Briquettes and refractories containing them

Abstract

To provide a graphite raw material enabled to decrease bulkiness and to further improve molding workability, while including expanded graphite.SOLUTION: The briquette includes a refractory raw material, expanded graphite, and a binder as main raw materials, with the expanded graphite having a mean particle size of from 50 to 500 μm, and a loose bulk density of from 0.01 to 0.50 g / cm3.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to briquettes comprising expanded graphite and refractory articles comprising briquettes. [Background technology]

[0002] 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 a graphite raw material. However, expanded graphite is bulky and deteriorates molding workability. For example, Patent Document 1 discloses a compressed and pulverized expanded graphite-containing brick, which is made of 0.5 to 40% by weight of a carbonaceous material and contains compressed and pulverized expanded graphite (expanded graphite) as the carbonaceous material. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 8-081256 Summary of the Invention [Problem to be solved by the invention]

[0004] The expanded graphite in Patent Document 1 is compressed to improve molding workability, but it is still bulky and the molding workability is insufficient.

[0005] The present disclosure has been made in consideration of the above-mentioned circumstances, and has an object to provide a graphite raw material that contains expanded graphite, while reducing bulkiness and further improving molding workability, and a refractory material that maintains spalling resistance and has even more excellent corrosion resistance. [Means for solving the problem]

[0006] One aspect of the present disclosure is The main raw materials include a refractory raw material, expanded graphite, and a binder, 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 present invention relates to a briquette characterized in that

[0007] This makes it possible to provide a graphite raw material in the form of a briquette that contains expanded graphite, has a reduced bulkiness, and can further improve the molding workability.

[0008] 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.

[0009] This makes it possible to further reduce the bulkiness and further improve the molding workability.

[0010] 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.

[0011] This makes it possible to provide a refractory having superior corrosion resistance while maintaining spalling resistance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] A preferred embodiment of the present disclosure will be described in detail below. Note that the embodiment described below does not unduly limit the contents of the present disclosure described in the claims, and all of the configurations described in the embodiment are not necessarily essential as a means for solving the problems of the present disclosure.

[0013] The briquette of the present embodiment 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 This makes it possible to reduce the bulk of the briquette while still containing the expanded graphite, and to further improve the molding workability.

[0014] <Refractory raw 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.

[0015] There is no particular restriction on the magnesia raw material, so long as it is one generally used for magnesia-carbonaceous refractories, and examples thereof include electrofused magnesia, seawater magnesia, natural magnesia, sintered magnesia, etc. The purity of the magnesia raw material is preferably MgO: 98 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.

[0016] 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. The composition of the spinel is stoichiometric composition: MgAl 2 O 4 (Al 2 O 3 : 71.7 mass%, MgO: 28.3 mass%), and Al from the stoichiometric composition 2 O 3 There are various compositions of spinel, such as alumina-rich spinel containing a large amount of alumina and magnesia-rich spinel containing a large amount of MgO, and the spinel raw material of this embodiment may be any of these.

[0017] 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, and natural alumina. 2 O 3 The purity of is preferably 95% by mass or more, in which case the corrosion resistance is improved.

[0018] The silicon carbide raw material is not particularly limited as long as it is generally used for graphite-containing refractories. The purity of SiC is preferably 95 mass% or more. In this case, the corrosion resistance is improved and the oxidation of graphite can be suppressed.

[0019] <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.

[0020] 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 and 0.01 to 0.30 g / cm 3 is preferable, and 0.05 to 0.20 g / cm 3 is more preferable. By setting the average particle size and loose bulk density of the expanded graphite in this range, 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 the shape is preferably accordion-shaped.

[0021] 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 whose volume and mass are known, subtracting the mass of the iron box-shaped container from the total mass of both, and dividing the mass of the object to be measured by the volume of the iron box-shaped container.

[0022] 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, 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 of this embodiment is 0.5 to 2.0 g / cm 3is preferable, and 1.5 to 1.9 g / cm 3 This makes it possible to suppress the bulkiness and further improve the molding workability.

[0023] <Binder> The binder is not particularly limited as long as it is generally used for graphite-containing refractories, and examples thereof 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 thereof include liquid, powder, and the like. 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 by adding 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 thereof 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.

[0024] <Briquette manufacturing method> 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 appropriately selected. As described later, the hardness of the briquette is preferably such that the shape is broken when the briquette is placed in a mold, pressurized, and molded to produce a refractory. 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, and improves corrosion resistance while maintaining spalling resistance.

[0025] <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.

[0026] <Graphite raw material> Examples of graphite raw materials 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.

[0027] <Small additives> The refractory material of the present embodiment may contain a small amount of additives that are generally used in graphite-containing refractories, such as antioxidants, carbon black, powdered pitch, etc. Examples of the antioxidant include Al, Si, B 4 Examples include C, SiC, and Al-Mg alloys. EXAMPLES

[0028] Hereinafter, embodiments of the present disclosure will be described in detail.

[0029] 1. Briquette Examples 1.1 Briquette production After the expansion treatment, the expanded graphite 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 each 0.15 g / cm. 3 , 98% were accordion shaped.

[0030] 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. Table 1 shows the composition and molding pressure of briquettes A to U. [Table 1]

[0031] 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 to L, the contents of expanded graphite and magnesia raw material were changed from 5.0 to 40.0 parts by mass and from 60.0 to 95.0 parts by mass, respectively. For briquettes M to 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 to L, and fixed at 3.0 parts by mass for briquettes M to 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.

