JP2007223890A - Silicon carbide sintered compact, sliding member and mechanical seal ring each using the same, and mechanical seal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem wherein because the shape of the open pores on the surface of a silicon carbide sintered compact is not specified, it is difficult to adjust the extent to which a lubricating fluid is supplied according their shape when the compact is used as a sliding member using the lubricating fluid. <P>SOLUTION: The sintered compact is a silicon carbide sintered compact having pores open to the surface, wherein at least one aspherical open pore having a minor diameter/major diameter ratio of 0.2 to 0.8 exists in a region confined by an arbitrary 20 μm diameter circle on the surface, provided that the major diameter is the intervertex diameter of the circumscribed circle of the open pore, and the minor diameter is a segment line between the points at which a line which passes the midpoint of the major diameter and rectangularly crosses it crosses the circumference of the open pore. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention includes a silicon carbide sintered body, a mechanical seal ring used for a shaft sealing device such as an automobile cooling water pump, a refrigerator, and the like, and the mechanical seal ring. Regarding mechanical seals.

  A sliding member using a ceramic sintered body is applied to, for example, a mechanical seal ring used for a mechanical seal of a fluid device by utilizing its wear resistance. The mechanical seal is one of the shaft seal devices used in the rotating parts of various machines for the purpose of completely sealing the fluid, and the mechanical seal ring is in sliding contact with the rotating parts of the various machines, and the shaft follows the wear of the sliding surface. It consists of a rotating ring that can move in the direction and a stationary ring that does not move, and functions to limit fluid leakage at the end face substantially perpendicular to the axis of rotation.

  FIG. 4 is a partial sectional view showing an example of a mechanical seal using a conventional mechanical seal ring. This mechanical seal has a mechanical seal ring 22 that exerts a sealing action by sliding a sliding surface 21b of a rotating ring 22b that is an annular body having a convex portion on a sliding surface 21a of a fixed ring 22a that is an annular body. It is a device using. The mechanical seal ring 22 is attached between a rotating shaft 23 that transmits a driving force by a driving mechanism (not shown) and a casing 24 that rotatably supports the rotating shaft 23, and a fixed ring 22a and a rotating ring 22b. The mutual sliding surfaces 21 a and 21 b are installed so as to form a vertical surface with respect to the rotating shaft 23.

  The rotating ring 22b is supported in a cushioning manner by the packing 26, and a coil spring 29 is installed on the side of the packing 26 opposite to the rotating ring 22b so as to wind the rotating shaft 23. By pressing the packing 26 with the force (predetermined force of the coil spring), the sliding surface 21b of the rotating ring 22b is pressed against the sliding surface 21a of the fixed ring 22a to slide. .

  A collar 28 is fixed to the rotating shaft 23 by a set screw 27 on the side opposite to the side where the coil spring 29 presses the packing 26, and is installed as a stopper of the coil spring 29. On the other hand, the fixed ring 22a that is in contact with the sliding surface 21b of the rotating ring 22b via the sliding surface 21a is supported by a shock absorbing rubber 25, and the shock absorbing rubber 25 is located inside the casing 24 that is an outer frame of the shaft seal device. It is attached and supports the fixing ring 22a.

  When the rotating shaft 23 rotates, the collar 28 rotates together, and the packing 26 pressed by the elastic force of the coil spring 29 and the sliding surface 21b of the rotating ring 22b supported by the packing 26 are pressed. By rotating while rotating, the sealing action is performed between the fixed ring 22a and the sliding surface 21a. When such a mechanical seal is attached to a fluid device (not shown), it is used by being attached so that the fluid device is disposed on the extension of the collar 28 side with respect to the mechanical seal ring 22.

  At this time, the fluid used in the fluid device penetrates to the inside surrounded by the casing 24, but the sealing action by the O-ring 30 provided between the packing 26 and the rotating shaft 23, and the mechanical seal ring The fluid is prevented from leaking outside from the shaft seal device by the sealing action of the 22 sliding surfaces 21a and 21b. At this time, the fluid sealed by the mechanical seal is referred to as a sealing fluid 31, and a part of the fluid enters between the sliding surfaces 21a and 21b of the mechanical seal ring 22 and acts as a lubricating liquid. Sliding characteristics can be obtained.

  The members used for the mechanical seal ring 22 are mainly carbon materials, cemented carbides, silicon carbide sintered bodies, and alumina sintered bodies. In recent years, they have high hardness and high corrosion resistance, and sliding Porous silicon carbide sintered bodies having a low friction coefficient and excellent smoothness are often used. As a conventional porous silicon carbide sintered body for a sliding member such as a mechanical seal ring, the following is disclosed.

  For example, Patent Document 1 describes a silicon carbide sintered body having pores having an average pore diameter of 0.5 to 10 μm at a porosity of 2 to 18% by volume, and the production of this silicon carbide sintered body is described. First, a granule A having an average particle size of 80 μm obtained by mixing and granulating a sintering aid with silicon carbide powder and granulating silicon carbide powder having a particle size of 0.3 to 0.6 μm. Then, granules B having an average particle diameter of 80 μm, which are obtained by granulating silicon carbide powder having a particle diameter of 5 to 9 μm, are prepared and mixed. Since the granule A and the granule B have the same particle size, but the particle size of the silicon carbide powder constituting the granule A is different, the granule A is a coarse granule having many voids, and the granule B is a dense granule having few voids. . Next, granule A and granule B are mixed and pressure-molded to obtain a molded body, and then the molded body is fired in an argon atmosphere at a temperature of 2050 ° C. for 2 hours to obtain the silicon carbide sintered body. can get.

  Patent Document 2 describes a silicon carbide sintered body containing 3 to 13% by volume of independent pores having an average pore diameter of 10 to 40 μm as a porosity, and a method for producing this silicon carbide sintered body was prepared. After adding spherical pore-forming agents such as polystyrene beads by emulsion polymerization, spherical starch, bulbous spheres, etc. to the raw material, the pore-forming agent is decomposed and sublimated in the degreasing process, and baked at a temperature of 2050 ° C. in an argon atmosphere. Is.

  Patent Document 3 has pores having a porosity of 2 to 12% by volume and an average pore diameter of 50 to 500 μm, and the pores are substantially spherical and are uniformly distributed in the sintered body. A sintered body is described, and the method for producing the sintered body of silicon carbide comprises 75 to 95% by mass of silicon carbide powder, 0.3 to 3% by mass of a sintering aid such as boron, boron carbide, aluminum, and aluminum nitride. , Carbon sources such as phenol resin and coal tar pitch 0.3 to 20% by mass, binders such as polyvinyl alcohol and acrylic resin 1.2 to 5% by mass, pore forming agents such as crosslinkable acrylic resin and vinyl resin 0 After pressing the mixture of 5 to 7% by mass to obtain a molded body, the molded body is fired at a temperature of 2060 to 2200 ° C. in an inert gas atmosphere such as argon, helium and neon. .

  Patent Document 4 discloses a silicon carbide having a porosity of 4 to 18% by volume, an average pore diameter of 60 to 200 μm, the pores being sealed, and the pores having a spherical shape. A sintered body is described, and a method for producing this silicon carbide sintered body is to add a pore forming agent such as polystyrene, polymethyl methacrylate, polyamide or the like to the prepared raw material, and then decompose the pore forming agent in the degreasing step. Sublimation and firing at a temperature of 2070 ° C. in an argon atmosphere.

