JPH02308823A - Production of short fiber preform for composite material - Google Patents

Abstract

PURPOSE:To readily obtain the title preform free from dispersion of density by pouring a short fiber dispersion into a cylindrical mold in which a porous inner mold having desired shape is provided, pressurizing the short fiber dispersion with a pressurizing body to filter the short fiber dispersion and mold the separated short fiber and drying the resultant wet short fiber molded article. CONSTITUTION:A short fiber dispersion 4 (e.g. obtained by dispersing an alumina based short fiber, etc., into a dispersing medium such as water) is poured into a cylindrical mold 1 in which a porous inner mold 3 (preferably consisting of a porous material having open cells, 0.5-5.0mum porous size and 30-60% pore ratio and having >=75kgf/cm<2> compression strength) is provided and filtered by pressurizing the short fiber dispersion with a pressurizing body 5 from the other end opening and the separated short fiber is molded under pressure while removing liquid in a space part between the pressurizing body 5 and porous inner mold 3 and the resultant wet short fiber molded article is dried to readily provide the aimed preform even in complex shape.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a method for manufacturing a short fiber preform for a composite material, which is impregnated with plastic, metal, etc. and used as a fiber skeleton when manufacturing a fiber-reinforced composite material. It is related to.

[Conventional technology]

Short fibers such as alumina short fibers and silicon carbide whiskers have high strength, so they are aggregated to form a preform, which is then infiltrated or impregnated with metal or plastic. Used for manufacturing reinforced composite materials. Regarding such short fiber preforms, there are methods such as dispersing the short fibers in water or an organic solvent, filtering it, molding it, or pressurizing it to form it into a predetermined shape, and then drying it. , a method has been proposed in which a short fiber dispersion is uniformly filtered under a predetermined pressure to form a predetermined shape. For example, ■
: JP-A-60-161400 discloses that whiskers are dispersed in water or an organic solvent, flowed into a filtration device, gas is injected into the upper closed space of the filtration device, and high-speed filtration is performed under pressure. By drying the wet whisker cake, a composite whisker preform (hereinafter referred to as “
A method of manufacturing a preform (abbreviated as "preform body") is disclosed. In addition, ■: Japanese Patent Application Laid-open No. 59-226319 discloses that a quarter mold is prepared, and a whisker dispersion is filled into the split mold, and the joints of the split molds and the wall surface of the outer mold are removed. A method has also been proposed in which the air and dispersion medium inside are sucked out and molded. Also ■: Japanese Patent Application Publication No. 1983
Publication No. 143533 discloses that a porous female mold with a predetermined shape is placed in a filtration tank, and a whisker dispersion liquid is introduced into the filtration tank to perform a filtration operation. A method is disclosed in which a preform is manufactured by filling the whisker-filled porous female mold with whiskers, then recovering the porous female mold filled with whiskers, and drying the obtained wet whisker molded product.

[Problems to be solved by the invention] However, the above-mentioned JP-A-60-1614
The method described in Publication No. 00 can only produce preforms with extremely simple shapes such as cylinders, so it is difficult to manufacture preforms with complex shapes that are used as skeletons for producing fiber-reinforced composite materials with complex shapes. The problem is that it cannot be handled. Therefore, its uses are limited. Furthermore, in the method (2) described in JP-A-59-226319, when the dispersion medium is sucked, a phenomenon occurs in which the dispersion medium is locally strongly sucked, which causes the obtained preform to have a high density. There is a problem in that variations in density (density unevenness) occur, which can cause cracks or deformation when impregnating metals, plastics, etc. Furthermore, in the method described in JP-A No. 61-143533, molding is performed by flowing the whisker dispersion liquid into the entire filtration tank containing the female mold, so the female mold is not buried in the deposited whiskers. Become. Therefore, in order to recover the female mold filled with whiskers from the deposited whiskers after molding, it is necessary to manually remove the whisker cake around the female mold, making it difficult to efficiently manufacture whisker preforms. Can not. In addition, whiskers deposited on the outer periphery of the female mold,
It is damaged because it is subjected to compressive force during filtration, and therefore it is inconvenient to collect and reuse it.

