JPH11314142A - Nozzle for continuous casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a cast slab excellent in product quality after rolling while simultaneously preventing the clogging of a tundish nozzle and the erosion of inner wall of the nozzle, in a method for continuously casting a steel. SOLUTION: At the time of continuously casting molten metal, relating to the nozzle l fitted to the tundish, a gas pool part 2 is disposed in the thick thickness part of the nozzle in the circumferential direction of the nozzle and also, a gas flow-out passages (penetrating holes 6a, 6b, 6c) are arranged from the gas pool part 2 toward the inner surface 5 of the nozzle in the vertical direction of the nozzle, so that the differences of the gas flowing quantities among the gas flow-out passages in the vertical direction of the nozzle are reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for continuous casting of steel, which is intended to produce a slab of excellent product quality after rolling while simultaneously preventing blockage of a tundish nozzle and erosion of the inner wall of the nozzle. A continuous casting method.

[0002]

2. Description of the Related Art Conventionally, a high alumina material is generally used as a material for a tundish nozzle. However, Al ₂ O ₃ clusters, which are nonmetallic inclusions, are cast on the surface of the nozzle bore when casting aluminum killed steel. And had a disadvantage that the nozzle was easily clogged.

[0003] Even if the material of the upper nozzle of the tundish is another material, in the case of continuous casting (sequential casting), for example, when casting molten steel in the ladle for several charges, the molten steel temperature before the ladle replacement is changed. reduction also contribute to promote the Al ₂ O ₃ deposition phenomenon, gradually Al ₂ deposition of O ₃ proceeds, eventually case often occurs that becomes impossible casting nozzle clogging occurs , Suffered enormous damage and had to be improved. The adhesion of Al ₂ O ₃ in the nozzle may cause the nozzle to eventually block during casting and reduce the casting speed, or it may be necessary to clean the closed portion from above the nozzle, thereby reducing the quality of the casting slab. It often deteriorated or hindered the casting operation.

Various methods are conceivable to prevent the nozzle blockage as described above. An inert gas is caused to flow out to the inner surface of the nozzle to prevent Al ₂ O _{3 from} adhering to the inner surface of the nozzle or the metal. Techniques have been developed (for example, Japanese Utility Model Laid-Open No. 1-3257, JP-A-4-319055).

FIG. 7 shows an example of a conventional nozzle disclosed in the above-mentioned publication, in which a gas pool 2 is provided inside a thick portion of a main body of a nozzle 1, and an inert gas is externally provided in the gas pool 2. Is supplied through the supply pipe 4 and is
The inert gas is caused to flow out to the nozzle inner surface 5 through a plurality of gas outflow passages 3 provided in the downward direction (longitudinal direction) toward the nozzle inner surface 5 to prevent Al ₂ O _{3 and the} like from adhering to the nozzle inner surface 5. I have.

[0006]

FIG. 6 is a graph showing the result of investigating the state of gas outflow from the gas outflow path of the nozzle 1 by immersing the conventional nozzle 1 shown in FIG. 7 in a mercury tank. The gas pool 2 is provided in a nozzle 1 having an inner diameter of 1 mm, and a diameter of 0.
Uniform through-holes 6 of 3 mm 15 pieces arranged to form a gas outflow passage, the Ar gas having a pressure of 2.0 kg / cm ² was supplied to the gas pool 2, produced by gas ejected from the through holes 6 The number of gas bubbles is visually counted, and the number of gas bubbles changes depending on the position of the gas outflow path in the upward and downward directions of the nozzle. As is clear from FIG. No. 1 to No. Up to 7, the number of generated bubbles decreases as going downward. No air bubbles were generated from the outflow path belonging to the lower part after 8.

As can be seen from the above experimental results, in the through-holes 6 having the same diameter, there is a difference in the number of generated bubbles in the upward and downward directions of the nozzle (a difference in the amount of gas flowing out, and as a result, It appears that the gas does not flow out evenly. This may be due in part to the head differences in mercury.

The present invention has developed a new nozzle which does not cause a difference in the gas outflow amount in the upward and downward directions of the nozzle or reduces the difference even if it occurs. It is an object of the present invention to provide a nozzle capable of securing a uniform gas outflow amount in a downward direction, and to solve the above problems.

