JP7662955B2 - Briquettes and refractories containing them - Google Patents

Description

The present disclosure relates to briquettes containing expanded graphite and refractories containing briquettes.

Graphite-containing refractories have excellent corrosion resistance and spalling resistance and are used in various industrial furnaces. In particular, it is known that spalling resistance can be improved by using expanded graphite as the graphite raw material. However, expanded graphite is bulky and deteriorates molding workability. Therefore, for example, Patent Document 1 discloses a compressed and crushed expanded graphite-containing brick, which is a carbon-containing brick made of 0.5 to 40% by weight of carbonaceous material and contains compressed and crushed expanded graphite (expanded graphite) as the carbonaceous material.

Japanese Patent Application Publication No. 8-081256

The expanded graphite in Patent Document 1 is compressed to improve molding workability, but it is still bulky and the molding workability is insufficient.

The present disclosure has been made in consideration of the above-mentioned circumstances, and aims to provide a graphite raw material that contains expanded graphite but has reduced bulk and can further improve molding workability, and a refractory material that has even better corrosion resistance while maintaining spalling resistance.

One aspect of the present disclosure is
The main raw materials include a refractory raw material, expanded graphite, and a binder,
The expanded graphite relates to a briquette characterized in that the average particle size is 50 to 500 μm and the loose bulk density is 0.01 to 0.50 g/cm ³ .

This allows us to provide graphite raw material in the form of briquettes that contain expanded graphite while reducing bulk and further improving molding workability.

In one aspect of the present disclosure,
The content of the expanded graphite is preferably more than 0.0 part by mass and not more than 40.0 parts by mass per 100.0 parts by mass of the total content of the expanded graphite and the refractory raw material.

This reduces the bulk and improves molding workability.

Another aspect of the present disclosure is
The present disclosure relates to a refractory material comprising the briquette according to one embodiment of the present disclosure as a main raw material.

This makes it possible to provide a refractory with even better corrosion resistance while still maintaining spalling resistance.

A preferred embodiment of the present disclosure will be described in detail below. Note that the present embodiment described below does not unduly limit the content of the present disclosure described in the claims, and not all of the configurations described in the present embodiment are necessarily essential as a solution to the present disclosure.

The briquette of this embodiment contains a refractory raw material, expanded graphite, and a binder as main raw materials, and the expanded graphite has an average particle size of 50 to 500 μm and a loose bulk density of 0.01 to 0.50 g/cm ^3. This allows the briquette to contain expanded graphite while reducing its bulkiness, thereby further improving the molding workability.

<Refractory materials>
The refractory raw material of the present embodiment is not particularly limited as long as it is a general refractory raw material used for standard refractories, and examples thereof include magnesia raw materials, spinel raw materials, alumina raw materials, silicon carbide raw materials, and the like.

There are no particular limitations on the magnesia raw material, so long as it is one that is generally used for magnesia-carbonaceous refractories, and examples include electrofused magnesia, seawater magnesia, natural magnesia, sintered magnesia, etc. The purity of the magnesia raw material is preferably MgO: 98% by mass or more. In this case, the corrosion resistance of the magnesia-carbonaceous refractory is improved and the magnesia-carbon reaction can also be suppressed.

The spinel raw material is not particularly limited as long as it is generally used for graphite-containing refractories, and examples thereof include electrofused spinel, sintered spinel, etc. There are various compositions of spinel, such as stoichiometric composition: MgAl ₂ O ₄ (Al ₂ O ₃ : 71.7 mass%, MgO: 28.3 mass%), alumina-rich spinel containing more Al ₂ O ₃ than the stoichiometric composition, magnesia-rich spinel containing more MgO, etc., and the spinel raw material of this embodiment may be any of them.

The alumina raw material is not particularly limited as long as it is generally used for graphite-containing refractories, and examples _thereof include fused alumina, sintered alumina, natural alumina, etc. The purity of _Al2O3 is preferably 95 mass% or more. In this case, corrosion resistance is improved.

There are no particular restrictions on the silicon carbide raw material, so long as it is one that is generally used in graphite-containing refractories. The purity of the SiC is preferably 95% by mass or more. In this case, corrosion resistance is improved and oxidation of graphite can be suppressed.

<Expanded graphite>
The expanded graphite of this embodiment is obtained as follows. First, sulfuric acid, nitric acid, or the like is added and infiltrated between layers of highly crystalline natural graphite such as scaly graphite to form a graphite intercalation compound. Next, the graphite intercalation compound is rapidly heated to 800°C to 1000°C (expansion treatment) to form expanded graphite. Next, the expanded graphite is rolled at a pressure of 10 MPa or more using a roll or the like to form a graphite sheet. The thickness of the graphite sheet and the bulk density of the expanded graphite may be adjusted by adjusting the rolling pressure. Finally, the graphite sheet is pulverized to a size of 1 mm or less. There is no particular limitation on the pulverization method as long as it is a commonly used method, and for example, a pulverizer equipped with a pin mill or the like may be used. In this case, the particle size of the expanded graphite can be adjusted by adjusting the interval between the pins and the number of rotations.

