JP4733420B2 - Immersion tube for vacuum degassing equipment - Google Patents

Description

The present invention relates to a dip tube for vacuum degassing apparatus having excellent durability.

  RH or DH vacuum degassing apparatuses are known as vacuum degassing apparatuses that remove nonmetallic inclusions in molten steel, adjust components, and the like. The vacuum degassing apparatus is equipped with a dip tube that serves as a molten steel circulation path between the vacuum chamber and the ladle.

  The dip tube is formed by covering the inner and outer circumferences and the lower side of a cylindrical metal core with a refractory, and the lower side is used by immersing it in molten steel in a ladle. Since the molten steel flows through the inner hole, the wear of the refractory is particularly remarkable even in the vacuum degassing apparatus. When wear of the refractory progresses, it is repaired with a spraying material or patching material made of an irregular refractory. When repair is difficult, it is removed from the top flange and replaced with a new one.

  The dip tube is preheated at a high temperature of about 800 ° C. to 1000 ° C. before use. This is because if the molten steel is passed directly without preheating, the refractory is cracked due to thermal shock and the durability is greatly reduced. This preheating is generally performed with a dip tube attached to the vacuum chamber. In some cases, the preheating mainly of the dip tube and the vacuum chamber and the dip tube are preheated at the same time. In either case, the preheating is mainly performed on the inner peripheral surface through which the molten steel flows.

  As the refractory covering the inner periphery of the cylindrical metal core, a regular refractory made of refractory brick is generally used, but there is a case of an irregular refractory. On the other hand, since the refractory covering the outer periphery is not supported by the pressure as in the case of the inner periphery, an indeterminate refractory that can be easily supported by a locking traction metal such as a stud is used.

  When preheating the dip tube, there is a problem that cracks are likely to occur in the outer periphery-shaped refractory. Cracks cause the molten steel intrusion to melt the cylindrical cored bar and the stud erected on it and cause the refractory under the dip tube to melt or drop off. In particular, when a crack propagates from the lower end surface of the dip tube to the inner peripheral portion, it is greatly damaged in a V shape at an early stage along the crack, the cylindrical metal core is melted, and the life of the dip tube is remarkably shortened. Moreover, molten steel contamination by the nitrogen pick-up caused by the air intrusion from the crack is caused.

  Although repair with a spraying material or a patching material is performed for cracks, repair materials and repair man-hours are required, and further hot repairs are required, which is not preferable in terms of work safety.

Therefore, as a means for imparting strength and suppressing cracks on the irregular shaped refractory on the outer periphery, for example, addition of metal fibers (Patent Document 1), attachment of a wire mesh (including expanded metal) to a stud erected on a cylindrical metal core ( Patent Documents 2 and 3) have been proposed.
JP 2001-131630 A JP-A-10-140230 JP-A-10-219341

  However, the addition of the metal fiber causes the metal fiber to intervene in the entire refractory structure. If a sufficient amount of metal fiber is added to suppress cracking, the corrosion resistance and the hot strength of the refractory are reduced. On the other hand, the attachment of the wire mesh to the stud is limited to the reinforcement of the refractory support function of the stud, and a sufficient effect for crack suppression cannot be obtained.

  This invention makes it a subject to suppress the crack of the outer periphery indeterminate form refractory which causes the refractory of the lower part of a dip tube to melt and drop off, or causes a nitrogen pickup.

The present invention relates to a dip tube for a vacuum degassing apparatus in which an inner periphery and an outer periphery of a cylindrical metal core having a flange at its upper end are covered with a refractory, and a stud in which the cylindrical metal core is erected on its outer peripheral surface. has a periphery refractory of at least the cylindrical core metal of the refractory and castable refractory, and to the outer peripheral castable refractory, and from the outer peripheral surface not in contact with the stud in the thickness direction of 5 That is, a wire mesh is embedded in the circumferential direction of the dip tube at a position equal to or less than 1 / min.

  The dip tube obtained according to the present invention is extremely effective for suppressing cracks in the outer periphery-shaped refractory. The mechanism seems to be due to the following reasons.

