Nozzle for continuous casting

Abstract

The present invention can suppress a decrease in the discharge amount of gas discharged from a through-hole in an externally inserted nozzle for continuous casting, which is used under the condition of being fitted to a stopper. Specifically, this nozzle for continuous casting is an externally inserted nozzle (A) for continuous casting, which is positioned below a stopper (B) for controlling the flow rate of molten steel during continuous casting of molten steel, is fitted to the stopper (B), and is attached to and detached from the outside of a molten steel container, and is provided with a nozzle body (1) comprising a refractory material and having an inner hole (11) through which the molten steel passes in the vertical direction. The nozzle body (1) is integrally provided with: an expanded-diameter section (12) which includes a fitting section (121) to which the stopper (B) is fitted, and in which the diameter of the inner hole (11) increases toward the upper end of the nozzle body (1); and a linear section (13) which is continuous downward from the lower end of the expanded-diameter section (12) and which has a linear inner hole (11). A gas pool (14) is provided only on the straight section (13), and a through-hole (15) that communicates with the gas pool (14) and discharges gas from the expanded-diameter section (12) is provided on the nozzle body (1).

Description

Technical Field

[0001] The present invention relates to a nozzle for continuous casting that fits with a stopper rod in the continuous casting of molten steel, and the stopper rod is used for flow control when discharging molten steel from a molten steel container such as a tundish. Background Art

[0002] In the continuous casting of molten steel, in the fitting region of the fitting portion of a nozzle body including a stopper rod and a nozzle for continuous casting, there are cases where inclusions such as alumina adhere, making it difficult to control the flow rate. As a countermeasure against the adhesion of inclusions to such a fitting region, for example, Patent Document 1 discloses a through-hole type nozzle for continuous casting that can discharge gas from a through-hole communicating with an air chamber provided in the nozzle body to the fitting region.

[0003] However, for example, as shown in paragraph 0003 of Patent Document 2, in the method of attaching and detaching a nozzle for continuous casting to a molten steel container such as a tundish, it can be roughly divided into an "outer insertion type" that attaches and detaches from the outside of the molten steel container and an "inner insertion type" that attaches and detaches from the inside of the molten steel container. In the case of the "outer insertion type", in order to be able to attach and detach from the outside of the molten steel container, the nozzle body has a shape in which its outer diameter decreases as it faces upward, and in the case of the "inner insertion type", in order to be able to attach and detach from the inside of the molten steel container, the nozzle body has a shape in which its outer diameter decreases as it faces downward. That is, the nozzle for continuous casting disclosed in Patent Document 1 is of the "inner insertion type".

[0004] Patent Documents Patent Document 1: Japanese Unexamined Patent Application Publication No. 2020-146702 Patent Document 2: Japanese Unexamined Patent Application Publication No. 10-305357 Summary of the Invention

[0005] When the inventors of the present invention repeatedly conducted tests on an outer insertion type nozzle for continuous casting with an air chamber and through-holes provided in the nozzle body under the condition of fitting with a stopper rod, a phenomenon of a decrease in the discharge amount of the gas discharged from the through-holes was frequently observed.

[0006] The technical problem to be solved by the present invention is to suppress a decrease in the discharge amount of the gas discharged from the through-holes in an outer insertion type nozzle for continuous casting used under the condition of fitting with a stopper rod.

[0007] When the inventors of the present invention recovered a nozzle for continuous casting in which a phenomenon of a decrease in the discharge amount of gas discharged from a through-hole was observed and investigated its cross section and the like, it was found that cracks were generated in the upper part of the nozzle body including the fitting portion with the stopper rod. Since the cracks were connected to the through-hole or the gas chamber, air leakage occurred. As a result, a phenomenon of a decrease in the discharge amount of gas due to a decrease in the back pressure of the gas occurred. In addition, it was also found that this phenomenon was particularly likely to occur in the case of "externally inserted type". That is, in the case of the "externally inserted type", since the nozzle body has a shape in which its outer diameter decreases upward, the thickness of the refractory becomes particularly thin in the upper part of the nozzle body including the fitting portion with the stopper rod. As a result, cracks are likely to occur.

[0008] Based on such an analysis of the current situation, the inventors of the present invention obtained the following insight: in order to solve the above problems, it is effective to provide the gas chamber not in the upper part of the nozzle body including the fitting portion with the stopper rod (the "diameter-expanded portion" described later), but only in the lower part thereof (the "linear portion" described later), and thus the present invention was completed.

