EP3375544B1 - Horizontal strip casting installation with optimised casting belt - Google Patents

Description

The invention relates to a system for horizontal strip casting of a pre-strip made of metal.

From the German patent specification DE 44 07 873 C2 a horizontal strip caster for producing a pre-strip from steel is known. The belt caster has a melting vessel from which the melt is poured through a casting nozzle onto a horizontally rotating casting belt. For cooling the casting belt, a cooling device is arranged under an upper run of the casting belt. On the cooled casting belt, the applied melt solidifies to form a pre-belt. In the area between the casting nozzle and the solidified pre-strip, the strip caster has a housing into which a gas flow is introduced in order to create a reducing or oxidizing atmosphere or an inert gas atmosphere for the melted and the solidifying pre-strip. The gas flow is introduced via nozzles which are arranged in a ceiling element of the housing. In order to be able to influence the surface of the solidifying sliver, the gas flow is varied with regard to its temperature and its speed and pressure profile.

From the German patent specification DE 10 2011 010 040 B3 a horizontal strip caster is also known for producing a pre-strip from steel. A circulating casting belt of the belt caster is coated with a coating compound consisting of a carrier liquid and additives in the area of an upper side facing the pre-belt before a melt is applied. These additives are a wide variety of metals or metallic oxides / nitrides / borides with which the material properties of the sliver can be influenced in a targeted manner. Before the coating mass is cohesively combined with the applied melt by melting, the carrier liquid is removed in a drying unit. In addition to the complete melting of the coating compound and the associated alloying of the pre-strip in the area of mixing, a firmly adhering coating of the steel strip can alternatively be created, the thickness of which can be used to control the heat transfer between the casting strip and the pre-strip and thus the cooling rate of the melt or the pre-strip.

Also the German Offenlegungsschrift DE 10 2012 001 469 A1 relates to a horizontal strip caster for producing a pre-strip. An applied melt solidifies on a casting belt, which is subjected to conditioning in an inline process after the pre-strip has completely solidified. This conditioning comprises at least one of the treatments annealing, drying, straightening, brushing, cleaning, descaling, stretching, smoothing or coating. Possible permanent coatings are ceramics or metal / ceramic compounds. Dispersion layers made of BN, nitrides, oxides or carbides can be used as renewable coatings. The heat transfer between the casting belt and the pre-strip can be controlled on the basis of the coating.

The disclosure document WO 2007/071225 A1 relates to a horizontal strip caster for producing a pre-strip from, in particular, lightweight structural steel. A casting belt is proposed which is provided with a structure in order to reduce the heat transfer and the contact between itself and the strand that has solidified to form a pre-belt. This structure has beads running in the longitudinal direction or knobs distributed over the surface, which are embossed into the casting belt from above.

From the European patent specification EP 0 874 703 B1 a method for producing cast belts is known. To treat the casting belt, which can consist of carbon steel, chromium molybdenum steel or also various copper alloys, it is provided that irregularities are introduced into the outer surface of the casting belt in order to improve the uniformity of the heat transfer. The surface irregularities are produced in the form of grooves or depressions by a laser or mechanical processing on the surface, the depths of which are between 1 and 40% of the thickness of the casting belt.

The German Offenlegungsschrift DE 28 56 472 relates, among other things, to strip casting with a rotating mold for casting aluminum and aluminum alloys. The mold has a roughened surface to control the heat transfer when it comes into contact with the molten metal for the first time. The mold surface has a roughness pattern, which consists of a regular arrangement of pyramidal or truncated cone-like elevations, so that the melt only the tips of these elevations of the mold surface touched.

It is generally known that in the production of sliver strip with a strip thickness of 6 to 25 mm, edge defects often occur, which manifest themselves in an edge of the sliver strip that is flattened towards the edge and in cracks in the edge areas. The occurrence of flattened edges leads to rolling defects and can thus cause edge cracks. The cracks occur in the edge areas of the cast pre-strip and are approximately 30 mm to 100 mm away from the edge. A cooling-related deformation of the melt also occasionally leads to mechanical stresses in the structure of the casting belt, which only cause the sliver to lift off the casting belt only locally and which furthermore lead to cracks in the sliver, since the material only comes close to the solidification point at high temperatures has a low hot ductility. The bulging then leads to the melt shifting in the direction of the middle of the belt and thus already solidified dendrites to come to the belt surface, on which no lid has been formed up to this point in time. This leads to an open porosity, preferably in the areas close to the edge, which leads to surface and structural defects when the tape is processed. These cracks with surface contact also lead to material defects during further processing, which is why the material has to be trimmed and profitability is reduced. The formation of a dense, non-open-pored surface can be hindered by the low heat dissipation on the upper side of the strip and a correspondingly lower solidification rate and unfavorable flow boundary layers due to the flow of the atmosphere.

