EP2483017B1 - Mould - Google Patents

Description

The invention relates to a mold plate with the features of claim 1.

During casting, in particular continuous casting of metals, in particular steel, mold plates made of copper materials experience a considerable heat load, which is very high especially in the region of the casting bath level and in particular in fast casting continuous casting plants with casting speeds of significantly more than 2 m / min. This heat load leads to material changes in the copper material or to cracks, whereby the service life of the mold is greatly reduced.

In fast casting continuous casting plants, e.g. in thin slab plants, today almost exclusively a CuAg alloy is used as the copper material. Especially when new mold plates are used for the first time, they must be taken out of the production process and replaced after a relatively short time, since bulges occur in the casting or bath mirror area. Due to the bulges, it can lead to a flow of the underlying material, so that the bulge is ultimately durable and the corresponding mold plate must be reworked.

Copper based on a CuCrZr, a CuCoBe or a CuNiBe alloy shows less bulging, but tends to sink Thermal cycling earlier crack formation than CuAg-based copper materials. Therefore, copper materials based on CuCrZr, CuCoBe or CuNiBe, especially in the rapid continuous casting process of slabs, are used only in exceptional cases.

It belongs to the state of the art to provide casting molds with grooves or grooves in order to reduce thermal stresses in the casting mold ( US 3,437,128 . DE 12 96 746 B . JP 2004 19 5517 A . JP 62 114745 A . EP 0 237 318 A2 ). Partially, the grooves are filled to increase the life of the mold. The grooves are filled with more ductile metals than those of the casting mold in order to allow a greater elongation of the surface layers of the forming part of the casting mold without the risk of penetration of cast metal into the grooves ( DE 12 96 746 B ). Another approach is to introduce particularly hard materials into the grooves to provide improved protection against wear ( US Pat. No. 3,349,836 ).

The invention is based on the object to show a mold plate, in which both bulges and cracks in the bathroom mirror area can be avoided, whereby the service life of the molds can be increased and copper materials in particular CuCrZr-, CuCoBe- or CuNiBe alloys during rapid casting can be used.

The invention is achieved by a mold plate having the features of patent claim 1.

The subclaims relate to advantageous developments.

It is essential that at least one expansion joint is arranged in the casting surface, wherein the expansion joint has a width which is so small that no molten metal penetrates into the expansion joint during the casting process. Due to the expansion joints, it is favored that the copper material can expand in several directions according to the heat loads. As a result, unilateral bulges of the mold are avoided. Harmful internal stresses can be reduced or completely avoided. In addition, a rapid cooling of the molds without cracking is possible.

A special feature is that the width of the expansion joint is chosen very small, and so small that a molten metal can not enter the expansion joint due to their surface tensions. With the mold according to the invention different metal melts can be cast, but especially steel, aluminum or copper alloys.

The expansion joints have the function of compensating for thermal expansions of the material areas lying between the expansion joints and preventing the formation of cracks during rapid cooling. By default, molds on their contact side to the molten metal plan or performed with very light surface textures, where overall there is still a nearly flat surface. These textures have a relatively small influence on the conditions in the bath level of molten metal. An expansion joint is not to be understood as a surface texture, but basically has a much greater depth than width. The ratio between depth and width is at least 10: 1, in particular 20: 1 to 50: 1. The expansion joints have a very narrow width, which lies in a range of 0.1 to a maximum of 0.4 mm. The mouth-side width should not be greater than 0.4 mm during the casting process, ie at maximum thermal load on the casting mold. It is no larger than 0.4 mm even at room temperature.

The width of the expansion joints depends not only on the surface tension of the molten metal, but also on the distance of the expansion joints. Primarily, it must be ensured that no molten metal penetrates into the expansion joints. On the other hand, however, the expansion joint must also be wide enough to be able to compensate for the thermal expansion of adjacent material areas. It is considered advantageous if the width at least in the region of the mouth, ie at the casting area near the expansion joint, during the casting process by at least 90% reduced compared to the measured width at room temperature. Preferably, the expansion joints are arranged at a distance from each other, which is chosen so that the expansion joints are closed by thermal expansion during the casting process in the maximum mouth side. That is, the expansion joints are open at room temperature, but are sized and arranged to close largely or completely by thermal expansion.

