Manufacturing method of sliding bearing

Abstract

To provide a method for manufacturing a slide bearing comprising an excellent frictional wear characteristic and capable of being suitably used, for example, even under a non-lubrication condition or a high surface pressure condition.SOLUTION: A manufacturing method for a slide bearing comprises: (1) a step of mixing powder of a polytetrafluoroethylene resin and powder of an additive other than the polytetrafluoroethylene resin; (2) a step of compressing and firing the mixed powder obtained in the step (1); (3) a pulverization step of pulverizing a fired body obtained in the step (2); (4) a step of mixing a pulverized body obtained in the step (3) with a base resin; (5) a step of pelletizing a mixture obtained in the step (4); and (6) a step of performing molding using pellets obtained in the step (5).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a sliding bearing. [Background technology]

[0002] For example, sliding bearings are widely used as bearings that rotatably support a rotating body on a support shaft. Generally, sliding bearings are lighter, have a simpler structure, have fewer parts, and are less expensive than rolling bearings. For example, sliding bearings made of synthetic resin are manufactured by injection molding using pellets.

[0003] Conventionally, in order to improve the friction and wear characteristics of sliding bearings made of synthetic resins, various fillers have been mixed into the base resin. For example, a commonly known resin material is one in which polytetrafluoroethylene (PTFE) resin and other fillers are blended with polyamide resin. One known method for manufacturing such sliding bearings involves melt-kneading a mixture of the base resin and the raw materials for the fillers to produce pellets, and then molding the pellets (see, for example, Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 63-251448 [Patent Document 2] Japanese Patent Application Publication No. 7-41666 [Patent Document 3] Japanese Patent Application Laid-Open No. 2012-102189 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, synthetic resin sliding bearings have been used in a wide variety of environments, even under harsh conditions. While the friction and wear characteristics of sliding bearings have been improved by selecting a variety of fillers, there is a demand for further improvements in friction and wear characteristics due to demands for energy conservation and other factors. Similar demands exist for sliding bearings used in harsh conditions, such as high surface pressure (approximately 5 MPa), and for sliding bearings used without lubrication and at high surface pressure in environments where lubricating oil cannot be used.

[0006] The present invention was made in light of these circumstances, and has an object to provide a method for manufacturing a sliding bearing that has superior friction and wear characteristics to conventional sliding bearings made of synthetic resin, and that can be suitably used even under unlubricated conditions or high surface pressure conditions, for example. [Means for solving the problem]

[0007] The method for manufacturing a sliding bearing of the present invention is a method for manufacturing a sliding bearing, characterized in that it comprises the following steps: (1) mixing a powder of PTFE resin with a powder of an additive other than the PTFE resin; (2) compressing and sintering the mixed powder obtained in step (1) above; (3) pulverizing the sintered body obtained in step (2) above; (4) mixing the pulverized body obtained in step (3) above with a base resin; (5) pelletizing the mixture obtained in step (4) above; and (6) molding using the pellets obtained in step (5) above.

[0008] The pulverized body obtained in step (3) is characterized in that the additive particles have their entire or partial surfaces covered with the PTFE resin. Here, "covered with PTFE resin" refers to a state in which the additive particles are dispersed within a mass of PTFE resin or a state in which at least a portion of the surface of the additive particles is encapsulated in PTFE resin. This includes, for example, a state in which the additive particles are entirely enveloped in PTFE resin, and a state in which the additive particles are enveloped in PTFE resin so that a portion of their surface is exposed. Note that "covered with PTFE resin" does not include a state in which the additive particles and PTFE resin particles are simply adhered to each other. Here, the additive particles and PTFE resin particles refer to individual powder units (single powder particles) of the additive or PTFE resin, and do not specify the shape of the individual powders. For example, this concept includes shapes such as spherical, scaly, and fibrous.

[0009] The pulverized body obtained in the step (3) is characterized by having an average particle size of 100 μm to 200 μm.

[0010] In the step (1), the blending amount of the PTFE resin is greater than the blending amount of the additive, and the blending amount here is based on volume.

[0011] The additive other than the PTFE resin is at least one of graphite and coke.

