Tube mould

Abstract

The invention relates to a pipe mold 100 and a method for producing a metal pipe string in a continuous casting plant. The pipe mold 100 comprises: a hollow pipe body 110 with an annular cross-section and with an upper pouring area 112 for molten metal and a lower outlet area 114 for the pipe string 50. The inner contour of the hollow pipe body 110 is wider in the pouring area than in the outlet area. Furthermore, the pipe mold 100 has a mandrel 120 projecting into the pouring area of ​​the hollow pipe body.In order to further develop such a known tubular mold 100 with an already extended pouring area in such a way as to make pouring a metal melt even easier, it is proposed that the inner contour of the annular cross-section of the tubular mold hollow body 110 in the pouring area 112 is formed in the form of a first ellipse a and / or the outer contour of the cross-section of the mandrel 120 in the pouring area is formed in the form of a second ellipse b; that the principal axis of the second ellipse b is rotated relative to the principal axis of the first ellipse a by an angle α>0°; and that the minor axis of the first ellipse is larger than the principal axis of the second ellipse.

Description

[0001] The invention relates to a tubular mold for producing a metal tubular strand in a continuous casting plant. Furthermore, the invention relates to methods for casting the tubular strand.

[0002] Figure 8 shows the structure of a classic tubular mold 100, as it has traditionally been used to produce pipe strands. It essentially consists of a tubular mold hollow body 110 with a mandrel 120 extending into it for casting the pipe strand 50. The casting direction is designated by the reference symbol G. The tubular mold 100 is filled with molten metal to cast the pipe strand. The molten metal is initially held in a ladle 20, is directed from the ladle into an intermediate container 30, and is finally directed from the intermediate container into the tubular mold 100 via a dip tube 40 located to the side of the mandrel 120.

[0003] Some conventional tube molds for casting hollow bodies incorporate internal cooling in the form of spray cooling. A spray cooling system with nozzles through which water is sprayed onto the inside of the tube strand can be flanged to the mandrel. While this type of cooling is efficient, it poses the problem that the resulting steam requires complex removal. From a safety perspective, a oxyhydrogen explosion can occur in the event of an internal breakthrough within the cast tube strand, which can cause significant damage to the continuous casting plant and pose a serious hazard to the operating crews.

[0004] German Auslegeschrift 1136797 discloses a tubular mold according to the preamble of patent claim 1 for producing a metal tubular strand in a continuous casting plant. Specifically, the tubular mold disclosed therein comprises a hollow tubular mold body with an upper pouring area for a molten metal and a lower outlet area for the tubular strand. The pouring area of ​​the tubular mold is widened compared to the inner diameter of the tubular mold hollow body, which corresponds to the outer diameter of the tubular strand to be cast. A mandrel extends into the pouring area of ​​the tubular mold hollow body, which has internal cooling and is capable of eccentric movement.

[0005] Based on this prior art, the invention seeks to further develop a known tubular mold with an already expanded pouring area to further facilitate the pouring of molten metal. Furthermore, the invention seeks to further develop known methods for casting a tubular strand to improve the production of the tubular strand in the mold.

[0006] This object is achieved with regard to the tubular mold by the subject matter of patent claim 1.

[0007] Due to the claimed design of the inner contour of the tubular mold hollow body in the pouring area in the shape of an ellipse, a first widening of the annular gap between the tubular mold hollow body and the mandrel is initially realized there. Furthermore, the mandrel in the pouring area is stressed with an elliptical outer contour in cross-section perpendicular to the casting direction, wherein the main axes of the two ellipses are rotated relative to one another by the angle α > 0°. In this way, according to the invention, a second widening of the annular gap is realized in the pouring area. In this respect, the annular gap in the present invention is doubly widened. In other words: the guiding idea of ​​the invention is not the pouring of molten metal into an elliptical mold, but rather pouring into an enlarged annular gap between two molds, i.e. between the tubular mold hollow body and the mandrel in their respective claimed embodiments.This double extension is created by rotating the two ellipses relative to each other. The angle α is measured, for example, between the two principal axes of the two ellipses.

