JP2011156553A - Method for maintaining tundish - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for maintaining a tundish that hardly casues peeling-off trouble of a repairing material and a covering material. <P>SOLUTION: The method for maintaining the tundish includes: (a) a step of cooling the tundish having finished continuous casting and removing residual steel slag inside the tundish and a deteriorated lining refractory; (b) a step of suppressing a rate of minute particles with a particle diameter of <75 μm occupying refractory aggregate to ≤25 mass%, using powdery silicate indicating ≥40 mass% of solubility when dissolved in 10°C water for five minutes as a binder, and spraying the repairing material containing a hardening accelerator formed of a lime compound to the inner surface of the tundish together with working water; and (c) a step of spraying a covering material containing ≥35 mass% of the minute particles with the particle diameter of <75 μm with respect to the refractory aggregate to the sprayed body of the repairing material together with the working water. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for preparing a tundish used for continuous casting of steel in an iron making process.

  In continuous casting of steel, the function of adjusting the injection rate of molten steel into the mold, the function of homogenizing the composition and temperature of the molten steel, and the function of removing inclusions in the molten steel, A tundish as an intermediate container placed between the mold and the mold is essential.

  FIG. 1 shows a sectional view of the tundish. The tundish has a structure in which a permanent layer 2, a base material layer 3, and a coating layer 4 are laminated in this order inside the iron skin 1. Usually, the permanent layer 2 is made of a brick containing alumina, the base material layer 3 is made of an alumina-silica amorphous refractory, and the covering layer 4 is made of a magnesia amorphous refractory.

  Since the remaining steel slag has adhered to the inner surface of the tundish that has been continuously cast, and the covering layer 4 and the base material layer 3 (hereinafter collectively referred to as the lining refractory), It cannot be reused as it is. Therefore, the tundish that has been continuously cast is provided for reuse after being maintained.

  Tundish maintenance is generally performed according to the following flow. End of continuous casting → Water cooling of tundish → Removal of steel residue in tundish → Deteriorated lining refractory, specifically removal of coating layer 4 and part of base material layer → Base material layer 3 Spraying the repair material onto the removed portion → Blowing the coating material to form the coating layer 4 → Preheating the tundish → Resuming continuous casting.

  In the maintenance flow, the repair material used for repairing the base material layer 3 is made by adding at least a binder to a refractory aggregate made of a material that matches the base material layer 3. As the repair material, a material using powder silicate as a binder (see Patent Document 1 or the like) or a material using alumina cement (see Patent Documents 2 and 3, etc.) is mainly used.

  A repair material using a phosphate as a binder is also known, but depending on the steel type, the use of phosphate may be restricted, so that a large amount of phosphate is not desired.

  In spraying the repair material, it is desired that the adhesion rate to the inner surface of the tundish is good, that is, the rebound loss is small. In this regard, in the spraying technique for the amorphous refractory, the proportion of fine particles having a particle size of less than 75 μm (hereinafter sometimes simply referred to as fine particles) in the refractory aggregate constituting the irregular refractory is 25% by mass or less. In this case, it is considered that the amorphous refractory does not have enough stickiness and rebound increases, which is not preferable (see Patent Document 4). Therefore, conventionally, even in the repair material, the proportion of fine particles in the refractory aggregate is about 35% by mass.

  In general, in the spraying technology for amorphous refractories, a curing accelerator is used to prevent the sprayed amorphous refractory from dripping, but in the spraying of repair materials for tundish, its construction is applied. Since the thickness is not so thick, and even if it is thick, it is at most about 30 mm, so a curing accelerator is not necessarily used (see Patent Documents 1 and 2).

JP 61-158873 A Japanese Patent Laid-Open No. 11-123508 JP 60-127372 A JP-A-5-238837

  In order to reduce the thermal energy required for preheating the tundish before resuming continuous casting, it is desirable to finish spraying the repair material and the covering material before the tundish is cooled too much.

  In this regard, the remaining steel slag and deteriorated lining refractories can be removed remotely by an actuator while the tundish is in a high temperature state, so that the repair material can be sprayed at a high temperature of 200 ° C or higher on the inner surface of the tundish. You can look into it.

