Method and device for cooling and guiding a beam blank in a curved secondary cooling zone of a beam blank caster

Abstract

A device for cooling and guiding a beam blank in a curved secondary cooling zone of a beam blank caster includes an intrados web support roller with a cylindrical bearing surface that is interrupted by grooves. The grooves are designed so as to avoid an over-flow generating cooling water dam up behind the intrados web support roller by channeling sufficient cooling water underneath the intrados web support roller axially through the intrados channel of the beam blank. The cooling water overflow produces a quench of the intrados tips of the flanges, which results in transverse cracks of these tips during straightening of the beam blank.

Description

FIELD OF THE INVENTION

The present invention relates to a method and a device for cooling and guiding a beam blank in a curved secondary cooling zone of a beam blank caster.

BACKGROUND OF THE INVENTION

Since the 1960s it is known in the art of steel making to produce by continuous casting near-net-shape sections for rolling I-beams or H-beams. These sections have a dog-bone-like cross-section with a web and two flanges and are called beam blanks.

A typical beam blank caster comprises a continuous casting mould with a heavily cooled copper mould that forms a steel strand having a solidified outer shell surrounding a still molten core. Solidification of this strand is completed by spray cooling in a secondary cooling zone, in which the beam blank is guided along a curved path in a vertical plane, so that its flanges are vertical. It will be noted that the beam blank presents along this curved path a so called intrados channel, which is delimited between its vertical flanges at the side of the intrados face (i.e. the concave face) of the curved web, and an extrados channel, which is delimited between its vertical flanges at the side of the extrados face (i.e. the convexe face) of the curved web. An extraction and straightening unit, which is located behind the secondary cooling zone, straightens the bent beam blank and pushes the latter onto a horizontal run-out table.

A device for guiding a beam blank in a curved secondary cooling zone of a beam blank caster typically comprises a set of guiding and support rollers co-operating to define the curved path for the beam blank and to avoid a bulging of the shell by the ferrostatic pressure of the liquid steel it contains. A plurality of intrados web support rollers bear in the intrados channel on the intrados web face, whereas a plurality of extrados web support rollers bear in the extrados channel on the extrados web face. Further guiding rollers bear on the tip and lateral surfaces of the flanges.

Spray cooling of the strand in the secondary cooling zone is achieved by means of a plurality of cooling water spray nozzles, which may be either standard spray nozzles or so called air mist nozzles. These spray nozzles are arranged around the strand so as to spray the cooling water (respectively a water-air mist) mainly on the perimeter surfaces of the most massive zones of the beam blank, i.e. the intrados and extrados connections surfaces between the flanges and the web and the outer faces of the flanges. Part of the cooling water evaporates in contact with the hot surfaces of the beam blank. The cooling water that does not evaporate drops down at the extrados side, whereas at the intrados face it flows axially through the intrados channel of the beam blank.

It is well known in the art of continuous casting that optimising cooling and support of the strand in the secondary cooling zone a beam blank caster is—because of the dog-bone-like cross-section of the beam blank—a rather complex problem and has always been and still is the object of expensive research programs. Sophisticated computer programs have e.g. been conceived to selectively control the cooling water flow directed on the different zones of the beam blank in function of various parameters. Arrangement and sizing of the guiding rolls are continuously reconsidered to provide a better support of the bent beam blank in the continuous casting zone.

Despite these constant efforts to optimise cooling and support conditions of the strand in a beam blank caster, it has as yet not been possible to eliminate some major drawbacks. Such a major drawback is e.g. the formation of transverse cracks in the intrados flange tips when the beam blank is straightened in the straightening unit. These transverse cracks are observed in particular, but not exclusively, in large section and high strength beam blanks. Although it is very likely that the transverse defects are due to an undesired quench of the tips of the flanges, it has not yet been possible to reliably avoid these cracks by a more selective control of the cooling water sprays.

U.S. Pat. No. 3,923,093 discloses an apparatus for continuously casting metal in various cross-sectional shapes, such as blooms, billets and “dog-bones” of various proportions. In this casting apparatus, the guiding rolls are disposed in tiers along the path of the continuously cast metal. The position of the guiding rolls in each tier is adjustable so as to be able to configure different cross-sections between the guiding rolls. It will be appreciated that this patent contains no specific teaching relating to the prevention of transverse cracks in the intrados flange tips of beam blanks.

