EP1792675A2 - Mold for continuous casting of metal - Google Patents

Abstract

A permanent chill mold (1) for the continuous casting of metal comprises a mold cavity (2) having a pouring slot (3), an exit opening (4) and a casting cone (6). At least one concave bulging (7) is provided that extends in the casting direction (G), which begins at a distance (A) below a predetermined casting bath level position (5) and extends up to the exit opening. The beginning of the concave bulging is in an initial region that extends 30-70 (preferably 50)% of the mold cavity length (L), measured from the pouring slot. The distance between the predetermined casting bath level position and the concave bulging is greater than 10 (preferably greater than 20)% of the length (L) of the mold cavity. Conicity at the deepest part of the concave bulging decreases down to at most 0% per meter. Conicity at edges of the bulgings decreases to 0.6-1.5% per meter. Adjacent bulgings form an undulating profile, and an imaginary center line of the undulating profile forms a determining optimum line for design of the permanent chill mold with regard to conicity. The concave bulging is produced at least partially by a depositing method. A contour of the concave bulging is produced at least partially by material removal.

Description

The invention relates to a mold for the continuous casting of metal with the features of the preamble of claim 1.

Tubular molds of copper or copper alloys for casting profiles of steel or other high melting point metals have been widely described in the art. Mold tubes usually have a uniform wall thickness in a horizontal cross-sectional plane, which increases in the strand direction due to the internal conicity of the mold tube. The conicity can be the same over the entire length of the mold. But it can also be used over the length variable Konizitäten used, in particular, the conicity in the region of the pouring be greater and decrease in the casting direction in order to follow the shrinkage of the cast strand during cooling particularly well and thereby ensure good heat dissipation.

Basically, measures for optimizing the conicity have the predominant goal of improving the heat dissipation in the casting direction by adapting the inner contour to the shrinkage of the strand shell. The majority of molds used today is optimized in terms of taper to a certain operating point, the operating point of several parameters depends, such. Casting speed, steel composition and cooling conditions. If If there are deviations from the predetermined operating point, the geometry selected can lead to disturbances in the casting process and the quality of the strand, because with the onset of solidification of the molten metal in the casting mirror, the so-called strand shell forms on the strand. If the geometry of the mold tube is incorrect, the strand shell can lift off and twist or, in the opposite case, that is to say if the shrinkage is too low, can lead to high friction on the mold tube. A jerking of the strand, strand breaks or even breakthroughs can be the result. The air gap between mold tube and strand shell also causes uneven heat dissipation, the strand shell melts again with the result of external and internal cracks in the strand. There are therefore many efforts to adjust the conicity exactly to a particular application, thereby achieving optimal casting speeds.

In the EP 0 958 871 A1 For this purpose, it is proposed that the conicity varies at least in a partial length of the casting cone along a circumferential line such that each section of the circumferential line forms a smooth curve between the corner regions and the conicity decreases in the casting direction. Although this embodiment of the mold cavity for a certain set of parameters represents the theoretically optimal geometry, in practice, nevertheless parameter fluctuations occur, for example due to the temperature control or by changing steel compositions, which make it impossible to permanently maintain the predetermined operating point of the mold exactly.

On this basis, the invention has the object to show a mold for continuous casting of metals, in which high casting speeds can be driven at desired strand quality even if there are deviations from the operating point and change the shrinkage ratios of the metal within the mold.

This object is achieved in a mold with the features of claim 1.

It is essential in the case of the mold according to the invention that at least one concave bulge extending in the casting direction is provided, which starts at a distance below a predetermined pouring mirror position and extends up to the outlet opening. Preferably, a plurality of concave bulges are provided so that in the lower height portion of the mold to a certain extent a wave-shaped profiling over the entire circumference or even partial circumference areas results, in contrast to the normally straight side surfaces. The at least one concave bulge allows that the strand shell of the solidified metal in deviations from the operating point, that is, when the shrinkage is changed, more or less in the bulge provided for it. However, the strand shell is always guided safely, so that, for example, a twisting or rhomboidity of the strand shell can be avoided. For casting parameters that lead to increased shrinkage, the proposed mold geometry allows the strand shell to be guided preferably on the higher lying surfaces, that is to say on the edges of the concave bulges. In the reverse case, that is, if the shrinkage of the strand shell is too low, it can dive slightly more in the concave bulges. Despite the immersion, the friction between the strand shell and the hollow body is substantially less than in cross-sectional contours with substantially straight circumferential contours.