[0009]

The gist of the present invention lies in the following means. (1) In a nozzle to be mounted on a tundish for continuous casting of molten metal, a gas pool is arranged in the nozzle circumferential direction in a thick portion of the nozzle, and the gas pool is directed upward and downward from the gas pool toward the inner surface of the nozzle. The continuous casting nozzle is provided with a gas outflow passage so as to reduce a gas flow difference between the outflow passages in the upper and lower directions of the nozzle. (2) The gas outflow passage is a through-hole, and the through-holes are divided into a plurality of stages in the upper and lower directions of the nozzle, and the cross-sectional areas of the through-holes are equalized for each group. (1) The continuous casting nozzle according to (1), wherein the nozzle is made smaller and the cross-sectional area of the through-hole is made larger in order toward the lower group. (3) The continuous casting nozzle according to (1), wherein the cross-sectional area of the through-hole of the gas outflow passage is gradually increased in the upper and lower directions of the nozzle toward the lower side.

(4) The continuous casting nozzle according to (2) or (3), wherein a cross section of the through hole of the gas outflow passage is formed in a circular shape. (5) In (4), when setting the diameter of each through-hole of the gas outflow path in the upward and downward directions of the nozzle, the through-hole diameter of the second and subsequent through-holes from the top is determined based on the following equation (1). Nozzle for casting. Φn = (K / (K− (n−1) ρgh) ^1/4 nφ1 (1) where Φn: diameter of through-hole at the nth stage from the top (mm) K: constant ρ: continuous casting Metal specific gravity (g / cm ² ) g: Gravity (g / cm ² ) h: Through hole interval (mm) nφ1: Diameter of first through hole (mm) from above

(6) The gas outflow passage is formed of a porous refractory having a high porosity, and the gas outflow passage is divided into a plurality of stages in the upper and lower directions of the nozzle, and the porosity of the porous refractory in the group is defined. (1), wherein the porosity of the upper group is reduced, and the porosity is sequentially increased toward the lower group. (7) The gas outflow passage is formed of a porous refractory having a high porosity, and the gas outflow passages are grouped into a plurality of stages in the upward and downward directions of the nozzle to make the outflow passage cross-sectional areas in the groups equal, The continuous casting nozzle according to (1), wherein the cross-sectional area of the outflow passage in the upper group is reduced, and the cross-sectional area of the outflow passage is gradually increased toward the lower group. (8) The continuous casting nozzle according to (6) or (7), wherein the cross-sectional area of the flow passage in the group of each stage is gradually increased from the top to the bottom.

(9) The gas outflow passage is formed of a porous refractory, and the cross-sectional area of the cross-sectional area on the upper side in the upward and downward directions of the nozzle is reduced, and the cross-sectional area is sequentially increased toward the lower side. The nozzle for continuous casting as described. (10) The continuity according to (1), wherein the gas outflow passage is divided into two groups in the upper and lower directions of the nozzle, the upper group is formed of a porous refractory having a high porosity, and the lower group is a through hole. Nozzle for casting. (11) In (10), the cross section in which the cross-sectional area of the porous refractory of the upper group is gradually increased from top to bottom, and the cross-sectional area of the through-hole of the lower group is gradually increased from top to bottom. Nozzle for casting.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION As described in the above section, the present inventors have made the gas outflow passage cross-sectional area uniform in the upward and downward directions of the nozzle, so that the gas amount passing through the gas outflow passage will not be equal. Therefore, various studies have been made on this solution, and as a result, many embodiments have been proposed, and the present invention has been successfully developed.

Hereinafter, the present invention will be described with reference to the drawings. FIG. 1 shows an example in which gas outflow paths are grouped into a plurality of stages in the upper and lower directions of the nozzle (three groups in this example). The gas outflow paths are formed as thin through holes 6 and the cross-sectional area of the through holes 6 for each group ( The same applies to the vertical direction, the same applies hereinafter), the cross-sectional area of the through-hole 6a on the upper side (first group) is reduced, and the through-hole 6
The case where the cross-sectional area is increased to b and 6c is shown (the number of gas outflow paths is set to 15 in this example, and the same applies hereinafter).

FIG. 2 shows an example in which the gas outflow path is formed as a through-hole 6 and its cross-sectional area gradually increases from the upper side to the lower side in the upward and downward directions of the nozzle. FIG. 3 shows that the gas outflow path is made of a porous refractory 7 having a high porosity, and the gas outflow path is located above the nozzle.
The porous refractory 7 is divided into groups in the downward direction (three groups in this example), and the porosity of the porous refractory 7 is made different for each group.
This is an example in which the porosity of a is lowered, and the porosity is sequentially increased to 7b and 7c toward the lower side (second and third groups). In this case, the porosity of the porous refractory 7 is made the same without grouping the gas outflow passages, and the cross-sectional area of the porous refractory 7 which sequentially forms the gas outflow passage from the upper part of the nozzle to the lower part is increased. By doing so, it is possible to equalize the gas outflow amount in the upward and downward directions.

