JPS62103105A - Slip casting molding die - 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] The present invention relates to a slip casting mold, and particularly to a mold suitable for the slip casting method used for molding ceramic products for engines.

[Conventional technology]

Ceramic powder is suspended in a dispersion medium solution and peptized.

A slip casting method is known in which the slurry is made into a fluidized slip and poured into a plaster mold in which a product cavity is formed.

When this slip casting method is used to manufacture an outer mold that defines a cavity, which is the outer shape of a ceramic product, or a ceramic product that has a cavity, it is used as a mold such as a core that forms the cavity. Foamed plastics made of foamed polystyrene or foamed polyurethane are sometimes used (for example, JP-A-51-109005, JP-A-49-1-2906, etc.).

[Problem that the invention seeks to solve]

By the way, a mold made of foamed plastic such as foamed polystyrene used for slip casting molding has unevenness on its surface due to the influence of bubbles due to foaming, and has a poor surface roughness of about 300 μm in maximum height. For this reason, when slip casting molding is performed using this mold, the surface roughness of the portion of the obtained ceramic product that was in contact with this mold becomes poor. Due to this poor surface roughness, the strength of the ceramic product as a sintered body becomes low, resulting in insufficient durability.

In addition, in slip casting molding, water or an organic solvent such as benzene is used as a dispersion medium solution, but when silicon carbide (S i C) is used as a ceramic powder, benzene is used rather than water as a dispersion medium solution. The higher the density of the ceramic product, the stronger it becomes.

However, when a mold made of expanded polystyrene is used and benzene is used as a dispersion medium solution, the mold is dissolved by the benzene, making slip casting impossible. Therefore, the conventional method has been to apply wax to the surface of a mold made of expanded polystyrene. However, when using wax, when removing the wax,
The wax melts due to heating and soaks into the ceramic molded body.

When the wax is decomposed in a nitrogen gas atmosphere, a large amount of carbon remains inside the ceramic, which causes problems such as blistering in the sintered body during firing, resulting in a decrease in strength.

For this reason, even if a mold made of foamed plastic such as expanded polystyrene is used, the surface roughness is good, and even when benzene is used as a dispersion medium solution, a foamed polystyrene mold can be used, and it has high strength. There was a desire for a device that would allow a sintered body (ceramic product) to be obtained.

[Means for solving problems]

The above problem is solved by using the slip casting mold of the present invention as described below.

Here, the slip casting mold of the present invention is characterized in that a polymer coating is formed on the surface of a foamed plastic molded into a desired shape. -.- First invention Furthermore, the slip casting mold of the present invention is characterized in that a polymer film insoluble in an organic dispersion medium is formed on the surface of a foamed plastic molded into a desired shape. ...-Second invention In the present invention, foamed polystyrene, foamed polyurethane, etc. can be used as the foamed plastic. These can be formed into a desired mold shape by injection molding, extrusion molding, or the like, or a commercially available foamed polystyrene material may be cut into a desired mold shape by machining.

Furthermore, in the present invention, a resin film or a rubber film can be used as the polymer film formed on the surface of the foamed plastic. At this time, any type of resin or rubber may be used, but if an organic solvent such as benzene is used as the dispersion medium solution, as in the second invention, a high It is necessary to use a molecular coating, such as polyvinyl alcohol.

The easiest way to form a polymer film on foamed plastic is to immerse the foamed plastic molded into the desired mold shape in a resin liquid or rubber liquid, pull it out, and dry it. Rubber fluid may be applied or sprayed onto the foamed plastic surface.

[Effect]

According to the slip casting mold of the present invention, a polymer film with a surface roughness better than that of the foamed plastic surface is formed on the surface. The surface roughness of the molded body also improves. By improving this surface roughness, the sintered body,
That is, the strength of the ceramic product is improved.

Furthermore, since a polymer coating that is insoluble in organic dispersion media is provided on the surface of the foamed plastic, it has become possible to use foamed polystyrene as a mold, which previously could not be used because it dissolves in organic dispersion media.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

(First Example) As a first example, an example will be shown in which a diesel sub-combustion chamber is formed of ceramic using the core of the slip casting mold according to the first invention.