Non-Patent Document 1 discloses thermal shock resistance coefficient R and thermal conductivity of a porous silicon carbide sintered body having a relative density of 90 to 92% in Table 1.
JP-A-9-132478 JP-A-2-55273 JP-A-7-33550 Japanese Patent Laid-Open No. 4-331784 Journal of American Society of Lubrication Engineers, Forms of Silicon Carbide and Their Effects on Seal Performance, volume 40 [6], 356-363 (June 1984)

  However, since the silicon carbide sintered body of Patent Document 1 uses a coarse granule with many voids and a dense granule with few voids in the production method, open-pores are not used after firing. The shape tends to cause distortion between the granule A and the granule B, and the lubricating liquid retained in the open pores used when used as a sliding member is appropriately drained to the sliding surface during repeated sliding. Since it is difficult, the sliding characteristics will be low. In addition, there is a problem that cracks propagating between strains generated by the granules A and B are likely to occur, and the strength of the sintered body is likely to be reduced.

  The silicon carbide sintered body of Patent Document 2 is directly added with a pore-forming agent having high compressive strength and easily recovering elastically after pressure molding, such as emulsion-polymerized polystyrene beads, spherical starch content, and valve spheres. Therefore, there has been a problem that microcracks starting from pores are likely to occur during elastic recovery after pressure molding or degreasing.

  Since the silicon carbide sintered body of Patent Document 3 has a pore forming agent such as a crosslinkable acrylic resin or vinyl resin added as it is, after the pressure forming, as with the silicon carbide sintered body of Patent Document 2. There was a problem that microcracks starting from the pores were likely to occur during recovery of elasticity and degreasing. Furthermore, since these pores have a relatively large average pore diameter of 50 to 500 μm, mechanical frictional heat generated instantaneously at the start of sliding is used under severe usage conditions that are susceptible to thermal shock. When applied to a seal ring, there was a problem of insufficient strength.

  Although the silicon carbide sintered body of Patent Document 4 has excellent sealing properties because the pores are sealed, on the other hand, it is difficult to form a good liquid lubricant film on the sliding surface, and the sliding characteristics There was a problem that could not be raised. Further, since the average pore diameter of the pores is relatively large as 60 to 200 μm, there is a problem that the strength is insufficient to be applied to the mechanical seal ring used under the above severe use conditions. .

  In the silicon carbide sintered body proposed in Patent Documents 2 to 4, a pore-forming agent is added to improve the slidability when used as a sliding member, but the surface of the obtained sintered body Since the shape of the open pores is not defined, it is difficult to adjust the degree of the outflow of the lubricant due to the shape of the open pores when used as a sliding member using a lubricant.

  Further, the silicon carbide sintered bodies proposed in Patent Documents 1 to 4 have low strength, and the thermal shock resistance coefficient R ′ that is strongly influenced by the strength is never high. As a result, high-temperature frictional heat is instantaneously generated at the start of sliding, and there is a problem that the thermal shock resistance is insufficient to be applied to a mechanical seal ring used under severe usage conditions that are susceptible to thermal shock. It couldn't be solved.

  On the other hand, when calculating the thermal shock resistance coefficient R ′ from the thermal shock resistance coefficient R and the thermal conductivity of the porous silicon carbide sintered body having a relative density of 90 to 92% disclosed in Table 1 of Non-Patent Document 1, Its value is 28842 W / m. Although it can be said that the thermal shock resistance is considered to some extent, it cannot be said that it is sufficient for application to the mechanical seal ring used under the above severe use conditions.

  The present invention has been made in view of the above-described problems, and its object is to provide a silicon carbide sintered body used for a sliding member such as a mechanical seal ring having excellent sliding characteristics and excellent thermal shock resistance. There is to do.

  The present invention is a silicon carbide sintered body having open pores opened on the surface, wherein the diameter of the circumscribed circle of the open pores is a major axis in a region within a circle having a diameter of 20 μm on the surface, and the major axis The ratio of the short diameter to the long diameter is 0.2 or more and 0.8 or less when a straight line intersecting the straight line passing through the midpoint of the long diameter and the open pore is a short diameter. It has one or more open pores.

  The major axis of the non-spherical open pore is 1 μm or more and 20 μm or less.

  The minor diameter of the non-spherical open pore is 1 μm or more and 10 μm or less.

  The non-spherical open pores are dispersed in a three-dimensional network having an average diameter of 10 μm to 150 μm.

  The ratio of the number of the non-spherical open pores to the number of all open pores 100% opened on the surface is 80% or more.

  The area occupancy ratio of all open pores opening on the surface with respect to 100% of the surface area is 5% or more and 12% or less.

The distribution density of all the open pores on the surface is 2.5 × 10 ⁴ pieces / mm ² or more and 12.5 × 10 ⁴ pieces / mm ² or less.

  The silicon carbide sintered body of the present invention is characterized in that the thermal shock resistance coefficient R ′ defined by the following formula (2) is 29000 W / m or more.

R = S · (1−ν) / (E · α) (1)
S: Three-point bending strength (Pa)
ν: Poisson's ratio E: Young's modulus (Pa)
α: Thermal expansion coefficient at 40 to 400 ° C. (× 10 ⁻⁶ / K)
R ′ = R · k (2)
Where k: thermal conductivity (W / (m · K))
The sliding member of the present invention is characterized in that these silicon carbide sintered bodies are used at least on the sliding surface.

  The mechanical seal ring of the present invention includes a fixed ring and a rotating ring that contact and slide each other sliding surfaces via a lubricating liquid, and at least one of the fixed ring and the rotating ring is made of the sliding member. It is characterized by.

  Furthermore, the mechanical seal of the present invention includes a mechanical seal ring.

  The silicon carbide sintered body of the present invention has one non-spherical open pore in which the ratio of the minor axis to the major axis is 0.2 or more and 0.9 or less in a region within an arbitrary circle having a diameter of 20 μm on the surface. Since it has the above, it is easy to hold the lubricating liquid in the non-spherical open pores when used as a sliding member, and the held lubricating liquid does not flow instantaneously to the sliding surface but is gradually supplied. High sliding characteristics can be maintained for a long time.

  In the silicon carbide sintered body of the present invention, the nonspherical open pores have a major axis of 1 μm to 20 μm, or a minor axis of the open pores of 1 μm to 10 μm. Since the lubricating liquid is sufficiently retained and can be gradually discharged, high sliding characteristics can be maintained for a long time when the lubricating liquid is supplied to the sliding surface when used as a sliding member.

  In the silicon carbide sintered body of the present invention, the open pores have a strong tendency to be arranged along grain boundaries separating the three-dimensional network, so the non-spherical open pores have a three-dimensional network shape with an average diameter of 10 to 150 μm. By arranging the non-spherical open pores, the non-spherical open pores are regularly arranged to some extent, and thus can have stable sliding characteristics.

  In the silicon carbide sintered body of the present invention, since the ratio of the number of non-spherical open pores to the number of all open pores 100% opened on the surface is 80% or more, the lubricating liquid is gradually applied over the entire surface. Since it is supplied, high sliding characteristics can be maintained for a long time.

  In the silicon carbide sintered body of the present invention, the area occupation ratio of all open pores opening on the surface with respect to 100% of the surface area is 5% or more and 12% or less. The ratio of communication is reduced, and the lubricating liquid supplied to the surface is reduced from being transmitted through the open pores connected to it. As a result, it is less likely to leak to the outside, so that high sliding characteristics are maintained while maintaining sealing performance. can get.