The expansion joints can be arranged parallel and / or transversely to the casting direction. The expansion joints may also be arranged in certain patterns, for example in honeycomb form or diamond shape. The expansion joints can be made straight or curved in their course. The expansion joints need not all have the same cross-section or the same length. The design and arrangement of the expansion joints depends on the specific application.

Depending on the position of the expansion joints they can be arranged in different distances. In principle, however, the aim is to arrange the expansion joints so that they close at the mouth side during the casting process.

For manufacturing reasons, the side walls of the expansion joints can be parallel to each other at room temperature. In principle, it is also possible to form the expansion joints as undercuts or with a width that is slightly larger towards the mouth side than towards the bottom of the joint. The choice of the joint geometry is made dependent on the temperature gradient in the respective area of the casting mold.

The expansion joints should contribute to the absence of tension within the mold. Therefore, the joint bottom of the expansion joints may either be at an angle to the side walls of the expansion joints, i. be square, or even rounded, to avoid voltage spikes.

Essential for the function of the stress compensation is that the expansion joints have a certain minimum depth. In particular, the depth of the expansion joints should be such that the deepest, ie the lowest point of the expansion joints, is thermally as free of stress as possible by cooling. The casting mold is always cooled. For this purpose, cooling channels in the form of cooling grooves or cooling holes are mounted on the back of the mold. The expansion joints are to extend to a depth of the mold in which occur due to the back cooling during the casting process no temperature-induced and leading to bulges of the mold tensions. For this purpose, the expansion joint may have a depth at its lowest point which is at least 8 mm.

The depth of the expansion joints may be downwards, i. in the casting direction, decrease as the temperature load continuously decreases with increasing distance from the casting mirror. The expansion joint must be designed so long that the joint bottom always remains sufficiently tension-free. The joint bottom can therefore run from top to bottom with decreasing depth at a shallow angle straight to the casting surface.

For a tension-free course is provided in particular that the depth of the expansion joint decreases towards the ends of the expansion joints. The joint bottom can be curved in a longitudinal section.

The expansion joints are temporarily closed for the casting start. For this purpose, a filler is provided, which dissolves during the casting process from the expansion joints. In this way, it is possible to provide expansion joints of relatively large width, which close only at elevated temperatures or are reduced in width so far that no molten metal can penetrate into the expansion joint. The filler is graphite paste.

The expansion joints are located in the area of the highest temperature load during casting. It is possible that the expansion joints start above the casting level, or that an upper end of the expansion joints is located above the casting level. It is also conceivable that the expansion joints are arranged completely below the casting mirror.

A particular advantage of the casting mold according to the invention is that due to the geometric design, copper materials based on a CuCrZr, CuCoBe or a CuNiBe alloy can also be used. It has been shown that when casting with CuAg alloys as a copper material for casting molds, especially in rapid casting, it can not be prevented that the near-surface layers of mold plates are heated to temperatures above 350 ° C in the bath level range, whereby a recrystallization of the copper material begins. As a result, the copper material becomes coarse-grained and soft and loses resistance to erosion and other attacks. A particular effect that is found in CuAg materials is the strong bulge at first use. The local bulge in the bathroom mirror area prevents adjustment of the narrow sides of the mold during casting. at A renewed casting start can cause large gaps between narrow side and broad side near the bulge.

