JP5126984B2 - Method for producing SiC-containing castable refractory - Google Patents

Description

The present invention relates to a method for producing a SiC-containing castable refractory .

  Conventionally, as a furnace material for various industries, there has been a demand for a castable refractory material having a spall resistance against a rapid temperature difference.

  As a technique for improving the spalling property of a refractory construction body, a technique for obtaining a refractory construction body by firing a SiC-containing castable refractory containing silicon carbide (hereinafter, SiC) at a high temperature has been widely adopted.

  As a technology for further improving the spall resistance of the castable refractory material, the applicant of the present application pulverizes a silicon nitride-bonded SiC refractory fired in advance in a nitrogen atmosphere in the refractory material constituting the castable refractory material. The technique which contains the obtained coarse grain (a diameter is 3 mm-25 mm) is disclosed (patent document 1).

  However, SiC has the property of being easily oxidized in a high-temperature oxidizing atmosphere of 900 ° C. or higher, and when the oxidation proceeds, the refractory construction body may be adversely affected such as cracking and corrosion resistance deterioration, and the refractory life may be shortened. It has been known. For this reason, as a furnace material used in a high-temperature oxidizing atmosphere, it is difficult to employ the technique described in Patent Document 1 (a technique based on the use of molten aluminum furnace material used at less than 900 ° C.). was there.

  Conventionally, in order to suppress the oxidation of SiC contained in the refractory construction body, a method for suppressing oxidation by densifying the refractory construction body to prevent oxygen from entering, and an antioxidant for the castable refractory material Attempts have been made to add.

  Among these, regarding the densification of the refractory construction body, since it is generally necessary to knead with water when constructing castable refractories, the construction body structure should be densified to a level that can exhibit a sufficient oxidation suppression effect. Is difficult.

  On the other hand, the addition of an antioxidant exhibits an antioxidant effect by using a low melting point substance (a substance that dissolves below the oxidation temperature of SiC particles) as an antioxidant and covering the periphery of the SiC particles. Therefore, in order for the antioxidant effect of the antioxidant to be effectively exhibited, the temperature of the refractory construction body may be raised to a temperature equal to or higher than the melting point of the antioxidant added to the castable refractory. Necessary. However, in general, castable refractories are installed in an end user's furnace and fired. Therefore, the temperature in the end user's furnace is appropriately controlled so that the refractory construction body exceeds the melting point of the antioxidant. It is difficult to raise the temperature, and there has been a problem that even if an antioxidant is added, there may be a case where a sufficient oxidation inhibitory effect cannot be exhibited. In addition, even in the same furnace, the refractory construction body temperature differs for each construction location of the castable refractory, and there may be a case where a sufficient oxidation suppression effect may not be exhibited at a location where the temperature stays below 1000 ° C. was there.

JP 2008-143757 A

An object of the present invention is an SiC-containing castable refractory material that solves the above-mentioned problems and has both spall resistance and oxidation resistance optimal as a furnace material used in a high-temperature oxidizing atmosphere, and comprising the SiC-containing castable refractory material. An object of the present invention is to provide a method for producing a SiC-containing castable refractory that can exhibit a sufficient oxidation-inhibiting effect even when the construction temperature of the object is 1000 ° C. or lower (500 ° C. to 1000 ° C.).

The present invention made in order to solve the above-mentioned problems is to provide a SiC raw material preparation step in which a SiC ingot is pulverized and particles having a diameter of 5 mm or less are classified to make a SiC raw material, and a molded body using the SiC raw material as a main raw material is 900 Firing in a high-temperature oxidizing atmosphere at a temperature of ℃ or higher to form an oxidation-resistant film on the surface of the molded body, pulverizing the fired body obtained by the firing, and classifying coarse particles having a diameter of 4 to 25 mm, It has the compounding process mix | blended in the refractory material which comprises a castable refractory material so that the content rate of this coarse grain may be 30-80 mass%.