Further, FIG. 4 shows that the gas outflow passage is divided into two groups in the upper and lower directions of the nozzle (not necessarily uniform), and the upper side (first group) is formed of a porous refractory 7 having a high porosity. In this example, the lower side (second group) is formed as a through hole 6. In order to prevent a difference in gas outflow amount between the porous refractory 7 and the through-hole 6, the porous refractory 7 in the upper stage should have a large porosity,
It is conceivable to increase the cross-sectional area of the gas outflow channel,
If the cross-sectional area of the gas flow passage is gradually increased from the upper side to the lower side for the porous refractory 7 and the through-hole 6, the effect of equalizing the gas outflow amount can be obtained. Such an embodiment is naturally included in the present invention. In providing the gas outflow passage, in the case of the through hole 6, the cross-sectional shape is not particularly limited, and various shapes such as a triangle, a polygon, and an ellipse can be considered. Are suitable.

Regarding the various forms of the aforementioned gas flow passage,
FIG. 5 shows a state when viewed from the inner surface side of the nozzle.
2A shows the state of the through hole 6 when the gas flow passage of the nozzle shown in FIG. 1 is viewed from the inner surface, and FIG. 2B shows the same for the nozzle shown in FIG. It was shown to.
FIG. 3C shows an example in which the porous refractory 7 shown in FIG. 3 is used as a flow passage. The porosity differs between the groups in the upward and downward directions (the porosity is large on the lower side). This shows a situation in which the cross-sectional area of the gas flow passage is given a difference between the upper and lower directions (increased in the downward direction). FIG. 4D shows FIG.
The upper part of the gas passage is porous refractory 7
The lower stage is an example in which the through-hole 6 is formed, and the porous refractory 7 and the through-hole 6 have a difference in cross-sectional area in the upper and lower directions (increased as going downward). It should be noted that the corresponding diagram for FIG. 7 is omitted.

In order to change the diameter of each gas through hole 6 (the cross-sectional shape is a perfect circle) in the upward and downward directions of the nozzle, the following method (1) is used to calculate the optimal through hole diameter of the second and subsequent stages from the top. Expressions are recommended. That is, Φn = (K / (K− (n−1) ρgh) ^1/4 nφ1 (1) where Φn: Through-hole diameter (mm) at the nth stage from the top K: Constant ρ: Continuous The specific gravity of the metal to be cast (g / cm ² ) g: gravity (g / cm ² ) h: through-hole interval (mm) nφ1: diameter of the through-hole at the first step from the top (mm) In the nozzle having the nozzle, the flow rate of the gas ejected to the inner surface of the nozzle is evenly distributed in the upward and downward directions of the nozzle, so that the generation of deposits on the nozzle is suppressed.

FIG. 1 showing the nozzle of the present invention out of FIG.
And (b) and (a), respectively, in FIG. 2 showing the gas outflow situation, wherein a gas pool is provided in a nozzle having an inner diameter of 1 mm, and 1
A gas outflow path is formed with five through holes, and 2.0 kg
/ Cm ² is supplied to the gas pool, and the number of gas bubbles generated by the gas flowing out of each gas outflow path is calculated as follows:
This figure shows a situation in which the number of generated gas outlets changes depending on the position of the gas outflow passage in the upper and lower directions of the nozzle. In addition,
The diameter of the through-hole (perfect cross-section circle) as the gas outflow path was designated
(No. 1 at the top and No. 15 at the bottom) are shown in Table 1.

[0020]

[Table 1]

As is apparent from FIG. 6, when the gas outflow paths are grouped into multiple stages (three stages in this example) in the upper and lower directions of the nozzle, the upper and lower directions in the group are also in the upper and lower directions. There is a difference in the gas outflow amount, and the number of generated bubbles is smaller in the lower part. However, it can be seen that it is clearly improved as compared with the gas outflow state in the conventional nozzle (FIG. 7).

In the case where the cross-sectional area (diameter of the through-hole 6) of the gas outflow path (diameter of the through-hole 6) gradually increases from the upper side to the lower side of each gas outflow path (through hole 6) in the upward and downward directions of the nozzle. Indicates that each through-hole No. The numbers of generated bubbles are almost the same in both cases, and it can be seen that there is little difference between the through holes 6 and a uniform gas flow rate is maintained. Although the above examples all show the upper nozzle of the tundish, the same can be said for the lower nozzle. The same effect can be expected of course when applied to a ladle nozzle. Further, as for the gas flowing out to the inner surface of the nozzle, only the Ar gas is described, but any inert gas which does not affect the molten steel can be used.

[0023]

In the present invention the injection of the molten steel by, according to the present invention, it is possible to avoid the adhesion of as Al ₂ O ₃ or bullion to the nozzle inner surface. In addition, since a stable casting operation can be maintained without causing clogging of the nozzle, it is possible to prevent interruption of casting due to an accident of the nozzle even in continuous casting,
The cast slab also has a large effect that contributes to an improvement in productivity, for example, it can ensure good quality with few defects.

