JP5544930B2 - Granulated powder, porous sintered body and metal filter - Google Patents

Description

  The present invention relates to a granulated powder, a sintered body, and a metal filter.

  As a method for molding metal powder, a compression molding method is known in which a mixture of metal powder and an organic binder is filled in a predetermined mold and compressed to obtain a molded body having a predetermined shape. The obtained molded body becomes a sintered metal body through a degreasing process for removing the organic binder and a firing process for sintering the metal powder. Such a technique is an example of a powder metallurgy technique, and since it can manufacture a large amount of a metal sintered body having a complicated shape depending on the shape of a mold, it has been widely used in many industrial fields in recent years.

  For example, a metal filter made of a sintered metal is used in many fields. Specifically, by passing a fluid such as liquid or gas through a porous metal sintered body, solids contained in the fluid are filtered out, or substances are adsorbed by chemical interaction. It is used for the technology of separating them. In addition, metal filters are useful for medical equipment filters, analytical equipment filters, and the like because they are excellent in corrosion resistance, heat resistance, and the like.

Patent Document 1 discloses a porous plate having a porosity of 35 to 55% obtained by sintering titanium powder produced by a gas atomizing method. This porous plate is manufactured by filling a spherical spherical particle of titanium having an average particle size of 10 to 150 μm in a sintering container without applying pressure, and sintering this.
However, since such a porous plate is molded without pressure, there is a problem that the bonding between the titanium powder particles tends to be insufficient, and the mechanical properties are low. Moreover, when shape | molding without a pressure, there exists a restriction | limiting in the shape which can be shape | molded.

JP 2002-66229 A

  An object of the present invention is to provide a granulated powder capable of producing a porous sintered body having both sufficient porosity and high mechanical properties, and a sintered body and a metal filter produced using the granulated powder. Is to provide.

The above object is achieved by the present invention described below.
The granulated powder of the present invention is a granulated powder formed by binding a plurality of metal particles with an organic binder,
The particles of the granulated powder have an A / B average of 0.1 or more and 0.4 or less when the minor axis is A and the major axis is B, and the cumulative particle size distribution based on mass The particle size when accumulated at 50% is 30 μm or more and 150 μm or less.
Thereby, the granulated powder which can manufacture the porous sintered compact which has sufficient porosity and high mechanical characteristics is obtained.

In the granulated powder of the present invention, the plurality of metal particles preferably have an a / b average of 0.5 or more and 1 or less, where a is the short diameter and b is the long diameter. .
Thereby, the fluidity | liquidity of metal powder improves especially, and when granulating metal powder, the uniformity of each particle | grains of granulated powder improves.
In the granulated powder of the present invention, the average particle diameter of the plurality of metal particles is preferably 1 μm or more and 30 μm or less.
Thereby, when the sintered body is finally obtained, the crystal structure formed therein can be made sufficiently small. As a result, the mechanical properties of the sintered body can be enhanced.

In the granulated powder of the present invention, the average particle size of the granulated powder is preferably 3 to 100 times the average particle size of the plurality of metal particles.
As a result, the granulated powder contains an optimum number of metal powder particles, so that the granulated powder is sufficiently imparted with a disintegrating property that disintegrates at the time of molding, and a certain degree of strength. As a result, when compression molding is performed, voids that cannot be filled between particles can be reliably left, and a porous sintered body can be reliably obtained.

In the granulated powder of the present invention, the granulated powder is preferably formed by pulverizing a granulated powder having a larger particle size with a roll crusher.
Thereby, the granulated powder can be efficiently and uniformly crushed and deformed.
In the granulated powder of the present invention, the metal particles are stainless steel particles,
The fluidity measured according to the fluidity test method for metal powder defined in JIS Z 2502 of the granulated powder is preferably 30 [seconds / 50 g] or more.
Thereby, a porous sintered body having both sufficient porosity and high mechanical properties can be obtained.

The sintered body of the present invention is manufactured using the granulated powder of the present invention, and has a relative density of 60% or more and 92% or less.
Thereby, a porous sintered body having a good balance between porosity and mechanical properties can be obtained.
The metal filter of the present invention is characterized by comprising the sintered body of the present invention.
Thereby, even in an environment where the differential pressure before and after the filter is large, a metal filter that can be used for a long time can be obtained.

It is a schematic diagram which shows the structure of the rolling granulation apparatus used in the manufacturing method of the granulated powder of this invention.

Hereinafter, the granulated powder, the sintered body, and the metal filter of the present invention will be described in detail based on preferred embodiments based on the accompanying drawings.
Conventionally, when manufacturing a metal filter from metal powder, it was manufactured by filling a metal powder into a container and sintering it in a non-pressurized state.
However, this method has a problem that the bonding between the particles of the metal powder tends to be insufficient, and the obtained metal filter has low mechanical properties.