Since the silicon carbide sintered body of the present invention has a distribution density of all open pores of 2.5 × 10 ⁴ pieces / mm ² or more and 12.5 × 10 ⁴ pieces / mm ² or less, the variation in size is small. Since the open pores are uniformly dispersed, higher sliding characteristics can be obtained.

  The silicon carbide sintered body of the present invention has a thermal shock resistance coefficient R ′ of 29000 W / m or more, so that high-temperature frictional heat is instantaneously generated during sliding and is severely used. Even under circumstances, the strength is high and the frictional heat can be released instantly, so that no cracks are generated.

  The sliding member of the present invention is preferably used as a sliding member because it comprises the silicon carbide sintered body having high sliding characteristics and thermal shock resistance.

  Since the mechanical seal ring and the mechanical seal of the present invention use a sliding member having high sliding characteristics and thermal shock resistance, at least one of the fixed ring and the rotating ring constituting them has a sliding characteristic over a long period of time. Can be expensive.

  FIG. 1 is a diagram schematically showing the state of pores when the silicon carbide sintered body of the present invention is used as a sliding member, where (a) is a plan view of a sliding surface, and (b) is a plan view. A sectional view in a direction perpendicular to the sliding surface (a sectional view taken along the line AA in FIG. 1A), (c) is a schematic diagram schematically showing a crystal structure. 2 is a diagram for explaining non-spherical open pores existing on the surface of the silicon carbide sintered body, and FIG. 3 is a mechanical seal which is a shaft seal device in which the silicon carbide sintered body is applied to a mechanical seal ring. It is a fragmentary sectional view showing an example.

  As shown in FIGS. 1A and 1B, the silicon carbide sintered body 1 of the present invention is open at the closed pores present in the sintered body and at least the surface that becomes the sliding surface of the sliding member. A plurality of open pores 2 are formed. The open pores 2 have a function of holding a lubricating liquid used when the sliding member slides, and serve to supply the lubricating liquid to the surface when the sliding member moves.

  The open pores 2 of the silicon carbide sintered body 1 have various shapes such as spherical and non-spherical shapes. The present invention is characterized by having non-spherical open pores as defined below, and these non-spherical pores are slidable. The effect | action which improves is made.

  As shown in FIGS. 2 (a) to 2 (d), the non-spherical open pores have a diameter of a circumscribed circle of the open pores as a major axis (A), and are orthogonal to the major axis (A), and a midpoint of the major axis (A). When the short axis (B) is the straight line where the straight line passing through and the open pores intersect, the ratio (B / A) of the short diameter (B) to the long diameter (A) is 0.2 or more and 0.8 or less. The pore 2a is referred to, and in the present invention, it is important to have at least one nonspherical open pore 2a in a region within a circle having an arbitrary diameter of 20 μm on the surface serving as a sliding surface.

  By setting the confirmation area of the non-spherical open pores 2a within a circle having a diameter of 20 μm, the distribution state of the open pores 2 on the sliding surface which is the surface of the silicon carbide sintered body can be observed in detail. Since the non-spherical open pores 2a are uniformly distributed over the entire surface by making the region 20 μm in diameter, the lubricating liquid retained in the non-spherical open pores 2a spreads over the entire sliding surface. It becomes.

  The ratio (B / A) of the short diameter (B) to the long diameter (A) of the non-spherical open pores 2a affects the sliding characteristics of the sliding member. If (B / A) is small, the ratio of the open pores 2 Since the shape of the opening becomes fibrous, the supply amount of the lubricating liquid tends to decrease, and when (B / A) is large, the shape of the opening of the open pores 2 becomes circular. The negative pressure required to supply the surface cannot be obtained, and there is a strong tendency that the lubricating liquid is not sufficiently supplied to the surface. From such a viewpoint, since the non-spherical open pores 2a having (B / A) of 0.2 or more and 0.8 or less can be uniformly dispersed over the entire surface of the silicon carbide sintered body of the present invention, Since the lubricating liquid retained in the non-spherical open pores 2a does not flow out to the surface instantaneously but is gradually supplied, high sliding characteristics can be maintained over a long period of time. Furthermore, the ratio (B / A) of the minor axis (B) to the major axis (A) is more preferably 0.5 or less, and the lubricant can be slid while being supplied at a more moderate speed. . 2A to 2D, the non-spherical open pores 2a are indicated by broken lines for easy understanding.

  Non-spherical open pores 2a include, for example, irregular-shaped open pores, substantially rod-shaped open pores, bowl-shaped open pores, bead-shaped open pores, etc. as shown in FIGS. 2 (a) to (d), respectively. As shown in FIG. 2 (c), when a straight line that is orthogonal to the major axis (A) and passes through the midpoint of the major axis (A) is drawn, if the straight line does not intersect the major axis (A), the extension The short diameter (B) is the distance between two points that intersect with the open pores. In addition, a region in an arbitrary circle having a diameter of 20 μm on the surface of the sintered silicon carbide is specified by a scanning electron microscope (SEM) with a magnification of 2000 to 4000 times, and an image obtained by a scanning electron microscope (SEM). The longer diameter (A) and the shorter diameter (B) can be measured.

  The size of the non-spherical open pores 2a affects the sealing performance and sliding characteristics. If the size of the non-spherical open pores 2a is increased, that is, if the major axis or the minor axis of the non-spherical open pores 2a is increased, the sealing performance may deteriorate when the non-spherical open pores 2a are connected. On the other hand, when the size of the non-spherical open pores 2a is reduced, that is, when the major axis or minor axis of the non-spherical open pores 2a is shortened, the lubricating liquid is not sufficiently supplied from the non-spherical open pores 2a to the surface and is high for a long period of time. There is a risk that the sliding characteristics cannot be maintained. Therefore, it is preferable that the major axis of the non-spherical open pores 2a be 1 μm or more and 20 μm or less, or the minor axis of the non-spherical open pores 2a is 1 μm or more and 10 μm or less. Since the lubricating liquid is sufficiently supplied into 2a, higher sliding characteristics can be maintained over a long period of time. Further, it is more preferable that the major axis of the non-spherical open pores 2a is 1 μm or more and 10 μm or less, and the minor axis is 1 μm or more and 5 μm or less.

  As shown in FIG. 1B, the closed pores present in the silicon carbide sintered body 1 are worn on the sliding surface, and the closed pores appear as open pores on the sliding surface. Therefore, even if the surface is worn by sliding, the non-spherical open pores 2a can be present on the sliding surface over a long period of time.

  The open pores 2 have a strong tendency to be arranged along the grain boundaries 4 separating the three-dimensional network formed by the aggregates 3 of crystal grains as shown in FIG. 1 (c), and depending on the size of the three-dimensional network, The sliding characteristics of the sintered body are affected.

  The size of the three-dimensional mesh formed by the non-spherical open pores 2a can be indicated by using the diameter D of the three-dimensional mesh in FIG. 1C, and the average of the diameter D of the three-dimensional mesh is 10 μm or more and 150 μm or less. It is preferable to do.

  The reason why the average diameter is set to 10 μm or more is that if it is less than 10 μm, the number of grain boundaries 4 that divide the three-dimensional network increases too much, and there is a possibility that the graining may occur during sliding to impair the sliding characteristics. This is because if the thickness exceeds 150 μm, the region in which the lubricating liquid is not locally supplied increases, which may impair the sliding characteristics. By setting the average diameter of the three-dimensional network to 10 μm or more and 150 μm or less, the non-spherical open pores 2a existing on the sliding surface are regularly arranged to some extent, and a sintered body having stable sliding characteristics is obtained. it can. Furthermore, it is more preferable that the average diameter of the three-dimensional network is 50 μm or more and 150 μm or less, and it is possible to effectively prevent degranulation and further improve the sliding characteristics.