  However, for example, when the remaining steel slag is significantly attached, or when the tundish is induction heating type and maintenance of the induction heating coil is required, manual repair is required. In some cases, the temperature of the inner surface of the tundish must be cooled to, for example, about room temperature to about 100 ° C. so that the water can enter.

  As described above, in the maintenance of the tundish, the temperature of the inner surface of the tundish when starting to spray the repair material can vary greatly between maintenance flows. Due to this, the following problems have arisen.

  When powdered silicate is used for the binder of the repair material, the tundish inner surface shows good adhesion when sprayed with construction water at a high temperature of 200 ° C or higher, but the tundish inner surface is applied at a low temperature of less than 200 ° C. When sprayed with water, peeling tends to occur during preheating.

  According to the study by the present inventors, the cause of this separation is due to the fact that the way of evaporation of the construction water from the spray construction body becomes slow when the temperature is low, and water vapor is trapped in the spray construction body. This is probably because a gap is formed between the sprayed construction body and the inner surface of the tundish.

  On the other hand, when alumina cement is used for the binder of the repair material, the tundish inner surface shows good adhesion when sprayed with construction water in a low temperature state of less than 100 ° C, but the tundish inner surface is in a high temperature state of 200 ° C or higher. When sprayed together with the construction water, the construction water evaporates from the spray construction body, so the time required for the hydration reaction of the alumina cement cannot be sufficiently secured and good adhesion cannot be shown. .

  When the repair material is peeled off, the covering material covering the repair material is also peeled off together. Even if the repair material does not peel off, only the coating material may peel off during preheating or during use. According to the study by the present inventors, one of the main causes of the peeling of the covering material is considered to be a difference in thermal expansion characteristics between the repair material and the covering material.

  An object of the present invention is to provide a tundish maintenance method that hardly causes troubles of peeling of a repair material and a covering material.

  According to one aspect of the present invention, (a) cooling the tundish after continuous casting, removing the remaining steel slag and deteriorated lining refractory inside the tundish, and (b) on the inner surface of the tundish, The proportion of fine particles in the refractory aggregate is suppressed to 25% by mass or less, and as a binder, powder silicate showing a dissolution rate of 40% by mass or more when dissolved in water at 10 ° C. for 5 minutes is used. A step of spraying a repair material containing a hardening accelerator together with the construction water, and (c) a coating material having a proportion of fine particles in the refractory aggregate of 35% by mass or more applied to the spray construction body of the repair material. And a tundish maintenance method having a step of spraying together.

  By controlling the proportion of fine particles in the fireproof aggregate of the repair material to 25% by mass or less, the air permeability of the sprayed construction body of the repair material is improved. Even if the step (a) is finished, the tundish Even if the inner surface is less than 200 ° C., the construction water is likely to evaporate from the repairing material spray construction body, and the occurrence rate of peeling due to the accumulation of water vapor in the spray construction body can be reduced.

  Despite suppressing the proportion of fine particles in the fireproof aggregate of the repair material, the use of powdered silicate that is easy to dissolve in water and the use of a curing accelerator also suppresses rebound loss during spraying. And the strength of the sprayed construction body can be ensured.

  Since the repairing material has a coarse structure with few fine particles and the covering material has a dense structure with relatively many fine particles, the biting property of the covering material to the sprayed construction body of the repairing material increases, so even the heat of both Even if the expansion rates are different, the coating material is difficult to peel off during preheating or during tundish use.

It is sectional drawing of a tundish.

  First, the structure of the repair material will be described.

  The repair material is formed by adding at least a binder and a hardening accelerator to the refractory aggregate.

  The refractory aggregate is made of an alumina material such as fused alumina, sintered alumina, bauxite, porphyry shale, calcined alumina, silica stone, volatilization so as to be a material consistent with the base material layer 3 in FIG. Siliceous raw materials such as silica and fused silica, alumina-siliceous raw materials such as wax, chamotte, clay, andalusite, sillimanite, kayanite and mullite, magnesia raw materials such as magnesia clinker, dolomite such as dolomite clinker One or more kinds selected from raw materials, carbonaceous raw materials, spinel raw materials, and pulverized products of used refractory materials containing these as main materials can be used.

