fired bearing

Abstract

A sintered bearing has bearing surface portions provided at two places separated in an axial direction of an inner peripheral surface, and a relief portion having an inner diameter larger than those of the bearing surface portions between the bearing surface portions, the sintered bearing containing metal powder and resin powder. The sintered bearing has a structure in which the metal powder is bonded by the resin powder interposed between the metal powder, and the resin powder is an epoxy resin powder containing a latent curing agent of thermosetting property.

Description

Technical Field

[0001] This invention relates to sintered bearings. Background Technology

[0002] As bearing components for small motors (small motors mainly refer to motors with small output, which are assembled in various products such as air conditioners, microwave ovens, computers, acoustic equipment, industrial equipment, and automobiles), sintered bearings are mostly used.

[0003] These sintered bearings are typically sintered bearings made of porous materials. The sintered bearings are used with lubricating oil contained in their internal pores. In this case, an oil film forms at the sliding portion with the shaft as the bearing moves relative to it, and this oil film supports the shaft.

[0004] Sintered bearings, as inexpensive and highly reliable bearings, are widely used in fan motors for home appliances, automobiles, and office automation (OA) equipment. Specifically, fan motors are used in cooling fans inside computers, televisions, and other home appliances; in refrigerators for circulation and cooling; in batteries for cooling; and in automobiles for stimulating temperature sensors. Demand for these motors is increasing year by year.

[0005] However, the frictional resistance of the sliding surface of a motor with low driving torque can easily affect its characteristics. At high speeds and in low-temperature environments, insufficient oil circulation and supply can hinder smooth operation. Furthermore, it can easily lead to a decrease in motor speed and an increase in current.

[0006] Therefore, conventionally, as described in Patent Documents 1 and 2, a clearance portion for reducing the rotational load on the motor is provided at the center of the bearing's inner diameter. That is, the bearing (sintered bearing) in Patent Document 1 has bearing faces provided at two axially separated locations along the inner circumferential surface (inner diameter surface), and a clearance portion with an inner diameter set larger than the inner diameter of the bearing faces is provided between the bearing faces.

[0007] In this case, a precision pressing process is performed after the sintering process to form the clearance section. Here, precision pressing refers to the process of re-pressing the raw material obtained through sintering into a mold to achieve high-precision dimensions and shape. That is, if the raw material is placed into the mold and pressure is applied by upper and lower punches, the raw material is pressed against the die and punches, and the deformation and dimensions of the raw material are corrected. Furthermore, there are two methods of precision pressing: positive precision pressing and negative precision pressing. Positive precision pressing involves pre-making the raw material larger than the final product size and pressing it into the mold during precision pressing, where it rubs against the die and core to improve precision. Negative precision pressing involves pre-making the raw material smaller than the final product size and compressing it within the mold, pressing it against the mold surface to improve precision.

[0008] Furthermore, in the structure described in Patent Document 1, multiple recesses (recesses) are provided on the bearing surfaces formed at both ends along the axial direction. By providing these recesses, the sliding area of ​​the bearing surface can be reduced, thereby lowering frictional resistance. Additionally, it is shown that the lubricant contained within each recess is drawn out between the bearing surface and the rotating shaft during rotation, thus reducing the coefficient of friction of the bearing surface.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent No. 6253134

[0012] Patent Document 2: Japanese Patent Application Publication No. 2010-31909 Summary of the Invention

[0013] The problem that the invention aims to solve

[0014] In conventional sintered bearings with clearance portions, as described above, a precision pressing process is performed after the sintering process to form the clearance portion by reducing the outer diameter. Therefore, the boundary between the sliding portion with the sliding surface and the clearance portion is formed smoothly.

[0015] Figure 12 The diagram shows a sintered bearing that has undergone a precision pressing process after the sintering process. In this way, if the precision pressing process is performed, a pair of bearing surfaces 51 and 52 are formed in the inner diameter portion of the bearing 50, a clearance portion 53 is formed between the bearing surfaces 51 and 52, and a conical surface 54 is formed between the inner diameter surface 53a of the clearance portion 53 and the bearing surface 52a of the bearing surface 52.

[0016] If the conical surface 54 is formed in this way, the sliding area may change (become larger) compared to the initial state due to wear of the sliding surfaces (bearing surfaces 51a and 52a, which are the inner diameter surfaces of bearing surfaces 51 and 52). If the sliding area changes in this way, the bearing characteristics may change.

[0017] Furthermore, because the outer diameter is reduced during the precision pressing process after forming and sintering, causing the inner diameter to shrink, the sintered body is easily affected by the overall length and outer diameter dimensions. Therefore, the dimension (axial dimension) L5 of the bearing surface 53a will deviate. In this case, the maximum possible deviation is approximately ±0.3 mm.