  The diameter of the three-dimensional mesh is an intercept method using a metal microscope equipped with a gauge for dimension measurement, with a magnification of 100 to 1000 times, and in the range of (200 to 1000) μm × (200 to 1000) μm. It may be measured by. When this intercept method is used, the grain size is measured from the number of grain boundaries 4 that divide the aggregate 3 of crystal grains on a straight line of a certain length from a photograph taken with a metal microscope, and the average is calculated. The diameter is a three-dimensional mesh. Here, it is preferable to use five or more straight lines so that the diameter of the three-dimensional mesh is not shifted.

  As described above, the non-spherical open pores 2a affect the speed at which the lubricating liquid is supplied. Therefore, the ratio of the number of non-spherical open pores 2a to the total number of open pores 2 opened on the surface. Is higher, the amount of the lubricating liquid supplied to the sliding surface increases and the sliding characteristics become better. Therefore, it is preferable to set this ratio to 80% or more, more preferably 85% or more.

This number ratio can be obtained from an image obtained in a range of 1200 μm ² at a magnification of 1000 to 5000 using a scanning electron microscope (SEM).

  The sealing performance, sliding characteristics and mechanical characteristics are affected by the area occupancy ratio of all open pores on the surface, and the area occupancy ratio of all open pores opened to the surface with respect to 100% of the surface area is 5% or more and 12%. Preferably, the ratio of the open pores 2 communicating with the other open pores 2 is reduced, and the lubricating liquid supplied to the sliding surface is reduced from being transmitted through the open pores 2 communicated. It works so as not to leak outside. Accordingly, since the lubricating liquid held in the open pores 2 can easily form a continuous fluid film on the sliding surface, it is possible to obtain high sliding characteristics, for example, high sealing performance required for a mechanical seal ring. it can. On the other hand, when the area occupancy is less than 5%, when the viscosity of the lubricating liquid is high, the lubricating liquid supplied from the open pores is small, so that a sufficient lubricating effect cannot be exhibited, and high sliding characteristics are obtained. There is a risk of not. Also, if the area occupancy exceeds 12%, the open pores 2 on the sliding surface are likely to communicate during sliding, so that the sealing performance required by, for example, a mechanical seal ring may be reduced. .

The area occupancy of all open pores was set to 100 times magnification using a metal microscope, the image of the sliding surface of the silicon carbide sintered body was captured with a CCD camera, and an image analyzer (manufactured by Nireco Corporation ( LUZEX-FS)), the measurement area of one visual field in the image may be measured as 9.0 × 10 ⁻² mm ² , the number of measurement visual fields is 10, and the total measurement area is 9.0 × 10 ⁻¹ mm ² .

  Here, the total open pores refer to open pores having a circumscribed circle diameter of 1 μm or more among all pores existing on the surface of the silicon carbide sintered body.

The open pores 2 present on the sliding surface are affected by the sliding characteristics depending on the distribution density. By setting the distribution density to 2.5 × 10 ⁴ pieces / mm ² or more and 12.5 × 10 ⁴ pieces / mm ² or less, the open pores with small variation in size are uniformly dispersed. Dynamic characteristics can be obtained.

  This distribution density can be obtained from an image obtained at a magnification of 1000 using a scanning electron microscope (SEM).

  The silicon carbide sintered body of the present invention has excellent thermal shock resistance in addition to the excellent sliding characteristics as described above, and a thermal shock resistance coefficient R ′ defined by the following formula (2) is 29000 W / m. That is important.

R = S · (1−ν) / (E · α) (1)
S: Three-point bending strength (Pa)
ν: Poisson's ratio E: Young's modulus (Pa)
α: Thermal expansion coefficient at 40 to 400 ° C. (× 10 ⁻⁶ / K)
R ′ = R · k (2)
Where k: thermal conductivity (W / (m · K))
Here, the thermal shock resistance coefficient R is a coefficient serving as an index of thermal shock resistance when rapidly cooled after heating, and the thermal shock resistance coefficient R ′ is the thermal shock resistance coefficient when cooled relatively slowly after heating. This is an index coefficient. The thermal shock resistance coefficient R ′ is set to 29000 W / m or more because high-temperature frictional heat is instantaneously generated during sliding, and the strength is high even under severe use conditions that receive thermal shock. This is because heat can be released instantly, and no cracks are generated.

To make the thermal shock resistance coefficient R ′ 29000 W / m or more, for example, the three-point bending strength (S) is 255 MPa or more, the Poisson's ratio (ν) is 0.17, the Young's modulus (E) is 333 GPa, and the thermal expansion The coefficient (α) may be 3.4 × 10 ⁻⁶ / ° C., and the thermal conductivity (k) may be 155 W / (m · k) (the values are combined with Table 6 and sample No. 40). In particular, it is preferable that the thermal shock resistance coefficient R ′ is 32000 W / m or more.

  The three-point bending strength (S) is JIS R 1601-1995, the Poisson's ratio (ν) and Young's modulus (E) are JIS R 1602-1995, and the thermal expansion coefficient (α) at 40 to 400 ° C. is JIS R 1618. -2002, thermal conductivity (k) may be measured in accordance with JIS R 1611-1997. When the mechanical seal ring is small and the dimensions of the test piece defined by each JIS standard cannot be cut out, a test piece that can be cut out as much as possible may be produced and the physical property values may be measured.

  In addition, when the silicon carbide sintered body of the present invention is used for a sliding member, the hardness of the surface which is a sliding surface affects the wear resistance, and the surface Vickers hardness Hv is set to 20 GPa or more and 25 GPa or less. Further, it is possible to easily suppress the wear of the mating sliding member in contact with the sliding member while keeping the wear resistance high. On the other hand, if the surface Vickers hardness Hv is less than 20 GPa, the sliding member made of a silicon carbide sintered body is likely to be worn, and if it exceeds 25 GPa, the wear of the sliding member on the opposite side is likely to proceed.

  The Vickers hardness Hv may be measured according to JIS R 1610-2003.

  Next, the manufacturing method of the silicon carbide sintered body of the present invention will be described.

  First, water, a sintering aid and a dispersing agent are added to the silicon carbide powder, mixed by a ball mill to form a slurry, a binder is added to the slurry, mixed, and then spray-dried to prepare silicon carbide granules. . The particle size of the granules is adjusted to be 10 to 200 μm. In particular, in order to make the three-dimensional network size in the fired body 10 to 150 μm, the particle size of the granules is 12.5 to 187.5 μm. You may adjust to.

  As the sintering aid, alumina powder and rare earth oxide powder such as yttria may be combined or carbon powder and boron powder may be combined. When carbon powder is used as part of the sintering aid, open pores Since free carbon is easily contained in the inside, and this free carbon flows out on the sliding surface and works as a lubricating liquid, the sliding characteristics are improved, so abnormal noise and linking occur at the beginning of sliding. Suitable for easy mechanical seal ring.

  Then, the pore-forming agent pulverized in advance is subjected to a classification treatment for adjusting the shape and size according to the major axis (a) and minor axis (b) of the pore-forming agent, and the classified pore-forming agent is granulated. After adding 0.5 to 10% by mass to the mixed raw material to form a mixed raw material, the mixed raw material is filled in a mold, and pressed and molded to obtain a molded body having a predetermined shape. In particular, in order to set the number ratio of the non-spherical open pores 2a to 100% of the total number of open pores 2 opened on the surface to 80% or more, resin beads made of silicone or polystyrene and acrylic-styrene copolymer are used as pore forming agents. It is preferable to use any one of suspension-polymerized non-crosslinkable resin beads composed of at least one kind of coalescence. This is because these resin beads have a low compressive strength of 1.2 MPa or less and can be easily pulverized.