In addition, when the container is filled with metal powder and sintered without pressure, the shape of the container is naturally limited. That is, since the container to be used needs to be a container having an open upper surface, a metal filter manufactured using this container inevitably has a horizontal upper surface. Therefore, there is a problem that the degree of freedom of the shape of the metal filter is impaired.
In addition, when no pressure is applied, the filling property of the metal powder tends to be non-uniform depending on the shape of the container. For this reason, the distribution of the voids and mechanical properties of the metal filter may be non-uniform.

Furthermore, since the whole container is baked, adhesion between the container and the metal filter is inevitable. As a result, the metal filter may be broken or cracked during release.
In view of such problems, the present inventor has intensively studied a granulated powder capable of producing a high-quality porous sintered body even when molded by a compression molding method. And when granulating metal powder, it discovered that the said problem could be eliminated by optimizing the shape of the granulated powder, and came to complete this invention.

The granulated powder of the present invention is a particulate material composed of a composition containing a metal powder and an organic binder, and is formed by binding a plurality of metal particles in the metal powder with an organic binder.
The granulated powder has an A / B average of 0.1 or more and 0.4 or less, where A is the minor axis of each particle and B is the major axis. The particle size when accumulated at 50% is 30 μm or more and 150 μm or less.

  Such a granulated powder can be formed into a porous molded body that includes continuous air holes and is compressed in a state where the collapse of the granulated powder has progressed to some extent. This is because the aspect ratio of the shape of the granulated powder represented by A / B is within the above-mentioned range and has a relatively long and different shape, so that even if the granulated powder is slightly collapsed, it is compression molded. It is considered that voids that cannot be filled remain between the particles, and densification more than necessary is suppressed.

At the same time, when the 50% cumulative particle size in the mass-based cumulative particle size distribution is within the above range, voids remain between the particles even after compression molding as described above.
Therefore, by using the granulated powder of the present invention, a sufficient porosity can be ensured even when molded by various molding methods such as compression molding. As a result, it is possible to obtain a porous sintered body having a complicated shape that cannot be manufactured by a conventional method and having both a sufficient porosity and high mechanical properties.
The aspect ratio A / B may be within the above range, but is preferably 0.15 or more and 0.35 or less.

On the other hand, the particle size at 50% accumulation in the mass-based cumulative particle size distribution may be within the above range, but is preferably 35 μm or more and 140 μm or less, and more preferably 40 μm or more and 130 μm or less.
Such a porous sintered body can be suitably used, for example, as a metal filter having excellent characteristics such as corrosion resistance and heat resistance.

In addition, when the metal powder is molded without pressure as in the prior art, the filling property of the powder tends to be non-uniform, whereas the compacting property becomes uniform by compressing under pressure. As a result, a sintered body that is uniform in the distribution of voids and mechanical properties can be obtained.
In addition, when A / B is below the lower limit value, each particle of the granulated powder becomes too long and has a significant anisotropy in the shape of the particle, so that the fluidity of the granulated powder is significantly reduced, Fillability becomes non-uniform due to the orientation of the particles. As a result, the distribution of voids and mechanical properties becomes non-uniform. On the other hand, when A / B exceeds the upper limit, since the granulated powder has a shape close to a sphere, the fluidity of the granulated powder becomes too high, and the voids generated between the particles become extremely small. As a result, the porosity of the obtained porous sintered body is significantly reduced.

  Further, when the particle size at the time of 50% accumulation (hereinafter also referred to as “average particle size”) in the cumulative particle size distribution on the mass basis is below the lower limit, each particle of the granulated powder becomes too small. As a result, voids between the particles are filled during compression molding. On the other hand, when the average particle size exceeds the upper limit, each particle of the granulated powder becomes too large, and the mechanical strength of the porous sintered body is significantly reduced.

  Further, the average particle size of the granulated powder is preferably 3 to 100 times the average particle size of the metal powder, more preferably 5 to 80 times, and more preferably 10 to 70 times. More preferably. As a result, the granulated powder contains an optimal number of metal powder particles, so that the granulated powder is sufficiently imparted with a disintegrating property that collapses at the time of molding, and a certain degree of strength. As a result, even if compression molding is performed, voids that cannot be filled between the particles can be reliably left.

The molded body formed using the granulated powder of the present invention is in a state where the granulated powder has collapsed to some extent by molding and has an appropriate binding force. It has sex. For this reason, it is not necessary to fire the entire container, and therefore there is no fear of adhesion between the sintered body and the container, so that the manufacturing yield can be significantly improved.
In addition, since it is not necessary to prepare a container for each molded body, this contributes to a reduction in the manufacturing cost of the porous sintered body.

