JPH0776132B2 - Degreasing method for ceramic molded products - Google Patents

Description

TECHNICAL FIELD The present invention relates to a degreasing method for ceramic molded articles.

[Prior Art] Generally, in the manufacturing process of ceramics, molding is performed in a state in which an organic binder is added to ceramic powder to impart fluidity. Various molding methods are known in addition to press molding, extrusion molding, and injection molding has the advantage that a ceramic molded product having a complicated shape can be obtained. However, in order to carry out injection molding, since the material needs to have high fluidity, the amount of the organic binder added becomes large, and a step of degreasing for removing the organic binder which is no longer needed after the molding is required.

In the degreasing process, the ceramic molded product is heated in the furnace, and it is important to set the heating conditions at this time.If the condition is not set properly, the ceramic molded product may crack or peel off the surface layer. To do. Particularly important heating conditions are the heating temperature, the supply amount of the gas that forms the atmosphere in the furnace, and the oxygen concentration in the gas that forms the atmosphere in the furnace.

First, regarding the heating temperature, if the ceramic molded product is overheated or the temperature is rapidly raised, the amount of decomposed gas generated by the decomposition of the organic binder per unit time becomes excessive, and the ceramic The gas pressure inside the molded product causes problems such as cracking, swelling, and peeling of the surface layer of the ceramic molded product.

In order to solve such a problem, conventionally, a temperature sensor such as a thermocouple is used to detect the temperature in the furnace for heating the ceramic molded product, and the temperature in the furnace is set in accordance with a preset heating program corresponding to the temperature in the furnace. The temperature was controlled.

However, the amount of decomposition gas generated by heating the organic binder in the ceramic molded product does not correspond to the temperature one-to-one. Therefore, even if the temperature is controlled based on the temperature in the furnace, the amount of decomposition gas generated may be excessive.

Regarding the supply amount of gas forming the atmosphere in the furnace, if the supply amount is appropriate, as shown in FIGS. 13 (a) to 13 (d), the decomposition gas 30 of the organic binder is in the atmosphere. It diffuses and is discharged to the outside of the furnace when the atmosphere is updated. However, when the supply amount is small, Fig. 13 (e) to (g)
As shown in, the atmosphere in the furnace is saturated with the decomposition gas 30, the transition to the decomposition gas 30 does not proceed near the surface of the ceramic molded product 20, the organic binder is tarified 31 and hardened, and the ceramic molded product There is a problem that the gas pressure of the decomposition gas 30 generated inside 20 cannot be released, and eventually the ceramic molded product 20 is broken. On the other hand, when the gas supply amount is excessive, decomposition gas is rapidly generated in the surface layer portion of the ceramic molded product, so that defects such as surface layer separation occur.

Thus, the supply amount of the gas that forms the atmosphere is an important factor, but it depends on the processing amount of the ceramic molded product, the shape of the ceramic molded product, etc., so it is optimal if the heating conditions are programmed in advance. There is a problem that it takes a lot of time to determine the value.

Regarding the amount of oxygen in the atmosphere, the more oxygen,
As shown in FIG. 14 (a), many carbon-carbon bonds in the organic binder are broken (indicated by a broken line in the figure), so that the decomposition gas becomes a low molecular weight and the volume of the decomposition gas generated becomes large. .
As a result, the gas pressure inside the ceramic molded product increases, and defects easily occur in the ceramic molded product. Conversely, if an inert gas such as nitrogen is used as the atmosphere,
As shown in Fig. (B), since the number of carbon-carbon bond breaking points is reduced, the decomposed gas becomes a polymer, which is advantageous in that defects in the ceramic molded product are less likely to occur, but the inert gas is generally expensive. However, when it is used in a degreasing process that requires a long time, a cost problem arises.

As a method for improving the drawbacks of detecting the temperature in the furnace and controlling the temperature in the furnace in accordance with the detected temperature by the temperature raising program, the weight of the ceramic molded product is detected in place of the temperature in the furnace, A method of controlling the temperature in the furnace based on the change in weight (see Japanese Patent Application Laid-Open No. 61-163172) or a method of detecting the concentration of a specific component of the cracked gas instead of the temperature in the furnace and detecting the concentration based on the change in concentration A method of controlling the internal temperature (Japanese Patent Laid-Open No. 627674) has been considered.

