JPH0737341B2 - Ceramic powder compact coating method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a powder of ceramic or the like for producing a ceramic product having a complicated shape such as a turbine wheel for turbocharge or a turbine wheel for gas turbine. The present invention relates to a method of forming a coating for preventing permeation of a hydrostatic pressure medium at the same time as deaeration of air in the molded body prior to hydrostatic pressing of the molded body.

[Prior Art] It is well known that hydrostatic pressing is performed for the purpose of homogenizing the density of a ceramic powder compact (including degreased body). In order to apply this hydrostatic pressurization method to the production of parts having a complicated shape such as a turbine wheel or a stator for a gas turbine engine, a hydrostatic pressurization film coating technique is required.

Japanese Patent Laid-Open Nos. 61-64801 and 61-69405 disclose prior arts in this field. That is, JP-A-61
JP-A-64801 discloses a method of filling a bag-shaped material of an elastic material and applying hydrostatic pressure, while JP-A-61-69405 discloses a method of forming a film on a molded article having a plurality of shapes. ing.

[Problems to be Solved by the Invention] In order to avoid the adverse effect of air in the molded body, it is desirable that the hydrostatic pressure step be performed after deaeration. It is important to form a coating film on the molded body to prevent the immersion of the pressurized medium. Among the above-mentioned conventional techniques, the technique disclosed in Japanese Patent Laid-Open No. 61-64801 is capable of degassing, but has a drawback that it cannot be applied to the production of parts having complicated shapes. The technique disclosed in Japanese Laid-Open Patent Publication No. -64905 has a problem that the degassing process cannot be performed.

The present invention has been made in view of the above circumstances, and an object thereof is to perform deaerating treatment during a film forming step prior to hydrostatic pressure application of a ceramic powder compact and to be used for manufacturing a component having a complicated shape. Another object of the present invention is to provide a method for forming a coating film for a ceramic powder compact, which is suitable for

[Means for Solving Problems] A method for forming a coating film for a ceramic powder molded body according to the present invention is a method of forming a ceramic powder molded body into a coating liquid containing bubbles contained in a coating liquid tank in a pressure chamber. An immersion step of immersing the ceramic powder compact in a state where a part of the ceramic powder compact is exposed from the liquid surface, and depressurizing the ceramic powder compact by placing the pressure chamber under a reduced pressure and at the same time coating the entire ceramic powder compact with a coating liquid. And a film forming step of forming a film on the surface of the ceramic powder compact by returning the pressure in the pressure chamber to the atmospheric pressure again after the degassing and burying process. To do.

That is, in the method for forming a coating film of the present invention, when a coating liquid (viscous liquid) containing bubbles is put under a reduced pressure, the phenomenon that the coating liquid surface rises due to defoaming is used to degas the ceramic powder compact. The feature is that a film is formed at the same time.

[Operation] According to the present invention, first, the ceramic powder compact is immersed in the coating liquid tank (containing the coating liquid containing air bubbles) in the pressure chamber, with a part of the ceramic powder molding exposed from the liquid surface. (Dip step). When decompression in the pressure chamber is started in this state, deaeration of the entire pressure chamber proceeds, and the ceramic powder compact thus immersed is deaerated through the open pores. By this deaeration, the bubbles contained in the coating liquid expand and the liquid surface rises, so that the ceramic powder compact is embedded in the coating liquid (immersion step). Then, when the pressure in the pressure chamber is returned to the atmospheric pressure again, the liquid surface is lowered, and the coating film is adhered to the entire surface of the deaerated ceramic powder compact. (Film forming step).

[Examples] Specific examples of the present invention will be described below. FIG. 1 is a longitudinal sectional view of an apparatus for carrying out the film forming method of the present invention, FIG. 2 is a plan view of the apparatus, and the principle of film formation by the apparatus shown in FIGS. 1 and 2 is described. Explanatory diagrams for doing so are shown in FIGS. 3, 4, and 5, respectively.

As described above, the method for forming a coating film for a ceramic powder compact of the present invention can be applied to various ceramic products having a plurality of shapes. Here, as an example, a case of applying it to the production of a turbine wheel will be described.

As shown in FIG. 1, the apparatus for carrying out the method of the present invention comprises a ceramic powder compact 1 (turbo wheel), a coating liquid tank 2, a coating liquid tank 2, and a coating liquid 3 containing bubbles, Turntable 4, turntable shaft 5,
Holding jig 6 for ceramic powder compact 1, partition 7, pressure pipe 8, valve 9, vacuum pump 10, controller 11, pressure chamber 13
A, drying chamber 13B, molded body setting chamber 13C, coating liquid discharge valve 1
4. A liquid discharge pipe 17, a coating liquid reservoir 18, a pump 19, a coating liquid supply pipe 20, and a supply port 21 and above. A signal 12 for controlling the valve 9 and a turntable stop signal 15 for controlling the coating liquid discharge valve 14 are supplied from the control unit 11.
Reference numeral 16 is a film formed on the ceramic powder compact 1.

Next, a method of forming a film by the apparatus of this embodiment will be described with reference to the principle diagram.