[0012] The base resin is at least one synthetic resin selected from thermoplastic polyimide (PI) resin, polyether ketone (PEK) resin, polyphenylene sulfide (PPS) resin, polyamide-imide (PAI) resin, polyamide (PA) resin, polyethylene (PE) resin, and polyacetal (POM) resin, and the step (6) is a step of injection molding using the pellets. [Effects of the Invention]

[0013] Unlike conventional methods for manufacturing sliding bearings, the method for manufacturing a sliding bearing of the present invention includes the above steps (1) to (3). Specifically, when producing pellets for injection molding, rather than simultaneously mixing the base resin and various additives to produce pellets, specific additive components are mixed, molded, and sintered separately from the base resin, then pulverized. The resulting pulverized material is then mixed with the base resin to produce pellets. As a result, the PTFE resin encapsulates additive particles, which exist as larger particles than the individual additive particles. This reduces the additive's resistance to detachment and peeling during sliding, improving wear characteristics. Furthermore, for example, if a hard additive is included to improve the wear characteristics of a sliding bearing, direct sliding can damage the mating material or increase the coefficient of dynamic friction. However, by encasing the additive particles in PTFE resin, the frequency of direct contact between the additive and the mating material during sliding is reduced, minimizing damage to the mating material and reducing the coefficient of dynamic friction. This allows for the production of a sliding bearing with excellent friction and wear characteristics.

[0014] In the above step (1), the amount of PTFE resin blended is greater than the amount of additive blended, so when the powder is made into a pulverized body in the subsequent step (3), the PTFE resin easily disperses and encapsulates the additive particles.

[0015] The additive is at least one of graphite and coke, and therefore, depending on the required characteristics of the bearing, the graphite can further contribute to improving the friction characteristics, and the coke can further contribute to improving the wear characteristics. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a perspective view showing an example of a sliding bearing manufactured by the manufacturing method of the present invention. [Figure 2] FIG. 1 is a diagram showing a process flow of a manufacturing method of the present invention. [Figure 3] FIG. 1 is a manufacturing process diagram of the ram extrusion method. [Figure 4] FIG. 2 is a diagram showing the particle size distribution of the pulverized body. [Figure 5] FIG. 1 is a diagram showing an outline of a ring-on-disc type testing machine. [Figure 6] FIG. 1 is a diagram showing the results of friction and wear tests of Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0017] An example of a sliding bearing manufactured using the manufacturing method of the present invention is shown in Figure 1. The sliding bearing 1 shown in Figure 1 consists of a single cylindrical resin member. For example, a shaft (not shown) serving as a mating member is inserted into the inner periphery of sliding bearing 1, and this shaft is rotatably supported by sliding bearing 1. In this case, the inner periphery of sliding bearing 1 forms the sliding surface that slides against the mating member.

[0018] The sliding bearing 1 is a molded article of a resin composition, and contains a base resin, PTFE resin, and additives other than PTFE resin. In the sliding bearing 1, at least some of the additive particles are present with their surfaces entirely or partially covered by PTFE resin. As a result, the additive particles are present in the base resin in clumps larger than the PTFE resin and the additive raw materials, and this allows for improved friction and wear properties compared to when each raw material is present in the base resin alone.

[0019] The sliding bearing 1 is used as a radial sliding bearing that supports a rotating member such as a drive shaft in the radial direction, or as a thrust sliding bearing that supports a rotating member in the thrust direction.

[0020] The sliding bearing is not limited to a sliding bearing made of a single resin member as shown in FIG. 1 , but may be made by combining multiple members. For example, the sliding bearing may be a composite of a resin member and a metal member. In this case, the resin member is formed on at least the sliding surface that slides against the mating member. For example, the sliding bearing may be manufactured by insert molding the pellets described below onto the inner circumferential surface of a cylindrical metal member.

