JP3129627B2 - Manufacturing method of molded body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a molded article, and more particularly, to a method of adding an excessive liquid to a raw material composed of a granular material, and subjecting the raw material to an elastic pressure through a hydrostatic pressure state by uniaxial pressure molding. The present invention relates to a method for manufacturing a molded article obtained by molding at a pressure within a range of deformation pressure to obtain a preformed article.

[0002]

2. Description of the Related Art Conventionally, in a method of manufacturing a compact by press-molding a granular raw material, additives such as a lubricant, a lubricant, a binder and the like are added to and mixed with the granular raw material. To form a preform. The preformed body obtained in this way is subjected to a degreasing step for removing the additive, and is sintered to form a formed body. However, this degreasing step requires a long time and must be performed very carefully. In addition, in order to prevent the shape of the preformed body from collapsing, degreasing is performed so that a small amount of additive remains, but the slightly remaining additive is formed by sintering the preformed body. When the molded body was completed, it became a cause of defining closed pores inside the molded body, which caused a decrease in the density and strength of the molded body.

In order to solve such a problem, Japanese Patent Application Laid-Open No. 4-212904 discloses a method in which a mixture obtained by adding a liquid to a raw material in the form of a granular material is subjected to uniaxial pressing to form an excess liquid. And a method of forming a preform by removing the same. According to this method, the pressure is transmitted via the liquid during uniaxial pressure molding, so that the pressure transmission efficiency is good, so that the rearrangement of the granular material proceeds, the density is increased, and the preformed body is formed. To prevent the shape from being collapsed.
Thus, little additives such as lubricants, lubricants, binders, etc. are needed. Further, even when the preform is molded by adding an additive, a path through which the liquid flows out during the uniaxial pressure molding is formed in the preform, and the additive is discharged through the path in the degreasing step. As a result, the degreasing efficiency increases. Further, it is described that a large molded product can be obtained.

[0004]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above, and has been made in view of the above, and has the size of a granular material larger than its density and the granular material having a low affinity for a liquid. In other words, a powder having a small intermolecular force, a material having a high density of the powder and not undergoing plastic deformation, or a plastic such as a cemented carbide or a cermet that is difficult to deform and has a specific gravity When the preformed body is formed by uniaxial pressure molding using the large composite powder as a raw material, the preformed body does not collapse or break, and therefore, is used for maintaining the shape of the preformed body after uniaxial pressing. An object of the present invention is to provide an excellent method for producing a molded article.

[0005]

In order to achieve the above object, the present invention comprises a first step of adding an excessive amount of liquid to a powdery raw material and mixing the raw material; A second step of obtaining a preformed body while removing the excess of the liquid by uniaxially pressing the mixture obtained in the above, and the preformed body obtained in the second step is an undried A third step of forming a thin film on the surface of the preformed body, and a fourth step of sintering the preformed body on which the thin film obtained in the third step is formed to obtain a formed body. , Is characterized by having.

[0006]

According to the method of manufacturing a molded article according to the present invention, the shape of the molded article can be maintained by forming a thin film on the surface of the molded article. It can be prevented from collapsing or breaking.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for producing a molded article according to the present invention will be described in detail below with reference to preferred embodiments and the accompanying drawings.

FIG. 1 is a longitudinal sectional view of a uniaxial press forming apparatus used in an embodiment of a method of manufacturing a molded article according to the present invention.
Is a perspective view showing a step of applying a thin film forming agent to the preform, FIG. 3 is a schematic diagram showing a state of the surface of the preform, and FIG. 4 is a graph showing the concentration of the thin film forming agent and the strength of the preform. It is a graph which shows a relationship.

The method for producing a molded article according to the present invention is applicable to a case where the size of the granular material is larger than the density of the granular material, or when the affinity between the granular material and the liquid is small, Materials with low inter-force, high granular material density and no plastic deformation, or composite granular materials such as cemented carbide and cermet that are difficult to plastically deform and have a large specific gravity As 12, water 14 is added and mixed well to form a mixture 16. Next, as shown in FIG.
Cavity 1 of uniaxial press forming apparatus 10
8 and press-molded to obtain a square pillar-shaped preform 2
Create 0. At this time, the mold 22 and the lower punch 24,
There is a slight gap between the upper punch 26 and the gap, from which excess water 14 contained in the mixture 16 flows out, and the raw material 12 is uniformly pressed through the water 14.