[Problems to be Solved by the Invention] However, in these conventional configurations, only the temperature inside the furnace is controlled, and only a part of the heating conditions of the ceramic molded product is controlled. Therefore, the generation of defects in the degreasing process cannot be completely removed. That is, as shown in FIG. 15, assuming that the air supply amount (broken line) is constant, the carbon monoxide concentration (solid line) generated as the decomposition gas is constant even if the temperature (two-dot chain line) is controlled. Increase rapidly. Therefore,
The decomposition gas destroys the ceramic molded product. Here, the alternate long and short dash line indicates the oxygen concentration. In the case of temperature control, even if the heater or the like is feedback-controlled based on the temperature detected by the sensor, the furnace and the ceramic molded product have large heat capacities and the temperature cannot be suddenly changed. However, there is a problem in that the occurrence of defects cannot be sufficiently prevented.

Further, a sensor such as a differential transformer is used to detect the weight of the ceramic molded product, but if the condensed substance of the decomposition gas adheres to the sensing rod, the movement of the sensing rod is hindered and the weight cannot be accurately detected. It will be.

The present invention is intended to solve the above problems, and an object of the present invention is to provide a degreasing method for a ceramic molded product, which prevents generation of defects in the ceramic molded product in the degreasing step.

[Means for Solving the Problems] In the present invention, in order to achieve the above object, at least carbon monoxide concentration in a decomposition gas generated by thermal division of an organic binder is detected, and a furnace according to the state is detected. By adjusting the heating conditions and the gas supply amount into the furnace, the heating rate and at least the carbon monoxide concentration are controlled simultaneously.

Also, by detecting the oxygen concentration in addition to the carbon monoxide concentration and adjusting the heating conditions of the furnace and the supply amount of gas into the furnace according to the state, the heating rate of heating and the carbon monoxide and oxygen can be adjusted. The concentration and the concentration may be controlled at the same time.

In addition, the state of the ceramic molded product is detected during the degreasing process, and other than the heating rate of heating of the furnace, the heating rate of heating the furnace, the supply amount of the gas forming the atmosphere in the furnace and the heating rate other than the heating rate. You may make it control the heating conditions of 1 at the same time.

[Operation] According to the above configuration, in the degreasing step of the ceramic molded product, the carbon monoxide concentration and the oxygen concentration are adjusted by adjusting the heating conditions of the furnace and the supply amount of the gas forming the atmosphere in the furnace. Since at least one of the above and the heating rate is simultaneously controlled, the occurrence of defects in the ceramic molded product is suppressed as compared with the case where only temperature control is performed. Here, in order to prevent the occurrence of defects such as cracking and swelling of the molded product due to an increase in the amount of decomposed gas generated from the molded product, it is desirable to control the heating temperature rising rate, and the decomposition gas in the atmosphere In order to prevent insufficient decomposition of the organic binder and insufficient release of decomposed gas from the molded product due to extremely high concentration, increase the air supply amount to decompose the organic binder and separate it from the molded product. It is desirable to promote. That is, as in the invention of claim 1 or claim 2, by detecting the concentration of a specific gas in the furnace, the concentration of the decomposed gas and its change with time are known, and based on this information, the heating conditions of the furnace and If the heating rate of heating and the concentration of a specific gas in the furnace are controlled at the same time by adjusting the gas supply rate to the furnace, only one of the heating rate and the gas supply rate is set. As compared with the case of controlling, it is possible to suppress the occurrence of defects such as cracking and swelling of the molded product in the degreasing step, and to significantly reduce the occurrence of sintering defects due to insufficient degreasing.

Example 1 A furnace 1 for heating and degreasing a ceramic molded article is
As shown in the figure, a heater 2 for setting temperature conditions in the furnace 1 is provided. Air is supplied into the furnace 1 through the valve 3, and an inert gas such as nitrogen is supplied through the valve 4. The openings of these valves 3 and 4 can be continuously adjusted. The gas forming the atmosphere in the furnace 1 is discharged to the outside through the discharge passage 5, and the discharge passage 5 is provided with a safety valve 6. Furthermore, in the discharge path 5,
A carbon monoxide concentration detector 7 and an oxygen concentration detector 8 are arranged. Here, the carbon monoxide concentration detector 7 detects the concentration of carbon monoxide contained in the decomposition gas generated from the ceramic molded product. Carbon monoxide concentration detector 7 (7a
Is a sensor section, 7b is a main body section, and an oxygen concentration detector 8 (8a
Is a sensor portion, 8b is a main body portion), and the output is input to the management computer 9 to set the temperature of the heater 2 and the valves 3 and 4 based on the concentrations of carbon monoxide and oxygen discharged from the furnace 1.
And the opening degree of are adjusted. The heater 2 is a thyristor 10 connected to the management computer 9 via an interface.
The heating and temperature raising conditions in the furnace 1 are set in this way. Further, the valves 3 and 4 are driven by opening regulators 11 and 12, such as step motors, which are connected to the management computer 9 through an interface, respectively, and the air supply amount and the inert gas supply amount into the furnace 1 are controlled. And are adjusted.