[0021] The manufacturing method of the present invention is a method for manufacturing the above-mentioned sliding bearing. The manufacturing method of the present invention for manufacturing a sliding bearing will be explained based on the flow diagram in Figure 2. As shown in Figure 2, this manufacturing method involves carrying out, in this order, (1) a powder mixing step, (2) a molding and sintering step, (3) a pulverizing step, (4) a mixing step, (5) a melt-mixing step, and (6) a molding step. Unlike conventional manufacturing methods, the manufacturing method of the present invention is characterized in that steps (1) to (3) are carried out before the (4) mixing step.

[0022] First, the various raw materials (base resin, PTFE resin, and additives other than PTFE resin) used in the production method of the present invention will be described.

[0023] The synthetic resin used as the base resin is not particularly limited, but it is preferable to use an injection-moldable synthetic resin. Examples of injection-moldable synthetic resins include thermoplastic PI resin, PEK resin, PPS resin, PAI resin, PA resin, PE resin, POM resin, and injection-moldable fluororesin. These resins may be used alone or in combination to form a polymer alloy.

[0024] Examples of PA resins include aliphatic polyamide resins such as polyamide 6 (PA6), polyamide 6-6 (PA66), polyamide 6-10 (PA610), polyamide 6-12 (PA612), polyamide 4-6 (PA46), polyamide 11 (PA11), and polyamide 12 (PA12), as well as aromatic polyamide resins with aromatic rings in the polymer backbone, such as polyamide 9T (PA9T), polyamide 6T (PA6T), and polymetaxylene adipamide (polyamide MXD-6). The numbers in each PA resin indicate the number of carbon atoms between amide bonds, and T represents a terephthalic acid residue.

[0025] PEK-based resins include polyetheretherketone (PEEK) resin, polyetherketone (PEK) resin, and polyetherketoneetherketoneketone (PEKEKK) resin.

[0026] PTFE resin is a solid lubricant that can improve the friction and wear characteristics of sliding bearings under dry conditions, for example. PTFE resin can be any of molding powders produced by suspension polymerization, fine powders produced by emulsion polymerization, and recycled PTFE. To stabilize fluidity, recycled PTFE is preferred because it is less likely to become fibrous due to shear during molding and to increase melt viscosity. Recycled PTFE refers to heat-treated (thermal history-added) powders and powders irradiated with gamma rays or electron beams. Examples include powders obtained by heat-treating molding powder or fine powder, powders obtained by further irradiating these powders with gamma rays or electron beams, powders obtained by crushing molding powder or fine powder compacts, powders obtained by subsequently irradiating with gamma rays or electron beams, and powders obtained by irradiating molding powder or fine powder with gamma rays or electron beams. Some types are further heat-treated after irradiation with gamma rays or electron beams. The 50% particle size of the PTFE resin used as the raw material is not particularly limited, but is preferably 10 μm to 50 μm in order to uniformly mix with additives other than the PTFE resin (hereinafter sometimes simply referred to as additives).

[0027] Any additive other than PTFE resin can be used without particular restrictions, as long as it is particulate and contributes to reducing friction and improving the wear resistance of the sliding bearing. Examples of additives include graphite, coke, calcium phosphate, calcium sulfate, molybdenum disulfide, tungsten disulfide, spherical silica, bronze powder, mica, talc, calcium carbonate, boron nitride, whiskers (calcium carbonate, potassium titanate, etc.), carbon fiber, and glass fiber. These may be used alone or in combination of two or more. The melting point of the additive is preferably higher than the melting point of PTFE resin (327°C).

[0028] The 50% particle size of the additives used in the raw material (when there are two or more additives, each 50% particle size) is not particularly limited, but is preferably 3 μm to 50 μm, more preferably 10 μm to 30 μm. The 50% particle size of the additives is preferably smaller than the 50% particle size of the PTFE resin.

[0029] The additive is preferably at least one of graphite and coke. Graphite is a solid lubricant that can improve the friction and wear characteristics of a sliding bearing under dry conditions, for example. Either natural graphite or artificial graphite may be used as the graphite. Graphite particles may be shaped like flakes, granules, or spheres, and any of these may be used. Coke can also improve the wear resistance of a sliding bearing under dry conditions, for example.

[0030] The 50% particle size (D 50 ) is the particle size at which the volume-based cumulative value reaches 50% when the particle size distribution is considered as a cumulative distribution, and can be measured, for example, using a particle size distribution measuring device that uses laser light scattering.

