Immersion tube for treating molten steel

Abstract

To provide an immersion tube having a long service life to be used over a long period of time without causing falling of an inner brick layer from a core metal even if molten metal infiltrates from a boundary between an inner shaped refractory and an inner unshaped refractory during use.SOLUTION: An immersion tube 1 has an inner shaped refractory 2 formed in a cylindrical shape by a refractory brick, a metal core 3, and an outer unshaped refractory 4 made of an unshaped refractory. The inner shaped refractory 2 is formed in a cylindrical shape by alternately assembling first refractory bricks 5a, 5a,... and second refractory bricks 5b, 5b,... in a vertically long rectangular parallelepiped shape in a circumferential shape, and a predetermined tapered part 2b is formed on the lower side of the outer circumference of the inner shaped refractory 2. A plurality of vertically long recessed grooves 7, 7,... having a fixed depth are formed on the tapered part 2b at even intervals.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a dipping tube for molten steel treatment used in a vacuum degassing device or the like.

Background Art

[0002] In the process of secondary refining of steelmaking, a dipping tube that circulates molten steel with its lower end immersed in the molten steel in a ladle is mounted on the lower end of a vacuum degassing device and used. As such a dipping tube, as in Patent Document 1, a cylindrical cored bar along a vertical axis and a plurality of substantially rectangular parallelepiped-shaped (prismatic with a trapezoidal or fan-shaped horizontal cross section) bricks are assembled in multiple stages inside the cored bar to form a thick cylindrical brick layer (inner shaped refractory), and a thick cylindrical shaped refractory formed on the outer periphery of the cored bar by solidifying a fluid shaped refractory (castable or the like) is known.

[0003] Further, in the dipping tube of Patent Document 1, in order to prevent the situation where the shaped refractory at the lower end falls off and the inner brick layer falls off due to repeated heating and cooling during use, a large number of recesses are provided on the back surface of the inner brick layer, and a flange-shaped support fitting is attached to the inner side at the lower end of the cored bar. Such a dipping tube is used by mounting a reflux tube on the upper side and connecting the reflux tube in a state where a joining flange provided at the lower end of the reflux tube is fixed to a joining flange provided at the upper end, and then mounting it on the lower end of the vacuum degassing device.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, since the immersion tube of Patent Document 1 mentioned above is formed of an amorphous refractory whose heat-resistant strength is inferior to that of the shaped refractory at the lower end portion, during use, the formed portion made of the amorphous refractory at the lower end is eroded by the molten steel flow, making it easier for heat to be transferred to the core metal. As a result, the core metal may deform, and the internal brick layer (shaped refractory) may slip off. Also, in order to solve such problems, a structure in which the internal brick layer is extended to the lower end may be adopted. However, if the internal brick layer is extended to the lower end in this way, a material boundary between the internal brick layer and the outer amorphous refractory will be formed on the lower end surface. Therefore, the molten metal (molten iron) may invade from the boundary (i.e., metal sticking occurs), causing the core metal to melt or deform due to the heat load caused by the molten metal. As a result, the internal brick layer may slip off the core metal, and the molten metal sucked up from the ladle may enter the joint surface with the reflux pipe (i.e., between the joint flange at the upper end and the joint flange of the reflux pipe). That is, the conventional immersion tube as in Patent Document 1 has an insufficient effect of preventing the internal brick layer from slipping off.

[0006] An object of the present invention is to solve the problems of the conventional immersion tube mentioned above, and even if molten metal invades from the boundary between the internal shaped refractory and the amorphous refractory during use, the internal brick layer does not fall off the core metal, and to provide an immersion tube for molten steel treatment that has a long service life and can be used over a long period of time.