Here, FIG. 1 is a sectional view showing the core of the slip casting mold according to the first embodiment of the present invention, and FIG. 2 is a sectional view showing the core of the slip casting mold according to the first embodiment of the present invention. FIG. 3 is a sectional view showing a state assembled into a mold.

Silicon nitride (s 13N4) powder 9 with an average particle size of 0.9 μm
0% by weight (hereinafter, all % indicates weight%), 5% alumina (Aj!zC)+) powder with an average particle size of 0.2 μm, and 5% Ittria (Y2O2) powder with an average particle size of 0.8 μm.
% are uniformly mixed using a ball mill.

To 100 parts by weight of the obtained mixed powder, 33.3 parts by weight of water as a dispersion medium solution and 0.6 parts by weight of surfactant ammonium polyacrylate were added and mixed in a ball mill for 6 hours to form a slip (slurry). Adjust.

Next, foamed polystyrene with a foaming rate of 30 times was used as the foamed plastic, and was molded into the core shape shown in FIG.

This expanded polystyrene core 1 is made of polyacrylic acid resin (
Polyacrylate coating 2 having a thickness of about 0.2 mm was formed as a polymer coating by immersing the sample in an aqueous emulsion solution, pulling it up, and drying it in the air for 2 hours. Then, the core 1 with the polyacrylate coating 2 formed thereon is assembled into a plaster mold 3, as shown in FIG. 2, and together with the plaster mold 3, a product cavity 4 in the shape of a diesel auxiliary combustion chamber is defined.

Subsequently, the slip, which has been sufficiently defoamed in a vacuum, is poured through the spout 5 of the plaster mold 3. Immediately after pouring 1) 0
Vibration was applied at 00 vp for 5 minutes to remove air bubbles from the air vent hole 6. After 5 minutes have passed, the vibration is stopped, the mold is broken, and the molded body in which the core 1 has been cast is taken out. After drying this formed body at 25°C for 12 hours and further at 45°C for 7 hours, it was heated to 450°C at a temperature increase rate of 5°C/min in a nitrogen atmosphere.
and the polyacrylate coating 2 is removed. Next, this molded body was placed in a firing furnace and fired at 1720° C. for 4 hours in a nitrogen atmosphere of 9.5 atmospheres. Thereafter, a ceramic chamber forming a diesel sub-combustion chamber was obtained by machining it to a predetermined size.

The surface roughness of the part of the obtained sintered body that was in contact with the core was
The maximum height was 8 μm, which was smaller than the surface roughness of the portion not in contact with the core, which was 14 μm. In addition, when the strength of the sintered body was examined using an internal pressure fracture test, the tensile strength σ was 4.
It was 13 kg/m''.

Note that no defects such as cracks or cracks occurred in the molded product after the core was removed.

(First Comparative Example) For comparison, a ceramic chamber was manufactured in substantially the same manner as in the first example except that a foamed polystyrene core without a polyacrylate coating was used.

The resulting ceramic chamber had a surface roughness of 300 μm at the maximum height in the part that was in contact with the core, and
As a result of an internal pressure fracture test conducted in the same manner as in the example, the tensile strength σ was 20 kg/am''.

(Second Example) A ceramic chamber was fabricated in substantially the same manner as in the first example except that a styrene-butadiene rubber film was formed as the polymer film instead of the polyacrylate film in the first example. was manufactured.

This ceramic chamber has the highest surface roughness and tensile strength.
Results similar to those in the example were obtained.

(Third Example) As a third example, an example will be shown in which a piston for a direct injection diesel engine is formed of ceramic using the core of the slip casting mold according to the second invention.

Here, FIG. 3 is a sectional view showing a core for slip casting molding according to a third embodiment of the present invention, and FIG. 4 is a sectional view showing a core for slip casting molding according to a third embodiment of the present invention. FIG. 3 is a cross-sectional view showing the assembled state.

