JP3210770B2 - Method for producing solid product form - 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 solid product from a fluid such as a slurry or a suspension obtained by kneading a powder of metal, ceramic or the like into a liquid by utilizing centrifugal force. The present invention relates to an improved and a method for producing a sintered body from the obtained green body.

[0002]

2. Description of the Related Art Conventionally, in the powder metallurgy industry or ceramic industry for producing a sintered body of a predetermined shape from powder of a metal, ceramic or a mixture thereof, various powders are preliminarily baked to be formed into a predetermined shape before firing. As a general method for producing a formed body, for example, an organic binder, a plasticizer, a solvent, and the like are added to various powders pulverized by a ball mill, and these are kneaded to prepare a slurry. A doctor blade method or a slurry spray method, in which a strip-shaped green sheet obtained by heating and drying is cut or punched out to obtain a flat shaped product after scraping with a fixed thickness onto a strip-shaped substrate while scraping with a blade A compression molding method and the like are known in which a molding powder obtained by spray-drying with a dryer is pressed into a fixed shape to obtain a formed product. That.

On the other hand, a simpler method is as follows.
There is a slip casting method in which a fine powder is dispersed in an aqueous sodium alginate solution or the like to prepare a slurry (slip), which is poured into a gypsum mold, dried and finished to a predetermined shape. As one type of such a slip casting method, as described in, for example, JP-A-1-179748, slurry is poured into a water-absorbent mold such as gypsum, and the centrifugal force of the mold is rotated. A method is known in which a slurry is formed on the inner surface of a mold to obtain a formed product.

[0004] However, these known methods have a problem that a large amount of equipment, time and heat are required for the drying step, or a problem that it is difficult to rapidly separate liquid components from the slurry. Therefore, the present inventors have previously proposed a method of manufacturing a formed body capable of solving such a problem (Japanese Patent Application No. 3-3).
No. 6340). That is, a fluid such as a slurry or a suspension is placed in a mold having a closed bottom, and the mold is set in a centrifuge so that the bottom faces outward in the radial direction of rotation of the centrifuge. After rotating for a predetermined time, a method was proposed in which the liquid separated at the top of the mold was removed to obtain a formed form.
In this method, the solid content in the fluid is settled in the mold by centrifugal force, and the liquid component is separated above the formed form, so that the solid-liquid separation is quickly performed, and a high particle filling rate can be achieved in a short time. As a result, it is possible to reduce the sintering temperature and increase the heating rate by reducing the binder, so that the production efficiency, dimensional accuracy, and yield of the sintered body can be improved.

[0005]

However, when the present inventors applied the method proposed above to forming fine ceramics having a complicated shape using a split mold as a mold, the following problems were encountered. It has been found. That is,
In the molding of fine ceramics, a slurry containing submicron-order powder is used. Therefore, when a high centrifugal force of about 10 kG or more is applied, the slurry easily leaks from the split surface of the split mold. For this reason, there is a difficulty in using the split mold especially in a complicated shape, and the shape of the generated feature is considerably restricted.

The present invention has been made in view of the above points, and an object of the present invention is to establish a centrifugal molding method which is hardly restricted by a shape by taking a means capable of manufacturing a product having a complicated shape by a centrifugal molding method. It is to plan.

[0007]

In order to achieve the above object, the present invention provides a method in which a predetermined amount of a fluid obtained by kneading powder into a liquid is filled and a mold having a bottom is fixed inside. The frame accommodated in the mold is set in the centrifuge such that the bottom of the mold faces outward in the radial direction of rotation of the centrifuge, and the mold is rotated by the centrifuge for a predetermined time. In removing and producing a solid product form,
A split mold was used as a mold, and the gap between the mold and the frame was filled with wax or a low melting point alloy to fix the mold.

[0008]

