Surface processing method for sliding member and sliding member

Abstract

To provide a method for processing a surface of a sliding member, capable of obtaining the sliding member having good frictional characteristics by a simple method.SOLUTION: A method for processing a surface of a sliding member 10 includes a step of placing a powder 30 on a surface of a base material 11, and a step of locally heating the surface of the base material 11 under conditions where the base material 11 does not melt by spot heating, thereby melting at least part of the powder 30.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a surface processing method for a sliding member and a sliding member.

Background Art

[0002] Patent Document 1 discloses a movable scroll having a pressure-receiving portion in the shape of a floating island. This movable scroll is described as being formed by high-precision casting using a mold formed by mixing sand and a special resin.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Attempts have been made to reduce frictional resistance by applying a texture to the surface of a sliding member. However, when forming a texture by casting as in the method disclosed in Patent Document 1, it is necessary to prepare a special mold, which complicates the manufacture of the sliding member. Further, in the method disclosed in Patent Document 1, the degree of freedom in the shape of the texture is low, and there is room for improvement in reducing frictional resistance.

[0005] The present invention has been made in view of the above conventional situation, and an object to be solved is to provide a surface processing method for a sliding member that can obtain a sliding member having good frictional characteristics by a simple method, and such a sliding member.

Means for Solving the Problems

[0006] The surface processing method for a sliding member of the present invention includes a step of disposing powder on the surface of a base material, and a step of locally heating the surface of the base material by spot heating under conditions where the base material does not melt, to melt at least a part of the powder.

[0007] According to the above-described surface processing method for sliding members, it is possible to provide sliding members with good friction characteristics using a simple method. [Brief explanation of the drawing]

[0008] [Figure 1] (A) A plan view of the texture according to Embodiment 1. (B) A cross-sectional view along line BB. [Figure 2] This is an explanatory diagram illustrating a surface processing method for sliding members. [Figure 3] This is an explanatory diagram illustrating the lubrication process. [Figure 4] (A) A plan view of the texture according to Embodiment 2. (B) A cross-sectional view along line BB. [Figure 5] This is an explanatory diagram illustrating a surface processing method for sliding members. [Figure 6] This is a SEM image of the powder used in the example. [Figure 7] This is an observation image of the laminated portion of Example 1, as seen under a microscope. [Figure 8] This is an observation image of the laminated portion of Example 2, as seen under a microscope. [Figure 9] This graph shows the results of analyzing multiple convex areas. [Modes for carrying out the invention]

[0009] Preferred embodiments of the present invention will be described. The powder comprises a first component and a second component having a lower melting temperature than the first component, and it is preferable to melt the second component in the step of melting at least a portion of the powder. With this configuration, the second component can adhere the first component well to the substrate. As a result, desired properties can be imparted to the sliding surface according to the properties of the first component.

[0010] In the step of melting at least a portion of the powder, it is preferable to form a plurality of protrusions on the locally heated area. With this configuration, a fine uneven shape can be imparted to the locally heated area, thereby providing the sliding surface with desired sliding properties.

[0011] The sliding member of the present invention is preferably a sliding member processed by the method described above. With this configuration, a sliding member having good frictional properties can be obtained by a simple method. The surface processing method for the sliding member and the sliding member according to the embodiment will be described in detail below.

[0012] <Embodiment 1> 1. Surface processing method for the sliding member 10 The surface processing method for the sliding member 10 of this embodiment includes the steps of placing powder 30 on the surface of the base material 11 and locally heating the surface of the base material 11 by spot heating under conditions in which the base material 11 does not melt, thereby melting at least a portion of the powder 30.

[0013] (1) Sliding member 10 As shown in Figures 1 and 3, the sliding member 10 has a sliding surface 10A that slides against the sliding surface 50A of the mating material 50. The sliding surface 10A is a plane-based surface on the sliding member 10. Lubricating oil LO is present between the sliding surface 10A of the sliding member 10 and the sliding surface 50A of the mating material 50. The sliding surface 50A of the mating material 50 is a plane-based surface parallel to the sliding surface 10A of the sliding member 10. From the viewpoint of improving friction characteristics, it is preferable that the sliding surface 50A of the mating material 50 is a surface that makes planar contact with the sliding surface 10A, rather than a surface that makes point-like contact with the sliding surface 10A, such as a spherical surface.