After the pressure molding, as shown in FIG. 2, the preformed body 20 is taken out of the uniaxial pressure molding apparatus 10 and immediately formed of a material for forming a thin film (hereinafter, referred to as a thin film forming agent), a developing agent, and a wetting agent. Is sprayed over the entire surface of the preform 20 with a sprayer 27 to form a thin film 28 (see FIG. 3).

The thin film forming agent used at this time is thin film 2
8 can be formed, melted in a solvent, easy to handle, and quickly decompose when degreasing.
It needs to evaporate. In order to satisfy the above conditions, it is preferable to selectively use any one of vinyl acetate, nitrocellulose, melamine resin, polystyrene resin, acrylic resin, polyamide resin, and cyanoacrylate. This thin film forming agent is used after being dissolved in a solvent. As the solvent at this time, there are acetone, alcohol, xylene, toluene, methylene chloride and the like, but considering its convenience, alcohol and acetone are suitable. The content of the thin film forming agent is determined by the thickness of the thin film 28 and the like, but is preferably 1 to 30% by weight, and more preferably about 3 to 20% by weight based on the solvent.

The developing agent is applied to the surface of the preform 20 by a thin film 28.
It is used to form evenly. The developing agent, ethyl benzoate, butyl benzoate, butyl butyrate, ethyl cellosolve, butyl cellosolve and the like,
The developing agent is added to the solvent in an amount of 0.5 to 10% by weight.

[0013] Wetting agents are used to prevent the solvent from drying rapidly and shrinking or cracking. Examples of the wetting agent include ethyl alcohol, propyl alcohol, isopropanol, and isobutynol.
40% by weight is added to the solvent.

As shown in FIG. 3, the space inside the preform 20 after the pressure molding is filled with water 14. Since the thin film forming agent is applied to the preformed body 20, the thin film forming agent rarely seeps into the preformed body 20,
The thin film 28 is uniformly formed on the surface of the preform 20.
Further, since the water 14 in the inside is evaporated from the surface of the preformed body 20, the pores 30 are formed in the formed thin film 28 innumerably. The presence of the pores 30 can be confirmed with an electron microscope.

After that, the preform 20 is forcibly dried by supplying cooling air for 48 hours, and then left in an atmosphere of 70 ° C. for 48 hours for natural drying. At this time, the water 14 evaporates through the pores 30. The dried preform 20 does not collapse or break due to the thin film 28 formed on the surface. Also, handling is easy.

Next, a degreasing step is performed. The temperature and time for degreasing were increased from room temperature at a rate of 10 ° C./min.
At 0 ° C, 450 ° C, and 650 ° C for 15 minutes and 30 minutes, respectively.
Hold for 30 minutes.

At the time of degreasing, the pores 30 are formed in the thin film 28 formed on the surface of the preformed body 20, so that the surface area of the thin film 28 is widened and decomposition is facilitated.

Then, these preforms 20 are heated at 10 ° C.
/ Min and nitrogen gas pressure 5 bar (5.1 kg / c
m ² ) and sintering in an atmosphere of 1780 ° C. for 2 hours to complete a molded body. This completed molded body has high strength because no closed pores remain therein and the density is high. In addition, it is possible to obtain a molded product larger than a conventional manufacturing method.

Next, a method for producing a molded article according to the present invention will be described using Experimental Examples 1 and 2. Experimental example 2
Is related to the concentration of the film forming agent and the strength of the preform. EXPERIMENTAL EXAMPLE 1 In the method for producing a molded body according to Experimental Example 1, first, 90% by weight of imido-decomposed silicon nitride having an average particle diameter of 0.6 μm, 7% by weight of yttrium oxide having an average particle diameter of 0.5 μm, and 3% by weight of aluminum oxide The raw material 12a consisting of was sufficiently wet-mixed. In addition, as the raw material 12a, a granular material that is generally said to be difficult to form by a conventional method for manufacturing a formed body was used.