[0008] The expanded pouring area for the molten metal according to the invention advantageously enables safe and facilitated pouring of the molten metal into the tubular mold. Therefore, tubular strands with thinner wall thicknesses can advantageously be continuously cast than was possible in the prior art. The claimed, preferably double-elliptical design of the pouring area advantageously enables the immersion of one or even two immersion tubes, since the claimed formation of a single ellipse or the claimed rotation of the two ellipses relative to each other at two points enlarges the pouring area. In the directions rotated by the angle α, the pouring area is tapered or narrowed. In other words: the distance between the inner mandrel and the outer mold is increased, thereby forming the locally expanded pouring area.This initially creates a pipe strand in the pouring area with circumferentially varying wall thicknesses; however, this is negligible in the pouring area for the uniform solidification of the melt, since the strand shell of the pipe strand to be cast that initially forms in the pouring area or shortly thereafter is still very thin and soft, i.e. still deformable.

[0009] The term "metal" refers in particular to steel, but also includes non-ferrous metals such as aluminum, lead, copper, nickel, tin and zinc, etc., as well as alloys of these metals.

[0010] The term "pipe string" refers to a cast string in the shape of a pipe.

[0011] The term "elliptical" represents any two-dimensional geometric shape that is longer in a longitudinal direction than across it. Examples include rectangles and egg-shaped outlines. The term is not limited to its strict mathematical definition.

[0012] The term "continuous" means the casting of a theoretically endless strand, or that the continuous casting plant is designed accordingly; in particular, the length of the strand is not limited by the configuration of the continuous casting plant. In contrast, "semi-continuous" means the casting of a strand whose length is limited by the configuration of the continuous casting plant.

[0013] The claimed tube mold advantageously enables the production of tube strands in a continuous casting operation using the said continuous casting plant. The claimed tube mold is advantageous compared to the state of the art in terms of both economic efficiency and the quality of the cast tube strands.

[0014] The inner contour of the hollow tube mold body in its exit area forms the outer contour of the cast tube string. The outer contour of the mandrel at its largest circumference determines the inner contour and, in particular, the inner diameter of the cast tube string.

[0015] According to one embodiment of the invention, a concentric shape of the inner contour of the hollow tubular mold body in its outlet region and the outer contour of the mandrel at its end facing the outlet region of the hollow tubular mold body advantageously ensures that the wall thickness of the tubular strand is uniform in the circumferential direction. This applies even though the wall thickness of the tubular strand in the pouring area of ​​the hollow tubular mold body is not constant due to the claimed design with the different ellipses on the outside of the mandrel and the inside of the hollow tubular mold body. The uniform wall thickness applies to any annular cross-section of the annular gap or tubular strand in the outlet region of the tubular mold.The uniform distribution of the wall thickness in the circumferential direction can be realized in particular for a circular-concentric configuration of the said inner contour and the said outer contour relative to each other in the exit area, as well as for elliptical-concentric configurations of the said inner contour and the said outer contour relative to each other. In the case of the concentric configuration of the exit cross-section of the mold with a mandrel, the deformation of the tubular strand takes place over the length of the mold from a cross-section formed by the two ellipses rotated relative to each other to a cross-section formed, for example, by two concentric circles. This deformation follows the shrinkage due to cooling of the two (inner and outer) strand shells.

[0016] According to a further embodiment of the invention, a first cooling circuit is provided for cooling the mandrel internally. The thus cooled mandrel absorbs heat from the surrounding tubing. The temperature difference between the inner surface / strand shell of the cast tubing and the outer surface of the cooled mandrel enables sufficiently effective heat dissipation from the inner (strand) surface of the cast tubing to the cooled mandrel by conduction and radiation.

[0017] According to the invention, a second cooling circuit is provided for cooling the optionally present at least one heat sink. The cooled surface of the heat sink also contributes to the desired cooling and solidification of the cast tubing strand on its inner surface / strand shell. In combination with the cooled mandrel, its cooling effect is enhanced. The first and second cooling circuits can - but do not have to - be operated simultaneously. The first and second cooling circuits can be one and the same cooling circuit, through which a single cooling medium flows. The cooling channels in the mandrel and, if applicable, in the at least one heat sink are then fluidly connected to one another.

