JP2022091022A - Furnace core tube composition, furnace core tube, and method of manufacturing furnace core tube - Google Patents

Abstract

To provide a furnace core tube composition from which a furnace core tube superior in strength, thermal shock resistance, and low thermal conductivity can be obtained; a furnace core tube made of the furnace core tube composition; and a method of manufacturing the furnace core tube with high working efficiency.SOLUTION: A furnace core tube composition to be used for centrifugal molding includes: aggregate particles consisting of ceramic A particles having specific gravity of 2.4-2.8 and a particle diameter of smaller than 3.5 mm and ceramic B particles having specific gravity 2.7-3.4 and a particle diameter of 100 μm or smaller; and a binding agent consisting of ceramic C particles. A furnace core tube is manufactured by centrifugal molding and includes cordierite particles and mullite particles, in which the cordierite particles and the mullite particles are integrally constituted. A method of manufacturing the furnace core tube comprises the steps of: mixing and kneading the furnace core tube composition to obtain a mixed/kneaded material; casing the mixed/kneaded material into a cylindrical molding die and performing centrifugal molding to obtain an uncured molded product; curing the uncured molded product while retaining the product in the molding die to obtain a cured molded product; and releasing and drying the cured molded product.SELECTED DRAWING: Figure 1

Description

The present invention relates to a composition for a furnace core tube, a furnace core tube, and a method for manufacturing the furnace core tube. More specifically, the present invention enhances a composition for a furnace core tube capable of obtaining a furnace core tube excellent in strength, thermal shock resistance and low thermal conductivity, a furnace core tube obtained from this furnace core tube composition, and work efficiency. The present invention relates to a method for manufacturing a furnace core tube that can be used.

Conventionally, a furnace core tube inserted and installed in an induction heating coil is manufactured by, for example, the following vibration casting molding method.
First, the raw material formulation for producing the furnace core tube is kneaded to prepare a kneaded product. The kneaded product becomes fluid by applying vibration.
Next, the kneaded product is poured into the gap between the vertically long cylindrical molding die and the cylindrical core made of foamed resin arranged at the center of the axial direction while applying vibration to the molding die. ..
After that, if left unattended, the raw material reacts with water, and the kneaded product solidifies to obtain a molded product. The obtained molded body is heated to remove water, and the core is contracted and taken out.

However, the above-mentioned vibration casting molding method has the following problems.
The kneaded product contains air bubbles, and these air bubbles coalesce during molding to increase the size. Some of these are floated and removed during molding, but most of them remain inside the molded body and appear on the inner and outer surfaces. Therefore, it is necessary to rework to fill the traces of air bubbles on the inner and outer surfaces of the molded product, which takes a lot of work time.
Further, when the core is pushed by the kneaded material and deformed during molding, the wall thickness of the molded body also changes depending on the position in the longitudinal direction.
Further, since the separation of the raw material particles and the floating separation of the bubbles occur, the characteristics vary depending on the position of the molded body in the longitudinal direction. This phenomenon becomes remarkable because the fluidity increases as the amount of water in the kneaded product increases.
Further, when the core is heated and removed, cracks are likely to occur in the molded body due to the expansion of the core before shrinkage or the drying shrinkage of the molded body.

Here, a method for producing a cylindrical molded body by centrifugal molding has been proposed (see, for example, Patent Document 1).
According to the centrifugal molding method, after the raw material kneaded material is put into a horizontally long cylindrical molding die, the molding die is rotated around the central axis of the cylinder as a rotation axis. The kneaded material having fluidity is pressed against the inner wall of the molding die by centrifugal force and spreads to form a cylindrical shape having a uniform thickness. When the number of revolutions is further increased, bubbles are first pushed out from the kneaded product, and then water is pushed out. Further curing and drying will improve the strength.
According to the centrifugal molding method, most of the bubbles are removed as compared with the vibration casting method, so that the density and strength are high.

Japanese Unexamined Patent Publication No. 1-1979748

However, when a cylindrical molded body is formed by the centrifugal molding method, when raw material particles having different densities are mixed and used, the high-density particles are on the outer surface side of the cylinder and the low-density particles are inside due to the centrifugal force. "Separation of raw material particles" that collects on the surface side tends to occur, and the characteristics tend to be non-uniform in the thickness direction.

The present invention solves the above-mentioned problems of the prior art, and is a composition for a furnace core tube capable of obtaining a furnace core tube excellent in strength, thermal shock resistance and low thermal conductivity, from this furnace core tube composition. It is an object of the present invention to provide a method for manufacturing a obtained furnace core tube and a furnace core tube having high work efficiency.

The present invention is as follows.
1. 1. A composition for a furnace core tube for producing a furnace core tube by centrifugal molding.
Bonding of aggregate particles composed of ceramic A particles having a specific gravity of 2.4 to 2.8 and a particle size of less than 3.5 mm and ceramic B particles having a specific gravity of 2.7 to 3.4 and a particle size of 100 μm or less, and ceramic C particles. A composition for a furnace core tube, which comprises a solid raw material comprising an agent and a solid raw material.
2. 2. When the total solid raw material is 100% by mass, the ceramic A particles are 35 to 55% by mass, the ceramic B particles are 27 to 39% by mass, and the ceramic C particles are 18 to 26% by mass. The composition for a furnace core tube according to.
3. 3. 2. Of the 35 to 55% by mass of ceramic A particles, 16 to 35% by mass of coarse particles having a particle size of 1.0 mm or more and less than 3.5 mm are contained. The composition for a furnace core tube according to.
4. 1. Ceramic A particles are cordylite, ceramic B particles are mullite, and ceramic C particles are fine alumina and high alumina cement. To 3. The composition for a furnace core tube according to any one of the above.

5. A furnace core tube manufactured by centrifugal molding.
A furnace core tube comprising cozy light particles and mullite particles, wherein the cozy light particles and the mullite particles are integrally formed.
6. 5. The cozy light particles include coarse particles having a particle size of 1.0 mm or more and less than 3.5 mm, and fine particles having a particle size of less than 1.0 mm. The furnace core tube described in.
7. 4. The cozy light particles have a particle size of less than 3.5 mm, and the mullite particles have a particle size of 100 μm or less. Or 6. The furnace core tube described in.
8. 5. A coat layer is formed on the inner surface of the furnace core tube on the inner surface side. ~ 7. The furnace core tube according to any one of the items.