[Brief description of the drawings]

FIG. 1 is a view showing an example of a nozzle according to the present invention, in which a gas outflow path is formed as a through hole, and the nozzles are grouped in an upward / downward direction.

FIG. 2 is a view showing another example of the nozzle of the present invention, in which the cross-sectional area of the gas outflow passage is gradually increased from the upper side to the lower side of the nozzle.

FIG. 3 is a view showing another example of the nozzle according to the present invention, in which a porous refractory is used for a gas outflow path and the nozzles are grouped in upper and lower directions.

FIG. 4 is a view showing another example of the nozzle of the present invention, in which the gas outflow passage is formed of a porous refractory in an upper stage and a through hole is formed in a lower stage.

FIG. 5 is a diagram showing a state in which a gas flow passage is viewed from the inner surface of the nozzle of the nozzle of the present invention

FIG. 6 is a view showing a state of generation of bubbles due to a difference in a position of a nozzle in a gas outflow path between the nozzle of the present invention and a conventional nozzle in the upper and lower directions.

FIG. 7 is a view showing a state of a gas outflow path (through hole) in a conventional nozzle in an upward and downward direction of the nozzle.

[Explanation of symbols]

 Reference Signs List 1 nozzle 2 gas pool 4 gas supply pipe 5 nozzle inner surface 6 through hole 7 porous refractory

Claims (11)

[Claims] In a nozzle to be mounted on a tundish for continuous casting of molten metal, a gas pool is disposed in a nozzle circumferential direction in a thick portion of a nozzle, and a nozzle inner surface is formed from the gas pool upward and downward from the nozzle. A gas outflow passage toward the nozzle, and a difference in gas flow rate between the outflow passages in the upward and downward directions of the nozzle is reduced. 2. The gas outflow passage is formed as a through-hole, and the through-hole is divided into a plurality of stages in the upward and downward directions of the nozzle so that the cross-sectional area of the through-hole is equal for each group. 2. The continuous casting nozzle according to claim 1, wherein the area is reduced and the cross-sectional area of the through-hole is gradually increased toward the lower group. 3. The continuous casting nozzle according to claim 1, wherein the cross-sectional area of the through-hole of the gas outflow passage is gradually increased in the upper and lower directions of the nozzle toward the lower side. 4. The continuous casting nozzle according to claim 2, wherein a cross section of the gas outlet passage is formed in a circular shape. 5. The method according to claim 4, wherein when setting the diameter of each through hole of the gas outflow passage in the upward and downward directions of the nozzle, the diameters of the through holes in the second and subsequent stages from the top are determined based on the following equation (1). Nozzle for continuous casting. Φn = (K / (K− (n−1) ρgh) ^1/4 nφ1 (1) where Φn: diameter of through-hole at the nth stage from the top (mm) K: constant ρ: continuous casting Metal specific gravity (g / cm ² ) g: Gravity (g / cm ² ) h: Through hole interval (mm) nφ1: Diameter of first through hole (mm) from above 6. The gas outflow passage is formed of a porous refractory having a high porosity, and the gas outflow passage is divided into a plurality of stages in the upper and lower directions of the nozzle, and the porosity of the porous refractory in the group is determined. 2. The continuous casting nozzle according to claim 1, wherein the porosity of the upper group is made lower, and the porosity is gradually increased toward the lower group. 7. The gas outflow passage is formed of a porous refractory having a high porosity, and the gas outflow passages are divided into a plurality of stages in the upward and downward directions of the nozzles so that the cross-sectional areas of the outflow passages in the groups are equalized. 2. The continuous casting nozzle according to claim 1, wherein the cross-sectional area of the outflow passage in the upper group is reduced, and the cross-sectional area of the outflow passage is gradually increased toward the lower group. 8. The method according to claim 6, wherein
A continuous casting nozzle characterized in that the cross-sectional area of the flow passage in each group of steps is gradually increased from the top to the bottom. 9. The gas outflow passage is formed of a porous refractory, and the cross-sectional area of the cross-sectional area in the upper and lower directions in the nozzle upper and lower directions is reduced, and the cross-sectional area is sequentially increased in the lower direction. The continuous casting nozzle according to claim 1. 10. The gas outlet path is divided into two groups in the upper and lower directions of the nozzle, the upper group is formed of a porous refractory having a high porosity, and the lower group is formed as a through hole. The continuous casting nozzle according to claim 1. 11. The cross-sectional area of the porous refractory of the upper group is gradually increased from the top to the bottom, and the cross-sectional area of the through-hole of the lower group is gradually increased from the top to the bottom. A continuous casting nozzle characterized by the following.