The aspect ratio A / B of the granulated powder is measured by, for example, a method of observing the granulated powder with various microscopes such as an electron microscope and an optical microscope and estimating the granulated powder artificially or through image processing. be able to.
Since such a granulated powder includes particles having irregular shapes as described above, it has a characteristic that the fluidity is slightly low.

  Specifically, when the metal powder is a stainless steel powder, the fluidity of the granulated powder is preferably 30 [second / 50 g] or more and 70 [second / 50 g] or less, and 33 [second / 50 g] or more. More preferably, it is 60 [seconds / 50 g] or less. By using the granulated powder having such fluidity, a porous sintered body having both sufficient porosity and high mechanical properties can be obtained with certainty.

The fluidity of the granulated powder is defined as the time when 50 g of the metal powder flows out through the funnel orifice, and can be measured by the metal powder fluidity test method specified in JIS Z 2502.
The apparent density [g / cm ³ ] of the granulated powder of the present invention is preferably 10% to 35%, more preferably 15% to 30% of the true density [g / cm ³ ] of the metal powder. It is more preferable that By using such granulated powder, a porous sintered body having both sufficient porosity and high mechanical properties can be obtained with certainty.

The apparent density of the granulated powder is a ratio between the mass and the volume of the granulated powder in a natural filling state, and can be measured by the apparent density test method for metal powder defined in JIS Z 2504. On the other hand, the true density of the metal powder is the true density of the metal material constituting the metal powder.
As described above, the granulated powder as described above contains a metal powder and an organic binder. Hereinafter, the metal powder and the organic binder will be described.

(Metal powder)
Examples of the material constituting the metal powder include Fe, Ni, Co, Cr, Mn, Zn, Pt, Au, Ag, Cu, Pd, Al, W, Ti, Ta, V, Mo, Nb, Zr, and Pr. , Nd, Sm, or an alloy (for example, stainless steel, Fe—Ni alloy) or an intermetallic compound containing one or more of these metals.

Among these, as the metal powder, titanium powder composed of a simple Ti or Ti-based alloy is particularly preferably used. A metal filter composed of a sintered body of titanium powder is excellent in corrosion resistance and heat resistance, and therefore does not need to be limited in the type of fluid to be passed, temperature, etc., and is particularly useful.
Examples of the Ti-based alloy include alloys containing metal elements such as Al, V, Nb, Zr, Ta, and Mo in addition to Ti. Specifically, Ti-6Al-4V, Ti-6Al-7Nb, etc. are mentioned.

Further, the Ti-based alloy may contain non-metallic elements such as boron (B), carbon (C), nitrogen (N), oxygen (O), silicon (Si) in addition to these metal elements. .
For such metal powder, water atomization method, gas atomization method, atomization method such as high-speed rotating water atomization method, reduction method, carbonyl method, pulverization method, etc. can be used. In particular, those produced by the atomizing method are preferably used. According to the atomizing method, a fine metal powder having a narrow particle size distribution (uniform particle size) can be obtained efficiently. Therefore, a porous sintered body having a uniform distribution of voids and mechanical properties can be reliably produced.

Moreover, according to the atomization method, a metal powder having a more spherical shape can be obtained. Thereby, the fluidity | liquidity of granulated powder improves and even when it shape | molds in a complicated shape, the porous sintered compact with uniform distribution of a space | gap and a mechanical characteristic is obtained.
Specifically, in the metal powder (a plurality of metal particles), when the minor axis of each particle is a and the major axis is b, the average of a / b is preferably about 0.5 or more and 1 or less. More preferably, it is about 7 or more and 1 or less. Thereby, the fluidity | liquidity of metal powder improves especially, and when granulating metal powder, the uniformity of each particle | grains of granulated powder improves.

The average particle size of the metal powder (particle size at 50% accumulation in the mass-based cumulative particle size distribution) is preferably 1 μm or more and 30 μm or less, more preferably 3 μm or more and 20 μm or less, and even more preferably 3 μm or more. 10 μm or less. When the metal powder having such a particle size finally obtains a porous sintered body, the crystal structure formed therein can be made sufficiently small. As a result, the mechanical properties of the porous sintered body can be enhanced.
The particle size of the metal powder and the particle size of the granulated powder are various particle sizes such as dynamic light scattering method, laser diffraction method, centrifugal sedimentation method, FFF (Field Fow Fractionation) method, electrical detector method, etc. It can be measured by a measuring method.