Although it is to be accepted in the mold designed according to the invention that the contact of the casting strand from the predetermined Gießspiegellage to the outlet opening is not completely solid and due to the resulting slightly worse cooling not quite maximum casting speeds can be driven, however, the process safety is significantly improved without noticeable loss of quality. In addition, the vast majority of the surface of the mold cavity is in direct contact with the melt or the solidifying strand shell, since the bulges do not extend over the entire length of the mold cavity, but only begin at a distance below the predetermined Gießspiegellage. This means that the region which lies above the bulges is essentially smooth, that is to say in particular has no such bulges as are only provided in the lower height region of the mold. Exceptions to this are, of course, pouring funnels, which begin, for example, in convex pipes at about the level of the casting mirror and extend approximately to half the length of the mold cavity.

Advantageous embodiments of the inventive concept are the subject of the dependent claims.

The at least one concave bulge begins in an initial region extending from 30% to 70%, preferably 40% to 60%, of the mold cavity length as measured from the gate. In particular, the at least one bulge begins halfway down the mold cavity. It is not mandatory that all bulges begin at exactly the same altitude. It is quite conceivable that the bulges begin at different altitudes. It is essential that the bulges begin in a region in which a sufficiently thick strand shell has already formed, which already has a certain dimensional stability. Therefore, the distance between the predetermined Gießspiegellage and the at least one concave bulge is to be sized sufficiently large. Preferably, the distance is greater than 10%, in particular greater than 20% of the length of the mold cavity. It is advantageous at least one concave bulge per surface of the mold cavity available.

It is considered particularly advantageous if the conicity decreases more rapidly in the lowest part of the at least one concave bulge than at the edge of the concave bulge. In particular, the taper in the deepest of the concave Bulge decreases to 0% per meter, while the conicity at the edges of the bulges decreases within a range of 0.6% per meter to 1.5% per meter. In other words, the depth of the bulges in the casting direction increases.

In the design of the mold according to the invention, a certain theoretical operating point is likewise to be assumed with regard to the conicity, the consequent course of the conicity in the region of the bulges being defined neither exclusively by the edges nor by the deepest of the bulge. Rather, it is provided that adjacent bulges form a wave profile, wherein the imaginary center line of the wave profile forms the decisive for the design of the mold with respect to the taper optimum line. When the working point of the mold is reached, this means that part of the strand shell moves into the bulges, while another part is supported on the edges or wave crests of the wave profile. In case of deviations of the shrinkage, that is in case of deviations from the optimum line, the strand shell is still guided by the concave bulges within the mold. It only comes to an increase or decrease in friction, but without the risk of strangling or strand breakage.

It is envisaged that the taper at the edges of the bulges, that is, at the wave crests, will decrease to within a range of 0.9% per meter to 1.1% per meter. For example, if the taper is to decrease from 2.5% per meter at the initial casting cone to 0.5% per meter and the conicity at the edges of the bulges is 1% and at the bottom of the concave bulge is 0%, it follows in that the center line of the wave profile corresponds approximately to a desired 0.5% per meter taper.

The maximum depth of the concave bulges measured from the edges of the bulges to the deepest is in a range of 0.3 mm to 1 mm, and is preferably about 0.5 mm. The depth increases due to the faster decrease in conicity in the deepest of the concave bulge in the casting direction, the maximum depth is reached at the outlet opening.