This invention was made in view of the above circumstances, and provides a method for manufacturing a preform body that can be formed into a complicated shape, does not cause variations in density, and does not require complicated operations for manufacturing. Its purpose is to provide.

(Means for Solving the Problems) In order to achieve the above object, the method for producing a short fiber preform body for a composite agent according to the present invention includes a filter medium provided at one end opening, and a filter medium placed above the filter medium. The short fiber dispersion is poured into a cylindrical mold, which has a porous inner mold of a desired shape, leaving only the outer periphery of the surface and covering the other parts, and pressurized into a plate form from the opening at the other end. A filtration operation is performed by applying pressure with the body, and the liquid is drained in the space between this pressure and the porous internal mold, and the short fibers are press-molded to create a wet short fiber molded body, which is then dried. Take composition.

[Function] That is, in the present invention, short fibers are formed using a cylindrical mold in which a filter material is provided at one end opening, and a porous internal mold of a predetermined shape is provided above the filter material with the outer periphery of the filter surface remaining. Since the dispersion is filtered under pressure, a substantially uniform pressure can be applied to the short fibers deposited on the porous internal mold. That is, since the pressurizing pressure is intensively applied to the central part of the cylindrical mold, the short fibers present in that part have a high density.

On the other hand, since little pressure is applied to the outer peripheral portion of the cylindrical mold, the short fibers present in that portion have a low density. In this invention, in order to improve the drainage of water from the outer periphery of the cylindrical mold, which tends to have a low density, and increase the density, the porous internal mold is used, leaving the outer periphery of the filtration surface of the cylindrical mold. This provides a uniform density throughout the short fiber cake deposited on the porous internal mold.

This is the greatest feature of this invention. Furthermore, by changing the shapes of the porous internal mold and the pressurizing body, the shape of the obtained preform can be freely changed from a complex shape to a simple shape. Therefore, it becomes possible to sufficiently cope with the production of fiber-reinforced composite materials having complicated shapes. In addition, the resulting wet short fiber molded product is formed in a cylindrical mold, and can be demolded simply by taking it out of the cylindrical mold. This eliminates the need for complicated manual work. As a result, the effect of improving the manufacturing efficiency of the preform body can also be obtained.

Next, this invention will be explained in detail.

The short fibers used in this invention include alumina short fibers, silicon carbide short fibers, zirconia short fibers, carbon short fibers, silicon carbide whiskers, silicon nitride whiskers,
Ceramic whiskers include alumina whiskers, potassium titanate whiskers, and graphite whiskers. These short fibers may be used alone or in combination depending on the purpose of the fiber-reinforced composite material. Such short ta fibers preferably have a length of 5 to 5001 Jm, preferably 5 to 300 μm.

Water is basically used as a dispersion medium for dispersing the short fibers. However, if the use of water is not preferred, solvents such as alcohols, hydrocarbons, and halogenated hydrocarbons may be used in place of water. Also,
In some cases, a hydrous alcohol obtained by mixing the above-mentioned alcoholic solvent and water is also used as a dispersion medium.

