JP2013082969A - Lower structure of vacuum degassing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lower structure of vacuum degassing apparatus having two circulating tubes improved in durability with a conduit through which a molten metal passes.SOLUTION: There is provided the lower structure of vacuum degassing apparatus. The circulating tube includes a circular sleeve having a cross section with center angle of ≥90° and ≤180° and a circulating tube body and has a complementary shape to form the conduit by being fitted. When a virtual line segment is defined by linking center points of two conduits on the cross section, both ends in the circumferential direction of the circular sleeve exist in a position having an angle of 45° or larger in the circumferential direction across the virtual line segment.

Description

  The present invention relates to a lower structure of a vacuum degassing apparatus for degassing by sucking molten metal put in a ladle or the like into a tank, and more specifically, durability of two reflux tubes each connected to a dip tube The present invention relates to a lower structure of a vacuum degassing apparatus with improved performance.

  A vacuum degassing apparatus is used for a process of adjusting the components of a molten metal, such as degassing hydrogen or nitrogen from a molten metal such as molten steel or decarburizing to remove carbon as CO. For example, in the RH (Ruhrstahl-Heraus) type vacuum degassing apparatus, generally, the upper structure having a canopy has an alloy inlet used for introducing an alloy as a component adjustment and an exhaust outlet for exhausting the atmosphere in the tank. In addition, the bottom of the furnace bottom is provided with two reflux pipes connected to the tip of the dip pipe, and the molten metal placed in the ladle is circulated into the tank. . As shown in FIG. 7, the upper structure and the lower structure of these vacuum degassing apparatuses may be formed to be separable like an upper tank and a lower tank by attaching a connection flange to each of them. It may be formed integrally without having.

  Among these, the lower structure arranged on the ladle side where the molten metal is put, sucks the molten metal from one dip tube, flows it into the tank through the reflux tube, and processes such as degassing in a vacuum Since the molten metal after treatment is returned to the ladle through the other reflux tube and dip tube, the damage is relatively severe. Among them, the dip tube whose tip is immersed in molten steel is generally RH type because it is conspicuous due to the action of the molten metal flow and the slag generated by the molten metal surface in the ladle. In the vacuum degassing apparatus, the molten metal is treated for about 40 to 250 charges and then replaced with a new dip tube.

  On the other hand, the reflux tube is not as large as the dip tube, but as the degassing process or the like is continued, cracks and cracks occur in the pipeline through which the molten metal passes. Once cracks are formed, molten metal will be inserted into the part and melting damage will be promoted. Therefore, before the life of the main body of the substructure is completed, a large scale centering on the conduit of the reflux pipe will be used. Repair work is required.

  In view of this, a technique has been employed in which a sleeve-shaped sleeve brick having a cylindrical structure is disposed in a reflux pipe to form a pipe line (see, for example, Patent Documents 1 and 2). That is, the conduit through which the molten metal passes is formed by a monolithic sleeve brick so as to eliminate joints in the conduit and prevent local damage due to insertion of the molten metal.

  In this regard, a technology that improves wear resistance and heat spalling by forming a cylindrical sleeve by casting a castable material in which a fluidity promoter and cement are added to an alumina-based raw material ( Patent Document 3) and a method of preventing melting damage at the boundary between the reflux tube and the dip tube by disposing the lower end of the cylindrical sleeve having an integral structure from the joining position of the reflux tube and the dip tube. Many improved techniques have been proposed, such as (see Patent Document 4). The actual situation is that this cylindrical sleeve is extracted from the reflux tube together with the replacement of the dip tube, replaced with a new one, and continues to operate.

JP-A-2-25513 JP-A-2-34714 JP 11-279629 A Japanese Patent Laid-Open No. 9-241721

  By the way, in the prior art, the present inventors have made a detailed examination again on cracks and the like generated in the conduit of the reflux pipe, which has been a factor in disposing the cylindrical sleeve as described above. That is, cracks and cracks may occur in pipes other than the joint parts of bricks, and cracks etc. may be confirmed even when pipes without joints are formed by irregular refractories, For these causes, structural analysis of the reflux tube was conducted based on the thermal stress calculation. As a result, cracks and cracks that occur in the conduit of the reflux pipe do not occur from the inside of the reflux pipe (the side of the pipeline through which the molten metal flows) as previously thought, but rather occur outside the reflux pipe. The conclusion was that it would be more reasonable to understand that it would reach the pipeline. It has also been found that cracks and cracks generated from the outside of the reflux tube are concentrated in a predetermined region.