A mixture 16 was prepared by adding 17% by weight of water 14 to 100% by weight of the raw material 12a and mixing well. Next, the mixture 16 is transferred to the uniaxial pressing apparatus 10.
Into a cavity 18 of 150MPa (1530k
gf / cm ² ) with a molding pressure of 12 × 12 × 8
Seven 6 mm preformed bodies 20a to 20g were prepared.

Experiments were conducted on seven types of thin film forming agents: vinyl acetate, nitrocellulose, melamine resin, polystyrene resin, acrylic resin, polyamide resin, and cyanoacrylate. Each thin film forming agent was applied by a sprayer 27 for each of the preforms 20a to 20g. The ratio of the solution was 3% by weight of a thin film forming agent, 7% by weight of a developing agent (3% by weight of butyl benzoate and 4% by weight of ethyl cellosolve), and 5% by weight of a wetting agent.
% By weight (3% by weight of ethyl alcohol and 2% by weight of isopropanol) were dissolved in acetone as a solvent.

Forty-eight hours after applying the solvent to the preforms 20a to 20g, cooling air was supplied and dried, and the three-point bending strength was measured (air-dry strength). Furthermore, it was left in an atmosphere of 70 ° C. for 48 hours, and then the three-point bending strength was measured (dry strength).

At this time, the preforms 20a to 20g
There was no breakage or breakage, handling was easy, and there was no trouble in transport.

After the measurement, the preforms 20a to 20g
Was subjected to a degreasing step. Degreasing temperature and time
The temperature is raised from the room temperature atmosphere at a rate of 10 ° C./min.
℃, 450 ℃, 650 ℃ for 15 minutes, 30 minutes, 3
Hold for 0 minutes.

Thereafter, these preforms 20a-20
g at a rate of 10 ° C./min and a nitrogen gas pressure of 5 bar (5.1
(kgf / cm ² ) for 2 hours in an atmosphere of 1780 ° C., and the three-point bending strength after molding was measured (strength after sintering).
Table 1 shows these measurement data.

Further, for comparison, the raw material 12 was
A total of 35% by weight of paraffin wax and paraffin wax was added to 0% by weight and mixed, followed by pressure molding to prepare a preform 20h. The preform 20h was left to dry in an atmosphere at 110 ° C. for 24 hours and dried, and then the three-point bending strength of the preform 20h was measured (see the dry strength in Table 1).

The preformed body 20h is placed in the atmosphere for 200 hours.
The temperature was raised at 5 ° C./min to 250 ° C., 2 ° C./min up to 250 ° C., and 2 ° C./hour above 250 ° C., and finally the temperature was raised to 500 ° C. to perform degreasing. The holding temperature is 150 ° C, 200
℃, 250 ℃, 300 ℃, 350 ℃, 450 ℃, 500
C. for 2 hours, 2 hours, 2 hours, 2 hours, 3 hours, 4 hours, and 10 hours, respectively.

Then, the preform 20h is heated at 10 ° C. /
And the nitrogen gas pressure is 5 bar (5.1 kgf / cm
^{In 2} ), sintering was performed for 2 hours in an atmosphere of 1780 ° C., and the three-point bending strength after molding was measured (strength after sintering). Table 1 shows the measurement data.

From the measurement data, it is found that the preforms 20a to 20g formed by the method according to the present invention have a higher strength after drying and sintering than the preform 20h formed by the method according to the prior art. Increased.

Further, the thickness of the preformed body 20h obtained by the method according to the prior art was at most about 10 mm.
With a to 20 g, it was possible to mold to a thickness of about 100 mm.

[0031]

[Table 1]

EXPERIMENTAL EXAMPLE 2 In the method of manufacturing a molded body according to Experimental Example 2, first, 87% by weight of JIS WC25 powder, 10% by weight of cobalt (Co) powder, 3% by weight of niobium carbide (NbC) powder. Was thoroughly mixed. Raw material 1
For 2b, a granular material which is said to be difficult to mold by a conventional method for producing a molded body was used.