[0018] Typically, in the sintering process, hydrogen, nitrogen, or a mixture thereof are required as heat treatment gases at high temperatures (around 700℃ to 900℃). Therefore, improvements are desired from an energy consumption perspective.

[0019] Furthermore, in cases where pits are formed as described in Patent Document 1, plastic processing methods such as shot peening, rolling, and embossing are disclosed in Patent Document 1 as methods for forming pits. Such processing requires additional processing equipment and time, and also presents problems in terms of productivity and cost, such as the manufacture of tools for plastic processing with protrusions.

[0020] Therefore, this application provides a sintering bearing that can reduce the contact area with the rotating shaft to achieve stable rotation, suppress the current value to a low level, increase the rotation speed, and eliminate the need for a sintering furnace for high-temperature holding, a large amount of electrical energy, and does not require hydrogen, nitrogen, or a mixture thereof as the processing gas.

[0021] Methods for solving problems

[0022] The present invention is a sintered bearing having bearing faces provided at two axially separated locations on its inner circumferential surface, and a clearance portion between the bearing faces having an inner diameter set larger than that of the bearing faces. The sintered bearing contains metal powder and resin powder, wherein the sintered bearing has a structure formed by bonding the metal powder with the resin powder sandwiched between the metal powder, and the resin powder is an epoxy resin powder containing a thermosetting latent curing agent.

[0023] According to the sintered bearing of the present invention, by compressing a mixed powder mainly composed of iron powder and resin, the strength of the compressed powder body can be improved and the inner diameter springback rate can be increased by utilizing the adhesiveness and flexibility of the resin. Furthermore, when the core pin is pulled out of the compressed powder body during powder molding by increasing the springback rate, the undercut portion formed by the unevenness of the bearing inner diameter surface, which is obtained by transfer forming on the unevenness of the core pin, can be forcibly pulled out. Thus, a rectangular clearance portion can be easily formed in the center of the bearing inner diameter.

[0024] The aforementioned sintered bearing is cured in an atmospheric atmosphere at approximately 200°C (here, approximately 200°C refers to 150°C to 250°C). Therefore, it eliminates the need for a sintering furnace required in conventional sintering processes to maintain high temperatures of 700°C to 900°C, and it eliminates the need for hydrogen, nitrogen, or other similar gases as the processing gas. Furthermore, the step provided on the core pin is directly transferred during molding, forming the step at the boundary between the sliding portion and the intermediate clearance portion. In other words, in this invention, the boundary between the sliding portion and the clearance portion can be formed without precision pressing, making it less likely to form the conical surface that occurs between the sliding portion and the clearance portion during precision pressing. In addition, the bearing surface (the inner diameter surface of the bearing surface) is formed through in-mold straightening during compression molding, and because it is sintered at a low temperature, dimensional changes can be reduced, and deviations in the axial length of the sliding surface can be minimized. (For example, this deviation can be set to approximately ±0.1 mm.) Furthermore, if a fine pressing process is performed after the sintering process, a clearance portion is formed by narrowing, thus causing an axial length deviation in the bearing surface. However, in this invention, which does not perform a fine pressing process, a clearance portion is not formed by narrowing, thereby reducing the axial length deviation of the bearing surface. If the axial length deviation of the bearing surface can be reduced, the sliding area between the shaft component and the bearing surface becomes stable, and the bearing characteristics become stable.

[0025] Furthermore, the sintered bearing of the present invention, after physically pressing iron powder into contact with each other or with resin powder through compression molding, is then thermally cured by firing to form a cross-sectional structure in which the iron powder is bonded together. Therefore, by melting and softening the resin during curing, and by clamping and fixing the resin components at the contact points (neck) between the powders, it is strengthened and reinforced, resulting in a material strength that is suitable for use as a bearing with relatively low loads.

[0026] In the mixture of metal powder and resin powder, to improve resilience, it is preferable that the metal powder comprises 95wt% to 99wt%, with the remainder being resin powder. The metal powder in the mixture is iron powder, which can be set to be coarse powder with an average particle size of 50μm to 200μm. If the average particle size is less than 50μm, it is difficult to form a resin film on the surface of the iron powder, resulting in reduced material strength. If the average particle size exceeds 200μm, the powder particles are coarse, resulting in large pores, causing oil leakage, increasing the frequency of metal-to-metal contact between the bearing surface and the rotating shaft, and deteriorating motor characteristics.

[0027] By using coarse iron powder with an average particle size of 50 μm to 200 μm, large pores can be formed integrally. Here, large pores refer to pores with an average diameter of 10 μm or more. In addition, metal powder (iron powder) is surrounded by resin powder, and micropores (average diameter less than 10 μm) are formed in the surrounded portion.