OBJECT OF THE INVENTION

The object of the present invention is to provide a solution for reliably avoiding the aforementioned transverse cracks in the intrados flange tips. In accordance with the present invention this solution consists in an improved method, respectively an improved device, for cooling and guiding a beam blank in a curved secondary cooling zone of a beam blank caster, such as defined in claim 1, respectively claim 6.

SUMMARY OF THE INVENTION

It will first be appreciated that the present invention has the merit to have discovered that the intrados tips of the flanges are subjected to an excessive cooling due essentially to the fact that the intrados web support rollers (which are generally made as large as possible to provide the best support for the web) dam up the cooling water in the intrados channel to such an extent that an important part of this intrados cooling water flows over the tips of the flanges instead of being evacuated axially through the intrados channel of the beam blank. In other words, the intrados tips of the flanges are subjected to an undesired quench by a cooling water overflow, which is due to a dam-effect of the intrados web support rollers. This quench hardens the intrados tips of the flanges, whereby the latter get very sensible to the formation of transverse cracks during the straightening of the bent beam blank. It will be noted that the larger the cross-section of the beam blank, the more water has to be sprayed onto the intrados connections between the flanges and the web, and the higher the likelihood of observing a quench of the intrados tips of the flanges by a cooling water overflow. The situation is made even worse by the fact that large beam blank sections require a very good support of the web; i.e. web support rollers as large as possible, which are nearly perfect dam elements in the intrados channel of the beam blank.

It will further be appreciated that the present invention also has the merit to propose a solution for efficiently avoiding an undesired quench of the intrados tips of the flanges by an overflow of cooling water dammed up behind an intrados web support roller, which is designed as large as possible to provide the best possible support for the web. This solution consists in that the intrados web support roller is provided with a cylindrical bearing surface that includes groove means designed so as to avoid an overflow generating cooling water dam up behind the intrados web support roller by channelling sufficient cooling water underneath the intrados web support roller axially through the intrados channel, thereby avoiding a quench of the intrados tips of the flanges by overflow water. It will be appreciated that an advantageous side effect of the groove means is an improvement of the cooling of the intrados web support roller, which has of course a positive effect on its lifetime.

The groove means comprises for example a plurality of axially spaced ring-shaped grooves or a helical groove.

The groove means advantageously has chamfered or rounded edge surfaces as transition surfaces to the cylindrical bearing surface. These chamfered or rounded edge surfaces help to avoid surface marks on the intrados web face of the beam blank when the grooved intrados web support roller is pressed against the intrados web face.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1: is a section through a beam blank caster with a curved secondary cooling zone;

FIG. 2: is a section through a beam blank in the curved secondary cooling zone of the beam blank caster of FIG. 1, wherein an intrados web support roller is shown; and

FIG. 3: is an enlarged detail of the intrados web support roller of FIG. 2.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 shows a caster 10 for continuously casting “near-net-shape” sections for rolling I-beams or H-beams, which are generally called beam blanks. As shown in FIG. 2, such a beam blank 12 has a dog-bone-like cross-section with a web 14 and two flanges 16′, 16″.

In FIG. 1, reference number 18 refers to a tundish, i.e. a refractory-lined liquid steel distributor, which receives molten steel from a furnace ladle (not shown) to discharge it in a controlled manner into a vertical continuous casting mould 20. The latter includes a heavily cooled copper mould (not shown) that forms the beam blank 12 as a steel strand having a solidified outer shell surrounding a still molten core. At the outlet of the copper mould the partially solidified beam blank 12 is guided by a foot roller segment 22 into a curved secondary cooling zone 24, where its solidification is completed by spray cooling. (It will be noted that the wording “spray cooling” as used herein covers classical spray cooling and the so called “air mist cooling”.) At the outlet of the secondary cooling zone 24, the beam blank 12 passes into an extraction and straightening unit 26, which straightens the bent beam blank 12 before it guides it onto a horizontal run-out table 28.

The secondary cooling zone 24 comprises several guiding and spray cooling segments 30₁, 30₂, 30₃ and 30₄. Each of these guiding and cooling segments 30, to 304 comprises a frame 32 supporting a plurality of guiding and support rollers 34, 36. These guiding and support rollers 34, 36 co-operate to define in a vertical plane (i.e. the plane of FIG. 1) a curved path for the beam blank 12. A further object of the guiding and support rollers 34, 36 is to support the solidified shell of the beam blank 12 in such a way as to avoid its bulging by the ferrostatic pressure of the liquid steel it contains.