  Accordingly, the present inventors have fitted a sleeve having a circular cross section into a predetermined position of the reflux tube main body based on the above-described new knowledge, and the inner wall surface of the sleeve and the inner tube of the reflux tube main body are fitted. It was found that by forming a pipe line with a wall surface, the occurrence of cracks and cracks in the reflux pipe can be efficiently suppressed, and the present invention has been completed.

  Accordingly, an object of the present invention is to provide a lower structure in which the durability of the reflux tube in the vacuum degassing apparatus is improved.

That is, the present invention is a lower structure of a vacuum degassing apparatus having two reflux tubes each having a conduit through which molten metal passes, and each of the reflux tubes has a cross section of 90 ° or more with the reflux tube body. And an arc-shaped sleeve having a central angle of 180 ° or less, and these have complementary shapes, and the arc-shaped sleeve is fitted to a part of the reflux tube body, A pipe line is formed by the inner wall surface of the arc-shaped sleeve, and the center point O ₁ of the pipe line of _one of the circulating pipes P _{1 and} the pipe of the other circulating pipe P ₂ in the cross section of the two circulating pipes When the virtual line segment L is connected to the center point O _{2 of the} road, both ends in the circumferential direction of the arc-shaped sleeve S ₁ disposed in the reflux pipe P ₁ are both based on the virtual line segment L. with present on angle is 45 ° or more positions at the central point O ₁ in the, reflux condenser Both ends of ₂ to disposed the circumferential direction of the arc-shaped sleeve S ₂ are both present at a position angle at the center point O ₂ with respect to the virtual line segment L is 45 ° or more, vacuum de It is the lower structure of a gas apparatus.

  In the present invention, each of the two reflux tubes in the lower structure includes a reflux tube main body and an arc-shaped sleeve that are integrally fitted with each other having a complementary shape, and the inner wall surface of the reflux tube main body and the inner wall surface of the arc-shaped sleeve To form a conduit. Among these, the arc-shaped sleeve has a central angle of 90 ° to 180 ° in the cross section. If this central angle is less than 90 °, it will not be possible to reliably protect the positions of cracks and cracks that may occur in the reflux tube body as will be described in detail below. On the other hand, when heated during actual operation, a force is applied to the end of the sleeve in the circumferential direction due to the thermal expansion of the sleeve itself and the thermal expansion of the reflux tube body, so that the sleeve buckles when the center angle exceeds 180 °. There is a risk of cracking. In particular, when the sleeve is cylindrical as in the prior art, the stress applied to the sleeve cannot be released, and the sleeve itself is cracked in the longitudinal direction due to stress strain. Note that the fact that the reflux tube main body and the arcuate sleeve have complementary shapes means that the inner wall surfaces can be aligned to form a pipe line in a state where both are fitted together, and the reflux tube body Needless to say, this includes a case where an expansion absorbing material is disposed between the sleeve and the arcuate sleeve, or a case where a protrusion or the like is provided on the arcuate sleeve to prevent displacement.

Further, when the arc-shaped sleeve as described above is arranged in the main body of the reflux pipe, the center point O of the pipe line of _one of the reflux pipes P ₁ in the cross section of the two reflux pipes parallel to the bottom of the tank. ₁ and when the other reflux condenser P _2, line virtual line L connects the center point O ₂ of both ends in the circumferential direction of the arc-shaped sleeve S ₁ which is disposed reflux condenser P ₁ However, in any case, the angle at the center point O ₁ is 45 ° or more, preferably 60 ° or more with reference to the position of the virtual line segment L (assuming 0 °). The same applies to the arcuate sleeve S ₂ disposed in the reflux pipe P ₂ .

In other words, when both ends in the circumferential direction of the arc-shaped sleeve S ₁ are represented by the points A ₁ and B ₁ (that is, the arc-shaped sleeve has an arc A ₁ B ₁ having a central angle of 90 ° to 180 °). The angle between the line segment O ₁ A ₁ and the virtual line segment L is 45 ° or more, preferably 60 ° or more, and the angle between the line segment O ₁ B ₁ and the virtual line segment L is 45 ° or more, preferably Similarly, for the arc-shaped sleeve S ₂ , the angle formed by the line segment O ₂ A ₂ and the imaginary line segment L is 45 ° or more, preferably 60 ° or more, and the line segment. The angle formed by O ₂ B ₂ and the imaginary line segment L is 45 ° or more, preferably 60 ° or more.