CuCrZr-, CuCoBe- and CuNiBe-based copper materials do not or only very gradually change their material properties at the temperatures during casting. However, these copper materials also experience internal thermal stresses due to the heat introduced during the casting process. The sudden temperature fluctuations due to sudden changes in the level of the bath level or at the end of the casting process very quickly lead to cracks in these latter copper alloys, which undesirably limit the range of use of this copper alloy. With the invention, however, it is possible, in particular CuCrZr alloys having a chromium content of 0.65% and a zirconium content of 0.1% and CuCoBe alloys having a cobalt content of 1.0% and a beryllium content of 0.1% and CuNiBe Alloys with a nickel content of 1.5 wt .-% and a beryllium content of 0.2 wt .-% also for fast casting operations, especially in continuous casting molds use.

Due to their small width, the expansion joints can be machined, for example by using very thin saw blades. It is also possible to burn in the expansion joints with a laser or to produce them by suitable erosion processes. Other machining forms and the combination of the exemplified manufacturing processes are not excluded.

Figur 1

einen Querschnitt durch einen Teilbereich einer Gießform bei Raumtemperatur;

Figur 2

den Querschnitt der Figur 1 während des Gießbetriebs;

Figur 3

eine Gießform mit einer Beschichtung auf der Gießfläche;

Figur 4

eine Gießform mit Dehnfugen, die durch ein Umschmelzverfahren geschlossen worden sind;

Figur 5

einen Längsschnitt entlang der Linie V-V der Figur 4;

Figur 6a-c

Draufsichten auf eine Gießfläche einer Gießform mit unterschiedlich orientierten Dehnfugen.

The invention will be described below with reference to the FIGS. 1, 2 and 6 illustrated embodiments explained in more detail. The other figures are not embodiments for which protection is desired. They serve to illustrate the inventive idea. It shows:

FIG. 1

a cross section through a portion of a mold at room temperature;

FIG. 2

the cross section of FIG. 1 during the casting operation;

FIG. 3

a mold having a coating on the casting surface;

FIG. 4

a mold with expansion joints that have been closed by a remelting process;

FIG. 5

a longitudinal section along the line VV of FIG. 4 ;

Figure 6a-c

Top views of a casting surface of a mold with differently oriented expansion joints.

FIG. 1 shows a small section of a casting mold made of copper material, in particular in the form of a mold plate of a continuous casting mold.

FIG. 1 shows a cross section through a portion of a mold in the form of a mold plate. The casting mold 1 has a casting surface 2 facing a molten metal, not shown in more detail. In the casting surface 2, a plurality of expansion joints 3 are arranged, which run parallel to one another and are perpendicular to the casting surface 2. The expansion joints 3 are identically configured and have a width B which is so small that no molten metal penetrates into the expansion joint 3 during the casting process. In this embodiment, the width B is 0.4 mm. The expansion joints 3 are filled with a filler 4 in the form of graphite paste. During the casting process, this filler 4 dissolves from the expansion joints 3. At the casting start, it prevents the entry of molten metal in the expansion joints. 3

The illustrated expansion joints 3 are open at their mouth side 5. They have a depth T which is substantially greater than the width B and is preferably at least 8 mm. The expansion joints 3 extend into a depth region of the casting mold 1, which lies close to cooling recesses 6 which project from the back 7 of the illustrated casting mold 1 into the casting mold 1. The cooling recesses 6 are flowed through by cooling water. The depth T of the expansion joints 3 is dimensioned such that the lowest of the expansion joints 3 is free from thermal stresses by cooling in the region of the cooling recesses 6. However, it is inevitable that the copper material of the mold 1 thermally expands close to the casting surface 2, as in FIG. 2 can be seen. Since the temperature in the region of the casting surface 2 is the greatest, the mouth 8 of the expansion joints 3 closes during the casting process, so that no molten metal penetrate into the expansion joint 3 can. The expansion joints 3 therefore have during the casting process from the groove bottom upwardly conically narrowing cross-section.