First, in the dipping step, the ceramic powder compact 1 is placed on the holding jig 6 in the coating liquid tank 2 of the pressure chamber 13A. The holding jig 6 is preferably made of a material that easily peels off, such as Teflon, in consideration of taking out the molded body 1 performed later. In this case, as shown in the principle diagram of FIG. 3, the ceramic powder compact 1 is placed on the holding jig 6 with a part thereof exposed from the liquid surface.

Next, move to the burial process, operate the vacuum pump 10 and
Reduce the pressure in 13A. When the pressure reduction is started, the entire pressure chamber 13A is degassed, and the ceramic powder compact 1 is degassed through the open pores (not shown) of the ceramic powder compact 1, and at the same time, as shown in FIG. The bubbles 22 in the liquid 3 expand, the liquid surface rises, and the entire ceramic powder compact 1 is embedded in the coating liquid 3.

After that, when the film forming step is started and the pressure in the pressure chamber 13A is returned to the atmospheric pressure, the liquid surface is lowered and the film 16 is formed on the degassed ceramic powder compact 1 as shown in FIG.
The depressurized state is switched to the atmospheric pressure state by detecting the time when the ceramic powder compact 1 is buried in the coating liquid 3 by the liquid level, time or pressure value, and the signal from the control unit 11 is detected.
This is done by opening valve 9 at 12.

A coating is formed through the above fixing. After forming this coating, the turntable 4 is rotated to dry the coating 16, and the ceramic powder compact 1 covered with the coating 16 is sent to the drying chamber 13B. At this time, the rotation stop signal 15 of the turntable 4 opens the coating liquid discharge valve 14 constituting the coating liquid discharge valve mechanism provided in the coating liquid tank 2 to remove the coating liquid 3 not used for coating, After that, the temperature required for drying is maintained. Although this temperature varies depending on the kind and amount of the solvent, a rapid temperature rise is not desirable, and it is preferable to maintain the atmosphere at 15 to 60 ° C. In the drying chamber 13B, after taking out the film-formed ceramic powder compact, the turntable 4 is further rotated to newly supply the supply port 2 into the coating liquid tank 2 in the setting chamber 13C.
The coating liquid 3 is filled from 1 and the next ceramic powder forming body is set on the holding jig 6. Valve after completing the previous processing steps
The coating liquid 3 discharged through 14 is stored in the coating liquid storage 18, in which air is contained as bubbles and then pump 1 is again used.
9. Through the coating liquid supply pipe 20 and the supply port 21, it is injected into the coating liquid tank 2 as described above. These coating liquid discharge discharge valve 14,
Liquid discharge pipe 17, coating liquid reservoir 18, pump 19, coating liquid supply pipe 20
And the supply port constitute a coating liquid circulation system.

EFFECTS OF THE INVENTION According to the coating film forming method of the present invention, degassing treatment can be performed during the film forming step prior to hydrostatic pressure application, and the coating liquid for the molded body, which was conventionally manually applied. Since it is possible to automate the soaking process, it is possible to reduce man-hours. Further, since the control system can control the film forming process, the thickness of the film can be freely adjusted and the quality of the film can be improved. Further, since the bubbles in the coating can be eliminated, even if the temperature is raised more rapidly than usual in the drying, the coating is not broken due to the expansion of the bubbles, and the quality of the coating can be improved also from this point.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of an apparatus used for carrying out the method for forming a coating film for a ceramic powder compact of the present invention, and FIG. 2 is a plan view of the apparatus of FIG. FIG. 3, FIG. 4 and FIG. 5 are views for explaining the principle of the film forming method. 1 …… Ceramic powder compact 2 …… Coating liquid tank 3 …… Coating liquid 6 …… Holding jig, 9 …… Valve 10 …… Vacuum pump, 11 …… Control unit 13A …… Pressure chamber 14 …… Coating Liquid discharge valve (valve mechanism for discharging coating liquid) 16 …… Coating film 17 …… Liquid discharge pipe (coating liquid circulation system) 18 …… Coating liquid storage (coating liquid circulation system) 19 …… Pump (coating liquid circulation system) 20 …… Coating liquid supply pipe (coating liquid circulation system) 21 …… Supply port (coating liquid circulation system) 22 …… Bubbles

Claims (3)

[Claims] 1. Immersing a ceramic powder compact in a coating liquid containing air bubbles contained in a coating liquid tank in a pressure chamber with a part of the ceramic powder compact being exposed from the liquid surface. A step of placing the pressure chamber under a reduced pressure to deaerate the ceramic powder compact, and at the same time burying the whole ceramic powder compact in the coating solution; A method for forming a coating film on a ceramic powder compact, comprising: returning the pressure in the pressure chamber to atmospheric pressure again; and forming a coating film on the surface of the ceramic powder compact. 2. The method for forming a coating film on a ceramic powder forming body according to claim 1, wherein the coating solution tank is provided with a valve mechanism for discharging the coating solution. 3. The method for forming a coating film on a ceramic powder compact according to claim 1, wherein the coating solution tank is connected to a coating solution circulating system for allowing the coating solution to contain the bubbles.