[0018] The at least one heat sink is preferably fixedly or movably attached to the lower end of the mandrel and in this respect represents an optional mandrel extension. The maximum outer diameter of the heat sink is less than or equal to the outer diameter of the mandrel at its end facing the outlet of the tubular mold, i.e. preferably less than the inner diameter of the tubing to be cast. Due to the said relationship of the outer diameters, in particular a largely contactless cooling of the cast tubing in its interior by the heat sink is made possible. In order to prevent the friction between the inner surface of the cast tubing and the outside or surface of the mandrel and / or the heat sink from becoming too great, the mandrel and / or the heat sink attached to the mandrel is preferably conical with a tapered end.The conical heat sink is attached to the lower end of the mandrel in such a way that the wider end of the conical heat sink points toward the exit area of ​​the tubular mold, because in this example the heat sink extends beyond the exit area of ​​the mold in the casting direction. Several heat sinks can be hung one behind the other in the form of a chain. The chain can then be attached to the lower end of the mandrel, i.e., the end facing the exit area of ​​the tubular mold hollow body.

[0019] The said conical design of the mandrel and / or the attached heat sink advantageously creates a gap between the strand shell on the inner surface of the cast tubular strand and the heat sink or the mandrel. This gap can advantageously be flooded with a protective gas, e.g. nitrogen or a noble gas such as argon or helium, which advantageously only reduces oxidation. To introduce the protective gas into the said gap, a continuous line for the protective gas is formed in the mandrel and preferably also in the heat sink, which line can be connected to a protective gas source. At least one outlet opening for the protective gas to escape into the said gap, in particular an annular gap, is formed in the mandrel and / or in the heat sink.

[0020] According to a further embodiment, the mandrel and / or the at least one heat sink are coated with graphite on their exterior to ensure a type of emergency running property or lubrication upon contact with the inner strand shell of the cast tubing. Such a coating can minimize the gap between the inner strand shell and the heat sink and possibly eliminate it.

[0021] Furthermore, it is proposed to provide a mandrel oscillation device and / or a hollow body oscillation device. The former serves to oscillate the mandrel and any attached at least one cooling element in the casting direction. The latter serves to oscillate the hollow tubular mold body in the casting direction. According to the invention, the two oscillation devices preferably operate independently of one another. This is advantageous because the lubrication conditions between the outer surface of the tubular strand to be cast and the inner surface of the tubular mold body (first contact surface), on the one hand, and between the inner surface of the tubular strand to be cast and the outer surface of the mandrel (second contact surface), on the other hand, can vary greatly.Although the lubrication conditions at both contact surfaces are essentially determined by the added casting powder or casting oil, the lubrication conditions at both contact surfaces can, as mentioned, be very different due to different flow conditions of the molten metal.

[0022] The preferably independent oscillations of the mandrel and the hollow tubular mold body according to the invention make it possible to individually adapt the parameters of the oscillations to the lubrication conditions on or in the respective contact surfaces and thus to realize overall optimized conditions for the strand lubrication.

[0023] The oscillation parameters for the hollow tubular mold body and the mandrel can be, for example, the stroke, i.e. the amplitude, the frequency or the oscillation shape. According to the invention, these oscillation parameters can be set independently of one another for the mandrel and the mold in order to optimize the lubrication conditions in the respective contact surfaces. A phase shift between the hollow body oscillation and the mandrel oscillation is also conceivable. Likewise, the oscillation of the mandrel can, for example, be stopped and the mold oscillation continued, and vice versa. This allows a further degree of freedom for different casting process situations, such as when pouring on or at the start of casting, during so-called composite casting or at the controlled end of casting, as well as in the event of malfunctions. For this purpose, the mandrel oscillation is designed with regard to the drive technology, the control system and theControl and mechanical guidance are preferably constructed completely independently of the hollow body oscillation.

[0024] According to one embodiment of the present invention, the hollow body of the tubular mold has an inner diameter of at least 350 mm in its exit area. This enables the casting of a tubular strand with an outer diameter of at least 350 mm.

[0025] For the inventive casting process using a tubular mold, outer diameters of this size and larger offer the advantage that, even with relatively thin wall thicknesses, sufficient productivity for industrial production can be ensured. The relatively large outer diameter, combined with a relatively thin wall thickness of, for example, 50 mm, ensures that the cast tubular strand has only a relatively short metallurgical length, even at high casting speeds. This relatively short metallurgical length and the resulting limited mandrel length reduce system complexity and enable reliable hollow casting.