The method of dispersing the above-mentioned short fibers in a dispersion medium uses 4 to 20 times the amount of the short fibers, preferably about 10 times the amount (by weight,
This is carried out by using a dispersion medium of the same level (hereinafter the same), adding short fibers to the dispersion medium, and using mechanical stirring, ultrasonic dispersion, or a combination of these. In this case, the dispersed state of the short fibers is preferably such that the individual short fibers are completely loosened and uniformly dispersed in the dispersion medium. Depending on the type of short fibers, it may be difficult to disperse them, so it is preferable to adjust the pH of the dispersion medium or use a dispersant such as ammonium polyacrylate to improve dispersibility. The short fiber dispersion prepared in this manner is filtered and molded using, for example, a device such as that illustrated in Fig. 1.That is, the above-mentioned device includes a circular cylindrical mold 1 and a A filter 2 made of metal or ceramic filter media is provided at the opening on the bottom side, a porous internal mold 3 having a predetermined shape is installed near the opening of the cylindrical mold 1, and a filter 2 is provided at the bottom opening of the cylindrical mold 1. The porous inner mold 3 is equipped with a plunger 5 for pressurizing the short fiber dispersion 4.
is provided with the outer periphery of the filtration surface remaining, rather than covering the entire surface of the filtration surface of the filter 2, and in order to leave the outer periphery, the outer periphery of the porous interior 3 and the cylindrical mold A gap 3a is formed between the inner circumferential surface of No. 1 and the inner circumferential surface of No. 1. The gap size of the gap 3a is usually set within a range of 20 to 100 μm. That is, when the size of the gap 3a is below the above range, removal of the dispersion medium mainly occurs at the center of the porous internal mold, and therefore the removal rate of the dispersion medium becomes different between the center and the outer circumferential side. There is a tendency for variation in density (density unevenness) to occur in the short fiber molded product obtained. On the other hand, if the above range is exceeded, the removal of the dispersion medium tends to occur mainly from the outer periphery, so the opposite phenomenon to that described above occurs, and the short fibers in the short fiber dispersion 4 Since the short fibers pass through the filtration surface together with the dispersion medium from the outer circumference and are removed outside the mold, the utilization efficiency of the short fibers deteriorates.

Therefore, it is preferable that the dimension of the gap 3a be set within the range of 20 to 100 μW.

Reference numeral 6 designates a hollow base portion attached to the lower side of the opening at one end of the cylindrical mold 1, and reference numeral 7 represents a vacuum suction port provided in the base portion 6.

The porous internal mold 3 is made of a porous material having communicating pores, and is made of, for example, gypsum, a porous material made of polyvinyl alcohol foam hardened with phenol resin, sintered metal, ceramic, etc. There is. The one in FIG. 1 has a shape made by bending a thin-walled material and is, so to speak, a hollow body, but it may also be a solid body. In particular, the pore diameter of the communicating pores is 0.5 to 5.0 μm, and the porosity is 30 to 60 μm.
% is preferable. If the pore size and porosity are below the above range, it will be difficult to remove the dispersion medium from the short fiber dispersion 4 by filtration, and even if it can be removed, the time required for removal will be long, resulting in poor work efficiency. A trend can be seen. In this case, if you try to increase the pressure of the plunger 5 to improve the efficiency of dispersion medium removal, the pressure of the plunger 5 will deform or damage the porous internal mold 3. It is not possible to increase the pressing force by much. Conversely, if the pore size and porosity exceed the above range,
If the filtration speed of the dispersion medium becomes too high, there will be a time lag in the removal of the dispersion medium between various parts (in the vertical direction or different wall thicknesses) of the produced wet short fiber molded body. As a result, for example, the dispersion medium is removed quickly from the lower side or the thinner portion, and is removed later from the upper side or the thicker portion. This causes problems such as variations in density and cracks in the wet short fiber molded product. Furthermore, short fibers enter into each of the communicating pores of the porous internal mold 3 and block the pores, leading to a decrease in the removal efficiency of the dispersion medium, and ultimately leading to clogging and rendering the mold unusable. Become.

When producing a wet short fiber molded body using the above-mentioned apparatus, the short fiber dispersion liquid 4 is flowed into the cylindrical mold with the plunger 5 raised. From this state, the plunger 5 is sucked under reduced pressure from the deliquid lower part of the base 6.
lower. As a result, in the space between the plunger 5 and the porous internal mold 3, the short fiber dispersion 4 is drained and pressure molded to form a wet short fiber molded body. During this filtration operation, the dispersion medium in the short fiber dispersion 4 is filtered through the pores of the porous internal mold 3 to the lower side thereof, and only the short fibers are deposited on the upper side of the porous internal mold. In this case, there is a gap 3a on the outer circumferential side of the filter lotus surface, which cooperates with the filtration surface below to drain water faster than on the center side of the filtration surface, while maintaining that speed appropriately. . As a result, the density difference between the center side, to which the pressure of the plunger 5 is concentrated, and the outer circumferential side, to which less pressure is applied, is eliminated, and the entire density of the wet short fiber molded body becomes uniform. If the pressing force of the plunger 5 exceeds the strength of the porous internal mold 3, the porous internal mold 3 will be deformed or damaged. Therefore, the porous internal mold 3 needs to have a compressive strength sufficient to withstand the pressing force of the plunger 5. Therefore, in this invention, the compressive strength of the porous internal mold 3 is set to 75 kg-f/
It is set to ctR. Then, the obtained wet short fiber molded product is removed from the mold by lifting the cylindrical mold 1 relatively upward from the base portion 6, and then dried. As a result, the desired preform body is obtained. The produced wet short fibers may be dried separately from the porous internal mold 3, or may be dried in an integrated state. The preform body thus obtained has the same shape as the space between the plunger 5 and the porous internal mold 3, as shown in FIG. In this case, it is molded to have the same shape as the piston head of a car. Therefore, by infiltrating this preform body 8 with a matrix material such as metal 1 alloy, a piston head can be obtained. The fiber-reinforced composite material thus obtained is free from cracks and cracks, and is in good condition despite its fairly complex shape.

