Sliding member

Abstract

A sliding member according to the present disclosure comprises: a first member that contains a ceramic as the main component and has a first sliding surface; and a second member that contains a ceramic as the main component and has a second sliding surface that is capable of sliding with respect to the first sliding surface. The first sliding surface has a protruding surface shape. An inner region of the second sliding surface is in contact with an inner region of the first sliding surface, and an outer region of the second sliding surface is spaced apart from an outer region of the first sliding surface. At least one of the first member and the second member is provided with a flow path for water or for a liquid having a surface tension lower than that of water. The first and the second sliding surfaces are each a semi-specular surface.

Description

Sliding member

[0001] The present disclosure relates to a slide member.

[0002] Ceramics are hard, rigid, and wear-resistant, and are used as ceramic disc valves in hot and cold water mixer taps and automotive valves for controlling the flow rate of coolant. Patent Document 1 describes a ceramic valve for controlling the flow rate of coolant containing ethylene glycol. Such ceramic valves use relatively hard ceramics, or the sliding surfaces are coated with a film (e.g., a carbon-based film) that has better wear resistance than the base material.

[0003] Japanese Patent Application Laid-Open No. 2022-13428

[0004] The slide member according to the present disclosure includes a first member containing ceramic as a main component and having a first slide surface, and a second member containing ceramic as a main component and having a second slide surface capable of sliding relative to the first slide surface. The first slide surface is convex. The inner region of the second slide surface is in contact with the inner region of the first slide surface, and the outer region of the second slide surface is spaced apart from the outer region of the first slide surface. At least one of the first member and the second member is provided with a flow path for water or a liquid having a surface tension lower than that of water. The first slide surface and the second slide surface are semi-mirror surfaces.

[0005] Another slide member according to the present disclosure includes a first member containing ceramic as a primary component and having a first slide surface, and a second member containing ceramic as a primary component and having a second slide surface slidable relative to the first slide surface. The first slide surface is convex. The inner region of the second slide surface is in contact with the inner region of the first slide surface, and the outer region of the second slide surface is spaced apart from the outer region of the first slide surface. At least one of the first member and the second member is provided with a flow path for water or a liquid having a surface tension lower than that of water. The sum of the kurtosis Sku1 of the inner region of the first slide surface and the kurtosis Sku2 of the inner region of the second slide surface is greater than the sum of the kurtosis Sku3 of the outer region of the first slide surface and the kurtosis Sku4 of the outer region of the second slide surface.

[0006] Yet another slide member according to the present disclosure includes a first member containing ceramic as a primary component and having a first slide surface; and a second member containing ceramic as a primary component and having a second slide surface slidable relative to the first slide surface. The first slide surface is convex. An inner region of the second slide surface is in contact with the inner region of the first slide surface, and an outer region of the second slide surface is spaced apart from the outer region of the first slide surface. At least one of the first member and the second member is provided with a flow path for water or a liquid having a surface tension lower than that of water. The sum of the arithmetic mean roughness Sa1 of the inner region of the first slide surface and the arithmetic mean roughness Sa2 of the inner region of the second slide surface is greater than the sum of the arithmetic mean roughness Sa3 of the outer region of the first slide surface and the arithmetic mean roughness Sa4 of the outer region of the second slide surface.

[0007] 1 is a plan view showing a slide member according to an embodiment of the present disclosure.

[0008] Conventional ceramics are difficult to provide sufficient sliding properties. Furthermore, those using a wear-resistant film require a film fabrication process, and if the film peels off, the sliding properties are likely to deteriorate. Therefore, there is a demand for sliding components that can maintain excellent sliding properties and sealing properties over a long period of time.

[0009] The laminate according to the present disclosure has the configuration described in the section on means for solving the above problems, and thereby maintains excellent sliding properties and sealing properties for a long period of time.

[0010] As described above, the slide member according to the present disclosure includes a first member containing ceramic as a main component and a second member containing ceramic as a main component. The slide member according to the present disclosure will be described with reference to FIGS. 1 and 2. FIG. 1 is a plan view showing a slide member 10 according to one embodiment of the present disclosure. FIG. 2 is an explanatory view showing a cross section taken along line X-X shown in FIG. 1.

[0011] The first member 1 is not limited as long as it contains ceramic as a main component. Examples of ceramics contained in the first member 1 include ceramics containing forsterite, steatite, cordierite, composite oxides containing aluminum, magnesium, and silicon, aluminum oxide (alumina), and zirconium oxide (zirconia) as main components. In addition to the main component, secondary components such as silica, calcia, boron oxide, calcium carbonate, barium carbonate, alumina, zirconia, zircon, and spinel may be contained. Only one secondary component may be used, or two or more secondary components may be used in combination.

