Graphite bearing and method of manufacturing the same

Abstract

The graphite bearing includes: 78 mass% or more and 98 mass% or less of carbon including a carbon component in spheroidal graphite and an uncarbonized resin, 12 mass% or less and 2 mass% or more of a volatile component in the resin, and 10 mass% or less and 0 mass% or more of a component other than the carbon and the volatile component. Further, a total of the carbon, the volatile component, and the component other than the carbon and the volatile component is set to 100 mass%. The graphite bearing can be manufactured by net or near net shape, and does not require a resin impregnation and a metal impregnation or the like. The graphite bearing has less cracks when pressed into a housing, and has high radial strength.

Description

Technical Field

[0001] This invention relates to graphite bearings and their manufacturing methods. Background Technology

[0002] The common manufacturing method for graphite bearings involves impregnating a graphite mold body with resin under reduced pressure for an extended period, then cutting the graphite into the required shape and machining it into the bearing shape. Resin impregnation is necessary to improve the strength of graphite bearings; without it, they may be unable to support radial loads, for example, due to insufficient radial strength (also known as radial compressive strength). This method is inefficient due to its time and labor requirements, and in particular, it suffers from the following problems:

[0003] 1) Resin impregnation requires a long time.

[0004] 2) Due to the inability to uniformly impregnate the resin into the molded body, material loss increases, and

[0005] 3) The bearing needs to be cut out from the molded body and machined into the shape of the bearing.

[0006] The graphite bearing is pressed into a hole in the housing. The inner diameter of the hole in the housing is smaller than the outer diameter of the graphite bearing. The graphite bearing is assembled in the housing while being compressed. At this time, if the strength of the graphite bearing is insufficient, cracks will occur, and the cracks will easily propagate along the radial direction of the graphite bearing.

[0007] The related prior art is shown. In Patent Document 1 (JPS52-38516A), graphite, carbon black, and a binder of tar and pitch are mixed and sintered at 1100–1200°C into shapes such as bearings. The strength of the bearing is then improved by impregnation with furan resin.

[0008] Patent document 2 (JP4575911B) discloses, as a prior example, the manufacture of an isotropic graphite substrate by CIP molding (cold isostatic pressing), followed by cutting out the substrate and machining it to form a bearing (

[0052] -

[0054] ). In the embodiments, it is disclosed that a mixture of graphite and coke, and a binder such as tar or pitch, is molded. It is then sintered at 1000°C for 0.5 months, followed by infiltration of molten metal in a vacuum furnace (

[0039] -

[0049] ). While machining is easier in these embodiments, long-term sintering and metal infiltration are required.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: JPS52-38516A

[0012] Patent Document 2: JP4575911B Summary of the Invention

[0013] The problem that the invention aims to solve

[0014] The objective of this invention is to provide a graphite bearing and a method for manufacturing the same.

[0015] 1) It can be manufactured using net shape or near net shape methods, thus eliminating the need for resin impregnation and metal impregnation processes.

[0016] 2) Fewer cracks and other faults occur when the casing is pressed in, and

[0017] 3) The radial strength is close to the axial strength.

[0018] Methods for solving problems

[0019] The graphite bearing of the present invention comprises: 78% by mass and 98% by mass of carbon, which includes carbon components comprising spherical graphite and uncarbonized resin; 12% by mass and 2% by mass of volatile components in the resin; and 10% by mass and 0% by mass of components other than carbon and volatile components. Furthermore, the total of carbon, volatile components, and components other than carbon and volatile components is 100% by mass. Preferably, the carbon is primarily composed of spherical graphite, for example, 60% by mass or more of the carbon is spherical graphite. The carbon comprises spherical graphite and carbon components in uncarbonized resin, and may also include amorphous carbon such as coke. Furthermore, in this specification, "uncarbonized" includes everything from completely uncarbonized to incompletely carbonized. In addition, it is preferable to set the volatile component to 12% by mass and 3% by mass or more, and particularly preferably to 10% by mass and 5% by mass or more.