This is based on the fact that the present inventors conducted structural analysis of the reflux tube by thermal stress calculation. That is, in the vicinity of the crotch portion on the furnace bottom side formed by the _two reflux tubes P ₁ and P ₂ , there is a place where high tensile stress is applied to the outer wall surface of the reflux tube body, and there is a virtual cross section of the two reflux tubes. It was found that cracks and cracks occurred by concentrating on a region on an arc having a central angle of 45 ° in both directions across the line segment L. For this reason, an arc-shaped sleeve as described above is provided on the pipe line side so as to cover at least the region so as to prevent the progress of cracks and cracks.

The reason why such tensile stress occurs is not completely clarified, but it is considered that the stress is caused by the difference in thermal expansion between the working surface side (pipeline side) through which the molten metal flows and the outside. Further, as the vacuum degassing apparatus is actually operated, the reflux pipes P ₁ and P ₂ positioned in both the left and right directions with the midpoint m of the imaginary line segment L as the base point are connected to the tips of the dip pipes respectively connected thereto. Since it shows a widening behavior (opens in a square shape), it is assumed that this is one of the factors that cause concentration of stress in the above-mentioned places. The arc-shaped sleeve is preferably arranged in accordance with the length of the reflux tube, but it is also possible to arrange the arc-shaped sleeve so that a part of the tip side penetrates the dip tube side.

  In the present invention, an arcuate sleeve may be fitted to a part of the reflux tube body by interposing an expansion absorbing material such as mortar between the reflux tube body and the arcuate sleeve. Specifically, an expansion absorber is provided at the back side of the arc-shaped sleeve (opposite to the pipe line side) or at the end in the circumferential direction of the arc-shaped sleeve to provide an expansion allowance. It is good to absorb thermal expansion. Especially, if an expansion | swelling absorber is distribute | arranged to the both ends of an arc-shaped sleeve, the stress distortion concerning a sleeve itself can be relieve | moderated effectively and the durability of a reflux tube can be improved further.

  The means for forming the arc-shaped sleeve is not particularly limited, and may be formed into a predetermined shape by press molding or cast molding. Preferably, isostatic pressing (CIP) is performed. It is preferable to obtain an arc-shaped sleeve. In general, hydrostatic pressure molding is infinite multi-axial pressure, so it is possible to obtain a uniform molded product compared to uniaxial molding with a die press, and eliminate joints and refractory boundaries. Therefore, in obtaining the arc-shaped sleeve forming a part of the pipe line as in the present invention, it is preferable that the possibility of unnecessary insertion of molten metal can be eliminated.

  The thickness of the arc-shaped sleeve is desirably at least 70 mm, assuming a substructure in a general RH type vacuum degassing apparatus. In particular, if the durability of the reflux tube is ensured in accordance with the life of the vacuum degassing apparatus in consideration of the consumption of the arc-shaped sleeve (chemical erosion) due to operation, the thickness should preferably be 150 mm or more. Is good. Although the durability is further improved as the thickness of the arc-shaped sleeve is increased, it is considered that a thickness of about 200 mm is sufficient not only for practical effects but also for economic reasons.

  Further, the arcuate sleeve is formed with a protrusion or a groove at a circumferential end or a part of the back surface, or the diameter of the arcuate sleeve is gradually reduced toward the bottom of the tank ( It is also possible to prevent deviation from the main body of the reflux tube by reducing the thickness). Further, the arc-shaped sleeve may be disposed lower than the bottom of the tank, and the top of the sleeve may be restrained by a part of the reflux tube main body to prevent floating.

In addition, as a material for forming the arc-shaped sleeve, it is generally desirable to use a basic material in consideration of corrosion resistance, slag resistance, etc., but a neutral material or an acidic material can also be used depending on use conditions. . However, when an arc-shaped sleeve is obtained by hydrostatic pressure molding or press molding, it is desirable to use a material containing carbon in consideration of slidability during production. Examples of such a carbon-containing material include materials such as MgO—C, Al ₂ O ₃ —C, ZrO ₂ —C, and ZrO ₂ —CaO—C (ZCG).