The expanded graphite of this embodiment has an average particle size of 50 to 500 μm, preferably 100 to 400 μm, and more preferably 150 to 350 μm, as measured by a laser method. The expanded graphite of this embodiment has a loose bulk density of 0.01 to 0.50 g/cm ³ , preferably 0.01 to 0.30 g/cm ³ , and more preferably 0.05 to 0.20 g/cm ^3. By setting the average particle size and loose bulk density of the expanded graphite within these ranges, the bulkiness of the graphite raw material can be suppressed, and molding workability can be further improved. In addition, the fixed carbon content and external shape of the expanded graphite of this embodiment are preferably 96% or more, and accordion-shaped, respectively.

In this specification, loose bulk density refers to the value obtained by gently placing the object to be measured into an iron box-shaped container with known volume and mass, subtracting the mass of the iron box-shaped container from the total mass of the two, and dividing the mass by the volume of the iron box-shaped container.

The content of the expanded graphite in the briquette of this embodiment is preferably more than 0.0 part by mass and not more than 40.0 parts by mass, and more preferably 1.0 to 30.0 parts by mass, per 100.0 parts by mass of the total content of the expanded graphite and the refractory raw material. The loose bulk density of the briquette of this embodiment is preferably 0.5 to 2.0 g/ ^cm3 , and more preferably 1.5 to 1.9 g/ ^cm3 . This makes it possible to suppress the bulkiness and further improve the molding workability.

<Binder>
The binder is not particularly limited as long as it is generally used for graphite-containing refractories, and examples of the binder include thermosetting (resol type) or thermoplastic (novolac type) phenolic resins, ethylene glycol, and the like. The form of the binder is not particularly limited as long as it is generally used, and examples of the binder include liquid and powder. Binders with low viscosity at room temperature and binders whose viscosity has been reduced by heating to a certain temperature are particularly preferred because they can be uniformly dispersed with the addition of a small amount. In addition, the binder does not have to be a resin as long as it is generally used for unfired bricks, and examples of the binder include polysaccharide solutions such as molasses, and inorganic compounds such as silicates. The content of the binder in the briquette of this embodiment is preferably 1.0 to 5.0 parts by mass, more preferably 2.0 to 4.5 parts by mass, relative to 100.0 parts by mass of the total content of the expanded graphite and the refractory raw material.

<Method of manufacturing briquettes>
The method for producing briquettes of this embodiment includes a step of kneading a mixture containing a refractory raw material, expanded graphite, and a binder, and a step of forming the mixture with a briquette machine. The briquette machine is a machine that pours raw materials into a double-roll molding machine (briquette mold) to mold a granulated material (briquette), and a known machine can be used. The briquette size and the briquette mold are not particularly limited and can be selected appropriately. As described later, the hardness of the briquette is preferably such that the shape is distorted when the briquette is placed in a mold, pressurized, and molded to produce a refractory material. Therefore, the linear pressure between the double rolls of the briquette machine is preferably 70 to 1000 kN/m, more preferably 90 to 400 kN/m. This increases the graphite content in the refractory material, and improves corrosion resistance while maintaining spalling resistance.

<Refractories>
The refractory of the present embodiment includes the briquette of the present embodiment as a main raw material, and may include a refractory raw material, a graphite raw material, a binder, and/or a small amount of additives as auxiliary raw materials. This allows the refractory to further improve its corrosion resistance while maintaining its spalling resistance. A method for producing the refractory of the present embodiment includes a step of putting the briquette of the present embodiment as a main raw material into a mold, pressurizing and molding the briquette to obtain a molded body, and a step of subjecting the molded body to heat treatment such as drying and firing.

<Graphite raw material>
Examples of the graphite raw material include commercially available solid graphite such as flaky graphite, amorphous graphite, carbon black, anthracite, artificial graphite, etc. These graphite raw materials may be used alone or in combination of two or more kinds.

<Small amount of additives>
The refractory of the present embodiment may contain a small amount of additives as long as they are generally used in graphite-containing refractories, such as antioxidants, carbon black, powdered pitch, etc. Examples of the antioxidant include Al, Si, _B4C , SiC, and Al-Mg alloys.

The following describes in detail an embodiment of this disclosure.

1. Example 1.1 Briquette Production After the expansion treatment, the briquette was rolled into a sheet and crushed to obtain expanded graphite. The average particle size of the expanded graphite was measured by a laser method and found to be 250 μm. The loose bulk density, fixed carbon content, and external shape of the expanded graphite were 0.15 g/cm ³ , 98%, and accordion-shaped, respectively.

