JP2001106572A - Manufacturing process of graphite crucible - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a firing process of a graphite crucible in the atmosphere, which enables shortening of firing time, reduction in energy consumption and improvement in working environment by using an oxidation inhibitor employed in a conventional technique. SOLUTION: This manufacturing process comprises: mixing a phenolic resin used as a binder with a powdery raw material consisting of graphite, a refractory material such as silicon carbide or alumina, powdery metallic silicon and frit to obtain a raw material mixture; forming the raw material mixture into a green body; and heating the green body in two firing stages; wherein, in a first firing stage, the green body is subjected to heat treatment at about 220-300 deg.C in the atmosphere and, thereafter, the whole surface of the heat-treated body is coated with an oxidation inhibitor, and then, in a second firing stage, such rapid temperature elevation of the coated body as to raise its temperature to about 850-1,000 deg.C within about one hour in the atmosphere, is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a graphite crucible including a firing step in an air atmosphere.

[0002]

2. Description of the Related Art FIG. 2 is a flowchart showing an example of a conventional method for manufacturing a graphite crucible. In the example shown in FIG. 2, first, the graphite-containing powder as the main raw material and the auxiliary raw material (binder)
Is mixed at a predetermined ratio (step S1 in FIG. 2), and the mixture is heated and kneaded, and then pulverized (step S2), and then molded and pressure-formed (step S1). S3). Thereafter, the mold is removed and the necessary outer surface processing and cutting are performed (Step S4), and the work of "coke filling" for filling the gap between the refractory container containing the molded body and the molded body with coke breeze is performed. (Step S5). This coke filling is performed in order to keep the periphery of the molded body under a reducing atmosphere so that the molded body is not oxidized in the next primary firing (heating at about 1000 to 1300 ° C.).
And the molded body is subjected to the following primary firing (about 1000 to 1300
This is performed as a pre-step of the primary firing step in order to prevent deformation at the stage of (heating at ° C.). The next primary firing step is for reducing and firing the compact at about 1000 to 1300 ° C., and is performed continuously for about 9 days (step S6). By this primary firing, the tar pitch or phenol resin as the binder is carbonized. After the primary firing, an antioxidant (glaze) is applied to the entire surface of the molded body by spraying or the like (step S7). Next, a secondary firing step for melting and vitrifying the antioxidant (glaze) is performed (Step S8). This secondary firing is performed at about 850 to 1000 ° C. in an air atmosphere, and is performed continuously for about 1 to 3 hours. Thereafter, each fired body (molded body) is inspected (step S9) and shipped (step S1).
0).

As described above, in the conventional method for manufacturing a graphite crucible, firing of the formed body is performed by two heat treatments of primary firing and secondary firing. In the primary firing step, the object to be fired is placed in a refractory container, and the gap is filled with coke blaze to prevent oxidation of the organic binder such as phenolic resin and tar pitch, and graphite, and a closed reducing atmosphere is filled. 1000-130 in the lower firing furnace
Heat treatment is performed at a temperature of 0 ° C. Next, in the secondary firing step, an antioxidant is applied to the surface of the object to be fired which has been subjected to the heat treatment in the primary firing step, and then about 8 mm in a firing furnace in an air atmosphere.
The antioxidant is melted at a temperature of 50 to 1000C.

[0004]

In the conventional method for manufacturing a graphite crucible described above, in particular, in the primary firing step, the heating period (about 9 days) of the object to be fired (molded body) and the cooling time are required. There is a problem that it takes a long time to reduce work efficiency. Further, in the conventional method, it is necessary to fill the gap between the compact and the refractory container containing the compact with the coke breeze before the primary firing, but this "coke filling" operation is complicated in a bad environment. Work, which greatly impairs the work efficiency of the whole manufacturing process and worsens the working environment.
There is a problem that a large loss occurs in terms of thermal efficiency due to the presence of the coke breathe.

In order to solve these problems, conventionally,
There has been proposed a method in which the atmosphere in the furnace is changed to a non-oxidizing atmosphere with an inert gas or the like in the primary firing step, and the object to be fired is heated (Japanese Patent Application Laid-Open Nos. 60-77170 and 07-1).
However, in this method, a large amount of inert gas is required in order to form a non-oxidizing atmosphere, so that an economic problem such as an increase in manufacturing cost remains. Also, a method has been proposed in which a special antioxidant film having a specific composition is formed and then subjected to secondary baking in an oxidizing atmosphere (Japanese Patent Application Laid-Open No. 07-07107)
However, in this method, it is necessary to use a special antioxidant having a specific composition, so that there remains a problem that its use is restricted due to its functional problem.