(Organic binder)
The organic binder binds the particles in the metal powder.
Examples of the organic binder include polyolefins such as polyethylene, polypropylene, and ethylene-vinyl acetate copolymer, acrylic resins such as polymethyl methacrylate and polybutyl methacrylate, styrene resins such as polystyrene, polyvinyl chloride, and polyvinylidene chloride. Various resins such as polyesters such as polyamide, polyethylene terephthalate, polybutylene terephthalate, polyether, polyvinyl alcohol, polyvinyl pyrrolidone or copolymers thereof, various waxes, paraffin, higher fatty acids (eg stearic acid), higher alcohols, higher alcohols Examples include various organic binders such as fatty acid esters and higher fatty acid amides, and one or more of these can be used in combination.

Among these, as the organic binder, those containing polyolefin as a main component are preferable. Polyolefin has a relatively high decomposability with a reducing gas. For this reason, when polyolefin is used as the main component of the organic binder, the molded product can be reliably degreased in a shorter time.
Moreover, it is preferable that the content rate of an organic binder is about 2 mass% or more and 20 mass% or less of the whole composition, and it is more preferable that it is about 5 mass% or more and 10 mass% or less. When the content of the organic binder is within the above range, a certain degree of disintegration is imparted to the granulated powder, and shape retention is imparted to the molded body. As a result, a porous sintered body having a sufficient porosity and high dimensional accuracy can be obtained without firing the entire container.

(Production method of granulated powder)
Next, a method for producing the granulated powder of the present invention will be described.
Hereinafter, prior to the description of the method for producing the granulated powder, the granulator used in this production method will be described.
FIG. 1 is a schematic diagram showing the configuration of a rolling granulator used in the method for producing granulated powder of the present invention. In addition, Fig.1 (a) is a longitudinal cross-sectional view of a rolling granulation apparatus, FIG.1 (b) is the sectional view on the AA line of Fig.1 (a).

The rolling granulator 1 includes a processing container 10 for performing granulation, a blade 20 and a cross screw 30 disposed in the processing container 10, and a spray nozzle 40.
As shown in FIG. 1A, the processing container 10 has a bottom part 11 and a side wall part 12 erected from the bottom part 11, and the side wall part 12 has an inner diameter and an outer diameter from the upper side to the lower side. It has a gradually increasing weight shape (for example, a truncated cone shape). Since the processing container 10 (side wall portion 12) has such a shape, the powder blown up from the outer peripheral side of the processing container 10 by the blade 20 in the processing container 10 falls to the center side of the processing container 10. Such airflow can be formed. As a result, the powder can be processed without unevenness, and a granulated powder having a sharp particle size distribution can be efficiently produced.

Further, the processing container 10 has an opening on the upper side, and a lid portion 13 is mounted so as to close the opening.
The blade 20 includes a base 23 and three rotary blades 21, 21, 21 having one end fixed to the base 23 and provided radially at substantially equal intervals.
A through hole 110 is provided at the center of the bottom 11 of the processing container 10, and the rotation drive shaft 22 is inserted through the through hole 110.

The upper end of the rotational drive shaft 22 is fixed to the base 23, and the lower end is connected to a rotational drive source (not shown). Then, the rotational drive shaft 22 is rotationally driven in the forward and reverse directions by the rotational drive source, whereby the blade 20 rotates.
Further, the rotary blades 21, 21, and 21 are respectively fixed to be inclined with respect to the rotary drive shaft 22 so that the front side in the rotation direction of the blade 20 is a downward slope. Thereby, with rotation of the blade 20, the powder can be effectively jumped up and the airflow as described above can be formed.

A through hole 130 is provided in the side wall portion 12 of the processing container 10, and the rotation drive shaft 31 is inserted into the through hole 130.
One end of the rotation drive shaft 31 is fixed to the cross screw 30 and the other end is connected to a rotation drive source (not shown). Then, the rotational screw 31 is rotated in the forward and reverse directions by the rotational driving source, whereby the cross screw 30 is rotated.

The spray nozzle 40 is provided through the lid portion 13 attached to the processing container 10, and the supply port is located in the processing container 10. Thereby, it is comprised so that a solvent can be sprayed in the processing container 10. FIG. By spraying the solvent from the spray nozzle 40, a downward air flow is generated in the vicinity of the spray nozzle 40.
Here, the operation of the rolling granulator 1 as described above, that is, a method for producing a granulated powder using the rolling granulator 1 will be described. The granulated powder production method using the rolling granulator 1 is an example of the granulated powder production method of the present invention, and it goes without saying that the granulated powder production method of the present invention is not limited thereto. .

Next, a method for producing granulated powder using the rolling granulator 1 will be described.
The method for producing granulated powder is to granulate metal powder by rolling and / or flowing metal powder while supplying an organic binder solution (binder solution).
First, metal powder is put into the processing container 10 of the rolling granulation apparatus 1 as described above. Then, the metal powder is rolled and / or fluidized by stirring with the blade 20.

