JPS62100481A - Dewaxing furnace for ceramics - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Scope of Application in Industry 1-] The present invention relates to a degreasing furnace for ceramics that decomposes and volatilizes a forming aid added to a powder compact of ceramics for firing.

[Prior art and problems to be solved] Ceramic products are molded by adding organic molding aids (binder, lubricant, l-11 plasticizing agent) to the ceramic raw material powder. '41) by firing it at high temperature and sintering it.

High-purity raw materials obtained by recent synthesis methods do not have plasticity in themselves like the traditional clay for ceramics, so in order to give them preferable plasticity during molding, 1: Adding a molding aid is necessary. 62 and 11- are unavoidable.

In particular, recently, injection molding, which can be produced by humans with high precision and can be manufactured by humans, is becoming mainstream for complex-shaped products such as turbine brakes and -F. Diameter 1μ
It is known that if 30 to 40 parts by weight of the molding aid is mixed with the ceramic of m, a good molded body cannot be obtained.

Also, in the extrusion molding method, which is suitable for molding long objects such as pipes and honeycombs, depending on the type of raw material, 10 to 20
Heavy parts also require molding aids.

The molding aid varies depending on the type, but the amount is approximately 100 to 50.
It decomposes thermally in the 0°C range. Therefore, if the temperature increase rate when firing the compact is not appropriate, the decomposition of the components will occur within a very narrow temperature range, leading to a localized rise in the steam flow.
Defects such as cracks and blisters will occur in the molded product.

For this reason, molded bodies containing molding aids in polyacids are subjected to a degreasing process as a pre-firing treatment, and the temperature rise rate is generally controlled with high precision in a degreasing firing furnace or in an inert atmosphere. The molding aid is decomposed and removed.

This step is the most time-consuming step in the manufacturing process. That is, first, as shown in Figure 4, the heating deoxidation curves for many organic molding aids are determined at constant jl and temperature rate, and then quantitative In consideration of this, the heating-decrease curve is selected so that it gradually decreases with respect to temperature.

Next, for the molded article containing the combination of molding aids determined in this way, the temperature increase rate and temperature increase steps are determined while taking into account the thermal decomposition temperature of each aid, and what is actually done? The molded body is then heated and fired. At this time, a procedure is followed in which the above-mentioned temperature increase conditions are revised several times in consideration of the occurrence of defects and the like.

Furthermore, in the degreasing step, it may not be possible to obtain a good molded product by simply increasing the temperature slowly. In other words, for molded products that have a narrow thermal decomposition temperature range and undergo rapid thermal decomposition, they are held at the temperature at which thermal decomposition begins, or they are heated repeatedly in small increments. It is necessary to control the disassembly, and in such a case it also takes a great deal of time to set the rows 4'4.

Also, Schiff. Since the temperature conditions are set on the safe side, the degreasing time itself becomes extremely long.
-Procedures were being implemented. Therefore, there has been a need for a degreasing furnace that allows highly accurate temperature control.

The purpose of the present invention is to provide a degreasing furnace for ceramics that can solve the drawbacks of the prior art described above, reliably prevent cracking of molded bodies during degreasing, and can significantly shorten the degreasing time. .

[Means for solving problems]

In order to achieve the above object, the present invention uses a vacuum furnace to decompose and volatilize (degrease) a forming aid added to a ceramic molded body, and detects changes in the degree of vacuum during a one-temperature process (heating). , while predicting the rate of pyrolysis gas generation.
This allows automatic control of the heating rate in real time.

The present invention will be explained in detail below based on examples.

〔Example〕

FIG. 1 shows the configuration of a degreasing and firing furnace according to an embodiment of the present invention. This firing furnace has a furnace core tube 2 that accommodates a compact 1 to be degreased, a heating furnace 3 that heats the furnace core tube 2, and a temperature controller 4. 5, the inside of the furnace is suctioned, and a vacuum wound 6 is provided to measure the degree of vacuum inside the furnace.

Here, a Villany vacuum gauge with a meter relay is used as the vacuum gauge 6, and the relay operation signal is input to the temperature controller 4 so that changes in the degree of vacuum in the furnace are reflected in temperature control in real time. Further, the temperature is measured by the temperature measuring device 9 and inputted to the temperature controller 4.

In other words, set the Pirani vacuum 416 button to a desired degree of vacuum, and when the indicator needle for the degree of vacuum in the furnace exceeds the measured value due to the generation of pyrolysis gas during heating of the seal, the relay is activated. Then, the constant temperature increase rate program in temperature control is stopped to maintain the temperature to suppress thermal decomposition, and when the degree of vacuum in the furnace is reduced, heating is resumed at a constant temperature increase rate.

FIGS. 2(a) and 2(b) show an example of the operation of the above-mentioned degreasing furnace.
The graph shows the change over time in the degree of vacuum when the inside of the furnace is brought into a closed state with the vacuum pump 5 and heated at a constant temperature increase rate by yJ and the temperature curve. The height of the vacuum degree curve corresponds to the generation of pyrolysis gas, t, f, and 5. The higher the peak height, the faster the gas generation rate, which has an adverse effect on the molded product. The height of this peak 7 changes depending on the temperature increase rate,
As the temperature increase rate increases by -L, the gas generation rate increases and the peak value also increases.