  The refractory aggregate is composed of coarse particles having a particle size of 1 mm or more, medium particles having a particle size of 75 μm or more and less than 1 mm, and fine particles having a particle size of less than 75 μm. In the repair material, it is necessary to suppress the proportion of fine particles in the refractory aggregate to 25% by mass or less in order to facilitate the dissipation of water vapor from the sprayed construction body. In order to increase the particle size composition of the refractory aggregate and further promote the dissipation of water vapor, the proportion of coarse particles in the refractory aggregate is preferably 15% by mass or more.

  As the binder, powder silicate (hereinafter referred to as “water-soluble powder silicate”) having a dissolution rate of 40% by mass or more when dissolved in water at 10 ° C. for 5 minutes is used. Here, water refers to purified water, and the dissolution rate is a value when the dissolution is promoted by stirring with a stirrer or the like.

  Powdered silicates are well known as binders. However, since general powder silicate is obtained by rapidly dehydrating and pulverizing an alkali silicate aqueous solution by spray drying or the like, the powder silicate particles obtained have a fine particle size of 180 μm or less. The particle shape is a hollow sphere, and since it has a spherical shape, the surface area is minimal, so there is room for improvement in terms of increasing the dissolution rate in water.

  Therefore, by crushing the powdered silicate obtained by the above conventional method to an extent that the average particle size is ½ or less, for example 70 μm or less, preferably 50 μm or less, and destroying the hollow structure, Since the dissolution rate with respect to water increases with the increase in the surface area, it can be formed into a readily water-soluble powder silicate. Note that a known technique such as a vibration mill, a ball mill, or a pulverizer can be used for the crushing treatment.

  In this specification, the average particle diameter means a volume average particle diameter corresponding to the central cumulative value of a cumulative curve measured with a laser diffraction / scattering particle size distribution meter. Further, in the present specification, the particle size of the particle being equal to or larger than d means that the particle is a particle size remaining on the sieve having an opening d defined in JIS-Z8801, and the particle size of the particle is less than d. , Meaning that the particles are of a particle size that passes through the same sieve.

The molar ratio of SiO ₂ / M ₂ O (M is Na or K) (hereinafter referred to as “silicic acid ratio”) in the readily water-soluble powder silicate is preferably 3 or less. Thereby, the melt | dissolution rate with respect to water can be raised further. Powdered silicates with a silicate ratio of 3 or less can be obtained by spray drying an alkali silicate aqueous solution with a silicate ratio of 3 or less. It can also be obtained by adjusting the ratio of silica to 3 or less.

  The addition amount of the easily water-soluble powdered silicate is preferably 3 to 10% by mass on the basis of 100% by mass of the refractory aggregate. When the content is 3% by mass or more, sufficient adhesive strength can be obtained, and when the content is 10% by mass or less, seizure to the base can be prevented.

  As the curing accelerator, one or more selected from lime compounds such as slaked lime, quicklime, calcium carbonate, calcium aluminate and the like can be used. The addition amount is preferably 1 to 8% by mass on the basis of 100% by mass of the refractory aggregate. By setting the content to 1% by mass or more, a remarkable hardening accelerating action can be exhibited with respect to the easily water-soluble powdered silicate, and by setting the content to 8% by mass or less, the corrosion resistance can be prevented from being lowered.

  In addition, the repair material may include additives such as organic fibers and a dispersant.

  As the organic fiber, for example, one or more selected from pulp, vinylon fiber, polypropylene fiber, polyethylene fiber, polyester fiber and the like can be used.

  The organic fiber is generally added for the purpose of forming a water vapor ventilation path, but in this embodiment, it is added for the purpose of reducing the rebound loss. That is, when the proportion of fine particles in the refractory aggregate is suppressed, rebound is likely to occur, but rebound can be suppressed by the organic fiber acting as a buffer material.

