EP3235579B2 - Strand guiding device and method for supporting a cast strand - Google Patents

Description

The invention relates to a method for supporting a cast strand with a rectangular cross-section according to claim 1.

According to the prior art, strand guiding devices are known in the continuous casting of slabs with a rectangular cross section, in which guide rollers, so-called foot rollers, with a cylindrical outer contour for strand support on the narrow side of the strand shell box are used. In 8 such a guide roller, which has a cylindrical outer contour, is shown in cross section. In the ideal case, such cylindrical foot rollers can be used to guide or hold the strand shell box in a rectangular shape. However, after contact with such foot rollers, ie downstream or behind these foot rollers in the transport direction of the cast strand, the cast strand tends to bulge again due to the ferrostatic internal pressure of the liquid steel and the creep processes occurring within the strand shell. In such a case, the slab produced deviates from the desired cross section.

Another disadvantage of using guide rolls with a cylindrical outer contour to support slabs is that higher compressive forces occur at their edges because the strand shell is pressed against the roll edge by the internal pressure of the liquid steel. If the guide roller is set too far against the strand shell box, this leads to pressure points that can appear as visible tracks on the finished slab.

Out of DE 101 19 550 A1 a method and a device for producing continuously cast starting material are known. Here, a cast strand is a

Subjected to preliminary profiling by rollers with a convex outer contour being pressed into the surface of the strand shell on the long side. As a result, a concave groove is formed on the surface of the cast strand on its long side, the concave groove being enlarged or reshaped by the use of further rollers with a larger diameter. In any case, the contact of the rollers with a convex outer contour leads to a permanent deformation of the cast strand that is not reversible.

DE 195 20 939 C1 shows a strand guiding device with the features of the preamble of claim 1 or of claim 3. In this case, carriers are provided on the outlet side of the continuous casting mold, on which rollers for guiding the strand are arranged. In order to adapt to a changing shrinkage of the strand, it is provided that the carrier, and thus the rollers attached thereto, can be adjusted transversely to the direction in which the strand is drawn off. The individual rollers, which are rotatably mounted on the respective brackets, each have a cylindrical cross section, and thus suffer from the disadvantages mentioned above.

From the article by Chang Ho Moon et al. "Effect of the Roll Surface Profile on Centerline Segregation in Soft Reduction Process"; ISIJ International, Vol. 52 (2012), No. 7, 13 July 2012, pages 1266-1272 is a generic strand guide device with the features of the preamble of claim 1 and claim 3 is known.

Accordingly, the object of the invention is to use simple means to optimize the desired shape accuracy of a cast strand during continuous casting.

This object is achieved by a method having the features specified in claim 1. An advantageous further development of the invention is defined in the dependent claim.

A strand guide device is used to support a cast strand with a rectangular cross section, namely when the cast strand emerges from the continuous casting mold in a transport or withdrawal direction. For this purpose, the strand guide device comprises at least one guide roller, which is rotatably mounted about an axis of rotation, wherein the guide roller can be brought into contact with the cast strand with its outer contour running in the direction of the axis of rotation, in order to suitably guide and support the cast strand. The outer contour of the guide roller is convex and designed in such a way that its longitudinal extension along the axis of rotation is adapted to a narrow side of the rectangular cast strand. For the purposes of the present invention, this means that the overall length of the guide roller in the direction of its axis of rotation, and thus also the course of the crowned, convex outer contour of this guide roller, correspond at most to a length of the strand shell box on the narrow side of the rectangular cast strand. In this case, the convex outer contour of the guide roller is crowned, with the convex, outwardly curved curve of the guide roller beginning directly at the end faces of the guide roller and running in the direction of the central area of the guide roller.

According to a further embodiment, the strand guide device comprises at least one guide roller, which is rotatably mounted about an axis of rotation, wherein the guide roller can be brought into contact with the cast strand with its outer contour running in the direction of the axis of rotation, in order to suitably guide and support the cast strand. The outer contour of the guide roller is spherically convex, with the largest diameter of the outer contour of the guide roller in comparison to a diameter of the guide roller at the roller ends, ie on its end face, having a maximum value of 1.5 and a minimum value of 1.0. Such a guide roller can be provided to be employed either against the narrow side of a cast strand or against the longitudinal side of a cast strand.