[0020] The method for manufacturing a graphite bearing according to the present invention is characterized by comprising the following steps: preparing a mixture containing 60% to 90% by mass of carbon containing spherical graphite and excluding resin, 30% to 10% by mass of resin, and 10% to 0% by mass of components other than carbon and volatile components of the graphite bearing; extruding the mixture using a mold to form a bearing matrix; and sintering the bearing matrix at a temperature where the resin is not completely carbonized, such that the carbon composition comprising spherical graphite and carbon in the resin is 78% to 98% by mass, the volatile components in the resin are 12% to 2% by mass, and the components other than carbon and volatile components are 10% to 0% by mass. Furthermore, the description of graphite bearings in this specification is directly applicable to the method for manufacturing graphite bearings.

[0021] The graphite bearing of the present invention can be manufactured by extrusion molding, eliminating the need for cutting from graphite blocks and machining the bearing shape. Furthermore, the dimensional changes caused by sintering are minimal, thus allowing for the production of sintered bodies close to the target size (near-net-shape to net-shape sintered bodies) through extrusion molding and sintering. Moreover, the present invention includes steps such as sintering after extrusion molding to a size slightly larger than the target size, and grinding towards the target size. In addition, the present invention eliminates the need for resin impregnation, metal impregnation, or other similar treatments. In other words, the present invention enables the efficient manufacture of graphite bearings.

[0022] For the graphite bearing of the present invention, the ratio of the strength in the pressing direction during extrusion molding (hereinafter referred to as "strength in the pressing direction") to the strength in the interlaminar direction during extrusion molding (hereinafter referred to as "strength in the interlaminar direction") is close to 1. The pressing direction is the same as the axial direction of the graphite bearing, and the interlaminar direction is perpendicular to the pressing direction and is the same as the radial direction in the graphite bearing. Furthermore, the strength in the pressing direction and the strength in the interlaminar direction are strengths measured by a three-point bending test using a plate-shaped specimen. In contrast, the axial strength and radial strength described later are compressive strengths measured according to the shape of the graphite bearing, and the shape of the specimen and the measurement method are different. Generally speaking, the strength in the pressing direction is higher than the strength in the interlaminar direction, but in the present invention, their ratio can be made close to 1. In addition, if the strength in the interlaminar direction is high, cracks and the like can be reduced when pressed into the housing. As described above, the present invention can provide a graphite bearing with fewer failures when pressed into the housing. In the present invention, the ratio of the strength in the pressing direction to the strength in the interlaminar direction is, for example, 1 or more and 2 or less, preferably 1 or more and 1.8 or less, and particularly preferably 1 or more and 1.6 or less.

[0023] Because the ratio of axial strength to radial strength of the graphite bearing of the present invention is close to 1 (radial strength is close to axial strength), the graphite bearing can support a large load in the radial direction.

[0024] Preferably, the uncarbonized resin is composed of both a thermoplastic resin and a thermosetting resin. Particularly preferred is that the thermoplastic resin is polyphenylene sulfide (PPS) and the thermosetting resin is a phenolic resin.

[0025] Preferably, the spherical graphite has an average particle size of 10 μm or more and 20 μm or less, and an aspect ratio of 2 or less. Preferably, it contains 88% by mass or more and 98% by mass of carbon comprising carbon components from spherical graphite and uncarbonized resin, and 12% by mass or less and 2% by mass of volatile components from the resin, with the total of carbon and volatile components being 100% by mass. That is, it does not contain any components other than carbon and volatile components. More preferably, it contains 60% by mass or more and 84% by mass of spherical graphite, 0% by mass or more and 22% by mass of amorphous carbon with an average particle size larger than that of spherical graphite, 8% by mass or more and 15% by mass of carbon components from uncarbonized resin, and 3% by mass or more and 12% by mass of the volatile components, with the total of spherical graphite, the amorphous carbon, the carbon components from the uncarbonized resin, and the volatile components being 100% by mass. Attached Figure Description

[0026] Figure 1 This is an electron microscope image of spherical graphite.

