JP3252486B2 - Ceramics molding 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 ceramic molding method for molding a powder material by a rubber press.

[0002]

2. Description of the Related Art A method called a rubber press is known as a method for producing a molded body having a desired shape using powder materials such as metals and ceramics as raw materials. According to this method, a powdery material is filled in a deformable and watertight mold formed of a mold or a rubber mold, and the mold is placed in a pressurizing chamber of a cold isotropic hydrostatic device (CIP) and molded. The powder material is compressed and molded by applying water pressure from the four circumferences of the mold. Japanese Patent Application No. 59-7003
Japanese Patent Application Laid-Open Publication No. H11-146,009 describes a method for producing a ceramic powder compact as described below. As shown in FIG.
A lubricant layer 23 is formed using a powder such as boron nitride (BN) on the surface of the core metal 20 provided with the ceramic material 1, and a ceramic powder aggregate 24 containing a binder is placed thereon. A rubber mold 22 is put on the assembly and sealed with a band 25.
1. Degas the air in the rubber mold. Next, when this is put into a hydrostatic tank and pressurized, the integrated body 24 is consolidated through the rubber mold 22 to form a molded body 26 as shown in FIG. 6B. When the volume of the integrated body 24 shrinks, since the lubricant layer 23 is interposed between the cored bar 20 and the integrated body, the ceramic powder is uniformly compressed, and the whole is formed to have a uniform density.
It is also described that powders of graphite, pyrophyllite, fluorine resin, polyacetal, polyethylene and the like can be used as the lubricant.

[0003] Even when an umbrella-type valve for intake and exhaust of an engine is made of ceramic, ceramic powder is molded by a rubber press. When an umbrella-type valve for intake and exhaust of an engine is formed by a rubber press, as shown in FIG. 1A, one end of a rubber mold 2 is sealed upside down with a mold 1, and ceramic powder 3 is put therein and vibration is applied. 1B, and the other end is sealed with a large-diameter mold 4 shown in FIG. 1B, placed in a pressure tank 6 shown in FIG. 1C, and compression molded by hydrostatic pressure.

[0004]

FIG. 5 shows an umbrella-type valve formed by the rubber press described above. 5A is a front view, and FIG. 5B is a bottom view. As shown in FIG.
Cracks 13 enter the bottom surface (top surface of the valve head) 12 and peel off thinly. This defect rate reaches 50% or more. this is,
When the ceramic powder in contact with the inner surface 4a of the mold 4 shrinks, it is considered that cracks will occur in the molded body because it hardly slips at this portion. Even if chrome plating is performed on the inner surface 4a of the mold 4 to perform mirror finishing, the defect rate is not improved. Therefore, as described in the above-mentioned publication, the inner surface 4
When a lubricant layer is formed by applying a powder of boron nitride (BN) to a by spraying, and rubber pressing is performed using this rubber mold, cracks do not occur on the bottom surface of the molded umbrella-shaped valve. However, during the molding of the umbrella-type valve, boron nitride powder adheres to the inner surface 4a of the mold 4 to cause slippage and prevent cracking. However, this powder partially mixes into the inside of the molded body. I will. When this molded body is fired, boron nitride does not sinter at the firing temperature of silicon nitride, which is a raw material of ceramics, and thus remains in a powder state. Therefore, when the umbrella-shaped valve is finish-ground after firing, small holes appear as defects on the surface of the finished product. Also,
If boron nitride powder having a diameter of about 50 μm is present near the surface without sintering, the strength of the product is greatly reduced, resulting in a defective product.

The present inventor has conducted various experiments on a sheet-like sliding material instead of a powdery lubricant. A, B, C in FIG.
Is a front view of an umbrella-shaped valve molded body when a vinyl sheet is arranged on the inner surface 4a of the mold 4 and rubber pressing is performed;
Figure 2 shows a bottom view and the inside of the mold. The rim of the head of the umbrella-shaped valve 9 is formed almost straight, but the wrinkles are left on the bottom 9a of the umbrella-shaped valve 9 on the entire surface at the bottom 9a of the umbrella-shaped valve 9 during compression molding. A wrinkled vinyl sheet 9c is stuck to the inner surface 4a of 4 and remains. In experiments using adhesive tapes and rubber sheets,
Good results were not obtained because traces of inclusions remained on the umbrella-shaped valve formed in the same manner, and the adhesive tape stuck to the mold surface. The present invention, by interposing a paper sheet between the powder material and the mold inner surface, prevents the powder lubricant from being mixed into the molded body when the powder lubricant is applied to the mold inner surface. It is another object of the present invention to provide a method for forming ceramics which does not cause cracks in a formed body even when a powdery lubricant is not used.

[0006]

SUMMARY OF THE INVENTION According to the present invention, a space is formed between a mold and a rubber mold in a liquid-tight manner with a powder material, and the mold is formed by applying hydrostatic pressure from the surfaces of the mold and the rubber mold. In the method for molding a body, a method for molding ceramics includes disposing a paper sheet on a surface where the mold and the powder material are in contact with each other.

[0007]

During the compression molding, the paper sheet disposed at the interface between the powder material and the mold shrinks homogeneously and isotropically, so that no crack occurs in the compact. Further, when the lubricant is applied to the mold surface, the lubricant does not mix into the molded body, so that the strength does not decrease.