The present invention has been made in view of the state of the prior art described above, and employs a method of performing primary firing under an air atmosphere (under an oxidizing atmosphere), and a conventional oxidizing method used in the prior art. While using the preventive material as it is, the above-mentioned problems of the prior art are solved, that is, shortening of the firing time of the compact in the manufacturing process of the graphite crucible, energy saving, improvement of work efficiency, and improvement of work environment are realized. It is an object of the present invention to provide a method for producing a graphite crucible that can be used.

[0007]

Means for Solving the Problems The present inventor has conducted intensive studies in order to solve the above-mentioned problems, and as a result, has set heating conditions for a material to be fired in a primary firing step in an air atmosphere (oxidizing atmosphere). Research has led to the success of the present invention. In the present invention, a molded product of a graphite material using a phenol resin as a binder is prepared in the first stage under an air atmosphere at about 220 to 30%.
After performing the heat treatment in the low temperature range of 0 ° C., in the second stage,
This is a production method characterized by performing carbonization firing of a binder in an air atmosphere simultaneously with baking of an antioxidant.

That is, in the present invention, a molded product using a phenolic resin as a binder is subjected to a first baking step in an air atmosphere (under an oxidizing atmosphere) for about 2 hours.
The temperature is raised to 20 to 300 ° C. and heat treatment is performed for about 3 hours or more.
In the first stage baking step, the phenol resin in the molded product is hardened and volatile components (ethylene glycol, acetone, phenol, formaldehyde, ammonia gas, amine gas, etc.) contained in the phenol resin are removed. Gasify. The gasification of the volatile components contained in the phenol resin in the first stage baking step, together with the curing of the phenol resin, makes the shape of the molded body extremely stable. That is,
Due to gasification of volatile components contained in the phenolic resin, gas is emitted from the molded body during a rapid temperature increase treatment (described later) in the second baking step, and the application state of the antioxidant is broken. Rolling and deformation of the shape of the molded body will not occur.

In the first firing step of the present invention, the heating in the atmosphere (oxidizing atmosphere) is set to about 220 ° C. or more as described above because the heating temperature is about 220 ° C.
If the temperature is lower, cracks and blisters may be generated in the fired body in the subsequent second firing step. Further, in the first stage baking step of the present invention, the heating in the air atmosphere (under the oxidizing atmosphere) was set to about 300 ° C. or less as described above in the state where the antioxidant was not applied to the surface. If the heating temperature of the molded body exceeds about 300 ° C., the phenol resin binder is oxidized and deteriorated. From the above,
The heat treatment temperature in the first stage is preferably in a temperature range of about 220 to 300C.

Next, after the first-stage firing step, a conventionally used antioxidant is applied to the surface of the molded article, and after drying, the second-stage firing step is performed in an air atmosphere under an air atmosphere. Within about 1 hour (or within about 30 minutes) from the start of the two-stage firing step, the maximum temperature of the molded body is about 850 ° C. or more and 1 hour or more.
The molded body is rapidly heated to a temperature of 000 ° C. or lower, and then about 1-2 hours (or 1-2.5 hours,
Or 1 to 3 hr) heating is continued. In the second-stage firing step, the antioxidant applied to the molded body is melted and melted.
Along with vitrification, the phenol resin as the binder is carbonized.

In the second firing step of the present invention, the maximum temperature of the rapid temperature rise is set to about 850 ° C.
The temperature within the range of not more than ℃ is defined as the firing temperature required for melting the antioxidant and forming a glass coating on the surface of the molded product in the above temperature range of not less than about 850 ° C and not more than 1000 ° C. (That is, if the firing temperature at this time exceeds 1000 ° C., a glass coating may not be properly formed with an antioxidant generally used conventionally. However, the composition of the antioxidant used 850 ° C. depending on the melting temperature).
This is because the above temperature range is a temperature at which the phenol resin binder can be carbonized. Further, as described above, in the second-stage baking step of the present invention, the time for rapidly raising the temperature to about 850 ° C. or more and 1000 ° C. or less is limited to about 1 Hr or less. If the time required to elevate the temperature to about 1 hour has passed, the time required for the antioxidant to melt and form a glass coating will be prolonged.
This is because before the antioxidant is melted, an oxide layer is formed on the surface layer of the fired object (formed body). From the above, about 85
The time required to elevate the temperature to 0 ° C. or more and 1000 ° C. or less is preferably within about 1 hour. In addition, in order to reliably melt the antioxidant (glaze) while the molded body is not oxidized, the molded body is heated to about 850 ° C. or more and 1000 ° C. or less within about 30 minutes after the start of the second-stage firing step. It is desirable to raise the temperature rapidly to the temperature of
In some cases, the surface of the molded body and its vicinity may begin to oxidize).