Next, the control procedure of the temperature, the air supply amount, and the inert gas supply amount will be described. First, when the temperature in the furnace 1 is raised with the air supply amount kept constant, the organic binder in the ceramic molded article is thermally decomposed as the temperature rises, and the carbon monoxide concentration in the furnace 1 also rises. To do. Furthermore, when the temperature rises, the thermal decomposition of the organic binder becomes active, and the carbon monoxide concentration rapidly increases. Here, when the carbon monoxide concentration exceeds a predetermined value set in advance, the opening degree of the valve 3 is adjusted so that the oxygen supply amount into the furnace 1 is decreased, and at the same time, the supply amount of the inert gas is reduced. The opening of the valve 4 is adjusted so as to increase. At this time, the total amount of gas supplied into the furnace 1 is controlled to increase. At the same time, the energizing energy to the heater 2 is reduced via the thyristor 10 to moderate the temperature rise in the furnace 1. When the above control is performed, the total amount of the atmosphere increases and the atmosphere is quickly updated to remove the decomposition gas in the surface layer of the ceramic molded product. Is more likely to pop out of the surface layer, and the ceramic molded product is prevented from swelling. Further, since oxygen is contained in the atmosphere, the organic binder in the surface layer portion of the ceramic molded product is decomposed into low molecules, and a passage for decomposed gas generated from the inside of the ceramic molded product is formed. Further, by updating the atmosphere, the temperature in the furnace 1 is lowered, the decomposition of the organic binder is suppressed, and the amount of the decomposed gas generated is increased by the increase of the inert gas amount and the decrease of the oxygen amount in the atmosphere. Suppressed. That is, since the increase in gas pressure inside the ceramic molded product is suppressed, it is possible to prevent the ceramic molded product from bulging or cracking. In this method, until the decomposition gas is generated from the organic binder, an atmosphere of only air is mainly used, and when the generation amount of the decomposition gas is increased, the mixing ratio of the inert gas is increased. The amount can be made relatively small, and the cost increase can be suppressed as compared with the case where only the inert gas is used.

[Embodiment 2] In this embodiment, as shown in FIG. 2, the temperature inside the furnace 1 is detected by the temperature sensor 13, and based on the output of the temperature sensor 13 and the control signal from the computer 9. The thyristor 10 is controlled by the program controller 14. That is, in the first embodiment, the temperature control is performed only by changing the atmosphere in the furnace, but in the present embodiment, the temperature in the furnace 1 is also taken into consideration.
Further, a flow meter 15 is arranged in the discharge path 5.

The temperature inside the furnace 1 is basically the program controller 14
Feedback control is performed via the, and in addition to that, control is performed in accordance with changes in the state of the atmosphere (monoxide concentration, oxygen concentration) in the furnace 1 as in the first embodiment. Therefore, as shown in FIG. 3, the rate of increase in temperature (two-dot chain line) in the furnace 1 is high at first, but when the carbon monoxide concentration (solid line) exceeds a predetermined value, the rate of temperature increase is decreased. The air supply amount (thick broken line) is reduced, and the inert gas supply amount (thin broken line) is increased. Here, the oxygen concentration (dashed line) in the atmosphere also decreases as the air supply amount decreases. When degreasing proceeds in this way, a peak value of the carbon monoxide concentration is obtained, and thereafter, the carbon monoxide concentration decreases. At the time when the concentration of carbon monoxide becomes substantially constant, the organic binder inside the ceramic molded product is almost removed, so the air supply amount is increased again, and the inert gas supply amount is decreased.
Increase the temperature rise rate. In this way, by performing control according to the concentration of carbon monoxide, it is possible to efficiently degrease in a relatively short time while minimizing the supply amount of the inert gas.

[Embodiment 3] In this embodiment, as shown in FIG. 4, the program controllers 14 and 16 control the air supply amount without using a computer. That is, in this embodiment, only the air is supplied without supplying the inert gas, and the program controller 16 is operated according to the carbon monoxide concentration in the furnace 1 detected by the carbon monoxide concentration detector 7. The amount of air supplied is feedback-controlled. here,
The supply amount of air is controlled so that the carbon monoxide concentration maintains a substantially constant value. The temperature inside the furnace 1 is detected by the temperature sensor 13, and the heater 2 is passed through the program controller 14.
Is feedback controlled. The temperature is controlled independently of the state of the atmosphere, and the rate of temperature rise is large initially,
When the temperature in the furnace 1 reaches a predetermined value, the temperature increase rate is reduced, and when the temperature reaches another predetermined value, the temperature increase rate is increased again.