  The purpose of preheating the dip tube is to preheat the inner peripheral surface of the dip tube in order to mitigate thermal shock caused by the molten steel when the dip tube is used. Generally, it is carried out by passing a gas burner flame through the inner hole of the dip tube. Even if the outer peripheral surface of the dip tube is heat-dried after construction, preheating is not performed.

  When the inner circumference side of the dip tube is heated at a high temperature during preheating, a temperature gradient is generated from the inner circumference side to the outer circumference side in the refractory, and a difference in thermal expansion is caused by the temperature difference. Unlike the inner peripheral refractory, the outer peripheral refractory is in contact with the atmosphere on the outside, so the temperature gradient becomes extremely large.

  In the outer periphery refractory, a compressive stress acts on the inner peripheral side and a tensile stress acts on the outer peripheral side due to a difference in thermal expansion caused by this temperature gradient. In general, the characteristics of a refractory are strong against compressive stress but weak against tensile stress. Therefore, the tensile stress generated on the outer peripheral side during preheating causes a crack in the outer periphery-shaped refractory.

  According to the present invention, a wire mesh is embedded in the vicinity of the outer periphery of the outer periphery-shaped refractory, so that the tensile stress on the outer periphery that is received during preheating is locked by the wire mesh, thereby suppressing the occurrence of cracks in the outer periphery-shaped refractory. As a result, it exhibits an excellent effect in preventing the lower refractory from damaging or falling off and reducing the nitrogen pickup, which is an important and unique problem of the dip tube.

  In the prior art, the inlay of the wire mesh to the outer periphery-shaped refractory is attachment to a stud erected on the cylindrical core metal. It is not embed | buried near the outer periphery of an outer periphery indefinite shape refractory like this invention. Even if there is an effect of strengthening the support of the outer peripheral irregular refractory to the cylindrical core metal, there is no action of locking against the tensile stress on the outer peripheral side, and the crack suppressing effect of the present invention cannot be obtained.

  In the present invention, the burying position of the wire mesh with respect to the height direction of the dip tube is preferably the entire height direction of the dip tube in order to ensure the effect of suppressing cracks. The dropout of the refractory in the dip tube mainly occurs at the lower part of the dip tube. In addition, air that causes nitrogen pickup enters from a crack at the lower part of the dip tube in order to bypass the lower end portion of the cylindrical cored bar of the dip tube. For this reason, the burial position of the wire mesh with respect to the height direction of the dip tube needs to be provided at least below the dip tube, which is directly effective in preventing refractories from dropping or preventing nitrogen pickup by suppressing cracks. Specifically, for example, it is embedded in an area of at least one third from the lower end in the dip tube height direction.

  The operation of the vacuum degassing apparatus moves up and down every time the molten steel is processed in the ladle. As the dip tube repeats dipping and pulling up with respect to the molten steel, slag adheres and accumulates on the outer periphery of the dip tube. If the slag adheres excessively, the immersion tube cannot be sufficiently immersed in the molten steel pan. In the case of the RH type vacuum degassing apparatus, since two dip tubes are mounted in parallel, the dip tubes are connected to each other by slag, so that it is difficult to replace the dip tubes. For this reason, the attached slag is appropriately removed with an instrument such as a picker. In this invention, although the position of the wire mesh is on the outer peripheral side of the dip tube, since the wire mesh is embedded in the irregular refractory, the wire mesh is not peeled off when removing the slag.

  Although preheating of the dip tube is performed by heating the inner peripheral surface, it is inevitable that part of the hot air at that time also travels to the lower end of the outer periphery of the dip tube. When the wire mesh is exposed, it is softened by this hot air, and the action of locking the tensile stress of the amorphous refractory is impaired. In addition, the wire mesh may fall off due to thermal expansion. In the present invention, since the wire mesh is embedded in the irregular refractory, there is no such problem.

  In the construction of the dip tube, in the construction of the refractory on the outer periphery of the cylindrical core metal, after arranging a wire mesh on the inner peripheral surface of the outer peripheral formwork, the amorphous refractory is placed between the cylindrical core metal and the outer peripheral formwork. The metal net can be embedded accurately and easily at a position in the vicinity of the outside in the thickness direction of the outer periphery indefinite refractory.