The invention according to claim 2 is the method for producing a SiC-containing castable refractory according to claim 1, wherein, in the firing step, the SiC raw material includes V, Ca, Fe, Ba, Cu, B, P, Si, Al. , Ti is replaced with SiO ₂ These are added as a film formation accelerator, mixed and molded, and the obtained molded body is fired at 900 ° C. to 1500 ° C. for 3 hours or more in an oxidizing atmosphere.

Invention of Claim 3 is a manufacturing method of the SiC containing castable refractory of Claim 1, In this baking process, the molded object which uses the said SiC raw material as a main raw material is 1350-1500 degreeC in nitrogen atmosphere. After firing for 1 to 30 hours, firing is then performed in an oxidizing atmosphere.

According to a fourth aspect of the present invention, in the method for producing a SiC-containing castable refractory according to the first aspect, in the firing step, a predetermined amount of metallic Si is placed on a molded body using the SiC raw material as a main raw material. The firing is performed at 1450 ° C. to 1650 ° C. for 3 to 30 hours.

In general, a pure SiC ingot is a spongy crystal having a high porosity (30 to 40%), so that only coarse particles of about 4 to 5 mm can be obtained even if the SiC ingot is pulverized. In the method for producing a SiC-containing castable refractory according to the present invention, a SiC raw material is prepared by pulverizing a SiC ingot , classifying particles having a diameter of 5 mm or less, and using the SiC raw material as a main raw material. Firing in a high-temperature oxidizing atmosphere of 900 ° C. or higher to form an oxidation-resistant film on the surface of the molded body, crushing the fired body obtained by the firing, and classifying coarse particles having a diameter of 4 to 25 mm In order to obtain a coarse particle having a diameter of 4 to 25 mm by having a blending step of blending in the refractory material constituting the castable refractory material so that the content of the coarse particle is 30 to 80% by mass. It was possible to provide a SiC-containing castable refractory material that has both spall resistance and oxidation resistance optimal as furnace materials used in high-temperature oxidizing atmospheres. In addition, the inclusion of SiC refractory crushed grains containing an oxidation-resistant coating formed in advance as a refractory material is sufficient even when the construction temperature of the SiC-containing castable refractory is 1000 ° C. or lower (500 ° C. to 1000 ° C.). It was possible to provide a castable refractory containing SiC capable of exhibiting an excellent oxidation inhibiting effect.

It is a figure which shows the lifter using the SiC containing castable refractory of this invention.

  Preferred embodiments of the present invention are shown below.

  The SiC-containing castable refractory of the present invention contains 20 to 80% by mass of pulverized grains of SiC-containing refractory having an oxidation resistance function, and the crushed grains contain coarse grains having a diameter of 4 to 25 mm. .

  Hereinafter, each material used in the present invention will be described.

  The refractory containing SiC in which an oxidation resistant film is formed by firing can be manufactured, for example, by the following method.

After the SiC ingot is manufactured and pulverized by the so-called Atchison method of synthesizing SiC by heating and heating the raw material silica stone / silica sand and carbon material in an Atchison-type electric furnace and reducing the silica stone / silica sand (SiO ₂ ) with carbon (C) Then, particles of 4 to 5 mm or less are classified to obtain SiC raw materials. Next, any one of V, Ca, Fe, Ba, Cu, B, P, Si, Al, and Ti is added to the SiC raw material as a SiO ₂ film formation accelerator, and these are mixed and molded to obtain a porosity. A molded body having 5 to 15% and a bulk specific gravity of 2.5 to 2.9 is obtained. Thereafter, the molded body is fired at 900 ° C. to 1500 ° C. for 3 hours or more in an oxidizing atmosphere to produce the oxide-bonded SiC refractory.