  Further, the reflux pipe body is not particularly limited as long as it is provided with a pipe line formed with an arc-shaped sleeve, and the shape thereof may be formed using shaped bricks or amorphous refractories, or a combination thereof. it can. In the present invention, the circular tube is formed by fitting an arc-shaped sleeve at a predetermined position with respect to the reflux tube main body. However, other sleeves are prevented from being arranged on the reflux tube main body. It is not a thing.

  The lower structure of the vacuum degassing apparatus according to the present invention may be any structure provided with two reflux tubes as described above, and usually, a dip tube is connected to the tip of each of the reflux tubes. In addition, the surroundings of the refractory including the reflux pipe body and the dip pipe are covered with an iron skin to form a lower structure. This lower structure may be formed integrally with the upper structure that constitutes the vacuum degassing apparatus, and is divided into an upper tank and a lower tank via a connection flange (a three-tank structure including an intermediate tank). ) May be formed. Then, using the principle of the gas lift pump from the dip tube having the gas blowing holes, the molten metal such as molten steel put in the ladle is sucked up and passed through the tank, and the molten metal is circulated to the other reflux tube side. Then, a predetermined degassing process or the like is performed.

  According to the present invention, with respect to the pair of reflux tubes forming the lower structure, a sleeve having a circular cross section is fitted into a predetermined position of the reflux tube body, and the inner wall surface of the sleeve and the inner wall surface of the reflux tube body are fitted. Since the pipe is formed by the above, it is possible to efficiently suppress the occurrence of cracks and cracks that may occur in the circulating pipe main body. Therefore, it can be set as the lower structure which improved the durability of the reflux tube.

FIG. 1 is an explanatory perspective view showing a state of a longitudinal section of a lower structure of a vacuum degassing apparatus according to the present invention. FIG. 2 is a cross-sectional explanatory view of the cross section of the reflux tube in the lower structure as viewed from the furnace bottom side. FIG. 3 is a cross-sectional explanatory view showing a modified arrangement example of the arc-shaped sleeve in the reflux tube. FIG. 4 is a graph showing the thermal stress distribution in the circumferential direction of the reflux tube. FIG. 5 is a schematic diagram for explaining the measurement position of the reflux tube in the graph of FIG. FIG. 6 is a graph showing the thermal stress distribution in the circumferential direction of the arc-shaped sleeve in the present invention. FIG. 7 shows a schematic cross-sectional view of an RH type vacuum degassing apparatus.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.
FIG. 1 is a perspective explanatory view showing a longitudinal section of an example of the lower structure 1 in the vacuum degassing apparatus of the present invention. The lower structure 1 according to this embodiment includes a lower structure body 2, two reflux pipes 3 having a pipeline 4 for returning and returning molten metal, and two dip pipes 5. And the dip tube 5 are connected to each other by flanges 6 and 7 which are respectively provided, and are fastened and fixed by bolts (not shown). The lower structure 1 is provided on the lower structure main body 2 and can be connected to an upper structure (not shown) of the vacuum degassing apparatus by a flange 8. And the lower structure main body 2 and the reflux tube 3 form the lower structure 1 by covering the outer peripheral side surfaces thereof with the iron skin 16.

  Among these, the reflux tube 3 has a reflux tube main body 9 made of an irregular refractory, and an arc-shaped sleeve 10 (only half of which is shown in FIG. 1) having a circular cross section. Each pipe line 4 is formed by the inner wall surface of the reflux pipe body 9 and the inner wall surface of the arc-shaped sleeve 10, and includes the dip pipe body 12 made of an irregular refractory material that forms the pipe path 11 of the dip pipe 5. The walls are all prepared. In addition, the irregular refractory forming the reflux pipe main body 9 forms a tank bottom 14 so as to surround the laying brick 13 serving as Nakanoshima, and temporarily melted metal together with the side wall brick 15 forming the lower structure main body 2. Therefore, it is possible to perform degassing treatment and the like. On the other hand, a crotch portion 17 is formed on the furnace bottom side so as to be sandwiched between the two reflux tubes 3. With respect to the arc-shaped sleeve 10 disposed in these reflux tubes 3, the positional relationship with respect to the reflux tube main body 9 will be described below with reference to FIG.