9.5. ~ 7. The method for manufacturing a furnace core tube according to any one of the above items.
The kneading step of kneading the composition for a furnace core tube to obtain a kneaded product, and
A molding step of pouring the kneaded product into a cylindrical molding die and centrifuging to obtain an uncured molded product.
A curing step of obtaining a cured molded product by curing the uncured molded product while holding it in the molding die, and
A method for manufacturing a furnace core tube, which comprises a drying step of removing and drying the cured molded body to obtain a furnace core tube.
10. In the molding step, the centrifugal rotation is the first step in which the peripheral speed of the inner surface of the cylindrical mold for molding is 0.8 to 1.6 m / s, and the second step in which the centrifugal rotation is 1.9 to 2.5 m / s. 9. It consists of a stage and a third stage of 2.7 to 4.5 m / s. The method for manufacturing a furnace core tube according to.
11.8. The method for manufacturing a furnace core tube according to the above.
A kneading step of kneading the composition to obtain a kneaded product, and
The first molding step of pouring the kneaded product into a cylindrical molding die and centrifuging to obtain an uncured molded product.
The first curing step of obtaining a cured molded product by curing the uncured molded product while holding it in the molding die, and
A second molding step of applying a coating agent containing the raw material to the inner surface of the cured molded product and then centrifuging to obtain a molded product with an uncured coated layer.
The second curing step of removing and curing the molded body with the uncured coat layer to obtain the molded body with the cured coat layer,
A method for manufacturing a furnace core tube, which comprises a drying step of drying the molded body with a cured coat layer to obtain a furnace core tube.
12. The first molding step and the second molding step are the first step in which the centrifugal rotation is 0.8 to 1.6 m / s as the peripheral speed of the inner surface of the cylindrical mold for molding. 11. It consists of a second stage of 1.9 to 2.5 m / s and a third stage of 2.7 to 4.5 m / s. The method for manufacturing a furnace core tube according to.
13.9. To 12. A furnace core tube manufactured by the manufacturing method according to any one of the above.

The composition for a furnace core tube of the present invention is a bone composed of ceramic A particles having a specific gravity of 2.4 to 2.8 and a particle size of less than 3.5 mm and ceramic B particles having a specific gravity of 2.7 to 3.4 and a particle size of 100 μm or less. Since it contains a raw material composed of a material particle and a binder composed of ceramic C particles, a furnace core tube having excellent strength, thermal shock resistance and low thermal conductivity can be obtained.
Further, when the total amount of the raw material is 100% by mass, the ceramic A particles are 35 to 55% by mass, the ceramic B particles are 27 to 39% by mass, and the ceramic C particles are 18 to 26% by mass, the strength and thermal impact resistance are further increased. And a furnace core tube having excellent low thermal conductivity can be obtained.
When 16 to 35% by mass of coarse particles having a particle size of 1.0 mm or more and less than 3.5 mm are contained in the 35 to 55% by mass of the ceramic A particles, the furnace core is more excellent in strength, thermal impact resistance and low thermal conductivity. You can get a tube.
Further, when the ceramic A is cordylite, the ceramic B is mullite, and the ceramic C is fine alumina or high alumina cement, a furnace core tube having excellent strength, thermal shock resistance and low thermal conductivity can be obtained. be able to.

The furnace core tube manufactured by the centrifugal molding of the present invention includes cozy light particles, mullite particles, and alumina particles, and the cozilite particles, the mullite particles, and the alumina particles are integrally formed, so that the strength thereof is high. It can be excellent in thermal shock resistance and low thermal conductivity.
Further, when the cozy light particles are a furnace core tube containing coarse particles having a particle size of 1.0 mm or more and less than 3.5 mm and fine particles having a particle size of less than 1.0 mm, the strength and heat impact resistance are further increased. And can be excellent in low thermal conductivity.
Further, when the cordillite particles have a particle size of less than 3.5 mm and the mullite particles have a particle size of 100 μm or less, the strength, thermal impact resistance and low thermal conductivity can be further improved.
When the coat layer is formed on the inner surface on the inner surface side of the furnace core tube, the inner surface can be made smooth in particular.

The method for producing a furnace core tube of the present invention is a kneading step of kneading a composition for a furnace core tube to obtain a kneaded product, and pouring the kneaded product into a cylindrical molding die and centrifuging the uncured molded product. In the case of obtaining a cured molded product by curing the uncured molded product while holding it in the molding mold, and in the case of removing and drying the cured molded product to obtain a furnace core tube. It is possible to manufacture a furnace core tube having excellent strength, thermal shock resistance and low thermal conductivity, and to improve work efficiency.
Further, in the molding step, the first step in which the centrifugal rotation is 0.8 to 1.6 m / s as the peripheral speed of the inner surface of the cylindrical mold for molding, and the first step in which the centrifugal rotation is 1.9 to 2.5 m / s. When it is composed of two steps and a third step of 2.7 to 4.5 m / s, a furnace core tube having even better characteristics can be manufactured.
The method for producing the furnace core tube of the present invention is a kneading step of kneading the composition for the furnace core tube to obtain a kneaded product, and pouring the kneaded material into a cylindrical molding die and centrifuging to uncured. The first molding step of obtaining a molded body, the first curing step of curing the uncured molded body while holding it in the molding die to obtain a cured molded body, and the coating containing the raw material on the inner surface of the cured molded body. The second molding step of centrifuging after applying the agent to obtain a molded product with an uncured coat layer, and the second curing to obtain a molded product with a cured coat layer by demolding and curing the molded product with an uncured coat layer. In the process and when the molded product with the cured coat layer is dried to obtain a furnace core tube, it is possible to obtain a furnace core tube having excellent strength, thermal shock resistance and low thermal conductivity and having a smooth inner surface.
Further, the first molding step and the second molding step are the first step in which the centrifugal rotation is 0.8 to 1.6 m / s as the peripheral speed of the inner surface of the cylindrical mold for molding, and 1.9 to 2 When it is composed of the second stage of 5.5 m / s and the third stage of 2.7 to 4.5 m / s, a furnace core tube having even better characteristics can be manufactured.
The furnace core tube obtained by the production method of the present invention is particularly excellent in strength, thermal shock resistance and low thermal conductivity.