[0031] Each step of the manufacturing method of the present invention will be described below.

[0032] (1) Powder mixing process This step involves mixing powder of PTFE resin with powder of additives other than PTFE resin. The amounts of PTFE resin and additives (if two or more additives are used, the total amount; the same applies below) are not particularly limited, but from the viewpoint of making it easier to cover the surfaces of additive particles, it is preferable that the amount of PTFE resin is greater than the amount of additives. The compounding ratio of additive to PTFE resin is preferably (1:1.2) to (1:5), and more preferably (1:2) to (1:4).

[0033] The mixing method is not particularly limited, and for example, dry mixing can be carried out using a Henschel mixer, a ball mixer, a ribbon blender, a Loedige mixer, an Ultra Henschel mixer, or the like.

[0034] (2) Forming and firing process This step involves compressing and firing the mixed powder obtained in step (1) above. For example, the ram extrusion method is used in this step. This method involves continuously filling, compressing, firing, and cooling the mixed powder within a cylinder. An example of the ram extrusion method is shown in Figure 3. As shown in Figure 3, a ram extruder 2 has a hopper 3, a ram 4, and a single cylinder 5 having a filling section 5a, a firing section 5b, and a cooling section 5c. Mixed powder 6 is introduced into the cylinder from the hopper 3 of the ram extruder 2, compressed by the ram 4, fired as it moves within the cylinder, and finally cooled and extruded from the tip of the cylinder. This produces a fired body (sintered body) 7.

[0035] The molding temperature in the ram extrusion method is set to a temperature higher than the melting point of the PTFE resin (327°C), for example, at 330°C to 400°C. The molding speed is set to, for example, 0.5 mm / h to 5 mm / h. In FIG. 3, the PTFE resin powder contained in the mixed powder 6 moves inside the cylinder while gradually melting, and a sintered body of the PTFE resin composition in which the additive is dispersed is obtained. The molten PTFE resin adheres to the additive particles, enveloping at least a portion of each particle.

[0036] The step (2) is not limited to the ram extrusion method described above, and may be carried out by a method in which molding and sintering are performed in stages. For example, the mixed powder may be filled into a mold and compression-molded, and then the molded body may be removed from the mold and sintered in a sintering furnace to obtain a sintered body. In this case, the sintering temperature is set to a temperature higher than the melting point of the PTFE resin (327°C), for example, 330°C to 400°C.

[0037] (3) Crushing process This step is a step of pulverizing the fired body obtained in the above step (2). For pulverization, for example, a pulverizer such as a cutter mill, a hammer mill, a pin mill, or a jet mill can be used, or an appropriate combination of these may be used.

[0038] In step (3), the pulverized material after pulverization may be sieved. A sieve of a desired mesh size can be used for sieving. For example, it is preferable to sieve particles that pass through a 60-mesh sieve (openings of 250 μm). Furthermore, it is preferable that the pulverized material after step (3) has an average particle size of 100 μm to 200 μm as determined by sieving. A sonic vibration sieving measuring device can be used to measure this average particle size.

[0039] (4)Mixing process This step involves mixing the pulverized material obtained in step (3) with a base resin. The compounding ratio of the base resin to the pulverized material is, for example, 1:2 to 4:1. The mixing method is not particularly limited, and the same method as in step (1) can be used.

[0040] In this step, some of the additives described above may be mixed in. Also, additives other than the additives described above may be mixed in. Examples of such additives include pigments such as iron oxide, titanium oxide, and carbon black.

[0041] (5) Melt mixing process This step is a step of pelletizing the mixture obtained in the above step (4). Specifically, the mixture is melt-kneaded in a melt extruder such as a twin-screw extruder to obtain pellets. In addition, additives other than the PTFE resin and the above-mentioned additives may be added by adopting a side feed when melt-kneading in a twin-screw extruder or the like.