A mixture containing the refractory raw material, expanded graphite, and a binder was kneaded, and the mixture was molded in a briquette machine to obtain briquettes A to U. The compositions and molding pressures of briquettes A to U are shown in Table 1.

Magnesia raw material, spinel raw material, alumina raw material and/or silicon carbide raw material were used as the refractory raw material. Phenol resin was used as the binder. For briquettes A-L, the contents of expanded graphite and magnesia raw material were changed from 5.0 to 40.0 parts by mass and 60.0 to 95.0 parts by mass, respectively. For briquettes M-U, one or more of magnesia raw material, spinel raw material, alumina raw material and silicon carbide raw material were selected as the refractory raw material. The binder content was changed from 2.0 to 4.0 parts by mass for briquettes A-L, and fixed at 3.0 parts by mass for briquettes M-U, relative to the total content of expanded graphite and refractory raw material of 100.0 parts by mass. The molding pressure of the briquette machine was changed from 98 to 980 kN/m.

1.2 Measurement and Evaluation Methods Briquettes A to U were subjected to the following measurements and evaluations.

<Loose bulk density>
The loose bulk density is determined by gently placing the object to be measured in an iron box-shaped container with known volume and mass, subtracting the mass of the iron box-shaped container from the total mass of the two, and dividing the mass by the volume of the iron box-shaped container; in this example, the loose bulk density is the average value of 10 measurements. If there are voids in the container and the molding pressure of the briquettes is weak, some may lose their shape, but the measurement was performed including these cases.

<Molding workability>
The molding workability was evaluated by the loose bulk density. When a given mass of briquettes was put into a molding die, the more the amount that fits into the die, the better the molding workability, and the more the amount that overflows from the die, the worse the molding workability. Therefore, the higher the loose bulk density of the briquettes, the better the molding workability. A value of 1.50 g/ ^cm3 or more was evaluated as excellent: ◎, a value of 0.85 g/cm3 or ^more but less than 1.50 g/ ^cm3 was evaluated as good: ○, and a ^value of less than 0.85 g/cm3 was evaluated as poor: ×.

1.3 Measurement and Evaluation Results The measurement and evaluation results are shown in Table 1.

As can be seen from Table 1, all of the briquettes A to U had a loose bulk density of 0.85 g/ ^cm3 or more, and had good molding workability. In addition, the higher the molding pressure of the briquette machine, the more excellent the molding workability of the obtained briquettes.

The content of the expanded graphite was preferably more than 0.0 parts by mass and not more than 40.0 parts by mass, more preferably 1.0 to 30.0 parts by mass, relative to 100.0 parts by mass of the total content of the expanded graphite and the refractory raw material. The loose bulk density of the briquette was preferably 0.5 to 2.0 g/ ^cm3 , more preferably 1.5 to 1.9 g/ ^cm3 . This made it possible to suppress the bulkiness of the graphite raw material and further improve the molding workability. The content of the binder was preferably 1.0 to 5.0 parts by mass, more preferably 2.0 to 4.5 parts by mass, relative to 100.0 parts by mass of the total content of the expanded graphite and the refractory raw material.

2. Refractory Examples 2.1 Manufacture of Refractory The raw material of the refractory was placed in a rectangular parallelepiped molding frame measuring 900 mm long x 180 mm wide x 150 mm high, molded under a pressure of 147 MPa, and dried at 250°C for 24 hours to obtain a refractory. If necessary, the refractory was processed into a predetermined shape to obtain a test piece of the refractory. As the raw material of the refractory, in Examples 1 to 21, briquettes A to U obtained in "1. Briquette Examples" were used, and in Comparative Examples 1 to 8, clay was used in which the raw materials of the same composition as those of briquettes A to U used in Examples 1 to 21 were simply kneaded. The briquettes used in the examples, the composition of the raw materials, and the composition of the raw materials in the comparative examples are shown in Tables 2 and 3.

As the refractory raw material, magnesia raw material was used in Table 2, and one or more selected from magnesia raw material, spinel raw material, alumina raw material, and silicon carbide raw material were used in Table 3.

2.2 Measurement and Evaluation Methods The following measurements and evaluations were carried out on the test specimens.

<Porosity>
The porosity was measured in accordance with JIS R2205 (method of measuring apparent porosity, water absorption rate and specific gravity of refractory bricks).