  At the same time, the binder solution is sprayed from the spray nozzle 40. The binder solution in the mist state wets the metal powder and binds the particles of the metal powder. As a result, the metal powder is granulated, and the granulated powder 80 is obtained. The granulated powder 80 gradually moves (rolls) to the outer peripheral side (side wall portion 12 side) of the processing container 10 as the blade 20 rotates, and is spun up by the rotary blade 21. The granulated powder 80 that has been bounced down descends on the center side of the processing vessel 10 and is rolled by the blade 20 again. When such a series of processes is repeated, shaping is performed and a granulated powder 80 close to a true sphere is formed. As a result, a dense granulated powder having a short interparticle distance can be obtained.

Further, in the process of granulation, when the particles being granulated come into contact with the rotating cross screw 30, particles having a large particle diameter (particles having a high degree of granulation) are crushed. Thereby, excessive granulation is suppressed and the particle size distribution of the granulated powder is controlled to a narrow width.
The binder solution may be supplied by any method, for example, by putting it in the processing container 10 in advance, but it is preferable to spray from above as shown in FIG. Thereby, since the binder solution is uniformly and sufficiently supplied to the granulated powder 80 bounced up by the blade 20, the shape and size of the granulated powder 80 can be made uniform. In particular, when the granulated powder 80 floats in the air, the entire surface of the particles of the granulated powder 80 is wetted evenly by contacting with the binder solution, so that the homogenization becomes more remarkable. As a result, a granulated powder 80 having a uniform particle size distribution is obtained.

Examples of the solvent used for the binder solution include inorganic solvents such as water, carbon disulfide, and carbon tetrachloride, and organic solvents such as methanol, ethanol, n-propanol, and isopropanol.
Here, the number of rotations of the blade 20 per unit time (hereinafter simply referred to as “the number of rotations”) is not particularly limited as long as the rolling of the granulated powder 80 can be ensured to the minimum, but for example, 50 rpm or more and 500 rpm or less. Is preferably about 100 rpm or more and 300 rpm or less. When the rotational speed of the blade 20 is within the above range, the granulated powder 80 can be efficiently rolled and granulated efficiently. Moreover, since a moderate compaction state is obtained, it can be set as the granulated powder with a higher apparent density. As a result, it is possible to obtain a granulated powder 80 that is denser and has a particularly narrow particle size distribution width.

  On the other hand, when the rotation speed of the blade 20 is less than the lower limit, rolling and jumping up of the granulated powder 80 becomes insufficient, which may cause uneven granulation. Moreover, there is a possibility that the compaction will be insufficient, resulting in a granulated powder 80 with a low apparent density, and a granulated powder 80 that is not spherical and has an irregular shape and poor fluidity. On the other hand, when the rotation speed of the blade 20 exceeds the upper limit, the granulated particles are crushed by the blade 20 and there is a possibility that the amount of powder that does not progress is increased.

Moreover, the rotation speed per unit time of the cross screw 30 at the time of granulation is not specifically limited, For example, it is preferable that it is about 50 rpm or more and 3500 rpm or less, and it is more preferable that it is about 100 rpm or more and 3000 rpm or less. Thereby, particle | grains with a big particle diameter can be crushed and particle diameter can be equalize | homogenized, preventing excessive crushing.
The supply rate of the binder solution is not particularly limited, but is preferably, for example, from 20 g / min to 1000 g / min, more preferably from 30 g / min to 800 g / min, and more preferably from 50 g / min to 600 g. More preferably, it is less than / min. When the supply rate of the binder solution is a value within the above range, the particle size distribution of the obtained granulated powder 80 is made sharper while the bonding (granulation) of the metal powder by the binder solution proceeds without unevenness. Can do.

On the other hand, when the supply rate of the binder solution is less than the lower limit value, there is a possibility of causing uneven granulation. On the other hand, if the supply rate of the binder solution exceeds the upper limit, granulation may proceed excessively. As a result, the obtained granulated powder 80 may have a wide particle size distribution.
Further, the concentration of the organic binder in the binder solution is preferably 0.5% by weight to 20% by weight, more preferably 1% by weight to 15% by weight, and more preferably 2% by weight to 10% by weight. More preferably, it is as follows.

The granulation treatment time (stirring time) is not particularly limited, but is preferably 1 minute to 90 minutes, more preferably 2 minutes to 85 minutes, and more preferably 3 minutes to 80 minutes. More preferably. Thereby, the residual of ungranulated granulated powder can be suppressed and the particle size distribution of the obtained granulated powder 80 can be made sufficiently sharp.
On the other hand, when the granulation treatment time is less than the lower limit, a relatively large amount of small particle size powder (such as ungranulated metal powder) may remain. On the other hand, when the granulation treatment time exceeds the upper limit, a solvent is directly applied to a powder having a relatively large particle size (a lump of powder that does not roll or flow), which may cause uneven granulation. There is.