In the last-mentioned embodiment, the outer contour of the guide roller is designed in such a way that its longitudinal extension along the axis of rotation is adapted to a narrow side of the rectangular cast strand.

In the method according to the invention for supporting a cast strand with a rectangular cross section, it is provided that at least one rotatably mounted guide roller has a crowned, convex outer contour, the outer contour of the guide roller being formed by a continuous, convex, outwardly curved curve without a point of inflection, consisting of one or more radii, and the guide roller with this outer contour is placed against one side of the cast strand, while the cast strand still has elastic properties in an area near the edge, with the largest diameter (D_max) of the outer contour of the guide roller compared to a diameter (D_min) of the guide roller on its front side in the ratio assumes a maximum value of 1.5 and a minimum value of 1.0, and that in the transport direction (T) of the cast strand, a plurality of guide rollers are provided in alignment one behind the other and are jointly set against one side of the rectangular cast strand, with the individual guide rollers - downstream of the transport direction (T) of the cast strand - the crowning of the outer contour increases in such a way that the quotient of the largest diameter (D_max) of the outer contour of a guide roller to the diameter (D_min) of the guide roller on its end face increases.

The invention is based on the essential finding that the strand shell of the cast strand, as long as it still has elastic properties in an area near the edge immediately after leaving the continuous casting mold, through contact with the guide rollers, which, as explained, have a crowned convex outer contour targeted concave shape is imposed, which counteracts the tendency of the strand shell to bulge. Here, the measure of the crowning of the outer contour of a guide roller is suitably matched to the respective manufacturing parameters and the steel grade produced. This means that the crowning of the outer contour, which is determined by the ratio of the largest diameter of the roller surface to the diameter at the roller ends of the guide roller, is only selected to be large enough to compensate for the tendency of the strand shell to bulge . In any case, it is important for the invention that the contact of the strand shell of the cast strand with a guide roller of the strand guide device should not result in permanent deformation of the cast strand at the point of contact with the guide roller. This is ensured by the fact that the guide roller of the strand guide device is brought into contact with the cast strand at a time when the cast strand still has elastic properties.

The crowned, convex outer contour of a guide roller is optimized for the individual problem that arises for a specific type of steel and its manufacturing parameters. Correspondingly, the crowned, convex outer contour of a guide roller can be designed differently to adapt to the individual case, with the ratio of the largest diameter of the roller surface to the diameter of the roller surface at the roller ends, i.e. on a front side of the guide roller, being in the range between 1.5 and 1. 0 moves. Within this range of the two mentioned diameters relative to one another, the outer contour of the guide roller can be suitably adapted to the respective application.

Thanks to the crowned, convex design of the outer contour of a guide roller, which is placed against one side of the cast strand immediately after it leaves the continuous casting mold, the bulging of the cast strand or a slab can be compensated for without excessive edge effects.

Ideally, the extent to which the outer contour of a guide roller is of convex crowned design is offset by the tendency of the strand shell of the cast strand to bulge to zero. As a result of this interaction, which results from the contact of the crowned, convex outer contour of a guide roller with the strand shell of the cast strand, a desired uniform rectangular shape is formed for the strand shell in cross section.

In an advantageous development of the invention, the at least one guide roller of the strand guide device is rotatably accommodated in a cage mount. Such a cage mount is characterized by a robust and inexpensive construction and ensures a secure rotational mount for the guide roller, also taking into account the considerable forces that act on the guide roller during continuous casting.

In an advantageous development of the invention, it can be provided that several guide rollers are provided, each with a crowned, convex outer contour, with at least one guide roller being set against the narrow side of a cast strand, and with at least one further guide roller being set against the long side of the cast strand.

According to the invention, the tendency of the strand shell of a cast strand to bulge is counteracted in that a plurality of guide rollers are provided, namely aligned one behind the other in the transport direction of the cast strand. All of these guide rollers are expediently accommodated in a rotatably mounted manner together in a cage mount of the strand guide device.