The distribution density of all open pores existing on the sliding surface depends on the ratio of the pore forming agent to the granule, and the distribution density of open pores existing on the sliding surface is 2.5 × 10 ⁴ pieces / mm ² or more and 12 In order to make it 5 × 10 ⁴ pieces / mm ² or less, the ratio of the pore-forming agent to the granules may be 2 to 8% by mass.

  The obtained molded body was heated in a nitrogen atmosphere for 10 to 40 hours as necessary, held at 450 to 650 ° C. for 2 to 10 hours, then naturally cooled and degreased, for example, 1800 to 2100 ° C. Thus, a silicon carbide sintered body can be obtained by holding and firing for 3 to 5 hours. In the temperature rising process in degreasing or firing, the pore-forming agent is burnt out or thermally decomposed to form pores.

  In addition, the area occupation ratio of the open pores existing on the sliding surface depends on the ratio of the pore forming agent to the granules, and in order to make this area occupation ratio 5% or more and 12% or less, the pore forming agent for the granules The ratio may be 2 to 8% by mass.

  Moreover, it is also possible to adjust the shape of the open pores obtained by controlling the sintering state by adjusting the addition amount of the sintering aid without using the pore forming agent.

  The obtained sintered body may be subjected to processing such as grinding and polishing on the sliding surface as necessary. For example, the sliding surface is flat with a double-headed grinding machine or a surface grinding machine, and the average particle size is 3 μm. After roughing with an alumina lapping machine using diamond abrasive grains, the mirror surface is set so that the arithmetic average height Ra is 0.98 μm or less with a tin lapping machine using diamond abrasive grains having an average particle diameter of 1 μm. It may be processed. The reason why the arithmetic average height Ra is set to 0.98 μm or less is to maintain the sealing performance.

  According to the manufacturing method as described above, it is possible to obtain a silicon carbide sintered body that secures strength as a sliding member, has excellent sliding characteristics, and does not generate cracks at a low cost.

  FIG. 3 is a partial cross-sectional view showing an example of a mechanical seal to which a mechanical seal ring made of a silicon carbide sintered body of the present invention is applied.

  This mechanical seal has a mechanical seal ring 6 that exerts a sealing action by sliding a sliding surface 16b of a rotating ring 6b that is an annular body having a convex portion on a sliding surface 16a of a fixed ring 6a that is an annular body. It is a device using. The mechanical seal ring 6 is attached between a rotating shaft 7 that transmits a driving force by a driving mechanism (not shown) and a casing 8 that rotatably supports the rotating shaft 7, and includes a fixed ring 6 a and a rotating ring 6 b. The mutual sliding surfaces 16 a and 16 b are installed so as to form a vertical surface with respect to the rotating shaft 7.

  The rotating ring 6b is supported in a cushioning manner by the packing 10, and a coil spring 12 is installed on the side of the packing 10 opposite to the rotating ring 6b so as to wind the rotating shaft 7. By pressing the packing 10 with an urging force (preset coil spring force), the sliding surface 16b of the rotating ring 6b is pressed against the sliding surface 16a of the fixed ring 6a to slide. . On the side opposite to the side where the coil spring 13 presses the packing 10, the collar 12 is fixed to the rotating shaft 7 by the set screw 11 and is installed as a stopper of the coil spring 13.

  On the other hand, the fixed ring 6a that is in contact with the sliding surface 16b of the rotating ring 6b through the sliding surface 16a is supported by a buffer rubber 9, and the buffer rubber 9 is disposed inside the casing 8 that is an outer frame of the shaft seal device. It is attached to support the fixing ring 6a. When the rotary shaft 7 rotates, the collar 12 rotates together, and the packing 10 pressed by the elastic force of the coil spring 13 and the sliding surface 16b of the rotating ring 6b supported by the packing 10 are pressed. By rotating while rotating, the sealing action is performed between the fixed ring 6a and the sliding surface 16a. When such a mechanical seal is attached to a fluid device (not shown), the fluid seal is used so that the fluid device is disposed on the extension of the collar 12 side with respect to the mechanical seal ring 6.

  At this time, the fluid used in the fluid device penetrates into the inside surrounded by the casing 8, but the sealing action by the O-ring 14 provided between the packing 10 and the rotating shaft 7, and the mechanical seal ring 6 prevents the fluid from leaking outside from the mechanical seal. At this time, the fluid sealed by the mechanical seal is referred to as a sealing fluid 15, and a part of the fluid enters between the sliding surfaces 16 a and 16 b of the mechanical seal ring 6 and acts as a lubricating liquid. On the other hand, the rotating ring 6 b is supported in a cushioning manner by the packing 10, and the buffer rubber 9 and the packing 10 also have a function of absorbing vibration generated by the rotation of the rotating shaft 7. In the mechanical seal shown in FIG. 3, the fixing ring 6 a is an annular body, and the rotating ring 6 b is an annular body having a convex portion. On the contrary, the fixing ring 6 a is an annular body having a convex portion, The rotating ring 6b can be an annular body.

  The mechanical seal ring 6 includes a fixed ring 6a and a rotating ring 6b that abut against each other sliding surfaces 16a and 16b via a lubricating liquid, and at least one of the fixed ring 6a and the rotating ring 6b is the present invention. It is preferable to be made of a silicon carbide sintered body.

  In the silicon carbide sintered body 1 of the present invention, when the rotating ring 6b starts to slide, dynamic pressure is first generated by the air flow on the sliding surfaces 16a and 16b, and then on the non-spherical open pores 2a. A negative pressure lower than the dynamic pressure acts on the lubricating liquid held in the non-spherical open pores 2a, and this lubricating liquid can be appropriately supplied to the sliding surfaces 16a and 16b. High mechanical seal ring 6.

  Examples of the present invention will be specifically described below, but the present invention is not limited to these examples.

Example 1
First, a predetermined amount of carbon powder, boron powder, a dispersant and water was added to silicon carbide powder, and the mixture was put into a ball mill and then mixed for 48 hours to form a slurry. A binder was added to the slurry as a molding aid, mixed, and then spray-dried to prepare silicon carbide granules having an average particle size of 80 μm.

  Next, the non-crosslinkable polystyrene previously pulverized and polymerized as a pore-forming agent is classified according to the long diameter (a) and the short diameter (b), and the classified non-crosslinkable polystyrene is treated with each granule. 7.5 mass% was added to and mixed to make a mixed raw material. Table 1 shows the median value (Median) of the major axis (a) and minor axis (b) of the classified non-crosslinkable polystyrene. The mixed raw material was filled in a mold, and pressed in a thickness direction at a pressure of 98 MPa to form a molded body having a ring shape.

  The obtained molded body was heated in a nitrogen atmosphere for 20 hours, held at 600 ° C. for 5 hours, and then naturally cooled and degreased. Then, the sintered body having the open pores 2 was obtained by burning and holding the pore forming agent at 1900 ° C. for 4 hours to burn or pyrolyze the pore forming agent in the temperature rising process.