Means for Solving the Problems

[0007] Among the present inventions, the invention described in claim 1 is an immersion tube for molten steel treatment, which comprises a core bar formed in a cylindrical shape by metal, an inner shaped refractory (inner shaped refractory layer) formed in a cylindrical shape by refractory bricks and provided inside the core bar, and an outer unshaped refractory (outer unshaped refractory layer) made of unshaped refractory provided to cover the outside of the core bar. The inner shaped refractory is formed in a cylindrical shape by circumferentially assembling vertically long rectangular parallelepiped refractory bricks, and a tapered portion inclined so as to have a smaller diameter from top to bottom is formed on the lower side of the outer periphery of the inner shaped refractory. A plurality of vertically long concave grooves having a certain depth are formed at equal intervals in the tapered portion.

[0008] The invention described in claim 2 is characterized in that, in the invention described in claim 1, the depth of the concave groove is adjusted to be 10 mm or more and 50 mm or less.

[0009] The invention described in claim 3 is characterized in that, in the invention described in claim 1, the inner shaped refractory is formed by alternately assembling the following refractory bricks a and b. a. A first refractory brick in a vertically long rectangular parallelepiped shape, with an inclined surface formed on the lower side of the outer periphery so as to have a smaller radial width from top to bottom. b. A second refractory brick in a vertically long rectangular parallelepiped shape, with an inclined surface formed on the lower edge of the outer periphery so as to have a smaller radial width from top to bottom, and the outer diameter of the formed portion of the inclined surface being smaller than that of the first refractory brick.

Effect of the Invention

[0010] The immersion tube according to claim 1 has a predetermined tapered portion formed on the lower side of the outer periphery of the inner shaped refractory, and a plurality of vertically long concave grooves having a certain depth are formed at equal intervals in the tapered portion. Therefore, since the surface area of the inner shaped refractory in contact with the outer unshaped refractory is large, the dropping of the inner shaped refractory (such as shaped bricks) can be effectively suppressed, and thus it can be used for a long period of time (that is, it has a long service life).

[0011] Since the concave groove formed in the tapered portion on the lower side of the outer periphery of the inner shaped refractory of the immersion tube according to claim 2 is adjusted to a predetermined depth, it is possible to effectively suppress the cracking and peeling damage of the outer unshaped refractory (such as castable) in contact with the inner shaped refractory, so it can be used for a very long period of time.

[0012] The immersion tube according to claim 3 is formed in the invention according to claim 1 by alternately assembling two types of refractory bricks with different outer diameters at the formation part of the inclined surface on the outer periphery of the inner shaped refractory. Since each refractory brick is difficult to be melted (melted by the heat of molten metal), the whole inner shaped refractory is difficult to be deformed, so it is possible to very effectively suppress the dropping of the inner shaped refractory and can be used for an extremely long period of time.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0014] Hereinafter, an embodiment of the immersion tube according to the present invention will be described in detail with reference to the drawings. <Structure of the dipping tube> Figs. 1 to 3 show an example of a dipping tube according to the present invention. The dipping tube 1 is composed of an inner shaped refractory 2, a core bar 3, an outer unshaped refractory 4, etc.

[0015] Fig. 4 shows the inner shaped refractory 2. The inner shaped refractory 2 is formed into a thick cylindrical shape with a height of about 650 mm and a certain diameter (inner diameter = about 400 mm, outer diameter = about 700 mm) by circumferentially and alternately (in a staggered manner) assembling (fixing with mortar) first refractory bricks 5a, 5a,... made of magnesia-carbon material and second refractory bricks 5b, 5b,... also made of magnesia-carbon material so that the upper and lower positions do not shift.

[0016] Fig. 5 shows the assembled first refractory brick 5a and second refractory brick 5b. The first refractory brick 5a has a vertically long rectangular parallelepiped shape (the horizontal cross-section is trapezoidal or fan-shaped and the outer peripheral surface is inclined like a prism) with a predetermined height (about 600 mm) and a predetermined thickness (circumferential width of the outer peripheral surface = about 91 mm). On the lower side of the outer periphery, an inclined surface (flat surface) 6a is formed so that the radial width decreases from top to bottom. The inclined surface 6a is inclined at about 15° with respect to the vertical axis.