FIG. 2 shows a cross section of the two reflux tubes 3 parallel to the tank bottom 14 and is a view seen from the furnace bottom side. In this figure, for the sake of convenience, the right reflux tube 3 is the reflux tube P ₁ , the left is the reflux tube P _2, and the arc-shaped sleeve 10 disposed in the reflux tube P ₁ is the arc-shaped sleeve S _1. The recirculation pipe P ₂ is an arcuate sleeve S ₂ . Here, the case where the two arc-shaped sleeves S ₁ and S ₂ each have a center angle of 180 ° is shown, and is fitted into the reflux tube main body 9 so that the back surfaces thereof face each other. Then, when a virtual line segment L by connecting the center point O ₂ of the reflux condenser P line center point O ₁ of 4 ₁ and the pipe 4 reflux condenser P _2, in the circumferential direction of the arc-shaped sleeve S ₁ Both ends are located at a position where the angle at the center point O ₁ is 45 ° or more, preferably 60 ° or more, both based on the position of the virtual line segment L (assuming 0 °). To same for both ends in the circumferential direction of the arc-shaped sleeve S _2. In FIG. 2, both end portions of the _two arc-shaped sleeves S ₁ and S ₂ are in a state where the angles at the center points O ₁ and O ₂ are 90 ° (with respect to the imaginary line segment L). The line segments O ₁ A ₁ , O ₁ B ₁ , O ₂ A ₂ , and O ₂ B ₂ have a 90 ° angle).

  Further, the arc-shaped sleeve is disposed so that both ends in the circumferential direction thereof are asymmetric with respect to the imaginary line segment L as shown in FIG. 3 if the conditions described above are satisfied. It doesn't matter. Furthermore, as shown in FIG. 3, even if the arc on the inner wall surface side (or the back side) protrudes or a protrusion is provided at the end, the end is not completely aligned in the radial direction, It does not matter as long as the effects of the present invention are exhibited.

  The means for obtaining the lower structure 1 according to this embodiment is not particularly limited, but the following method can be exemplified. For example, an iron skin 16 that covers the outer peripheral side surfaces of the lower structure main body 2 and the reflux pipe 3 and includes the flange 8 on the lower structure main body side and the flange 6 on the reflux pipe side at both ends is used as an outer frame. A curing surface is formed along the flange 6 on the tube side. Next, the arc-shaped sleeve 10 formed by press molding, casting molding, or the like is placed at a predetermined position, and the core that forms the conduit 4 of the reflux pipe 3 or the core of the laying brick 13 is inserted, and castable in the gap. (Unshaped refractory) is poured and filled, cured and dried to form the tank bottom 14. At that time, sheet mortar or the like may be applied in advance to the back surface of the arc-shaped sleeve 10 or the end face in the circumferential direction, and an expansion absorbing material may be interposed between the obtained reflux tube main body 9. Then, the lower structure 1 can be obtained by building the side wall bricks 15 and the like to complete the lower structure main body and connecting the separately formed dip tube 5.

  Alternatively, a portion corresponding to the shape of the arc-shaped sleeve 10 is provided in the core that forms the pipe line 4 of the reflux pipe 3, the castable is poured into the core, and after curing and drying, the core is removed, and the back surface and the circumferential direction The mortar may be dried by inserting an arc-shaped sleeve 10 coated with mortar on the end face. Furthermore, a core that is enlarged over the entire circumference by the thickness of the arc-shaped sleeve 10 is inserted, castable is poured, and after curing and drying, the core is removed from the frame. Apply the mortar to the end face in the circumferential direction of each arcuate sleeve obtained by dividing it into two in the vertical direction) and combine it so that it becomes cylindrical again, and apply the mortar to the back of each arcuate sleeve You may make it insert in a predetermined position. Of course, the reflux tube main body 9 can also be formed using bricks in addition to the castable.

Next, the structural analysis of the circulating pipe by the thermal stress calculation, which was referred to when determining the arrangement position of the arc-shaped sleeve, will be described.
First, regarding the lower structure of the prior art, the thermal stress applied to one reflux tube during operation was analyzed along its circumferential direction. That is, in the lower structure of the present invention shown in FIG. 1, the circular flow tube main body forming the pipe is formed in the lower structure when the pipe 4 is formed only by the circular flow pipe main body 9 without providing the arc-shaped sleeve 10. Thermal stress was measured along the circumferential direction on the inner side (duct side) and the outer side of 9. The results are shown in FIG. The horizontal axis of the graph of FIG. 4 is 180 ° from the crotch side to the opposite side, with the position where the imaginary line segment L and the reflux tube body 9 intersect as shown in FIG. This was rotated, and the position was changed by 10 ° during this period, and the distribution of thermal stress in the circumferential direction was calculated. In this calculation, the finite element method was used to calculate the temperature change data of the actual vacuum degassing tank.