As described above, according to the method for manufacturing a graphite crucible according to the present invention, coke blaze is filled in the gap between the refractory container and the molded body, which is the primary firing, and the maximum temperature is about 1000 to 1000. Instead of performing heat treatment at 1300 ° C. for a long period of time, heat treatment in a low temperature range of about 220 to 300 ° C. in an air atmosphere (under an oxidizing atmosphere) can be substituted. It is evident that it greatly contributes to the improvement of the quality.

Next, an outline of the method for manufacturing a graphite crucible according to the present invention will be described with reference to the flowchart of FIG. In the method for producing a graphite crucible of the present invention, first, a graphite-containing powder as a main raw material and a sub-raw material (binder) are used.
Is mixed at a predetermined ratio (step S11 in FIG. 1), and the mixture is heated and kneaded, then pulverized (step S12), and then molded and pressure-formed (step S13). Thereafter, the mold is removed and necessary external surface processing and cutting are performed (step S14). Next, as a first-stage sintering step, the molded body was subjected to about 220
Baking at about 300 ° C. for about 3 hours (Step S1)
5). In the firing in the first stage, the phenol resin as a binder contained in the molded body is hardened,
Volatile components (ethylene glycol, acetone, phenol, formaldehyde, ammonia gas, amine gas, etc.) contained in the phenol resin are gasified. The gasification of the volatile components contained in the phenol resin in the first stage baking step, together with the curing of the phenol resin, makes the shape of the molded body extremely stable. That is, due to gasification of the volatile components contained in the phenolic resin, when the temperature is rapidly increased in the subsequent baking step of the second step, gas is emitted from the molded body, and the application state of the antioxidant is broken or the molding is performed. The shape of the body is not deformed. When the first stage firing is completed, an antioxidant (glaze) is applied to the entire surface of the molded body by spraying or the like (step S16). Next, a second stage baking process is performed (step S17). This second-stage calcination is performed by rapidly raising the temperature to 850 to 1000 ° C. within about 60 minutes (more preferably, within about 30 minutes) in the atmosphere, and thereafter, for about 1 to 2 hours (or (Approximately 1 to 2.5 hours). In the second baking step, the antioxidant (glaze) is melted and vitrified, and the phenol resin as the binder is carbonized. Thereafter, each fired body (molded body) is inspected (the same step S18),
It is shipped (step S19).

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. To a graphite crucible powder raw material composed of natural graphite, silicon carbide, alumina, metal silicon powder, and frit, add 12% resol type phenol resin as a binder, heat knead, cool, and pulverize the material. Filled into a graphite crucible molding mold composed of a frame, press-molded with a hydrostatic press to form an outer diameter of 85
A graphite crucible compact having a size of 5 mm and a height of 690 mm was obtained. The obtained molded body was heated to 300 ° C. at a heating rate of 50 ° C./Hr in a propane gas furnace as a first stage firing step,
r heat treatment. The SiO ₂ 12.2% graphite crucible was heat treated in the first step, the _{Al 2 O 3 19.8%, B} 2 O
₃ was coated with an antioxidant for an aluminum melting and holding graphite crucible having a composition of 58.7%, Na ₂ O at 3.4%, and CaO at 5%, and dried at 100 to 200 ° C. After that, as a second stage baking step, it was inserted into a propane gas furnace heated and maintained at 850 ° C., heated for 2 hours, taken out of the furnace, and baked with an antioxidant, and simultaneously completed carbonization of a phenol resin binder. . The obtained graphite crucible is
As a result of comparison with a graphite crucible of the same material and the same shape fired by a conventional firing method, as shown in Table 1 below, almost the same physical characteristics were exhibited. When the product of the present invention was put to practical use, the service life was 6 months, which was almost the same as that of the conventional product.