[0014] The sliding member 10 includes a base material 11 and a laminated portion 22. The material of the base material 11 is not particularly limited, but a metal is preferable. Examples of the material of the base material 11 include iron-based metals, titanium-based metals, stainless steel-based metals, zinc-based metals, aluminum-based metals, magnesium-based metals, nickel-based metals, etc. The metal may be a pure metal or an alloy containing two or more metal components. Among these, from the viewpoint of versatility, it is preferable to be an iron-based metal such as carbon steel (S45C) and cast iron (FC250). Further, when used as a biocompatible sliding member such as an artificial joint, a titanium-based metal may be used from the viewpoints of corrosion resistance and biocompatibility.

[0015] The material of the laminated portion 22 is not particularly limited. The powder 30 serving as the material of the laminated portion 22 is preferably a metal powder or a thermoplastic resin powder. Examples of the metal powder include tin. The powder 30 of the present embodiment has a component having a melting temperature lower than that of the base material 11 as the main component. The particle shape of the powder 30 may be any of spherical, plate-like, and rod-like. The size of the powder 30 is not particularly limited and may be appropriately set according to the height of the laminated portion 22 and the surface processing method.

[0016] (2) Texture 20 As shown in FIG. 1, the texture 20 is constituted by a laminated portion 22 laminated on the surface of the base material 11. Specifically, the texture 20 has an island-like laminated portion 22 and a recess 21 provided so as to surround the laminated portion 22. A plurality of laminated portions 22 are provided. The recess 21 has a continuous shape. The texture 20 of the present embodiment is a so-called convex texture.

[0017] The plurality of laminated portions 22 constitute a pressure-receiving surface portion that receives surface pressure. The laminated portion 22 has a substantially circular shape in plan view. The upper surface of the laminated portion 22 may be a substantially flat surface or may have a plurality of convex portions as described later. Also, the side surface of the laminated portion 22 may be a surface substantially perpendicular to the surface of the base material 11, and may be inclined inward of the laminated portion 22 as it goes upward from the surface of the base material 11 from the viewpoint of reducing the friction coefficient. The area ratio of the plurality of laminated portions 22 is not particularly limited, but is preferably larger than the area ratio of the concave portion 21. The height of the laminated portion 22 can be controlled by appropriately adjusting the material of the powder 30 and the deposition height of the powder 30 in the step of disposing the powder 30 on the surface of the base material 11.

[0018] From the viewpoint of reducing and stabilizing the friction coefficient, when the laminated portion 22 has a substantially circular shape in plan view, the ratio of the height of the laminated portion 22 to the diameter of the laminated portion 22 (height of the laminated portion 22 / diameter of the laminated portion 22) is preferably 1 / 10000 or more and 1 / 100 or less. That the laminated portion 22 has a substantially circular shape in plan view may include, for example, in addition to a perfect circular shape in plan view, a shape that tapers in one direction, an elliptical shape, etc. In the case of such a shape other than a perfect circular shape, the equivalent diameter of the area circle can be calculated from the area of the laminated portion 22 in plan view and used as the diameter of the laminated portion 22.

[0019] The concave portion 21 constitutes an oil reservoir portion where the lubricating oil LO accumulates. The concave portion 21 has a groove shape surrounding the entire circumference of the laminated portion 22. The grooves surrounding each of the plurality of laminated portions 22 in the concave portion 21 communicate with each other to form a mesh shape. The bottom surface of the concave portion 21 exposes the base material 11.

[0020] (2) Surface processing method The surface processing method of the sliding member 10 includes a step of disposing the powder 30 on the surface of the base material 11 and a step of locally heating the surface of the base material 11 by spot heating under conditions where the base material 11 does not melt to melt the powder 30. Specifically, the surface processing method of the sliding member 10 includes a powder disposing step, a heating step, and a cleaning step. The cleaning step is an optional step. Hereinafter, it will be described while referring to FIG. 2.

[0021] The powder placement step involves evenly sprinkling the powder 30 onto the surface of the substrate 11. Then, the powder 30 is deposited on the surface of the substrate 11. The height of the deposited powder 30 can be adjusted according to the height of the layered section 22. Before the heating step, the powder 30 is placed on the surface of the substrate 11 in contact with the substrate 11 but not in an adhesive state.