  The addition amount of the organic fiber is preferably 0.05 to 0.5% by mass on the basis of 100% by mass of the fireproof aggregate. By setting it as 0.05 mass% or more, the effect of rebound prevention becomes remarkable, and the fall of corrosion resistance can be prevented by restraining to 0.5 mass% or less.

  Examples of the dispersant include alkali metal phosphates such as sodium tripolyphosphate, sodium hexametaphosphate, sodium ultrapolyphosphate, sodium hexametaphosphate, polycarboxylate such as sodium polycarboxylate, alkylsulfonate, aromatic One or more selected from sulfonates, sodium polyacrylate, sodium sulfonate, and the like can be used. The addition amount is preferably 0.01 to 1% by mass on the basis of 100% by mass of the refractory aggregate.

  Hereinafter, the configuration of the covering material will be described.

  The covering material is formed by adding at least a binder to the refractory aggregate. The difference between the coating material and the repair material is that the proportion of fine particles in the fireproof aggregate is relatively increased, the binder is not limited to the water-soluble powder silicate, and the hardening accelerator is not essential. It is. This will be specifically described below.

  The refractory aggregate can be configured to include, for example, a magnesia material such as magnesia clinker, a calcia material such as calcia clinker, and the like so as to be a material that matches the coating layer 4 of FIG. In addition, a siliceous raw material such as silica stone and an alumina-silica raw material such as clay may be included. Generally, since the fireproof aggregate of the covering material is different from the fireproof aggregate of the repair material, the thermal expansion characteristics of both are different.

  The refractory aggregate is composed of coarse particles having a particle size of 1 mm or more, medium particles having a particle size of 75 μm or more and less than 1 mm, and fine particles having a particle size of less than 75 μm. In the covering material, in order to improve the biting property of the repair material to the spray construction body, it is necessary that the proportion of the fine particles in the fireproof aggregate is 35% by mass or more. From the viewpoint of improving the bite structure of the repair material to the sprayed construction body by making the particle structure of the fireproof aggregate dense, the proportion of coarse particles in the fireproof aggregate is preferably less than 15% by mass. More preferably, it is 5 mass% or less.

  The binder is not particularly limited. Since the proportion of fine particles in the refractory aggregate is 35% by mass or more, the viscosity of the coating material can be sufficiently secured when sprayed together with the construction water, and rebound does not easily occur. It is not necessary to use salt. Thus, for example, ordinary powdered silicate can be used. However, a water-soluble powder silicate may be used for the binder of the covering material.

  In addition, additives such as a curing accelerator, organic fibers, or a dispersant may be included in the coating material.

  Hereinafter, a tundish maintenance method will be described.

  First, after completion of continuous casting, the operation of removing the immersion nozzle from the tundish is performed, and the tundish is transferred from the continuous casting position to the maintenance position (transfer process). Usually, when the maintenance position is reached, the temperature of the inner surface of the tundish is, for example, about 800 to 1000 ° C.

  Next, the tundish is cooled (cooling process). Usually, by supplying water into the tundish, the temperature of the inner surface of the tundish is lowered to, for example, 600 ° C. or less, specifically, 400 to 500 ° C. One of the purposes of this cooling process is to solidify the remaining steel sheet in the tundish. The tundish may be cooled by air cooling or natural standing.

  Next, the remaining steel slag solidified in the tundish and the deteriorated lining refractory are removed (removal step). Specifically, after removing the solidified steel sheet, the covering layer 4 is removed, and the deteriorated portion of the base material layer 3 is removed.

  Normally, the remaining steel slag and the deteriorated lining refractory are removed remotely by an actuator. In this case, since the removal operation can be performed while the tundish is in a high temperature state, the removal operation can be completed without lowering the temperature of the inner surface of the tundish to less than 200 ° C.

  However, when the remaining steel plate is significantly attached to the inner surface of the tundish, or when the tundish is induction heating type and maintenance of the induction heating coil is required, the inner surface of the tundish is, for example, room temperature to about 100 ° C., for example, After cooling to about 80 °, the worker enters the inside of the tundish and performs maintenance work together with the above removal work.

  Next, in order to repair the base material layer 3, a repair material is sprayed on the inner surface of the tundish together with construction water (a repair material spraying step). The construction thickness of the repair material is such as to fill the removed portion of the base material layer 3, for example, about 5 to 30 mm.