The German patent application DE 10 2005 062854 A1 , which is considered to be the most relevant prior art, discloses a system for horizontal strip casting of a pre-strip made of metal, with a casting belt with a central area and laterally adjoining edge areas, the casting belt in the area of a the upper side facing the solidifying pre-strip is equipped with a surface structure, and the surface structure has been created by a stamping deformation of the casting strip.

The present invention is based on the object of creating a system for the horizontal strip casting of a pre-strip made of metal, with which an improved geometry and surface of the pre-strip, an increased output and thus a substantial improvement in economic efficiency are achieved.

This object is achieved by a system for horizontal strip casting of a pre-strip made of metal with the features of claim 1. Advantageous refinements are given in claims 2 to 12

According to the invention, a system for horizontal strip casting of a pre-strip made of metal has a casting belt with a central area and laterally adjoining edge areas, the casting belt being equipped with a surface structure in the area of an upper side facing the solidifying pre-strip. An improved geometry and surface of the pre-strip, an increased output and thus a significant improvement in economic efficiency are achieved by the fact that the surface structure is created by a stamping deformation of the casting strip.

In connection with the present invention, an embossing deformation is understood to mean a manufacturing method in which embossments or elevations are created on the upper side of the casting belt together with oppositely arranged elevations or embossing on the underside of the casting belt. Elevations on the upper side of the casting belt thus correspond at the same point with impressions on the underside of the casting belt or vice versa. In this manufacturing process, there may be deviations between the shape of the embossments or elevations on the top and bottom in order to obtain or optimize the desired shape on the top. Overall, this embossing process is particularly suitable for the production of casting belts that it is simple and inexpensive and only material is shifted in the thickness direction of the casting belt by the embossing and thus the original dimensions of the casting belt are retained. There are no or hardly any changes in the length and width of the casting belt, which would result in corresponding reworking.

Furthermore, it applies to the claimed casting belt that its surface structure has a first pattern in the central area and a pattern different from the first pattern in the edge areas.

Finally, in the area of an upper side facing the solidifying pre-strip, the claimed casting belt has a different pattern in the edge areas up to a maximum of 25 cm from the edge in the direction of the middle of the belt and an embossing depth of the structure that is 20 to 75% higher.

By changing the casting strip material and / or the casting strip geometry and structure, the uniform heat dissipation is advantageously effected by preventing the cast pre-strip from lifting off. The homogenization of the cooling conditions across the strip width counteracts any deformation of the cast pre-strip (U-shape). In particular, a different solidification of the pre-strip caused by uneven heat transfer is counteracted and local porosities and voids, which often occur linearly in the casting direction, are thus avoided. Overall, an improvement in the quality, the surface and the geometry of a pre-strip produced, in particular in the case of alloys with low Al contents - preferably Al <0.8% by weight - is achieved through the homogenization of the cooling conditions. The output is also increased and thus the profitability.

It is preferably provided that the casting belt is made of a material with a material, at least in the region of an upper side facing the solidifying preliminary belt

Thermal conductivity of greater than 90 W / mK (at 40 ° C), in particular greater than 100 W / mK (at 40 ° C), is produced and has a casting tape thickness of 0.5 to 3 mm, in particular 1 to 3 mm. Particularly suitable materials are aluminum, an aluminum alloy, copper or a copper alloy.

The use of aluminum, aluminum alloy, copper or copper alloy as casting tape material also enables the casting tape thickness to be increased with the same or improved heat dissipation, which counteracts buckling of the casting tape and, in particular, homogenizes the heat dissipation over the surface.

In an alternative or additional embodiment it is provided that the casting belt is provided with a surface structure at least in the area of an upper side facing the solidifying pre-belt and the surface structure is preferably a teardrop, pyramid, diamond, bead or point pattern with a depth of 0.075 to 0.8 mm in the sense of embossments or elevations. This results in a stiffening of the structure and the downward dissipation of heat is increased and homogenized, and heat conduction is also improved within the casting belt. The result is that, following the production by means of stamping deformation, the casting belt is arranged on an underside of the casting belt, elevations or embossments which lie opposite the embossings or elevations on the upper side of the casting belt.

As an alternative or in addition, a combination of Al- or Cu-containing cast strip material and a surface structure is also possible.