The expansion joints 3 are ideally arranged at a distance A from one another, which is dimensioned such that the distance A, measured at room temperature, plus the width B, measured at room temperature, the distance C of the mouths 8 of the expansion joints during the casting corresponds. In other words, the condition A + B = C holds. In this state, there are no thermal stresses in the region of the mouth 8 and thus not bulges of the mold 1 in the direction of the molten metal. Upon cooling, the distance C of the mouths 8 decreases again to the distance A at room temperature. The expansion joints 3 open again at the mouth, so that there is no cracking within the casting surface 2 or the casting mold 1. The side walls 9 of the expansion joint 3 then run parallel to each other again, as in FIG. 1 is shown, and are no longer at an angle to each other, as it is FIG. 2 shows.

FIG. 3 shows a variant in which the mouth side 5 of the expansion joint 3 is closed by a wear-reducing coating 10. The expansion joints 3 prevent cracking of the copper material in this variant or contribute to avoid bulges. This works in particular even if the coating 10 has been removed by progressive wear of the mold 1.

In addition to the embodiment of the FIG. 3 It should be noted that the bottom of the joint 11 is rounded off by way of example for all other embodiments. The joint base 11 may also be angular, as in the embodiments of the Figures 1 and 2 can be seen.

The embodiments of the FIG. 4 is different from the one of FIG. 3 in that the expansion joints 3 are not closed on the outlet side by a coating 10, but by a remelting process, such as, for example, the friction stir welding.

FIG. 5 shows a sectional view taken along the line VV of FIG. 4 , It can be seen that the depth T of the expansion joint 3 decreases toward its ends 12.

In particular, the joint base 11 is rounded to a certain extent in the longitudinal direction of the expansion joint 3. The transition from the lowest of the expansion joint 3 to the casting surface 2 is thus not abrupt, but continuously.

The Figures 6a-c show three different embodiments of a possible course of the expansion joints 3. These are each views of the casting surface 2 of a mold 1. In the variant according to FIG. 6a the expansion joints 3 extend parallel to each other in the casting direction G of the molten metal, which flows past the casting mold in the image plane from top to bottom. The alternative embodiment according to FIG. 2 shows expansion joints 3, which are oriented transversely to the casting direction G. The variant according to FIG. 6c shows crossing expansion joints 3, so that a checkerboard or honeycomb pattern arises. Any other orientation of the expansion joints 3 is possible. The course of the expansion joints is not necessarily linear straight, but may be curved. Just as the course of the expansion joints may vary, it is possible to vary the depth, width and spacing of the expansion joints 3.

Reference numerals:

1 -

mold

2 -

casting surface

3 -

expansion joint

4 -

filler

5 -

mouth side

6 -

cooling recess

7 -

back

8th -

muzzle

9 -

Side wall

10 -

coating

11 -

Primer

12 -

The End

A -

distance

B -

width

C -

distance

G -

casting

T -

depth

Claims (7)

1. Mould made of a copper material having a casting surface (2) that faces a metal melt, wherein at least one expansion joint (3) is arranged on the casting surface (2), the expansion joint (3) having a width in the range from 0.1 to 0.4 mm, the ratio of the depth (T) to the width (B) being at least 10 : 1 and the expansion joint (3) being filled with a filler in the form of a graphite paste.
2. Mould according to claim 1, characterised in that the depth (T) of the expansion joints (3) decreases towards the ends (12) of the expansion joints (3).
3. Mould according to claim 1 or 2, characterised in that side walls (9) of the expansion joints (3) extend parallel to one another at ambient temperature.
4. Mould according to one of claims 1 to 3, characterised in that the expansion joints (3) are arranged in the region of the highest temperature stress on the mould plate (1).
5. Mould according to one of claims 1 to 4, characterised in that the copper material is a CuCrZr, a CuCoBe or a CuNiBe alloy.
6. Mould according to one of claims 1 to 5, characterised in that the base (11) of the expansion joint (3) has a transition radius.
7. Mould according to one of claims 1 to 7, characterised in that the ratio between the depth (T) and width (B) of an expansion joint (3) is in the range from 20 : 1 to 50 : 1.

Images