Annular weir

An annular weir is fixed at a bottom of a tundish and just under a long nozzle of a ladle in a continuous casting apparatus. The annular weir includes a cavity which has a substantially circular shaped transverse section. The cavity includes: an upper side opening configured to receive a stream of molten metal from an upper side through the long nozzle; an inner protrusion which is annular in shape and which extends toward an inner side from an upper end of an inner wall of the cavity; a first space on an inner side of the inner protrusion; and a second space which communicates with the first space 13a and which is on a lower side of the first space.

TECHNICAL FIELD

The present invention relates to annular weirs fixed at bottoms of tundishes in continuous casting apparatuses to receive incoming molten metal delivered from upper sides.

BACKGROUND INFORMATION

In order to continuously cast molten metal such as molten steel, the molten steel in ladles is delivered to tundishes for a time and then is delivered to molds.

In order to obtain cast pieces high in purity, sufficiently floating and separating non-metal inclusions in the molten steel delivered to the tundishes from the ladles is essential. In order to sufficiently float and separate the non-metal inclusions, conditions known as short circuiting and high speed flows of the molten steel in the tundishes have to be controlled. The short circuiting refers to the shortest paths molten steel, which is delivered to the tundishes from the ladles, may take to the molds.

Preventive measures against the short circuiting include disposing weirs in the tundishes. The weirs are obstacles against the incoming molten steel, which is delivered to the tundishes from the ladles, to reach immersion nozzles, thereby preventing short circuiting. Also, the weirs lengthen paths the streams of molten steel, which is delivered to the tundishes, take to the molds, thereby promoting the float and separation of the non-metal inclusions in the molten steel.

Unfortunately, however, the weirs do not always control speeds produced by upward streams of the molten steel, which is delivered to the tundishes, which impacts bottoms of the tundishes, and which rebounds upward. High speed upward streams or high speed streams toward side walls of the tundishes posterior to the upward streams may promote slag entrainment on a surface of bath or may shorten time for the streams of the molten steel to pour into the molds. As a result, this configuration does not leave sufficient time for the float and separation of the non-metal inclusions.

In this connection, a weir4shown inFIG. 1has been disclosed (see, for example, Patent document 1).

RELATED ART DOCUMENTS

Patent Documents

FIG. 1illustrates the weir4disposed at a bottom of a tundish6in such a manner that an opening2of the weir4is just under a long nozzle5of a ladle. The weir4includes refractory material and has a concave shaped opening3formed therein, which has a substantially convex shaped cross section. An inner circumferential surface1of the concave shaped opening3is semicircular in cross section and an upper surface of the concave shaped opening3has the opening2.

As molten metal is directed into the concave shaped opening3of the weir4from the long nozzle5, as shown by arrows inFIG. 1, when the molten metal impacts the bottom of the concave shaped opening3and rebounds upward, the weir4tightens up the upward stream, and the upward stream interferes an incoming stream from the long nozzle5. This configuration is expected to slow opposing upward and downward streams each other, control high speed flows, and prevent the short circuiting to immersion nozzles7.

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

Unfortunately, however, the invention of Patent document 1 still has problems such as possibility of slag entrainment on a surface of bath in a tundish6, and possibility of damages on the long nozzle5, which includes refractory material. The invention also has rooms for improvement. For example, interference between downward streams from the long nozzles5and upward streams which are rebounded may be too weak to slow the upward streams.

Patent document 1 indicates that the weir4may have optional shapes, including a rectangular shape in plane shown inFIG. 2. Even with this configuration, the weir4does not perform a sufficient effect and may cause harmful effect. Since fluid leans in a direction with the least stress, the upward stream which is rebounded mainly leans toward shorter sides, in other words, in a longitudinal direction of the tundish in case of the weir4ofFIG. 2having the rectangular shape. Accordingly, this configuration does not achieve an original object of increasing time it takes for incoming molten metal to reach the immersion nozzles7such that impurities naturally float slowly to the top of the bath.

Therefore, an object of the present invention is to provide a weir capable of controlling the high speed flows as well as preventing short circuiting of the molten metal.