In the above baking, Si in the molded body reacts with oxygen in the atmosphere to generate SiO ₂ , and the vitreous SiO ₂ coats the surroundings (grain boundaries) of the SiC particles, thereby binding the SiC particles. I am letting. Thus, by baking at 900 ° C. to 1500 ° C. for 3 hours or more, a uniform and dense coating film of SiO ₂ can be formed around the SiC particles (grain boundaries). The coating of SiO ₂ can prevent the oxidation of SiC. More preferably, the fired product is further held in an oxidizing atmosphere at 600 ° C. to 1000 ° C. for 3 hours or longer to form a SiO ₂ coating film on the surface of the internal pores of the fired product.

In the SiC refractory manufactured by this method, at least one of oxides, carbides and borides of V, Ca, Fe, Ba, Cu, B, P, Si, Al, Ti is an oxide, It is contained in an amount of 0.01 to 6% by mass in terms of carbide and boride. Such an inorganic oxide acts as a SiO ₂ production accelerator that promotes the reaction in which Si in the molded body and oxygen in the atmosphere react to produce SiO ₂ . When such an inorganic oxide is contained less than 0.010.1% by mass, the oxidation resistance is particularly poor, and the spalling resistance and corrosion resistance are also deteriorated. On the other hand, when it contains exceeding 6 mass%, spalling resistance and corrosion resistance deteriorate.

  Moreover, the refractory containing SiC which formed the oxidation resistant film by baking can also be manufactured with the following method, for example.

After the SiC ingot is manufactured and pulverized by the so-called Atchison method of synthesizing SiC by heating and heating the raw material silica stone / silica sand and carbon material in an Atchison-type electric furnace and reducing the silica stone / silica sand (SiO ₂ ) with carbon (C) Then, particles of 4 to 5 mm or less are classified to obtain SiC raw materials. Next, a molded body obtained by mixing and molding the SiC particles (consisting of coarse particles, intermediate particles, and fine particles) and a predetermined amount of Si powder is obtained at 1350 to 1500 ° C. in a nitrogen atmosphere. By baking for 30 hours (Hr), a silicon nitride-bonded SiC refractory is manufactured, and then baking is performed in an oxidizing atmosphere. In the SiC refractory manufactured by this method, at least one of oxides, carbides and borides of V, Ca, Fe, Ba, Cu, B, P, Si, Al, Ti is an oxide, It is contained in an amount of 0.01 to 6% by mass in terms of carbide and boride.

By firing in the nitrogen atmosphere, Si in the molded body reacts with nitrogen in the atmosphere, and silicon nitride is generated around the SiC particles (grain boundaries), so that the SiC particles can be bonded. Furthermore, a glassy SiO ₂ coating can be formed on the surface of the silicon nitride-bonded SiC refractory by subsequent firing in an oxygen atmosphere.

  Furthermore, the refractory containing SiC in which the oxidation-resistant film is formed by firing can also be produced by the following method, for example.

After the SiC ingot is manufactured and pulverized by the so-called Atchison method of synthesizing SiC by heating and heating the raw material silica stone / silica sand and carbon material in an Atchison-type electric furnace and reducing the silica stone / silica sand (SiO ₂ ) with carbon (C) Then, particles of 4 to 5 mm or less are classified to obtain SiC raw materials. Next, the SiC particles (consisting of coarse particles, intermediate particles, and fine particles) and an organic binder are formed into a predetermined shape, and then a predetermined amount of metal Si is placed on the formed body at 1450 ° C. to 1650 ° C. for 3 to 3 hours. By baking for 30 hours, a metal Si bonded SiC refractory having an oxidation resistant coating is produced.

  The SiC-containing castable refractory according to the present invention contains cement in addition to the pulverized particles obtained by pulverizing the refractory containing SiC having an oxidation-resistant film formed by firing as described above. Cement is intended to improve the strength of the construction body, and is not particularly limited as long as it is usually used for an irregular refractory. Among them, JIS types 1, 2 and 3 are suitable. . The blending amount of cement is preferably 1 to 5% by mass, and more preferably 2 to 4% by mass. The amount of cement is set to 1 to 5% by mass in order to sufficiently function as a binder, 1% by mass or more is necessary, and 5% by mass or less is applied when the amount exceeds this. This is because the amount of water added for kneading at the time increases, and the porosity of the dried product at the time of construction is increased. In addition, when the amount of water is large, it takes a long time to dry and develop strength.