[0042] (6) Molding process This step involves molding the pellets obtained in step (5) above into a desired shape. The molding method can be injection molding or extrusion molding. For example, injection molding is performed as follows: The pellets are loaded into the hopper of an injection molding machine, and then introduced from the hopper into a cylinder. The pellets are then heated and melted by a heater within the cylinder, while being pushed by a screw, passing through a metering section and filling the nozzle with molten resin for one shot of a molded product. Molten resin is then injected from this nozzle through a gate to fill a cavity of the desired shape, thereby molding the molded product.

[0043] After the molding process, machining such as polishing is carried out as necessary to produce a sliding bearing.

[0044] With regard to the resin composition of the sliding bearing, the base resin contained in the sliding bearing preferably accounts for 40% to 90% by volume, and more preferably 50% to 80% by volume, of the entire resin composition. Furthermore, the pulverized bodies contained in the sliding bearing preferably account for 10% to 60% by volume, and more preferably 20% to 50% by volume, of the entire resin composition. Furthermore, it is preferable that the amount of PTFE resin blended into the pulverized bodies be greater than the amount of additives blended into the pulverized bodies.

[0045] The sliding bearings produced by the production method of the present invention are used, for example, as sliding bearings for automobile parts, electronic and electrical equipment parts, machine parts, office equipment parts, etc.

[0046] There are no particular restrictions on the conditions under which sliding bearings can be used, but because they have excellent friction and wear properties and can be used under harsh conditions, they are suitable for, for example, non-lubricated conditions (dry conditions) without the use of a lubricant, and for high surface pressure conditions. Examples of high surface pressure conditions include surface pressures of 3 MPa to 10 MPa and surface pressures of 5 MPa to 10 MPa. [Example]

[0047] Test pieces for friction and wear tests of Examples and Comparative Examples were prepared according to the following procedure. The raw materials used were PA12 resin, PTFE resin (50% particle size: 40 μm), coke (50% particle size: 20 μm), and graphite (50% particle size: 20 μm). The PTFE resin used was a calcined product. In this test example, coke and graphite were used as additives.

[0048] Example (1) PTFE resin powder was mixed with coke and graphite to obtain a mixed powder. (2) The mixed powder was molded by ram extrusion (molding temperature: 360°C to 390°C, molding speed: 0.8mm / h to 1.6mm / h) and fired to obtain a fired body (sintered body). (3) The fired material was coarsely pulverized (particle size: about 1 mm) using a cutter mill and finely pulverized (particle size: about 200 μm) using a hammer mill to obtain a pulverized material, which was then classified using a 60 mesh sieve (opening: 250 μm). (4) The classified pulverized material was mixed with PA12 resin. (5) The mixture was melt-mixed to obtain pellets. (6) The pellets were injection molded to prepare a molding material, which was then machined to prepare a cylindrical test piece. The dimensions of this test piece were an inner diameter of 17 mm, an outer diameter of 21 mm, and a height of 4 mm. The inner and outer diameters indicate the dimensions of the sliding part.

[0049] Figure 4 shows the particle size distribution of the pulverized material after 60-mesh classification in steps (1) to (3). The particle size distribution in Figure 4 shows the results of particle size distribution measurement using eight different mesh sizes: 38 μm, 53 μm, 75 μm, 106 μm, 150 μm, 212 μm, 300 μm, and 425 μm. The peak diameter of the particle size distribution of the pulverized material was significantly larger than the 50% particle diameter of each of the raw materials: PTFE resin, coke, and graphite. The average particle diameter of the pulverized material after 60-mesh classification, as measured by the sieving method, was 100 μm to 200 μm.

[0050] Comparative Example (A) PTFE resin powder, coke, graphite, and PA12 resin were mixed in one step. (B) The mixture was melt-mixed to obtain pellets. (C) The obtained pellets were used to prepare a molding material by injection molding, and a cylindrical test piece of the same dimensions as in the example was prepared by machining.

[0051] The compositions of the test pieces of the examples and comparative examples are shown in the following Table 1. As shown in Table 1, each test piece consists only of a base resin, a PTFE resin, coke, and graphite.