Next, water 14 was added to the raw material 12b and mixed well to prepare a mixture 16. The mixture 16 is filled into the cavity 18 of the uniaxial pressing apparatus 10 and pressurized at a forming pressure of 1000 kgf / cm ² to form a preformed body 20i.
It was created. The size of the preform 20i is a length 8
0 mm, width 12.5 mm, thickness 8 to 10 mm.

Immediately after the preforming, a coating solution was applied to the entire surface of the preformed body 20i. The coating liquid at this time was prepared by dropping nitrocellulose as a thin film forming agent into acetone as a solvent. In this case, a solvent having a nitrocellulose concentration of 0 to 30% by weight was prepared and applied to the preform 20i at each concentration.

Next, the preform 20i coated with the coating solution was dried at 60 ° C. for 48 hours. The dried preformed body 20i was cut into a length of 40 mm, and the three-point bending strength was measured. This result is shown by the solid line 32 in FIG.

In order to prevent the preform 20i from collapsing or breaking during transportation, the preform 20i must have a pressure of 0.7 MPa.
(7.14 kgf / cm ² ) or more was required (see the solid line 34 in FIG. 4). As can be seen from the graph of FIG. 4, sufficient strength was obtained when the concentration of nitrocellulose was about 2% or more, but when the concentration of nitrocellulose exceeded 25%, cracks occurred when the preform 20i was dried. (See the hatched portion 36 in FIG. 4).

Therefore, in Experimental Example 2, after the preforming, the coating liquid in which the thin film forming agent was dissolved at an appropriate concentration was applied to the preformed body 20.
i, the dried preformed body 20i
It was found that the handling and transportation were facilitated without increasing the strength and causing cracks.

[0038]

According to the method for producing a molded article according to the present invention, the following effects and advantages can be obtained.

When the size of the granular material is larger than its density, when the affinity between the granular material and the liquid is low, that is, when the function of the intermolecular force is small, or when the density of the granular material is small. However, even if a material that does not undergo plastic deformation or plastic deformation is difficult such as a cemented carbide or cermet, and a composite powder having a large specific gravity is used as a raw material, uniaxial pressure molding is performed to produce a preformed body Since a material for forming a thin film is used, the preform has excellent shape retention characteristics and can be prevented from being broken or broken even when dried. Therefore, an effect that the handling as the preformed body becomes easy is obtained.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a molding apparatus used in an embodiment of a method for producing a molded article according to the present invention.

FIG. 2 is a perspective view showing a step of applying a thin film forming agent to the surface of a preform.

FIG. 3 is a schematic view illustrating a state of a surface of a preform.

FIG. 4 is a graph showing the relationship between the concentration of a thin film forming agent and the strength of a preform.

[Explanation of symbols]

10. Uniaxial pressure molding device 12, 12a, 12
b ... raw material 14 ... water 16 ... mixture 18 ... cavity 20, 20a-20
i: Preformed body 27: Sprayer 28: Thin film 30: Pores

──────────────────────────────────────────────────続 き Continued on the front page (72) Mitsuo Kuwahara 1-10-1 Shinsayama, Sayama-shi, Saitama Honda Engineering Co., Ltd. (58) Field surveyed (Int. Cl. ⁷ , DB name) B22F 3/24 102

Claims (4)

(57) [Claims] 1. A first step of adding and mixing an excessive amount of liquid to a raw material in the form of powder and granules, and forming the mixture obtained in the first step by uniaxial pressure molding, whereby the excess amount of the liquid is obtained. A second step of obtaining a preform while removing the component; and a third step of forming a thin film on the surface of the preform while the preform obtained in the second step is not dried. And a fourth step of sintering the preformed body on which the thin film obtained in the third step is formed to obtain a formed body. 2. A method according to claim 1, wherein said third step of forming a thin film is a step of applying a material for forming a thin film to said preformed body. How to make the body. 3. The method for manufacturing a molded article according to claim 1, wherein said third step of forming a thin film is a step of spraying a material for forming a thin film onto said preformed body. Method for producing a molded article. 4. The method for producing a molded article according to claim 1, wherein the material for forming the thin film used in the third step is vinyl acetate, nitrocellulose, a melamine resin, or a polystyrene resin. , An acrylic resin, a polyamide resin, and a cyanoacrylate.