thickness 6 of the mold side plate 2, typically measuring in the new state between 20 mm and 40 mm, is considered to be 100%. For this reason, the corrected new state in the region of the upper melt surface, as illustrated, is only 80%, while a further reduction, resulting from resurfacing for wear, of thickness 6 reduced initially to 80% is limited to approximately 5 mm final thickness 6a (FIG. 2). In addition, a coolant-passage flow cross-section 7 at the upper melt surface region 5 can be reduced proportionally so as to reduce the thickness 6 of the mold side plate 2 (FIG. 2) in order to further improve the cooling effect. These measures are applicable for all currently employed designs of what is called a CSP funnel mold and also with conventional mold plates. Here more extensive milling out can be used to reduce the minimized coolant-passage flow cross-section 7 between the hot face and the coolant at the upper melt surface 5. The coolant-passage flow cross-section 7 is initially not reduced more than 80% of the new state of the given starting coolant-passage flow cross-section.

FIG. 2 shows the resulting final thickness 6a of the mold side plate 2 after a plurality of resurfacings for wear, cracks, and the like on the hot face, where a single resurfacing can consist in a removal of copper material ranging from 0.3 mm-1.5 mm, at maximum 3.0 mm.

At the upper melt surface 5 and up to a mold outlet 9, the coolant-passage flow cross-section 7 is created in each case by a filler piece 10 attached on the outer face and composed of ambient-temperature-resistant material. The filler piece can be adjustable at least to reduce the coolant-passage flow cross-section 7.

FIG. 3 illustrates an embodiment of continuous-casting mold 1 for a two-part cassette mold, the upper melt surface 5 being shown together with the region 5a of higher heat-flux density in a pour direction 13 within the funnel 11. The so-called cassette mold is composed essentially of the above-described mold side plate 2 and an adapter backing plate 14, between which the coolant passage 4 runs and through which the coolant 1a is circulated. Here too, the individual coolant passages 4 in the region below the upper melt surface 5 can be milled more deeply into the material. Correspondingly shaped displacement bodies 15 reduce the coolant-passage flow cross-section 7 and increase the coolant speed in this region.

In FIG. 3, at least the mold side plates 2 are designed as cassette plates that on the outer face rest in expandable form on cooled adapter plates 14 that do not necessarily have to be composed of copper alloy. A separate displacement body 15 is provided here on the adapter plate 14 to form the minimum coolant-passage flow cross-section 7. The displacement body 15 is designed with different shapes, and can be stored and replaced.

In FIG. 4, the coolant passages 4 are provided in groups in a width direction 8 in the mold side plate 2. Both the reduction of thickness 6 of the mold side plates 2 as well as the reduction in the coolant-passage flow cross-section 7 are effected as a function of a dissimilar position of the given coolant passage 4 in the width direction 8. It is possible to create groups of different numbers of coolant passages 4. Fastening threaded holes 16 are provided between the vertical rows of the coolant passages 4.

LIST OF REFERENCE NUMBERS

1  continuous-casting mold
1a coolant
1b mold cavity
2  mold side plate
3  mold end plate
4  coolant passage
5  upper melt surface (region)
5a region of high heat-flux density
5b region of low heat-flux density
6  thickness of the mold side plate
6a final thickness after material removed by milling
7  minimized coolant-passage flow cross-section
8  width direction
9  mold outlet
10 filler piece
11 funnel-shaped extension
12 immersion lance
13 pour direction
14 adapter plate
15 displacement body
16 threaded fastening holes

Claims

1. A continuous-casting mold for molten metals, in particular, for molten steel, comprising mold side plates surrounded by water boxes for the circulation of coolant, the plates defining a mold cavity with a parallel and/or curved path, and mold end plates composed of copper alloy, on the outer face of which a plurality of coolant passages are provided that at a region of the upper melt surface have a minimum coolant-passage flow cross-section with a thickness reduction of the respective mold side plate, wherein a spacing between the hot face and the coolant passage base of the mold side plate in the new state as the conventional normal thickness is reduced by at least 20% down to 80%, and a further reduction, resulting from resurfacings, of the thickness initially reduced to 80% is limited to an approximately 5 mm final thickness by a final resurfacing.

2. The continuous-casting mold according to claim 1 wherein the coolant-passage flow cross-section at the upper melt surface is reduced proportionally to the reduction in the thickness of the mold side plate.

3. The continuous-casting mold according to claim 2 wherein the coolant-passage flow cross-section is reduced not more than 80% of the new state of the initial coolant-passage flow cross-section.

4. The continuous-casting mold according to claim 1 wherein both the reduction in the thickness of the mold side plates as well as the reduction in the coolant-passage flow cross-section is a function of positions of the given coolant passage in the width direction.

5. The continuous-casting mold according to claim 1 wherein the mold side plate is reduced in thickness between 5 mm and 10 mm up to a maximum of 15 mm in 3-10 resurfacings, wherein a single resurfacing consists in removing approximately 0.3 mm to 1.5, at maximum 3 mm, of copper material.

6. The continuous-casting mold according to claim 1 wherein the coolant-passage flow cross-section at the upper melt surface and down to the mold outlet in each case consists of a filler piece attached on the outer face and composed of normal-temperature-resistant material.

7. The continuous-casting mold according to claim 6 wherein the filler piece is adjustable at least in order to reduce the coolant-passage flow cross-section.

8. The continuous-casting mold according to claim 1 wherein at least the mold side plates are designed as cassette plates that in expandable form rest on the outer face on cooled adapter plates.

9. The continuous-casting mold according to claim 8 wherein a separate displacement body is provided on the adapter plate to create the minimum coolant-passage flow cross-section.

10. The continuous-casting mold according to claim 8 wherein the displacement body is designed having different shapes, is stored, and attached so as to be replaceable.

11. A continuous-casting mold into which molten steel is poured and converted into a strand, the mold comprising: a pair of upright and horizontally spaced side walls having outer cold faces turned away from each other and confronting inner hot faces;a pair of end walls bridging the side walls and forming therewith an upwardly open mold cavity in which the molten metal has an upper melt surface; anda respective structure forming with each of the cold faces a respective array of passages extending past a region adjacent the upper melt surface, each passage being of reduced flow cross section in a region adjacent the upper melt surface, each passage lying below the region outward at a predetermined horizontal spacing from the respective hot face, each passage further lying at the region at a closer spacing equal to at least 5 mm and between 20% and 80% of the predetermined spacing below the region.

12. The continuous-casting mold defined in claim 11 further comprising means for pouring molten steel into the cavity such that the steel forms in the cavity a melt having the upper melt surface.

13. The continuous-casting mold defined in claim wherein the reduction in flow cross section of the passages at the region is proportional to the reduction in the spacing.

14. The continuous-casting mold defined in claim 11 wherein the passages are spaced horizontally in each side plate and reduction in flow cross section varies outward from a central location in the respective side plate.

15. The continuous-casting mold defined in claim 11 wherein the structure is a separate plate fitted to the respective cold face.