JP7302543B2 - monolithic refractories - Google Patents

Description

TECHNICAL FIELD The present invention relates to a monolithic refractory used in steelworks.

In recent years, the ratio of monolithic refractories to the refractories used in steelworks is increasing. In particular, monolithic refractories, which are constructed by mixing raw materials and water in steelworks, are widely used as lining refractories for molten steel ladles used in secondary refining.

Since molten steel is at a high temperature exceeding 1600°C, lining refractories that can withstand such high temperatures include alumina-magnesia-based monolithic refractories, alumina-magnesia-spinel-based monolithic refractories, and graphite. A monolithic refractory containing added graphite is used. In addition to raw materials such as alumina, magnesia, spinel, and graphite, such monolithic refractories are made by adding a binder for solidification and a dispersant for making them homogeneous when mixed with water. It is a mixture of things. These raw materials, binders, and additives are mixed with water in the factory and poured directly into the molten steel ladle and molded, or molded in the mold that forms the shape of the refractory lining of the molten steel ladle. After removing the frame, it can be used as a refractory lining by drying.

As the binder used for the monolithic refractory, a metal oxide-based binder is preferred because strength at high temperatures is required, and alumina cement is generally used. However, alumina cement contains CaO. At a high temperature of 1600°C or higher, which is the temperature at which a molten steel ladle is used, the CaO component forms low-melting-point substances together with Al ₂ O ₃ , MgO, and SiO ₂ , and may cause a decrease in hot strength and chemical corrosion. rice field.

Due to such problems caused by CaO, the use of cement containing strontium aluminate instead of CaO has been proposed. Patent Literature 1 and Patent Literature 2 propose a binder for monolithic refractory made of SrAl ₂ O ₄ and a technology related to monolithic refractory using the binder. Further, as a binder containing no CaO, Patent Document 3 proposes cast monolithic refractories using silica sol.

Patent No. 5290125 Patent No. 6499464 Patent No. 6296635

However, cement containing strontium aluminate has a problem in that its strength is low one day after construction, compared to alumina cement, especially when the temperature is low, such as in winter. Similarly, when silica sol or alumina sol is used, there is a problem that it does not cure in one day when the temperature is low such as in winter. Monolithic refractories are often constructed in places where they are used in factories. They are poured directly into the construction site or into a formwork, and after being molded, they develop strength and stabilize their shape as soon as possible. Desired.

An object of the present invention is to provide a monolithic refractory which does not contain CaO and has good workability and which can develop strength early even at low temperatures.

Conventionally, alumina sol, silica sol, and cement containing strontium aluminate are known to be used as binders for monolithic refractories. However, as described above, when the ambient temperature is as low as 10° C. or less, the curing time is long, and sufficient properties as a monolithic refractory for on-site construction could not be exhibited. Therefore, by combining magnesia with an appropriate particle size, alumina sol or silica sol, and cement containing strontium aluminate in an appropriate blend, sufficient strength as a monolithic refractory can be developed in a short period of about one day after construction even at low temperatures. The present inventors have found that it is possible to achieve this, and have developed the present invention.

That is, the present invention contains alumina as a main component, magnesia having a particle size of 0.3 mm or less in an amount of 3% by mass or more and 10% by mass or less, and cement containing strontium aluminate in an amount of 5% by mass or more and 7% by mass or less. A monolithic refractory characterized by containing 0.5% by mass or more and 6% by mass or less of an alumina sol or a silica sol on the basis of 100% by mass of a refractory material.

In addition, in the monolithic refractory according to the present invention configured as described above,
(1) The refractory material further contains 1% by mass or more and 25% by mass or less of spinel,
(2) The refractory material further contains 0.1% by mass or more and 10% by mass or less of graphite,
(3) It is considered that the pH of each of the alumina sol and the silica sol is 7 or higher, which is a more preferable solution.

According to the monolithic refractory according to the present invention, when constructing a monolithic refractory used as a lining refractory of a molten steel ladle that holds molten steel at a high temperature exceeding 1600 ° C., the time to develop strength is appropriately set. In addition to being able to control it, it is possible to prevent the formation of low-melting substances that cause a decrease in hot strength at high temperatures and chemical corrosion when used as a lining refractory.

A monolithic refractory according to the present invention is a monolithic refractory made of a refractory material containing alumina and magnesia as main components as aggregates. Here, the refractory material is mainly composed of alumina, and contains 3% to 10% by mass of magnesia having a particle size of 0.3 mm or less, and 5% to 7% by mass of cement containing strontium aluminate. contains. A monolithic refractory is obtained by adding 0.5% by mass or more and 6% by mass or less of alumina sol or silica sol to 100% by mass of this refractory material.