[0026] According to a further embodiment, the ratio of the inner diameter of the hollow mold body, i.e. the outer diameter of the cast pipe strand, to the radial distance between the inside of the hollow mold body and the outside of the mandrel, i.e. to the wall thickness of the cast pipe strand, in the outlet region of the pipe mold is in a range between 1:4 and 1:25, preferably between 1:8 and 1:12. This enables the casting of a pipe strand with a ratio of outer diameter to wall thickness between 1:4 and 1:25, preferably 1:8 to 1:12. This has the advantage that a sufficient wall thickness from the casting process is still available for any forming in a subsequent rolling process.

[0027] The continuous casting plant with the tubular mold according to the invention for casting a pipe strand can be either a purely vertical plant, in which the pipe strand is guided vertically until it solidifies, or an arc-shaped continuous casting plant.

[0028] The above-mentioned object is further achieved by methods for casting a pipe strand according to claims 17 and 21. The advantages of these solutions correspond, on the one hand, to those previously mentioned with reference to the tubular mold. On the other hand, however, the claimed, preferably independent oscillation of the tubular mold hollow body and of the mandrel improves the lubrication of the freshly cast pipe strand in the tubular mold and thus facilitates its production. The alternatively or additionally claimed internal cooling of the mandrel and the cooling elements optionally attached to it also promotes the cooling of the pipe strand in the tubular mold and thus the production of the pipe strand.

[0029] Further advantageous embodiments of the invention of the dependent claims.

[0030] The invention is accompanied by 8 figures, where Figure 1 shows a first exemplary embodiment of a continuous casting plant with the tubular mold according to the invention; Figure 2 shows a cross-section through the pouring area of ​​the tubular mold according to the invention; Figure 3 shows a longitudinal section through the outlet area of ​​the tubular mold according to the invention; Figure 4 shows a second exemplary embodiment of the tubular mold according to the invention; Figure 5 shows a third exemplary embodiment of the tubular mold according to the invention; Figure 6 shows a horizontal cross-section through the cast tubular strand in the outlet area of ​​the tubular mold; Figure 7 shows a mold or hollow body oscillation in comparison to a mandrel oscillation; and Figure 8 shows a continuous casting plant for a tubular mold according to the prior art. shows.

[0031] The invention will be described below with reference to the above Figure 1 - 7described in detail in the form of exemplary embodiments. In all figures, identical technical elements are designated by identical reference numerals. The exemplary embodiments mentioned below can be operated not only individually but also in combination with one another.

[0032] The Figure 1 shows a tube mold 100 according to the present invention for producing a tube strand 50 made of metal in a continuous casting plant, as described in the introduction with reference to Figure 7 was described.

[0033] The tubular mold 100 consists of a hollow tubular mold body 110 with an annular cross-section across its entire height. It has an upper pouring area 112 for pouring in a molten metal and a lower outlet area 114 for the freshly cast and not yet fully solidified tubular strand 50. In addition to the hollow tubular mold body 110, the tubular mold 100 has at least one mandrel 120 extending into the pouring area 112. An annular gap is formed between the inner side of the hollow tubular mold body 110 and the outer surface of the mandrel 120, in which the tubular strand to be cast forms when filled with molten metal. For the sake of simplicity, the annular gap and the tubular strand are denoted equally by the reference numeral 50.

[0034] Figure 2shows a cross-section through the pouring area 112 of the tubular mold hollow body 110 transversely to the casting direction G. The inner contour of the annular cross-section of the tubular mold hollow body 110 - and thus the outer boundary of the annular gap 50 - is designed in the form of a first ellipse and designated by the reference symbol a. The outer contour of the mandrel 120, at its point with the largest diameter in the pouring area 112, is designed according to the invention in the form of a second ellipse and designated by the reference symbol b. The annular gap 50 for pouring in the molten metal is located between the contours a, b. The inner contour of the tubular mold hollow body 110 forms the outer boundary of the annular gap or the pouring area 112. The outer contour of the cross-section through the mandrel 120 at its point with the largest diameter forms the inner boundary of the annular gap.In the annular gap 112, the poured metal melt solidifies progressively in the casting direction G and thus the desired pipe strand is formed with the strand shells on its outside and inside.

