JP2601614B2 - Ceramic firing method - Google Patents

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 material, which is improved in firing a ceramic material to be fired while suppressing defects generated during firing and enabling firing in a short time.

[0002]

2. Description of the Related Art In ceramics, when a turbocharger or turbine rotor having a complicated shape is formed by injection molding or casting, a large amount of an organic binder such as a thermoplastic resin or wax is added to the ceramic powder in order to enhance 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 molded body injection by heat decomposition or dissolution with an organic solvent before sintering. In degreasing by heating and sintering, which is one method of the degreasing, cracks and deformation may occur in the molded body, and in order to prevent this, the temperature must be increased over time, and Had the problem of taking a long time.

[0003] In the case of firing ceramics containing a clay component, such as porcelain, among organic ceramics, organic substances inside the ceramics are left as carbon deposits in the fired ceramics, so that one of the base materials is not affected. A phenomenon in which the portion swells, so-called bubbling, may occur. When trying to solve this,
In this case, too, the heating time has to be extended, which is disadvantageous in that it takes time.

[0004]

As described above, in a ceramic body to be fired, cracks or bubbling may occur in removing organic substances, and it takes a long time to heat and bake to prevent this. There is.

[0005] The present invention has been made in view of such circumstances, and an object of the present invention is to provide a method of firing a ceramic capable of shortening the firing time, in addition to eliminating the occurrence of cracks and bubbles. To provide.

[0006]

According to a first aspect of the present invention, there is provided a method for firing a ceramic, the method comprising: heating a ceramic body to be fired to obtain a fired body; The invention is characterized in that the combustibles existing in the object to be fired are oxidized and removed by increasing the temperature (the invention of claim 1).

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

[0008] The ceramic firing method according to the third invention is characterized in that the oxygen concentration of the atmosphere in the process from the temperature range in which the water of crystallization of the clay component is released to the temperature range in which the fired body shifts from the porous state to the dense state. The invention is characterized in that the combustibles existing in the object to be fired are oxidized and removed by increasing the temperature (the invention of claim 3).

[0009]

According to the investigation by the present inventors, the following has been found.
The ceramic fired body shifts from a porous state to a dense state in a certain temperature range. Here, by increasing the oxygen concentration during the porous state, it is possible to burn and remove combustible substances (organic substances) contained in the fired body in a good and short time. In addition, even if the oxygen concentration is increased in a temperature range higher than the temperature range in which the combustibles contained in the fired body are carbonized, the combustibles (organic substances) can be satisfactorily burned and removed in a short time.

According to the first aspect of the present invention, the oxygen concentration is increased in the process of the porous body of the ceramic body to oxidize and remove the combustibles, so that the air having a high oxygen concentration is effectively contained in the body. Enters and combustibles burn well in a short time.

[0011] In the invention according to claim 2, in a temperature range equal to or higher than a temperature range in which combustibles contained in the body to be fired are carbonized,
Increasing the oxygen concentration in the atmosphere oxidizes and removes the combustibles present in the fired body. In this case, the combustibles burn well in a short time.

Further, in the invention according to claim 3, the process from the temperature range in which the water of crystallization of the clay component contained in the ceramic fired body is released to the temperature range in which the fired body shifts from the porous state to the dense state. By increasing the oxygen concentration in the atmosphere to oxidize and remove flammable substances present in the fired body, air having a high oxygen concentration effectively enters the fired body, and the flammable substances are burned well in a short time. I do. This makes it possible to reduce the baking time while suppressing the occurrence of bulk.

[0013]

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

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

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

Now, a case in which an insulator fired body which is a ceramic fired body is accommodated in the furnace 1 and fired will be described.
Now, the raw material composition of the object to be fired is, for example, 30 to 3 feldspars.
4%, silica sand 2-6%, clay 35-39%, alumina 3 ~
7% and 12-16% of pottery stone. In FIG. 1, the body diameter is 1
The heat curve of the to-be-fired body of the solid insulator of 25 mm and length of 700 mm is shown. Now, as for the temperature change in the furnace 1, as shown in the heat curve D of FIG. 1, the temperature is first raised to approximately 230 ° C. in approximately 3.5 hours, and then increased to 700 ° C. in approximately 3 hours. And ramp up to approximately 1000 ° C. in approximately 3.2 hours. Thereafter, the temperature in the furnace 1 is maintained at a temperature around 1000 ° C. After the temperature is maintained for 7.3 hours, the sintering temperature is raised to approximately 1250 ° C., and the temperature is maintained at 1250 ° C. for a predetermined time and then cooled at a predetermined cooling rate.

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

That is, the clay component of the insulator fired body changes its porous state by releasing water of crystallization within a range of approximately 400 ° C. to 650 ° C. During this time, steam is filled between particles and oxygen Is prevented. Then, as shown in FIG. 2, when the release of the water of crystallization is completed, the porosity and the air permeability increase, and the porous state is promoted (approximately 700 ° C. or higher). The sintering by vitrification starts and the porous state shifts to a dense state (almost 1000 ° C.). Therefore, by enriching the in-furnace oxygen concentration in the temperature range of 700 ° C. to 1000 ° C., oxygen effectively invades the insulator body and the organic matter burns well in a short time. As a result, the baking time can be shortened while the occurrence of bubbling is suppressed.