[0027] Figure 2 This is an electron microscope image of spherical graphite with an aspect ratio of 1.23.

[0028] Figure 3 This is an electron microscope image of spherical graphite with an aspect ratio of 1.95.

[0029] Figure 4 These are electron microscope images of the pressurized surface of flake graphite; the left image is a SEM image, and the right image is an EDX image.

[0030] Figure 5 These are electron microscope images of the pressurized surface of spherical graphite; the left image is a SEM image, and the right image is an EDX image.

[0031] Figure 6 This is a cross-sectional view of the graphite bearing in an embodiment.

[0032] Figure 7 This diagram schematically illustrates the occurrence of cracks in a graphite bearing when it is pressed into the housing. Detailed Implementation

[0033] The following illustrates the preferred embodiments for carrying out the invention. The invention is not limited to these embodiments, but is determined based on the claims, and those skilled in the art can modify the embodiments by adding well-known elements.

[0034] Example

[0035] Graphite bearing composition

[0036] The composition of graphite bearings is:

[0037] • Carbon (spherical graphite, carbon components in uncarbonized resin, and other carbons such as coke),

[0038] • Volatile components in resin, and

[0039] • Components other than carbon and volatiles. Components other than carbon and volatiles include solid lubricants such as tungsten disulfide, metals, and other elements besides carbon, and their content can be determined through elemental analysis. Other carbons include amorphous carbon such as coke, which is an aggregate with a larger average particle size compared to spherical graphite. Other carbons also include flake graphite.

[0040] Determination of volatile components

[0041] The volatile components in graphite bearings (hereinafter referred to as "bearings") are determined as follows: A sample of a specified weight is collected from the bearing, pulverized, and then passed through a thermogravimetric differential thermal analysis (TG-DTA) apparatus. The temperature is increased from room temperature to 900°C under a nitrogen flow. The weight at the beginning and end of the heating process is measured. The difference between these weights is divided by the weight at the beginning of the heating process, and the resulting value is taken as the concentration of volatile components in the bearing.

[0042] Determination methods for thermoplastic and thermosetting resins

[0043] If a sample collected from a bearing is analyzed using GCMS (Gas Chromatography-Mass Spectrometry), the decomposition products of the resin components can be detected. This allows for the analysis of the types of resin contained in the bearing.

[0044] spheroidal graphite

[0045] Spheroidal graphite is graphite with a shape that is close to a sphere, and is a term used in contrast to flake graphite and the like. Figures 1-3 The image shown is a scanning electron microscope (SEM) image of spherical graphite. In this invention, spherical graphite refers to graphite composed of graphite particles with an aspect ratio (ratio of the major axis to the minor axis of the particle) of 2 or less. Figure 2 , Figure 3 The thin lines represent the long and short axes of the graphite particles. Figure 2 The aspect ratio of the dimensions is 1.23. Figure 3 The value is 1.95.

[0046] Figure 4 The image shows a SEM image (left) and an EDX image (right: energy-dispersive X-ray analysis) of the pressurized surface of flake graphite. Figure 5The image shows a SEM image (left) and an EDX image (right) of the pressurized surface of spheroidal graphite. In the image of the pressurized surface, flake graphite forms a square shape, while spheroidal graphite forms an approximately spherical shape. Flake or spheroidal graphite can be identified using both SEM and EDX images. Figure 4 , Figure 5 The representative graphite particles were labeled.

[0047] Graphite shape, strength and dimensional stability of sintered bodies

[0048] The strength and dimensional stability of the sintered bodies were evaluated using spherical and flake graphite. In 75 parts by weight of spherical graphite with an average particle size (D50) of 17 μm (Example), or 75 parts by weight of flake graphite with an average particle size (D50) of 70 μm (Comparative Example), 8 parts by weight of amorphous carbon (coke), 12 parts by weight of PPS resin, and 5 parts by weight of phenolic resin were mixed, each totaling 100 parts by weight. Each material was used as a test specimen for strength in the compressive direction and interlaminar direction, and a 20 mm × 10 mm × 5 mm cuboid was extruded. For the test specimen for strength in the compressive direction, the thickness direction was considered the compressive direction. For the test specimen for strength in the interlaminar direction, the long side with a length of 20 mm was considered the compressive direction.