[0035] To clarify the shapes of ellipses, the major and minor axes of the ellipses are shown in Fig. 2each designated by a reference symbol. The major axis of the first ellipse a is designated by the reference symbol a.1 and its minor axis by the reference symbol a.2; the following applies: a.1 > a.2. Analogously, the major axis of the smaller second ellipse b is designated by the reference symbol b.1 and its minor axis by b.2; the following applies: b.1 > b.2. The major axis b.1 of the second ellipse b is rotated relative to the major axis a.1 of the first ellipse a by an angle α, here for example α = 90°. Any other angle α with 0° < α ≤ 90°, for example 40° ≤ α ≤ 90°, preferably 80° ≤ α ≤ 90°, are conceivable. In this respect, the two ellipses a and b are also rotated relative to one another by the angle α. At the same time, the minor axis a.2 of the larger first ellipse a is larger than the major axis b.1 of the second ellipse b. Regarding the advantages of this inventive design of the pouring area, reference is made to the above statements in the general part of the description.

[0036] As it passes through the tubular mold 100, the freshly cast tubular strand 50, with its slowly solidifying inner and outer strand shells, undergoes a shrinkage of approximately 1% in its circumferential length. The geometry of the tubular mold 100 accommodates this, as its inner surface tapers in the casting direction G from the pouring area 112 to the exit area 114 of the tubular mold, following the shrinkage of the progressively solidifying metal; see the longitudinal section through the tubular mold 100 according to Figure 3 The exact shrinkage and the local distribution of shrinkage over the length of the mold depends on the casting conditions and the steel grade.

[0037] The following applies to the clear radial distance D between the outer diameter of the mandrel (120) and the inside of the tubular mold hollow body (110) in the pouring area, in particular at the level of the bath level: 50 mm < D < 90 mm.

[0038] The inner contour 111 of the hollow tubular mold body 110 changes in the casting direction G not only for the purpose of adapting to the shrinking metal, but also for the purpose of achieving a preferably constant distribution of the wall thickness d of the tubular strand 50 in the circumferential direction with a desired geometric cross-sectional shape of the tubular strand 50 in the outlet region 114 of the hollow tubular mold body 110.

[0039] According to the invention, the inner contour 111 of the hollow tubular mold body 110 continuously transitions from its elliptical shape in the pouring area 112 in the casting direction G into an elliptical shape with a smaller main axis compared to the inlet area 112 or into a circular shape in the outlet area 114. In addition, according to the invention, the outer contour 121 of the mandrel 120 also continuously transitions from its elliptical shape at the end of the mandrel 120 facing the pouring area 112 of the tubular mold 100 in the casting direction G into an elliptical shape with a smaller main axis compared to the inlet area or into a circular shape at the end of the mandrel 120 or the cooling body facing the outlet area 114 of the tubular mold 100; see Fig. 6 .

[0040] In Figure 1It can also be seen that, for example, three heat sinks 140-1, 140-2, and 140-3 are attached in the form of a chain to the end of the mandrel 120 facing the outlet region 114. The mandrel 120 itself, and preferably also at least some of the heat sinks, are traversed by a continuous cooling channel 132, which is connected to a cooling circuit 130. A cooling medium flows in the cooling circuit and the cooling channels, with which the mandrel and preferably also the heat sinks 140-1, 140-2, 140-3 are cooled from the inside. The cooling medium does not escape to the outside of the mandrel or the heat sinks. The mandrel and the heat sinks are cooled from the inside with the cooling medium. The mandrel and the cooled heat sinks cooled in this way are suitable for absorbing ambient heat radiating from the inner wall of the surrounding freshly cast tubing string and thus cooling the surrounding tubing string 50 from the inside.

[0041] The maximum outer diameter DK of the heat sink is preferably less than or equal to the outer diameter DD of the mandrel at its end facing the outlet 114 of the tubular mold, i.e., in particular, the inner diameter of the tubular strand to be cast. Regarding the associated advantages, reference is made to the general part of the description above.