[0017] On the other hand, the second refractory brick 5b has a vertically long rectangular parallelepiped shape with the same height and the same thickness as the first refractory brick 5a. Similar to the first refractory brick 5a, an inclined surface (flat surface) 6b is formed at the lower edge of the outer periphery so that the radial width decreases from top to bottom. The inclined surface 6b is inclined at about 15° with respect to the vertical axis, similar to the inclined surface 6a of the first refractory brick 5a. Also, the outer diameter of the formed part (the whole) of the inclined surface 6b is shorter by a certain length than that of the first refractory brick at any height position.

[0018] Therefore, in the inner shaped refractory in which the first refractory bricks 5a and the second refractory bricks 5b are alternately assembled, a sizing portion 2a having a cylindrical shape with a certain diameter and thickness is formed on the upper side, and below the sizing portion 2a, a tapered portion 2b having a substantially inverted conical shape (i.e., a tapered shape that gradually becomes smaller in diameter from top to bottom) and a cylindrical shape is continuously provided, and a plurality of vertically long concave grooves 7, 7... having a certain depth (about 30 mm) and a certain width (circumferential width = about 91 mm) are formed at equal intervals in the tapered portion 2b (i.e., as shown in FIG. 5(b), steps +α and -α between the first refractory brick 5a and the second refractory brick 5b are formed at equal intervals in the tapered portion 2b). Note that the sizing portion 2a of the inner shaped refractory 2 is in a state of being fastened by a band iron (not shown).

[0019] On the other hand, as shown in FIGS. 1 to 3, the core metal 3 is formed in a cylindrical shape by a metal (steel) plate, and a sizing portion 3a having a certain diameter is provided from the central portion to the upper end (from the central portion in the height direction to the upper end). At the upper end of the core metal 3, a flange (joining flange) 11 having a flat donut shape is fixed (welded) so as to protrude outward.

[0020] Further, a lower tapered portion 3c having a width of about 130 mm is continuously provided at the lower end of the sizing portion 3a of the core metal 3 so as to gradually become smaller in diameter downward. The lower tapered portion 3c is inclined at about 15° with respect to the vertical direction. In addition, a large number of anchors 10, 10... formed by bending a cylindrical steel bar into a substantially V shape or a substantially Y shape are welded in a scattered manner on the outer peripheral surface (sizing portion 3a and lower tapered portion 3c) of the core metal 3.

[0021] Then, the above-described inner shaped refractory 2 is inserted inside the core metal 3 and is arranged concentrically with a gap of a predetermined distance. Therefore, the sizing portion 3a of the core metal 3 is arranged parallel to the outside of the sizing portion 2a of the inner shaped refractory 2 with a distance of about 28 mm, and the lower tapered portion 3c of the core metal 3 is arranged parallel to the outside of the tapered portion 2b of the inner shaped refractory 2 with a distance of about 20 mm.

[0022] On one hand, an outer unshaped refractory (outer unshaped refractory layer) 4 is provided on the outside of the inner shaped refractory 2 (including the inside and outside of the core metal 3). The outer unshaped refractory 4 is a castable (alumina-based castable) which is an unshaped refractory having fluidity. It is formed by pouring (casting) it into a formwork covering the core metal 3 with the inner shaped refractory 2 inserted therein and then solidifying and drying it. And the thickness between the outer circumference of the sizing part 3a and the surface layer of the outer unshaped refractory 4 is about 100 mm.

[0023] Furthermore, the castable constituting the outer unshaped refractory 4 is filled without any gap in the gap between the lower tapered part 3c of the core metal 3 and the inner shaped refractory 2. And the unshaped refractory that has entered the gap between the lower tapered part 3c of the core metal 3 and the inner shaped refractory 2 and the unshaped refractory constituting the outer unshaped refractory 4 are integrated (in a continuous state). Also, the lower end surface of the outer unshaped refractory 4 thus integrated forms the same surface as the lower end surface of the inner shaped refractory 2 (the lower end surface of the immersion tube 1 itself) (that is, the lower end of the inner shaped refractory 2 has reached the lower end of the immersion tube 1).