  As a spraying method, dry-type spraying is performed by feeding spray material (repair material) into the transport pipe and transporting it by air, and adding water to the spray material in the nozzle connected to the transport pipe or the tip of the transport pipe. The attaching method is preferred. The amount of water added to the repair material is, for example, about 15 to 25% by mass with respect to the repair material.

  By suppressing the proportion of fine particles in the fireproof aggregate of the repair material to 25% by mass or less, even when the inner surface of the tundish is less than 200 ° C. at the time of completion of the removal process, Since it is difficult for water vapor to accumulate, it is possible to dissipate most of the construction water from the repairing material spray construction body before spraying the coating material described later, and to prevent peeling during preheating.

  Despite suppressing the proportion of fine particles in the fireproof aggregate of the repair material, the rebound loss can be suppressed and the spray construction body by using the water-soluble powdered silicate and the hardening accelerator in combination. The strength of the can be ensured.

  In addition, since powder silicate is used for a binder, when a tundish inner surface is 200 degreeC or more, it is needless to say that a favorable adhesive rate is obtained. Thus, since the repair material can cope with a wide temperature range from low temperature to high temperature, the convenience that the repair material does not need to be properly used depending on the temperature of the inner surface of the tundish is obtained.

  Next, in order to form the coating layer 4, the coating material is sprayed onto the repair material spray construction body together with the construction water (coating material spraying step). The construction thickness of the covering material is, for example, about 25 to 30 mm. A dry spraying method is also preferable as the coating material spraying method. The amount of water added to the coating material is about 20 to 30% by mass.

  By setting the repair material to have a structure with less fine particles and the cover material to have a structure with relatively more fine particles, it is possible to improve the biting property of the cover material to the sprayed construction body of the repair material, that is, the adhesiveness.

  In other words, since the repair material has a small particle content and a medium particle size and high coarse particle content, the surface of the repair material sprayed body is uneven. Since the coating material has more fine particles and is denser than the repair material, the coating layer is formed in a state in which the coating material is fitted into the uneven portion. Due to such a joint structure between the two, even if the thermal expansion coefficients of the two differ, it is difficult for the covering material spray construction body to peel off from the repair material spray construction body during preheating or during tundish use. .

  Next, the tundish that has been repaired is preheated (preheating step). The preheating is performed at a high temperature rising rate of, for example, about 1000 ° C./2 hours to 1200 ° C./2 hours, unlike a general drying process of an irregular refractory. After preheating, the tundish is ready for reuse.

  The tundish to be serviced is not particularly limited. However, induction heating type tundish requires maintenance of the induction heating coil. Due to the fact that the temperature tends to fluctuate greatly, the repair material and the covering material are likely to be peeled off. Therefore, the present invention is particularly significant when applied to induction heating tundish.

  In addition, in a tundish whose side surface is cut to 70 ° or more, the repair material and the covering material sprayed on the side surface are more easily peeled off than a tundish whose side surface is inclined to less than 70 °. For this reason, it is significant to apply the present invention to a tundish whose side faces are cut at 70 ° or more to prevent the repair material and the covering material from peeling off.

  Hereinafter, the first experiment will be described.

  Spray the repair material onto the test surface at room temperature using the dry spray method. The amount of construction water added is 20% by mass on the repair material. After spraying, the rebound from the test surface is collected, and the adhesion rate is determined according to the formula: “Adhesion rate = (total amount of repair material sprayed−rebound amount) / total amount of repair material sprayed”. According to the adhesion rate, four grades of ◎, ○, Δ, and × were evaluated.

  Table 1 shows the structure of the repair material and the evaluation result of the adhesion rate.

In Table 1, as the water-soluble powdered silicate, powdered sodium silicate adjusted to an average particle size of 42 μm by pulverizing an alkali silicate aqueous solution by spray drying with a vibration mill was used. This easily water-soluble powdered silicate has a SiO ₂ content of 50 to 53 mass%, a Na ₂ O content of 18 to 19 mass%, and a silicate ratio of 2.70 to 2.90. When 20 g is charged and stirred with a stirrer for 5 minutes, the dissolution rate is 48 mass%.