[0042] Figure 4 shows a second embodiment of the tubular mold according to the invention. It differs from the first embodiment, as shown in the Figure 1is shown, only in that a protective gas source 150 is provided here for providing protective gas, which can be introduced via a line 152 into the mandrel 120 and optionally also into the cooling bodies 140 attached thereto. In particular, at its lower end facing the outlet region 114 of the tubular mold 100, outlet openings 154 are provided for the protective gas to exit from the mandrel 120. Alternatively or in addition to the mandrel 120, lines 152 and outlet openings for the protective gas can also be provided in the cooling bodies 140 (in Fig. 4(not shown). The shielding gas emerging from the outlet openings 154 spreads into the annular gap located there between the tapered mandrel and the inner wall of the freshly cast tubing 50, which have no contact in the lower region of the mandrel 120, as well as generally into the inner cavity of the cast tubing located further down, where it causes reduced oxidation.

[0043] Figure 5Finally, a third exemplary embodiment of the present invention is shown, which comprises, in addition to the hollow body oscillation device 170, as already known from the preceding figures, a mandrel oscillation device 160. As the name suggests, the hollow body oscillation device 170 serves to oscillate the tubular mold hollow body 110 in the casting direction G during the pouring of the molten metal into the tubular mold 100 and during an initial cooling of the tubular strand 50 forming in the tubular mold. In contrast, the mandrel oscillation device 160 is designed to oscillate the mandrel 120 and optionally also the cooling bodies 140 attached thereto in the casting direction G during the pouring of the molten metal into the tubular mold 100 and during an initial cooling of the tubular strand 50 forming in the tubular mold.It is important for the present invention that, as described and justified in the general part of the description above, the mandrel oscillation device 160 and the hollow body oscillation device 170 can be operated completely independently of each other. Alternatively, the two oscillation devices can also be operated synchronously or be of a uniform design.

[0044] This is also reflected in Fig. 7 , in which the mandrel oscillation is illustrated in the top left and the hollow body or mold oscillation in the top right. The respective oscillation parameters are preferably set individually and independently of each other, as described in the introduction. The setting is preferably made depending on the respective lubrication conditions between the inner wall of the hollow tubular mold body 110 and the melt on the one hand, and the outer wall of the mandrel and the melt on the other. Fig. 7It can be seen that the mandrel 120, for example, oscillates at a significantly higher frequency than the hollow tubular mold body 110. The dependence of the different frequencies for the mandrel f D and the hollow mold body f K on the casting speed V g is shown in the middle figure of Fig. 7 Both frequencies increase with increasing casting speed. However, the frequency of the mandrel oscillation increases significantly more than the frequency of the hollow body oscillation.

[0045] In the individual figures, specific embodiments are sometimes shown separately. Nevertheless, all described embodiments, such as the hollow body oscillation, the mandrel oscillation, the cooling, and / or the introduction of the protective gas, can also be implemented in combination with one another. List of reference symbols

[0046] 20Ladle for molten metal 30Intermediate vessel 40Dip tube 50Pipe string; Annular gap 100 Tubular mold 110 Tubular mold hollow body 111 Inner contour 112 Pouring area 114 Exit area 120 Mandrel 121 Outer contour 130 Cooling circuit 132 Cooling channel 140 Heat sink general 140-1 Heat sink 140-2 Heat sink 140-3 Heat sink 150 Shielding gas source 152 Line for shielding gas 154 Outlet opening for shielding gas from the mandrel 160 Mandrel oscillation device 170 Hollow body oscillation device 210 Strand guide a First ellipse or side ellipse d Wall thickness D Wall thickness DD Outer diameter of the mandrel at the outlet end DK Maximum outer diameter of the heat sink GG Pouring direction T nD (%) = T nD / TD , TD = 1 / f DT nD Negative strip time mandrel TD total period time mandrel VD oscillation speed mandrel t oscillation time V g casting speed f D oscillation frequency mandrel T nK (%) = T nK / T , TK = 1 / f KT nK Negative strip time of the mold TK Total period time of the mold VK Oscillation speed of the mold t Oscillation time V g Casting speed f K Oscillation frequency of the mold

Claims

1. A tubular mold (100) for producing a continuously or semi-continuously cast metal tubular strand (50) in a continuous casting plant (200), comprising: a tubular mold hollow body (110) with an annular cross-section and with an upper pouring area (112) for a melt of the metal and a lower outlet area (114) for the tubular strand (50), wherein the inner contour of the tubular mold hollow body (110) in the pouring area is expanded compared to the inner contour of the tubular mold hollow body (110) in the outlet area; and a mandrel (120) projecting into the pouring area of ​​the tubular mold hollow body; characterized by that the inner contour of the annular cross-section of the tubular mold hollow body (110) in the pouring area (112) is in the form of a first ellipse (a) and / or the outer contour of the cross-section of the mandrel (120) in the pouring area is in the form of a second ellipse (b).