Means of Solving the Problems

In order to achieve the above-mentioned object, according to a first aspect of the invention, an annular weir (11) is provided, the annular weir (11) being fixed at a bottom of a tundish and just under a long nozzle (15) of a ladle in a continuous casting apparatus, the annular weir (11) including a cavity (13) which has a substantially circular shaped transverse section, the cavity (13) including: an upper side opening configured to receive a stream of molten metal from an upper side through the long nozzle (15); an inner protrusion (13d) which is annular in shape, the inner protrusion (13d) extending toward an inner side from an upper end of an inner wall of the cavity (13); a first space (13a) on an inner side of the inner protrusion (13d); and a second space (13b) which communicates with the first space (13a), the second space (13b) being on a lower side of the first space (13a).

In addition, according to a second aspect of the invention, an annular weir (11) is provided, the annular weir (11) being fixed at a bottom of a tundish (12) and just under a long nozzle (15) of a ladle in a continuous casting apparatus, the annular weir (11) including a cavity (13) which has a substantially circular shaped transverse section, the cavity (13) including: an upper side opening configured to receive a stream of molten metal from an upper side through the long nozzle (15); an inner protrusion (13d) which is annular in shape, the inner protrusion (13d) extending toward an inner side from an inner wall of the cavity (13); a third space (13c) on an upper side of the inner protrusion (13d); a first space (13a) which communicates with the third space (13c), the first space (13a) being on a lower side of the third space (13c) and on an inner side of the inner protrusion (13d); and a second space (13b) which communicates with the first space (13a), the second space (13b) being on a lower side of the first space (13a).

In addition, according to a third aspect of the present invention, an inside diameter (D1, Da) of the first space (13a) is within a range of 4 times to 5 times a diameter of a discharge hole (15a) of the long nozzle (15), and an inside diameter (D2, Db) of the second space (13b) is within a range of 1.2 times to 1.5 times the inside diameter (D1, Da) of the first space (13a).

In addition, according to a fourth aspect of the present invention, height (H) of the annular weir (11) is within a range of ⅙ to ¼ of height of a surface of a bath in operation.

In addition, according to a fifth aspect of the present invention, the cavity (13) is a bore that bores in an upper and lower direction.

In addition, according to a sixth aspect of the present invention, an inside diameter (Dc) of the third space (13c) is within a range of 1 time to 1.1 times the inside diameter (Db) of the second space (13b).

In addition, according to a seventh aspect of the present invention, the inside diameter (Dc) of the third space (13c) is gradually increased from a lower side toward an upper side.

In addition, according to an eighth aspect of the present invention, an annular weir (11) is provided, the annular weir (11) being fixed at a bottom of a tundish (12) and just under a long nozzle (15) of a ladle in a continuous casting apparatus, the annular weir (11) including a cavity (13) which has a substantially circular shaped transverse section, the cavity (13) including: an upper side opening configured to receive a stream of molten metal from an upper side through the long nozzle (15); a plurality of inner protrusions (13d) which are annular in shape, the plurality of inner protrusions (13d) extending toward an inner side from an inner wall of the cavity (13); and a plurality of spaces divided by the plurality of inner protrusions (13d), the plurality of spaces in an upper and lower direction communicating with each other.

Symbols in parentheses show constituents or items corresponding to the drawings.

According to the present invention, the stream of molten metal, which is directed by the long nozzle into the cavity of the annular weir, impacts the bottom of the tundish or the annular weir, and rebounds upward. This configuration prevents short circuiting of the molten metal to immersion nozzles immersed in a mold.

The inner protrusion tightens up an upward stream and the upward stream interferes a downward stream from the long nozzle. This configuration slows the opposing upward and downward streams each other and increases time for the molten metal to reach the immersion nozzles.

This configuration promotes float and separation of the non-metal inclusions in the molten metal, thereby improving quality of cast products.

Especially, with the configuration that the inside diameter of the first space is within the range of 4 times to 5 times the diameter of the discharge hole of the long nozzle and the inside diameter of the second space is within the range of 1.2 times to 1.5 times the inside diameter of the first space, the upward stream and the downward stream interfere with each other without fail and speed of the molten metal is controlled.

In addition, with the configuration that the height of the annular weir is within the range of ⅙ to ¼ of the height of the surface of the bath in operation, possibility of surface turbulence in the bath caused by the upward stream is low and therefore, slag entrainment on the surface of the bath is minimized.

In addition, with the configuration that the cavity is the bore that bores in the upper and lower direction, the annular weir is simply manufactured at a low cost. The bore does not cause any structural disadvantage for the bottom of the tundish substitutes for a bottom of the annular weir.