Moreover, you may make it spray (supply) the solvent which can melt | dissolve an organic binder with respect to the granulated powder 80 as needed. Thereby, the shape and size of the granulated powder 80 can be further uniformed.
Next, the granulated powder 80 thus formed is crushed by various crushing methods. Thereby, the irregular shaped granulated powder as described above (the granulated powder of the present invention) is obtained.

Examples of the crusher that performs crushing include a roll crusher, a jaw crusher, a ball mill, a disk mill, a roll mill, a hammer mill, a pin mill, and a bead mill.
Among these, a roll crusher is preferably used. According to the roll crusher, the spherical granulated powder 80 can be efficiently and uniformly deformed. As a result, the granulated powder of the present invention can be obtained reliably. Also, according to the roll crusher, the crushed particles are slightly compressed, so that the mechanical properties of the final porous sintered body can be enhanced.

The roll crusher may be a single crusher using one set of rolls or a double crusher using two or more sets of rolls.
Moreover, although the separation distance between rolls is suitably set according to the average particle diameter of the granulated powder after crushing, it is, for example, about 0.01 mm to 5 mm. By appropriately changing the separation distance between the rolls, the aspect ratio and average particle diameter of the obtained granulated powder can be controlled. For example, the aspect ratio and the average particle diameter can be reduced by narrowing the space between the rolls.

Also, the aspect ratio and average particle diameter of the granulated powder can be controlled by changing the pressure when extruding the granulated powder before crushing between rolls. For example, by increasing the pressure, the aspect ratio And the average particle size can be increased.
In addition, although the technique common to the rolling granulation method, the fluidized bed granulation method, or the rolling fluidized granulation method which is one of the granulation methods has been described above, the granulation method is not limited thereto. Alternatively, a spray drying (spray drying) method or the like can be used.
Here, the use of the granulated powder of the present invention is not particularly limited. For example, a porous body obtained by manufacturing a molded body containing the granulated powder, in particular, sintering a molded body containing the granulated powder. It can use suitably for manufacture of a quality sintered compact.

(Method for producing sintered body)
Hereinafter, an example of the manufacturing method of a sintered compact is demonstrated.
<Molding>
First, using the granulated powder of the present invention as described above, it is molded by a press molding machine to produce a molded body having a desired shape and size. Thereby, while having sufficient porosity, a molded object with high shape retention property is obtained.

It should be noted that the shape and size of the molded body to be manufactured is determined in consideration of the shrinkage due to subsequent degreasing and sintering. The molding method is not limited to press molding, and may be compression molding, injection molding, or the like.
Alternatively, the molding step may be omitted and the container may be simply fired with the granulated powder filled in the container. When this method is used, a sintered body having a particularly high porosity can be obtained.

<Degreasing treatment>
A degreasing treatment (debinding treatment) is performed on the molded body obtained in the molding step described above to obtain a degreased body. The degreasing treatment is not particularly limited, but a non-oxidizing atmosphere, for example, in a vacuum or a reduced pressure state (for example, 1 × 10 ⁻¹ Torr or more and 1 × 10 ⁻⁶ Torr or less), or nitrogen gas, argon gas, hydrogen gas, The heat treatment is performed in a gas such as ammonia decomposition gas. In this case, the conditions for the heat treatment are slightly different depending on the decomposition start temperature of the organic binder, but are preferably about 100 ° C. to 750 ° C. and about 0.5 hours to 40 hours, more preferably 150 ° C. to 700 ° C. The following is about 1 hour to 24 hours.

Further, degreasing by such heat treatment may be performed in a plurality of steps (stages) for various purposes (for example, for shortening the degreasing time). In this case, for example, a method in which the first half is degreased at a low temperature and the second half at a high temperature, a method in which low temperature and high temperature are repeated, and the like can be mentioned.
Note that the organic binder may not be completely removed by the degreasing treatment, and for example, a part of the organic binder may remain at the time of completion of the degreasing treatment.

<Baking>
The degreased body obtained in the degreasing process described above is fired and sintered in a sintering furnace to obtain a desired sintered body. By this firing, the metal powder constituting the granulated powder diffuses and grows. As a result, a porous sintered body having a sufficient porosity and high mechanical properties can be obtained.
Although the firing temperature during firing varies slightly depending on the composition of the granulated powder, for example, when an Fe-based alloy powder is used, it is preferably 800 ° C. or higher and lower than 1400 ° C., and 900 ° C. or higher and 1350 ° C. or lower. Is more preferable. When the firing temperature is within the above range, a porous sintered body having high mechanical properties can be obtained while preventing voids from disappearing.