  The pulverized grains of refractory containing SiC, in which an oxidation resistant film is formed by firing, are obtained by classifying coarse grains having a diameter of 4 to 25 mm, and are blended so that the content is in the range of 20 to 80% by mass. The When the content is less than 20% by mass, the spalling properties are deteriorated together with the corrosion resistance. On the other hand, when the content exceeds 90% by mass, the corrosion resistance deteriorates and the strength decreases. By containing coarse grains having a diameter of 4 to 25 mm, it is possible to improve the spalling resistance due to the crack progress suppressing effect of the refractory. In general, a pure SiC ingot is a spongy crystal having a high porosity (30 to 40%), so that only coarse particles of about 4 to 5 mm can be obtained even if the SiC ingot is pulverized. In the present invention, by firing a refractory containing coarse particles of about 4 to 5 mm obtained by pulverizing the SiC ingot, an oxidation resistant film is formed on the surface of SiC contained in the refractory, Thereafter, by pulverizing the refractory containing SiC on which the oxidation resistant film is formed, coarse particles having a diameter of 4 to 25 mm can be obtained.

  The SiC-containing castable refractory of the present invention further contains 5 to 30% by mass of the ultrafine powder of SiC and the ultrafine powder of mullite in the total amount of ultrafine powder. Since the SiC ultrafine powder does not have an oxidation-resistant film formed on the surface, it is easily oxidized in the presence of oxygen and functions as a powerful reducing agent. Therefore, for example, when manufacturing a lifter using a SiC-containing castable refractory containing the SiC ultrafine powder, the SiC ultrafine powder functions as a reducing agent, effectively preventing oxidation of metal anchors in the lifter. can do.

  Further, the SiC-containing castable refractory according to the present invention usually contains a dispersant in the range of 0.001 to 0.25% by mass, preferably 0.01 to 0.2% by mass. The dispersant has an action of dispersing aggregates of fine particles and ultrafine powder in the refractory material, specifically, condensed phosphates such as sodium hexametaphosphate, sodium tripolyphosphate, alkali metal polyphosphoric acid, β -Naphthalene sulfonate formalin condensate, melamine sulfonate formalin condensate, amino sulfonic acid and its salt, lignin sulfonic acid and its salt, polyacrylic acid and its salt, alkali metal carbonate, oxycarboxylate, polycarboxylic acid It is preferable to use surfactants such as acids and salts thereof, citric acid carbonate, and tartaric acid carbonate, and these can be used alone or in combination. When the added amount of the dispersant exceeds 0.25% by mass, there are adverse effects such as curing delay and strength reduction, the viscosity at the time of kneading increases more than necessary, and workability deteriorates. In addition, if the addition amount of a dispersing agent is less than 0.001 mass%, the dispersion effect may not be sufficient.

  The SiC-containing castable refractory of the present invention is constructed in a predetermined shape by adding, kneading and pouring a predetermined amount of a dispersant and water. For example, the lifter shown in FIG. 1 can be manufactured by pouring the kneaded material into a mold having an anchor and solidifying the mold. Moreover, after arrange | positioning this lifter in a furnace, this kneaded material can be poured directly into the circumference | surroundings, and the furnace wall in which the anchor is arrange | positioned can be constructed.

  As physical properties of the construction body constructed using the SiC-containing castable refractory according to the present invention, the strength (measured as bending strength) is 10 MPa or more and the spall resistance (ΔMOR = standard fired bending strength− (predetermined test) The bending strength)) measured after abruptly putting in and out of the temperature in the furnace has a characteristic of 2 MPa or less. If the strength is less than 10 MPa, the strength is not sufficient for the life of the refractory, and if the thermal shock resistance is 2 MPa or more, it may cause damage such as cracking of the refractory due to temperature change.