2. Tubular mold (100) according to claim 1, characterized in thatthe major axis of the second ellipse (b) is rotated to the major axis of the first ellipse (a) by an angle α>0°; and that the minor axis of the first ellipse is larger than the major axis of the second ellipse.

3. Tubular mold (100) according to one of the preceding claims, characterized by that the inner contour (111) of the tubular mold hollow body (110) continuously transitions from its elliptical shape in the pouring area (112) in the pouring direction (G) into an elliptical shape with a smaller main axis compared to the pouring area or into a circular shape in the outlet area (114).

4. Tubular mold (100) according to claim 3, characterized by that the inner contour (111) of the tubular mold hollow body (110) increasingly narrows in the casting direction (G) from the pouring area (112) to the outlet area (114) - following the shrinkage of the increasingly solidifying metal.

5. Tubular mold (100) according to one of the preceding claims, characterized by that the outer contour (121) of the mandrel (120) transitions from its elliptical shape at the end of the mandrel (120) facing the pouring area (112) of the tubular mold (100) or at its location with the largest diameter in the casting direction (G) continuously into an elliptical shape with a smaller main axis compared to the pouring area or into a circular shape at the end of the mandrel (120) facing the outlet area (114) of the tubular mold (100).

6. Tubular mold (100) according to one of claims 3 to 5, characterized by that the elliptical or circular shape of the inner contour (111) in the outlet region of the tubular mold hollow body (110) is concentric with the elliptical or circular shape of the outer contour (121) of the mandrel (120) at its end facing the outlet region of the tubular mold hollow body (110).

7. Tubular mold (100) according to one of the preceding claims, characterized by thata first cooling circuit is provided; and that the mandrel (120) has cooling channels in its interior which are connected to the first cooling circuit for passing a first coolant for cooling the mandrel (120).

8. Tubular mold (100) according to one of the preceding claims, characterized by that at least one cooling body (140-1) is provided which can be movably attached to the end of the mandrel (120) facing the outlet region (114) of the mold (100) or is fixedly arranged there; that a second cooling circuit is provided; that the heat sink (140-1) has cooling channels in its interior which are connected to the second cooling circuit for passing a second coolant for cooling the heat sink (140-1).

9. Tubular mold (100) according to claim 8, characterized by that the first and second cooling circuits are identical or the same; thatthe cooling channels in the mandrel (120) and in the heat sink (140-2) are fluidly connected to one another; and that the first and second coolants are identical or the same.

10. Tubular mold (100) according to claim 8 or 9, characterized by that the maximum outer diameter of the heat sink is less than or equal to the outer diameter of the mandrel (120) at its end facing the outlet region (114) of the tubular mold (100).

11. Tubular mold (100) according to claim 9 or 10, characterized by that the heat sink is conical and is attached to or fastened to the end of the mandrel (120) facing the outlet region (114) in such a way that the heat sink tapers in the casting direction G.

12. Tubular mold (100) according to one of claims 8 to 11, characterized by thatin the mandrel (120) and preferably also in the cooling body, a continuous line for a protective gas is formed for connection to a protective gas source; and that at least one outlet opening (114) for the protective gas is formed in the mandrel (120) and / or in the heat sink.

13. Tubular mold (100) according to one of the preceding claims; characterized by that the mandrel (120) is designed in its length and arranged in the tubular mold (100) in such a way that the end of the mandrel (120) facing the outlet region (114) of the tubular mold (100) is located in front of the lower end of the tubular mold, at the level of the lower end of the tubular mold (100) or behind the lower end of the tubular mold (100) in the casting direction G.

14. Tubular mold (100) according to one of claims 8 to 13, characterized by that at least one heat sink is coated with graphite on its outside.