[0012] The second member 2 is also not limited as long as it contains ceramic as a main component. Examples of ceramics contained in the second member 2 include forsterite, steatite, cordierite, composite oxides containing aluminum, magnesium, and silicon, and ceramics containing aluminum oxide (alumina) and zirconium oxide (zirconia) as main components. In addition to the main component, secondary components such as silica, calcia, boron oxide, calcium carbonate, barium carbonate, alumina, zirconia, zircon, and spinel may be contained. Only one secondary component may be used, or two or more secondary components may be used in combination.

[0013] In this specification, the term "major component" in a ceramic refers to a component that accounts for 60% by mass or more of the total 100% by mass of the components that make up the ceramic. The components that make up the ceramic can be identified using an X-ray diffraction device using CuKα radiation. The content of each component can be determined, for example, using an ICP (Inductively Coupled Plasma) emission spectrometer or an X-ray fluorescence analyzer.

[0014] The shapes and sizes of the first member 1 and the second member 2 are not limited and are set appropriately depending on the device in which the sliding member 10 is used, etc. For example, in Fig. 1, the first member 1 and the second member 2 both have a circular shape when viewed in a plan view.

[0015] The first member 1 is provided with a flow path 11 for flowing a liquid. The size and number of the flow paths 11 are set appropriately depending on the device in which the sliding member 10 is used, etc. The second member 2 is also provided with a flow path 21 for flowing a liquid. The size and number of the flow paths 21 are also set appropriately depending on the device in which the sliding member 10 is used, etc. Liquid flows when the flow paths 11 of the first member 1 and the flow paths 21 of the second member 2 overlap, and the flow rate of the liquid is controlled by the degree of overlap. In the sliding member 10, the first member 1 is provided with a flow path 11 and the second member 2 is provided with a flow path 21. However, it is sufficient that the flow paths for flowing a liquid (flow paths 11, 21) are formed in at least one of the first member 1 and the second member 2.

[0016] In order to control the degree of overlap between the flow paths 11 and 21, i.e., to control the flow rate of the liquid, the first member 1 and the second member 2 are arranged to be slidable. Specifically, as shown in Fig. 1 , the first member 1 and the second member 2 are arranged to abut against each other, and the second member 2 has a structure in which it rotates around a rotation axis 3. The abutting surfaces between the first member 1 and the second member 2 become sliding surfaces. By rotating the second member 2, the degree of overlap between the flow paths 11 of the first member 1 and the flow paths 21 of the second member 2 is controlled, thereby controlling the flow rate of the liquid.

[0017] The liquid flowing through the flow paths (flow paths 11, 21) provided in the sliding member 10 is water or has a surface tension lower than that of water. In other words, the liquid flowing through the flow paths (flow paths 11, 21) is not limited to water or a liquid with better wettability than water. Examples of liquids with a surface tension lower than that of water include alcohols. Examples of alcohols include alcohols with five or fewer carbon atoms in the molecule. Examples of such alcohols include methanol, ethanol, and ethylene glycol. As long as the liquid has a surface tension lower than that of water, it may be a mixed solution such as a hydrous alcohol. The wettability of water or a liquid with a surface tension lower than that of water can be improved by making the sliding surface convex or increasing the surface roughness.

[0018] When the first member 1 and the second member 2 mainly contain alumina, the first sliding surface 1 a and the second sliding surface 2 a are ground or polished surfaces, and the liquid flowing through the flow paths (flow paths 11, 21) has a surface tension lower than that of water, the sliding member 10 exhibits superior sliding properties for the following reasons.

[0019] The wettability of a rough surface is expressed by the Wenzel equation, and as the surface roughness increases, a hydrophilic surface becomes more hydrophilic and a hydrophobic surface becomes more hydrophobic. The wettability of ceramics varies depending on the final processing step (whether it is a fired surface, a ground surface, or a polished surface). The ground or polished surface of alumina has a contact angle with water of approximately 90°, and water wettability is hardly affected by surface roughness. On the other hand, liquids with a lower surface tension than water (e.g., ethylene glycol has a surface tension approximately two-thirds that of water) have a smaller contact angle with the ground or polished surface of alumina than water, making it more likely to wet. Therefore, by making the first sliding surface 1a and the second sliding surface 2a semi-mirror-finished, wettability is further improved. As a result, excellent sliding properties are maintained over a long period of time.