Note that the cylindrical mold 1 is not limited to a cylinder. 3 to 8 square tubes, etc.
A polygonal cylindrical shape is also acceptable.

Next, examples will be described.

[Example 1] (1) Preparation of short fiber dispersion liquid Alumina short fibers 80 with an average diameter of 3 μm and an average length of 500 μm
parts by weight and 800 parts by weight of water were stirred and dispersed for 2.5 minutes in a juicer mixer to prepare a uniform dispersion of short alumina fibers.

(2) Production of porous internal mold 73 parts by weight of water was added to 100 parts by weight of gypsum (grade A) manufactured by Noritake Co., Ltd., and the mixture was stirred and poured according to a conventional method.

After curing and drying, a porous internal mold 3 having the same shape as that shown by reference numeral 3 in FIG. 1 was prepared. The pore diameter of this thing is 4.8μ
m, porosity is 60%, and compressive strength is 78 kg-f/
It was c+fi.

(3) Manufacture of preform body The porous internal mold 3 described above was installed in a cylindrical mold 1 with a diameter of 80 m as shown in FIG. is the same as that in Fig. 1. However, the filter 2 is made of ceramic, and the same applies to the following examples). Next, the short fiber dispersion liquid 4 was added and vacuum suctioned from the liquid removal lower part of the base part 6. At this time, plunger 5
was pressed and pressurized. As a result, water in the short fiber dispersion liquid 4 passes through the porous internal mold 3 and is discharged from the pores of the filter 2 to the outside of the apparatus. Then, the pressurized filtration operation was continued so that the density of the wet whisker molded body formed in the space between the plunger 5 and the porous internal mold 3 was 0.50 g/c+fl, and the molding was completed. Thereafter, the cylindrical mold 1 was removed from the base 6, and the wet whisker molded body was extruded and demolded using the plunger 5, and then dried to produce the desired preform.

[Examples 2 to 11] (1) Preparation of short fiber dispersion 70 parts by weight of β-type silicon carbide whiskers with an average diameter of 0.5 μm and an average length of 25 μm and 700 parts by weight of water were mixed using ultrasonic waves and a blade stirrer. A dispersion of silicon carbide short fibers was prepared by stirring and dispersing for 1 minute.

(2) Production of porous internal mold As the porous internal mold, a continuous pore porous material (manufactured by Kanebo Co., Ltd., Microlite) made of polyvinyl alcohol and phenol resin (pore diameter 0.2 to 10 μm, porosity 20 to 80
%, compressive strength of 60 to 144 kg·f/cyit), and was machined into the shape shown in FIG. 1.

(3) Production of preform body The porous internal mold described above was assembled into a cylindrical mold in the same manner as in Example 1, and the short fiber dispersion liquid was poured into it, so that the density of the wet whisker molded body was 0.64 g / The pressure filtration operation was continued until ci. A preform body was manufactured in the same manner as in Example 1 except for the above.

In the above examples, the gap between the porous internal mold and the cylindrical mold, clogging of the pores of the porous internal mold, deformation or buckling of the porous internal mold, time required for filtration molding, and formed wet whisker molded product The difference in density inside is shown in the table below.