(A) It is a schematic perspective view which shows the state of putting a raw material into a molding die. (B) It is a schematic perspective view which shows the molding process which obtains the uncured molded body by centrifugal molding. (C) It is a schematic perspective view which shows how the lid material is removed from a molding die, and the water exuded on the inner surface of an uncured molded body is discharged. (D) It is a schematic perspective view which shows the curing process which cures an uncured molded article, and obtains a cured molded article. (E) It is a schematic perspective view which shows the process of drying a cured compact and obtaining a furnace core tube. (A) It is a schematic perspective view which shows the state which the coating agent is added after the 1st curing step. (B) FIG. 3 is a schematic perspective view showing a second molding step of centrifuging to obtain a molded product with an uncured coat layer. (C) It is a schematic perspective view which shows the 2nd curing process which cures the molded article with an uncured coat layer, and obtains the molded article with a cured coat layer. (D) It is a schematic perspective view which shows the process of heating and drying a molded body with a hardened coat layer, and obtaining a furnace core tube.

The matters shown here are for illustrative purposes and embodiments of the present invention, and are the most effective and effortless explanations for understanding the principles and conceptual features of the present invention. It is stated for the purpose of providing what seems to be. In this regard, it is not intended to show structural details of the invention beyond a certain degree necessary for a fundamental understanding of the invention, and some embodiments of the invention are provided by description in conjunction with the drawings. It is intended to clarify to those skilled in the art how it is actually realized.

Hereinafter, the present invention will be described in detail with reference to the drawings.
[1] Composition for a furnace core tube The composition for a furnace core tube of the present invention is a composition for obtaining a furnace core tube by centrifugal molding.
It contains a raw material consisting of aggregate particles and a binder.
The aggregate particles are particles forming a skeleton for exhibiting the characteristics of the composition for a furnace core tube, and include ceramic A particles having different specific gravity and particle size, and ceramic B particles.

The ceramic A particles have a specific gravity of 2.4 to 2.8 and a particle size of less than 3.5 mm, preferably a specific gravity of 2.4 to 2.8 and a particle size of 0.1 mm or more and less than 3.5 mm, and have a specific gravity of 2. It is more preferable that the particle size is 5.5 to 2.7 and the particle size is 0.3 mm or more and less than 3.3 mm.
The ceramic A particles are not particularly limited, and examples thereof include compound oxides containing two or more of alumina, silica, and magnesia. More specifically, cozy light (2MgO · 2Al _{2O 3.5SiO 2), steatite (MgO · SiO 2 ) and the} like can be mentioned, and cozy light is particularly preferable. Kojilite has a small coefficient of thermal expansion and excellent thermal shock resistance.
The ceramic A particles can be sieved into coarse particles having a particle size of 1 mm or more and less than 3.5 mm and fine particles having a particle size of less than 1.0 mm, and the mixing ratio thereof can be adjusted as described later.

The ceramic B particles have a specific gravity of 2.7 to 3.4 and a particle size of 100 μm or less, preferably a specific gravity of 2.8 to 3.2 and a particle size of 5 μm or more and 100 μm or less, preferably 2.7 to 3.2. The particle size is more preferably 5 μm or more and 70 μm or less, and the specific gravity is 2.7 to 3.1, and the particle size is particularly preferably 5 μm or more and 70 μm or less.
The ceramic B particles usually have a specific density of 2.7 to 3.1, and are relatively close to the ceramic A particles having a specific density of 2.4 to 2.8. Therefore, when the particles are mixed with the ceramic A particles and centrifugally molded, the separation tendency of the high specific density particles unevenly distributed on the outer surface side can be alleviated.
Further, the ceramic B particles have a particle size of 100 μm or less, and many of them have a smaller particle size than the ceramic A particles. Since the ceramic B particles enter the gaps between the ceramic A particles, the entire particles are densely filled. , By kneading, it is more evenly dispersed.
The ratio of the ceramic particles A to the ceramic particles B is not particularly limited, but the mass% ratio is preferably ceramic particles A: ceramic particles B = 55 to 65:35 to 45, and ceramic particles A: ceramic particles B =. It is more preferably 57 to 59: 41 to 43.

The ceramic B particles are not particularly limited, and examples thereof include compound oxides containing two or more of them such as alumina, silica, magnesia, silicon carbide, and silicon nitride. More specifically, for example, mullite (3Al _{2 O 3.2SiO 2 ), sialon (SiN 4 · Al 2 O 3 ) and the like} can be mentioned, and mullite is particularly preferable.
When the ceramic B particles are mulite, the thermal conductivity is about 1/8 of that of alumina, and the thermal conductivity of the entire material can be suppressed to be smaller than when alumina is used as the ceramic B particles.
Further, the coefficient of thermal expansion of mullite is about 2/3 of the coefficient of thermal expansion of alumina, and it moves so as to reduce the coefficient of thermal expansion of the material, which is advantageous for improving the thermal impact resistance. Further, the specific gravity of mullite is about 3.0, which is close to the specific density of about 2.6 of cozy light. Therefore, even if mullite is mixed with cozy light, it is difficult to cause separation of mullite particles and cozy light particles during centrifugation, and a furnace core tube having a uniform composition can be obtained.
On the other hand, since alumina has a large specific gravity of about 3.9, when it is mixed with cozy light and centrifugally molded, it is easy to cause separation of alumina particles and cozy light particles. That is, a large amount of alumina particles are present on the outer surface side of the furnace core tube, and a large amount of cozy light particles are present on the inner surface side, so that it is difficult to obtain a furnace core tube having a uniform composition.