[0052] <Friction and wear test> The dynamic friction coefficient was measured using a ring-on-disk type testing machine using test pieces from the examples and comparative examples. The amount of wear was calculated from the dimensional changes before and after the test. An overview of the ring-on-disk type testing machine is shown in Figure 5. The ring-on-disk type testing machine is a testing device that applies a pressing force to a fixed test piece 8 and rotates a mating material 9 under specified conditions to measure the dynamic friction coefficient and amount of wear. Reference numeral 10 denotes a load cell.

[0053] The conditions for the ring-on-disc test are as follows: Surface pressure: 5MPa Speed:5.28m / min Atmosphere: Dry Temperature: normal temperature Exam time: 50 hours Number of tests: Example (n=1), Comparative Example (n=2) Counterpart material: SUS304 Dimensions: φ33 x φ6 x 6 mm (turned, surface roughness 0.5 μmRa)

[0054] The changes in the dynamic friction coefficient in the ring-on-disk test for the examples and comparative examples are shown in Figure 6. Table 1 also shows the amount of wear over 50 hours calculated from the dimensional change of each test piece before and after the test.

[0055] [Table 1]

[0056] As shown in FIG. 6, the coefficient of dynamic friction after 50 hours was reduced by approximately 30% in the example compared to the comparative example. Furthermore, as shown in Table 1, the wear amount of the test specimens of the examples was reduced to about 1 / 3 or less compared to the wear amount of the test specimens of the comparative examples.

[0057] From the above, it can be seen that the sliding bearing produced by the method of the example was able to reduce the dynamic friction coefficient and wear amount compared to a sliding bearing produced by a conventional method with the same raw material composition. [Industrial Applicability]

[0058] A sliding bearing produced by the manufacturing method of the present invention has excellent friction and wear properties and can be suitably used, for example, even under unlubricated conditions or high surface pressure conditions, and therefore can be widely used as a manufacturing method for sliding bearings. [Explanation of symbols]

[0059] 1. Plain bearing 2 Ram extruder 3 Hopper 4. Ram 5 cylinders 6 Mixed powder 7. Fired body 8 Test pieces 9 Counterpart 10 load cells

Claims

1. A method for manufacturing a sliding bearing, comprising: (1) mixing a powder of polytetrafluoroethylene resin with a powder of an additive other than the polytetrafluoroethylene resin; (2) compressing and firing the mixed powder obtained in the step (1); (3) a pulverization step of pulverizing the fired body obtained in the step (2); (4) mixing the pulverized material obtained in the step (3) with a base resin; (5) pelletizing the mixture obtained in the step (4); (6) a step of molding the pellets obtained in the step (5); Equipped with a method for producing a sliding bearing, wherein in the pulverized body obtained in step (3), the additive has a surface that is entirely or partially covered with the polytetrafluoroethylene resin.

2. The method for producing a sliding bearing according to claim 1, characterized in that the pulverized bodies obtained in step (3) have an average particle size of 100 μm to 200 μm.

3. 3. The method for producing a sliding bearing according to claim 1 or claim 2, characterized in that in step (1), the blended amount of the polytetrafluoroethylene resin is greater than the blended amount of the additive.

4. The method for manufacturing a sliding bearing according to any one of claims 1 to 3, characterized in that the additive is at least one of graphite and coke.

5. the base resin is at least one synthetic resin selected from the group consisting of thermoplastic polyimide resins, polyether ketone resins, polyphenylene sulfide resins, polyamide-imide resins, polyamide resins, polyethylene resins, and polyacetal resins; The method for manufacturing a sliding bearing according to any one of claims 1 to 4, characterized in that step (6) is a step of injection molding using the pellets.

6. A method for manufacturing a sliding bearing, comprising: (1) mixing a powder of polytetrafluoroethylene resin with a powder of an additive other than the polytetrafluoroethylene resin; (2) compressing and firing the mixed powder obtained in the step (1); (3) a pulverization step of pulverizing the fired body obtained in the step (2); (4) mixing the pulverized material obtained in the step (3) with a base resin; (5) pelletizing the mixture obtained in the step (4); (6) a step of molding the pellets obtained in the step (5); Equipped with A method for producing a sliding bearing, wherein the additive is at least one of graphite and coke.

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