  Thereafter, the surface of the sintered body is ground with a surface grinder to obtain a flat surface, and after roughing with an alumina lapping machine using diamond abrasive grains having an average grain diameter of 3 μm, diamond grains having an average grain diameter of 3 μm are also formed. Using a tin lapping machine, mirror surface processing was performed so that the arithmetic average height Ra was 0.98 μm or less, and the sample No. 1 was a fixing ring 6a which was an annular body having an outer diameter of 26 mm and an inner diameter of 19 mm. 1-9 were obtained.

  The arithmetic average height Ra was measured using a stylus type surface roughness meter in accordance with JIS B 0601-2001, and the measurement length, cutoff value, and stylus scanning speed were 5 mm, 0.8 mm, and It was measured as 0.5 mm / second. Further, the ratio (A / B) of the minor axis (B) to the major axis (A) of the non-spherical open pores 2a on the sliding surface obtained by mirror finishing is 2,000 magnifications using a scanning electron microscope (SEM). It was obtained by observing a range of (300 to 3000) μm × (300 to 3000) μm at ˜20,000 times.

  After that, the ring 6a is an annular body having an outer diameter of 26 mm and an inner diameter of 19 mm having a convex portion with an outer diameter of 24 mm and an inner diameter of 21 mm, and the sliding surfaces 16 a and 16 b of the rotating ring 6 b made of carbon are brought into contact with each other. In contact with each other and slid under the following conditions, the coefficient of friction during sliding was measured.

<Sliding conditions>
Relative speed: 8 m / s, surface pressure: 500 kPa, lubricating liquid: water, sliding time: 100 hours Note that the relative speed is 11.25 mm away from the center of the rotating shaft toward the outer periphery (hereinafter referred to as position). The rotation speed of the rotating ring 6b with respect to the fixed ring 6a. The surface pressure is a pressure per unit area of the rotating ring 6b with respect to the fixing ring 6a, and a preset pressure F is applied to the sliding surface 16b of the rotating ring 5b to bring the fixing ring 6a and the rotating ring 6b into contact with each other. The area was calculated by measuring the outer diameter and inner diameter of the convex portion of the rotating ring 6b with a gauge at a magnification of 50 using a metal microscope equipped with a gauge for measuring dimensions.

As for the friction coefficient μ, the torque T is used to measure the rotational torque T at the position P of the rotating ring 6b during sliding, and this rotational torque T is applied to the area of the sliding surface 16b by surface pressure. The obtained pressure F and the value obtained by dividing the distance from the center of the rotating shaft to the position P by 11.25 mm. That is, the friction coefficient μ is μ = T / 11.25F, and the value is shown in Table 1.

  As shown in Table 1, the ratio of the short diameter (B) to the long diameter (A) of the non-spherical open pores 2a (B / A) is 0.2 or more and 0.8 or less. 1, 2, 4, 5, 7 to 9, and 11 to 14, the lubricating liquid retained in the non-spherical open pores 2a does not instantaneously flow out to the sliding surface, but is gradually supplied. Is as low as 0.3 or less and can be said to maintain high sliding characteristics for a long time.

  In particular, sample No. 1 in which the major axis of the non-spherical open pores is 1 to 20 μm and the minor axis is 1 to 10 μm. 5, 7-9, 11, and 12 have a low friction coefficient of 0.25 or less, and can be said to maintain high sliding characteristics for a long period of time.

  On the other hand, the sample No. 2 in which the ratio (B / A) of the minor axis (B) to the major axis (A) of the non-spherical open pores 2a is less than 0.2. Nos. 3 and 10 could not sufficiently supply the lubricating liquid to the sliding surface, and the coefficient of friction was as high as 0.45 or more. In addition, the ratio of the minor axis (B) to the major axis (A) of the non-spherical open pores 2a (B / A) exceeds 0.8. In No. 6, since the lubricating liquid could not be supplied to the sliding surface at an appropriate timing, the friction coefficient was as high as 0.45.

(Example 2)
First, a predetermined amount of carbon powder, boron powder, a dispersant and water was added to silicon carbide powder, and the mixture was put into a ball mill and then mixed for 48 hours to form a slurry. After adding and mixing a binder as a molding aid to this slurry, spray drying was performed to prepare silicon carbide granules having an average particle size of 10 to 250 μm as shown in Table 2.

  Next, 7.5% by mass of a non-crosslinkable polystyrene that has been pulverized and suspension-polymerized in advance as a pore-forming agent is added to and mixed with a granulated raw material, and then the mixed raw material is filled in a mold. A molded body having a ring shape was formed by pressurizing and molding in the thickness direction at a pressure of 98 MPa.

  Then, after producing a ring-shaped molded body in the same manner as in Example 1, degreasing and firing were performed to obtain a sintered body, and the surface was ground with a surface grinder to obtain a flat surface, followed by an alumina lapping machine. The sample No. 1 is a fixed ring 6a which is an annular body having an outer diameter of 26 mm and an inner diameter of 19 mm, which is rough-finished with a tin lapping machine and mirror-finished so that the arithmetic average height Ra is 0.98 μm or less. 15-19 were obtained.

  Here, the ratio (B / A) of the minor axis (B) to the major axis (A) of the non-spherical open pores 2a was determined by the same method as the method shown in Example 1.

  In addition, for the diameter of each three-dimensional mesh formed by non-spherical open pores, using a metal microscope equipped with a gauge for measuring dimensions, multiplying the magnification by 1000 times, from the range of 1000 μm × 1000 μm, using the intercept method, Five straight lines were drawn on the photograph of each sample, the particle diameter was measured from the number of grain boundaries 4 that divide the aggregate 3 of crystal grains, and the average was calculated to obtain the average diameter of the three-dimensional network.

  Thereafter, the fixed ring 6a and an annular body having an outer diameter of 26 mm and an inner diameter of 19 mm, each having a convex portion with an outer diameter of 24 mm and an inner diameter of 21 mm, and a rotating ring 6b made of carbon are connected to the sliding surfaces 16a, 16a, 16b was brought into contact and slid under the following conditions, and the coefficient of friction μ during sliding was measured. The arithmetic average height Ra and the friction coefficient μ were measured by the same method as that shown in Example 1.

<Sliding conditions>
Relative speed: 12 m / s, surface pressure: 300 kPa, lubricant: water, sliding time: 200 hours

  As shown in Table 2, a sample No. 1 having an average diameter of 3 μm or more and 10 μm or more and 150 μm or less. In Nos. 16 to 18, since the non-spherical open pores 2a are regularly arranged, the lubricating liquid is uniformly supplied to the sliding surface, the friction coefficient is as low as 0.2 or less, and the sliding characteristics are good. .

  On the other hand, the sample No. 1 in which the average diameter of each three-dimensional mesh formed by the non-spherical open pores 2a is less than 10 μm. No. 15 has many grain boundaries that divide the three-dimensional network. During sliding, degranulation occurred and the coefficient of friction was as high as 0.3. In addition, Sample No. with an average diameter of each three-dimensional network exceeding 150 μm. In No. 19, the region where the lubricating liquid was not locally supplied increased, and the friction coefficient was as high as 0.35.

(Example 3)
First, a predetermined amount of carbon powder, boron powder, a dispersant and water was added to silicon carbide powder, and the mixture was put into a ball mill and then mixed for 48 hours to form a slurry. A binder was added to the slurry as a molding aid, mixed, and then spray-dried to prepare silicon carbide granules having an average particle size of 80 μm.

  Next, 7.5% by mass of non-crosslinkable polystyrene that was pulverized and suspension-polymerized using a ball having a diameter shown in Table 3 with a pulverization time of 15 hours as a pore-forming agent was added to and mixed with the granules. After forming the mixed raw material, each of the mixed raw materials was filled in a mold, and pressed and molded at a pressure of 98 MPa in the thickness direction to obtain a molded body having a ring shape.