[0024] <Method of using the immersion tube> FIG. 6 shows an example of the method of using the immersion tube 1 configured as described above. The immersion tubes 1 are used in a pair of two, connected to the circulation pipe fixed at the lower end of the vacuum degassing device 11, and immersed in the molten metal (molten iron) S in the ladle 14 at the lower end. One of the two immersion tubes 1, 1 installed in such a way (the left immersion tube 1a in FIG. 6) functions as the riser tube, and the other (the right immersion tube 1b in FIG. 6) functions as the downcomer tube. Then, in the vacuum degassing device 11, when the upper tank 12 and the lower tank 13 are put in a vacuum state and an inert gas (argon gas or the like) is blown into the immersion tube 1a which is the riser tube through the pipe, the molten metal in the ladle 14 is drawn to the lower tank 13 side and rises through the molten metal passage (inside the inner shaped refractory 2) of the immersion tube 1a which is the riser tube, and then descends through the molten metal passage of the immersion tube 1b which is the downcomer tube and returns to the ladle 14 to circulate. In the process of such circulation, degassing of the molten metal is performed.

[0025] In the immersion tubes 1a and 1b, when degassing is carried out while being attached to the vacuum degassing device 11 as described above, a situation may occur where the molten metal enters from the boundary between the inner shaped refractory 2 and the outer unshaped refractory 4. However, at the lower end of the inner shaped refractory 2 of the immersion tubes 1a and 1b, a gap G with a certain width is formed between the tapered portion 2b and the lower tapered portion 3c of the core metal 3, and the gap G is filled with the unshaped refractory that constitutes the outer unshaped refractory 4. Therefore, it is extremely unlikely that the molten metal that has entered from the boundary reaches the core metal 3 or that the temperature of the core metal rises rapidly due to the heat of the molten metal.

[0026] Also, in the tapered portion 2b of the inner shaped refractory 2 of the immersion tubes 1a and 1b, vertically long concave grooves 7, 7... are formed at equal intervals. Therefore, since the contact area with the outer unshaped refractory 4 is extremely large, the restraining force (holding force) of the outer unshaped refractory 4 on the inner shaped refractory 2 is large, and it is unlikely that the inner shaped refractory 2 slips down with respect to the outer unshaped refractory 4. Furthermore, even if, by any chance, the inner shaped refractory 2 slips down with respect to the outer unshaped refractory 4, the lower tapered portion 3c that has entered the inside of the core metal 3 receives the portion at the lower end of the inner shaped refractory 2, so that the situation where the inner shaped refractory 2 falls out of the outer unshaped refractory 4 does not occur.

[0027] <Effect of the immersion tube> As described above, the immersion tube 1 is formed in a cylindrical shape by circumferentially assembling vertically long rectangular parallelepiped-shaped refractory bricks (first refractory bricks 5a, 5a... and second refractory bricks 5b, 5b...) for the inner shaped refractory 2. In addition, a predetermined tapered portion 2b is formed on the lower side of the outer periphery of the inner shaped refractory 2, and a plurality of vertically long concave grooves 7, 7... with a certain depth are formed at equal intervals in the tapered portion 2b. Therefore, since the surface area of the inner shaped refractory 2 in contact with the outer unshaped refractory 4 is large, the dropping of the inner shaped refractory 2 can be effectively suppressed, and it can be used over a long period of time (that is, it has a long life).

[0028] In addition, since the depth of the concave grooves 7, 7 formed in the tapered portion 2b on the lower side of the outer periphery of the inner shaped refractory 2 of the dipping tube 1 is adjusted to approximately 30 mm, it is possible to effectively suppress the cracking and peeling damage of the outer unshaped refractory 4 in contact with the inner shaped refractory 2, and it can be used for a very long period of time.