In order to avoid material stresses within the cast strand and to achieve a uniform wear pattern of the mold cavity, it is considered advantageous to arrange the concave bulges in a symmetrical in cross-section rectangular, polygonal or cylindrical mold cavity. In the case of a cross-sectionally cylindrical mold cavity, the bulges are preferably arranged diametrically. For cylindrical mold cavities, the number of concave bulges may also be odd. In this case, a uniform distribution, i. a rotationally symmetrical distribution of the bulges over the circumference sought, the arc extends between two adjacent recesses over 360 ° / n, where n = number of bulges. In the case of a rectangular or polygonal mold cavity, in a preferred embodiment, concave bulges are accordingly provided in each mold side.

Cracks or kinks in the course of the conicity can be avoided by virtue of the fact that the conicity of the hollow shaped body which is location-dependent in the casting direction is a curve which can be described by a continuous function. This means in particular that the concave bulges do not start abruptly, but have a smooth, rounded as possible transition, which can be described by a continuous curve. Alternatively, the contour can also be described by a suitable and sufficiently large number of straight line sections. Also in the circumferential direction, that is, transversely to the casting direction, the contour of the concave bulges should be a curve that can be described by a function that can be described as continuous in the ideal case. Alternatively, the contour may be composed of straight lines and / or circular sections. By rounded and smooth as possible transitions, the friction between the strand shell and the mold cavity can be reduced.

The mold according to the invention can be reshaped to contour without cutting. Of course, for the formation of at least one concave bulge and a machining is possible. It is considered particularly advantageous if the contour of the at least one concave bulge is at least partially produced by a deposition process. Deposition processes within the meaning of the invention are preferably electrolytic deposition processes in which metals such as e.g. Chromium, copper and nickel or their alloys are deposited on the inner surface of the mold cavity. The desired contour of the concave bulges can be achieved by suitable electrode guidance or the electrode geometry, so that different thicknesses of coating are obtained. In principle, it may be sufficient to produce the desired geometry of the concave bulges exclusively by the deposition process. However, if concave bulges with large depths are desired, it may be desirable to combine a chipless or chip forming with a deposition process so that the contour of the at least one concave bulge is at least partially made by a deposition process. Basically, a coating of the mold cavity is recommended to increase the wear resistance and thus the life of the mold. For this reason, too, it is expedient to provide thicker coatings on the edges of the concave bulges than in the deepest of the concave bulges, since in the deepest a lesser wear is to be expected than at the exposed edges of the bulges.

The contour of the at least one concave bulge may be at least partially, i. optionally in combination with another processing method, produced by a deposition process, e.g. by an etching process, erosion, laser ablation or by electrochemical processes.

Figur 1

im Längsschnitt eine Seitenwand einer Kokille;

Figur 2

Ausschnitte aus zwei unterschiedlichen Querschnittsebenen I und II der Figur 1 in vergrößerter Darstellung;

Figur 3

die Konizität der Seitenwand der Kokillenplatte der Figur 1, aufgetragen über ihre Länge;

Figur 4

eine perspektivische Ansicht eines Kokillenrohrs in Blickrichtung auf den Kokillenaustritt;

Figur 5

die Konizität einer Seitenwand der Kokille der Figur 4, aufgetragen über ihre Länge;

Figur 6

einen Teilbereich einer Kokillenplatte mit zwei konkaven Ausbauchungen in einer ersten Ausführungsform und

Figur 7

einen Teilbereich einer Kokillenplatte mit zwei konkaven Ausbauchungen in einer zweiten Ausführungsform.

The invention will be explained in more detail with reference to an embodiment shown in the schematic drawings. Show it:

FIG. 1

in longitudinal section a side wall of a mold;

FIG. 2

Excerpts from two different cross-sectional planes I and II of Figure 1 in an enlarged view;

FIG. 3

the taper of the side wall of the mold plate of Figure 1, applied over its length;

FIG. 4

a perspective view of a Kokillenrohrs in the direction of the Kokillenaustritt;

FIG. 5

the taper of a side wall of the mold of Figure 4, applied over its length;

FIG. 6

a portion of a mold plate with two concave bulges in a first embodiment and

FIG. 7

a portion of a mold plate with two concave bulges in a second embodiment.