In the present invention, instead of alumina cement, cement containing magnesia, alumina sol or silica sol, and strontium aluminate having a particle size of 0.3 mm or less is contained. It is now possible to obtain high strength and excellent corrosion resistance.

Further, when only alumina sol or silica sol was used without using alumina cement or strontium cement, it was not hardened after one day at 5°C. However, by using alumina sol and silica sol together with strontium cement, it started to harden after 1 day at 5°C. Alumina sol and silica sol each have a pH range in which a stable dispersion state can be maintained, but due to factors such as the addition of alkali, the charge balance in the colloidal solution is disrupted, causing aggregation of colloidal particles and gelation. Alumina sol and silica sol are gelled to function as a binder.

In the case of alumina-magnesia monolithic refractories, magnesia is the alkalinity source, but the dissolution rate of the alkalinity source in water becomes slower as the temperature is lower. Therefore, it does not harden. On the other hand, the dissolution rate of Sr(OH) ₂ is sufficiently high even at low temperatures, and the pH can be raised quickly. Therefore, it was found that the combination of cement containing strontium, alumina sol, and silica sol can shorten the gelation time, shorten the curing time, and improve the curing strength.

According to the present invention, instead of alumina cement that is usually used for monolithic refractories, cement containing magnesia, alumina sol or silica sol, and strontium aluminate having a particle size of 0.3 mm or less is used in combination. Corrosion resistance and hot strength are improved because the amount of low-melting-point substances produced is reduced.

In the present invention, the content of magnesia having a particle size of 0.3 mm or less is 3% by mass or more and 10% by mass or less. This is because if the content of magnesia having a particle size of 0.3 mm or less is less than 3% by mass, the change in pH during construction of the monolithic refractory is small, and the alumina sol or silica sol is difficult to aggregate and harden. In addition, if the magnesia with a particle size of 0.3 mm or less exceeds 10% by mass, the melting point of the melt, which is a reaction product of the slag and the monolithic refractory, may decrease, and the slag tends to penetrate deeper, resulting in a molten steel ladle. This is because the exfoliation damage due to structural spalling becomes thicker when used in a refining vessel such as. The reason why magnesia with a particle size of 0.3 mm or less is used is that magnesia has a larger coefficient of thermal expansion than alumina, and if the particle size of magnesia is large, the monolithic refractory as a product is likely to crack. This is because magnesia and alumina form spinels at 1300° C. or higher, but if the grain size of magnesia is large, the reaction rate of spinel formation is slow and unreacted magnesia remains in the center of the formed spinels.

Further, in the present invention, the amount of alumina sol or silica sol is 0.5% by mass or more and 6% by mass or less with respect to 100% by mass of the refractory material. If the amount of alumina sol or silica sol is less than 0.5%, the sol is less likely to agglomerate and a strength capable of removing the frame cannot be obtained. If the amount of alumina sol or silica sol exceeds 6% by mass, the amount of water content during construction increases, and a compact construction cannot be obtained. Further, it is desirable to use alumina sol having a pH of 7 or more. Alumina sol aggregates around pH 11, but if you use a weakly basic and stabilized alumina sol such as a combination of lactic acid and ammonia water, aggregation will progress slowly due to the buffering effect even if it is mixed with magnesia. You get enough time. It is also desirable to use silica sol having a pH of 7 or more.

Here, the pot life is the time that the monolithic refractory can be used after being kneaded. In steelworks, it is applied in multiple steps, but if the pot life is too short, the refractory that is applied last is applied first and has already hardened when it is vibrated by core vibration (formwork vibration) after construction. cracks occur in the refractory

Furthermore, in the present invention, the cement containing strontium aluminate is 5% by mass or more and 7% by mass. If the amount of cement containing strontium aluminate is less than 5% by mass, the strength required for deframing cannot be obtained. If the cement containing strontium aluminate exceeds 7% by mass, the alumina sol or silica sol agglomerates quickly, and a sufficient pot life for construction cannot be obtained. As the cement containing strontium aluminate, for example, commercially available cement containing about 30 to 50% by mass of SrAl ₂ O ₄ and about 70 to 50% by mass of Al ₂ O ₃ can be used.

Furthermore, in the present invention, raw materials other than the above include alumina and/or spinel, alumina and/or spinel, and graphite. Additives such as silica fume and clay; various dispersants such as polyether, polycarboxylic acid, polymer, and naphthalenesulfonic acid; Various additives commonly used in monolithic refractories, such as various metals such as metal aluminum powder, carbides such as silicon carbide and boron carbide, and carbons such as carbon black and pitch, can be used.