The binder binds and integrates ceramic particles with each other, and is composed of ceramic C particles. The binder is not particularly limited as long as it bonds ceramic particles to each other, and may be, for example, fine alumina or high alumina cement.
The fine alumina improves the dispersibility of the raw material formulation and facilitates the flow, and the ceramic A particles and the ceramic B particles can be further dispersed and made uniform. Fine alumina
It is preferably an ultrafine powder. If it is an ultrafine powder, the bondability with high alumina cement can be enhanced. Specifically, the particle size of the fine alumina is preferably 0.1 μm or more and 20 μm or less, more preferably 0.2 μm or more and 10 μm or less, and particularly preferably 0.5 μm or more and 10 μm or less.
High alumina cement becomes a hydrated cured product in the presence of water and bonds ceramic particles to each other. By increasing the amount of alumina (Al ₂ O ₃ ) component in the cement, heat resistance can be improved. can. The particle size of the high alumina cement is preferably 0.1 μm or more and 200 μm or less, more preferably 0.2 μm or more and 100 μm or less, and particularly preferably 0.3 μm or more and 75 μm or less.
Further, when the total mass of the high alumina cement is 100, the amount of alumina is preferably 70 to 90% by mass, and more preferably 75 to 85% by mass.
The blending ratio of fine alumina and high alumina cement is not particularly limited, but the mass ratio is preferably fine alumina: high alumina cement = 15 to 30:70 to 85, and fine alumina: high alumina cement = 20 to. It is more preferably 25:75 to 80.

The ratio of the aggregate particles of the solid raw material to the binder is not particularly limited, but the mass ratio is preferably aggregate particles: binder = 70 to 85:15 to 30, and aggregate particles: binder. = 75 to 80: 20 to 25 is more preferable.
Further, when the total solid raw material is 100% by mass, it is preferably 35 to 55% by mass of the ceramic A particles, 27 to 39% by mass of the ceramic B particles, and 18 to 26% by mass of the ceramic C particles, and the ceramic A particles 40. It is more preferably to 50% by mass, 30 to 36% by mass of the ceramic B particles, and 20 to 24% by mass of the ceramic C particles.

Of the 35 to 55% by mass of the ceramic A particles, it can be composed of only fine particles having a particle size of 0.1 mm or more and less than 1.0 mm. By composing only fine particles having a particle size of 0.1 mm or more and less than 1.0 mm, it is possible to prevent the particles from protruding from the inner surface on the inner surface side of the furnace core tube manufactured by centrifugal molding and to form a smooth inner surface. ..
On the other hand, among the 35 to 55% by mass of the ceramic A particles, 16 to 35% by mass, more preferably 18 to 32% by mass, of coarse particles having a particle size of 1.0 mm or more and less than 3.5 mm can be contained. By containing the coarse particles to this extent, the thermal impact resistance of the manufactured furnace core tube can be made more excellent.

[2] Furnace core tube The "furnace core tube" is manufactured by centrifugal molding, and is usually cylindrical like the furnace core tube 10 shown in FIG. 1 (d). The dimensions are not particularly limited, but are usually 70 to 160 mm in outer diameter, 5 to 15 mm in wall thickness, and 500 to 900 mm in length. The furnace core tube 10 protects the coil from the heat and scale generated by the heated and red-heated columnar material by installing the columnar material such as steel in the heat treatment and installing it inside the induction heating (IH) coil. Furthermore, if the water-cooled tube that supports the steel material passing through the tube is damaged, it has the role of protecting the water from reaching the coil and causing an electrical short circuit.
For example, when a columnar steel material that requires forging is pushed in from one end side of the furnace core pipe 10, heated while passing through the inside of the furnace core pipe 10 and discharged from the other end side, the steel material has reached a temperature at which forging is possible. Can be obtained.

The furnace core tube 10 includes cozy light particles and mullite particles, and the cozy light particles and the mullite particles are integrally formed.
Since Kojilite has a small coefficient of thermal expansion and is excellent in heat impact resistance, it can be said that the furnace core tube is excellent in heat impact resistance. Further, since mullite has a smaller thermal conductivity than, for example, alumina, the thermal conductivity of the furnace core tube can be suppressed to a small value. Further, since mullite has a smaller coefficient of thermal expansion than, for example, alumina, it is advantageous for improving the thermal impact resistance of the furnace core tube.
Further, the specific gravity of mullite is about 3.0, which is close to the specific density of about 2.6 of cozy light. Therefore, even if the mullite particles are mixed with the cozy light particles, it is difficult to cause the separation of the raw material particles at the time of centrifugation, so that the mullite particles can be easily mixed uniformly and the composition of the furnace core tube can be made uniform.

The particle size of the cozy light particles is not particularly limited, but is preferably 0.1 mm or more and less than 3.5 mm. If it is less than 0.1 mm, the thermal impact resistance becomes insufficient, and if it is 3.5 mm or more, particles may protrude or fall off from the inner surface on the inner surface side of the furnace core tube.
The particle size of the mullite particles is not particularly limited, but is preferably 5 μm or more and 100 μm or less, and more preferably 5 μm or more and 70 μm or less. If it is less than 5 μm, the characteristics cannot be fully exhibited, and if it exceeds 100 μm, it is difficult for the cozy light particles to enter the gaps and the filling density of the material of the furnace core tube is lowered.

The cozy light particles can be composed of only fine particles having a particle size of less than 1.0 mm, and the protrusion from the inner surface can be within an allowable range. However, from the viewpoint of heat impact resistance, the cozy light particles preferably contain coarse particles having a particle size of 1.0 mm or more.
Further, the cozy light particles preferably contain coarse particles having a particle size of 1.0 mm or more and less than 3.5 mm, and fine particles having a particle size of 0.1 mm or more and less than 1.0 mm.
The blending ratio of the coarse grains and the fine grains is not particularly limited, but the mass ratio is preferably coarse grains: fine grains = 40 to 700: 30 to 60, and coarse grains: fine grains = 45 to 67 :. It is more preferably 33 to 55.

When coarse-grained cordylite is contained, it is preferable that a coat layer is formed on the inner surface of the furnace core tube on the inner surface side. As shown in FIG. 2D, in the furnace core tube 20, a coat layer 30 is formed on the inner surface of the furnace core tube 10 on the inner surface side. The coat layer 30 can have the same composition as that of the furnace core tube 10, but the particle size of the cordillite is preferably 0.1 to 0.7 mm, preferably 0.1 to 0.5 mm. Is even more preferable.
By the coat layer 30, the inner surface of the furnace core tube 20 on the inner surface side can be made a smooth surface by preventing the protrusion of coarse-grained cordierite.