That is, in this embodiment, the control is performed as shown in FIG. 5, and the carbon monoxide concentration (solid line) is made substantially constant. Air supply (thick broken line)
Is almost constant, the carbon monoxide concentration will start to drop when the decomposition of the organic binder inside the ceramic molded product progresses to some extent.Here, the carbon monoxide concentration will be substantially constant by increasing the air supply amount. Keep it at. Further, the temperature (two-dot chain line) is set to increase at a high rate after reaching the temperature at which the organic binder in the ceramic molded product is sufficiently decomposed.

Also in this example, defects such as cracking of the ceramic molded product and swelling of the ceramic molded product did not occur during the degreasing process.

[Embodiment 4] In this embodiment, as a basic structure of the embodiment 1 or the embodiment 2, as shown in FIG.
20 states are monitored and this is also used as control data. That is, in the furnace 1, a window 21 surrounded by a water cooling jacket is formed above the ceramic molded product 20, and an image pickup device 22 composed of a television camera is arranged above the window 21. The image pickup device 22 is connected to a color analyzer 23, which is a color computer connected to the management computer 9, and a signal corresponding to the color of the ceramic molded product is sent to the management computer 9. The color analyzer 23 obtains the yellowness ΔY by the following formula. That is, first, when the tristimulus values are X, Y, and Z, the value YI is set as follows.

Here, when the initial value of YI is YI ₀ , the yellowness ΔYI is defined as ΔYI = YI−YI ₀ . The yellowness ΔYI corresponds to the degreasing rate (solid line) as shown in FIG. 7. Therefore, the management computer 9 determines the degreasing rate according to the yellowness ΔYI,
The air supply amount, the inert gas supply amount, and the temperature are controlled.

The control is performed as follows. As shown in FIG.
First, immediately after the start of degreasing, only air is supplied (thick broken line), and the temperature in the furnace 1 rises. Furthermore, when the temperature rises and the organic binder begins to decompose, the ceramic molded article 20 begins to change color due to the decomposition and partial carbonization of the organic binder (two-dot chain line). Since the management computer 9 determines the degreasing rate based on the color of the ceramic molded product 20, when the degreasing rate reaches a preset predetermined value, the air supply amount into the furnace 1 is reduced to reduce the amount of inert gas. The supply amount (thin broken line) is increased, and the temperature rise rate in the furnace 1 is reduced. At this time, the oxygen concentration (dashed line) decreases. Also, the total amount of gas supplied into the furnace 1 is set to increase. As a result, the decomposed gas on the surface layer of the ceramic molded product is removed, and the escape path for the decomposed gas from the inside of the ceramic molded product is formed to prevent the ceramic molded product from bulging. Further, the atmosphere in the furnace 1 is renewed to cool the ceramic molded product, and the inert gas is supplied to suppress the rapid decomposition of the organic binder. Thus, when the degreasing progresses sufficiently, the air supply amount is increased again and the inert gas supply amount is decreased.

[Example 5] In Example 4, the degreasing rate was determined by observing the color of the ceramic molded product, but in this Example, as shown in FIG. Light from a light source 26 such as a He—Ne laser provided outside the furnace 1 is provided to the reflecting mirror 25 through a window 27, and the light reflected by the reflecting mirror 25 passes through the window 28 to the outside of the furnace 1. It is designed to be observed by the light receiver 29 of. The reflecting mirror 25 is wrapped in a water cooling jacket and cooled to 50 ° C.

The control is performed as follows. As shown in Figure 10,
First, immediately after the start of degreasing, only air is supplied (thick broken line), and the temperature in the furnace 1 rises. At this time, the reflector 25
Has a large reflectance (two-dot chain line), and most of the light from the light source 26 reaches the light receiver 29. When the temperature rises and the organic binder starts to decompose, the decomposed gas near the surface of the reflecting mirror 25 is cooled and cohesively adheres to the reflecting mirror 25, so that the reflectance decreases. When the reflectivity starts to drop sharply in this way, the management computer 9 reduces the air supply amount into the furnace 1 and supplies the inert gas (thin broken line).
Is further increased, and the rate of temperature rise in the furnace 1 is reduced. At this time, the oxygen concentration (dashed line) decreases. Also, the total amount of gas supplied into the furnace 1 is set to increase. Thus, when the degreasing progresses sufficiently, the air supply amount is increased again and the inert gas supply amount is decreased.

