Method for producing foundry ingots

Abstract

The invention relates to a method for producing foundry ingots (1), in particular from steel, wherein liquid metal is discharged into an ingot mold (15) which is open at the bottom or a static mold either directly from a casting ladle (11) or via an intermediate vessel (12), and when an ingot mold (15) which is open at the bottom is used, the at least partially solidified foundry ingot (1) is drawn from the ingot mold (15) in the direction of the longitudinal axis (5) by means of a drawing piston (28), which is vertically movable in the direction of a longitudinal axis (5) of the foundry ingot (1) and on which the foundry ingot (1) is at least indirectly arranged.

Description

[0001] Process for producing cast blocks

[0002] State of the art

[0003] The invention relates to a method for producing cast blocks, in particular made of steel, having the features of the preamble of claim 1.

[0004] A method having the features of the preamble of claim 1 is known from DE 10 2017 108 394 A1 by the applicant. The method known from the cited document is characterized in that the resulting cast ingot is rotated at least temporarily around its longitudinal axis during the casting process so that its microstructure in the solidified state has a high quality. High quality here means that the cross-section of the resulting cast ingot is as homogeneous and free of segregation as possible, and with as few or as small pores and cavities as possible. For this purpose, a device for carrying out the known method has a withdrawal die that is vertically movable and rotatable in the direction of the longitudinal axis of the cast ingot, on which the cast ingot is at least indirectly arranged, wherein the withdrawal die serves to withdraw the cast ingot from the mold during the casting process.

[0005] Disclosure of the invention

[0006] The method according to the invention for producing cast ingots, in particular of steel, with the features of claim 1 has the advantage that it surprisingly enables the desired high quality, ie a homogeneous and segregation-free cross-section of the cast ingot with as few or as small a size pores and cavities as possible, even if the turning or rotation of the cast ingot only takes place when the casting process is completed.

[0007] A completed casting process is understood in the context of the invention to mean that either no further liquid metal is poured into the mold to form the cast ingot, or the point in time at which at least 95% of the liquid metal melt has been poured into the mold to produce the respective cast ingot and / or that the partially solidified cast ingot has been moved from the casting position to another treatment position. The method according to the invention is particularly used for cast ingots that have a relatively large cross-section and thus typically also a relatively high mass with correspondingly long solidification times. In particular, the method according to the invention makes it possible to separate the casting process from the rotation process of the mold or the cast ingot in terms of time and, if necessary, also space. This can, for example, result in a simplified design of the withdrawal die and, if necessary, also makes it possible toto be able to dispense with devices for rotating or turning the casting block arranged in the casting chamber of the foundry plant.

[0008] In the latter case, after the end of the casting process, it is sufficient to move the ingot to an area outside the casting chamber, where the molten metal is discharged into the mold, and rotate it there around its longitudinal axis. During this post-treatment period of the ingot, the casting chamber can be prepared, for example, for a new casting process, so that the method according to the invention also enables particularly high productivity of the foundry plant.

[0009] Alternatively, it is of course also conceivable to rotate the casting block around its longitudinal axis in the area of ​​the casting chamber, i.e. below the device for pouring the liquid metal.

[0010] Against the background of the above explanations, it is therefore provided in a method according to the invention for producing cast blocks with the characterizing features of claim 1 that the cast block has a cross-sectional area of ​​at least 0.2m 2 and that the casting block is rotated at least temporarily about its longitudinal axis after the end of the casting process.

[0011] Advantageous further developments of the method according to the invention for producing cast blocks are listed in the subclaims.

[0012] There are different options for how the casting block is rotated after the end of the casting process, depending, for example, on the geometry or cross-sectional area of ​​the casting block, the material used and other parameters.

[0013] In a first variant of the process, the turning of the cast ingot is carried out continuously until it has completely solidified. Alternatively, however, it is also possible for the turning of the cast ingot to take place intermittently until it has completely solidified.

[0014] Regardless of whether the cast ingot is rotated continuously or intermittently, a preferred variant of the rotation or turning of the cast ingot is for the rotation of the cast ingot in at least one direction of rotation with a changing angular speed. The changing angular speed enables improved mixing of the metal in the area of ​​the solidification front between the already solidified area of ​​the cross-section of the cast ingot and the still liquid core of the cast ingot due to the turbulence that occurs there as a result of the speed differences.

