JPH069276A - Method for calcining ceramic - Google Patents

Abstract

PURPOSE:To shorten a calcination time, while preventing the generation of cracks and blisters. CONSTITUTION:The concentration of oxygen is held at 12-15% in an oven in a temperature region of 700-1000 deg.C and in a holding temperature region of approximately 1000 deg.C. Namely, the oxygen concentration of the atmosphere is enhanced in a process ranging from a temperature region for releasing the crystal water of clay components to a temperature region for transferring a calcination article from a porous state into a dense state. Thereby, organic substances contained in the article are burnt off in a good state in a short time without generating blisters.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for firing a ceramic which is improved so that defects occurring during firing can be suppressed and firing can be performed in a short time.

[0002]

2. Description of the Related Art In ceramics, when a turbocharger or turbine rotor having a complicated shape is molded by injection molding or casting, a large amount of organic binder such as thermoplastic resin or wax is added to the ceramic powder to improve the moldability. Is added to form a ceramic molded body. A molded body containing a large amount of an organic binder requires a degreasing step of removing the organic binder from the casting of the molded body by thermal decomposition or dissolution with an organic solvent before sintering. Degreasing by heating and baking, which is one of the methods for degreasing, may cause cracks and deformations in the molded body from the past. To prevent this, the temperature must be raised over time, There was a problem that it took quite a long time.

[0003] Among ceramics, particularly in the case of firing a body to be fired containing a clay component such as porcelain, organic matter inside remains as carbon deposits in the body to be fired, and A phenomenon in which the part swells up may occur. When trying to solve this,
In this case as well, the heating time must be lengthened, and there is a problem that it takes time.

[0004]

As described above, in the ceramic object to be fired, there is a possibility that cracks and burrs may occur when removing the organic substance, and if it is attempted to prevent this, it will take time for heating and firing. There is.

The present invention has been made in view of the above circumstances, and an object thereof is a method of firing a ceramic which can eliminate the occurrence of cracks and burrs and can shorten the firing time. To provide.

[0006]

According to a first aspect of the present invention, there is provided a method for firing a ceramic material, comprising: heating a ceramic body to be fired to obtain a fired body; and oxygen concentration of an atmosphere in a process in which the body is in a porous state. Is increased to remove the combustibles existing in the body to be oxidized by oxidation (the invention of claim 1).

A ceramic firing method according to a second aspect of the present invention is a firing method in which a ceramic body to be fired is heated to obtain a fired body, in a temperature range equal to or higher than a temperature range in which a combustible substance contained in the fired body is carbonized. The present invention is characterized in that the combustible substance existing in the body to be fired is oxidized and removed by increasing the oxygen concentration of the atmosphere (the invention of claim 2).

According to the third aspect of the present invention, in the method for firing a ceramic, the oxygen concentration in the atmosphere is changed from the temperature range where the water of crystallization of the clay component is released to the temperature range where the body to be fired transitions from a porous state to a dense state. Is increased to remove the combustibles existing in the body to be oxidized by oxidation (the invention of claim 3).

[0009]

According to the investigation by the present inventor, the following has been found.
The ceramic fired body transitions from a porous state to a dense state in a certain temperature range. Here, if the oxygen concentration is increased during the porous state, it is possible to satisfactorily burn and remove combustible substances (organic substances) existing in the body to be fired in a short time. Further, even if the oxygen concentration is increased in a temperature range higher than the temperature range in which the combustible substance existing in the fired body is carbonized, the combustible substance (organic substance) can be burned and removed satisfactorily and in a short time.

[0010] In the invention of claim 1, however, the oxygen concentration is increased in the process of the porous body to be burned to oxidize and remove the combustible substances, so that the air having a high oxygen concentration is effectively used in the body to be fired. Intrudes, and combustibles burn well in a short time.

According to the second aspect of the present invention, in a temperature range equal to or higher than the temperature range in which the combustible material in the body to be fired is carbonized,
Increasing the oxygen concentration in the atmosphere oxidizes and removes the combustible substances existing in the body to be fired, and in this case as well, the combustible substances satisfactorily burn in a short time.

Further, in the invention of claim 3, the process from the temperature range where the water of crystallization of the clay component contained in the ceramic body to be fired is released to the temperature range where the body to be fired is changed from a porous state to a dense state. Thus, by increasing the oxygen concentration of the atmosphere, the combustible substances existing in the body to be burned are oxidized and removed, so that air with a high oxygen concentration effectively penetrates into the body to be burned, and the combustible substances burn well in a short time. To do. Thereby, it is possible to shorten the firing time while suppressing the generation of burrs.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS. FIG. 3 shows a combustion device. A burner 2 is provided on a furnace wall 1a of the furnace 1. The burner 2 is supplied with fuel and air from a fuel supply port 3 and a combustion air supply port 4, respectively, and burns a combustion gas toward a furnace 1. It is designed to inject (flame).