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. As shown in Table 1, the total baking time with the temperature holding region near 1000 ° C.
In the case of the heat curve D according to the present embodiment, the time is 5.5 hours, which is also 10.5 hours as shown in Table 1, which can be reduced by 5 hours.

[0020]

[Table 1] The heat curve B in FIG.
In this case, as shown in Table 1, the region of 700 ° C. to 1000 ° C. is baked in approximately 2.2 hours, and the holding region near 1000 ° C. is approximately 5.8.
Fired in time. This can also eliminate the occurrence of bubbles. In this case, the firing time in the 700 ° C. to 1000 ° C. region and the holding region in the vicinity of approximately 1000 ° C. is approximately 8 in total.
The firing time can be reduced by 7.5 hours as compared with the conventional case.

FIG. 4 shows the relationship between the oxygen concentration, the heat area, and the presence or absence of black spots in a solid insulator fired body having a body diameter of 125 mm. Thermal area is "temperature" x "time"
(° C. · h), and particularly from approximately 700 ° C. to 1
The thermal area in the holding region around 000 ° C. (regions B ′ and C ′ in FIG. 1) is shown. The curve K in FIG.
The area between 1 and K2 is a bubbling generation limit zone, and the curve K in FIG. 4 shows an example of the bubbling generation limit when the substrate having the raw material composition shown in FIG. 4 is fired. The region above the curve K1 is a region where the blackout prevention effect is observed. For example, in the case of the heat curve D (when the oxygen concentration is 12 to
15%), the thermal area was 10050 ° C. · h, and it can be seen that no bubbling was observed. In the case of heat curve B (oxygen concentration is 17 to 21%), the heat area is 7670 ° C.
H, indicating that no occurrence of bulkiness was observed.

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

In this case, the wax exudes at 60 to 70 ° C., which is the melting point of paraffin wax, and the wax starts to be porous.
The exuded wax is made porous at around 180 ° C. where it is thermally decomposed, and is further made porous in a temperature range of 250 ° C. or more (carbonized temperature range) where the decomposed wax burns. In the present example, oxygen was supplied in a temperature range of 250 ° C. or higher where the porous body of the object to be fired was advanced, and the oxygen in the furnace was reduced to 30%. As a result, the organic binder, which is a combustible material, can be completely removed, thereby preventing the occurrence of cracks and deformation, and the time required for degreasing is as short as 250 hours.

In the conventional method of supplying the atmosphere (this is indicated by the heat curve T), the required time for degreasing requires 300 hours, but in this embodiment, the time can be greatly reduced.

[0025]

As apparent from the above description, the present invention has the following effects. According to the first aspect of the present invention, in firing the ceramic fired body, the oxygen concentration is increased in the process in which the fired body is in a porous state, and the combustible material is oxidized and removed. Burning can be performed, and the firing time can be shortened while suppressing generation of cracks.

According to the second aspect of the present invention, in firing the ceramic fired body, the oxygen concentration of the atmosphere is increased in a temperature range equal to or higher than the temperature range in which the combustibles contained in the fired body are carbonized. Since the combustibles existing in the fired body are oxidized and removed, the combustibles can be satisfactorily burned in a short time in this case, and the firing time can be shortened while suppressing the generation of cracks.

According to the third aspect of the invention, when firing the ceramic fired body containing the clay component, the fired body shifts from the porous state to the dense state from the temperature range in which the water of crystallization of the clay component is released. In the process up to the temperature range, by increasing the oxygen concentration of the atmosphere to oxidize and remove the combustibles existing in the fired body, air having a high oxygen concentration effectively enters the fired body, and the combustibles are reduced. In this case, the fuel is burned satisfactorily in a short period of time, whereby the baking time can be shortened while suppressing the occurrence of black.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a firing time and a furnace temperature related to a first embodiment 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 thermal area for the occurrence of black spots

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

[Explanation of symbols]

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)

(57) [Claims] In a firing method of heating a ceramic fired body to obtain a fired body, a combustible material contained in the fired body is increased by increasing an oxygen concentration of an atmosphere while the fired body is in a porous state. A firing method for ceramics, which comprises removing by oxidation. 2. A firing method for heating a ceramic fired body to obtain a fired body, wherein the oxygen concentration of the atmosphere is increased in a temperature range equal to or higher than a temperature range in which combustibles contained in the fired body are carbonized, A sintering method for a ceramic, comprising oxidizing and removing combustible substances existing in the object to be sintered. 3. A method for obtaining a fired body by heating a ceramic fired body containing a clay component, wherein a temperature at which the fired body shifts from a porous state to a dense state from a temperature range in which water of crystallization of the clay component is released. A method for firing a ceramic, comprising: oxidizing and removing flammable substances contained in the object to be fired by increasing the oxygen concentration of the atmosphere in the process up to the region.