Silicon carbide (S i C) powder 9 with an average particle size of 0.45 μm
8%, 1% amorphous boron powder with an average particle size of 1 μm, and 1% amorphous carbon powder with an average particle size of 0.1 μm are uniformly mixed in a ball mill. After drying the obtained mixed powder, 28 parts by weight of benzene and 1.5 parts by weight of a polycarboxylic acid nonionic surfactant were simultaneously added as a dispersion medium solution to 100 parts by weight of this mixed powder, and 6 parts by weight of a polycarboxylic acid nonionic surfactant were added in a ball mill. Adjust slip by mixing time.

Next, foamed polystyrene with an expansion rate of 30 times was used as the foamed plastic, and was molded into the core shape shown in FIG.

This foamed polystyrene core 1 is immersed in an aqueous emulsion solution of polyvinyl alcohol, pulled up and placed in the air for 2 hours.
By drying for a period of time, a polymer film with a thickness of about 0.
A polyvinyl alcohol coating 7 of two cranes was formed. Then, the core l on which this polyvinyl alcohol coating 7 is formed
As shown in FIG. 4, it is assembled into a plaster mold 3, and together with this plaster mold 3, a piston-shaped product cavity 4 for a direct injection diesel engine is defined.

Subsequently, the slip, which has been sufficiently defoamed in a vacuum, is poured through the spout 5 of the plaster mold 3. Immediately after pouring 1) 0
Vibration was applied at 00 vp for 5 minutes to remove air bubbles from the air vent hole 6. After 5 minutes have elapsed, the vibration is stopped, and after the ink is deposited, the mold is separated and the molded body in which the core 1 has been cast is taken out. After drying this formed body at 25° C. for 12 hours and further at 45° C. for 7 hours, it was heated to 450° C. at a temperature increase rate of 5° C./min in a nitrogen atmosphere.
Core 1 and polyvinyl alcohol coating 7 are removed.

Next, this molded body was placed in a firing furnace and fired at 2100° C. for 1 hour in an argon gas atmosphere of 1 atm.

As a result, a piston for a direct injection diesel engine with a density of 97% was obtained. Also, this piston is similar to the first embodiment,
The surface roughness was good.

Multiple test pieces of 3n x 4 cranes x 45 am were cut out from this direct injection diesel engine piston, and the surface was
It was finished with μm diamond paste and subjected to a three-point bending strength test. As a result, the three-point bending strength was 58~58 at room temperature.
84kg/Tsuru2.64~F35kg/w at 1200°C
", 68-92 kg/m at 1400°C".

(Second Comparative Example) In the third example, when a polystyrene foam core was placed in a plaster mold without forming a polyvinyl alcohol film on the surface and slip was poured into the plaster mold, the core dispersed the slip. It dissolved in benzene used as a medium solution and could not be molded.

(Fourth Example) In the third example, water was used instead of benzene as the dispersion medium solution, diethylamine was used instead of the polycarboxylic acid nonionic surfactant, and 33 parts of water was added to 100 parts by weight of the mixed powder. A piston for a direct injection diesel engine was produced in substantially the same manner as in Example 3, except that a slip was prepared by mixing 0.5 parts by weight of diethylamine and 0.5 parts by weight of diethylamine.

The density of the resulting piston for a direct injection diesel engine was 92%. From this direct injection diesel engine piston, 3 cranes x 4 m x 45 u +
A plurality of test pieces were cut out, the surfaces were finished with 1 μm diamond paste, and a three-point bending strength test was conducted. As a result, the three-point bending strength is 43 to 52 at room temperature and 43 to 55 kg at 2.1200°C.
The strength was 38 to 44 kg/mm'' at ℃.The reason why the strength was lower than that in the third example is that water is less effective than benzene in dispersing carbon, which is a sintering aid, and water vapor is less effective at dispersing silicon carbide. This is thought to be caused by oxidation.

(Fifth Example) In the third example, direct injection was performed in substantially the same manner as in the third example, except that a styrene-butadiene rubber film was formed as the polymer film instead of the polyvinyl alcohol film. Manufactured pistons for diesel engines.