According to the above method, the gap between the split mold and the frame is filled with wax or a low melting point alloy, and the split mold is fixed in the frame. Leakage of the fluid from the dividing surface of the mold can be prevented. At the same time, the solid-liquid separation of the fluid in the mold is quickly performed by the centrifugal force, so that a high yield and in a short time, the reproducibility of the original mold is very good, and a formed form with a high particle filling rate is obtained. can get. In addition, similarly to the above-mentioned method proposed by the present inventors, the fluid can be molded without being affected by the concentration, viscosity, and dispersion state of the fluid, and the binder can be reduced. . As a result, the rate of temperature rise during firing is increased, and the degreasing and firing temperature can be reduced.Therefore, from the shaped body obtained by the method of the present invention, a high production efficiency and a good dimensional stability at a high product production rate are obtained. A sintered body can be manufactured. The method of the present invention is particularly advantageous for producing complex shaped articles.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. (Preparation) A cylindrical split mold 2 having a dividing surface 2a (bottom portion) and a dividing surface 2b is set in a frame 1 including a cylindrical tubular member 1a and a disc-shaped bottom lid 1b. After the molten wax or the low melting point alloy 3 is injected into the gap of the split mold 2, it is allowed to cool to solidify the wax or the low melting point alloy 3 ((a) in FIG. 1).
reference). A predetermined amount of the slurry 4 is filled into the split mold 2 (see FIG. 1).
(B)). The slurry 4 is obtained by adding a dispersant and a solvent (water, organic solvent, etc.) to a powder of metal, ceramic or a mixture thereof, which has been previously ground to a predetermined average particle size by a ball mill, and kneading.

(Molding) Frame 1 prepared in this way
Is contained in a container 10 and set in the centrifuge 5 as shown in FIG. At this time, the frame 1 is set so that the bottom lid 1b side faces outward in the radial direction of rotation of the centrifuge 5. And centrifuge 5
, The high-density solid component in the slurry 4 is gradually settled to the bottom side of the split mold 2 by centrifugal force, and the liquid component 6 is separated to the upper portion thereof. When the operation is stopped, most of the liquid components 6 are separated at the upper part of the split mold 2, and a solid product 7 is obtained below the separated liquid form 6 (see FIG. 1 (c)). At this time, the number of revolutions of the centrifuge 5 is determined by the particle size and density of the powder, the viscosity of the solvent, the processing temperature and the like. For example, a powder slurry having an average particle size of 0.2 to 0.4 μm requires a gravity multiple of about 10 to 20 KG. If the gravity multiple is too small, the upper part of the formed form 7 after molding is completely filled. No, the molding time becomes extremely long. In this case, the particle filling rate of the obtained formed body 7 is about 60 to 65%.

(Liquid removal) Only the upper liquid component 6 is removed from the inside of the split mold 2 in the above-described state to form the formed form 7 alone (see FIG. 1 (d)).

(Removal of Mold) The bottom cover 1b of the frame 1 is removed from the tubular member 1a, the tubular member 1a is heated from the outside, and the split mold 2 is removed (see FIG. 1 (e)). Next, after removing the wax or the low melting point alloy attached to the outer surface of the split mold 2, the split mold 2 is removed.
Is divided into the divided surfaces 2a and 2b to obtain a formed feature 7.

(Drying) Thereafter, the formed product 7 thus obtained is placed in a drying furnace and dried by heating at a low temperature.
The drying time varies depending on the size of the formed product. For example, after drying at 40 ° C. for 6 hours, at 70 ° C. for 6 hours, and further at 100 ° C. for 2 hours, drying can be performed.

(Degreasing, Firing) Finally, the dried green body 7 is fired in a furnace. At this time, in order to remove the binder, dispersant, and the like contained in the formed body 7 in advance, the material is heated at a heating rate of, for example, about 120 ° C./hour to be degreased (calcined). The sintered body is obtained by heating at a heating rate of about ° C / hour.

Therefore, in the above embodiment, in the forming step, the split mold 2 backed up with wax or a low melting point alloy is used.
The solid component in the slurry 4 is settled by the centrifugal force in the split mold 2 without the slurry 4 in the inside leaking from the dividing surface, and the liquid component 6 is separated above the formed form 7, so that the solid component is lost. The solid-liquid separation is quickly performed without substantially generating
80% or higher yield and 60% particle filling rate in a short time
As described above, the generated form 7 having the same shape as the prototype is obtained.

Further, unlike the usual slip casting method, molding can be performed without being affected by the concentration, viscosity and dispersion state of the slurry 4 (or suspension).
Further, it is not necessary to vacuum degas the slurry 4 (or suspension) before molding. The binder may be about 1/3 of the usual slip casting method, and as a result, the degreasing and firing temperature can be lowered, so that the dimensional stability and yield of the sintered body are improved. Further, for example, a small precision product having a thickness of 0.2 mm or less can be formed, and a wide range of applications including a large product can be achieved.

In the above embodiment, the fluid to be molded is a slurry obtained by kneading a powder with a dispersant and a binder, but the present invention is not limited to this embodiment.
It is also possible to set the suspension in which the powder is simply dispersed in the solvent in a centrifuge, and to perform molding by centrifugal force.