[0008]

FIG. 1 is an explanatory view of a molding step according to the present invention.
First, as shown in FIG. 1A, one end of a rubber mold 2 is sealed upside down with a mold 1, and the powder 3 of silicon nitride is put therein, and the mixture is vibrated to be filled densely. 1B, and a boron nitride (BN) powder is sprayed on the inner surface 4a shown in FIG. 1B to form a lubricant layer, and the other end is sealed with a large-diameter mold 4; Is the CI shown in FIG. 1C.
It is put into the pressure tank 6 of the P apparatus and compression molded at a hydrostatic pressure of ² ton / cm ² for 1 minute. The demolded molded product is placed in a nitrogen gas atmosphere (10 kgf / cm ² ) at 1700 to 1900.
Bake at ℃. This sintered product is finished and ground into a product shape using a diamond grindstone.

FIG. 2 shows an inner surface of an umbrella-shaped valve molded product and a mold formed by the above-described molding method. 2A, 2B, and 2C are a front view, a bottom view, and a view showing an inner surface of a mold of an umbrella-shaped valve molded body. The peripheral portion 7a of the head of the umbrella-shaped valve molded body 7 is
Although inclined slightly inward, its diameter D1 is approximately equal to the diameter of the straight umbrella-shaped valve molding 9 shown in FIG. 4A. The paper sheet 5 is adhered to the bottom 7b of the umbrella-shaped valve molded body 7, the diameter of which is the same as the diameter of the bottom 7b of the umbrella-shaped valve molded body 7, and the bottom surface 4a of the mold 4 is clean. is there. When the paper sheet is peeled off, the bottom 7b of the umbrella-shaped valve molded body 7 has a rough surface, but has no wrinkles or deformation and no cracks.

Next, another embodiment will be described. As shown in FIG. 1A, one end of a rubber mold 2 is sealed upside down with a mold 1, and the powder 3 of boron nitride is put therein and vibrated to fill it evenly. The steps up to covering the removed paper sheet 5 are the same as in the previous embodiment. Next, the inner surface 4a of the mold 4 is sealed with the large-diameter mold 4 at the other end without applying a lubricant.
C into the pressure tank 6 of the CIP device shown in FIG.
Compression molded for 1 minute at a hydrostatic pressure of cm ² .

FIG. 3 shows an umbrella-shaped valve formed body formed by the above-described forming method. FIGS. 3A and 3B are a front view and a bottom view of the umbrella-shaped valve formed body. Umbrella shaped molded valve 8
The periphery 8a of the head is slightly outwardly inclined and has a diameter D2.
Is slightly larger than the diameter D1 of the umbrella-shaped valve molded body 7 shown in FIG. 2A. When the paper sheet stuck to the bottom portion 8b of the umbrella-shaped valve molded body 8 is peeled off, the bottom portion 8b has a rough surface and a slight chip 8c is generated at the peripheral edge. However, there is no wrinkle or deformation on the bottom surface, and the notch 8c at the peripheral edge is within the range of the finish grinding allowance.

In the above embodiment, a paper sheet is used in which copy paper is punched in a circular shape between the inner surface of the mold and the powder material. However, even if the paper sheet is not high-quality paper such as copy paper, cardboard or cardboard can be used. If not, medium paper can be used. Even if the lubricant is not applied to the inner surface of the mold, no molding failure occurs and the paper does not stick to the inner surface of the mold. It is preferable to use a lubricant, but the lubricant is not limited to expensive boron nitride, but a material such as graphite which has good slippage, does not have an adhesive property to a mold, and does not penetrate into paper can be used.

The paper sheet is inexpensive, easy to process in shape, does not stick to the mold, has good workability, shrinks homogeneously and isotropically during pressure molding, and does not crack the molded body.
In the above-described first embodiment, the lubricant is applied to the bottom surface 4a of the mold 4, but a lubricant in which the lubricant is applied in advance to one side of the paper sheet may be used. Further, in the actual paper examples described above, the paper sheet is used only for the large-diameter mold 4 side, but it is needless to say that the paper sheet can be used for the small-diameter mold 1 as well. For example, FIG.
Other shapes as shown in FIG.

[0014]

According to the present invention, during the compression molding of a rubber mold, the paper sheet disposed on the interface between the powder material and the mold shrinks homogeneously and isotropically, and the molded article does not crack. Further, when the lubricant is applied to the mold, the lubricant does not mix into the molded body, so that the strength does not decrease. Furthermore,
Paper sheets are inexpensive, easy to shape, and do not stick to the mold, so that productivity is good.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a molding step of the present invention.

FIG. 2 is a view showing a molded body and a mold surface according to the first embodiment.

FIG. 3 is a view showing a compact according to a second embodiment.

FIG. 4 is a diagram showing a molded body and a mold surface according to a comparative molding method.

FIG. 5 is a view showing a molded article obtained by a conventional molding method.

FIG. 6 is an explanatory view of a conventional molding method.

[Explanation of symbols]

Reference Signs List 1 mold 2 rubber mold 3 powder material 4 mold 5 paper sheet

Claims (1)

(57) [Claims] 1. A method of filling a powder material into a space formed in a liquid-tight manner between a mold and a rubber mold, and applying a hydrostatic pressure from surfaces of the mold and the rubber mold to form a molded body. A method for forming ceramics, comprising disposing a paper sheet on a surface where a mold and a powder material are in contact with each other.