[0020] As shown in Fig. 2, the first member 1 has a first sliding surface 1a. The first sliding surface 1a has a convex shape. As shown in Fig. 2, the second member 2 has a second sliding surface 2a. There are no limitations on the shape of the second sliding surface 2a as long as it can slide against the first sliding surface 1a.

[0021] 2, the inner region r1 of the second sliding surface 2a is in contact with the inner region r1 of the first sliding surface 1a, and the outer region r2 of the second sliding surface 2a is spaced apart from the outer region r2 of the first sliding surface 1a. Therefore, as long as the second sliding surface 2a has a shape that allows it to slide against the first sliding surface 1a, is in contact with the first sliding surface 1a in the inner region r1, and is spaced apart from the first sliding surface 1a in the outer region r2, the second sliding surface 2a may have a planar, convex, or concave shape. In consideration of the processability of the second sliding surface 2a, it is preferable that the second sliding surface 2a have a planar shape.

[0022] The inner region r1 refers to the region where the first sliding surface 1 a and the second sliding surface 2 a are in contact when the first member 1 and the second member 2 are in contact without being pressed against each other. The outer region r2 refers to the region other than the inner region r1, i.e., the region where the first sliding surface 1 a and the second sliding surface 2 a are not in contact with each other.

[0023] The distance between the outer region r2 of the second sliding surface 2a and the outer region r2 of the first sliding surface 1a is not limited. The distance may be, for example, 3 μm or more and 9 μm or less at the widest point when the first member 1 (first sliding surface 1a) and the second member 2 (second sliding surface 2a) are in contact without being pressed. Both the first member 1 and the second member 2 contain ceramics as a main component and therefore have relatively high rigidity. Therefore, even in a pressed state, the distance between the outer region r2 of the second sliding surface 2a and the outer region r2 of the first sliding surface 1a is hardly affected.

[0024] In the slide member 10 according to one embodiment, the first slide surface 1a and the second slide surface 2a are semi-specular. A surface having a surface roughness smaller than the wavelength of visible light is referred to as a specular surface or a smooth surface, while a surface having a surface roughness larger than the wavelength of visible light is referred to as a rough surface or a matte surface. A semi-specular surface is a surface having a surface roughness intermediate between a specular surface and a rough surface, that is, approximately the wavelength of visible light. In this specification, a semi-specular surface refers to a surface having an arithmetic mean roughness Sa of 0.2 μm or more and 0.8 μm or less.

[0025] The first sliding surface 1a and the second sliding surface 2a are semi-mirror-finished, the first sliding surface 1a is convex, and the second sliding surface 2a is shaped so as to be able to slide relative to the first sliding surface 1a, contacting the first sliding surface 1a in the inner region r1 and spaced apart from the first sliding surface 1a in the outer region r2. This configuration reduces the sliding area between the first sliding surface 1a and the second sliding surface 2a, improving wettability with liquids. Therefore, the sliding member 10 according to one embodiment can maintain excellent sliding properties over a long period of time. Furthermore, both the first sliding surface 1a and the second sliding surface 2a are semi-mirror-finished. Therefore, even if the first sliding surface 1a and the second sliding surface 2a are spaced apart in the outer region r2, the sealing performance is improved.

[0026] Instead of being semi-mirror-finished, the first sliding surface 1a and the second sliding surface 2a may have the following configuration (A) or (B): (A) The sum of the kurtosis Sku1 of the inner region r1 of the first sliding surface 1a and the kurtosis Sku2 of the inner region r1 of the second sliding surface 2a is greater than the sum of the kurtosis Sku3 of the outer region r2 of the first sliding surface 1a and the kurtosis Sku4 of the outer region r2 of the second sliding surface 2a. (B) The sum of the arithmetic mean roughness Sa1 of the inner region r1 of the first sliding surface 1a and the arithmetic mean roughness Sa2 of the inner region r1 of the second sliding surface 2a is greater than the sum of the arithmetic mean roughness Sa3 of the outer region r2 of the first sliding surface 1a and the arithmetic mean roughness Sa4 of the outer region r2 of the second sliding surface 2a.

[0027] In the configuration (A), the kurtosis Sku indicates the degree of peaking in the height distribution, and the larger the kurtosis Sku, the sharper the shape. In the case of the configuration (A), the sum of the kurtosis Sku1 and the kurtosis Sku2 is relatively large. Therefore, the inner region r1 of the first sliding surface 1a and the inner region r1 of the second sliding surface 2a have surfaces including relatively sharp irregularities. Furthermore, the first sliding surface 1a has a convex shape. As a result, the sliding area between the first sliding surface 1a and the second sliding surface 2a in the inner region r1 is reduced, and the wettability of the liquid is also improved. Therefore, the sliding member 10 according to one embodiment can maintain excellent sliding properties for a long period of time.