(Specific Example) Next, a specific example of the present invention will be described. A slurry having the composition shown in Table 1 below was prepared.

[0019]

[Table 1]

The above slurry has a viscosity of 80 to 2000 mPa · s.
Met. Then, the above-mentioned slurry is sequentially subjected to the preparation, molding, liquid removing, and demolding steps described above, and has a diameter of 10 mm, a height of 50 mm,
A product form weighing about 10 g was obtained. The wax used was paraffin wax, and the operation time of the centrifuge was 40 minutes. The properties of the green body thus obtained are shown in Table 2 below.
It is as follows.

[0021]

[Table 2]

Next, the bulk density and the relative density when the formed body was dried as described above and then fired for 2 hours while changing the firing temperature are shown in Table 3 below.

[0023]

[Table 3]

As shown in Table 3, a high-purity alumina sintered body can be obtained at a very low firing temperature and for a short firing time. Observation by SEM of the high-purity alumina sintered body obtained at a sintering temperature of 1220 ° C. shows that this sintered body has a fine and dense structure with an average particle size of 0.6 to 0.7 μm. No special differences were found. When the dimensional change was examined between the split mold and the sintered body, the dimensional change (shrinkage) rate of the sintered body with respect to the split mold was about 14.5%, and the standard deviation of the dimensional change rate was 0.29%. Was. As described above, since the variation was not more than 3/1000, a highly accurate sintered body was obtained. Therefore, since the sintered body has very good reproducibility of the prototype, it is possible to obtain a formed body and a sintered body having the same shape as the prototype, and the effect of the present invention is clearly shown.

In the present invention, in addition to the high-purity alumina as in the above-described embodiments, a material obtained by adding magnesia, silica, titania, etc. to alumina (ie, forsterite, mullite, cordierite, etc.), beryllia, magnesia porcelain, etc. Of various ceramics, so-called cemented carbide, cermet, ferrite, and other porcelain parts, and other sintered metals. Next, examples of the wax of the present invention include an ester of a fatty acid and a higher monohydric or dihydric alcohol, montan wax, ozokerite, microcrystalline wax, pentratam and the like, in addition to the paraffin wax as in the above specific examples. The low melting point alloy of the present invention has a Bi-Pb-Sn-
Cd-In alloy, Bi-Pb-Sn with a melting point of 58.0 ° C
-In alloy, Bi-Pb-Sn-Cd with a melting point of 70.0 ° C
Alloys and the like.

[0026]

As described above, according to the method of the present invention, a method for producing a formed body from a fluid such as a slurry or a suspension obtained by kneading a powder of a metal, a ceramic or the like into a liquid is provided as follows. The fluid is placed in a split mold backed up with wax or a low melting point alloy, and the split mold is rotated for a predetermined period of time by centrifugal force. The solid component of the body is allowed to settle, and the liquid component is separated at the top of the solid component. An identical shaped product is obtained.

Further, since the firing temperature can be lowered and the heating rate can be increased by reducing the amount of the binder, the formed product thus obtained is dried, degreased and fired to obtain the same shape as the original. , Ie, a sintered body having extremely good dimensional stability, can be manufactured with high manufacturing efficiency and yield.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing each step of a molding method according to an embodiment.

FIG. 2 is a conceptual diagram illustrating an operation state of a centrifuge.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Frame 20 Split type 2a Dividing surface 2b Dividing surface 3 Wax or low melting point alloy 4 Slurry 5 Centrifuge 7 Forming body 8 Motor 9 Swing rotor

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-56-144911 (JP, A) JP-A-62-94303 (JP, A) JP-A-5-65504 (JP, A) JP-A-1- 297209 (JP, A) JP-A-62-148209 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B28B 1/20 B28B 7/00 B28B 17/00

Claims (2)

(57) [Claims] 1. A frame in which a predetermined amount of a fluid obtained by kneading powder into a liquid is filled and a mold having a bottom is fixed and accommodated therein. After setting the mold so that it faces outward and rotating the mold by a centrifuge for a predetermined time, the liquid separated at the top of the mold is removed, and a solid mold is manufactured. A method for producing a solid formed body, wherein a gap between a mold and a frame is filled with wax or a low melting point alloy to fix the mold. 2. A method for producing a sintered body by drying, degreasing and calcining the formed body obtained by the method according to claim 1.