  The present invention is extremely effective in suppressing cracks in the outer periphery-shaped refractory during preheating. And the effect excellent in the damage prevention of the lower refractory which is the important and peculiar subject of a dip tube, and reduction of a nitrogen pickup can be exhibited.

  When constructing the dip tube, after placing a wire mesh on the inner peripheral surface of the outer mold, cast the amorphous refractory between the cylindrical cored bar and the outer mold to obtain the thickness of the outer peripheral irregular refractory. The wire mesh can be embedded accurately and easily at a position near the outside in the vertical direction.

  An example of the present invention applied to a dip tube of an RH vacuum degassing apparatus will be described with reference to the drawings. 1 is a longitudinal sectional view thereof, and FIG. 2 is a sectional view taken along line AA of FIG.

  The cylindrical metal core 1 is made of metal, and has a flange 2 for making the dip tube attachable to and detachable from the reflux tube located at the lower part of the vacuum chamber at the upper end. A large number of studs 6 are erected on the outer peripheral surface of the cylindrical metal core 1 in order to firmly support the outer peripheral irregular refractory 5 a on the cylindrical metal core 1. The shape of the stud 6 is not limited to the V shape shown in the figure, and may be a Y shape, a T shape, a net shape, or the like.

  The material of the outer periphery indefinite refractory 5a is, for example, alumina, alumina-silica, alumina-magnesia, alumina-spinel. Appropriate amounts of binder, dispersant, etc. are added, water is added and kneaded, and cast. Moreover, you may add 4 mass% or less metal fiber with respect to a refractory raw material in the range which does not impair the effect of this invention as needed.

  The RH type vacuum degassing apparatus has a dip tube and a riser tube and a descender tube. In the case of a dip tube as a riser pipe, although not shown in the figure, an inert gas pipe necessary for raising the molten steel by a gas lift may be included.

  The refractory provided on the inner periphery of the cylindrical metal core 1 may be a regular refractory or an irregular refractory. Since the inner peripheral surface of the dip tube is heavily worn due to contact with the molten steel flow, the regular refractory 3 having a high structure strength is preferable. Specific examples of the material of the fixed refractory 3 include magnesia-chromia brick and magnesia-carbon brick.

  In order to support the fixed refractory 3, a receiving metal fitting 4 a is provided below the fixed refractory 3. In the example of the figure, the metal fitting 4a has a pin shape, penetrates the cylindrical metal core 1, and the base end portion is fixed by welding. The gap between the regular refractory 3 and the cylindrical cored bar 1 is filled with an irregular refractory 5b or the like.

  The burying position of the wire mesh 7 with respect to the thickness direction of the outer periphery indefinite refractory 5a is in the vicinity of the outer side in the thickness direction of the outer periphery indefinite refractory 5a. The effect of the present invention cannot be obtained at the center or the cylindrical cored bar 1 side with respect to the thickness direction of the outer periphery-shaped refractory.

The tensile stress applied to the outer periphery-shaped refractory 5a during preheating is larger toward the outer side, and cracks are generated from the outer peripheral surface. For this reason, it is more effective for crack suppression that the wire mesh 7 is embedded as close to the outer peripheral surface as possible. More specifically, it is set to a position of 1/5 or less from the outer peripheral surface with respect to the thickness direction of the outer peripheral irregular refractory 5a . Preferably, the outer peripheral surface of the outer periphery-shaped refractory 5a and the outer surface of the wire net 7 are embedded substantially in the same position.

  The wire mesh 7 is embedded along the circumferential direction of the dip tube. With respect to the height direction, although it is provided in the entire height in the figure, the occurrence of cracks is directly connected to the cause of refractory falloff and nitrogen gas pickup, for example, at least 3 minutes from the lower end in the dip tube height direction It may be embedded in one area.

  FIG. 3 shows another dip tube according to the present invention. Here, an example in which a portion corresponding to the lower portion of the cylindrical metal core 1 is covered with the irregular refractory 5c. By extending the wire mesh 7 embedded in the above-mentioned outer periphery indefinite refractory 5a downward, the wire mesh 7 is also embedded in the vicinity of the outside of the lower amorphous refractory 5c.

