JPS6287464A - Method of dewaxing ceramic formed body - 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 Field of Industrial Application This invention relates to a degreasing method for removing an organic binder from an injection-molded ceramic body by thermally decomposing it.

As is well known in the art, ceramic powder is mixed with an organic binder,
The injection molding method, which involves injecting this into a mold, is suitable for molding products with complex shapes, and also enables mass production, so it is widely used for automobile engine parts.

By the way, this resin needs to be removed before sintering the ceramic molded body, and is degreased by thermal decomposition.

Conventionally, this degreasing is carried out by heating in an inert atmosphere such as N2 gas in order to suppress the occurrence of defects such as blisters due to rapid thermal decomposition of the resin, and to prevent explosions. However, for ceramic molded bodies with a large volume or thick parts, the degreasing effect extends to the inside, so the temperature is quite high (50'C).
If the temperature is not raised to (above), sufficient degreasing will not occur. Moreover, since the temperature is raised at a very slow rate so that the degreasing reaction proceeds slowly, it takes a long time to heat the product to a high temperature, which poses the problem of poor working efficiency.

For this reason, there is a demand for degreasing in the atmosphere after the degreasing in the inert gas atmosphere has progressed to some extent.

Problems to be Solved by the Invention However, with this conventional degreasing method,
Ceramic molded bodies are heated in a heating chamber, and there is a risk of explosion when transitioning from introducing inert gas to introducing air, and while introducing air, making it a dangerous work environment. The problem arises.

The basic object of the present invention is to solve the above-mentioned problems, and to provide a degreasing method that can reliably and safely degrease an injection-molded ceramic molded body.

Means for Solving the Problems That is, the present invention provides a ceramic molding method in which preliminary degreasing is performed by introducing an inert gas into a heating chamber in which a ceramic molded body is placed and heated, and then air is introduced for re-degreasing. In the body degreasing method, a detection unit is provided to detect the explosive gas concentration in the heating chamber, and when the explosive gas concentration in the heating chamber is less than a predetermined value when transitioning from the preliminary degreasing to the re-degreasing, , the introduction of inert gas into the heating chamber is stopped and air is introduced, and if the gas concentration is above a predetermined value, the introduction of inert gas into the heating chamber is stopped and air is continued without being introduced. The present invention is characterized in that during re-degreasing, the introduction of air is stopped and the inert gas is introduced when the gas concentration is equal to or higher than a predetermined value.

Note that it is desirable that the predetermined value of the gas concentration be the lower explosive limit value.

Effect According to the present invention, when transitioning from preliminary degreasing in which an inert gas is introduced into the heating chamber to re-degreasing in which air is introduced,
When the gas concentration in the heating chamber is less than a predetermined value, the introduction of inert gas is stopped and air is introduced to cause the transition, and as long as the gas concentration is less than the predetermined value during re-degreasing, the introduction of inert gas is stopped. The installation continues. On the other hand, during the transition, if the gas concentration is equal to or higher than a predetermined value, the transition to re-degreasing in which air is introduced is not performed, and the inert gas is continuously introduced. Furthermore, when the gas concentration reaches a predetermined value or higher during re-degreasing, the introduction of air is stopped and an inert gas is introduced.

Note that if the predetermined value of the gas i degree is set as the lower explosion limit value, explosion within the heating chamber can be effectively prevented.

It should be noted that the lower this predetermined value is set than the lower explosive limit, the higher the safety can be (usually 174 to 1
/3).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An apparatus for carrying out the method of the present invention will be described with reference to FIG. A heating chamber 3 for storing an injection-molded ceramic molded body 2 is arranged in the heating furnace 1, and a heater (not shown) for raising the temperature inside the heating chamber 3 is arranged in the heating chamber 3. Further, an exhaust duct 3a for exhausting gas in the heating chamber 3 is provided. The exhaust gas from the exhaust duct 3a passes through the heating furnace 1 and is exhausted to the outside of the heating furnace 1 from a duct (not shown). Further, a nitrogen gas introduction pipe 4 and an air introduction pipe 5 are connected to the heating chamber 3, and each introduction pipe has a flow meter 4a having a flow rate detector (not shown).

5a are connected, and solenoid valves 4b and 5b are roughly provided. Further, one end of a duct 6 for gas concentration detection is connected to the heating chamber 3, and a gas concentration detection section 7 disposed outside the heating furnace 1 is connected to the other end of this duct 6. The gas concentration detection section 7 includes a cooler 7a for cooling the gas introduced from the heating chamber 3, and a gas detector 7b for detecting the concentration of the gas cooled by the cooler 7a. The output of this gas detector 7b is connected to a program controller 1 heater 8 and a gas alarm 9 fixed to the outer surface of the heating furnace 1. The heating furnace 1 is also equipped with a damper 10, which ventilates the inside and outside of the heating furnace 1 during exhaust, and in order to uniformly heat the interior of the heating furnace 1 and the outside, the cracked gas is heated uniformly. Fan 1a for dispersing and sending it out of the furnace and for smooth cooling
is provided.