[0009] That is, according to one aspect of the present invention, the following nozzle for continuous casting can be provided. A nozzle for continuous casting, which is of the externally inserted type, is located below a stopper rod for controlling the flow rate of molten steel and is fitted with the stopper rod during continuous casting of molten steel, and is detachably attached from the outside of the molten steel container, and is characterized in that it includes a nozzle body made of a refractory having an inner hole through which molten steel passes in the vertical direction, the nozzle body integrally has: a diameter-expanded portion including a fitting portion fitted with the stopper rod, and the diameter of the inner hole expands toward the upper end of the nozzle body; and a linear portion that continues downward from the lower end of the diameter-expanded portion, and the inner hole is linear, a gas chamber is provided only on the linear portion, a through-hole that communicates with the gas chamber and discharges gas from the diameter-expanded portion is provided on the nozzle body.

[0010] According to the present invention, it is possible to suppress a decrease in the discharge amount of gas discharged from the through-hole in an externally inserted type nozzle for continuous casting that can be used under the condition of being fitted with a stopper rod. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a vertical cross-sectional view of a nozzle for continuous casting, which is an embodiment of the present invention. Figure 2 is a vertical cross-sectional view of an existing nozzle for continuous casting. SYMBOL DESCRIPTION A, A'-upper nozzle (externally inserted upper nozzle for continuous casting); B-stopper rod; C-crack; 1-nozzle body; 11-inner hole; 111-central axis of the inner hole; 12-diameter-expanded part; 121-fitting part with the stopper rod; 122-lower end of the diameter-expanded part; 13-straight part; 131-upper end of the straight part; 14-air chamber; 141-upper end of the air chamber; 15-through hole; 16-gas inlet hole. Detailed implementation mode

[0012] In Figure 1 it, one implementation mode of the present invention, namely, a nozzle for continuous casting, is shown by a vertical cross-section. The continuous casting nozzle A shown in the same figure is an externally inserted upper nozzle that can be disassembled and assembled from the outside (lower side) of a molten steel container, i.e., a pouring basin. During continuous casting of molten steel, it is fitted with a stopper rod B that controls the flow rate when discharging molten steel from the pouring basin to the mold.

[0013] The upper nozzle A includes a nozzle body 1 made of refractory. The nozzle body 1 has a molten steel passage, i.e., an inner hole 11, in the vertical direction. Here, the vertical direction refers to the direction along the central axis 111 of the inner hole 11, and the vertical cross-section refers to the cross-section along the central axis 111 of the inner hole 11.

[0014] On the upper nozzle A, the nozzle body 1 integrally has a diameter-expanded part 12 and a straight part 13. That is, the diameter-expanded part 12 and the straight part 13 are integrally formed by integral molding of refractory. Among them, the diameter-expanded part 12 includes a fitting part 121 that fits with the stopper rod B and has a shape in which the diameter of the inner hole 11 expands toward the upper end of the nozzle body 1. In addition, the straight part 13 continues downward from the lower end 122 of the diameter-expanded part 12, and the inner hole 11 has a straight shape. Here, the inner hole 11 having a straight shape means that, in the vertical cross-section, the inner hole 11 is defined by a straight line, and it is not necessary for the diameter of the inner hole 11 to be constant. For example, when forming the inner hole 11, a core rod is usually used for forming. When the core rod is pulled out after forming, in order to facilitate the pulling out of the core rod, the core rod may be formed into a tapered shape that expands downward. In this case, the diameter of the inner hole 11 also expands in a tapered shape (linearity) downward, but this shape is also called a straight shape. On the other hand, on the diameter-expanded part 12, in the vertical cross-section, the inner hole 11 is defined by a curve. Therefore, on the nozzle body 1, the diameter-expanded part 12 and the straight part 13 can be clearly distinguished.

[0015] Here, since the upper nozzle A is "externally inserted", the nozzle body 1 has a so-called tapered shape in which its outer diameter decreases as it goes upward. Therefore, on the upper part of the nozzle body 1, i.e., the diameter-expanded part 12, the thickness of the refractory becomes particularly thin as it goes upward.

[0016] On the other hand, an air pocket 14 is provided on the straight portion 13. To be more precise, the air pocket 14 is provided only on the straight portion 13 and not on the diameter-expanded portion 12. This is because, as described above, on the diameter-expanded portion 12, the thickness of the refractory becomes particularly thin toward the upper side. That is, by providing the air pocket 14, which is a void and may be a starting point for crack generation, only on the straight portion 13 of the upper nozzle A and not on the diameter-expanded portion 13 where the thickness of the refractory is thin, the generation of cracks on the diameter-expanded portion 12 can be suppressed. From another perspective, since there is no air pocket 14 on the diameter-expanded portion 13 of the upper nozzle A, the structural strength of the diameter-expanded portion 13 is improved. As a result, the generation of cracks on the diameter-expanded portion 13 can be suppressed. In addition, although on the upper nozzle A, the air pocket 14 is provided on the entire circumference in the circumferential direction of the nozzle body 1 so as to surround the inner hole 11, it is not necessarily required to be provided on the entire circumference and may be provided on a part of the circumferential direction.