In addition, powdered sodium silicate No. 3 has an average particle size of 104 μm obtained by pulverizing an alkali silicate aqueous solution by spray drying, an SiO ₂ content of 56 to 61% by mass, an Na ₂ O content of 17 to 20% by mass, silica The one with a ratio of 3.15 to 3.35 was used. This general powdered sodium silicate No. 3 has a dissolution rate of less than 5% by mass, specifically 3.7% by mass when charged with 50 g of purified water at 10 ° C. and stirred with a stirrer for 5 minutes. .

  Comparative Example a is a conventional example in which the proportion of fine particles in the refractory aggregate is as large as 35% by mass, and because sufficient viscosity is imparted, it exhibits good adhesion even when using ordinary powdered sodium silicate. However, with such a dense repair material, water vapor tends to be trapped in the sprayed construction body, so that peeling is likely to occur.

  Comparative example b is one in which the number of fine particles is reduced as compared with comparative example a, and the ease of water vapor removal may be improved, but the adhesion rate is inferior. As described above, when the proportion of fine particles in the refractory aggregate is suppressed, a decrease in the adhesion rate is recognized.

  Comparative Example c is obtained by replacing the binder of Comparative Example b with a readily water-soluble powdered silicate, and is inferior in adhesion rate because no curing accelerator is used.

  In Example a, although the proportion of fine particles in the refractory aggregate was suppressed to 25% by mass or less, the water-soluble powdered silicate, the curing accelerator, and the organic fiber were used in combination. Achieved the same adhesion rate.

  In Examples b to e, the proportion of fine particles was reduced as compared with Example a or organic fibers were omitted, and an acceptable adhesion rate was exhibited although it was inferior to Example a. From this result, it can be seen that, when fine particles are suppressed, the adhesion rate can be improved by combining at least a readily water-soluble powder silicate and a curing accelerator.

  In addition, it can be seen from the comparison between Examples a and b and the comparison between Examples d and e that the adhesion rate is further improved when organic fibers are added. In a system in which fine particles are reduced, rebound loss tends to occur, so the significance of adding organic fibers is particularly great.

  Hereinafter, the second experiment will be described.

  A repair material is sprayed by a dry spraying method on a vertical test surface formed by stacking bricks having a predetermined initial temperature vertically and horizontally. After spraying, a predetermined number of bricks are cut out from the test surface, heated at a temperature increase rate (1200 ° C./2 hours) simulating a preheating process, and the shear strength between each brick and the sprayed construction is measured. Find the average value. According to the value, the adhesive strength was evaluated in four levels, ◎, ○, Δ, and ×. The adhesive strength was individually evaluated when the initial temperature of the brick was 30 ° C. (low temperature) and when it was 200 ° C. (high temperature).

  Table 2 shows the structure of the repair material and the evaluation result of the adhesive strength. In Table 2, the same water-soluble powder silicate and powder sodium silicate No. 3 as those in Table 1 were used.

  Comparative example d is a conventional example in which alumina cement is used as a binder, and is inferior in adhesive strength at high temperatures. This is considered to be because the hydration reaction of the alumina cement did not proceed sufficiently because the construction water rapidly evaporated at high temperatures. On the other hand, when alumina cement is used, even if water vapor is trapped in the sprayed construction body, it is effectively used for the hydration reaction, and therefore shows good adhesive strength at low temperatures.

  Comparative example e is a conventional example using powdered sodium silicate No. 3 as a binder and is inferior in adhesive strength at low temperatures. The reason for this is that the evaporation of construction water slows down at low temperatures, and a gap is formed between the spray construction body and the test surface due to the accumulation of water vapor in the repair construction body. Conceivable.

  Comparative Example f is an example in which the proportion of fine particles is reduced as compared with Comparative Example e, and the adhesiveness at a low temperature is slightly improved compared to Comparative Example e because the water vapor is easily removed from the sprayed construction body. Insufficient. Thus, it is difficult to improve the adhesion at low temperatures simply by reducing the fine particles. The reason for this is presumed that normal powdered sodium silicate could not give sufficient strength to the sprayed body.