The guide rollers, which are arranged in alignment one behind the other, are each provided with a different crowned, convex outer contour. Correspondingly, for the guide rollers arranged in alignment one behind the other, there are different contour characteristics in relation to their crowned, convex outer contour. In this case, it is provided that in the case of a guide roller which - as seen in the transport direction of the cast strand - is further from the continuous casting mold, the quotient formed from the largest diameter of the outer contour or the roller surface to the diameter of the guide roller on its front side is greater than in the Compared to a guide roller which - seen in the transport direction of the cast strand - is closer to the continuous casting mold. In this way, a gentle support for the strand shell of the cast strand is achieved by the plurality of guide rollers with a crown which increases in the transport direction of the cast strand, in order to counteract the undesirable bulging of the strand shell at the same time.

In an advantageous further development of the invention, a connecting device is provided with which the strand guiding device can be positively attached to a continuous casting mold or adjacent thereto. The guide rollers are subject to pronounced wear during continuous casting. Accordingly, the connection device makes it possible to dismantle the strand guide device from the continuous casting mold if necessary and to replace it with a new strand guide device. For this purpose, a lifting device can be provided for the strand guide device, by means of which the strand guide device can be lifted upwards in the vertical direction. Such a lifting device can be in the form of a ring eye which can be fastened, for example, to an upper side of the cage holder, for example by means of a screw connection.

By equipping the strand guide device with the connection device mentioned, it is thus possible to provide an exchangeable roller unit for continuous casting, which can be exchanged in a short time if required—either in the event of wear or to adapt to special types of steel. For this purpose, the strand guide device can be lifted vertically upwards out of the continuous casting mold by a crane or the like by means of the lifting device.

In an advantageous further development, the strand guiding device also comprises an elongated copper plate which—seen in the direction of transport of the cast strand—is provided upstream of the guide roller(s). The copper plate can expediently be attached to the mentioned cage holder. In this way, the cage mount, in which at least one guide roller is rotatably mounted, and the copper plate attached to it form an advantageous exchange module that can be quickly dismantled from the continuous casting mold and can therefore be exchanged.

Exemplary embodiments of the invention are described in detail below using a schematically simplified drawing.

• Fig. 1a-c
  jeweils Seitenansichten von Führungsrollen nach verschiedenen Ausführungsformen,
• Fig. 2
  eine Perspektivansicht und eine Seitenansicht einer Strangführungseinrichtung,
• Fig. 3-5
  jeweils Perspektivansichten einer, zu Zwecken der Veranschaulichung, teilweise demontierten Stranggieß-Kokille (Ausschnitt der Gießform), in Verbindung mit Strangführungseinrichtungen,
• Fig. 6
  eine Perspektivansicht einer Stranggießkokille (Ausschnitt der Gießform), aus der Strangführungseinrichtungen herausgehoben sind,
• Fig. 7
  eine Perspektivansicht einer Stranggießkokille (Ausschnitt der Gießform), in der die Strangführungseinrichtungen bestimmungsgemäß eingebaut sind, und
• Fig. 8
  eine Seitenansicht einer herkömmlichen Führungsrolle.

Show it:

• Fig. 1a-c
  each side views of guide rollers according to different embodiments,
• 2
  a perspective view and a side view of a strand guide device,
• Figures 3-5
  each perspective view of a continuous casting mold partially dismantled for the purpose of illustration (detail of the casting mold), in connection with strand guiding devices,
• 6
  a perspective view of a continuous casting mold (detail of the casting mold), from which the strand guide devices are lifted out,
• 7
  a perspective view of a continuous casting mold (detail of the casting mould), in which the strand guiding devices are installed as intended, and
• 8
  a side view of a conventional guide roller.

A strand guide device 10 for guiding and supporting a cast strand 12 is described, the strand guide device 10 having at least one rotatably mounted guide roller 14 for this purpose.