[0015] It is particularly preferred if the rotation of the cast ingot occurs in alternating directions, with the angle of rotation in one direction being at least 45°. Changing the direction of rotation when rotating the cast ingot temporarily creates particularly strong turbulences or differences in the relative speed between the already solidified and the still liquid metal in the solidification front between the solidified area of ​​the cast ingot and the still liquid core of the cast ingot. This promotes the mixing of the still liquid metal to improve quality.

[0016] Furthermore, it can be provided that the pause times are changed during intermittent rotation of the cast ingot, preferably such that the pause times become shorter as the cast ingot solidifies. The background to this consideration is that the rotational angular velocity when rotating the cast ingot at the solidification front of the cross-section of the cast ingot is reduced as the cast ingot solidifies, since the solidification front moves towards the core of the cast ingot. As a result, the difference between the rotational speed tends to decrease due to reduced speed differences between the already solidified metal in the region of the solidification front and the still liquid material, which negatively affects mixing. This situation can be counteracted by faster changes or shorter pause times between the rotational movements of the cast ingot.

[0017] In principle, it is possible for the solidifying ingot to be rotated in a position below the ladle or tundish, as is the case during the casting process. This is particularly suitable if the vertically adjustable drawing-off ram is already equipped with appropriate rotating devices for rotating the mold.

[0018] Alternatively, it is also possible for the ingot to be rotated in a position where the ingot is positioned laterally relative to the casting position, or outside a casting chamber where the metal is poured into the mold. Such a method enables, in particular, faster access to the casting chamber area and thus the possibility of converting or preparing the casting system for casting a new ingot more quickly.

[0019] If long stationary molds (i.e. molds whose length corresponds to the length of the casting ingot plus an additional free space above the casting ingot) are used instead of short, water-cooled molds, it is particularly advantageous, in connection with the turning of the casting ingot while it is still on the drawing-off die, if the casting ingot is rotated together with the mold. This makes it possible, for example, to implement the device for turning the casting ingot using corresponding rollers or similar devices that are arranged in operative connection with the outside of the mold and / or the casting ingot. Furthermore, it is also conceivable for the casting ingot to be partially still in the mold for turning. In this case, the casting ingot has a round cross-sectional area, whereby the casting ingot is rotated independently of the mold, which is arranged in a rotationally fixed manner with respect to the longitudinal axis of the casting ingot.When using a standing crucible (with a closed bottom), the rotation of the casting block can also take place together with the standing crucible.

[0020] Further advantages, features and details of the invention will become apparent from the following description of preferred embodiments of the invention and from the drawings.

[0021] Short description of the drawings

[0022] Fig. 1 shows in a highly simplified longitudinal section a device for producing a cast block and

[0023] Fig. 2a to

[0024] Fig. 2d exemplary diagrams to explain the rotation of the casting block after the end of casting.

[0025] Embodiments of the invention

[0026] The device 10 shown in Figure 1 serves to produce a cast block 1 made of metal 2, in particular steel, with a cross-sectional area of ​​preferably more than 0.2m 2and a length of, for example, up to 5m or even greater. The cross-sectional area of ​​the cast block 1 can, for example, be circular, rectangular, or square, or any other desired shape.

[0027] The device 10 comprises a pouring ladle 11, from which the liquid metal 2 can be discharged via a possibly present distribution vessel 12 with a pouring nozzle 13 into a downwardly open, short, water-cooled mold 15. The mold 15 has a section 16 facing the distribution vessel 12, which section can optionally be surrounded by an induction coil 17 or heating device for heating the mold 15. On the side facing away from the distribution vessel 12, a section 18 of the mold 15 adjoins the upper section 16, which section can optionally be radially surrounded by an electromagnetic stirrer 19. The casting level 3 of the molten metal is located, for example, in the region of the lower section 18 of the mold 15, wherein the casting level 3 can be covered by powder (not shown) for (heat) insulation. Furthermore, it should be mentioned that the internal cross-section of the mold 15 is adapted to or corresponds to the cross-section of the cast ingot 1 to be formed.

[0028] It should also be mentioned that in the illustrated embodiment, the mold 15 is designed as a short, water-cooled mold 15 radially enclosing the casting ingot 1, as is known from the prior art in continuous casting. However, it is also possible to use a long, usually uncooled, downwardly open or sleeve-shaped mold 15 instead, the length of which corresponds to the length of the casting ingot 1 plus an additional free space above the casting ingot 1, as is known per se from the prior art. Alternatively, a so-called standing crucible can be used, which has a bottom. On the side facing away from the tundish 12, a cooling device 21 is optionally arranged below the mold 15 and is arranged in operative connection with the casting ingot 1.Optionally, a further electromagnetic stirrer 22 can be provided below the mold 15, which is arranged to be movable longitudinally in the direction of the double arrow 23 in the direction of a longitudinal axis 5 of the casting block 1.