[0032] 1.2 Measurement and evaluation methods Briquettes A to U were subjected to the following measurements and evaluations.

[0033] <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 was 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.

[0034] <Molding workability> The molding workability was evaluated by the loose bulk density. When a given mass of briquettes is poured into a molding die, the more the amount that fits into the die, the better the molding workability is, and the more the amount that overflows from the die, the worse the molding workability is. Therefore, the higher the loose bulk density of the briquettes, the better the molding workability is, and the lower the loose bulk density is, the better the molding workability is. 3 Above: ◎, 0.85g / cm 3 More than 1.50g / cm 3 Less than 0.85g / cm 3Anything less than this was rated as unacceptable: ×.

[0035] 1.3 Measurement and evaluation results The measurement and evaluation results are shown in Table 1.

[0036] From Table 1, the loose bulk density of briquettes A to U is all 0.85 g / cm 3 As described above, the molding workability was good. Moreover, the higher the molding pressure of the briquetting machine, the more excellent the molding workability of the obtained briquettes.

[0037] The content of the expanded graphite is preferably more than 0.0 part 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 is 0.5 to 2.0 g / cm 3 is preferable, and 1.5 to 1.9 g / cm 3 was more preferable. This made it possible to suppress the bulkiness of the graphite raw material and further improve 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, per 100.0 parts by mass of the total content of the expanded graphite and the refractory raw material.

[0038] 2. Examples of refractories 2.1 Refractory manufacturing The refractory raw materials were 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 refractory raw materials, in Examples 1 to 21, briquettes A to U obtained in "1. Examples related to briquettes" were used, respectively, and in Comparative Examples 1 to 8, clay was used in which 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 their raw materials, and the composition of the raw materials in the Comparative Examples are shown in Tables 2 and 3. [Table 2] [Table 3]

[0039] As the refractory raw material, in Table 2, a magnesia raw material was used, and in Table 3, one or more materials selected from a magnesia raw material, a spinel raw material, an alumina raw material, and a silicon carbide raw material were used.

[0040] 2.2 Measurement and evaluation methods The test pieces were subjected to the following measurements and evaluations.

[0041] <Porosity> The porosity was measured according to JIS R2205 (Method of measurement of apparent porosity, water absorption and specific gravity of firebricks).

[0042] <Corrosion resistance (corrosion index)> The corrosion resistance was evaluated by the high-frequency lining method. The test temperature was 1700°C, and the corrosion agent was CaO / SiO 2 A synthetic slag with a mass ratio of 2.8 was used. 400 g of the corrosion agent was added at a time and replaced every hour, and the test was continued for a total of 6 hours. After the test, the test pieces were cut in a direction perpendicular to the operating surface to measure the corrosion area, and the corrosion index was calculated by taking the corrosion area of ​​Comparative Example 4 as 100. Compared to the Comparative Examples with the same raw material composition, the smaller the corrosion index, the better the corrosion resistance was. A value of 10.0 or more was evaluated as excellent (◎), and a value of more than 0.0 but less than 10.0 was evaluated as good (○).

[0043] <Spalling resistance (reduction rate of elastic modulus)> Spalling resistance was evaluated by the rate of decrease in elastic modulus due to a rapid heating and quenching test. That is, the refractory was processed into a rectangular parallelepiped of a given 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 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 was measured before and after the rapid heating and quenching test, and the rate of decrease in elastic modulus was calculated using 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 x 100

[0044] The smaller the rate of decrease in elastic modulus, the better the spalling resistance. Less than 10.0% was rated as excellent (◎), 10.0% or more but less than 30.0% was rated as good (○), and 30.0% or more but less than 60.0% was rated as fair (△).

[0045] <Maintaining spalling resistance> The closer the elastic modulus reduction rate is to the comparative example with 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 but less than 7.0%, it was evaluated as good (○), and when it was 7.0% or more but less than 16.0%, it was evaluated as fair (△).

[0046] 2.3 Measurement and evaluation results The measurement and evaluation results are shown in Tables 2 and 3.

[0047] In 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 lower and the corrosion resistance was improved in the Examples using briquettes. This is thought to be because a denser compact was obtained by forming briquettes rather than by forming the clay as is, i.e., the workability of forming was improved.

[0048] The content of the expanded graphite in the briquette is preferably more than 0.0 part 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, which is considered to suppress the bulkiness of the graphite raw material and further improve the molding workability.

[0049] With reference to Examples 7 to 10 and Comparative Example 4, in Examples 9 and 10, the spalling resistance was maintained to a satisfactory level (△), but it was still usable without any problems. This is believed 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, so that the briquettes became hard and did not lose their shape sufficiently when pressed and molded to produce a refractory material, and the raw materials were not compacted as evenly as in Comparative Example 4. Therefore, it is believed that the linear pressure between the double rolls of the briquette machine is preferably 70 to 1000 kN / m, and more preferably 90 to 400 kN / m.

[0050] As can be seen from Table 3, it was possible to further improve the corrosion resistance while maintaining the spalling resistance not only for magnesia-carbon refractories but also for various refractories containing expanded graphite.

[0051] As a result, briquettes were obtained that can reduce bulkiness and further improve molding workability. In addition, by using these briquettes, refractories were obtained that can maintain spalling resistance and further improve corrosion resistance.

[0052] Although the present embodiment has been described in detail as above, it will be easily understood by those skilled in the art that many modifications are possible without substantially departing 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 meaning or the same 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

1. A method for producing a briquette-based product comprising the steps of: 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 is characterized by:

2. 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.

Images