FIG. 2 shows a cross-section through the beam blank 12 in such a guiding and cooling segment 30₁. It will be noted that the bent beam blank 12 has its flanges 16′, 16″ vertical and that its curved web 14 has an intrados face 38 (i.e. a concave face) and an extrados face 40 (i.e. a convex face). The bent beam blank 12 consequently presents a so called intrados channel 42, which is delimited between its vertical flanges 16′, 16″ at the side of the intrados face 38 of the curved web 14, and an extrados channel 44, which is delimited between its vertical flanges 16′, 16″ at the side of the extrados face 40 of the curved web 14.

Reference number 46 identifies an intrados web support roller, which bears on the intrados web face 38 in the intrados channel 42. An extrados web support roller 48, which bears on the extrados web face 40 in the extrados channel 44, is schematically represented in FIG. 2 by doted lines. In addition to the intrados and extrados web support rollers 40, some or all of the guiding and spray cooling segments 30, to 304 may further include intrados flange support rollers 50′, 50″ bearing on the intrados tips 52′, 52″ of the flanges 16′, 16″, extrados flange support rollers 54′, 54″ bearing on the extrados tips 56′, 56″ of the flanges 16′, 16″, and lateral guide rollers 58′, 58″ bearing on the lateral outer faces 60′, 60″ of the flanges 16′, 16″.

Spray cooling of the beam blank 12 in the secondary cooling zone 24 is achieved by means of a plurality of cooling water spray nozzles 62 (or spray ramps). These spray nozzles 62 are arranged over the whole length of the secondary cooling zone 24 around the beam blank 12 so as to spray the cooling water or the air mist mainly on the perimeter surfaces of the most massive zones of the beam blank 12, i.e. the intrados and extrados connections surfaces between the flanges 16′, 16″ and the web 14 and the lateral outer faces 60′, 60″ of the flanges 16′, 16″. (It will be noted that the wording “spray nozzles” is used to cover standard spray nozzles as well as so called “air mist nozzles”, which form an air-water mist). Part of the cooling water sprayed onto the beam blank 12 evaporates in contact with the hot surfaces of the latter. The cooling water that does not evaporate, drops down at the extrados side, whereas at the intrados side it flows into the intrados channel 42 of the beam blank 12.

In accordance with an important aspect of the present invention, the intrados web support roller 46 includes a cylindrical bearing surface (globally identified by reference number 64) that is regularly interrupted by ring-shaped grooves 66. These axially spaced grooves 66 are designed as groove means for channelling sufficient cooling water between the rotating intrados web support roller 46 and the intrados face 38 of the web 14, so as to prevent an excessive dam up of cooling water behind the intrados web support roller 46. It is indeed a merit of the present invention to have found out that in prior art beam blank casters the intrados tips 52′, 52″ of the flanges 16′, 16″ are often subjected to an undesired quench that is essentially due to the fact that the intrados web support rollers 46, which should be made as large as possible to provide the best support for the web 14, dam up the cooling water in the intrados channel 42 to such an extent that an important part of this intrados cooling water flows over the intrados tips 52′, 52″ of the flanges 16′, 16″. This undesired quench hardens the intrados tips 52′, 52″ of the flanges 16′, 16″, so that they are very sensible to the formation of transverse cracks during straightening of the bent beam blank 12 in the extracting and straightening unit 26. In conclusion, by designing the axially spaced grooves 66 so as to prevent an excessive cooling water dam up behind the intrados web support roller 46 and thereby a quench generating overflow over the intrados tips 52′, 52″ of the beam blank 12, it is possible to avoid generation of transverse cracks in the intrados tips 52′, 52″ of the flanges 16′, 16″ during straightening of the beam blank 12. It will be appreciated that a side effect of the grooves 66 in the intrados web support roller 46 is an improvement of the cooling of the intrados web support roller 46, which has of course a positive effect on its lifetime.