Figure 1 shows a longitudinal section of the wall of a mold 1 for continuous casting of metal. The illustration is purely schematic, is in no way to scale and is merely illustrative of the inventive concept.

The mold 1 is formed symmetrically with respect to its central longitudinal axis MLA. The mold 1 is made of copper or a copper alloy and is cooled from the outside in a manner not shown, so that a molten metal introduced into the mold 1 solidifies from outside to inside and forms a strand shell. The illustrated mold 1 has for this purpose a specially contoured mold cavity 2, wherein the conicity K on the shrinkage behavior of the Molten metal is set. The mold cavity 2 has a pouring opening 3 and an outlet opening 4. The casting direction is indicated by the arrow G. During the continuous casting process, the molten metal is held within a predetermined Gießgliegellage 5. The Gießspiegellage 5 varies due to the process within certain limits to the predetermined Gießspiegellage 5, that is, the desired position. The mold 1 is cooled from the outside, thereby sets below the Gießspiegellage 5 a solidification of the molten metal, it forms the strand shell, which shrinks in the course. The casting cone denoted by 6 compensates for the volume decrease of the melt or the strand shell to some extent. The conicity K of the casting cone 6 changes in the longitudinal direction of the mold 1. The taper K starts at about 2.5% per meter and decreases in the casting direction G up to about 0.5% per meter.

The mold 1 according to the invention is divided into two different height ranges in this embodiment. The upper height range H1 extends from the pouring opening 3 to half the length L of the mold 1. The lower height range H2 begins in the middle of the mold 1 and extends to the outlet opening 4. It is essential that the lower height range H2 at a distance A below the predetermined Gießspiegel position 5 begins, since the lower height range H2 has a very special contouring to compensate for different degrees of shrinkage. This contouring begins only in the lower height range H2, where a sufficiently solid strand shell has formed. In the mold 1 according to the invention extending concave bulges 7 are provided in the casting direction G, which extend to the outlet opening 4. The depth T of the bulges 7 increases in the casting direction G. The bulges 7 do not start abruptly, but have a depth T, which increases slowly in the casting direction G. A smooth transition to the upper height range H1 results from the fact that the bulges 7 in the casting direction G have a more strongly decreasing conicity K2 in the deepest 9 of the bulges 7 than at their edges 8. Details will be explained below with reference to FIG.

FIG. 2 shows, with a double-dotted line, the surface contour of the casting cone 6 in the region of the cross-sectional plane I, as shown in FIG. The second line represents the course of the surface contour at the outlet opening 4. It should be noted that the curves are greatly oversubscribed for illustration and therefore not coincide with the dimensions of Figure 1. It can be seen that the amplitude in the cross-sectional plane II is greater than in the cross-sectional plane I. This means that the depth T of the bulges in the casting direction G increases. In the cross-sectional plane I, the depth T1 is only about half as large as in the cross-sectional plane II, where between the lowest 9 and the mold cavity 2 facing edge 8, the depth T2 is to be measured. At the same time, it can be seen that the conicity K decreases more sharply in the deepest 9 of the bulges 7 than between the edges 8, since the deepest 9 in this illustration have a smaller distance from one another than the edges 8.

The mold 1 is designed so that the middle position MI or MII of the drawn wave profile 10 corresponds to the relevant in terms of taper optimum line. In this case, the respective center line M1, M2 is composed of the kokillenlängsrichtungsabhängigen position of the deepest 9 and the edges 8 of the bulges 7 together. FIG. 3 clarifies this situation. It can be seen that the conicity K in the vicinity of the pouring opening 3 is relatively high at 2.5% per meter and decreases continuously in the casting direction G. Approximately in the middle of the mold at L / 2 begin the bulges 7, wherein the total conicity K of the conicity K1 and the taper K2 composed. The conicity K1 is measured in each case at the edges 8 of the bulges 7 and indicated by a dot-dash line. The conicity K2 is measured at the respective deepest points of the bulges 7 and is indicated by a dashed line. The conicity K1 at the edges 8 decreases only slowly and moves in the order of 1% per meter. On the other hand, the conicity K2 decreases more rapidly in the lowest 9 of the bulges 7 and is even 0% per meter at the outlet opening 4 of the mold 1. The superposition of the conicities K1, K2 leads to the total conicity K in the order of about 0.5% per meter.