In the Figures 1a, 1b and 1c are each shown different embodiments for a guide roller 14 in cross section. The guide rollers 14 are each mounted so as to be rotatable about an axis of rotation 16 and have an outer contour 18 which runs in the longitudinal extension along the axis of rotation 16 and is of crowned, convex design. A maximum diameter D_max of a guide roller 14 , which is present approximately in a central area 20 thereof, is greater than a minimum diameter D_min of the guide roller, which is present at one end of the roller or at an end face 19 of the guide roller 14 . The design of the crowned, convex outer contour 18 of a guide roller 14 is selected in such a way that the ratio of the maximum diameter D_max of the roller surface to the minimum diameter at a roller end or at a front side of the guide roller 14 satisfies the condition: $$1.5\le \mathrm{D\_max}/\mathrm{D\_min}\le 1.0.$$

A comparison of the various embodiments for a guide roller 14 according to Figures 1a, 1b and 1c shows that the radii for the convex outer contour 18, with which the crowning of the individual guide rollers 14 is defined, are different.

In the embodiments according to Figures 1a and 1b the outer contour 18 of the guide roller 14, starting from its end faces 19, initially has a constant diameter. This area, in which the outer contour 18 is initially cylindrical, can have a longitudinal extension of between 5-50 mm. Only after this cylindrical area does the outer contour 18 assume a curved course, as explained in a crowned, convex shape.

In the embodiment according to Fig. 1b the diameter of the outer contour 18 of the guide roller 14 increases, starting from the end face 19 in the direction of the central area 20 up to a turning point W, with the increase or growth of the diameter decreasing again from this turning point until the central area 20 is reached. The curved course of the outer contour 18 up to the turning point W, starting from the end face 19, is defined by a first radius R1, the curved course of the outer contour 18 between the turning point W and the central area 20 being defined by a second radius R2. In this case, the first and second radius R1, R2 can each have a value of 1 mm or more, as a result of which "soft" curves are ensured for the outer contour 18.

For a simplified illustration, in the embodiment of FIG Fig. 1b the radii R1, R2 and the turning point W are shown only for the area of the guide roller 14 to the left of the center. It goes without saying that the guide roller 14 is preferably formed symmetrically with respect to its center, so that the radii R1, R2 and the turning point W for the outer contour 18 are also provided in the area to the right of the center.

Another feature of the embodiment according to Fig. 1b is that the central region 20 of the outer contour 18 of the guide roller 14 has a constant diameter and is therefore of cylindrical design.

According to the embodiment 1c is characterized in that its outer contour 18 is formed by a continuous convex outwardly curved curve without a point of inflection, it being possible for this curve to have one or more radii. This outwardly curved curve can have a predetermined distance from the end face 19 of the guide roller 14, with the representation according to FIG 1c this predetermined distance has the value zero. In other words, in the embodiment according to FIG 1c the convex outwardly curved curve directly at the end faces 19 of the guide roller 14, and then runs in the direction of the central region 20. Alternatively, it is possible that in this embodiment the predetermined distance from the end face 19 at which the outwardly curved curve for the outer contour 18 begins, has a value of up to 50 mm.

According to a further (not shown) embodiment, for example, a combination of Figures 1b and 1c possible. This means that the outwardly curved curve of the outer contour 18, as in 1c illustrates, in its central portion 20 may have a cylindrical portion of fixed diameter, as in FIG Fig. 1b illustrated.

A guide roller 14 of the strand guide device 10 serves the purpose of being set against a strand shell box 21 of the cast strand 12 . In the Figures 1a, 1b and 1c It is illustrated in each case that a guide roller 14 is pressed or employed against a narrow side 22 of the cast strand 12, which has a rectangular cross section. It can be seen that a length of the guide roller 14 along its axis of rotation 16 is shorter than a length of the narrow side 22 of the cast strand 12. In this way, the outer contour 18 of a guide roller 14 with its longitudinal extent along the axis of rotation 16 is attached to the narrow side 22 of the Cast strand 12 adjusted with a rectangular cross section.

In the Figures 1a-1c a still liquid sump of the cast strand 12 is symbolized by the reference symbol “23”. In contrast, an edge area of the cast strand 12, in particular on a narrow side 22 thereof, with which the guide roller 14 is brought into contact, is already hardened, but only to the extent that such a hardened area of the cast strand 12 still has elastic properties.