As shown in the enlarged detail of FIG. 3, a ring-shaped groove 66 has two ring-shaped side walls 68′, 68″ and two chamfered and rounded ring-shaped edge surfaces 70′, 70″ as transition surfaces between the side walls 68′, 68″ and the cylindrical bearing surface 64. These chamfered and rounded transition surfaces 70′, 70″ help to avoid surface marks on the intrados web face 38 of the beam blank 12.

Referring back to FIG. 2 it will be noted that the intrados web support roller 46 also has chamfered edge surfaces 72′, 72″ at both of its ends. It will be appreciated that these chamfered edge surfaces 72′, 72″ allow to work with a web support roller 46 being in contact with a flat central portion of the web face 38 over the whole width of the latter, without risking to produce surface marks in the rounded web-flange connections 76′, 76″, when the beam blank 12 or the web support roller 46 is subjected to lateral movements.

The dimensions of the cooling water channelling grooves 66 will be fixed in function of the cooling water flow that has to be channelled between the rotating intrados web support roller 46 and the intrados face 38 of the web 14, so as to prevent an excessive dam up of cooling water behind the intrados web support roller 46. Typical dimensions of the grooves are for example as follows: width 10-20 mm; depth 3-12 mm. The width of the ring-shaped cylindrical bearing surface 64 subsisting between two successive grooves 66 is typically in the range of 10-20 mm. This ring-shaped cylindrical bearing surface 64 can however be broader if fewer grooves are needed to avoid a quench producing cooling water overflow.

Claims

1-9. (canceled).

10. A method for passing a beam blank through a curved secondary cooling zone of a beam blank caster, said beam blank comprising a web with an intrados face and an extrados face and two lateral flanges, said flanges delimiting an intrados channel and an extrados channel, said method comprising:

guiding said web with the help of intrados web support rollers bearing on said intrados web face in said intrados channel and extrados web support rollers bearing on said extrados web face in said extrados channel, so as to define a curved path for said beam blank, wherein at least one of said intrados web support rollers has a cylindrical bearing surface that guides said web over substantially the whole width of said intrados web face;

spraying cooling water onto said beam blank, whereby cooling water flows through said intrados channel; and

channelling a sufficient amount of said cooling water flowing through said intrados channel between said intrados web face and said cylindrical bearing surface, which guides said web over substantially the whole width of said intrados web face, by means of groove means arranged in said cylindrical bearing surface, in such a way to avoid an overflow generating cooling water dam up behind said at least one intrados web support roller.

11. The method as claimed in claim 10, wherein said groove means comprises a helical groove in said cylindrical bearing surface.

12. The method as claimed in claim 11, wherein said helical groove has chamfered or rounded edge surfaces as transition surfaces to said cylindrical bearing surface.

13. The method as claimed in claim 12, wherein said groove means comprises a plurality of axially spaced ring-shaped grooves in said cylindrical bearing surface.

14. The method as claimed in claim 13, wherein said ring-shaped grooves have chamfered or rounded edge surfaces as transition surfaces to said cylindrical bearing surface.

15. A device for cooling and guiding a beam blank in a curved secondary cooling zone of a beam blank caster, said beam blank comprising a web with an intrados face and an extrados face and two lateral flanges, said flanges delimiting an intrados channel and an extrados channel, said device comprising:

spray means for spraying cooling water onto said beam blank;

at least one intrados web support roller bearing on said intrados web face in said intrados channel and having a cylindrical bearing surface guiding said web over substantially the whole width of said intrados web face; and

extrados web support rollers bearing on said extrados web face in said extrados channel; wherein:

said intrados web support rollers and said extrados web support rollers cooperate to define a curved path for said beam blank; and

said cylindrical bearing surface of said at least one intrados web support roller includes groove means designed so as to avoid an overflow generating cooling water dam up behind said intrados web support roller by channelling sufficient cooling water between said intrados web support roller and said intrados web face axially through said intrados channel.

16. The device as claimed in claim 15, wherein said groove means comprises a helical groove in said cylindrical bearing surface.

17. The device as claimed in claim 16, wherein said helical groove has chamfered or rounded edge surfaces as transition surfaces to said cylindrical bearing surface.

18. The device as claimed in claim 17, wherein said groove means comprises a plurality of axially spaced ring-shaped grooves in said cylindrical bearing surface.

19. The method as claimed in claim 18, wherein said ring-shaped grooves have chamfered or rounded edge surfaces as transition surfaces to said cylindrical bearing surface.