In the furnace wall 1a of the furnace 1, the burner 2
An oxygen supply port 5 is provided at a position slightly away from
An oxygen supply piping system 6 is connected to the oxygen supply port 5. That is, the oxygen piping system 6 includes an oxygen reservoir 7, a valve 8, a control valve 9, a flow meter 10 and a solenoid valve 1.
Oxygen is supplied to the oxygen supply port 5 through 1.

The control valve 9 is controlled by the oxygen concentration control device 12. This oxygen concentration control device 12
Is supplied with an output signal from an oxygen sensor 13 provided to detect the oxygen concentration in the furnace 1, and an output signal from a temperature sensor 14, and The oxygen concentration control device 12 is the furnace 1
When the internal temperature reaches a predetermined temperature range, a preset oxygen concentration set value is compared with this output signal, and the control valve 9 is controlled according to the comparison result. Feedback control is performed so that the concentration becomes the oxygen concentration set value.

Now, description will be given of a case where an insulator firing object, which is a ceramic firing object, is housed in the furnace 1 and fired.
Now, the raw material composition of the object to be fired is, for example, feldspar 30 to 3
4%, silica sand 2-6%, clay 35-39%, alumina 3-
7% and ceramic stone 12-16%. In Figure 1, the body diameter is 1
The heat curve of the object to be fired of a solid insulator having a length of 25 mm and a length of 700 mm is shown. Now, regarding the temperature change in the furnace 1, as shown in the heat curve D of FIG. 1, the temperature is first raised to about 230 ° C. in about 3.5 hours, and then raised to 700 ° C. in about 3 hours. Then, the temperature is raised to about 1000 ° C. in about 3.2 hours. After that, the temperature in the furnace 1 is maintained at a temperature around 1000 ° C. Then, when this temperature holding is performed for 7.3 hours, the temperature is raised to a sintering temperature of about 1250 ° C., this 1250 ° C. is held for a predetermined time, and then cooled at a predetermined cooling rate.

In this case, the temperature inside the furnace 1 is from 700 ° C to 10 ° C.
In the range of 00 ° C., oxygen-rich air or oxygen gas with an increased oxygen concentration is supplied, and feedback control is performed so that the oxygen concentration in the furnace is 12% to 15%. As a result, the organic matter, which is a combustible substance in the body to be fired on the insulator, satisfactorily burns.

That is, the clay component of the insulator to be burned releases crystal water within a range of approximately 400 ° C. to 650 ° C. and changes into a porous state, but during this time, vapor is filled between the particles and oxygen is generated. Will be blocked. Then, as shown in FIG. 2, when the release of water of crystallization is completed, the porosity and the air permeability are increased to promote the porous state (about 700 ° C. or higher). Sintering due to this vitrification starts and the porous state shifts to a dense state (approximately 1000 ° C.). Therefore, by enriching the oxygen concentration in the furnace in the temperature range of 700 ° C. to 1000 ° C., oxygen effectively penetrates into the sintered body of the insulator, and the organic matter burns well in a short time. As a result, the firing time can be shortened while suppressing the generation of burrs.

A heat curve J in FIG. 1 shows a conventional heat curve when the oxygen concentration is set to 8% to 10% by the secondary air. The conventional heat curve J is 700 ° C. to 1000 ° C. As shown in Table 1, the total firing time with the temperature holding region around 1000 ° C. is almost 1
In contrast, in the case of the heat curve D of the present embodiment, it is 10.5 hours as shown in Table 1, which can be shortened by 5 hours.

[0020]

[Table 1] In addition, the heat curve B in FIG. 1 has an oxygen concentration of 17%.
.About.21%, and in this case, as shown in Table 1, the 700.degree. C. to 1000.degree. C. region is fired in approximately 2.2 hours, and the holding region near 1000.degree. C. is approximately 5.8.
Baking in time. This also eliminates the occurrence of black spots. In this case, the firing time in the 700 ° C. to 1000 ° C. region and the holding region near 1000 ° C. is about 8 in total.
This is time, and the firing time can be shortened by 7.5 hours as compared with the conventional case.

FIG. 4 shows the relationship between the oxygen concentration, the heat area, and the occurrence of burrs in a solid insulator to-be-baked object having a body diameter of 125 mm. Thermal area is "temperature" x "time"
(° C · h), especially from approximately 700 ° C to 1
The thermal area in the holding region (regions B ′ and C ′ in FIG. 1) around 000 ° C. is shown. Then, this curve K of FIG.
Between 1 and K2 is a burke generation limit zone, and a curve K in FIG. 4 shows an example of a burke generation limit when the base material having the raw material composition shown in FIG. 4 is fired. The region above the curve K1 is the region where the effect of preventing burrs is observed. For example, in the case of heat curve D (oxygen concentration of 12 to
15%), the heat area is 10050 ° C · h, and it is understood that no burrs are generated. In the case of heat curve B (oxygen concentration is 17 to 21%), the heat area is 7670 ° C.
・ It becomes h, and it can be seen that there is no occurrence of blurring.