Therefore, the meter relay set Pirani vacuum gauge 6 is configured to operate the relay at an arbitrary peak height relay setting value 8 (Figure (b)), and when the vacuum degree in the furnace reaches that value, a signal is sent to the temperature controller 4. If the temperature rise is stopped by sending the temperature, the peak of the degree of vacuum will become smaller, as shown in FIG. 4(b), and rapid thermal decomposition can be suppressed.

[Specific usage example]

An example of conventional degreasing and firing conditions is shown in FIG. 3(a). This is for an extrusion molded product of a mixed raw material of silicon carbide and colloidal graphite, containing 15 to 20 parts by weight of a metrose-based binder, 3 parts by weight of a lubricant, and 15 to 15 parts by weight of a dispersant. , stepwise heating was performed, and it took 12 hours from room temperature to 400°C.

On the other hand, FIG. 3(1)) shows the change over time in the degree of vacuum in the furnace and the temperature when degreasing is performed using the degreasing and firing furnace according to the present invention. In this molded product, cracks occur under the condition that the V in the furnace (vacancy level reaches 1.0 Torr), so automatic control was performed with the relay setting value set at 6 Torr. Temperature rate 2℃/
When the vacuum level inside the furnace exceeds 6 Torr due to gas generation due to thermal decomposition, the vacuum gauge relay is activated, and the temperature controller stops heating, and the temperature is increased. hold. As a result, the degreasing step was completed in about 5 hours, reducing the degreasing time to about 1/2 compared to the conventional method, and a good molded article without cracks was obtained.

In the conventional method, based on the basic thermal decomposition data of the molding aid,
In the end, we decided on a fired pulrogram through trial and error, but the present invention automatically raises the temperature while detecting the actual thermal decomposition situation, making it safe and efficient against cracking. Degreasing and firing is possible. In addition, even if you change the type or amount of the molding aid, or add other aids,
It has the advantage that it can be applied without problems.

= 7 - Note that the detection sensitivity of pyrolysis gas in the degreasing furnace of the present invention is almost determined by the relationship between the volume of the furnace core tube and the evacuation capacity of the vacuum pump. If you use one with an exhaust capacity that lasts for seconds, there will be no problem.

Further, as another example of controlling the temperature increase rate by detecting the degree of vacuum in the furnace, the following embodiment is also possible. In other words, even if the temperature increase is stopped and the temperature is maintained when the vacuum level in the furnace drops below a certain value (as in the above example), it is possible to produce a compact that continues to generate high-V pyrolysis gas. In some cases, it is also possible to perform two-step temperature control in which thermal decomposition is stopped by lowering the temperature until the degree of vacuum in the furnace reaches a set value or higher, and then the temperature is raised again when the degree of vacuum in the furnace reaches or exceeds the set value. .

〔Effect of the invention〕

As described in detail below, according to the present invention, it is possible to automatically set appropriate thermal decomposition (degreasing) conditions regardless of the type or star of the molding aid, so it is not possible to prevent cracking, etc. as in conventional methods. Not only does it completely eliminate the need for experiments, etc., which were considered necessary to determine the appropriate conditions from the viewpoint of degreasing, but the degreasing treatment time can be increased because the temperature increase rate can be increased in a temperature range unrelated to thermal decomposition. The time required for this process is extremely short, which brings great benefits to the industry in terms of energy conservation.

Furthermore, it can prevent cracking during firing (IF), improve product yield, help save resources, and in the case of engineering ceramics, greatly improve reliability. j-I can.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the configuration of a ceramic degreasing furnace according to an embodiment of the present invention, and FIG. (b) is a diagram showing changes over time in the vacuum degree and temperature inside the furnace, Figures 3 (a) and (b) are diagrams showing the results of control records in the oil record example, and Figure 4 is a diagram showing various types of FIG. 3 is a diagram showing the thermal decomposition characteristics of a molding aid. ■... Ceramic molded body, 2... Furnace tube, ; 3...
- Heating section, 4...Temperature controller, 5...VC empty pump, 6...Vacuum section, 9...Temperature measuring device.

Claims (2)

[Claims] (1) In a furnace that heats and degreases a ceramic powder molded body formed using an organic molding aid, there is a closed container capable of maintaining the inside of the furnace at a pressure below atmospheric pressure, a vacuum pump, a pressure gauge, and the temperature inside the furnace. The apparatus is configured to detect gas generation due to thermal decomposition and evaporation of the forming aid as furnace pressure, predict changes in the pressure, and automatically control thermal decomposition conditions in advance. A degreasing furnace for ceramics characterized by: (2) The temperature controller operates a relay to stop the temperature increase control in progress when the pressure in the furnace exceeds the set value for a pressure value that can be set arbitrarily, and instead maintains the temperature. 2. The degreasing furnace for ceramics according to claim 1, which has a control function for controlling the temperature of the ceramics.