[0028] Furthermore, the sum of kurtosis Sku3 and kurtosis Sku4 is relatively small. Therefore, the outer region r2 of the first sliding surface 1a and the outer region r2 of the second sliding surface 2a have a relatively smooth surface including irregularities. As a result, the wettability of the liquid is reduced. Therefore, even if the first sliding surface 1a and the second sliding surface 2a are separated in the outer region r2, the sealing performance is improved.

[0029] In the case of configuration (B), the sum of the arithmetic mean roughness Sa1 and the arithmetic mean roughness Sa2 is relatively large. Therefore, the inner region r1 of the first sliding surface 1a and the inner region r1 of the second sliding surface 2a have surfaces including relatively rough irregularities. Furthermore, the first sliding surface 1a has a convex shape. As a result, the sliding area between the first sliding surface 1a and the second sliding surface 2a in the inner region r1 is reduced, and the wettability of the liquid is also improved. Therefore, the sliding member 10 according to one embodiment can maintain excellent sliding properties for a long period of time.

[0030] Furthermore, the sum of the arithmetic mean roughness Sa3 and the arithmetic mean roughness Sa4 is relatively small. Therefore, the outer region r2 of the first sliding surface 1a and the outer region r2 of the second sliding surface 2a have a surface that includes relatively smooth irregularities. As a result, the wettability of the liquid is reduced. Therefore, even if the first sliding surface 1a and the second sliding surface 2a are separated in the outer region r2, the sealing performance is improved.

[0031] The first sliding surface 1a and the second sliding surface 2a may be semi-mirror-finished or may have at least one of the configurations (A) and (B). Furthermore, the first sliding surface 1a and the second sliding surface 2a may have both the configurations (A) and (B). That is, as long as the first sliding surface 1a and the second sliding surface 2a have at least one of the configurations (A) and (B) or semi-mirror-finished, excellent sliding properties can be maintained over a long period of time, and sealing properties can also be improved.

[0032] The surface texture of the first sliding surface 1a and the second sliding surface 2a is measured, for example, using a non-contact laser microscope. Specifically, the arithmetic mean roughness Sa and kurtosis Sku are measured using a laser microscope VK-X1100 manufactured by Keyence Corporation, with the measurement mode set to color ultra-depth, a measurement magnification of 1200x (50x objective and 24x eyepiece), and a measurement range of approximately 60 μm x approximately 80 μm. The measurement pitch, cutoff filter λs, and cutoff filter λc are appropriately set according to the surface shape of the measurement area. Measurements are taken at multiple locations (five or more points), and the average value is used as the measurement value.

[0033] The shape of the first sliding surface 1a is not limited as long as it has a convex shape. For example, when the first member 1 is viewed in cross section, if the thickness of the central portion of the first member 1 (i.e., the portion where the rotation shaft 3 is located) is the thickest and the thickness of the outer periphery of the first sliding surface 1a is the thinnest, the first sliding surface 1a can be said to have a convex shape. Specifically, if the thickness of the first member 1 gradually decreases from the central portion to the outer periphery of the first member 1, the first sliding surface 1a has a convex shape. In this case, the first sliding surface 1a may be a curved surface having a curvature in the radial direction.

[0034] When the thickness of the first member 1 gradually decreases from the central portion toward the outer periphery of the first member 1, the first sliding surface 1 a may be a curved surface having a curvature in the radial direction. This curvature in the radial direction may decrease with increasing distance from the central portion of the first member 1.

[0035] Furthermore, when the first member 1 is viewed in cross section, the first sliding surface 1 a may have a parabolic shape. In this specification, the term "parabolic shape" refers to a shape that is expressed by a two-dimensional approximation formula ax where the position (distance from the rotation axis 3) on the first sliding surface 1 a is x (μm) and the height (thickness of the first member 1) is y (μm). ２ +bx+c R ２ means that the R ２ may be 0.99 or greater.

[0036] Two-dimensional approximation formula ax ２ In +bx+c, a may be -5E-9 or less, in which case the virtual parabola y = ax ２ The curvature |2a| of the apex of +bx+c is 1E-8 or more. When such a condition is satisfied, the contact area between the first sliding surface 1a and the second sliding surface 2a is reduced. As a result, the sliding member 10 according to one embodiment can maintain excellent sliding properties for a long period of time. Depending on the application of the sliding member 10, for example, when emphasis is placed on sliding properties while maintaining sealing properties, the two-dimensional approximation formula ax ２ In +bx+c, a should be set to be equal to or smaller than -5E-9.