Due to the additional bulges 7 in the lower height range H2 of the mold 1, it is possible to compensate for parameter fluctuations caused by different casting temperatures, alloy composition or by different layers of the mold level within certain limits. Clamping of the strand, which lead to a strand stumbling, strand breaks or even strand breaks, thereby avoided.

FIG. 4 shows a perspective view of a mold 11, the reference numbers to FIGS. 1 and 2 which have already been introduced being used below to describe the geometry. The mold cavity 2 of the mold 11 is divided in the casting direction G substantially into two sections. The pouring opening 3 facing the upper height range is smooth, with approximately half the length of the mold 11 is followed by a lower height range, which has a plurality of concave bulges. In each case a concave bulge 7 is provided in the middle of each mold side 12. In addition, the corner regions 13 between two adjoining Kokillenseiten 12 are provided with bulges 7. All bulges 7 are viewed transversely to the casting direction, performed rounded, which is a juxtaposition of curve sections. In essence, in the mold 11 of Figure 4 is that the concave bulges 7 start at a certain distance below the predetermined Gießspiegellage and extend to the outlet opening 4. The geometry of the bulges 7 is selected such that, with regard to the conicity, an optimum line results, which is defined neither by the deepest 9 nor the edge 8 of the bulges 7, but by the superimposition of all the conicities.

5 shows the course of the conicity of the exemplary embodiment of FIG. 4. It can be seen that the taper K3 is initially constant in the region of the pouring opening and then continuously decreases in the casting direction. The conicity K3 initially decreases quite sharply, with the graph K3 flattening in the direction of the outlet opening 4. In the lower altitude range, ie from about U2, start the concave bulges 7 in the individual Kokillenseiten 12. K4 stands in this context for the conicity, which is measured in the lowest 9 of the bulges 7. K5 stands for the conicity measured at the edges 8 of the bulges 7. The taper K4 in the deepest of the bulges 7 drops to 0 at L / 2, while the conicity at the edges 8 of the bulges 7 is about 1. The mean taper K3 lies between conicities K4 and K5.

Figures 6 and 7 show sections of Kokillenseiten 12, in each of which differently configured bulges 7a, 7b are introduced. The length of the bulges 7a, 7b with respect to the illustrated Kokillenseite 12 is irrelevant in this context, since only the geometry of the bulges 7a, 7b to be explained.

The depth T and the width B of the bulges 7a, 7b continuously increase in the casting direction. However, it can be seen that the radius R1 of the bulge 7a is constant over the entire length. This geometry results from a penetration of a relative to the surface of the mold side 12 slightly inclined circular cylinder with the mold side 12. To obtain a transverse to the casting direction G rounded geometry, the transitions to the edges 8 of the bulges 7 a were rounded.

The embodiment of Figure 7 differs from the previous one in that the radius of the bulges in the casting direction increases. It can be seen that the radius R2 at the narrow end of the bulge 7b is smaller than the radius R3 at the wide end of the bulge 7b. This geometry results from a penetration of the mold plate 12 with a circular cone, wherein the vertical axis of the circular cone runs parallel to the surface of the mold cavity. Of course, this circular cone can also be additionally inclined to vary the depth and width of the bulge 7b. Also in this embodiment, the edges 8 of the bulge 7b are rounded, so that on the exit side results in a sense a corrugated profile.