[0029] Furthermore, the dipping tube 1 is formed by alternately assembling two types of refractory bricks (first refractory bricks 5a, 5a and second refractory bricks 5b, 5b) in which the inner shaped refractory 2 has different outer diameters at the forming portions of the inclined surfaces on the outer periphery. Since each refractory brick is less likely to be damaged by melting (melting due to the heat of the molten metal), the whole of the inner shaped refractory 2 is less likely to be deformed, so that the dropping of the inner shaped refractory 2 can be very effectively suppressed, and it can be used for an extremely long period of time.

[0030] <Modification example of dipping tube> The dipping tube according to the present invention is not limited to the aspects of the above-described embodiments at all, and the materials, shapes, structures, sizes, etc. of the inner shaped refractory, the core metal, the outer unshaped refractory, etc. can be appropriately changed as necessary without departing from the gist of the present invention.

[0031] For example, the outer unshaped refractory is not limited to the one formed of an alumina-based castable as in the above-described embodiment, and it can be changed to the one formed of a castable other than the alumina castable such as an alumina-magnesia-based castable.

[0032] In addition, the inner shaped refractory is not limited to being formed by assembling refractory bricks made of magnesia-carbon material as in the above embodiment, and can be changed to those formed by assembling refractory bricks made of various acidic refractories, neutral refractories, and basic refractories other than magnesia-carbon materials, such as refractory bricks made of magnesia-chrome material or refractory bricks made of silicon carbide material. When the inner shaped refractory is formed by assembling refractory bricks made of a basic refractory mainly composed of magnesia-carbon material or magnesia-chrome material, it is preferable because the erosion resistance against molten steel is good and the anti-drop performance of the inner shaped refractory of the immersion tube is better.

[0033] In addition, the vertically long concave groove provided on the outer periphery of the tapered portion of the inner shaped refractory is not limited to being formed by alternately assembling two types of refractory bricks (first refractory brick and second refractory brick) with different outer diameters at the formation portion of the outer inclined surface as in the above embodiment, and it is also possible to arrange the first refractory brick with a large outer diameter at the formation portion of the outer inclined surface or the second refractory brick with a small outer diameter at the formation portion of the outer inclined surface continuously in the circumferential direction (for example, arranging a plurality of second refractory bricks between adjacent first refractory bricks). In addition, it is also possible to form the concave groove by periodically assembling three or more types of refractory bricks with different thicknesses (width in the circumferential direction) in the circumferential direction. When the concave groove is formed by alternately assembling two types of refractory bricks (first refractory brick and second refractory brick) with different outer diameters at the formation portion of the outer inclined surface as in the above embodiment, there is an advantage that the anti-drop performance of the inner shaped refractory is extremely good.

[0034] Moreover, the depth of the concave groove is not limited to 30 mm as in the above embodiment, and can be appropriately changed within the range of 10 to 50 mm as required. Table 1 below shows the results of examining the degree of cracking and peeling damage of the outer amorphous refractory 4 by changing the depth of the concave groove. From this Table 1, it can be seen that when the depth of the concave groove is adjusted to be 10 mm or more and 50 mm or less, it is possible to effectively prevent the cracking and peeling damage of the outer amorphous refractory 4.

[0035]

Table 1

[0036] Also, the inner shaped refractory is not limited to having a constant depth of the concave groove as in the above embodiment, and can be changed to one in which the depth of the concave groove becomes deeper as it goes downward (that is, the inclination angle of the inclined surface of the second refractory brick is larger than the inclination angle of the inclined surface of the first refractory brick), etc. In addition, when the depth of the concave groove is constant as in the above embodiment, there is an advantage that the anti-drop performance of the inner shaped refractory becomes extremely good. In addition, the number of concave grooves provided in the inner shaped refractory is not limited to 12 as in the above embodiment, and it is necessary to appropriately change according to the size and weight of the inner shaped refractory, etc.