(Margins below) As is clear from the table above, the obtained preform has no cracks or cracks, has a very small density difference and is uniform, and also has whiskers in the pores of the porous internal mold during manufacturing. It can be seen that there is almost no clogging of the mold or deformation of the porous internal mold, and it is possible to achieve molding in a short time.

[Example 12] (1) Preparation of whisker-/alumina short fiber dispersion β-type silicon carbide whiskers with an average diameter of 0.5 μm and an average length of 25 μm and alumina short fibers with an average diameter of 3 μm and an average length of 500 μm were prepared. , a mixture was prepared so that the ratio by volume was 1/1. Next, add 70 parts by weight of this to 84 parts by weight of water.
0 parts by weight of polyacrylic acid ammonium salt (manufactured by Sannobuco ■, Nopcosanto RFA) as a dispersant.
) was blended at a weight percentage of 0.5% based on the solid content. Next, this was stirred for 1 minute using an ultrasonic wave and a blade type stirrer to uniformly disperse the mixture, thereby producing a whisker/alumina short fiber dispersion.

(2) Production of porous internal mold Sintered stainless steel powder (SUS304), pore size 3μ
m, porosity 35%, compressive strength 400kg・f/cIll
A porous internal mold 3 (having the same shape as that shown in FIG. 1) was manufactured.

(3) Manufacture of preform body The above-mentioned internal mold was assembled into a cylindrical mold in the same manner as in Example 1 so that the gap between the two was 50 μm. From this point on, the process was carried out in the same manner as in Example 1, so that the density of the wet short fiber molded body was set to Q,
N-pressure filtration was performed until the concentration reached 48 g/C+fl to produce a preform.

Appearance inspection of the obtained preform body.

As a result of destructive testing using soft X-rays and X-ray CT, it was found that, as in the case of whiskers alone, no cracks or cracks were observed inside or outside the preform, and the density difference was 1.1%, which was homogeneous. .

〔Effect of the invention〕

As described above, according to the present invention, it is possible to easily manufacture a preform body with a complicated shape, which was difficult to manufacture using conventional techniques, without causing variations in density, and without any complicated process. No work required. Therefore, it becomes possible to efficiently manufacture short fiber preform bodies having complicated shapes at low cost.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a molding apparatus used in the present invention, and FIG. 2 is a sectional view of a preform obtained by the apparatus. 1... Cylindrical mold 2... Filter 3... Porous internal mold 3a... Gap 4... Short fiber dispersion liquid
5... Plunger patent applicant Kanebo Co., Ltd. Kobe Steel, Ltd.

Claims (5)

[Claims] (1) A cylindrical molding in which a filtration material is provided at one end opening, and a porous internal mold of a desired shape is provided above the filtration material, leaving the outer periphery of the filtration surface and covering the rest. The short fiber dispersion liquid is introduced into the mold and filtered by applying pressure with a pressure body from the other end opening, and the short fibers are removed while being drained in the space between the pressure body and the porous internal mold. A method for producing a short fiber preform for composite materials, which comprises pressurizing and forming a wet short fiber molded product, and drying the same. (2) The short fiber preform body for composite materials according to claim (1), wherein the porous internal mold is formed of a continuous pore porous material having a pore diameter of 0.5 to 5.0 μm and a porosity of 30 to 60%. Manufacturing method. (3) The compressive strength of the porous internal mold is 75 kg・f/cm^
The method for producing a short fiber preform body for composite materials according to claim (1), wherein the number of fibers is set to 2 or more. (4) The short fibers are from the group consisting of alumina short fibers, silicon carbide short fibers, zirconia short fibers, carbon short fibers, silicon carbide whiskers, silicon nitride whiskers, alumina whiskers, potassium titanate whiskers, and graphite whiskers. The method for producing a short fiber preform for a composite material according to claim 1, wherein the at least one selected short fiber is a short fiber preform. (5) The method for producing a short fiber preform for a composite material according to claim (1), wherein the width of the outer periphery of the filtration surface covered with the porous internal mold is set to 20 to 100 μm.