15. Tubular mold (100) according to one of the preceding claims, characterized by that a mandrel oscillation device (160) is provided for oscillating the mandrel (120) and the optionally attached at least one cooling body in the casting direction G.

16. Tubular mold (100) according to one of the preceding claims, characterized by that a hollow body oscillation device (170) is provided for oscillating the tubular mold hollow body (110) in the casting direction (G).

17. Tubular mold (100) according to one of the preceding claims, characterized by that for the clear radial distance D between the outer diameter of the mandrel (120) and the inside of the tubular mold hollow body (110) in the pouring area, in particular at the level of the bath level, the following applies: 50 mm < D < 90 mm.

18. Tubular mold (100) according to one of the preceding claims, characterized by thatthe clear inner diameter of the hollow mold body in the outlet area is at least 350mm.

19. Tubular mold (100) according to one of the preceding claims, characterized by that the ratio of the inner diameter of the hollow mold body to the radial distance between the inside of the hollow mold body and the outside of the mandrel in the outlet area of ​​the tubular mold is in a range between 1:4 and 1:25, preferably between 1:8 and 1:

12.

20. A method for casting a metal pipe string (50) using the tubular mold (100) according to one of the preceding claims, comprising the following steps: - pouring a liquid melt of the metal into the tubular mold (100), in particular into its annular gap between the tubular mold hollow body (110) and the mandrel (120); - cooling at least the tubular mold hollow body (110) to at least partially solidify the melt into the pipe string within the tubular mold; and - extracting the at least partially solidified pipe string from the tubular mold (100) characterized by that the hollow tubular mold body (110) and / or the mandrel (120) oscillate in the casting direction (G) during pouring, cooling and / or extraction.

21. Method according to claim 20; characterized by that the hollow tubular mold body (110) and the mandrel (120) oscillate simultaneously; thatbut the oscillation parameters, such as oscillation frequency, oscillation speed, oscillation stroke and / or negative strip time for the hollow body oscillation and the mandrel oscillation are set independently of one another and individually, in particular depending on the lubrication conditions between the inner wall of the tubular mold hollow body (110) and the melt on the one hand and the outer wall of the mandrel and the melt on the other hand.

22. Method according to claim 20 or 21, characterized by that the phase shift between the hollow body oscillation and the mandrel oscillation is also adjusted.

23. Method according to one of claims 20 to 22, characterized by that the mandrel (120) and preferably also the heat sinks (140) attached to the mandrel are traversed by a cooling channel (132) and are internally flowed through by a coolant.

24. A method for casting a metal pipe string (50) using the tubular mold (100) according to any one of the preceding claims 1-19, comprising the following steps: - Pouring a liquid melt of the metal into the tubular mold (100), in particular into its annular gap between the tubular mold hollow body (110) and the mandrel (120); - Cooling at least the tubular mold hollow body (110) to at least partially solidify the melt into the pipe string within the tubular mold; and - Extracting the at least partially solidified pipe string (50) from the tubular mold (100) characterized by that In addition to the tubular mold hollow body (110), the mandrel (120) and preferably also the cooling bodies (140) attached to the mandrel are cooled from the inside.

25. Method according to claim 24, characterized by thatthe tubular mold hollow body (110) and / or the mandrel (120), optionally with attached cooling bodies (140), oscillate in the casting direction (G) during pouring, cooling and / or extraction.

26. Method according to claim 25; characterized by that the hollow tubular mold body (110) and the mandrel (120) oscillate simultaneously; that but the oscillation parameters, such as oscillation frequency, oscillation shape, oscillation speed and / or negative strip time for the hollow body oscillation and the mandrel oscillation are set independently of one another and individually, in particular depending on the lubrication conditions between the inner wall of the tubular mold hollow body (110) and the melt on the one hand and the outer wall of the mandrel and the melt on the other hand.

27. Method according to one of claims 20 to 26, characterized by that the pipe string is cast with an outer diameter of at least 350mm.

28. Method according to one of claims 20 to 27 characterized by that the pipe string is cast with an outer diameter to wall thickness ratio of between 1:4 and 1:25, preferably 1:8 to 1:

12.

29. experienced according to one of claims 20 to 28, characterized by that the strand is cast continuously or semi-continuously.

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