This piston for a direct injection diesel engine had the same results as the third example in both surface roughness and tensile strength.

(Sixth Example) As a sixth example, an example will be shown in which an exhaust valve of a reciprocating engine is formed of ceramic using the outer mold of the slip casting mold according to the first invention.

Here, FIG. 5 is a sectional view showing the outer mold of the slip casting mold according to the sixth embodiment of the present invention, and FIGS. 6 to 9 are sectional views of the slip casting mold according to the sixth embodiment of the present invention. FIG. 3 is a cross-sectional view showing a method for manufacturing ceramic exhaust pulp using an outer mold.

Silicon nitride (Si3N4) powder 96 with an average particle size of 0.9 μm
%, alumina with average particle size 0.2 p m (/l!203
) with 2% powder and an average particle size of 0.8 μm (
2% of Y z O:+ ) powder was mixed uniformly using a ball mill. To 100 parts by weight of the obtained mixed powder, 33.3 parts by weight of water as a dispersion medium solution and 0.4 parts by weight of surfactant ammonium polyacrylate are added, and mixed in a ball mill for 6 hours to adjust slip. .

Next, using foamed urethane as the foamed plastic,
It was molded into the outer shape shown in FIG. This foamed urethane outer mold 21 was immersed in a polyacrylic acid resin (polyacrylate) emulsion aqueous solution 22, as shown in FIG. After dipping, it is pulled up and dried in the air for 2 hours to form a polymer film with a thickness of about 0, as shown in Figure 7.
．． A 2 mm polyacrylate coating 23 was formed. Then, as shown in FIG. 8, the outer mold 21 with the polyacrylate coating 23 formed thereon is placed on a plaster board 24, and together with the plaster board 24, a product cavity 25 in the shape of a ceramic exhaust valve is defined.

Subsequently, the slip 26 that has been sufficiently degassed in a vacuum is poured into the outer mold 21 from above. Immediately after pouring 1) 0
Vibrate at 00vp for 5 minutes to remove air bubbles from above. 5
After a minute has elapsed, the vibration is stopped, the mold is broken out, and the molded body in which the outer mold 21 has been cast is taken out. The formed body was dried at 25°C for 12 hours and then at 45°C for 7 hours, and then dried at 5°C in a nitrogen atmosphere.
The outer mold 21 and the polyacrylate coating 23 are removed by heating to 450° C. at a temperature increase rate of 1/min. Next, this molded body was placed in a firing furnace and fired at 1740° C. for 4 hours in a nitrogen atmosphere of 9.5 atmospheres. Thereafter, the ceramic exhaust valve 27 shown in FIG. 9 was obtained by machining it to a predetermined size.

The surface roughness of the part of the obtained sintered body that was in contact with the outer mold was
The maximum height was 8 μm, which was smaller than the surface roughness of the portion not in contact with the outer mold, which was 14 μm. In addition, when the strength of the sintered body was examined by a tensile strength test, the tensile strength σ was 5
Qkg/w”.

Note that no defects such as cracks or cracks occurred in the molded product after the outer mold was removed.

(Third Comparative Example) For comparison, a ceramic exhaust valve was manufactured in substantially the same manner as in the first example except that an outer mold made of urethane foam without a polyacrylate coating was used.

The resulting ceramic exhaust valve had a surface roughness of 300 μm at the maximum height in the part that was in contact with the outer mold, and as a result of a tensile strength test conducted in the same manner as in the first example, the tensile strength σ was 21 kg/m''.

(Seventh Example) In the sixth example, the ceramic exhaust was carried out in substantially the same manner as in the sixth example, except that a styrene-butadiene rubber film was formed as the polymer film instead of the polyacrylate film. Manufactured a valve.

This ceramic exhaust valve had surface roughness and tensile strength similar to those of the sixth example.

(Eighth Example) The sixth example differs in that polystyrene foam is used instead of urethane foam as the plastic foam.