  In addition, as a physical characteristic of the construction body constructed using the SiC-containing castable refractory according to the present invention, the thermal conductivity is 6 W / (m · K) or more, the strength is 13 MPa or more, and the apparent porosity is It is more desirable to be 13% or less.

Next, specific examples of the present invention will be described.
First, as shown in Table 1, the composition and content of SiC-containing castable refractories including SiC refractory crushed grains, mullite fine powder, cement, SiC and mullite ultra-fine powder having an oxidation resistance function are changed. The test was conducted (Examples 1 to 11, Comparative Examples 1 to 3).

  The physical properties of the test pieces dried after adding water to the SiC-containing castable refractories having the respective compositions shown in Table 1 after being kneaded were measured and evaluated. The results are shown in Table 1. The measurement method and conditions of physical characteristics are as follows.

Strength (bending strength):
The strength (bending strength) was obtained by applying a load to the center of the upper surface of the test piece (40 × 40 × 160 mm) supported by the lower end of both ends in the longitudinal direction with a testing machine (basically, the maximum load was obtained). According to JIS R2213, sample shape and measurement span are different).

Spall resistance:
The spall resistance was obtained by putting a test piece (40 × 40 × 160 mm) into and out of a furnace at 600 ° C. or 800 ° C., and substituting the measured bending strength into the following formula.
ΔMOR = Standard fired bending strength— (The bending strength measured after abruptly moving into and out of the furnace at the specified test temperature)

Thermal conductivity:
The measurement of thermal conductivity was performed according to JIS R2168.

Rating:
As shown in Examples 1 to 4 and Examples 6 to 11 , the crushed particles of SiC-containing refractory having an oxidation resistance function are contained in an amount of 20 to 80% by mass, and the crushed particles have a diameter of 4 to 25 mm. In the case where the coarse particles were included, even when the construction body temperature remained at 600 ° C., it had a bending strength of 10 MPa or more and had sufficient spall resistance. On the other hand, as shown in Comparative Example 1, when the content of the pulverized grains of the SiC-containing refractory having an oxidation resistance function is less than 20% by mass, a decrease in spall resistance is observed. As shown in FIG. 3, when the content of pulverized grains of the SiC-containing refractory having an oxidation resistance function exceeds 80% by mass, a decrease in bending strength was observed.

1 Lifter 2 Construction body of castable refractory containing SiC 3 Anchor

Claims (4)

SiC raw material preparatory step of grinding SiC ingot and classifying particles having a diameter of 5 mm or less to make SiC raw material,
A firing step of firing a molded body mainly composed of the SiC raw material in a high-temperature oxidizing atmosphere of 900 ° C. or higher to form an oxidation-resistant film on the surface of the molded body;
In the refractory material constituting the castable refractory material, the fired body obtained by the firing is pulverized, coarse particles having a diameter of 4 to 25 mm are classified, and the content of the coarse particles is 30 to 80% by mass. The manufacturing method of the SiC containing castable refractory characterized by having the mixing | blending process to mix | blend. In the firing step,
Any one of V, Ca, Fe, Ba, Cu, B, P, Si, Al, and Ti is added to the SiC raw material as SiO. ₂ The composition according to claim 1, which is added as a film formation accelerator, mixed and molded, and the obtained molded body is fired at 900 ° C to 1500 ° C for 3 hours or more in an oxidizing atmosphere. A method for producing a SiC-containing castable refractory. In the firing step,
The molded body containing the SiC raw material as a main raw material is fired at 1350 to 1500 ° C. for 1 to 30 hours in a nitrogen atmosphere, and subsequently fired in an oxidizing atmosphere. A method for producing a SiC-containing castable refractory. In the firing step,
The SiC according to claim 1, wherein a predetermined amount of metal Si is placed on a molded body containing the SiC raw material as a main raw material and fired at 1450 ° C. to 1650 ° C. for 3 to 30 hours. A method for producing a castable refractory material.

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