[0029] Provided beneath the cast ingot 1 is a plate 25, which may be cooled and forms a base 26 for the cast ingot 1 on the side facing the cast ingot 1. The plate 25 is connected to a withdrawal ram 28, which is connected to a longitudinal column 30 via a cross member 29. The cross member 29 or the withdrawal ram 28 is arranged so that it can be raised and lowered in the direction of the longitudinal axis 5 by means of a drive (not shown). Furthermore, it is provided that the plate 25 is also rotatably mounted about the longitudinal axis 5 and can generate an active rotation of the cast ingot 1 about the longitudinal axis 5 by means of a drive 32.

[0030] By way of example, it is shown that the rotation of the plate 25 and the cast block 1 occurs clockwise according to the arrow 33. The drive 32 is preferably designed such that, depending on the application, it can move the cast block 1 or the plate 25 but also in an oscillating manner, for example by at least 45° around a central position of the cast block 1, as well as at different rotational angular speeds w according to a predetermined speed profile, which will be explained in more detail below.

[0031] If no plate 25 rotatable about the longitudinal axis 5 by means of a drive 32 is provided, rollers 35 acting on the outer circumference 6 of the cast block 1 above the plate 25 can be used as an alternative, for example, which rollers 35 are each rotatably mounted about an axis 36 and driven by a drive 37. Typically, several such rollers 35 are provided, preferably at equal angular intervals around the longitudinal axis 5.

[0032] During the production of the cast ingot 1, the cast ingot 1 is withdrawn downwards from the mold 15 in the direction of the longitudinal axis 5 by means of the withdrawal punch 28. The withdrawal speed of the cast ingot 1 can be uniform or discontinuous, whereby, if necessary, a lifting of the cast ingot 1 in the direction of the mold 15 can also be provided in the meantime.

[0033] The liquid metal 2 solidifies within the casting block 1 from the outer circumference 6 of the casting block 1 in the direction of the longitudinal axis 5 in the region of a so-called solidification front EF.

[0034] After the regular end of the casting, it may be provided that liquid metal continues to be poured into the mold 15 in accordance with the disclosure of WO 2015 / 101553 A2 to compensate for the shrinkage of the molten metal.

[0035] Essential to the invention is that the rotation of the cast ingot 1 only begins after the end of casting, or at least only temporarily after the end of casting. Within the scope of the invention, the end of casting is understood in particular to be the point in time at which at least 95% of the molten metal for producing the respective cast ingot 1 has been poured into the mold 15.

[0036] The rotation of the casting block 1 about its longitudinal axis 5 can take place according to Fig. 1 in a position of the casting block 1 or the mold 15 in which the casting block 1 is still below the distribution vessel 12 or partially at the level of the mold 15, ie viewed in the horizontal direction it maintains the position it assumed during the casting process.

[0037] Alternatively, it can also be provided that the casting block 1 has been completely withdrawn or lowered from the mold 15 for turning and is located laterally below the distribution vessel 12 or is moved out of the area of ​​the casting chamber shown in Fig. 1 and is turned on a separate device or outside the casting chamber.

[0038] Figs. 2a to 2d show advantageous diagrams for explaining the rotation of the cast ingot 1. The angular velocity w of the cast ingot 1 about its longitudinal axis 5 is plotted against time t.

[0039] Firstly, Fig. 2a shows the case in which the angular velocity w over time t in the phases in which no acceleration or reversal of the direction of rotation of the cast ingot 1 takes place is constant and has the value + / - wi. Furthermore, the time periods Δt during which the cast ingot 1 rotates in one or the other direction of rotation are of equal length. This typically represents the simplest case of the rotation of the cast ingot 1. The angle of rotation during which the cast ingot 1 is rotated in a specific direction of rotation is at least 45°, but preferably a multiple thereof, e.g. 3600°, i.e. the cast ingot 1 is rotated ten times around its own longitudinal axis 5 before a reversal of the direction of rotation takes place.

[0040] Figure 2b illustrates the case in which the rotational angular velocity w is first continuously increased in one direction to the value +wi and then decreased again. After passing the zero point, it is then accelerated in the other direction to the value -CÜI and then decreased again. Thus, a continuous rotation of the casting ingot 1 takes place without any standstill phases.