[0022] The method of spot heating in the heating process is not particularly limited. Examples of spot heating methods include spot heating by irradiating with laser light, spot heating by applying electric current, and spot heating by bringing a heating element close. In each spot heating method, the conditions under which the substrate 11 does not melt can be appropriately set by adjusting the melting temperature of the substrate 11 or the heating position. The following description will focus on the method of spot heating by irradiating with laser light.

[0023] The heating step involves locally heating the surface of the substrate 11 by laser processing under conditions that the substrate 11 does not melt, thereby melting the powder 30. Laser processing can be performed using a laser processing machine 40 such as a CO2 laser processing machine. In the locally heated area, the molten powder 30 mixes with each other, cools, and solidifies. This forms a laminated portion 22. In other words, the heating step is a step of melting the powder 30 and forming a laminated portion 22 in the locally heated area. In laser processing, the conditions under which the substrate 11 does not melt are, for example, conditions under which the pulse width of the laser beam and the pulse energy density on the surface of the substrate 11 are appropriately set so that the maximum temperature reached on the laser irradiation surface does not exceed the melting temperature of the substrate 11.

[0024] The cleaning step is a process of removing powder 30 from the surface of the substrate 11 that is located outside the area where the laminated portion 22 is formed. Even if the cleaning step is not performed, if the recessed area 21 around the laminated portion 22 functions as an oil reservoir, the cleaning step does not need to be performed.

[0025] 2. Operation and Effects of this Embodiment According to the surface processing method for the sliding member 10 of this embodiment, a sliding member 10 with good friction characteristics can be manufactured using a simple method. In designing the texture 20, optimization of the texture pattern 20 and the height of the laminated portion 22 is required. According to the surface processing method for the sliding member 10 of this embodiment, multiple samples with different texture patterns 20 and laminated portion heights 22 can be easily created. Then, by performing sliding tests on each sample, a texture 20 with the desired friction characteristics can be obtained.

[0026] The reason why the frictional characteristics of the sliding member 10 can be improved, particularly the reduction of the coefficient of friction, is presumed to be due to the friction-reducing effect of the texture 20. The following describes the lubrication effect of the lubricating oil LO in the friction-reducing effect of the texture 20. However, the present invention is not limited in any way to these mechanisms of action.

[0027] In the sliding of the sliding member 10, it is desirable to reduce the frequency of solid contact in order to reduce friction. As shown in Figure 3, the sliding member 10 of this embodiment exhibits an oil film retention effect due to the generation of dynamic pressure caused by the lubricating oil LO in the recesses 21 being drawn to the upper surface of the laminated portion 22. In Figure 3, the arrows indicate the flow of the lubricating oil LO. Furthermore, with a configuration having multiple laminated portions 22 (convex texture), for example, compared to a configuration having multiple recesses 21 (concave texture), the recesses 21 can form a mesh-like flow path for the lubricating oil LO. Therefore, it is presumed that the circulation of the lubricating oil LO in the recesses 21 is improved during sliding, and the lubricating oil LO can be constantly supplied to the upper surface of the laminated portion 22, thereby suppressing oil film breakdown. It is presumed that this action reduces the frequency of contact between the sliding member 10 and the mating material 50, resulting in a smaller coefficient of friction. Furthermore, with the sliding member 10 of this embodiment, a wear particle trapping effect by the recesses 21 can also be expected. In the case of a convex texture, the concave 21 forms a continuous shape, so wear particles can be discharged to the outside of the sliding surface 10A along with the flowing lubricating oil LO.

[0028] In this embodiment, such a convex texture can be obtained by spot heating, rather than by conventional casting. The spot heating method allows for the appropriate adjustment of the shape, size, and pitch of the laminated portion 22 to form an optimal texture 20. Furthermore, the height of the laminated portion 22 can be easily adjusted by adjusting the deposition height of the powder 30. Thus, the spot heating method allows for a sliding member 10 with a high degree of freedom in the shape of the texture 20 and excellent frictional properties.

[0029] <Embodiment 2> The surface processing method for the sliding member 110 according to Embodiment 2 differs from Embodiment 1 in that the powder 130 used for processing is different. Components identical to those in Embodiment 1 are denoted by the same reference numerals and their detailed descriptions are omitted. The following description will be given with reference to Figures 4 and 5.