[0037] Alternatively, the two-dimensional approximation formula ax ２In +bx+c, a may be -2E-8 or more, in which case the virtual parabola y = ax ２ The curvature |2a| of the apex of +bx+c is 4E-8 or less. When such a condition is satisfied, the contact area between the first sliding surface 1a and the second sliding surface 2a increases. As a result, the sealing performance of the sliding member 10 according to one embodiment is improved. Depending on the application of the sliding member 10, for example, when emphasis is placed on sealing performance while maintaining sliding performance, the two-dimensional approximation formula ax ２ In +bx+c, a should be set to be equal to or greater than -2E-8.

[0038] The slide member 10 according to an embodiment of the present disclosure can maintain excellent sliding properties and sealing properties for a long period of time. Therefore, the slide member 10 according to an embodiment can be used in, for example, flow control valves (hot and cold water mixer taps, gas mixers, automotive coolant flow control valves, etc.), mechanical seals, slide bearings, and other members having a slide surface.

[0039] The method for manufacturing the slide member 10 according to the embodiment is not limited, and for example, the slide member 10 may be manufactured by the following procedure.

[0040] First, an embodiment of a method for manufacturing the first member 1 and the second member 2 made of ceramics containing alumina as a main component will be described.

[0041] Alumina powder and a sintering aid are mixed to obtain a mixed powder. The mixed powder is prepared by, for example, using alumina powder as a starting material, and blending the sintering aid in an amount of, for example, 0.4 mass % to 1.0 mass % based on 100 mass % of the mixed powder. Examples of the sintering aid include SiO ２ , MgO, and CaO. If necessary, the above-mentioned auxiliary components may be blended.

[0042] The resulting mixed powder and a solvent (e.g., ion-exchanged water) are then placed in a mill. After the powder is pulverized, an organic binder and a dispersant for dispersing the mixed powder are added and mixed to obtain a slurry. Examples of dispersants include acrylic acid ester copolymers and citric acid. One type of dispersant may be used alone, or two or more types may be used in combination. Examples of organic binders include acrylic emulsions, polyvinyl alcohol, polyethylene glycol, and polyethylene oxide. One type of organic binder may be used alone, or two or more types may be used in combination.

[0043] The obtained slurry is spray granulated to obtain granules, and then a uniaxial press molding device or a cold isostatic press molding device is used to obtain a disk-shaped molded body that will become the first member 1 and the second member 2. The molding pressure is 50 MPa or more and 160 MPa or less. The obtained molded body may be subjected to cutting or the like to form the portions that will become the flow paths 11 and 21 and the hole for inserting the rotating shaft 3. The flow paths 11 and 21 and the hole for inserting the rotating shaft 3 may be formed by cutting or the like on the ceramic after firing.

[0044] The resulting molded body is fired in an air atmosphere at a temperature of 1500° C. to 1700° C. to obtain ceramics containing alumina as a main component.

[0045] Next, one surface of the ceramic that will become the first member 1 is machined into a convex shape. Examples of methods for machining into a convex shape include lapping using a metal surface plate and diamond abrasive grains. Specifically, the radial shape of the machining area of ​​the surface plate (the area facing the machined surface of the valve body) is formed into a concave shape, and the surface plate is rotated and the valve body is polished by rotating and revolving, thereby machining into a convex shape. Alternatively, the machining area may be machined into a convex shape using a vertical axis circular table type grinding machine using a grinding wheel that has been formed into a concave shape.

[0046] When processing the surface into a convex shape, the amount of polishing is adjusted to obtain a semi-mirror finish. To obtain a semi-mirror finish, for example, polishing is performed to obtain an arithmetic mean roughness Sa of 0.2 μm or more and 0.8 μm or less. This procedure results in a first member 1 having a convex first sliding surface 1a. By polishing the outer region r2 more than the inner region r1, the arithmetic mean roughness Sa3 of the outer region r2 can be made smaller than the arithmetic mean roughness Sa1 of the inner region r1.

[0047] Generally, grinding with coarse abrasive grains increases surface roughness. On the other hand, performing polishing such as chemical mechanical polishing (CMP) for a long period of time smooths the surface shape. That is, the peaks of the surface convexities become smoother, and the kurtosis Sku becomes smaller. Therefore, even for surfaces with the same arithmetic mean roughness Sa, the sharper the peaks of the surface convexities, the greater the kurtosis Sku, and the smoother the peaks of the surface convexities, the smaller the kurtosis Sku. Thus, there is no correlation between the arithmetic mean roughness Sa and the kurtosis Sku, and they are parameters that can be controlled individually. By shortening the polishing time, such as CMP, in the inner region r1 and lengthening it in the outer region r2, the kurtosis Sku3 in the outer region r2 can be made smaller than the kurtosis Sku1 in the inner region r1.