[3] Method A for manufacturing a furnace core tube
The method A for producing a furnace core tube of the present invention includes a kneading step of kneading a composition for a furnace core tube to obtain a kneaded product, and pouring the kneaded product into a cylindrical molding die and centrifuging the uncured molded product. A molding step of obtaining a cured molded body by curing the uncured molded body while holding it in the molding die, and a drying step of removing and drying the cured molded body to obtain a furnace core tube. It is characterized by being provided with.

[Kneading process]
The kneading step is a step of kneading the composition for a furnace core tube to obtain a kneaded product. As the composition for the furnace core tube, the composition for the furnace core tube described in the above-mentioned [1] can be used.
The composition for the furnace core tube is mixed with water and kneaded so that the raw materials are uniform.
Appropriate fluidity is required to evenly distribute the kneaded material on the inner surface of the cylindrical molding die during molding.
The mixing ratio of the composition for the furnace core tube and water is not particularly limited as long as appropriate fluidity can be obtained, but when the whole composition for the furnace core tube (solid raw material) is 100% by mass, water is 20 to 30. It is preferably mixed with% by mass, and more preferably 22 to 28% by mass of water. If it is less than 20% by mass of water, it is difficult to spread the kneaded material evenly inside the molding die, and if it exceeds 30% by mass of water, the fluidity becomes too high and the raw material particles having different densities are separated. There is a problem that the material of the furnace core tube as a product becomes non-uniform due to the increase in size.

[Molding process]
The molding step is a step of pouring the kneaded product into a cylindrical molding die and centrifuging to obtain an uncured molded product. For example, as shown in FIG. 1A, the other end side 80b of the cylindrical molding die 80 is closed with the lid material 85b, and the kneaded product 10M is poured from the one end side 80a.
Next, as shown in FIG. 1 (b), the one end side 80a is closed with the lid material 85a to keep the molding die 80 horizontal and rotate it around its central axis. By doing so, the kneaded product 10M is held by centrifugal force on the inner wall of the cylindrical mold 80 with an even thickness. When the number of rotations is increased, air bubbles and water are pushed out from the kneaded product and cured to obtain an uncured molded product 10A. The shape of the uncured molded product 10A can be maintained even if the rotation is stopped. Centrifugal rotation is not particularly limited, but can be set to 0.8 to 4.5 m / s as the peripheral speed of the inner surface of the cylindrical shape for molding.
More effectively, the first stage where the peripheral speed is 0.8 to 1.6 m / s, the second stage where the peripheral speed is 1.9 to 2.5 m / s, and 2.7 to 4.5 m / s. It can consist of a third stage, which is s.
That is, in the first stage, the kneaded product 10M is spread over the cylindrical inner wall to a uniform thickness. Then, in the second step, the effect of the first step is ensured, and the bubbles contained therein are extruded and removed. Then, in the third step, water is extruded and removed to obtain an uncured molded product 10A.

[Curing process]
The curing step is a step of obtaining a cured molded product by curing the uncured molded product while holding it in a molding die. For example, as shown in FIG. 1 (c), the lid material 85a and / or 85b are removed from both end sides 80a or 80b of the molding die 80, respectively, and the water exuded on the inner surface of the uncured molded product A is discharged. Discharge. Then, as shown in FIG. 1 (d), the removed lid material 85a and / or 85b is attached and cured at room temperature. By doing so, the hydrated cured product produced by the reaction between the binder (for example, high alumina cement) and water bonds the aggregate particles to each other, and the strength is obtained. In this way, the cured molded product 10B having a strength that can be removed from the mold can be obtained.
The curing time is not particularly limited as long as the strength to enable demolding can be obtained, but is usually 12 hours or more, preferably 18 hours or more, and more preferably 24 hours or more.

[Drying process]
The drying step is a step of removing and drying the cured molded product to obtain a furnace core tube. For example, as shown in FIG. 1 (d), the furnace core tube 10 is obtained by removing the mold and drying it. Since the cured molded product 10B has moisture remaining inside, it is further heated and dried. The drying temperature is not particularly limited as long as water can be removed from the cured molded product 10B, but is usually 90 to 170 ° C., preferably 100 to 160 ° C., and more preferably 110 to 150 ° C.
From the above, the furnace core tube 10 is obtained. If necessary, processing or the like can be performed.

[4] Method B for manufacturing a furnace core tube
The furnace core tube manufacturing method B includes a kneading step of kneading the composition to obtain a kneaded product and a first molding step of pouring the kneaded product into a cylindrical molding die and centrifuging to obtain an uncured molded product. The first curing step of curing the uncured molded product while holding it in a molding die to obtain a cured molded product, and applying a coating agent containing a raw material to the inner surface of the cured molded product and then centrifuging. The second molding step of obtaining a molded body with an uncured coat layer, the second curing step of removing and curing the molded body with an uncured coat layer to obtain a molded body with a cured coat layer, and the molded body with a cured coat layer. It is characterized by comprising a drying step of drying to obtain a furnace core tube.
The main point that the furnace core tube manufacturing method B differs from the furnace core tube manufacturing method A is that it has a step of further applying a coating agent to the inner surface after obtaining a cured molded product.

[Kneading process]
The kneading step is a step of kneading the composition for a furnace core tube to obtain a kneaded product, and is as described in [3] [Kneading step] of the method A for manufacturing a furnace core tube.

[First molding process]
The first molding step is a step of pouring the kneaded product into a cylindrical molding die and centrifuging to obtain an uncured molded product, and [2] the [molding step] described in the furnace core tube manufacturing method A. (See FIGS. 1 (a) and 1 (b)).

[1st curing process]
The first curing step is a step of curing the uncured molded product while holding it in a molding die to obtain a cured molded product, as described in [2] [Curing step] described in [2] Furnace core tube manufacturing method A. (See FIG. 1 (c)).