Although the maximum temperature holding time during firing is appropriately set according to the sintering temperature, it is preferably about 0.5 hours or more and 8 hours or less, more preferably 0.75 hours or more and 5 hours or less. .
The firing atmosphere is not particularly limited, but is preferably a reduced pressure (vacuum) or non-oxidizing atmosphere. Thereby, characteristic deterioration due to metal oxidation can be prevented. A preferable firing atmosphere is a reduced pressure (vacuum) of 1 Torr or less (more preferably 1 × 10 ⁻² Torr or more and 1 × 10 ⁻⁶ Torr or less), or an inert gas such as nitrogen gas or argon gas of 1 Torr or more and 760 Torr or less. An atmosphere or a hydrogen gas atmosphere of 1 to 760 Torr is preferable.

Note that the firing atmosphere may change during firing. For example, first, the pressure is reduced to 1 × 10 ⁻² Torr or more and 1 × 10 ⁻⁶ Torr or less (vacuum), and can be switched to the inert gas as described above.
Moreover, you may perform baking by two steps or more. For example, primary firing and secondary firing with different firing conditions may be performed, and the firing temperature of the secondary firing may be higher than the firing temperature of the primary firing.

The porous sintered body obtained as described above may be used for any purpose. For example, it is suitable as a structural material used in metal filters, lightweight building materials, automobiles, aircraft, spacecrafts, and the like. Used for.
That is, the porous sintered body includes continuous air holes. For this reason, by allowing a fluid such as liquid or gas to pass therethrough, it is possible to filter solids contained in the fluid or to adsorb and separate substances by chemical interaction.

In addition, you may make it make various reactive substances adhere to the surface of the space | gap of a porous sintered compact as needed. Thereby, interaction with a fluid and a reactive substance can be performed efficiently.
The metal filter as described above is used in many industrial fields, and is particularly useful, for example, as a filter for medical equipment and analytical equipment.

The obtained porous sintered body has a relative density of about 60% to 92%. Since such a porous sintered body has a good balance between porosity and mechanical properties, it is useful, for example, as a metal filter that can be used for a long time even in an environment where the differential pressure before and after the filter is large. .
The relative density of the porous sintered body can be obtained by (100−porosity). Examples of the method for measuring the porosity include various pore distribution measuring methods such as a mercury intrusion method, a gas adsorption method, and a bubble point method.

The obtained porous sintered body has a three-point bending strength of about 2 MPa to 20 MPa. Such a porous sintered body has sufficient mechanical properties when used as a filter.
As mentioned above, although this invention was demonstrated based on suitable embodiment, this invention is not limited to these.
For example, the apparatus used for the manufacturing method of the granulated powder of this invention is not limited to the thing of embodiment mentioned above. For example, in the above-described embodiment, the description has been given by using the rolling granulator. However, the fluidized bed granulating apparatus that performs granulation by the fluid action, the rolling fluid granulator that performs granulation by the rolling fluid action, the spray You may make it use the spray-drying apparatus etc. to dry.

1. Production of granulated powder (Example 1)
<1> First, 25 kg of stainless steel powder (manufactured by Epson Atmix Co., Ltd., SUS-316, true density 7.98 g / cm ³ ) prepared by a water atomization method was prepared as a raw material powder. .
The aspect ratio a / b of the stainless steel powder used was 0.78.
<2> On the other hand, as an organic binder, 150 g of polyvinylpyrrolidone (BASF Co., Ltd.) powder was prepared and mixed with the raw material powder to obtain a mixture. Moreover, ion-exchange water was prepared as a solvent. The amount of solvent added was 50 g per 1 g of organic binder.

<3> Next, the mixture was put into a processing container of a tumbling granulator (manufactured by POWREC, VG-25). Then, while spraying ethanol (solvent) from the spray nozzle toward the mixture in the processing container, the mixture was rolled and granulated under the following granulation conditions to obtain a granulated powder.
<Granulation conditions>
・ Blade rotation speed: 200rpm
・ Cross screw speed: 2500rpm
・ Supply weight of solvent: 3.75 kg (25 g per 1 g of binder)
・ Solvent supply rate: 535 g / min ・ Granulation time: 7 minutes

<4> Next, the obtained granulated powder was put into a roll crusher, and the granulated powder was crushed. Thereby, the granulated powder of the present invention was obtained.
(Examples 2-6, Comparative Examples 1-4)
Granulated powders having the aspect ratios and average particle diameters shown in Table 1 were obtained, respectively, except that the separation distance between the rolls in the roll crusher and the pressure pushed out between the rolls were adjusted.

2. 2. Evaluation of Granulated Powder 2.1 Aspect Ratio The granulated powder obtained in each Example and each Comparative Example was observed with an SEM or a stereoscopic microscope, and the aspect ratio A / B was estimated from the observed image. The aspect ratio was estimated for 100 granulated powder particles, and the average value was used as the measured aspect ratio.