<Corrosion resistance (corrosion index)>
The corrosion resistance was evaluated by the high-frequency lining method. That is, the test temperature was 1700°C, and synthetic slag with CaO/SiO ₂ (mass ratio) of 2.8 was used as the erosion agent. 400 g of the erosion agent was charged at one time, and replaced every hour, and the test was continued for a total of 6 hours. After the test, the test piece was cut in a direction perpendicular to the operating surface to measure the corrosion damage area, and the corrosion damage index was calculated by taking the corrosion damage area of Comparative Example 4 as 100. The smaller the corrosion damage index is compared to the Comparative Example with the same raw material composition, the better the corrosion resistance is, and the index was evaluated as excellent (◎) when it was 10.0 or more, and as good (○) when it was greater than 0.0 and less than 10.0.

<Spalling resistance (reduction rate of elastic modulus)>
The spalling resistance was evaluated by the elastic modulus reduction rate in a rapid heating and quenching test. That is, the refractory was processed into a rectangular parallelepiped of a predetermined shape: 40 x 40 x 160 mm, and fired at 1000 ° C in a reducing atmosphere to obtain a test piece. The test piece was immersed in molten pig iron at 1680 ° C for 60 seconds, and then immersed in cold water for 15 seconds, and this operation was repeated twice (rapid heating and quenching test). The elastic modulus of the test piece before and after the rapid heating and quenching test was measured, and the elastic modulus reduction rate was calculated by the following formula. The elastic modulus was obtained from the ultrasonic propagation speed in the longitudinal direction of the test piece (160 mm length direction).
Elastic modulus decrease rate=(elastic modulus before test−elastic modulus after test)/elastic modulus before test×100

The smaller the rate of decrease in elastic modulus, the better the spalling resistance. Less than 10.0% was rated as excellent (◎), 10.0% to less than 30.0% was rated as good (○), and 30.0% to less than 60.0% was rated as fair (△).

<Maintaining spalling resistance>
The closer the elastic modulus reduction rate is to the comparative example having the same raw material composition, the better the spalling resistance is maintained. When the difference between the two was less than 3.0%, it was evaluated as excellent (◎), when it was 3.0% or more and less than 7.0%, it was evaluated as good (○), and when it was 7.0% or more and less than 16.0%, it was evaluated as acceptable (△).

2.3 Measurement and Evaluation Results The measurement and evaluation results are shown in Tables 2 and 3.

From Tables 2 and 3, when comparing examples and comparative examples with the same raw material composition (for example, Examples 1 and 2 and Comparative Example 1), the porosity was reduced and the corrosion resistance was improved in the examples that used briquettes. This is thought to be because a denser body was obtained by molding the briquettes than by molding the clay as is, i.e., the molding workability was improved.

The content of expanded graphite in the briquettes is preferably more than 0.0 parts by mass and not more than 40.0 parts by mass, and more preferably 1.0 to 30.0 parts by mass, per 100.0 parts by mass of the combined content of expanded graphite and refractory raw material. This is believed to have reduced the bulk of the graphite raw material and further improved molding workability.

Looking at Examples 7 to 10 and Comparative Example 4, in Examples 9 and 10, spalling resistance was maintained to a satisfactory level (△), but it was still usable without any problems. This is thought to be because the molding pressures of the briquettes used in Examples 9 and 10 were high at 490 kN/m and 980 kN/m, respectively, which made the briquettes hard, and when pressed and molded to produce refractory materials, the shape did not collapse sufficiently, and the raw materials were not compacted as evenly as in Comparative Example 4. Therefore, it is thought that the linear pressure between the double rolls of the briquetting machine is preferably 70 to 1000 kN/m, and more preferably 90 to 400 kN/m.

As can be seen from Table 3, it was possible to further improve the corrosion resistance while maintaining the spalling resistance for various refractories containing expanded graphite, not limited to magnesia-carbon refractories.

As a result, briquettes were obtained that were able to reduce bulk and further improve molding workability. In addition, by using these briquettes, refractories were obtained that could maintain spalling resistance while further improving corrosion resistance.

Although the present embodiment has been described in detail above, it will be readily apparent to those skilled in the art that many modifications are possible that do not substantially deviate from the novel matters and effects of the present disclosure. Therefore, all such modifications are included in the scope of the present disclosure. For example, a term described at least once in the specification together with a different term having a broader or similar meaning may be replaced with that different term anywhere in the specification. Furthermore, the configuration of the present embodiment is not limited to that described in the present embodiment, and various modifications are possible.

Claims (2)

Contains briquettes as the main raw material,
The briquette contains a refractory raw material, expanded graphite, and a binder as main raw materials,
The expanded graphite has an average particle size of 50 to 500 μm and a loose bulk density of 0.01 to 0.50 g/cm ³ . The refractory material according to claim 1,
A refractory material, characterized in that the content of the expanded graphite is more than 0.0 part by mass and 40.0 parts by mass or less, per 100.0 parts by mass of the total content of the expanded graphite and the refractory raw material.