Yet another alternative or additional embodiment provides that a casting belt with reduced thermal conductivity is used. Due to the reduced thermal conductivity of the casting belt, the downward dissipation of heat is delayed and thus the proportion of solidification from the upper side of the preliminary strip is increased and the formation of a cover on the upper side of the preliminary strip is promoted during casting. This is particularly advantageous in the case of steels with an increased tendency to surface defects and open porosity, in which a casting belt made of an alloy with a higher Thermal conductivity would otherwise cause the metallurgical center (area of residual solidification) in the cast sliver to shift towards the surface of the strip. The surface-sensitive grades include, in particular, alloys with an Al content of less than 0.8% by weight and a solidification interval of greater than 30 ° C., as well as steels with a high C and high Si content.

It is preferably provided that the casting belt is made of a material with a thermal conductivity of less than 35 W / mK (at 40 ° C) and a casting belt thickness of 0, to reduce and delay the downward heat dissipation, at least in the area of an upper side facing the solidifying pre-strip. 5 to 3 mm. Stainless steels, steels with a high Cr content and FeNi alloys are particularly suitable as materials. The low expansion coefficients of, for example, FeNi alloys, which additionally counteract buckling of the pre-strip, are particularly advantageous. Also advantageous in the case of stainless steel or steel with a high Cr content, the dense oxide layer (especially Cr ₂ O ₃ ) improves the separation behavior between the cast strip and the cast pre-strip.

In an alternative or additional embodiment it is provided that the casting belt is made of several materials, the casting belt in particular in the edge regions in each case up to a maximum of 25 cm from the edges viewed from another

Material exists as the middle part of the casting belt. Depending on the desired displacement of the metallurgical center, the casting belt can be constructed in such a way that materials with different thermal conductivities are used in a targeted manner in order to influence the local cooling conditions. The difference in thermal conductivity should be at least 20%. Aluminum, aluminum alloys, copper and copper alloys with a thickness of 0.5 to 3 mm are particularly suitable as materials in the middle of the strip. For the edge areas, materials made of micro-alloyed structural steel or stainless steel with a thickness of 0.5 to 3 mm are advantageous.

Yet another alternative or additional embodiment provides that the casting belt has a varying thickness over the belt width. The edge areas have a thickness that is at least 10% different from the center, and the transition between the areas of different thicknesses can take place both gradually and preferably continuously. This optimizes the heat dissipation.

In a further alternative or additional embodiment, it is provided that a casting belt with different material thicknesses between the central area and the edge area is used in conjunction with stainless steels or FeNi alloys with a thickness of 0.5 to 3 mm. The material is selected to be at least 10% thicker in the edge areas than in the central areas. This has the effect of reducing the heat dissipation.

Another alternative or additional embodiment provides that the casting belt consists of a microalloyed structural steel in the middle area and of a high Cr-containing steel or stainless steel in the edge area. The reduced thermal conductivity of the edge area of the casting belt advantageously reduces the heat dissipation, as a result of which an undesirably rapid cooling of the edge areas is avoided.

Furthermore, a further alternative or additional embodiment provides that the casting belt is completely or partially provided with a coating which preferably contains BN, ZrO ₂ , TiO ₂ , Al ₂ O ₃ or AlN. The layer thickness is chosen so that heat transfer is reduced by at least 5%. This reduces heat transfer from the cast pre-strip to the cast strip.

Overall, the reduced heat dissipation leads to a reduction in strip warpage (for example the known U-shape) of the pre-strip produced. This belt warping is caused, among other things, by excessive local heat dissipation in the area of the belt edges.

Overall, with the horizontal strip caster according to the invention, hot strip or sheet material in the desired thickness of 6 to 25 mm (measured in the middle of the strip) with good geometry and an improved surface can be produced from high-manganese or high-aluminum or high-silicon lightweight steels or other high or low-alloy steel.

• Figur 1 eine schematische Seitenansicht einer horizontalen Bandgießanlage,
• Figur 2a eine schematische Draufsicht eines strukturierten Gießbandes,
• Figur 2b eine schematische Draufsicht eines strukturierten Gießbandes und
• Figur 2c eine schematische Draufsicht eines strukturierten Gießbandes.

The invention is explained in more detail below using an exemplary embodiment shown in a drawing. Show it:

• Figure 1 a schematic side view of a horizontal strip caster,
• Figure 2a a schematic top view of a structured casting belt,
• Figure 2b a schematic top view of a structured casting belt and
• Figure 2c a schematic top view of a structured casting belt.