<Example 1>
Alumina-magnesia monolithic refractories and alumina-spinel-magnesia monolithic refractories containing sintered magnesia with a particle size of 0.3 mm or less in Tables 1 and 2 below contain alumina sol, silica sol, and strontium aluminate. Examples and comparative examples to which cement (hereinafter referred to as strontium cement) and alumina cement are applied are shown.

Each raw material was weighed and blended according to Tables 1 and 2 so that the powder was 2.5 kg, and then the blended powder, water, alumina sol, silica sol, and other liquids were placed in a refrigerator at 5 ° C. for 1 hour. Stored overnight. The next day, the mixture was taken out of the refrigerator and placed in a universal mixer. After stirring for 1 minute, a liquid such as water was added. After vibrating with a table-like vibrator for 30 seconds, it was stored in a refrigerator at 5°C. After one day, it was removed from the mold and subjected to a bending test according to JIS R 2553 using a universal testing machine.

Separately, each raw material was weighed and blended according to Tables 1 and 2 so that the amount of powder was 2.5 kg, and then placed in a universal mixer and stirred for 1 minute. After adding a liquid such as water, the mixture was further stirred for 3 minutes. After that, it was poured into a mold of 30×30×120 mm for the hot bending test and into a mold of 40×40×40 mm for the slag corrosion test. After pouring into the formwork, it was vibrated for 30 seconds with a table-like vibrator. After curing at 20° C. for one day, the mold was removed.

A sample of 30 × 30 × 120 mm was dried at 110 ° C. for 24 hours, then heat-treated in an electric furnace at 1400 ° C. for 3 hours, and the test temperature was controlled to 1400 ° C. In the electric furnace, the crosshead descending speed was 0.5 mm / A hot bending test was performed in minutes.

A sample of 40×40×40 mm was dried at 110° C. for 24 hours and then heat-treated in an electric furnace at 1650° C. for 1 hour. A hole of φ20× ₁₅ mm was made in the upper part of the sample, and _{Fe2O3 :} 0.9% by mass, _SiO2 : 5.0% by mass, _Al2O3 : 13.2% by mass, and _CaCO3 were placed in the hole. : 77.2% by mass and MgO: 3.8% by mass. After cooling, the dimensional change in the diameter of the hole before and after the test was measured and normalized to 100 for Comparative Example 1 to obtain the erosion index. The results are shown in Tables 1 and 2 below.

The results in Tables 1 and 2 show the following. First, in each of Inventive Examples 1 to 11, the bending strength after curing at 5° C. for 1 day was equal to or higher than that of Comparative Example 1, 0.8 MPa. If the bending strength after curing at 5°C for 1 day is 0.8 MPa or more, it can be determined that the strength is such that the frame can be removed the next day even in winter. Comparative Example 2, which uses 5% by mass of strontium cement, has a flexural strength of less than 0.8 MPa in Comparative Example 1 after curing at 5°C for 1 day, and it can be judged that in winter, the strength that can be removed from the frame on the next day cannot be obtained. . Comparative Example 3 using 1% by mass of alumina sol did not cure in one day. In Comparative Example 4 using 1% by mass of alumina sol and 4% by mass of strontium cement and Comparative Example 5 using 1% by mass of alumina sol and 7% by mass of alumina cement, similarly to Comparative Example 2, the bending strength after curing at 5° C. for 1 day was It is lower than 0.8 MPa of Comparative Example 1, and it can be judged that in winter, the strength that allows the frame to be taken off the next day cannot be obtained. Further, Inventive Examples 1 to 11 were higher than Comparative Example 1 in hot bending strength. Further, the erosion index of Inventive Examples 1 to 8 was equal to or lower than that of Comparative Example 1, indicating good corrosion resistance. Furthermore, the erosion index of Inventive Example 9 and Inventive Example 10 using alumina sol and silica sol for the alumina-spinel-magnesia monolithic refractories were compared using alumina cement for the alumina-spinel-magnesia monolithic refractories. The erosion index was smaller than that of Example 6, and the corrosion resistance was good.

<Example 2>
In Table 3 below, alumina-magnesia-graphite monolithic refractory containing 7% by mass of sintered magnesia with a particle size of 0.3 mm or less and 5% by mass of graphite, alumina-spinel-magnesia-graphite monolithic refractory , alumina sol, silica sol, strontium cement, and alumina cement.

According to Table 3, each raw material is separately blended with graphite only, and after weighing and blending so that the powder becomes 2.5 kg, the blended powder and liquid such as water are stored overnight in a refrigerator at 5 ° C. bottom. On the next day, remove from the refrigerator and put the powders other than graphite into a universal mixer. After stirring for 1 minute, add a liquid such as water and stir for 2 minutes. Add graphite and stir for an additional 1 minute. was poured into a mold of After vibrating with a table-like vibrator for 30 seconds, it was stored in a refrigerator at 5°C. After one day, it was removed from the mold and subjected to a bending test according to JIS R 2553 using a universal testing machine.