[Second molding process]
The second molding step is a step of applying a coating agent containing a raw material to the inner surface of the cured molded product obtained in the first curing step and then centrifuging to obtain a molded product with an uncured coated layer.
For example, after the curing step shown in FIG. 1 (c), as shown in FIG. 2 (a), the other end side 80b of the molding die 80 is closed with the lid material 85b, and a small amount is applied to the surface of the cured molded product 10B. Pour 30M of the coating agent.
As the coating agent 30M, the same material as the above-mentioned composition for a furnace core tube can be used, but it is preferable to use fine particles of less than 1 mm as the aggregate particles of the coating agent 30M. More specifically, among the aggregate particles of the coating agent 30M, the particle size of the ceramic A particles is more preferably 0.1 to 0.7 mm, and even more preferably 0.1 to 0.5 mm. .. The particle size of the ceramic B particles is preferably 5 to 100 μm, more preferably 10 to 70 μm.
Next, as shown in FIG. 2B, the one end side 80a is closed with the lid material 85a to keep the molding die 80 horizontal and rotate it around its central axis. By doing so, the coating agent 30M is applied to the inner surface of the cured molded product 10B by centrifugal force in a uniform thickness. When the rotation speed is increased, air bubbles and water are pushed out from the coating layer and cured, and the uncured coated layer 30A is formed on the surface of the cured molded body 10B, and the molded body 20A with the uncured coated layer is obtained. Even if the rotation is stopped, the shape of the molded body 20A with the uncured coat layer can be maintained.
Centrifugal rotation is not particularly limited, but can be set to 0.8 to 4.5 m / s as the peripheral speed of the inner surface of the cylindrical shape for molding.
More effectively, the first stage where the peripheral speed is 0.8 to 1.6 m / s, the second stage where the peripheral speed is 1.9 to 2.5 m / s, and 2.7 to 4.5 m / s. It can consist of a third stage, which is s. The effects of centrifugal rotation in the first to third stages are as described above.

[Second curing process]
The second curing step is a step of removing and curing the molded body with the uncured coat layer to obtain the molded body with the cured coat layer. Since the cured molded body 10B has already been formed in the molded body 20A with the uncured coated layer obtained in the second molding step, the molded body 20A is immediately demolded after the second molding step as shown in FIG. 2 (c). be able to. Then, by the second curing step, the uncured coat layer 30A becomes the cured coat layer 30B, and the molded body 20B with the cured coat layer becomes. The second curing step is performed at room temperature in a closed container (not shown). The curing time is not particularly limited as long as the cured coat layer 30B is formed, but is usually 12 hours or more, preferably 18 hours or more, and more preferably 24 hours or more.

[Drying process]
The drying step is a step of drying the molded product with a cured coat layer to obtain a furnace core tube. For example, as shown in FIG. 2D, after the second curing step, the furnace core tube 20 is obtained by drying. That is, since the molded product 20B with the cured coat layer has moisture remaining inside the cured coat layer 30B, it is further heated and dried. The drying temperature is not particularly limited as long as the moisture can be removed from the molded product 20B with the cured coat layer, but is usually 90 to 170 ° C., preferably 100 to 160 ° C., and more preferably 110 to 150 ° C.
As described above, the furnace core tube 20 having the coat layer 30 formed on the inner surface of the furnace core tube 10 on the inner surface side can be obtained. If necessary, processing or the like can be performed.
Since the inner surface of the furnace core tube 20 on the inner surface side is covered with the coat layer 30 made of fine aggregate particles, a smooth surface can be obtained.

Hereinafter, the present invention will be described in detail by way of examples based on drawings and the like.

[Example 1]
(1) Composition for furnace core tube A solid raw material for the composition for furnace core tube according to Example 1 shown in Table 1 was prepared.
As the aggregate particles, cordylite as ceramic A particles and mullite as ceramic B particles were used. Kojilite is composed of only fine particles having a specific gravity of 2.6 and a particle size of less than 1 mm, and mullite is composed of particles having a specific density of 3.0 and a particle size of 5 to 45 μm. The particle size of the fine alumina is 10 μm or less, and the particle size of the high alumina cement is 75 μm or less.

(2) Manufacture of furnace core tube <kneading process>
To 100% by mass of the solid raw material, 25% by mass of water was added and kneaded to obtain 10M of a kneaded product having appropriate fluidity.
<Molding process>
As shown in FIG. 1 (a), the kneaded product 10M is poured into a cylindrical molding die 80 (inner diameter 100 mm, length 700 mm), and as shown in FIG. 1 (b), the molding die 80 is horizontally placed. It was kept and rotated around its central axis. Centrifugal rotation is the first step in which the peripheral speed of the inner surface of the molding die 80 is 1.0 m / s, the second step in which the peripheral speed is 2.2 m / s, and the third step in which the peripheral speed is 3.7 m / s. did. That is, in the first stage, the kneaded product 10M is spread over the inner wall of the cylindrical shape to a uniform thickness, then in the second stage, the bubbles further contained are extruded and removed, and in the third stage, water is extruded and removed. To obtain an uncured molded product 10A.
<Curing process>
As shown in FIG. 1 (c), the lid materials 85a and 85b were removed from both ends of the molding die 80, and the water exuded on the inner surface of the uncured molded product 10A was discharged.
Then, as shown in FIG. 1 (d), the lid materials 85a and 85b were attached again, and the uncured molded product 10A was cured at room temperature for 15 hours. In this way, a cured molded product 10B having a strength that allows demolding was obtained.
<Drying process>
As shown in FIG. 1 (e), the cured molded product 10B was demolded and heated at 130 ° C. in a drying oven (not shown) to remove the water remaining inside.
Through the above steps, a furnace core tube 20 having an outer diameter of 100 mm, a wall thickness of 10 mm, and a length of 700 mm was obtained.

(3) Evaluation The obtained furnace core tube 20 did not require a smooth “repair” on the outer surface with no air bubble marks. The inner surface was an acceptable level for the product, although there were small protrusions of cozy light particles (fine particles).
A comparison with a vibration-cast molded product (hereinafter, simply referred to as "vibration-cast molded product") having substantially the same raw material composition (however, the coarse particles of cozilite are large and the ceramic particles are alumina) is obtained. The strength of 20 was 1.5 times that of the vibration cast molded product.
The thermal conductivity was 0.85 times that of the vibration cast product, which was excellent. The thermal impact resistance was inferior to that of the vibration cast molded product.
The poor thermal impact resistance was due to the fact that the cozy light consisted only of fine particles and did not sufficiently absorb thermal stress.