  As the type of wire mesh 7 used in the present invention, generally available materials such as an ingot wire mesh, a rhombus wire mesh, a woven wire mesh, a welded wire mesh, a crimp wire mesh, and an expanded metal can be used. The specifications are appropriately determined depending on the use conditions and the size of the dip tube. Specifically, it may be determined from the viewpoints of reducing the resistance to tensile stress at the time of preheating, filling of the irregular refractory into the mesh portion, and the wear thickness when the wire mesh is eluted after being immersed in molten steel as much as possible. The wire diameter is preferably φ10 mm or less, more preferably φ5 mm or less, for example, φ1.8 to 5 mm. The mesh pitch of the wire mesh is preferably 5 mm to 300 mm, more preferably 30 mm to 100 mm.

  The wire mesh may be made of any material that does not lower the tensile strength in the temperature range during preheating, and general steel materials such as normal steel and stainless steel, and those made of Al, copper, and other metals can be used. From the economical aspect and strength, plain steel and stainless steel are preferred.

  The longitudinal cross-sectional view of FIG. 4 shows the preferable construction method of the dip tube of the example of the present invention. The cylindrical cored bar 1 provided with the flange 2 at the upper end is turned upside down so that the flange 2 faces down, and the dip tube is installed upside down.

  The construction of the irregular refractories 5 a and 5 b is performed by arranging a wire mesh 7 on the inner peripheral surface of the outer peripheral mold 8 installed on the outer periphery of the cylindrical core 1, and then the cylindrical core 1 and the outer mold 8. This is done by pouring an irregular refractory between the two. When pouring, the cone-shaped distributor 9 is placed at the upper end as shown in the figure, and when the amorphous refractory is allowed to flow down from above, the efficiency is improved in the direction between the cylindrical cored bar 1 and the outer mold 8. Indefinite refractories can be introduced. In addition, the amorphous refractory imparts vibration to improve the filling rate. As a method for applying vibration, for example, a mold is placed on a vibration table, a vibrator is attached to the mold, and a rod-like vibrator is used.

  As described above, the metal mesh 7 is arranged on the inner peripheral surface of the outer mold frame 8, so that the embedding depth can be kept constant along the circumferential direction of the dip tube. Moreover, it is also easy to make the outer surface of the wire mesh 7, which is the most effective embedment position in suppressing cracking of the outer periphery-shaped refractory, substantially the same position as the outer surface of the outer periphery-shaped refractory.

  When the metal mesh 7 is arranged in close contact with the inner peripheral surface of the outer mold 8, the irregular refractory is given vibration during construction, so that it enters between the metal mesh 7 and the outer mold 8, and after the construction. The wire mesh 7 is entirely embedded in the irregular refractory 5a. In order to embed the wire mesh 7 with a depth, for example, metal wire protrusions are provided at various locations on the outer periphery of the wire mesh 7, and an indefinite refractory is poured in a state where a space is provided between the wire mesh 7 and the outer mold frame 8.

  The construction of the inner refractory is performed by stacking a fixed refractory or pouring an irregular refractory between a cylindrical cored bar and an inner peripheral formwork installed on the inner periphery thereof. The example in the figure is an example in which the fixed refractory 3 is used as the inner peripheral refractory, and therefore the inner peripheral formwork is not used.

  Although not shown in the figure, in the case of a dip tube in which the lower end portion of the cylindrical metal core is covered with the irregular refractory 5c, the irregular refractory material is also poured into the lower end portion of the cylindrical metal core (dipping during construction). Since the pipe is turned upside down, the amorphous refractory is poured into the uppermost portion.) After the amorphous refractories 5a, 5b, and 5c are solidified, the mold is removed and dried.

  About the dip tube of RH type vacuum degassing apparatus, the Example of this invention and its comparative example are shown. In each example, the inner diameter refractory was 400 mm inner diameter, the outer diameter was 900 mm, the height was 750 mm, the inner peripheral refractory was a magnesia-chromia brick, and the outer peripheral refractory was an alumina-magnesia amorphous refractory having a thickness of 95 mm.