[0041] Fig. 2c shows the case in which the cast ingot 1 rotates with increasing angular velocity w over time t, while at the same time the time periods At during which a rotation of the cast ingot 1 takes place in one or the other direction of rotation are reduced, as are the time periods At during which no rotation of the cast ingot 1 takes place.

[0042] Finally, Fig. 2d shows the case in which there are standstill phases between the rotations of the casting ingot 1, during which the casting ingot 1 is not rotated. The casting ingot 1 is thus rotated only intermittently.

[0043] The methods described so far can be modified or altered in a variety of ways without deviating from the inventive concept. For example, according to the enlarged section in Fig. 2d, it can be provided to superimpose a sinusoidal rotational speed component on the rotational speed w during the rotation of the cast ingot 1 in one direction of rotation, so that the rotational speed w fluctuates around a mean value. Combinations of the rotational angular velocity curves shown in Figures 2a to 2d can also be provided.

[0044] Furthermore, the device 10 can be modified in a variety of ways without deviating from the inventive concept.

[0045] 1 cast block

[0046] 2 Metal

[0047] 3 casting levels

[0048] 5 Longitudinal axis

[0049] 6 Outer circumference

[0050] 10 Device

[0051] 11 Ladle

[0052] 12 distribution vessel

[0053] 13 Pouring nozzle

[0054] 15 mold

[0055] 16 upper section

[0056] 17 Induction coil

[0057] 18 lower section

[0058] 19 stirrers

[0059] 21 Cooling device

[0060] 22 electromagnetic stirrer

[0061] 23 Double arrow

[0062] 25 plates

[0063] 26 stand space

[0064] 28 deduction stamps

[0065] 29 cross members

[0066] 30 Longitudinal column

[0067] 32 drive

[0068] 33 Arrow

[0069] 35 roll

[0070] 36 Axis 37 Drive co Angular velocity t Time

Claims

Claims 1. Method for producing cast blocks (1 ), in particular from Steel, wherein liquid metal is discharged either directly from a pouring ladle (11) or via an intermediate vessel (12) into a downwardly open mold (15) or a standing crucible, wherein the at least partially solidified cast ingot (1) is, when using a downwardly open mold (15), vertically movable in the direction of a longitudinal axis (5) of the cast ingot (1), Withdrawal punch (28), on which the cast block (1) is arranged at least indirectly, is withdrawn from the mold (15) in the direction of the longitudinal axis (5), characterized in that the cross-sectional area of ​​the cast block (1) is at least 0.2m 2 and that the casting block (1) is rotated at least temporarily about its longitudinal axis (5) after the end of the casting process.

2. Method according to claim 1, characterized in that the rotation of the cast block (1) takes place continuously until the cast block (1) has completely solidified.

3. Method according to claim 1, characterized in that the rotation of the cast block (1) takes place intermittently until the cast block (1) has completely solidified.

4. Method according to one of claims 1 to 3, characterized in that the rotation of the cast block (1) takes place in at least one direction of rotation with a changing rotational angular speed (w).

5. Method according to one of claims 1 to 4, characterized in that the rotation of the cast block (1) takes place with a changing direction of rotation, wherein the angle of rotation in one direction of rotation is at least 45°.

6. Method according to one of claims 3 to 5, characterized in that the pause times (At) between the rotation phases of the cast ingot (1) are changed, preferably in such a way that the pause times (At) become shorter with increasing solidification of the cast ingot (1).

7. Method according to one of claims 1 to 6, characterized in that the turning takes place in a position of the casting block (1) in which the casting block (1) is located in a position below the casting ladle (11) or the intermediate vessel (12), as during casting.

8. Method according to one of claims 1 to 6, characterized in that the turning takes place in a position of the casting block (1) in which the casting block (1) is located in a position arranged laterally to the casting position or outside a casting chamber.

9. Method according to one of claims 1 to 8, characterized in that the cast block (1) is located in a position outside the mold (15) for turning.

10. Method according to one of claims 1 to 8, characterized in that the cast block (1) is still partially in the mold (15) for turning, that the cast block (1) has a round cross-sectional area, and that the casting block (1) is rotated independently of the mold (15) arranged in a rotationally fixed manner with respect to the longitudinal axis (5) of the casting block (1), or that the casting block (1) is rotated together with a standing crucible.

Images