[0048] On the other hand, as for the ceramics that will become the second member 2, one surface may be subjected to lapping or the like as described above. The second member 2 does not necessarily have to be processed into a convex shape, and may be flat or concave. Therefore, it is sufficient to process one surface into the desired shape.

[0049] When one surface is processed, the amount of polishing is adjusted to obtain a semi-mirror finish. To obtain a semi-mirror finish, polishing is performed to obtain an arithmetic mean roughness Sa of 0.2 μm or more and 0.8 μm or less, as described above. This procedure results in a second member 2 having a second sliding surface 2 a. By polishing the outer region r2 more than the inner region r1, the arithmetic mean roughness Sa4 of the outer region r2 can be made smaller than the arithmetic mean roughness Sa2 of the inner region r1.

[0050] Furthermore, by shortening the polishing time such as CMP in the inner region r1 and lengthening it in the outer region r2, the kurtosis Sku4 in the outer region r2 can be made smaller than the kurtosis Sku2 in the inner region r1.

[0051] Next, the obtained first member 1 and second member 2 are combined so as to be slidable. Specifically, the first sliding surface 1a of the first member 1 and the second sliding surface 2a of the second member 2 are arranged so as to abut against each other. This abutting surface becomes the sliding surface. With the first member 1 and the second member 2 abutting against each other, the rotating shaft 3 is inserted into the hole for inserting the rotating shaft 3. By rotating the rotating shaft 3 automatically or manually, the first member 1 and the second member 2 can be slid against each other. In this manner, the sliding member 10 according to one embodiment is obtained.

[0052] Specifically, alumina powder with a purity of 96% was used as the starting material, and SiO was used as the sintering aid in 100% by mass of the mixed powder. ２ A mixed powder was obtained by mixing 0.5% by mass of ZnO, 0.1% by mass of MgO, and 0.1% by mass of CaO. The resulting mixed powder and ion-exchanged water as a solvent were placed in a grinding mill. The powder was then ground, and an organic binder and a dispersant for dispersing the mixed powder were added and mixed to obtain a slurry. An acrylic ester copolymer was used as the dispersant. Polyvinyl alcohol was used as the organic binder.

[0053] The resulting slurry was then spray-granulated to obtain granules. A uniaxial press molding machine was then used to obtain a disk-shaped molded body (molding pressure: 100 MPa) that would become the first member 1 and the second member 2. The resulting molded body was then cut to form the flow paths 11 and 21 and the hole for inserting the rotary shaft 3. The resulting molded body was fired at 1600°C in an air atmosphere to obtain a ceramic (diameter 40 mm, thickness 3 mm) containing alumina as the main component.

[0054] Next, one surface of the ceramic that would become the first member 1 was machined into a convex shape by the above-mentioned lapping process. When machining into a convex shape, the convex surface was machined so that the arithmetic mean roughness Sa was 0.5 μm, resulting in a semi-mirror finish. In this way, the first member 1 having the first sliding surface 1a was obtained. In this case, when the lowest position of the outer region r2 was used as the reference, one of the first sliding surfaces 1a was prepared in which the apex of the convex surface protruded by about 1 μm, and the other in which the apex of the convex surface protruded by about 5 μm.

[0055] On the other hand, one surface of the ceramic that would become the second member 2 was processed by the above-mentioned lapping process so that the arithmetic mean roughness Sa was 0.5 μm, forming a semi-mirror finish. In this way, the second member 2 having the second sliding surface 2 a was obtained.

[0056] The obtained first member 1 and second member 2 were arranged so that the first sliding surface 1 a of the first member 1 and the second sliding surface 2 a of the second member 2 were in contact with each other, and the rotating shaft 3 was inserted into the hole for inserting the rotating shaft 3. By this procedure, the sliding member 10 was obtained.

[0057] A sliding test was carried out using the obtained sliding member 10. In the sliding test, the first member 1 was set as the fixed side, the second member 2 was set as the driving side, ethylene glycol was dropped onto the contact surfaces (sliding surfaces), and the second member 2 on the driving side was caused to slide back and forth for 12 hours at a frequency of 1 Hz and a stroke of 1 mm.