[0049] The test samples of the Examples and Comparative Examples were sintered at 400°C. The sintering temperature was above the melting point of the thermoplastic resin. Furthermore, when sintering was carried out at a temperature slightly higher than the melting point, the resin hardly carbonized. In addition, the sintering temperature was set, for example, to below 500°C, a temperature at which neither the thermosetting resin nor the thermoplastic resin was completely carbonized.

[0050] For the test specimens of the Examples and Comparative Examples, the compressive direction strength and interlaminar direction strength were measured as three-point flexural strength. Furthermore, the dimensional changes before and after sintering were measured. In the Examples, the compressive direction strength was 57.4 MPa and the interlaminar direction strength was 40.4 MPa, with a ratio of 1.4. In the Comparative Examples, the compressive direction strength was 82.7 MPa and the interlaminar direction strength was 31.2 MPa, with a ratio as large as 2.7. Regarding the dimensional reduction rate before and after sintering, in the Examples, it was 0.35% in the compressive direction and 0.3% in the interlaminar direction, indicating low anisotropy in dimensional change. In the Comparative Examples, it was 0.4% in the compressive direction and 0.25% in the interlaminar direction, indicating high anisotropy in dimensional change.

[0051] Example

[0052] The raw material powders were mixed in accordance with the compositions shown in Table 1 (Examples) and Table 2 (Comparative Examples). Furthermore, the average particle size (D50) of the spherical graphite was 17 μm, and the average particle size (D50) of the flake graphite was 70 μm. Additionally, the other carbon was coke, which is amorphous carbon. The mixed powder was extruded into a bearing shape and sintered at 400°C. During sintering, the phenolic resin partially decomposed, causing the graphite particles to bond together, and the thermoplastic resin PPS melted and filled the gaps between the graphite particles. The strength of the sintered body was enhanced by the melting of the PPS resin. In the examples, the dimensional changes caused by sintering were approximately 0.3% in both the axial and radial directions, eliminating the need for grinding to adjust the bearing dimensions.

[0053] Figure 6 The shape of the graphite bearing 2 is shown. The bearing 2 is cylindrical with a hole 4 along its axial direction for accommodating a shaft (not shown). The outer diameter D of the bearing 2 is 8.9 mm, the diameter r of the hole 4 is 5.1 mm, the length L is 5.0 mm, and the upper and lower edges of the outer circumference are chamfered. Furthermore, the dimensions of the bearing 2 are arbitrary.

[0054] Figure 7 The diagram schematically illustrates the pressing of a graphite bearing 2 into a housing 6. The housing 6 is, for example, made of metal, and the bearing 2 is housed within a bore 8, through which a shaft (not shown) passes. The bearing 2 is pressed into the bore 8 while being compressed; during this process, cracks 11 may sometimes occur due to the stress acting within the bearing 2. Figure 7 As shown in the upper right, crack 11 mainly occurs in the interlayer direction (radial direction in the bearing) during extrusion molding.

[0055] For each graphite bearing in the examples and comparative examples, the strength in the compressive direction and interlaminar strength, axial strength and radial strength, volatile content, and the frequency of crack occurrence during indentation were measured. These data are shown in Table 1 (Examples) and Table 2 (Comparative Examples). Furthermore, the radial strength of bearing 2 was measured using the radial strength test method specified in (JIS) Z2507. Axial strength is the fracture strength when a compressive load is applied axially. Additionally, since the main component is graphite, lubricity was not an issue in either the examples or the comparative examples.

[0056] Table 1

[0057]

[0058] *The dimensional change rate is only recorded for the value in Example 1; the values ​​for other examples are similar.