2.2 Average Particle Size For the granulated powder obtained in each Example and each Comparative Example, the cumulative particle size based on mass was measured by a laser diffraction particle size distribution measuring device (Microtrack, manufactured by Nikkiso Co., Ltd., HRA9320-X100). The particle size at 50% accumulation in the distribution was obtained.
2.3 Apparent density About the granulated powder obtained by each Example and each comparative example, the apparent density was measured by the apparent density test method of the metal powder prescribed | regulated to JISZ2504.
2.4 Fluidity About the granulated powder obtained in each Example and each comparative example, the fluidity | liquidity was measured by the fluidity test method of the metal powder prescribed | regulated to JISZ2502.

3. Evaluation of Sintered Body 3.1 Relative Density The granulated powder obtained in each Example and each Comparative Example was molded under the molding conditions shown below.
<Molding conditions>
-Molding method: Press molding method-Molding shape: rectangular parallelepiped shape of 5 mm x 5 mm x 20 mm-Molding pressure: 300 MPa (3 t / cm ² )
Subsequently, the obtained molded body was degreased under the degreasing conditions shown below.

<Degreasing conditions>
・ Degreasing temperature: 600 ° C
Degreasing time: 1 hour Degreasing atmosphere: hydrogen gas atmosphere Next, the obtained degreased body was fired under the firing conditions shown below. This obtained the sintered compact.

<Baking conditions>
・ Baking temperature: 1150 ° C
-Firing time: 3 hours-Firing atmosphere: reduced pressure Ar atmosphere-Atmospheric pressure: 1.3 kPa (10 Torr)
Next, the density of the obtained sintered body was measured by a method according to the Archimedes method (specified in JIS Z 2501). Further, the relative density of the sintered body was calculated from the measured sintered density and the true density of the metal powder.

3.2 Mechanical properties Next, the three-point bending strength of the obtained sintered body was measured.
And the three-point bending strength about the sintered compact of the granulated powder obtained by the comparative example 1 was set to 1, and the relative value about other sintered bodies was calculated | required.
Table 1 shows the evaluation results of 2.1 to 2.4, 3.1, and 3.2.

As is clear from Table 1, the sintered body of the granulated powder obtained in each example has both a relatively low relative density and a relatively high mechanical property. That is, it can be said that these sintered bodies are porous sintered bodies having sufficient porosity and high mechanical properties.
On the other hand, the sintered compact of the granulated powder obtained in each comparative example had a high relative density or a significantly low one. Among these, it was confirmed that a sintered body having a high relative density cannot be used as a filter because the porosity is too low. In addition, it was confirmed that a sintered body having a remarkably low relative density cannot be used as a filter because of its low mechanical properties.

DESCRIPTION OF SYMBOLS 1 ... Rolling granulator 10 ... Processing container 11 ... Bottom part 110 ... Through hole 12 ... Side wall part 13 ... Cover part 130 ... Through hole 20 ... Blade 21 ... Rotary blade 22 ... Rotation Drive shaft 23 …… Base 30 …… Cross screw 31 …… Rotation drive shaft 40 …… Spray nozzle 80 …… Granulated powder

Claims (8)

It is a granulated powder for a porous sintered body that is molded by press molding and then sintered and used as a filter,
The granulated powder is
It consists of a particulate material formed by binding a plurality of metal particles with an organic binder , and
When the minor axis of the particulate matter is A and the major axis is B, the average of A / B is 0.1 or more and 0.4 or less, and
Granulated powder, wherein the particle size at 50% cumulative time in a cumulative particle size distribution of the mass is 30μm or more 150μm or less.   The granulated powder according to claim 1, wherein the plurality of metal particles have an average a / b of 0.5 or more and 1 or less, where a is the short diameter and b is the long diameter.   The granulated powder according to claim 1 or 2, wherein an average particle size of the plurality of metal particles is 1 µm or more and 30 µm or less.   The granulated powder according to any one of claims 1 to 3, wherein the granulated powder has an average particle size of 3 to 100 times the average particle size of the plurality of metal particles.   The granulated powder according to any one of claims 1 to 4, wherein the granulated powder is formed by crushing a granulated powder having a larger particle diameter with a roll crusher. The metal particles are stainless steel particles;
The granulation according to any one of claims 1 to 5, wherein the granulated powder has a fluidity measured in accordance with a metal powder fluidity test method specified in JIS Z 2502 of 30 [seconds / 50 g] or more. Powder. A porous sintered body characterized by being molded by press molding using the granulated powder according to any one of claims 1 to 6 and then sintered, and having a relative density of 60% or more and 92% or less. A metal filter comprising the porous sintered body according to claim 7.

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