  As can be seen from the graph shown in FIG. 4, the reflux tubes located in the left and right directions across the midpoint m of the imaginary line segment L are adjacent to each other at the shortest distance (angle = 0 °). A tensile stress of about 120 MPa is generated on the outer side of 9, and the tensile stress reaches a maximum exceeding 150 MPa at a position having an angle of 45 ° in the circumferential direction therefrom. Further, a tensile stress is generated at a high value up to a position having an angle of 60 ° in the circumferential direction, and the tensile stress gradually decreases as it is rotated along the circumferential direction, and the value becomes almost zero near an angle of 120 °. . On the other hand, on the inner side (the pipe line side) of the reflux pipe body 9, a compressive stress is generated at a high value up to the position of an angle of 60 °, as opposed to the relation of the tensile stress applied to the outer side, and thereafter. Gradually decreases in compressive stress and becomes almost constant around 120 °.

  Based on the structural analysis of the reflux tube by such thermal stress calculation, in the present invention, an arc-shaped sleeve is disposed corresponding to an arc region having a central angle of at least ± 45 ° across the virtual line segment L, Preferably, an arc-shaped sleeve is provided in correspondence with an arc region having a central angle of ± 60 ° across the imaginary line segment L so as to enhance the durability of the reflux tube.

  Therefore, the circular sleeve 10 having a center angle of 180 ° in the cross section is fitted to the reflux tube body 9 through a mortar so as to have the positional relationship shown in FIG. The thermal stress distribution in the circumferential direction on the back surface (outer surface) of the arc-shaped sleeve 10 was measured. The results are shown in FIG. The measurement environment and measurement conditions are the same as in the previous case, but the measurement range is 0 ° to 90 ° shown in FIG. 5 (because the arc-shaped sleeve has a central angle of 180 °). In addition, the arc-shaped sleeve used in this measurement is a cylindrical molded product having a thickness of 200 mm obtained by hydrostatic pressure molding, and is divided into two in the vertical direction.

  As can be seen from the graph of FIG. 6, it can be seen that the back surface of the arcuate sleeve 10 does not generate tensile stress in the entire circumferential range. That is, since the tensile stress generated outside the circulating tube body 9 described above is hardly transmitted to the arc-shaped sleeve 10, even if cracks or cracks occur outside the circulating tube body 9, The arcuate sleeve 10 can stop this. Further, when the thermal stress distribution on the working surface (inner side surface) of the arcuate sleeve 10 was also measured, a result almost the same as that shown in FIG. 6 was obtained, so that the arcuate sleeve 10 itself was broken. There is no risk of severe stress strain.

  Next, examples and comparative examples of the present invention will be described. In the following, the lower structure of an RH vacuum degassing apparatus capable of circulating 390 tons of molten steel per charge was formed. In manufacturing the reflux pipe 3, as described above, the iron skin 16 provided with the flange 8 on the lower structure main body side and the flange 6 on the reflux pipe side at both ends is used as an outer frame, and the reflux pipe is preliminarily provided. A curing surface was formed along the flange 6 on the side.

[Example 1]
First, a cylindrical molded product having an inner diameter φ700 mm × outer diameter φ1090 mm × height 1040 mm was prepared by hydrostatic pressing at a pressure of 1000 kg / cm ² using MgO—C powder containing 9 mass% graphite. After removing the frame, this cylindrically formed product was cut longitudinally with a diamond cutter into a semicircle, and an arc-shaped sleeve having a central angle of 180 ° in the cross section was obtained.

The obtained two arc-shaped sleeves were applied with basic mortar with a thickness of 2 mm (expansion allowance) on the back surface and the end surface in the circumferential direction, without being particularly processed without polishing. Arc-shaped sleeves were arranged so as to have a positional relationship as shown in FIG. 2, cores having an outer diameter of 700 mm were inserted, and Al ₂ O ₃ —MgO-based castables were poured into the gaps. After curing and drying, the lower structure main body is formed by lining a side wall brick of MgO-Cr ₂ O ₃ or the like, and a separately prepared dip pipe is attached to the reflux pipe side to form the lower structure according to the first embodiment. Was completed.