Separately, according to Table 3, each raw material was weighed and mixed so that 2.5 kg of powder with graphite alone was placed in a separate bag, then powders other than graphite were placed in a universal mixer, stirred for 1 minute, and then mixed with water, etc. After adding the liquid and stirring for 2 minutes, adding graphite and stirring for another minute, it was poured into a mold of 30 × 30 × 120 mm for hot bending test, and 40 × 40 × 40 mm for slag corrosion test. Poured into a mold. After pouring into the formwork, it was vibrated for 30 seconds with a table-like vibrator. After curing at 20°C for 1 day, the mold was removed.

A sample of 30 × 30 × 120 mm was dried at 110 ° C for 24 hours, then heat-treated in an electric furnace with coke breeze at 1400 ° C for 3 hours, placed in an electric furnace controlled at a test temperature of 1400 ° C with coke breeze, A hot bending test was performed at a crosshead lowering speed of 0.5 mm/min.

A sample of 40×40×40 mm was dried at 110° C. for 24 hours and then heat-treated at 1650° C. for 1 hour in an electric furnace while flowing nitrogen gas. A hole of φ20× ₁₅ mm was made in the upper part of the sample, and _{Fe2O3 :} 0.9% by mass, _SiO2 : 5.0% by mass, _Al2O3 : 13.2% by mass, and _CaCO3 were placed in the hole. 20 g of a reagent adjusted to : 77.2% by mass and MgO: 3.8% by mass was packed and heat-treated again at 1650°C for 1 hour in an electric furnace while flowing nitrogen gas. After cooling, the dimensional change in the diameter of the hole before and after the test was measured and normalized to 100 for Comparative Example 1 (Table 2) to obtain the erosion index.

The results in Table 3 show the following. First, in each of Inventive Examples 21 to 24, the bending strength after curing at 5 ° C. for 1 day is equal to or higher than 0.8 MPa in Comparative Example 1 (Table 2), and the frame can be removed the next day even in winter. strength. Inventive Examples 21 to 24 were also higher than Comparative Example 1 in hot bending strength. In addition, the erosion index of Inventive Example 21, Inventive Example 22, and Inventive Example 25, which are alumina-magnesia-graphite monolithic refractories, is equal to or lower than that of Comparative Example 11 using 7% by mass of alumina cement, and alumina- Inventive Example 23, Inventive Example 24, and Inventive Example 26, which are spinel-magnesia-graphite monolithic refractories, are equal to or lower than Comparative Example 12 using 7% by mass of alumina cement, and have good corrosion resistance. .

<Example 3>
In the alumina-magnesia monolithic refractory of Inventive Example 1 (Table 1), the blending of sintered magnesia was varied to confirm the effects of the invention. The results are shown in Table 4 below.

The results in Table 4 show the following. First, in Inventive Examples 31 and 32, the amount of sintered magnesia having a particle size of 0.3 mm or less in Inventive Example 1 was set to 3.0% by mass and 10.0% by mass, respectively. The flexural strength after day curing, the hot flexural strength at 1400°C, and the erosion index at 1650°C for 1 hour were all good. On the other hand, in Comparative Example 21 in which the amount of sintered magnesia with a particle size of 0.3 mm or less was 2.0% by mass, the bending strength after curing at 5 ° C. for 1 day was small, and the strength that could be removed the next day in winter. cannot be obtained. In Comparative Example 22, in which the amount of sintered magnesia having a particle size of 0.3 mm or less was 11.0% by mass, the erosion index was smaller than that of Comparative Example 1 (Table 2), but slag penetration was observed. was taken.

The monolithic refractory according to the present invention is not limited to the above examples, and various applications can be applied within the scope of the present invention. Application is possible.

Claims (4)

Alumina is the main component, and magnesia with a particle size of 0.3 mm or less is 3% by mass or more and 10% by mass or less, and cement containing strontium aluminate and substantially free of CaO is 5% by mass or more and 7% by mass or less. A monolithic refractory characterized by containing 0.5% by mass or more and 6% by mass or less of an alumina sol or a silica sol on the basis of 100% by mass of the contained refractory material. 2. The monolithic refractory according to claim 1, wherein the refractory material further contains 1% by mass or more and 25% by mass or less of spinel. 3. The monolithic refractory according to claim 1, wherein the refractory material further contains 0.1% by mass or more and 10% by mass or less of graphite. The monolithic refractory according to any one of claims 1 to 3, wherein the alumina sol and the silica sol each have a pH of 7 or higher.