Reference numerals:

1

- mold

2

- Mold cavity

3

- pouring opening

4

- outlet

5

- Gießspiegellage

6

- casting cone

7

- bulge

7a

- bulge

7b

- bulge

8th

- edge v. 7

9

- Deepest v. 7

10

- Wave profile

11

- mold

12

- Kokillenseite

13

- corner area

MLA

- Center longitudinal axis v. 1

G

- casting direction

H1

- upper altitude range

H2

- lower altitude range

L

- Length of the mold

A

- Distance between 5 and H2

B

- width v. 7a

T

- Depth

T1

- Depth

T2

- Depth

R1

- radius v. 7

R2

- radius v. 7a

R2

- radius v. 7b

MI

- middle position v. 10 at I

MII

- middle position v. 10 at II

K

- conicity

K1

- conicity

K2

- conicity

K3

- conicity

K4

- conicity

Claims (17)

Mold for continuous casting of metal with a mold cavity (2), wherein the mold cavity (2) has a pouring opening (3), an outlet opening (4) and a pouring cone (6), characterized in that at least one in the casting direction (G) extending , concave bulge (7, 7a, 7b) is provided, which starts at a distance (A) below a predetermined Gießspiegel (5) and extends to the outlet opening (4). Chill mold according to claim 1, characterized in that the beginning of the at least one concave bulge (7) is in an initial region, the initial region extending from 30% to 70% of the mold cavity length (L) measured from the pouring orifice (3). Chill mold according to claim 2, characterized in that the at least one concave bulge (7) begins halfway (L) of the mold cavity (2). Chill mold according to one of claims 1 to 3, characterized in that the distance (A) between the predetermined Gießspiegellage (5) and the at least one concave bulge (7) is greater than 10%, in particular greater than 20% of the length (L ) of the mold cavity (2). Chill mold according to one of claims 1 to 4, characterized in that the conicity (K, K3) in the lowest (9) of the at least one concave bulge (7) decreases faster than at the edge (8) of the at least one concave bulge (7). Chill mold according to one of claims 1 to 5, characterized in that the conicity (K2) in the deepest (9) of the at least one concave bulge (7) up to max. 0% per meter decreases. Chill mold according to one of claims 1 to 6, characterized in that the conicity (K1) at the edges (8) of the bulges (7) decreases within a range of 0.6% per meter to 1.5% per meter. Chill mold according to one of claims 1 to 7, characterized in that adjacent bulges (7) form a wave profile (10), wherein the imaginary center line (MI, MII) of the wave profile (10) for the design of the mold with respect to the taper (K ) forms a definitive optimal line. Chill mold according to one of claims 1 to 8, characterized in that the concave bulges (7) are arranged symmetrically in a rectangular in cross-section, polygonal or cylindrical mold cavity (2). Chill mold according to claim 9, characterized in that the concave bulges (7) are arranged diametrically in a cylindrical cross-section in the mold cavity (2). Chill mold according to one of Claims 1 to 9, characterized in that at least one concave bulge (7) is provided in each mold side (12) of a rectangular or polygonal mold cavity (2). Mold according to one of claims 1 to 11, characterized in that in the casting direction (G) location-dependent conicity (K) of the mold cavity (2) is a writable by a continuous function curve. Mold according to one of claims 1 to 11, characterized in that in the casting direction (G) location-dependent conicity (K) of the mold cavity (2) is defined by a juxtaposition of curved and / or straight sections. Chill mold according to one of claims 1 to 13, characterized in that the contour of the at least one concave bulge (7) transversely to the casting direction (G) is a writable by a continuous function curve. Chill mold according to one of claims 1 to 13, characterized in that the contour of at least one concave bulge (7) is defined transversely to the casting direction (G) by a juxtaposition of curved and / or straight sections. Chill mold according to one of claims 1 to 15, characterized in that the contour of the at least one concave bulge is at least partially produced by a deposition process. Chill mold according to one of claims 1 to 15, characterized in that the contour of the at least one concave bulge is at least partially produced by a removal process.

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