Example 6 In Example 5, the reflection mirror 25 was arranged in the furnace 1 to observe the change in reflectance. In this example, as shown in FIG. The degreased state is observed by transmitting light and detecting a change in transmittance.

That is, the light from the light source 26 provided outside the furnace 1 is introduced into the furnace 1 through the window 27, and the window 28 facing the window 27 is provided.
Through the light receiver 29 outside the furnace 1.

According to this configuration, as shown by the chain double-dashed line in FIG. 12, the transmittance between the light source 26 and the light receiver 29 decreases with the generation of decomposition gas, so by observing the transmittance. The state of the ceramic molded product can be determined. Where the first
In FIG. 12, the thick broken line indicates the air supply amount, the thin broken line indicates the inert gas supply amount, and the alternate long and short dash line indicates the oxygen concentration.

Although the carbon monoxide concentration in the decomposed gas is detected in each of the above-described embodiments, the concentration of other components (carbon dioxide or the like) in the decomposed gas may be detected. Furthermore, the concentrations of not only one type but also a plurality of types of components may be detected. In addition, in the fourth to sixth embodiments, the concentration of the decomposed gas may not be detected, and only the oxygen concentration may be detected. In the above embodiment, the mixing ratio of air and inert gas is variable, but only the air is supplied into the furnace 1 and the atmosphere is controlled by removing oxygen from the air by a method such as adsorption. May be.

[Advantages of the Invention] As described above, the present invention detects at least the carbon monoxide concentration in the decomposition gas generated by the heat splitting of the organic binder during the degreasing step, and according to the state, the heating conditions of the furnace are set. By controlling the heating rate and the carbon monoxide concentration at the same time by adjusting the heating rate and the gas supply rate to the furnace, only one of the heating rate and the gas supply rate is controlled. Compared with the above, it is possible to suppress the occurrence of defects such as cracking and swelling of the molded product in the degreasing step, and to significantly reduce the occurrence of sintering defects due to insufficient degreasing.

[Brief description of drawings]

FIG. 1 is a system configuration diagram showing Embodiment 1 of the present invention, and FIG.
2 is a system configuration diagram showing a second embodiment of the present invention, FIG. 3 is an operation explanatory diagram of the same as above, FIG. 4 is a system configuration diagram showing a third embodiment of the present invention, and FIG. FIG. 6 is a block diagram showing the essential parts of a fourth embodiment of the present invention, FIG. 7 is an explanatory view of the same principle as the above, FIG. 8 is an explanatory view of the same as above, and FIG. 9 is a schematic view of a fifth embodiment of the present invention. FIG. 10 is a diagram showing the construction of parts, FIG. 10 is a diagram for explaining the operation of the same, and FIG.
FIG. 13 is an operation explanatory diagram of the above, FIG. 13 and FIG. 14 are explanatory diagrams showing conventional problems, and FIG. 15 is an operational explanatory diagram of a conventional example. 1 ... Furnace, 2 ... Heater, 3,4 ... Valve, 7 ... Carbon monoxide concentration detector, 8 ... Oxygen concentration detector, 9 ... Management computer.

Claims (3)

[Claims] 1. At least one of decomposed gases generated by thermal splitting of an organic binder during a degreasing step of heating a ceramic molded article composed of ceramic powder and an organic binder in a furnace to remove the organic binder. It is possible to simultaneously control the heating rate and at least the carbon monoxide concentration by detecting the carbon oxide concentration and adjusting the heating conditions of the furnace and the gas supply amount into the furnace according to the state. Characteristic ceramic degreasing method. 2. Monooxidation in a split gas generated by thermal decomposition of an organic binder during a degreasing step of removing the organic binder by heating a ceramic molded product composed of ceramic powder and an organic binder in a furnace. By detecting the carbon concentration and the oxygen concentration and adjusting the heating conditions of the furnace and the supply amount of the gas into the furnace according to the state, the heating rate of heating, the carbon monoxide concentration and the oxygen concentration are simultaneously determined. Degreasing method for ceramic molded products characterized by controlling. 3. A state of the ceramic molded article is detected during a degreasing step of removing the organic binder by heating the ceramic molded article composed of ceramic powder and an organic binder in a furnace, and according to the state, A method for degreasing a ceramic molded article, characterized in that the heating rate of heating of the furnace and heating conditions other than the heating rate of heating such as the supply amount of gas forming the atmosphere in the furnace and the oxygen concentration are simultaneously controlled.