  Using the RH vacuum degassing apparatus having the substructure obtained above, the actual operation was performed by secondary refining of molten steel. As a result, the remaining thickness of the side wall bricks forming the lower structure body at 550 charges decreased, and the operation was stopped. At this time, neither cracks nor cracks were observed on the inner surface of the reflux tube main body and the arc-shaped sleeve forming the pipeline in both of the reflux tubes. Therefore, according to the lower structure of the present invention, the vacuum degassing apparatus itself can be used without requiring special repairs until the lifetime of the vacuum degassing apparatus itself.

[Example 2]
A cylindrical molded product having an inner diameter of 650 mm, an outer diameter of 1120 mm, and a height of 1040 mm was divided into two in the longitudinal direction to obtain an arc-shaped sleeve having a central angle of 180 ° in cross section. Next, the lower structure was completed in the same manner as in Example 1 except that the basic mortar was not applied to the arc-shaped sleeve, and both were arranged as they were on the outer frame made of iron skin.

  Using the RH-type vacuum degassing apparatus having the substructure obtained above, the actual machine was operated in the same manner as in Example 1. As a result, cracks and cracks could enter the pipe of the reflux tube even after 350 charges. Although there was no crack, the crack in the longitudinal direction became apparent at the approximate center of the arc-shaped sleeve at 500 charges, and the operation was stopped.

[Example 3]
The substructure was completed in the same manner as in Example 1 except that the basic mortar was not applied to the arc-shaped sleeve, and both were arranged as they were on the outer frame made of iron skin.

  Using the RH-type vacuum degassing apparatus having the substructure obtained above, the actual machine was operated in the same manner as in Example 1. As a result, cracks and cracks could enter the pipe of the reflux tube even after 350 charges. Although there was no crack, a crack toward the longitudinal direction became apparent at the center of the arc-shaped sleeve at 450 charges, and the operation was stopped.

[Example 4]
Each of the arc-shaped sleeves having the same size as that used in Example 1 was molded at a molding pressure of 2500 tons using a direct oil press. A basic mortar having a thickness of 2 mm was applied to the back surface and the circumferential end surface of the obtained arc-shaped sleeve (expansion allowance) to form a reflux tube and a lower structure main body in the same manner as in Example 1, and dipping A tube was attached to complete the substructure.

  Using the RH vacuum degassing apparatus having the substructure obtained above, the actual operation was performed by secondary refining of molten steel. As a result, cracks and cracks did not occur in the conduit of the reflux tube even after 350 charges, but the remaining thickness of the inner wall surface of the arc-shaped sleeve in the conduit of the reflux tube decreased at 480 charges. Wear was confirmed in a portion having a central angle of about 45 ° in both directions across an imaginary line segment L connecting the central points of two pipes, and the operation was stopped.

[Example 5]
The substructure was completed in the same manner as in Example 1 except that the arc-shaped sleeve having the same size as that used in Example 1 was replaced with a precast product of Al ₂ O ₃ —MgO.

  Using the RH-type vacuum degassing apparatus having the obtained substructure, the actual machine was operated in the same manner as in Example 1. As a result, cracks and cracks did not enter the conduit of the reflux pipe even after 350 charges. However, at the 380 charge, the remaining thickness of the inner wall surface of the arc-shaped sleeve is reduced, and a portion having a central angle of about 45 ° in both directions across the virtual line segment L connecting the center points of the two pipes. Cracks and cracks were confirmed, and the operation was stopped.

[Example 6]
A cylindrical molded product having an inner diameter φ700 mm × outer diameter φ1090 mm × height 1040 mm formed in the same manner as in Example 1 was cut into three longitudinal directions to obtain an arc-shaped sleeve having a central angle of 120 ° in cross section. It was. Using two of the obtained arc-shaped sleeves, basic mortar with a thickness of 2 mm was applied to the back surface and the end surface in the circumferential direction, respectively (expansion allowance). Then, at both ends in the circumferential direction of the arc-shaped sleeve forming the reflux pipe P ₂ , the angle mO ₂ A ₂ formed by the line segment L and A ₂ shown in FIG. It was placed an angle mO ₂ B ₂ and B ₂ as 70 °. Similarly, at both ends in the circumferential direction of the arc-shaped sleeve forming the reflux pipe P ₁ , the angle mO ₁ A ₁ formed by the line segment L and A ₁ is set to 50 °, and the other line segments L and B _The angle mO ₁ B ₁ formed with ₁ was set to 70 °. Except for these, a reflux tube and a lower structure main body were formed in the same manner as in Example 1, and a dip tube was attached to complete the lower structure.