  In Comparative Example g, an easily water-soluble powdered silicate was used as the binder, but the proportion of fine particles in the refractory aggregate was as large as 35% by mass, and the adhesive strength at low temperature was poor. That is, simply using easily water-soluble powdered silicate cannot suppress the accumulation of water vapor and cannot improve the adhesion at low temperatures.

  Examples f to h are excellent in adhesive strength at low and high temperatures. Adhesive strength can be increased by controlling the proportion of fine particles in the refractory aggregate to 25% by mass or less and using a water-soluble powder silicate. From the comparison between Example f and Comparative Example f, it can be seen that the use of the easily water-soluble powder silicate contributes to the improvement of the adhesive strength.

  In addition, if the proportion of fine particles in the refractory aggregate is too small, not only is it difficult to ensure the strength of the sprayed construction body, but also because the contact area with the base becomes small, the adhesive strength at low and high temperatures decreases. A trend is observed. For this reason, it can be said that the proportion of fine particles in the refractory aggregate is preferably 20% by mass or more.

  Hereinafter, the third experiment will be described.

  After spraying the repair material on the vertical test surface formed by stacking bricks vertically and horizontally with the dry spray method, spray the covering material on the repair material sprayed body with the dry spray method. . After spraying, a predetermined number of bricks are cut out from the test surface, heated at a temperature increase rate (1200 ° C / 2 hours) simulating a preheating process, and then in a hot state at 1200 ° C, a repairing material spraying body and coating Measure the shear strength between the material and the sprayed body, and determine the average value. Based on this value, the adhesive strength between the repair material and the coating material was evaluated in four stages: ◎, ○, Δ, and ×.

  Table 3 shows the mass ratio of the coarse particles having a particle diameter of 1 mm or more / fine particles having a particle diameter of less than 75 μm in the refractory aggregate and the evaluation results of the adhesive strength between the repair material and the coating material.

  In Table 3, the coating material was prepared by adding powdered sodium silicate No. 3 as a binder to a refractory aggregate made of magnesia clinker, and the particle size constitution of the refractory aggregate was adjusted as shown in Table 3. The repair material is a fire-resistant aggregate composed of coarse grains with a particle size of 1 mm or more made of chamotte, medium particles with a particle size of 75 μm or more and less than 1 mm of barn clay shale, and fine particles with a particle size of less than 75 μm made of fused alumina. Salt and a hardening accelerator were added, and the particle size constitution of the refractory aggregate was adjusted as shown in Table 3.

  As shown in Table 3, the repair material has a structure with less fine particles and the cover material has a structure with more fine particles than the case where the content of the fine particles is equal between the covering material and the repair material. Increases the adhesive strength. Moreover, the tendency for the adhesive strength between both to increase is recognized, so that content of the fine particle of a repair material is small. This is presumably because the coarseness of the surface of the repair material sprayed construction increases as the particle size composition of the repair material is coarser, and the biting of the covering material becomes more prominent.

  As mentioned above, although the specific example of this invention was demonstrated, this invention is not limited to this. For example, it will be apparent to those skilled in the art that various combinations and improvements are possible.

  DESCRIPTION OF SYMBOLS 1 ... Iron skin, 2 ... Perm layer, 3 ... Base material layer, 4 ... Covering layer.

Claims (1)

(A) cooling the tundish after continuous casting, removing the remaining steel slag inside the tundish and the deteriorated lining refractory;
(B) On the inner surface of the tundish, the proportion of fine particles having a particle size of less than 75 μm in the refractory aggregate is suppressed to 25% by mass or less, and 40% by mass or more when dissolved in water at 10 ° C. for 5 minutes as a binder. A step of spraying a repair material containing a hardening accelerator made of a lime compound together with construction water, using a powdered silicate exhibiting a dissolution rate of
(C) A tundish maintenance method comprising a step of spraying, together with construction water, a coating material in which the proportion of fine particles having a particle size of less than 75 μm in the refractory aggregate is 35% by mass or more on the repairing material spraying construction body .

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