[0059] Table 2

[0060]

[0061] *The rate of change in size is only recorded for Comparative Example 1.

[0062] In the embodiments, the interlaminar strength is high, the ratio of strength in the compressive direction to interlaminar strength is less than 1.6 and close to 1, and there are fewer cracks during indentation. In contrast, in Comparative Examples 1 and 2, the interlaminar strength is low, the ratio of strength in the compressive direction to interlaminar strength exceeds 2, and there are more cracks during indentation. Furthermore, the radial strength is high in the embodiments, and the bearing can support a large load in the radial direction, but the radial strength is low in Comparative Examples 1 and 2.

[0063] Although Comparative Example 3 used spherical graphite, its radial strength was low. This is because the volatile components were low, so the spherical graphite was not fully bonded by the thermosetting resin, or the gaps between the spherical graphite were not fully filled by the thermoplastic resin, thus it was inferred that it could not support loads in the radial direction.

[0064] Symbol Explanation

[0065] 2: Graphite bearings

[0066] 4: Hole

[0067] 6: Casing

[0068] 8, 10: Hole

[0069] 11: Crack

Claims

1. A graphite bearing comprising: 78 mass% or more and 98 mass% or less of carbon including carbon components in spheroidal graphite and uncarbonized resin, 12 mass% or less and 2 mass% or more of volatile components in the resin, and 10 mass% or less and 0 mass% or more of components other than carbon and volatile components, wherein the total of carbon, volatile components, and the components other than carbon and volatile components is 100 mass%, the average particle diameter of the spheroidal graphite is 10 μm or more and 20 μm or less, the aspect ratio is 2 or less, and the ratio of the axial compressive strength to the radial strength is 1 or more and 2 or less, the graphite bearing is cylindrical in shape, the uncarbonized resin is composed of both a thermoplastic resin which is polyphenylene sulfide (PPS) and a thermosetting resin which is phenol resin.

2. The graphite bearing of claim 1, wherein, it contains 12 mass% or less and 3 mass% or more of the volatile components.

3. The graphite bearing of claim 1, wherein, it contains: 88 mass% or more and 98 mass% or less of carbon including carbon components in spheroidal graphite and uncarbonized resin, and 12 mass% or less and 2 mass% or more of the volatile components, the total of carbon and the volatile components is 100 mass%.

4. The graphite bearing of claim 3, wherein it contains: 60 mass% or more and 84 mass% or less of spheroidal graphite, 0 mass% or more and 22 mass% or less of amorphous carbon having a larger average particle diameter than spheroidal graphite, 8 mass% or more and 15 mass% or less of carbon components in uncarbonized resin, and 3 mass% or more and 12 mass% or less of the volatile components, the total of spheroidal graphite, the amorphous carbon, carbon components in uncarbonized resin, and the volatile components is 100 mass%.

5. A method of manufacturing a graphite bearing, characterized by, it is manufactured by performing the following steps to manufacture a graphite bearing having a ratio of the axial compressive strength to the radial strength of 1 or more and 2 or less: a step of preparing a mixture containing 60 mass% or more and 90 mass% or less of carbon containing spheroidal graphite having an average particle diameter of 10 μm or more and 20 μm or less and no resin, 30 mass% or less and 10 mass% or more of resin composed of both a thermoplastic resin and a thermosetting resin, and 10 mass% or less and 0 mass% or more of graphite bearing components other than carbon and volatile components; a step of forming a cylindrical bearing precursor by extrusion molding of the mixture using a mold; and a step of sintering the bearing precursor at a temperature at which the resin is not completely carbonized in a manner such that the carbon including carbon components in spheroidal graphite and resin is 78 mass% or more and 98 mass% or less, the volatile components in the resin are 12 mass% or less and 2 mass% or more, and the graphite bearing components other than carbon and volatile components are 10 mass% or less and 0 mass% or more, the thermoplastic resin is polyphenylene sulfide (PPS) and the thermosetting resin is phenol resin.

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