  Using the RH-type vacuum degassing apparatus having the lower structure obtained above, and operating the actual machine in the same manner as in Example 1, the remaining thickness of the side wall bricks forming the lower structure body at 550 charges is reduced. The operation was stopped. At this time, neither of the two recirculation tubes is confirmed to have cracks or cracks on the inner surface of the recirculation tube main body and the arc-shaped sleeve forming the pipe, and special repairs are required until the life of the vacuum degassing device itself. It is also possible to use it.

[Comparative Example 1]
The substructure was completed in the same manner as in Example 1, except that the Al ₂ O ₃ —MgO-based castable was poured into the _two reflux tubes without forming the arc-shaped sleeve. Using the RH-type vacuum degassing device with the obtained substructure, the actual machine was operated by secondary refining of molten steel. At 350 charge, both cracked pipes were confirmed to have multiple cracks near the crotch. In particular, the operation was stopped because there was a relatively large crack at the center angle of about 45 ° in both directions across the virtual line segment L connecting the center points of the two pipes. .

[Comparative Example 2]
A cylindrical molded product having an inner diameter of 700 mm, an outer diameter of 1090 mm, and a height of 1040 mm was not divided in the vertical direction, and a pipe line was formed as it was with a cylindrical sleeve. That is, the same as in Example 1 except that a basic mortar having a thickness of 2 mm was applied to the back surface of the cylindrical sleeve (expansion allowance), and was arranged as it was on the outer frame made of iron skin to form two reflux tubes. Thus, the substructure was completed.

  Using the RH-type vacuum degassing apparatus having the substructure obtained above, the actual machine was operated in the same manner as in Example 1. As a result, cracks and cracks could enter the pipe of the reflux tube even after 350 charges. Although there were no cracks, the cracks randomly oriented in the longitudinal direction became apparent at a plurality of locations on the cylindrical sleeve at 430 charges, and the operation was stopped.

  The contents of the examples and comparative examples are summarized in Table 1 below.

1: lower structure, 2: lower structure main body, 3: reflux pipe, 4: pipe (circulation pipe), 5: dip pipe, 6: flange (reflux pipe), 7: flange (dip pipe), 8: flange ( Lower structure main body), 9: Circulating pipe main body, 10: Arc-shaped sleeve, 11: Pipe line (dip tube), 12: Dip pipe main body, 13: Laying brick, 14: Tank bottom, 15: Side wall brick, 16: Iron leather.

Claims (4)

A substructure of a vacuum degassing apparatus having two reflux tubes each having a conduit through which molten metal passes,
Each of the reflux tubes includes a reflux tube body and an arcuate sleeve having a central angle of 90 ° to 180 ° in cross section, and these have complementary shapes to each other. An arc-shaped sleeve is fitted to the portion, and a pipe line is formed by the inner wall surface of the reflux tube body and the inner wall surface of the arc-shaped sleeve; and
In cross-section of the two reflux condenser, when a virtual line L by connecting one of the center point of the reflux condenser P _1, line O ₁ and the other with the central point O ₂ of the conduit reflux condenser P _2, Both ends in the circumferential direction of the arc-shaped sleeve S ₁ disposed in the reflux pipe P ₁ are present at positions where the angle at the center point O ₁ is 45 ° or more with respect to the virtual line segment L. At the same time, both ends in the circumferential direction of the arc-shaped sleeve S ₂ disposed in the reflux pipe P ₂ are at positions where the angle at the center point O ₂ is 45 ° or more with respect to the virtual line segment L. A substructure of a vacuum degassing apparatus, characterized in that it exists.   The substructure of the vacuum degassing apparatus according to claim 1, wherein an arc-shaped sleeve is fitted with an expansion absorbent between the reflux tube body.   The lower structure of the vacuum degassing apparatus according to claim 1 or 2, wherein the arc-shaped sleeve has a thickness of at least 70 mm.   The lower structure of the vacuum degassing apparatus according to any one of claims 1 to 3, wherein the arc-shaped sleeve is obtained by hydrostatic pressure molding.

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