It is to be noted that Patent document 1 does not disclose that the inner protrusion is formed, the inside diameter of the first space is within the range of 4 times to 5 times the diameter of the discharge hole of the long nozzle, or the inside diameter of the second space is within the range of 1.2 times to 1.5 times the inside diameter of the first space, as the annular weir of the present invention.

MODE FOR CARRYING OUT THE INVENTION

Referring toFIG. 3toFIG. 5, an annular weir11according to an embodiment of the present invention will be described.

The annular weir11controls speed of molten metal delivered from a ladle within a tundish12in a continuous casting apparatus. The annular weir11includes a cavity13, which has a substantially circular shaped transverse section (horizontal cross section).

FIG. 3is a perspective view of the annular weir11according to the present invention.FIG. 4is a cross section of the annular weir11ofFIG. 3fixed on the tundish12.

The annular weir11includes refractory material and is prismatic in outward appearance. The annular weir11has the cavity13formed at a center thereof. The cavity13is a bore that bores in an upper and lower direction.

An inner protrusion13dis formed on an upper end of an inner wall of the cavity13. The inner protrusion13dis annular in shape and extends toward an inner side from the upper end.

The cavity13includes: a first space13aon an inner side of the inner protrusion13d;and a second space13bwhich communicates with the first space13aand which is on a lower side of the first space13a.The cavity13has a substantially convex-shaped longitudinal section.

The inner wall of the cavity13and an end surface of the inner protrusion13dextend vertically. The first space13aand the second space13bare formed on an uneven base with a step therebetween.

An inside diameter D1of the first space13ais within a range of 4 times to 5 times a diameter of a discharge hole15aof a long nozzle15. In the present embodiment, D1of the first space13ais 400 mm, and an inside diameter D2of the second space13bis 500 mm which is 1.25 times the inside diameter D1of the first space13a.The diameter of the discharge hole15aof the long nozzle15is 95 mm.

Height of a surface of a bath in operation is 1000 mm from a bottom of the tundish12. Height H of the annular weir11is ⅕ (200 mm) of height of the surface of the bath in operation in the tundish12. Heights H1, H2of the first space13aand the second space13bmeet H1=H2=½H.

As shown inFIG. 4, the annular weir11is fixed at the bottom of the tundish12in such a manner that the cavity13is just under the long nozzle15of a ladle not shown. While the cavity13does not include a bottom, the bottom of the tundish12substitutes for the bottom. The annular weir11is fixed by the same ways as ordinary weirs, by mortar for example.

InFIG. 3andFIG. 4, a body of the annular weir11is prismatic. But the outward appearance of the body of the annular weir11is not strictly limited. Examples of the outward appearance include a columnar shape in accordance with an inner part of the cavity13and a pyramidal trapezoid which spreads upward in accordance with a shape inside the tundish12.

With this configuration of the annular weir11, the stream of molten metal, which is directed by the long nozzle15into the cavity13of the annular weir11, impacts the bottom of the tundish12, and rebounds upward. As a result, this configuration prevents short circuiting of the molten metal to immersion nozzles16immersed in a mold.

The inner protrusion13dtightens up the upward stream and the upward stream interferes the downward stream from the long nozzle15. This configuration slows the opposing upward and downward streams each other and increases time for the molten metal to reach the immersion nozzles16.

In addition, with the configuration that the height H of the annular weir11is ⅕ of the height of the surface of the bath in operation, possibility of surface turbulence in the bath caused by the upward stream is low and therefore, slag entrainment on the surface of the bath is minimized.

This configuration promotes float and separation of the non-metal inclusions in the molten metal, thereby improving quality of the cast products.

In addition, above-described conditions prevent erosion on a top end of the long nozzle15(seeFIG. 5).

In addition, with the configuration that the cavity13is the bore that bores in the upper and lower direction, the annular weir11is simply manufactured at a low cost. The bore does not cause any structural disadvantage for a bottom of the tundish12substitutes for the bottom of the annular weir11.

Conditions for Embodiment 2 will be described.

In the present embodiment, the inside diameter D1of the first space13awas 450 mm and the inside diameter D2of the second space13bwas 550 mm.

The height H of the annular weir11, the height H1of the first space13a,and the height H2of the second space13bremain unchanged from Embodiment 1.

In Embodiment 3, the inside diameter D1of the first space13aand the inside diameter D2of the second space13bremain unchanged from Embodiment 1. The height H of the annular weir11was 250 mm, the height H1of the first space13awas 150 mm, and the height H2of the second space was 100 mm.