  Then, in the same manner as in Example 1, after forming a ring-shaped molded body, degreasing and firing were performed to obtain a sintered body, and the surface was ground with a surface grinder to be a flat surface, and then roughened with an alumina lapping machine. After the processing, mirror surface processing was carried out with a lapping machine made of tin so that the arithmetic average height Ra was 0.98 μm or less, and the sample no. 20-24 were obtained.

  Here, the ratio (B / A) of the minor axis (B) to the major axis (A) of the non-spherical open pores 2a was determined by the same method as the method shown in Example 1.

Further, the diameter of the circumscribed circle of the non-spherical open hole 2a is 1 μm or more and 20 μm or less with respect to all the open holes, and the shortest distance between the opposing surfaces of the inner walls of the non-spherical open hole 2a is 0.2 to 10 μm. The ratio of the number of open pores having one or more spherical open pores in a region within an arbitrary circle having a diameter of 20 μm is based on an image obtained in a range of 1200 μm ^{2 at} a magnification of 2000 using a scanning electron microscope (SEM). Asked.

  Thereafter, the fixed ring 6a and an annular body having an outer diameter of 26 mm and an inner diameter of 19 mm, each having a convex portion with an outer diameter of 24 mm and an inner diameter of 21 mm, and a rotating ring 6b made of carbon are connected to the sliding surfaces 16a, 16a, 16b was contacted and slid under the following conditions, and the coefficient of friction μ during sliding was measured. The value is shown in Table 3. The arithmetic average height Ra and the friction coefficient μ were measured by the same method as that shown in Example 1.

<Sliding conditions>
Relative speed: 5 m / s, surface pressure: 1 MPa, lubricating liquid: water, sliding time: 100 hours The relative speed and surface pressure were calculated by the same method as in Example 1.

  As shown in Table 3, the number ratio of the non-spherical open pores 2a to the total open pore number 100% is 80% or more. In Nos. 21 to 24, since the lubricating liquid is gradually supplied over the entire sliding surface, it can be said that the friction coefficient is as low as 0.2 or less and high sliding characteristics are maintained for a long time.

  On the other hand, in the case of sample no. No. 20 was found to have a portion where the lubricating liquid was not supplied to the entire sliding surface, and the friction coefficient was as high as 0.3.

Example 4
First, a predetermined amount of carbon powder, boron powder, a dispersant and water was added to silicon carbide powder, and the mixture was put into a ball mill and then mixed for 48 hours to form a slurry. A binder was added to the slurry as a molding aid, mixed, and then spray-dried to prepare silicon carbide granules having an average particle size of 80 μm.

  Next, after adding 0.5 to 10% by mass of non-crosslinkable polystyrene preliminarily pulverized and pore-polymerized as a pore-forming agent as shown in Table 4, the mixture is used as a mixed raw material. This mixed raw material was filled in a mold, and pressed and molded at a pressure of 98 MPa in the thickness direction to obtain a molded body having a ring shape.

  In the same manner as in Example 1, after forming a ring-shaped molded body, it was degreased and fired to obtain a sintered body, and the surface was ground with a surface grinder to obtain a flat surface, which was then roughened with an alumina lapping machine. After processing, the sample was mirror-finished with a lapping machine made of tin, and the sample No. 2 was a fixing ring 6a which was an annular body having an outer diameter of 26 mm and an inner diameter of 19 mm. 25-29 were obtained.

  Here, the ratio (B / A) of the minor axis (B) to the major axis (A) of the non-spherical open pores 2a was determined by the same method as the method shown in Example 1.

Further, the area occupation ratio of the open pores on the sliding surface was increased by 100 times using a metal microscope, and the image of the sliding surface of the sample was captured with a CCD camera, and an image analyzer (manufactured by Nireco Corporation ( LUZEX-FS)), the measurement area of one visual field in the image was measured as 9.0 × 10 ⁻² mm ² , the number of measurement visual fields was 10, and the total measurement area was 9.0 × 10 ⁻¹ mm ² .

  Thereafter, the fixed ring 6a and an annular body having an outer diameter of 26 mm and an inner diameter of 19 mm, each having a convex portion with an outer diameter of 24 mm and an inner diameter of 21 mm, and a rotating ring 6b made of carbon are connected to the sliding surfaces 16a, 16a, 16b was contacted and slid under the following conditions, and the coefficient of friction μ during sliding was measured. The value is shown in Table 4. The arithmetic average height Ra and the friction coefficient μ were measured by the same method as that shown in Example 1.

<Sliding conditions>
Relative speed: 20 m / s, surface pressure: 300 kPa, lubricating liquid: ethylene glycol, sliding time: 500 hours In addition, the relative speed and the surface pressure are calculated by the same method as in Example 1, and the sealing property is the sliding surface. The amount of the lubricating liquid leaked to the rotating shaft 7 side from between 16a and 16b was measured, and the amount was evaluated as the leakage amount.

  As shown in Table 4, the sample occupancy rate of all open pores with respect to 100% of the surface (sliding surface) is 5% or more and 12% or less. Nos. 26 to 28 had a friction coefficient of 0.25 or less, a leakage amount as low as 0 ml, and good sliding characteristics and sealing performance.

  On the other hand, Sample No. whose area occupancy of all open pores is less than 5%. Although No. 25 had good sealing performance, the friction coefficient was as high as 0.35, and good sliding characteristics could not be obtained. Sample No. with an area occupancy exceeding 12%. For No. 29, when a lubricating liquid having a high viscosity such as ethylene glycol was used, the friction coefficient was as low as 0.07 and good sliding characteristics were obtained, but the sealing performance was lowered.

(Example 5)
First, a predetermined amount of carbon powder, boron powder, a dispersant and water was added to silicon carbide powder, and the mixture was put into a ball mill and then mixed for 48 hours to form a slurry. A binder was added to the slurry as a molding aid, mixed, and then spray-dried to prepare silicon carbide granules having an average particle size of 80 μm.

  Next, a non-crosslinkable acrylic-styrene copolymer that has been previously pulverized and subjected to suspension polymerization as a pore-forming agent is added to and mixed with the ratio shown in Table 5 with respect to the granules to obtain a mixed raw material. The raw material was filled in a mold, and a molded body having a ring shape was formed by pressurizing and molding at a pressure of 98 MPa in the thickness direction.

  In the same manner as in Example 1, after forming a ring-shaped molded body, it was degreased and fired to obtain a sintered body, and the surface was ground with a surface grinder to obtain a flat surface, which was then roughened with an alumina lapping machine. After processing, the sample was mirror-finished with a lapping machine made of tin, and the sample No. 2 was a fixing ring 6a which was an annular body having an outer diameter of 26 mm and an inner diameter of 19 mm. 30-34 were obtained.

  Here, the ratio (B / A) of the minor axis (B) to the major axis (A) of the non-spherical open pores 2a was determined by the same method as the method shown in Example 1.

Further, the distribution density of all open pores on the sliding surface was determined from an image obtained in a range of 1200 μm ^{2 at} a magnification of 1000 using a scanning electron microscope (SEM).