[0015]

[Table 1]

Embodiment 2 A material obtained by adding 12% of a novolak-type phenol resin and 1.5% of hexamethylenetetramine as a binder to the same graphite crucible blending material as in the first embodiment, kneading under heating, cooling and pulverizing, is composed of a metal core and a rubber frame. Filled in a graphite crucible mold, press-molded with hydrostatic press, outer diameter 600mm, height 700
mm was obtained. The obtained molded body is
As a sintering step, the temperature was raised at a rate of 10
The temperature was raised to 250 ° C. at 0 ° C./Hr, followed by a heat treatment for 5 hours.
4 g of SiO ₂ was placed in the graphite crucible subjected to the first stage heat treatment.
2.0%, the _{Al 2 O 3 16.9%, B} 2 O 3 22.1
%, 7.8% of Si, 4.7% of Na ₂ O, and 4.7% of K ₂ O.
An antioxidant for a copper alloy melting graphite crucible having a composition of 5% and CaO of 1.6% was applied and dried. After that, as a second firing step, it was inserted into a propane gas furnace heated and maintained at 950 ° C., and after a heat treatment of 1.5 hours, taken out of the furnace.
Simultaneously with the baking of the antioxidant, the carbonization of the phenolic resin binder was completed. The obtained graphite crucible showed almost the same physical characteristics as shown in Table 2 below as a result of comparison with a graphite crucible of the same material and shape fired by a conventional firing method. When the product of the present invention was put to practical use, a service life of 80 times, almost the same as that of the conventional product, was obtained.

[0017]

[Table 2]

[0018]

As described above, the firing method of the graphite crucible according to the present invention makes it possible to greatly reduce the time required for the first firing step, as well as the coke breathing and fire resistance. Since the use of the container is not required, it has enormous effects on energy saving and improvement of the working environment. That is, in the present invention, a method of performing primary firing under an air atmosphere (under an oxidizing atmosphere) is employed (Japanese Patent Application Laid-Open Nos. 60-77170 and 07-118072).
As described in Japanese Patent Application Laid-Open Publication No. H11-260, the method in which the atmosphere in the furnace is set to a non-oxidizing atmosphere by an inert gas or the like in the primary firing step to heat the object to be fired is not adopted) and the normal oxidation used in the prior art is used. The graphite crucible is used while using the anti-oxidizing material as it is (without adopting a method of forming a special anti-oxidation film having a specific composition and then performing secondary firing in an air atmosphere as in JP-A-07-237734). In the manufacturing process, it is possible to shorten the firing time of the molded body, save energy, improve the work efficiency, and improve the work environment (eg, omit the work of filling the coke breathing which deteriorates the work environment and work efficiency).

[Brief description of the drawings]

FIG. 1 is a flowchart showing a method for manufacturing a graphite crucible according to the present invention.

FIG. 2 is a flowchart illustrating a conventional method for manufacturing a graphite crucible.

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Hamamoto 2-19-10, Nukumachi, Hikoshimada, Shimonoseki-shi, Yamaguchi F-term in Nissin Reflatec Co., Ltd. (reference) 4G032 AA04

Claims (2)

[Claims] 1. A molding step in which a phenol resin as a binder is mixed with a refractory raw material containing graphite as a main raw material, heated, kneaded, and pulverized, and then molded. About 3 at ℃
A first-stage baking step of heating for at least one hour, an application step of applying an antioxidant to the surface of the fired molded body, and Within about 60 minutes, the temperature is rapidly raised to a temperature of about 850 ° C. or more and 1000 ° C. or less, and at that temperature,
A second firing step of heating for a period of time. 2. A phenol resin as a binder is added to a refractory material such as silicon carbide and alumina, a powdered material containing metal silicon powder or frit containing graphite, and mixed, heated, kneaded, and formed. A first-stage baking step of heating the molded body at about 220 to 300 ° C. for 3 hours or more in an air atmosphere; and applying an antioxidant to the entire surface of the calcined molded body. And applying the antioxidant to the molded body, and rapidly raising the temperature of the molded body to about 850 ° C. or more and 1000 ° C. or less within the first about 30 minutes in the air atmosphere, 1 to
2. A method for producing a graphite crucible, comprising: a second-stage firing step of heating for 2.5 hours.