Furthermore, in Example 6, a polymer coating was formed on the surface of the molded plastic foam, but a polyacrylate coating, which is a polymer coating, was applied in advance to the cavity surface of the mold during molding of the plastic foam. The difference is that a polyacrylate film is formed on the surface of the expanded polystyrene at the same time as the molding.

The resulting ceramic exhaust valve has a surface roughness of 320 μm at the maximum height and a tensile strength of 47 kg/**
Although the surface roughness and strength are slightly inferior to the sixth embodiment, there is no step of dipping the foamed plastic in the polymeric coating material and drying it, and the polymeric coating material is applied to the foamed plastic mold. The manufacturing process can be simplified.

As mentioned above, from the first example, the second example, and the first comparative example, if the core for slip casting molding of the present invention is used, good surface roughness can be obtained even if the material is foamed plastic. I understand that.

In addition, the third example, the fourth example, the fifth example, and the second example
The comparative example shows that a silicon carbide sintered body with excellent high-temperature strength can be obtained by using benzene as a dispersion medium solution and using a benzene-insoluble polyvinyl alcohol coating as the polymer coating of the core.

Further, from the sixth example, the seventh example, and the third comparative example, it can be seen that good surface roughness can be obtained even when foamed plastic is used for the outer mold.

Furthermore, according to the eighth embodiment, as a method for forming a polymer film on the surface of a foamed plastic, the process can be simplified without significantly lowering the surface roughness and tensile strength by performing it simultaneously with the molding of the foamed plastic. I understand.

Regarding foamed plastics, urethane foam has the advantage that it can be easily removed by heating or using a solvent.

In addition, since urethane foam is highly flexible, it can absorb the shrinkage that occurs during drying of a molded body with a slip attached thereto, thereby preventing damage to the ceramic molded body. These can be used depending on the purpose.

Although specific embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, but includes various embodiments within the scope of the claims.

〔Effect of the invention〕

As described above, the slip casting mold of the present invention provides the following effects.

(a) As the surface roughness of the mold surface improves, the surface roughness of the molded body also improves. Therefore, the strength and durability of the ceramic product increases.

(b) It becomes possible to use a mold made of foamed plastic using an organic solvent such as benzene as a dispersion medium, and the strength of the ceramic product obtained is improved compared to when water is used as a dispersion medium.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a sectional view showing a slip casting core according to a first embodiment of the present invention, and FIG. 2 is a cross-sectional view of a slip casting core according to a first embodiment of the present invention. FIG. 3 is a cross-sectional view showing a slip casting molding core according to a third embodiment of the present invention, and FIG. 4 is a cross-sectional view showing a slip casting core according to a third embodiment of the present invention. FIG. 5 is a sectional view showing a state in which a casting core is assembled into a plaster mold; FIG. 5 is a sectional view showing a foamed plastic molded body of an outer mold for slip casting according to a sixth embodiment of the present invention; FIG. FIG. 5 is a cross-sectional view showing the foamed plastic molded body immersed in a solution of polymer coating material; FIG. 7 is a cross-sectional view showing the outer mold for slip casting according to the sixth embodiment of the present invention; Figure 8 is a sectional view of the outer mold for slip casting molding shown in Figure 7 assembled to a plaster board, and Figure 9 is a ceramic exhaust valve made using the outer mold for slip casting molding according to the sixth embodiment of the present invention. FIG. 1-----Single foam polystyrene core (foamed plastic) 2-----Polyacrylate coating (polymer coating) 3.-
1--Gypsum mold 4--Product cavity 5-1111--Pour spout 6--Air vent hole 7--Polyvinyl alcohol coating (polymer coating) Applicant Toyota Motor Corporation Company Figure 1 Figure 2 Figure 3 Section 4 Rooster No. 55! i No. 62 1) Figure 17

Claims (2)

[Claims] (1) A slip casting mold characterized by a polymer coating formed on the surface of a foamed plastic molded into a desired shape. (2) A slip casting mold characterized in that a polymer film insoluble in an organic dispersion medium is formed on the surface of a foamed plastic molded into a desired shape.