In the Figure 1 The schematic side view of a horizontal strip casting system 1 shown essentially consists of a melting vessel 2, a casting nozzle 3, a casting belt 4 and a housing 5. Liquid melt S, in particular metal melt, is transferred via the melting vessel 2 to the casting belt 4 via an adjoining casting nozzle 3 abandoned in the form of a strand or solidifying pre-strip V. Here, the endless casting belt 4 runs in a casting direction G around a front deflection roller 4a and a rear deflection roller 4b spaced therefrom in the casting direction G and conveys the solidifying pre-strip V in the casting direction G. on which the sliver V solidifies, and divide a lower strand 4d between the front and rear deflection rollers 4a, 4b. A strand 4c, 4d is understood to mean that part of the casting belt 4 extending between the deflection rollers 4a, 4b. The casting belt 4 runs essentially horizontally in the area of the upper run 4c and is cooled from below in the area of the upper run 4c by means of a cooling device 7 which covers almost the entire upper run 4c with the exception of short areas at the transition to the deflection rollers 4a, 4b acted upon by coolant, preferably water. For the sake of clarity, side delimitation elements which are usually present and extend in the casting direction G for the sliver V solidifying on the upper run 4c are not shown. The housing 5 of the horizontal strip caster 1 encloses the solidifying sliver V in an area between the casting nozzle 3 and an outlet 5b for the solidified sliver V from the housing 5. The housing 5 is provided in the usual way to the melt S in a reducing atmosphere , an oxidizing atmosphere, an inert gas atmosphere or a casting atmosphere, which is adapted to the chemical composition of the melt, to cast and to solidify to the pre-strip V. For this purpose, a gas feed line 5c and a gas discharge line 5d are connected to the housing 5 in the area of an upper and essentially horizontally extending ceiling element 5a of the housing 5. The gas supply line 5c is located in the area of the outlet 5b and the gas discharge line 5d in the area of the casting nozzle, so that the gas flows against the casting direction G in countercurrent to the solidifying pre-strip V or vice versa.

Such horizontal strip casting systems 1 are particularly suitable for the production of near-net-shape pre-strip with strip thicknesses in the range from 6 to 25 mm (measured in the middle of the strip) from high-manganese or high-aluminum or high-silicon lightweight steels, electrical sheets or other high or low-alloy steel.

the Figure 2a shows a structured surface of an upper side 4e of the casting belt 4 of the belt casting installation 1 in a first embodiment. This surface is provided with teardrop-shaped patterns 7, 8 with a depth or height of 0.075 to 0.8 mm in the sense of embossments or elevations. In this way, the structure of the casting belt 4 is stiffened and the heat dissipation downwards is increased and homogenized and the heat conduction within the casting belt is also improved. In a preferred embodiment, a first pattern 7 in a central area M on the surface of the casting belt 4 differs from a second pattern 8 of the surface of the casting belt 4 in the edge regions R laterally adjoining the central region M a width of up to a maximum of 25 cm - measured from the edge of the casting belt 4 - on. The second pattern 8 leads to a changed heat transfer, in particular to a reduced heat transfer in the edge areas R, compared to the central area M. According to the manufacturing process of the surface structure by embossing, on the underside of the casting belt 4 the embossments or elevations opposite, elevations or embossings with essentially the same shape can be found in the opposite way. In this manufacturing process, there may be deviations between the shape of the embossments or elevations on the top and bottom in order to obtain the desired shape on the top.

Another embodiment of the structured surface of the upper side 4e of the casting belt 4 is shown in FIG Figure 2b , in which a double-arranged teardrop-shaped pattern 7, 8 - a so-called. Duet pattern - with a depth or height of 0.075 to 0.8 mm in the sense of embossments or elevations. The further configuration is comparable to that previously Figure 2a described.

the Figure 2c shows yet another embodiment of a structured surface of the upper side 4e of the casting belt 4, which is provided with a pattern 7, 8 of laterally adjoining pyramids with a square base with a depth or height of 0.075 to 0.8 mm in the sense of embossments or elevations is. The further configuration is comparable to that previously Figure 2a described.

Alternatively or additionally, in addition to the teardrop-shaped and pyramidal patterns shown, surface structures with other types of teardrop and pyramid patterns and / or with diamond, honeycomb, beading, knob or dot patterns are also conceivable. In particular, trigonal-pyramidal to hexagonal-pyramidal patterns and / or also truncated pyramidal patterns can be selected. In the case of teardrop samples, the samples are based on DIN 59220. Transverse beads and elliptical knobs have a ratio of major to minor axis of 1.8 to 4.8 and are arranged at an angle of 30 to 90 ° to the casting direction G or at right angles to one another or alternately. In addition, both an ordered and a purely random, statistical arrangement of the patterns is possible.