[0058] As a result of the sliding test, the sliding member 10 obtained using the first member 1 whose convex apex protruded by about 1 μm had a friction coefficient of 0.195 at the start of the sliding test and maintained a relatively low friction coefficient of 0.285 even at the end of the sliding test. The sliding member 10 obtained using the first member 1 whose convex apex protruded by about 5 μm had a friction coefficient of 0.068 at the start of the sliding test and maintained a relatively low friction coefficient of 0.118 even at the end of the sliding test. Furthermore, in none of these sliding members 10 was there any leakage of ethylene glycol from the contact surfaces.

[0059] Therefore, it was found that the sliding member 10 obtained using the first member 1 whose apex of the convex surface protrudes by about 1 μm and the sliding member 10 obtained using the first member 1 whose apex of the convex surface protrudes by about 5 μm can both maintain excellent sliding properties and excellent sealing properties for a long period of time.

[0060] The embodiments of the present disclosure have been described above. However, the invention according to the present disclosure is not limited to the above embodiments, and various modifications and improvements are possible within the scope of the present disclosure as shown in (1) to (10) below.

[0061] (1) A slide member according to the present disclosure includes a first member containing ceramic as a primary component and having a first slide surface; and a second member containing ceramic as a primary component and having a second slide surface slidable relative to the first slide surface. The first slide surface is convex. The inner region of the second slide surface is in contact with the inner region of the first slide surface, and the outer region of the second slide surface is spaced apart from the outer region of the first slide surface. At least one of the first member and the second member is provided with a flow path for water or a liquid having a surface tension lower than that of water. The first slide surface and the second slide surface are semi-mirror surfaces. (2) Another slide member according to the present disclosure includes a first member containing ceramic as a primary component and having a first slide surface; and a second member containing ceramic as a primary component and having a second slide surface slidable relative to the first slide surface. The first slide surface is convex. The inner region of the second sliding surface is in contact with the inner region of the first sliding surface, and the outer region of the second sliding surface is spaced apart from the outer region of the first sliding surface. At least one of the first member and the second member is provided with a flow path for water or a liquid having a surface tension lower than that of water. The sum of the kurtosis Sku1 of the inner region of the first sliding surface and the kurtosis Sku2 of the inner region of the second sliding surface is greater than the sum of the kurtosis Sku3 of the outer region of the first sliding surface and the kurtosis Sku4 of the outer region of the second sliding surface. (3) Yet another sliding member according to the present disclosure includes a first member containing ceramic as a main component and having a first sliding surface, and a second member containing ceramic as a main component and having a second sliding surface slidable relative to the first sliding surface. The first sliding surface has a convex shape. The inner region of the second sliding surface is in contact with the inner region of the first sliding surface, and the outer region of the second sliding surface is spaced apart from the outer region of the first sliding surface. At least one of the first member and the second member is provided with a flow path for water or a liquid having a surface tension lower than that of water. The sum of the arithmetic mean roughness Sa1 of the inner region of the first sliding surface and the arithmetic mean roughness Sa2 of the inner region of the second sliding surface is greater than the sum of the arithmetic mean roughness Sa3 of the outer region of the first sliding surface and the arithmetic mean roughness Sa4 of the outer region of the second sliding surface.(4) In the slide member described in (1) above, the sum of the kurtosis Sku1 of the inner region of the first slide surface and the kurtosis Sku2 of the inner region of the second slide surface is greater than the sum of the kurtosis Sku3 of the outer region of the first slide surface and the kurtosis Sku4 of the outer region of the second slide surface. (5) In the slide member described in (1) above, the sum of the arithmetic mean roughness Sa1 of the inner region of the first slide surface and the arithmetic mean roughness Sa2 of the inner region of the second slide surface is greater than the sum of the arithmetic mean roughness Sa3 of the outer region of the first slide surface and the arithmetic mean roughness Sa4 of the outer region of the second slide surface. (6) In the slide member described in (2) above, the sum of the arithmetic mean roughness Sa1 of the inner region of the first slide surface and the arithmetic mean roughness Sa2 of the inner region of the second slide surface is greater than the sum of the arithmetic mean roughness Sa3 of the outer region of the first slide surface and the arithmetic mean roughness Sa4 of the outer region of the second slide surface. (7) In the sliding member according to (4) above, the sum of the arithmetic mean roughness Sa1 of the inner region of the first sliding surface and the arithmetic mean roughness Sa2 of the inner region of the second sliding surface is greater than the sum of the arithmetic mean roughness Sa3 of the outer region of the first sliding surface and the arithmetic mean roughness Sa4 of the outer region of the second sliding surface. (8) In the sliding member according to any one of (1) to (7) above, R of a two-dimensional approximation formula of position and height on the first sliding surface. ２ is 0.95 or more. (9) In the sliding member according to any one of (1) to (8) above, the liquid contains an alcohol. (10) In the sliding member according to (9) above, the alcohol is an alcohol having 5 or less carbon atoms in the molecule.