[0030] The powder 130 contains a first component and a second component having a lower melting temperature than the first component. In the powder 130, it is more preferable that the melting temperature of the second component is lower than the melting temperature of the first component and the melting temperature of the base material 11.

[0031] The first component is preferably one or more selected from the group consisting of solid lubricants, abrasives, and particles of biocompatible materials. Examples of solid lubricants include graphite and Teflon®. When the first component is a solid lubricant, it can be expected to reduce the coefficient of friction. When the first component is an abrasive, it can be expected to increase the coefficient of friction. Examples of biocompatible materials include hydroxyapatite. When the first component is a biocompatible material, the affinity between the biocompatible member and biological tissue can be improved on the sliding surface 10A of the biocompatible member. Such a configuration is suitable, for example, for the sliding surfaces of sliding members such as bone screws and artificial joints. In other words, by appropriately selecting and using the first component, desired properties can be imparted to the sliding surface 10A.

[0032] The second component functions as a binder that adheres the first component to the substrate 11. In powder 130, the second component can also function as a binder that binds the first components together. The second component can be the same component (material) as powder 30 in Embodiment 1, and its description is omitted.

[0033] The surface treatment method for the sliding member 110 involves a heating step in which at least a portion of the powder 130 is melted, thereby melting the second component. The heating step melts the second component without melting the first component, forming a laminated portion 122. In the laminated portion 122, the first component is bonded to the substrate 11 by the second component. In Figure 5, the dashed lines in the laminated portion 122 schematically represent the first component.

[0034] According to this embodiment, the second component can bond the first component to the substrate 11. As a result, desired properties can be imparted to the sliding surface 10A according to the properties of the powder 130. For example, if the powder 130 has self-lubricating properties, it can contribute to reducing the coefficient of friction.

[0035] <Embodiment 3> The surface processing method for the sliding member according to Embodiment 3 forms a plurality of protrusions 23 on a locally heated portion. Components identical to those in Embodiment 1 are denoted by the same reference numerals and their detailed descriptions are omitted.

[0036] Figures 8 and 9 show microscopic observations of the laminated portion 22 of Example 2. Multiple protrusions 23 can be seen formed in the locally heated areas. The reason for the formation of multiple protrusions 23 is not clear, but it is presumed that some of the molten powder 30 solidifies in a convex shape, thus forming multiple protrusions 23.

[0037] In this embodiment, a plurality of protrusions 23 are formed on the locally heated portion during the heating process. With this configuration, a fine uneven shape can be imparted to the locally heated portion, thereby providing the sliding surface 10A with desired sliding characteristics.

[0038] <Other Embodiments> This disclosure is not limited to embodiments, and the technical scope also includes, for example, the following embodiments.

[0039] (1) In the heating process, it is not necessary to form multiple protrusions on locally heated areas. For example, by adjusting the amount of powder and heating conditions, the molten powder may spread and wet the upper surface of the laminated portion, making it a substantially flat surface. In this case, it is presumed that the inclination angle of the side surface of the laminated portion is determined by the contact angle between the molten powder and the surface of the substrate. (2) The texture may have a plurality of recesses and a layered portion located between the plurality of recesses. This layered portion has a continuous shape. The texture is a so-called concave texture. (3) The sliding surface may be a surface based on a curved surface of the sliding member. An example of such a sliding surface is the outer circumferential surface of a cylindrical member. If the sliding surface of the sliding member is a surface based on a curved surface, it is preferable that the sliding surface of the mating material is also a surface based on a curved surface that extends parallel to the sliding surface of the sliding member. (4) The shape, size, and pitch of the laminated section can be changed as appropriate. The laminated section may have a tapered shape in the direction in which the mating material slides against the sliding member. In addition, on the actual sliding surface, the flow direction of the oil may be controlled by considering the flow path from the oil supply section, for example by arranging the elliptical-shaped laminated section at an angle in a plan view. With such a configuration, oil film breakdown can be suppressed and friction can be stabilized. Multiple laminated sections may include those of different sizes in a plan view. (5) Multiple layers may be arranged in a square grid or a face-centered square grid, in addition to a hexagonal grid. Similarly, in the case of a concave texture, multiple recesses may be arranged in a hexagonal grid, a square grid or a face-centered square grid. (6) The frictional properties improved by the texture are not limited to a reduction in the coefficient of friction. Because the surface processing method for the sliding member of this embodiment offers a high degree of freedom in the shape of the texture, it is also effective in improving frictional properties other than a reduction in the coefficient of friction. Depending on the performance required of the sliding member, the frictional properties improved by the texture may include reducing the range of fluctuation in the coefficient of friction, maintaining a predetermined coefficient of friction over a long period of time, or increasing the coefficient of friction. [Examples]

[0040] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to these examples.