[Example 2]
(1) Composition for furnace core tube A solid raw material for the composition for furnace core tube according to Example 2 shown in Table 1 was prepared.
As the aggregate particles, cordylite as ceramic A particles and mullite as ceramic B particles were used. Kojilite consists of 20% by mass of coarse particles having a specific gravity of 2.6 and a particle size of 1 mm or more and less than 3 mm and 25% by mass of fine particles having a particle size of less than 1 mm. Consists of particles. The particle size of the fine alumina is 0.5 to 10 μm, and the particle size of the high alumina cement is 75 μm or less.

(2) Manufacture of furnace core tube <kneading process>
It is the same as the kneading step of Example 1, and is as described above.
<First molding process>
It is the same as the molding process of Example 1, and is as described above.
<1st curing process>
It is the same as the curing process of Example 1, and is as described above.
<Second molding process>
As shown in FIG. 2A, the other end side 80b was closed with the lid material 85b, and a small amount of the coating agent 30M was poured into the inner surface of the cured molded product 10B obtained in the first curing step. The solid raw material of the coating agent 30M was the same as the solid raw material according to Example 1 except that the cozy light, which is an aggregate particle, was made into fine particles of 0.5 mm or less.
Next, as shown in FIG. 2B, the coating agent 30M is centrifuged by closing the one end side 80a with the lid material 85a, keeping the molding die 80 horizontal, and rotating it around its central axis. It was applied by force to the inner surface of the cured molded body 10B with an even thickness, and the uncured coated layer 30A was formed on the surface of the cured molded body 10B, and the molded body 20A with the uncured coated layer was obtained.
Centrifugal rotation includes a first step in which the peripheral speed of the inner surface of the molding die 80 is 1.0 m / s, a second step in which the peripheral speed is 2.2 m / s, and a third step in which the peripheral speed is 3.7 m / s. did.
That is, in the first stage, the coating agent 30M is spread over the inner wall of the cylindrical shape to a uniform thickness, then in the second stage, the bubbles contained in the coating agent 30M are further extruded and removed, and in the third stage, the bubbles contained therein are further extruded and removed. Water was extruded and removed from the coating agent 30M to obtain a molded body 20A with an uncured coating.

<Second curing process>
As shown in FIG. 2 (c), the molded product with the uncured coat layer was demolded and then cured at room temperature in a closed container (not shown). In this way, the uncured coat layer 30A became the cured coat layer 30B, and the molded product 20B with the cured coat layer was obtained. The curing time was 15 hours.

<Drying process>
As shown in FIG. 2D, the molded body 20B with a cured coat layer was heated and dried at a heating temperature of 130 ° C. to obtain a furnace core tube 20 having an outer diameter of 100 mm, a wall thickness of 10 mm, and a length of 700 mm. .. The furnace core tube 20 has a coat layer 30 formed on the inner surface of the furnace core tube 10 on the inner surface side.

(3) Evaluation The obtained furnace core tube 20 did not require a smooth “repair” on the outer surface with no air bubble marks.
With the cured molded product 10B without the cured coat layer, a smooth surface could not be obtained due to small protrusions of cozy light particles (coarse particles) on the inner surface. By forming the coat layer 30 on the inner surface, a smooth surface was obtained.
As a result of comparison with the vibration cast product, the strength of the obtained furnace core tube 20 was 1.5 times that of the vibration cast product.
The thermal conductivity was smaller than that of the vibration cast product, which was excellent. Since the purpose of using the furnace core tube is to protect the induction coil, it can be said that the smaller the thermal conductivity (the less heat is transferred), the more preferable it is.
The thermal shock resistance was equivalent to that of the vibration cast molded product. The "heat-resistant impact resistance" test is a comparative evaluation of the presence or absence of cracks generated when the inside of the test product (furnace core tube 20) is heated to 1200 ° C.
The reason why the thermal shock resistance was superior to that of Example 1 was that the coarse particles of Kojilite were blended so that the interface of the coarse particles acted as a place for absorbing internal stress, and the molded body received heat when it received a thermal shock. This is due to the effect of relaxing stress and preventing fracture.

[Example 3]
(1) Composition for furnace core tube A solid raw material for the composition for furnace core tube according to Example 3 shown in Table 1 was prepared.
As the aggregate particles, cordylite as ceramic A particles and mullite as ceramic B particles were used. Kojilite consists of 30% by mass of coarse particles having a specific gravity of 2.6 and a particle size of 1 mm or more and less than 3 mm and 15% by mass of fine particles having a particle size of less than 1 mm. Consists of particles. The particle size of the fine alumina is 0.5 to 10 μm, and the particle size of the high alumina cement is 75 μm or less.

(2) Manufacture of furnace core tube <kneading process>
It is the same as the kneading step of Example 1, and is as described above.
<First molding process>
It is the same as the molding process of Example 1, and is as described above.
<1st curing process>
It is the same as the curing process of Example 1, and is as described above.
<Second molding process>
It is the same as the molding process of Example 2, and is as described above.
<Second curing process>
It is the same as the curing process of Example 2, and is as described above.
<Drying process>
It is the same as the drying step of Example 2, and is as described above.

(3) Evaluation The obtained furnace core tube had almost the same characteristics as the furnace core tube obtained in Example 2. That is, the outer surface did not require a smooth "repair" without air bubble marks, and the strength was 1.5 times that of the vibration cast molded product. The thermal conductivity was also smaller than that of the vibration cast product, which was excellent. The thermal shock resistance was equivalent to that of the vibration cast molded product. These effects are as described in the evaluation of (3) of Example 2.

[Comparison example]
(1) Composition for furnace core tube A solid raw material for the composition for furnace core tube according to the comparative example shown in Table 1 was prepared.
As the aggregate particles, cordylite as ceramic A particles and alumina as ceramic B particles were used. Kojilite is composed of only fine particles having a specific gravity of 2.6 and a particle size of less than 1 mm, and alumina is composed of particles having a specific density of 3.9 and a particle size of 1 to 45 μm. The particle size of the fine alumina is 0.5 to 10 μm, and the particle size of the high alumina cement is 75 μm or less.
The difference from Examples 1 to 3 is that alumina is used instead of mullite as the ceramic B particles.