[0062] REFERENCE SIGNS LIST 1 First member 11 Flow path 1a First sliding surface 2 Second member 21 Flow path 2a Second sliding surface 3 Rotating shaft 10 Sliding member r1 Inner region r2 Outer region

Claims

1. A sliding member comprising: a first member containing ceramic as a main component and having a first sliding surface; and a second member containing ceramic as a main component and having a second sliding surface capable of sliding against said first sliding surface, wherein said first sliding surface is convex, an inner region of said second sliding surface is in contact with the inner region of said first sliding surface and an outer region of said second sliding surface is spaced apart from the outer region of said first sliding surface, at least one of said first member and said second member is provided with a flow path for water or a liquid having a surface tension lower than that of water, and said first sliding surface and said second sliding surface are semi-mirror surfaces.

2. A sliding member comprising: a first member containing ceramics as a main component and having a first sliding surface; and a second member containing ceramics as a main component and having a second sliding surface capable of sliding against said first sliding surface, wherein said first sliding surface is convex, an inner region of said second sliding surface is in contact with the inner region of said first sliding surface, and an outer region of said second sliding surface is spaced apart from the outer region of said first sliding surface, at least one of said first member and said second member is provided with a flow path for water or a liquid having a surface tension lower than that of water, and the sum of the kurtosis Sku1 of the inner region of said first sliding surface and the kurtosis Sku2 of the inner region of said second sliding surface is greater than the sum of the kurtosis Sku3 of the outer region of said first sliding surface and the kurtosis Sku4 of the outer region of said second sliding surface.

3. A sliding member comprising: a first member containing ceramic as a main component and having a first sliding surface; and a second member containing ceramic as a main component and having a second sliding surface capable of sliding against said first sliding surface, wherein said first sliding surface is convex, an inner region of said second sliding surface is in contact with the inner region of said first sliding surface, and an outer region of said second sliding surface is spaced apart from the outer region of said first sliding surface, at least one of said first member and said second member is provided with a flow path for water or a liquid having a surface tension lower than that of water, and wherein the sum of the arithmetic mean roughness Sa1 of the inner region of said first sliding surface and the arithmetic mean roughness Sa2 of the inner region of said second sliding surface is greater than the sum of the arithmetic mean roughness Sa3 of the outer region of said first sliding surface and the arithmetic mean roughness Sa4 of the outer region of said second sliding surface.

4. The sliding member according to claim 1, wherein the sum of the kurtosis Sku1 of the inner region of the first sliding surface and the kurtosis Sku2 of the inner region of the second sliding surface is greater than the sum of the kurtosis Sku3 of the outer region of the first sliding surface and the kurtosis Sku4 of the outer region of the second sliding surface.

5. The sliding member according to claim 1, wherein the sum of the arithmetic mean roughness Sa1 of the inner region of the first sliding surface and the arithmetic mean roughness Sa2 of the inner region of the second sliding surface is greater than the sum of the arithmetic mean roughness Sa3 of the outer region of the first sliding surface and the arithmetic mean roughness Sa4 of the outer region of the second sliding surface.

6. The sliding member according to claim 2, wherein the sum of the arithmetic mean roughness Sa1 of the inner region of the first sliding surface and the arithmetic mean roughness Sa2 of the inner region of the second sliding surface is greater than the sum of the arithmetic mean roughness Sa3 of the outer region of the first sliding surface and the arithmetic mean roughness Sa4 of the outer region of the second sliding surface.

7. The sliding member according to claim 4, wherein the sum of the arithmetic mean roughness Sa1 of the inner region of the first sliding surface and the arithmetic mean roughness Sa2 of the inner region of the second sliding surface is greater than the sum of the arithmetic mean roughness Sa3 of the outer region of the first sliding surface and the arithmetic mean roughness Sa4 of the outer region of the second sliding surface.

8. On the first sliding surface, R of the two-dimensional approximation formula of the position and height ２ 8. The sliding member according to claim 1, wherein is 0.95 or more.

9. A sliding member according to any one of claims 1 to 8, wherein the liquid includes an alcohol.

10. The sliding member according to claim 9, wherein the alcohol has five or less carbon atoms in the molecule.

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