[0037] Furthermore, the inner shaped refractory is not limited to being one in which the constant diameter part and the tapered part are integrally formed by assembling a plurality of types of vertically long refractory bricks in the circumferential direction as in the above embodiment. As shown in Fig. 7, it can also be changed to one in which the constant diameter part and the tapered part are separately formed (that is, a structure in which vertically long rectangular parallelepiped-shaped refractory bricks 5, 5... are assembled cylindrically on the upper part of a structure in which first refractory bricks 5a, 5a... provided with inclined surfaces 6a and second refractory bricks 5b, 5b... provided with inclined surfaces 6b are alternately assembled cylindrically), etc.

[0038] In addition, the immersion tube according to the present invention is not limited to the case where the gap between the tapered portion of the inner shaped refractory and the lower tapered portion of the core metal is adjusted to about 20 mm as in the above embodiment, and the gap can be appropriately changed as needed within the range of 5 mm or more and 30 mm or less. When the gap is less than 5 mm, it becomes difficult to fill the unfired refractory on the outside of the inner shaped refractory (the workability deteriorates), which is not preferable. On the contrary, when the gap exceeds 30 mm, if the damaged inner shaped refractory slips down with respect to the unfired refractory on the outside, the lower end portion of the inner shaped refractory cannot be received by the lower tapered portion of the core metal, and it becomes impossible to prevent the inner shaped refractory from falling out, which is not preferable. The gap between the tapered portion of the inner shaped refractory and the lower tapered portion of the core metal is more preferably 10 mm or more and 25 mm or less.

[0039] Also, in order to increase the holding strength of the unfired refractory on the outside, the core metal is not limited to the case where V-shaped or Y-shaped metal studs (round bars or the like bent into V-shaped or Y-shaped) are fixed (welded or screwed with bolts or the like) to the outer periphery of the lower side (constant diameter portion and lower tapered portion) as in the above embodiment, and metal studs having a shape different from V-shaped or Y-shaped such as cross-shaped or bolt-shaped may be fixed to the outer periphery of the lower side. In addition, the core metal can be changed to a structure in which a metal ring body (round bar or the like) is wound around the outer periphery of the lower end of the lower tapered portion in order to prevent the lower end of the lower tapered portion from opening due to the heat load.

Industrial Applicability

[0040] Since the immersion tube according to the present invention exhibits excellent effects as described above, it can be suitably used as a member that is attached to a vacuum degassing device when secondary refining molten steel and functions as a riser or a downcomer.

Explanation of Reference Numerals

[0041] 1 ·· Immersion tube 2 ·· Inner shaped refractory 2b ·· Tapered portion 3 ·· Core metal 4··Outer amorphous refractory 5a··First refractory brick 5b··Second refractory brick 6a··Inclined surface (first refractory brick) 6b··Inclined surface (second refractory brick) 7··Concave groove 11··Vacuum degassing device

Claims

1. A dipping tube for molten steel treatment, comprising a mandrel formed in a cylindrical shape by metal, an inner shaped refractory formed in a cylindrical shape by refractory bricks and provided inside the mandrel, and an outer unshaped refractory provided so as to cover the outside of the mandrel, wherein the inner shaped refractory is formed in a cylindrical shape by circumferentially assembling vertically long rectangular refractory bricks, and a tapered portion inclined so as to have a smaller diameter from above to below is formed on the lower side of the outer periphery of the inner shaped refractory, and a plurality of vertically long concave grooves having a certain depth are formed at equal intervals in the tapered portion. The dipping tube is characterized by this.

2. The dipping tube according to claim 1, wherein the depth of the concave groove is adjusted to be 10 mm or more and 50 mm or less.

3. The dipping tube according to claim 1, wherein the inner shaped refractory is formed by alternately assembling refractory bricks of the following a and b. a. A first refractory brick having a vertically long rectangular parallelepiped shape and having an inclined surface formed on the lower side of the outer periphery so as to have a smaller radial width from above to below b. A second refractory brick having a vertically long rectangular parallelepiped shape and having an inclined surface formed on the lower edge of the outer periphery so as to have a smaller radial width from above to below, and the outer diameter of the formed portion of the inclined surface is smaller than that of the first refractory brick

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