[0041] 1. Preparation of the powder Graphite powder was used as the material for the first component, and tin powder was used as the material for the second component. The graphite powder and tin powder were mixed so that the graphite content was 2% by mass relative to the total powder to obtain the example powder (Sn-C 2%). Figure 6 shows the image of the example powder observed with a scanning electron microscope (SEM).

[0042] 2. Laser processing (1) Example 1 Surface processing of a sliding member was performed using powder (Sn-C 2%). A substrate made of oxygen-free copper was prepared as the base material for the sliding member. Grooves with a depth of approximately 60 μm were formed on the surface of the substrate. The powder was evenly sprinkled on the surface of the prepared substrate. Laser processing was performed on the surface of the substrate with the powder on it in a dot-like texture pattern. The diameter of each dot was 1 mm. A CO2 laser processing machine was used for laser processing. The laser processing conditions were 70% intensity (21 W), speed 5 mm / s, and 2 irradiations. Figure 7 shows an observation image of the laminated portion of Example 1 as observed under a microscope.

[0043] Laser processing revealed that tin had melted, forming a layered structure that appeared black. The tin had also been observed to bond graphite to the substrate. Multiple protrusions were formed within the layered structure.

[0044] (2) Example 2 The surface of the sliding member was processed using powder (Sn-C 2%). A bronze substrate was prepared as the base material for the sliding member. Grooves approximately 60 μm deep were formed on the surface of the substrate. The powder was evenly sprinkled on the surface of the prepared substrate. A dot-like texture pattern was laser-processed onto the surface of the substrate on which the powder was placed. The diameter of each dot was 1 mm. The same CO2 laser processing machine as in Example 1 was used for laser processing. The laser processing conditions were 70% intensity (21W), 3 mm / s speed, and 5 irradiations. Figure 8 shows an observation image of the laminated portion of Example 2 as observed under a microscope.

[0045] Laser processing revealed that tin melted, forming a layered structure that appeared black. The tin was observed to be adhering graphite to the substrate. Multiple protrusions were formed in the layered structure. In Figure 8, the area enclosed by the white frame showed three protrusions arranged along the grooves of the substrate. Figure 9 is a graph showing the results of the analysis of the three protrusions in the area enclosed by the white frame. From this analysis, it was found that each of the three protrusions was raised by 20 μm-50 μm from its surroundings.

[0046] 3. Effects of the Examples This embodiment confirmed that a laminated portion can be formed on the sliding surface. The sliding surface having a texture formed by the laminated portion was confirmed to have low frictional resistance.

[0047] The present invention is not limited to the embodiments detailed above, and various modifications or changes are possible within the scope of the claims of this disclosure. [Explanation of Symbols]

[0048] 10,110…Sliding member, 10A…Sliding surface, 11…Base material, 20…Texture, 21…Recess, 22,122…Laminated portion, 23…Convex portion, 30,130…Powder, 40…Laser processing machine, 50…Mating material, 50A…Sliding surface

Claims

1. A step of placing a powder containing a component with a lower melting temperature than the substrate on the surface of the substrate, A surface processing method for a sliding member, comprising the step of locally heating the surface of the substrate by spot heating under conditions in which the substrate does not melt, thereby melting at least a portion of the powder.

2. The powder comprises a first component and a second component having a lower melting point than the first component. The surface processing method for a sliding member according to claim 1, wherein the second component is melted in the step of melting at least a portion of the powder.

3. A method for surface processing a sliding member according to claim 1 or claim 2, wherein a plurality of protrusions are formed on the locally heated portion in the step of melting at least a portion of the powder.

4. A sliding member processed by the method of claim 1 or claim 2, The sliding member has a stacked portion that forms a floating island shape and a recess provided surrounding the stacked portion, The laminated portion is a sliding member formed by melting at least a portion of the powder.

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