Upon contact with the spherically convex outer contour 18 of a guide roller 14, a correspondingly concave embossing is imposed on the narrow side 22 of the cast strand 12, as can be seen in the respective cross-sectional views of FIGS Figures 1a - 1c is illustrated. As already explained, is important in this context that this concave embossing, for the examples according to Figures 1a-1c on the narrow side 22 of the cast strand 12, is introduced into the edge region of the cast strand 12 as long as it still has elastic properties. Thus, by introducing such a concave embossing, the tendency of the cast strand 12 to bulge when there is no further contact with a guide roller 14 as a result of a movement of the cast strand in its transport direction T is compensated and ideally canceled out to zero . This then results in an ideal rectangular shape for the strand shell box 21 of the cast strand 12.

2 shows a further embodiment for a strand guide device 10, here both in a perspective view (upper area of 2 ) as well as in a side view (lower area of 2 ). In this embodiment, the strand guide device 10 comprises a cage mount 24 on or in which a plurality of guide rollers 14 are rotatably mounted. A copper plate 26 attached to the cage bracket 24 is also provided. With respect to a transport direction or withdrawal direction of the cast strand 12 in which 2 Symbolically denoted by the arrow "T", the copper plate 26 is provided upstream of the cage bracket 24 .

For the embodiment of a strand guide device 10 according to 2 it is separately pointed out that the combination of a cage holder 24 with a copper plate 26 attached to it forms a replacement module 27 which can be exchanged or replaced in a short time if necessary. For this exchange module 27 can - according to the representation of 2 - Be provided that on the cage bracket 24, a plurality of guide rollers 14 is attached. Deviating from the representation in 2 it can also be provided that only a single guide roller 14 is rotatably mounted on the cage mount 24 .

If several guide rollers 14 are attached to the cage mount 24, it is pointed out in this regard that their outer contour 18 each has a different sized crown, with the proviso that the crown, i.e. the above-mentioned quotient D_max/D_min, in the direction of the transport movement T of the cast strand 12 increases. In other words, the crowning of a corresponding guide roller 14 increases the further it is from a (in 2 not shown) continuous casting mold is objected to.

The use of the strand guide device 10 as an exchange module 27 is made possible by the fact that it has a connecting device 28 by means of which the strand guide device 10 is attached to a continuous casting mold 30 ( 3 ) or adjacent to it can be attached in a form-fitting manner. For example, this connecting device is designed in the form of a lateral bolt 28 which can snap into a retaining device 29 of the continuous casting mold 30 or an associated adjusting element 31 designed to complement it. A lifting device 32 , for example in the form of a ring eye, is screwed into an upper side of the copper plate 26 . Thus, the strand guide device 10 can be raised by a crane or the like in the vertical direction to be either inserted into the continuous casting mold 30 or lifted out.

In the perspective view according to 3 the continuous casting mold 30 is shown partially dismantled for the purpose of a simplified representation. It can thus be seen how a strand guide device 10 can be attached to the continuous casting mold 30 . In the image area on the left, a strand guide device 10 is shown in such a way that its bolts 28 are located just above the holding devices 29 that are provided on the free ends of the respective adjustment elements 31 . In the image area on the right, a strand guide device 10 is shown in a state when it has been lifted out of the continuous casting mold 30 .

figure 4 shows a perspective view of the continuous casting mold 30 of FIG 3 , now in a state when two strand guide devices 10 are attached or mounted to the adjusting devices 31 of the continuous casting mold 30. In this case, the bolts 28 are then engaged in the associated holding devices 29, resulting in a form-fitting attachment of the strand guide device 10 to the continuous casting mold 30.

figure 5 shows another perspective view of the continuous casting mold 30, now in a state when both strand guide devices 10 are lifted up out of the continuous casting mold 30. As already mentioned, such a lifting of the strand guide devices 10 can be effected by attaching traction means to the ring eyes 30 and then pulling them upwards using a crane or the like.

The 6 and 7 each show a perspective view of the continuous casting mold 30 of FIG 3 in a state when a front part 34 of the continuous casting mold 30 is mounted thereon. In detail, the strand guide devices 10 are shown in FIG 6 lifted out of the continuous casting mold 30 (in the same way as in figure 5 ), and in the representation of 7 used within the continuous casting mold. To illustrate a transport or withdrawal direction of the cast strand 12 in relation to the continuous casting mold 30, this direction is shown in FIG 7 symbolized by the arrow "T".