[0017] On the nozzle body 1, through holes 15 that communicate with the air pocket 14 and discharge gas from the diameter-expanded portion 12 are provided. In the present embodiment, a plurality of through holes 15 are provided at equal intervals along the circumferential direction of the nozzle body 1. In addition, on the nozzle body 1, gas introduction holes 16 that communicate with the air pocket 14 and introduce gas into the air pocket 14 are provided.

[0018] In the upper nozzle A having the above configuration, gas is introduced from the gas introduction hole 16 into the air pocket 14 and discharged from the diameter-expanded portion 12 into the molten steel through the through holes 15. At this time, since, as described above, on the upper nozzle A, the air pocket 14, which is a void and may be a starting point for crack generation, is provided only on the straight portion 13 and not on the diameter-expanded portion 12 where the thickness of the refractory is relatively thin, the generation of cracks on the diameter-expanded portion 12 can be suppressed. Thereby, a decrease in the discharge amount of the gas discharged from the through holes 15 due to a decrease in the back pressure of the gas can be suppressed.

[0019] Here, it is preferable that the upper end 141 of the air pocket 14 is located within a range of 10 mm or more and 100 mm or less below the upper end 131 of the straight portion 13. By making the upper end 141 of the air pocket 14 located 10 mm or more below the upper end 131 of the straight portion 13, the influence of the air pocket 14, which is a void and may be a starting point for crack generation, on the diameter-expanded portion 12 can be reduced, and thus the generation of cracks on the diameter-expanded portion 12 can be further suppressed. In addition, by making the upper end 141 of the air pocket 14 located 100 mm or less below the upper end 131 of the straight portion 13, the length of the through hole 15 can be shortened. Thereby, it is possible to facilitate the formation of the through hole 15 and reduce the pressure loss of the through hole 15. In addition, the upper end 131 of the straight portion 13 is also the lower end 122 of the diameter-expanded portion 12, in other words, is the boundary between the diameter-expanded portion 12 and the straight portion 13. Example

[0020] As an example of the present invention, the upper nozzle A shown in Figure 1 was supplied to actual operation (continuous casting of molten steel). In addition, as a comparative example, the upper nozzle A' shown in Figure 2 was also supplied to actual operation. The upper nozzle A' of this comparative example is such that the upper end 141 of the gas pool 14 is extended to the diameter-expanded portion 12 on the upper nozzle A of the example, and the other configurations are the same as those of the upper nozzle A of the example. In addition, on the upper nozzle A of the example, the gas pool 14 is arranged such that its upper end 141 is located at a position 35 mm below the upper end 131 of the straight portion 13.

[0021] During actual operation, when monitoring the back pressure and discharge amount of the gas on the upper nozzle A of the example and the upper nozzle A' of the comparative example respectively, no decrease in the back pressure and discharge amount was observed on the upper nozzle A of the example. On the other hand, a decrease in the back pressure and discharge amount was observed on the upper nozzle A' of the comparative example. In addition, after the actual operation was completed, when the respective upper nozzles A and A' were recovered and cross-sectionally observed, no cracks were observed on the upper nozzle A of the example. On the other hand, on the upper nozzle A' of the comparative example, as Figure 2 schematically shown, the generation of a crack C across the gas pool 14 was observed, and it is considered that the generation of such a crack is the cause of the decrease in the back pressure and discharge amount.

Claims

1. A nozzle for continuous casting, which is an externally inserted type, is located below a stopper for controlling the flow rate of molten steel and is fitted with the stopper during the continuous casting of molten steel, and is assembled and disassembled from the outside of the molten steel container. It is characterized in that it includes a nozzle body made of refractory material having an inner hole through which molten steel passes in the vertical direction. The nozzle body integrally has: a diameter-expanded portion including a fitting portion fitted with the stopper, and the diameter of the inner hole expands toward the upper end of the nozzle body; and a straight portion that continues downward from the lower end of the diameter-expanded portion, and the inner hole is linear. An air chamber is provided only on the straight portion. A through hole that communicates with the air chamber and discharges gas from the diameter-expanded portion is provided on the nozzle body.

2. The nozzle for continuous casting according to claim 1, It is characterized in that based on the upper end of the straight portion, the upper end of the air chamber is located within a range of 10 mm or more and 100 mm or less below.

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