According to the invention, in addition to the structuring of the surface of the top 4e of the casting belt 4 with a different pattern 8 in edge areas R of the casting belt 4, a 20 to 75% higher embossing depth of the pattern 7 of the structured surface of the casting belt 4 in edge areas R is possible, whereby a lifting of the solidifying pre-strip V in the edge area R during the casting process takes place and thereby the heat transfer in the edge area R is reduced.

List of reference symbols

1

horizontal strip caster

2

Melting vessel

3

Pouring nozzle

4th

Casting tape

4a

front pulley

4b

rear pulley

4c

upper run

4d

lower strand

4e

Top

5

Enclosure

5a

Ceiling element

5b

exit

5c

Gas supply line

5d

Gas discharge

6th

Cooling device

7th

first pattern

8th

second pattern

G

Pouring direction

M.

Middle area

R.

Edge area

S.

melt

V

Opening act

Claims (12)

1. Plant for horizontal belt-casting of a pre-strip (V) of metal, with a casting belt (4) with a centre region (M) and edge regions (R) laterally connected therewith, wherein the casting belt (4) is furnished in the region of an upper side (4e), which faces the hardening pre-strip (V), with a surface structure which is created by a pressing-through deformation of the casting belt (4),
   characterised in that

   the surface structure in the centre region (M) is different from the surface structure in the edge region (R) and

   the casting belt (4) at least in the region of an upper side (4e), which faces the hardening pre-strip (V), has in each of the edge regions (R) up to at most 25 centimetres from the edge as seen in the direction of the belt centre a different pattern and a pressing depth of the structure which is 20 to 75% higher.
2. Plant according to claim 1, characterised in that the casting belt (4) at least in the region of an upper side (4e), which faces the hardening pre-strip, is provided with a surface structure and the surface structure preferably has a drop-shaped, pyramidal, lozenge, bead-shaped or punctiform pattern with a depth of 0.075 to 0.8 millimetres in the sense of impressions or elevations.
3. Plant according to claim 2, characterised in that following production by pressing-through deformation [the casting belt (4)] there are arranged on a lower side of the casting belt (4) elevations or impressions which are opposite the impressions or elevations on the upper side (4e) of the casting belt (4).
4. Plant according to at least one of claims 1 to 3, characterised in that the casting belt at least in the region of an upper side (4e), which faces the hardening pre-strip, is produced from a material with a thermal conductivity of more than 90 W/mK (at 40° C).
5. Plant according to at least one of claims 1 to 3, characterised in that the casting belt at least in the region of an upper side (4e), which faces the hardening pre-strip, is produced from a material with a thermal conductivity greater than 100 W/mK (at 40° C).
6. Plant according to claim 4 or 5, characterised in that the material is aluminium, an aluminium alloy, copper or a copper alloy.
7. Plant according to at least one of claims 1 to 3, characterised in that the casting belt (4) at least in the region of an upper side (4e), which faces the hardening pre-strip (V), is produced from a material with a thermal conductivity of less 35 W/mK (at 40° C).
8. Plant according to claim 7, characterised in that the material is a stainless steel, a steel with high chromium content or an FeNi alloy.
9. Plant according to at least one of claims 1 to 8, characterised in that the casting belt (4) at least in the region of an upper side (4e), which faces the hardening pre-strip (V), is made from several materials, wherein the casting belt (4) in each of the edge regions (R) up to at most 25 centimetres as seen from the edges consists of a different material with a thermal conductivity differing by at least 20% from the centre region of the casting belt (4).
10. Plant according to at least one of claims 1 to 8, characterised in that the casting belt (4) at least in the region of an upper side (4e), which faces the hardening pre-strip (V), has a varying thickness over the belt width and the edge regions (R) have a thickness different by at least 10% relative to the centre regions (M) and the transition between the regions of different thickness takes place not only in steps, but also continuously.
11. Plant according to at least one of claims 1 to 10, characterised in that the casting belt (4) has different material thicknesses between centre region (M) and edge region (R) in conjunction with stainless steels or FeNi alloys and the material in the edge regions (R) is selected to be at least 10% thicker than in the centre regions.
12. Plant according to at least one of claims 1 to 11, characterised in that the casting belt (4) at least in the region of an upper side (4e), which faces the hardening pre-strip (V), is completely or partially provided with a coating which contains BN, ZrO₂, TiO₂, Al₂O₃ or AIN.

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