For the embodiment according to Figures 3-7 serve the strand guide devices 10, when they are mounted in the continuous casting mold 30, for the purpose of guiding a cast strand with a rectangular cross-section on its narrow side and supporting it appropriately. As can be seen, the guide rollers 14 of the strand guide devices 10 come into contact with the cast strand 12 immediately after the cast strand 12 has emerged from the continuous casting mold 30 . Correspondingly, an edge region of the cast strand 12 with which the crowned-convex guide rollers 14 come into contact still has elastic properties. This then leads to a concave embossing being imposed on this edge region of the cast strand 12 by contact with the crowned-convex guide rollers 14, with the tendency of the strand shell of the cast strand 12 to bulge, namely after the cast strand 12 on the guide rollers 14 has passed and then no longer has contact with the guide rollers 14, with the concave embossing to zero.

According to a further advantageous embodiment, a strand guiding device 10 can also have a guide roller which is brought into contact with a longitudinal side of the cast strand 12 . For example, such a leadership role is shown from figure 5 shown, and there provided with the reference numeral "15". Such a guide roller 15 also has a crowned, convex outer contour, as referred to above 1 explained, and serves to ensure that the introduction of a targeted concave embossing in the longitudinal side of the cast strand counteracts the tendency of the strand shell to bulge and thus compensates for such a bulging. In this respect, the functioning of a guide roller 15, which is brought into contact with the longitudinal side of a cast strand, corresponds, mutatis mutandis, to the functioning of a guide roller 14, which is set against the narrow side 12 of the cast strand 12.

Finally, it should be pointed out that a strand guide device 10 for supporting a cast strand 12 with a rectangular cross section can have a plurality of guide rollers 14, 15 which are set against both the narrow side 22 of the cast strand 12 and the longitudinal side of the cast strand 12, namely at a point in time if the cast strand 12 still has elastic properties in areas close to the edge both on its narrow side and on its long side.

Reference List

10

strand guiding device

12

casting strand

14

Guide roller (on the narrow side of the cast strand 12)

15

Guide roller (on the long side of the cast strand 12)

16

axis of rotation (of the guide roller 14)

18

Outer contour (of the guide roller 14)

19

face (of the guide roller 14)

20

Central area (of the guide roller 14)

21

strand shell box (of cast strand 12)

22

narrow side (of the casting strand 12)

23

Liquid sump (inside casting strand 12)

24

cage mount

26

copper plate

27

replacement module

28

connecting device

29

holding device

30

continuous casting mould

31

Adjustment device (of the continuous casting mold 30)

32

lifting device

34

Front part (of the continuous casting mold 30)

36

Conventional cylindrical roll

T

Transport direction (of the cast strand 12)

Claims (2)

1. Method of supporting a cast strip (12) with a rectangular cross-section, in which at least one rotatably mounted guide roller (14) has a spherically convex outer contour (18), wherein the outer contour (18) of the guide roller (14;15) is formed by a continuously convex outwardly curved curve, without a reversal point, from one or more radii, and the guide roller (14) is adjusted by this outer contour (18) against a side of the cast strip (12), whilst the cast strip (12) still has an elastic character in a region near the edge, wherein the largest diameter (D_max) of the outer contour (18) of a guide roller (14; 15) by comparison with a diameter (D_min) of the guide roller (14; 15) at the end thereof (19) has a ratio of at most the value 1.5 and at least the value 1,0, and that several guide rollers (14) are provided in alignment in succession in the transport direction (T) of the cast strip (12) and are adjusted in common against a side of the rectangular cast strip (12), wherein for the individual guide rollers (14) the sphericality of the outer contour (18) downstream of the transport direction (T) of the cast strip (12) increases in such a way that the quotient of largest diameter (D_max) of the outer contour (18) of a guide roller (14) with respect to the diameter (D_min) of the guide roller (14) at the end thereof is increasing.
2. Method according to claim 1, characterised in that several rotatably mounted guide rollers (14; 15) each with a spherically convex outer contour (18) are provided, wherein at least one guide roller (14) is adjusted against a narrow side (22) of the cast strip (12) and wherein at least one further guide roller (15) is adjusted against a long side (22) of the cast strip (12).

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