(2) Manufacture of furnace core tube In the <kneading step>, except that 20% by mass of water was added to 100% by mass of the solid raw material and kneaded, the <molding step>, <curing step>, and <drying step> In each case, the furnace core tube 10 was manufactured by the same process procedure as in Example 1.

(3) Evaluation The obtained furnace core tube 10 had no air bubble marks on the outer surface and was smooth and did not require "retouching". The inner surface was an acceptable level for the product, although there were small protrusions of cozy light particles (fine particles).
When compared with the vibration cast product, the strength was 1.5 times that of the vibration cast product. The thermal conductivity was 1.2 times that of the vibration cast product, which was inferior. The thermal conductivity is inferior to that of Examples 1 and 2, but the ceramic B particles of Examples 1 and 2 are mullite, whereas in this comparative example, they are alumina. caused by. That is, the thermal conductivity of mullite is about 1/8 that of alumina, and it can be said that the thermal conductivity of the entire material is increased by using alumina as the ceramic B particles.
Further, the coefficient of thermal expansion of mullite is about 2/3 of that of alumina, and it moves so as to reduce the coefficient of thermal expansion of the material, which is advantageous for improving the thermal impact resistance. Further, since the specific gravity of mullite is about 3/4 of that of alumina and it is difficult to cause separation of raw material particles during centrifugation, it can be said that it is advantageous to prevent heat impact fracture caused by inhomogeneity inside the material. Therefore, when alumina particles are used, the heat impact resistance is inferior.

The above examples are for illustration purposes only and are not to be construed as limiting the invention. Although the present invention has been described with reference to examples of typical embodiments, the wording used in the description and illustration of the invention is understood to be descriptive and exemplary rather than limited wording. As detailed herein, modifications may be made within the scope of the appended claims without departing from the scope or spirit of the invention in its form. Although specific structures, materials and examples have been referred to herein in detail of the invention, it is not intended to limit the invention to the disclosures herein, but rather the invention is claimed in the accompanying claims. It shall cover all functionally equivalent structures, methods and uses within the scope.

In the heat treatment performed when forging a steel material, it can be used in the technical field of a furnace core tube that protects the coil from the heat and scale generated by the steel material that is heated and red-hot by installing it inside the induction heating coil.

10; furnace core tube 10M; kneaded product, 10A; uncured molded body, 10B; cured molded body 20; furnace core tube 20A; molded body with uncured coat layer, 20B; molded body with hardened coat layer 30; coat layer, 30M; coating agent, 30A; uncured coating layer, 30B; cured coating layer

Claims (13)

A composition for a furnace core tube for producing a furnace core tube by centrifugal molding.
Bonding of aggregate particles composed of ceramic A particles having a specific gravity of 2.4 to 2.8 and a particle size of less than 3.5 mm and ceramic B particles having a specific gravity of 2.7 to 3.4 and a particle size of 100 μm or less, and ceramic C particles. A composition for a furnace core tube, which comprises a solid raw material comprising an agent and a solid raw material. The furnace core tube according to claim 1, wherein the ceramic A particles are 35 to 55% by mass, the ceramic B particles are 27 to 39% by mass, and the ceramic C particles are 18 to 26% by mass when the whole solid raw material is 100% by mass. Composition. The composition for a furnace core tube according to claim 2, which contains 16 to 35% by mass of coarse particles having a particle size of 1.0 mm or more and less than 3.5 mm among 35 to 55% by mass of ceramic A particles. The composition for a furnace core tube according to any one of claims 1 to 3, wherein the ceramic A particles are cordylite, the ceramic B particles are mullite, and the ceramic C particles are fine alumina and high alumina cement. .. A furnace core tube manufactured by centrifugal molding.
A furnace core tube comprising cozy light particles and mullite particles, wherein the cozy light particles and the mullite particles are integrally formed. The furnace core tube according to claim 5, wherein the cozy light particles include coarse particles having a particle size of 1.0 mm or more and less than 3.5 mm, and fine particles having a particle size of less than 1.0 mm. The furnace core tube according to claim 5 or 6, wherein the cozy light particles have a particle size of less than 3.5 mm, and the mullite particles have a particle size of 100 μm or less. The furnace core tube according to any one of claims 5 to 7, wherein a coat layer is formed on the inner surface of the furnace core tube on the inner surface side. The method for manufacturing a furnace core tube according to any one of claims 5 to 7.
The kneading step of kneading the composition for a furnace core tube to obtain a kneaded product, and
A molding step of pouring the kneaded product into a cylindrical molding die and centrifuging to obtain an uncured molded product.
A curing step of obtaining a cured molded product by curing the uncured molded product while holding it in the molding die, and
A method for manufacturing a furnace core tube, which comprises a drying step of removing and drying the cured molded body to obtain a furnace core tube. In the molding step, the centrifugal rotation is the first step in which the peripheral speed of the inner surface of the cylindrical mold for molding is 0.8 to 1.6 m / s, and the second step in which the centrifugal rotation is 1.9 to 2.5 m / s. The method for manufacturing a furnace core tube according to claim 9, comprising a step and a third step of 2.7 to 4.5 m / s. The method for manufacturing a furnace core tube according to claim 8.
The kneading step of kneading the composition for a furnace core tube to obtain a kneaded product, and
The first molding step of pouring the kneaded product into a cylindrical molding die and centrifuging to obtain an uncured molded product.
The first curing step of obtaining a cured molded product by curing the uncured molded product while holding it in the molding die, and
A second molding step of applying a coating agent containing the raw material to the inner surface of the cured molded product and then centrifuging to obtain a molded product with an uncured coated layer.
The second curing step of removing and curing the molded body with the uncured coat layer to obtain the molded body with the cured coat layer,
A method for manufacturing a furnace core tube, which comprises a drying step of drying the molded body with a cured coat layer to obtain a furnace core tube. The first molding step and the second molding step are the first step in which the centrifugal rotation is 0.8 to 1.6 m / s as the peripheral speed of the inner surface of the cylindrical mold for molding, and 1.9 to 2 The method for manufacturing a furnace core tube according to claim 11, further comprising a second step of 1.5 m / s and a third step of 2.7 to 4.5 m / s. A furnace core tube manufactured by the manufacturing method according to any one of claims 9 to 12.

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