As shown inFIG. 5, in Embodiment 2 and Embodiment 3, entrainment of the surface of the bath was slight, and therefore, resultant molten steel was high in purity. In addition, the long nozzle15was not eroded.

The results show that the inside diameter D1of the first space13ais preferably within the range of 4 times to 5 times the diameter of the discharge hole15aof the long nozzle.

In Comparative Example 1, the diameter D1of the first space13awas larger. As a result, as shown inFIG. 5, slag entrainment on the surface of the bath was promoted and the resultant molten steel was slightly inferior to the Embodiment in purity.

In Comparative Example 2, the diameter D1of the first space13awas smaller. As a result, entrainment of the surface of the bath was not observed, but the resultant molten steel was considerably inferior in purity.

In Comparative Example 3, the height H of the annular weir11was ⅓ of the height of the surface of the bath. As a result, the resultant molten steel was equivalent in purity but entrainment of the surface of the bath was considerable, thereby hampering steady operations.

In Comparative Example 4, the diameter D2of the second space13bwas 1.1 times the diameter D1of the first space13a.As a result, entrainment of the surface of the bath was slightly observed and the erosion on the top end of the long nozzle15after casting was so considerable that the long nozzle15became ineffective approximately at half number of heating.

Referring toFIG. 6toFIG. 8, the annular weir11according to another embodiment of the present invention will be described.

The annular weir11controls speed of molten metal delivered from the ladle within the tundish12in the continuous casting apparatus. The annular weir11includes the cavity13, which has the substantially circular shaped transverse section (horizontal cross section).

FIG. 6is a perspective view of the annular weir11according to the present invention.FIG. 7is a cross section of the annular weir11ofFIG. 6fixed on the tundish12.

The annular weir11includes refractory material and is prismatic in outward appearance. The annular weir11has the cavity13formed at the center thereof. The cavity13is the bore that bores between the upper end and the lower end.

The inner protrusion13dis formed at a substantial center in an upper and lower direction of the inner wall of the cavity13. The inner protrusion13dis annular in shape and extends toward the inner side from the substantial center.

The cavity13includes: a third space13con an upper side of the inner protrusion13d;the first space13aon the inner side of the inner protrusion13d;and the second space13bwhich communicates with the first space13aand which is on the lower side of the first space13a.

The inner wall of the cavity13and an end surface of the inner protrusion13dextend vertically. The third space13cand the first space13a,and the first space13aand the second space13bare formed on an uneven base with a step therebetween.

An inside diameter Daof the first space13ais within the range of 4 times to 5 times the diameter of the discharge hole15aof the long nozzle15. In the present embodiment, Daof the first space13ais 400 mm, and an inside diameter Dcof the third space13cand an inside diameter Dbof the second space13bare 500 mm, respectively, which is 1.25 times the inside diameter Daof the first space13a.The diameter of the discharge hole15aof the long nozzle15is 95 mm.

The height of the surface of the bath in operation is 1000 mm from the bottom of the tundish12. The height H of the annular weir11is ¼ (250 mm) of the height of the surface of the bath in operation in the tundish12. Heights Hc, Ha, Hbof the third space13c,the first space13a,and the second space13bmeet Hc=⅕ H, Ha=Hb=⅖ H.

As shown inFIG. 7, the annular weir11is fixed at the bottom of the tundish12in such a manner that the cavity13is just under the long nozzle15of the ladle not shown. While the cavity13does not include the bottom, the bottom of the tundish12substitutes for the bottom. The annular weir11is fixed by the same ways as ordinary weirs, by mortar for example.

InFIG. 6andFIG. 7, the body of the annular weir11is prismatic. But the outward appearance of the body of the annular weir11is not strictly limited. Examples of the outward appearance include the columnar shape in accordance with the inner part of the cavity13and the pyramidal trapezoid which spreads upward in accordance with the shape inside the tundish12.

With this configuration of the annular weir11, the stream of molten metal, which is directed by the long nozzle15into the cavity13of the annular weir11, impacts the bottom of the tundish12, and rebounds upward. As a result, this configuration prevents short circuiting of the molten metal to the immersion nozzles16, immersed in the mold.

The inner protrusion13dtightens up the upward stream and the upward stream interferes the downward stream from the long nozzle15. This configuration slows the opposing upward and downward streams each other and increases time for the molten metal to reach the immersions nozzles16.