Next, a second embodiment of the present invention will be described with reference to FIG. In the second embodiment, the organic binder is oxidatively removed and degreased from the ceramics sintered body containing the organic binder whose main component is paraffin wax. That is, a heat curve S in FIG. 5 shows an example of the present invention, in which heating from the start of heating to about 60 ° C. is performed at a heating rate of 1 ° C./h, and the temperature of about 60 ° C. is maintained for 70 hours. , And almost 30
The temperature is raised to 180 ° C over a period of time, and this 180 ° C is increased to 30 ° C.
The temperature is maintained for a period of time, after which the temperature is raised to approximately 550 ° C., and this 550 ° C. is maintained for a predetermined period of time and cooled.

In this case, the wax exudes and becomes porous at 60 to 70 ° C., which is the melting point of the paraffin wax,
The exuded wax is pyrolyzed around 180 ° C., and then the porosity proceeds to about 180 ° C., and the decomposed wax is further porous in a temperature range of 250 ° C. or higher (carbonization temperature range). Then, in this example, oxygen was supplied in the temperature range of 250 ° C. or higher where the porosity of the body to be fired progressed in this way, and the oxygen in the furnace was set to 30%. As a result, the organic binder, which is a combustible material, can be completely removed, and thus cracks and deformations can be prevented, and the degreasing time is as short as 250 hours.

In the conventional method of supplying the atmosphere (this is shown by the heat curve T), the degreasing time required is 300 hours, whereas in the present embodiment, the time can be greatly shortened.

[0025]

As is apparent from the above description, the present invention can obtain the following effects. According to the first aspect of the present invention, when firing the ceramic object to be fired, since the oxygen concentration is increased and the combustible material is oxidized and removed in the process in which the object to be fired is in a porous state, the combustible material is satisfactorily improved in a short time. It is possible to burn and shorten the firing time while suppressing the generation of cracks.

According to the second aspect of the present invention, when the ceramic object to be fired is fired, the oxygen concentration of the atmosphere is increased in a temperature range higher than the temperature range in which the combustible substance in the object is carbonized. Since the combustible substance existing in the fired body is removed by oxidation, the combustible substance can be satisfactorily combusted in a short time also in this case, and the firing time can be shortened while suppressing the generation of cracks.

According to the third aspect of the present invention, when the ceramic object to be fired containing the clay component is fired, the object to be fired is changed from the porous state to the dense state from the temperature range where the water of crystallization of the clay component is released. By increasing the oxygen concentration of the atmosphere in the process up to the temperature range, the combustible substances existing in the body to be burned are oxidized and removed, so that air with a high oxygen concentration effectively penetrates into the body to be burned, and the flammable substances are short. Combustion becomes excellent in time, which allows the firing time to be shortened while suppressing the generation of burrs.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a firing time and a furnace temperature related to the first example of the present invention.

FIG. 2 is a diagram showing changes in furnace temperature, porosity, and air permeability.

FIG. 3 is a diagram showing a schematic configuration of a firing apparatus.

FIG. 4 is a diagram showing the relationship between the oxygen concentration and the heat area with respect to the generation of swelling.

FIG. 5 is a diagram showing a relationship between firing time and furnace temperature related to the second embodiment of the present invention.

[Explanation of symbols]

Reference numeral 1 is a furnace, 2 is a burner, 5 is an oxygen supply port, 6 is an oxygen supply piping system, 9 is a control valve, and 12 is an oxygen concentration control device.

Claims (3)

[Claims] 1. A firing method for heating a ceramic body to be fired to obtain a body to be burned, thereby increasing a concentration of oxygen in an atmosphere while the body to be fired is in a porous state so that a combustible substance existing in the body is burned. A method for firing a ceramic, characterized by removing by oxidation. 2. In a firing method for heating a ceramic body to be fired to obtain a fired body, by increasing an oxygen concentration of an atmosphere in a temperature range equal to or higher than a temperature range in which a combustible substance existing in the body to be fired is carbonized, A method for firing a ceramic, characterized in that a combustible substance existing in the body to be fired is removed by oxidation. 3. A method for obtaining a fired body by heating a ceramic body to be fired containing a clay component, the temperature at which the body to be fired shifts from a porous state to a dense state from a temperature range in which crystallization water of the clay component is released. A method for firing a ceramic, characterized in that a combustible substance existing in the body to be fired is oxidized and removed by increasing an oxygen concentration in an atmosphere in a process up to the zone.