  Thereafter, the fixed ring 6a and an annular body having an outer diameter of 26 mm and an inner diameter of 19 mm, each having a convex portion with an outer diameter of 24 mm and an inner diameter of 21 mm, and a rotating ring 6b made of carbon are connected to the sliding surfaces 16a, 16a, 16b was contacted and slid under the following conditions, and the coefficient of friction μ during sliding was measured. The value is shown in Table 5. The arithmetic average height Ra and the friction coefficient μ were measured by the same method as that shown in Example 1.

<Sliding conditions>
Relative speed: 16 m / s, surface pressure: 300 kPa, lubricant: water, sliding time: 300 hours

  As shown in Table 5, the sample No. 5 has a distribution density of all open pores on the surface (sliding surface) of 5% or more and 12% or less. In Nos. 31 to 33, open pores with small variations in size were uniformly dispersed, so the friction coefficient was as low as 0.13 or less, and high sliding characteristics could be obtained.

On the other hand, Sample No. whose distribution density of all open pores on the sliding surface is less than 2.5 × 10 ⁴ / mm ² is used. No. 30 has a small coefficient of pore per unit area, so that an appropriate amount of lubricating liquid could not be supplied to the sliding surface. I could not. In addition, Sample No. with distribution density exceeding 12.5 × 10 ⁴ pieces / mm ² was obtained. No. 34 has a large number of pores per unit area, so that the interval between the pores is shortened, and graining occurs during sliding. This sample also has a high coefficient of friction of 0.3 and has good sliding characteristics. Couldn't get.

(Example 6)
First, a predetermined amount of carbon powder, boron powder, a dispersant and water was added to silicon carbide powder, and the mixture was put into a ball mill and then mixed for 48 hours to form a slurry. After adding and mixing a binder as a molding aid to the slurry, spray drying was performed to prepare silicon carbide granules having a particle size of 80 μm.

  Next, a non-crosslinkable acrylic-styrene copolymer that has been pulverized and suspension-polymerized in advance as a pore-forming agent is added to the granule at a ratio shown in Table 6 and mixed to obtain a mixed raw material. The raw material was filled in a mold, and a molded body having a ring shape was formed by pressurizing and molding at a pressure of 98 MPa in the thickness direction.

  Then, after producing a ring-shaped molded body in the same manner as in Example 1, degreasing and firing were performed to obtain a sintered body, and the surface was ground with a surface grinder to obtain a flat surface, followed by an alumina lapping machine. The sample No. 1 is a fixing ring 5a which is an annular body having an outer diameter of 26 mm and an inner diameter of 19 mm. 35-40 were obtained.

  Sample No. The three-point bending strength of 35 to 40 conforms to JIS R 1601-1995, and the Young's modulus and Poisson ratio both conform to the ultrasonic pulse method based on JIS R 1602-1995, and the shapes defined by these JIS standards. These samples were separately prepared and measured.

  Sample No. The coefficient of thermal expansion of 35 to 39 at 40 to 400 ° C. and the thermal conductivity in this temperature range are based on JIS R 1611-1995 and JIS R 1618-2002, respectively, and samples having shapes defined by these JIS standards are separately prepared. And measured.

Thereafter, the fixed ring 6a and an annular body having an outer diameter of 26 mm and an inner diameter of 19 mm having a convex portion with an outer diameter of 24 mm and an inner diameter of 21 mm, and a rotating ring 6b made of carbon are connected to the sliding surfaces 16a, 16a, 16b was contacted and slid under the following conditions.

<Sliding conditions>
Relative speed: 12 m / s, surface pressure: 1 MPa, lubricating liquid: ethylene glycol, sliding time: 100 hours and 1000 hours After 100 hours and 1000 hours from the start of sliding, using a metal microscope, magnification of 50 times The presence or absence was observed, and those in which no crack was confirmed were shown in Table 6 and those in which cracks were confirmed were shown in Table 6.

  As shown in Table 6, a sample No. with a thermal shock resistance coefficient R ′ of 29000 W / m or more was used. Since Nos. 36 to 40 have high strength and can release frictional heat instantaneously, no cracks were observed even after 1000 hours of sliding time.

  On the other hand, Sample No. with a thermal shock resistance coefficient R 'of less than 29000 W / m. No. 35 had low strength, and the frictional heat could not be released instantly, so that cracks occurred after a sliding time of 1000 hours.

It is the figure which represented the pore at the time of using the silicon carbide sintered compact of this invention for a mechanical seal ring, Comprising: (a) is a top view of a sliding surface, (b) is perpendicular | vertical to a sliding surface. FIG. 1C is an example of a schematic view showing that pores are arranged along a three-dimensional mesh. (A), (b), (c), (d) is the figure which represented typically each nonspherical pore. It is a fragmentary sectional view showing an example of a mechanical seal which is a shaft seal device which applied a silicon carbide sintered compact of the present invention to a mechanical seal ring. It is a fragmentary sectional view which shows an example of the mechanical seal which is a shaft seal apparatus using the conventional mechanical seal ring.

Explanation of symbols

1: Sintered silicon carbide 2: Pore, 2a: Non-spherical open pore 3: Aggregate of crystal particles 4: Grain boundary 6: Mechanical seal ring 6a: Fixed ring 6b: Rotating ring 7: Rotating shaft 8: Casing 9 : Buffer rubber 10: Packing 11: Set screw 12: Collar 13: Coil spring 14: O-ring 15: Sealing fluid 16a, 16b: Sliding surface

Claims (11)

  A silicon carbide sintered body having open pores opened on the surface, wherein the diameter of the circumscribed circle of the open pores is a major axis in a region within a circle having a diameter of 20 μm on the surface, and is orthogonal to the major axis. When the straight line passing through the midpoint of the major axis and the straight line where the open pores intersect is defined as the minor axis, the ratio of the minor axis to the major axis is one nonspherical open pore having a ratio of 0.2 to 0.8. A silicon carbide sintered body characterized by having two or more.   2. The silicon carbide sintered body according to claim 1, wherein a major axis of the non-spherical open pores is 1 μm or more and 20 μm or less.   3. The silicon carbide sintered body according to claim 1, wherein a minor axis of the non-spherical open pores is 1 μm or more and 10 μm or less.   4. The silicon carbide sintered body according to claim 1, wherein the non-spherical open pores are dispersed in a three-dimensional network having an average diameter of 10 μm to 150 μm.   5. The silicon carbide sintered body according to claim 1, wherein the ratio of the number of the non-spherical open pores to the number of all open pores 100% opened on the surface is 80% or more.   6. The silicon carbide sintered body according to claim 1, wherein an area occupation ratio of all open pores opened on the surface with respect to 100% of the surface area is 5% or more and 12% or less. . The distribution density of all the open pores on the surface is 2.5 × 10 ⁴ pieces / mm ² or more and 12.5 × 10 ⁴ pieces / mm ² or less. A sintered body of silicon carbide. A silicon carbide sintered body having a thermal shock resistance coefficient R ′ defined by the following formula (2) of 29000 W / m or more.
R = S · (1−ν) / (E · α) (1)
S: Three-point bending strength (Pa)
ν: Poisson's ratio E: Young's modulus (Pa)
α: Thermal expansion coefficient at 40 to 400 ° C. (× 10 ⁻⁶ / K)
R ′ = R · k (2)
Where k: thermal conductivity (W / (m · K))   A sliding member using the silicon carbide sintered body according to any one of claims 1 to 8 on at least a sliding surface.   A fixed ring and a rotating ring that contact and slide each other's sliding surfaces through a lubricating liquid, and at least one of the fixing ring and the rotating ring is made of the sliding member according to claim 9. Mechanical seal ring.   A mechanical seal comprising the mechanical seal ring according to claim 10.

Images