In addition, with the configuration that the height H of the annular weir11is ¼ of the height of the surface of the bath in operation, possibility of surface turbulence in the bath caused by the upward stream is low and therefore, slag entrainment on the surface of the bath is minimized.

This configuration promotes float and separation of the non-metal inclusions in the molten metal, thereby improving quality of the cast products.

In addition, above-described conditions prevent erosion on the top end of the long nozzle15(seeFIG. 8).

In addition, with the configuration that the cavity13is the bore that bores in the upper and lower direction, the annular weir11is simply manufactured at the low cost. The bore does not cause any structural disadvantage for the bottom of the tundish12substitutes for the bottom of the annular weir11.

Conditions for Embodiment 5 will be described.

In the present embodiment, the inside diameter Dcof the third space13cwas 550 mm, the inside diameter Daof the first space13awas 450 mm, and the inside diameter Dbof the second space13bwas 550 mm.

The height H of the annular weir11, the height Hcof the third space13c,the height Haof the first space13a,and the height Hbof the second space13bremain unchanged from Embodiment 4.

In Embodiment 6, the inside diameter Dcof the third space13c,the inside diameter Daof the first space13a,and the inside diameter Dbof the second space13bremain unchanged from

Embodiment 4. The height H of the annular weir11was 200 mm, the height Hcof the third space13cwas 50 mm, the height Haof the first space13awas 50 mm, and the height Hbof the second space13bwas 100 mm.

As shown inFIG. 8, in Embodiment 5 and Embodiment 6, entrainment of the surface of the bath was slight, and therefore, resultant molten steel was high in purity. In addition, the long nozzle15was not eroded.

The results show that the inside diameter Daof the first space13ais preferably within the range of 4 times to 5 times the diameter of the discharge hole15aof the long nozzle.

In Comparative Example 5, the diameter Dcof the third space13awas larger. As a result, as shown inFIG. 8, the resultant molten steel was slightly inferior to the Embodiment in purity.

In Comparative Example 6, the diameter Daof the first space13awas smaller. As a result, the resultant molten steel was considerably inferior in purity.

In Comparative Example 7, the height H of the annular weir11was ⅓ of the height of the surface of the bath. As a result, the resultant molten steel was equivalent in purity but entrainment of the surface of the bath was considerable, thereby hampering steady operations.

In Comparative Example 8, the diameter Dbof the second space13bwas 1.1 times the diameter Daof the first space13a.As a result, entrainment of the surface of the bath was observed, which was substantially of the same degree as Comparative Example 7.

In Comparative Example 9, the diameter Dcof the third space13cwas smaller than the diameter Dbof the second space13b.As a result, entrainment of the surface of the bath was observed, which was substantially of the same degree as Comparative Example 8. Also, erosion on the top end of the long nozzle15after casting was so considerable that the long nozzle15became ineffective approximately at half number of heating.

In the present embodiment, the inside diameter D2, Dbof the second space13bmay be within a range of 1.2 times to 1.5 times the inside diameter D1, Daof the first space13a.

In addition, the height H of the annular weir11may be within a range of ⅙ to ¼ of the height of the surface of the bath.

In addition, the inside diameter Dcof the third space13cmay be within a range of 1 time to 1.1 times the inside diameter Dbof the second space13b.

While the cavity13of the present embodiment is the bore, shape of the cavity13is not strictly limited. That is, the cavity13may include a bottom such that the cavity13does not bore the annular weir11.

In addition, the inside diameter of the third space13cmay be gradually increased from a lower side toward an upper side. In this configuration, a diameter on a lower end of the third space13cequals to a diameter on an upper end of the first space13a.

In addition, a plurality of inner protrusions13dmay be formed in the upper and lower direction. In this configuration, the plurality of inner protrusions13ddivide the cavity13into more spaces than the singular inner protrusion13d.

DESCRIPTION OF NUMERALS

1inner circumferential surface2opening3concave shaped opening4weir5long nozzle6tundish11annular weir12tundish13cavity13afirst space13bsecond space13cthird space13dinner protrusion15long nozzle15adischarge hole16immersion nozzleD1inside diameter of first spaceD2inside diameter of second spaceDainside diameter of first spaceDbinside diameter of second spaceDcinside diameter of third spaceH height of annular weirH1height of first spaceH2height of second spaceHaheight of first spaceHbheight of second spaceHcheight of third space