  In each example, the dip tube was turned upside down as shown in FIG. Brick is stacked on the inner periphery of the cylindrical core metal, and an outer peripheral mold is provided on the outer periphery, and the irregular refractory after kneading is vibrated with a rod-shaped vibrator between the outer peripheral mold and the cylindrical core metal. I poured it. A large number of V-shaped studs were erected on the outer peripheral surface of the cylindrical cored bar.

  Table 1 shows the wire mesh embedding conditions and test results in each example. In Examples 1 to 3, the wire mesh was disposed on the entire inner surface of the outer mold, and the outer peripheral irregular refractory was poured. Of these, in Examples 1 and 2, the outer peripheral surface of the metal mesh and the outer peripheral amorphous refractory were poured by pouring the outer peripheral amorphous refractory in a state where the metal mesh was placed in contact with the inner peripheral surface of the outer peripheral formwork. The outer peripheral surface was substantially in the same position. In Example 3, protrusions made of metal wires serving as spacers were provided everywhere on the outer surface of the metal mesh, so that the metal mesh was positioned at a depth of 10 mm from the outer peripheral surface of the outer peripheral amorphous refractory.

  Comparative Example 1 is an example in which a wire mesh is not embedded in the outer periphery-shaped refractory. Comparative Example 2 is an example in which a wire mesh is locked to a stud, and the position of the wire mesh is set to be approximately the center in the thickness direction of the outer periphery indefinite refractory.

  The inner surface of each dip tube was heated with an oxygen-LPG gas burner at 1000 [deg.] C. for 3 hours, and a comparative test was conducted on the occurrence of cracks in the outer periphery-shaped refractory.

  In the dip tube of the example, the crack occurrence situation immediately after the start of heating was not significantly different from that of the comparative example, but after the completion of heating for 3 hours, a clear large crack was generated in the comparative example. In the examples, the cracks were all about hair cracks. Moreover, the area ratio of the cracks is 100 for Comparative Example 1 and 1 or less for all Examples, confirming that the crack suppression effect of the present invention is remarkable. In addition, this crack suppression effect on the outer periphery-shaped refractory material can greatly contribute to the reduction of nitrogen pickup to the molten steel, which is one of the important issues of the dip tube.

Although not shown in the table, an actual machine test was conducted for Example 1 and Comparative Example 1. All were repaired with spraying material, patching material, etc. and used. As a result, the service life of the dip tube is due to wear, dropout, etc. of the lower amorphous refractory, while Comparative Example 1 is used 60 to 70 times, while Inventive Example 1 is 90 to 100 times. Met.

  As an application example of the present invention, a dip tube for an RH vacuum degassing apparatus has been described in the above description, but it can be applied to a dip tube for a DH vacuum degassing apparatus.

The longitudinal cross-section of the dip tube by the example of this invention is shown. The AA cross section of FIG. 1 is shown. The longitudinal cross-section of the other dip tube by the example of this invention is shown. The example of the preferable construction method of the dip tube by this invention is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cylindrical core metal 2 Flange 3 Fixed refractory 4a, 4b Receptacle 5a, 5b, 5c Unshaped refractory 6 Stud 7 Wire net 8 Outer frame 9 Cone-shaped distributor

Claims (2)

In a dip tube for a vacuum degassing apparatus in which an inner periphery and an outer periphery of a cylindrical metal core having a flange at the upper end are covered with a refractory, the cylindrical metal core has a stud erected on its outer peripheral surface, Of the refractories, at least the outer peripheral refractory of the cylindrical metal core is an irregular refractory, and the outer peripheral refractory does not contact the stud in the thickness direction and is one fifth or less from the outer peripheral surface. A dip tube for a vacuum degassing apparatus in which a wire mesh is embedded at the position of the dip tube in the circumferential direction.   The dip tube for a vacuum degassing apparatus according to claim 1, wherein the lower end portion of the cylindrical metal core is covered with an irregular refractory.

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