EXAMPLE Below, a case will be described in which an example of the present invention is carried out using the above-mentioned apparatus.

First of all, silicon nitride (S i 3 N4) 92VH
%, Ittria (Y203) 4wt%, Spinel (MCIA1204) 4Wj% and an organic binder (paraffin, EA, APP>) were mixed together and molded into the desired turbine wheel shape by injection molding. 2 is embedded in ceramic powder 11 and placed in heated chamber 3.Next, preliminary degreasing is performed by heating to 450°C at a temperature increase rate of 2°C/h while flowing nitrogen gas at 301/n+in from nitrogen gas introduction pipe 4. Thereafter, the gas detector 7b is activated to detect whether the gas concentration in the heated chamber 3 is less than the lower explosive limit of 173.This lower explosive limit is generated by thermal decomposition of the organic binder. Propylene <C31-15
>, propane (C3f-(8), pentene (C5H)
IO>, for example, when the total amount of hydrocarbons such as methane (CH4) is converted to propane, it is 2.1
%.

If the gas concentration is less than the lower explosive limit of 173 at the time of the detection, the program controller 8 to which the output from the gas detector 7b is applied closes the solenoid valve 4b to stop nitrogen gas from the nitrogen gas inlet pipe 4. Stop introducing the solenoid valve 5b.
The tube was opened and air was introduced through the air inlet tube 5 at a rate of 101/man to perform re-degreasing by holding the tube at 400'C for 5 hours, after which the heater was turned off and the tube was cooled. By this method, a fully degreased body without defects such as cracks and blisters was obtained.

In this method, when transitioning from the preliminary degreasing to re-degreasing, and during the progress of re-degreasing, if the gas concentration in the sealed container 3 reaches 173 or more, which is the lower explosive limit, as detected by the gas detector 7b, the electromagnetic the valve 5b is kept closed;
The solenoid valve 4b of the nitrogen gas introduction pipe 4 is set to the open state,
Nitrogen gas is introduced from this introduction pipe 4. In general, the gas alarm 9 to which the output from the gas detector 7h is applied is activated to issue an alarm. Further, the program controller 8 turns off the heater 3, and the fan 1a cools the inside of the heating chamber 3, and the damper 10 is fully opened to forcibly discharge the heated air and gas inside the heating chamber 3, thereby heating the chamber. Explosion is prevented by lowering the gas concentration in the lower part 3 and eliminating sources of fire that could cause an explosion.

In this embodiment, as mentioned above, when transitioning from pre-degreasing to re-degreasing, or if the explosive gas concentration exceeds the lower explosive limit of 173 during re-degreasing, the heater is turned off, the damper is fully opened, and the Although the gas alarm 9 is activated to issue an alarm, this is not necessarily necessary for the present invention. However, by performing such an operation, it is possible to ensure the avoidance of an explosion, and it is also possible to notify the surroundings of the danger. Furthermore, although nitrogen gas was used as the inert gas in this embodiment, other inert gases such as argon may also be used.

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, the gas concentration in the sealed container is detected during the transition from preliminary degreasing to re-degreasing and during the progress of re-degreasing, and when the gas concentration is less than a predetermined value. When the gas concentration exceeds a predetermined value, the degreasing is controlled to proceed, and when the gas concentration exceeds a predetermined value, the degreasing is stopped and an inert gas is introduced into the sealed container, so the degreasing work can be performed safely. Based on this method, degreasing work consisting of preliminary degreasing and re-degreasing can actually be carried out, which has the effect of obtaining a good degreased body without defects.

[Brief explanation of drawings]

FIG. 1 is a schematic plan view of an apparatus used in an embodiment of the present invention, FIG. 2 is a schematic front view, and FIG. 3 is a schematic right side view. 1...Heating furnace, 2...Ceramic molded body, 3.
・・Power Ro heat, 4... Nitrogen gas introduction pipe, 5...
Air introduction pipe, 7... Gas concentration detection section, 7b... Gas detector, 8... Program controller, 9
...Gas alarm, 10...Circulation/exhaust switching damper.

Claims (2)

[Claims] (1) In a method of degreasing a ceramic molded body in which preliminary degreasing is performed by introducing an inert gas into the heating chamber in which the ceramic molded body is placed and heated, and then re-degreasing is performed by introducing air, explosive A detection unit that detects the gas concentration is provided, and when the explosive gas concentration in the heating chamber is less than a predetermined value when transitioning from the preliminary degreasing to the re-degreasing, an inert gas is introduced into the heating chamber. is stopped and air is introduced, and if the gas concentration is equal to or higher than a predetermined value, the introduction of inert gas into the heating chamber is stopped and the inert gas is continuously introduced without introducing air;
A method for degreasing a ceramic molded body, characterized in that during re-degreasing, when the gas concentration is equal to or higher than a predetermined value, the introduction of air is stopped and an inert gas is introduced. (2) The method for degreasing a ceramic molded body according to claim 1, wherein the predetermined value of the gas concentration is a lower explosive limit value.