[0028] The preferred iron powder is a sponge-like iron powder that has pores inside the powder and is able to retain lubricating oil in these pores. Here, sponge-like iron powder refers to all of the porous iron powder (such as sponge iron powder) containing a large number of pores produced by reducing oxidized iron powder such as iron oxide with a gaseous or solid reducing agent. Therefore, this sponge-like iron powder has tiny pores that extend into the interior of the powder.

[0029] However, through this design, the internal cavities formed by the coarse powder, namely the large pores (micropores), ensure smooth oil supply and reduce oil interruption. The micropores formed by the resin coating inhibit oil leakage and have an oil accumulation effect. The micropores inside the iron powder have an oil retention effect and prevent outflow.

[0030] The resin powder may be an epoxy resin powder containing a thermosetting latent curing agent. Since the resin powder needs to be thermosetting during the firing process, a thermosetting epoxy resin is preferred.

[0031] Preferably, the sintered bearing has a cross-sectional structure formed by fixing the iron powder particles by the adhesive force of the resin instead of sintering based on the mutual diffusion between iron powder particles.

[0032] The mixed powder can be compressed and molded within the mold, resulting in a springback rate of over 0.2% in the inner diameter of the compressed powder body. This configuration allows for stable removal of the core pin after compression molding.

[0033] Preferably, the inner diameter of the clearance portion is 0.1% to 0.3% larger than the inner diameter of the bearing face, and the cross-sectional shape of the clearance portion is rectangular. By setting it to 0.1% or more, the clearance portion can effectively function to reduce the contact area with the rotating shaft. Furthermore, by having a rectangular cross-sectional shape, even if the bearing face wears, the area of ​​the bearing face will not change, making it less likely to cause changes in bearing characteristics. By setting it to less than 0.3%, the inner diameter of the clearance portion will not become excessively larger than the inner diameter of the bearing face, effectively preventing damage to the inner diameter surface of the bearing face, i.e., the bearing face, when the mandrel is pulled out.

[0034] Preferably, the inner diameter surface opening ratio (surface opening ratio of the bearing surface) of the bearing face is 40% to 80%. Surface opening ratio refers to the area ratio of all openings on the bearing surface, including not only openings that do not communicate with the internal vents as described above, but also openings that do communicate with the internal vents. Thus, by increasing the surface opening ratio of the bearing surface, the contact area can be reduced, resulting in more stable rotation.

[0035] Alternatively, an enlarged diameter portion with an axially outward opening can be provided at the outer end edge of the bearing face. In this way, by providing the enlarged diameter portion, lubricating oil flows into the inner diameter surface of the bearing face, i.e., the sliding part between the bearing face and the rotating shaft, and oil supply to the sliding part can be stably provided.

[0036] Ideally, the inner surfaces of the bearing face, the clearance portion, and the enlarged diameter portion should have approximately equal surface opening ratios. This setting ensures well-balanced rotation. Here, "approximately equal" implies that there may be slight deviations due to design errors, manufacturing errors, assembly errors, etc. These deviations are included.

[0037] The axial length of each expanded section is preferably set within the range of 0.2 mm to 2.0 mm. When it is less than 0.2 mm, it is difficult to function as an oil retainer. If it exceeds 2.0 mm, the bearing surface of the bearing face becomes smaller, making it difficult to stably and reliably pivot the rotating shaft.

[0038] As a sintered bearing, it is preferably used as a bearing component in a motor. In this way, by using a bearing component for a motor, a high-quality motor (small motor) that can achieve stable rotation over a long period of time can be provided.

[0039] Invention Effects

[0040] In this invention, a sintered bearing is obtained that reduces the contact area with the rotating shaft, resulting in stable rotation; suppresses current values, increasing rotational speed; eliminates the need for a sintering furnace for high-temperature holding, large amounts of electrical energy, and eliminates the need for hydrogen, nitrogen, or mixtures thereof as the processing gas. Furthermore, it becomes a sintered bearing with excellent lubrication performance / sliding characteristics by reducing the frequency of oil cut-off and metal-to-metal contact with the rotating shaft. In particular, in motor bearings with an expanded diameter section, even during high-speed rotation or in low-temperature environments, oil circulation and supply function smoothly, improving oil cut-off and achieving good sliding. As a result, it can improve the reduction of motor speed and speed instability, thereby improving motor characteristics. Additionally, it can reduce the increase of current values, achieving a reduction in power consumption. Attached Figure Description

[0041] Figure 1 This is a simplified cross-sectional view of the sintered bearing of the present invention.

[0042] Figure 2 This is the manufacturing process of the sintered bearing of the present invention.

[0043] Figure 3A The diagram shows the compression forming process of the sintered bearing of the present invention, and is a front view showing the state in which the concave and convex portions of the core pin are transferred onto the pressed powder.

[0044] Figure 3B The diagram illustrates the compression forming process of the sintered bearing of the present invention, and is a simplified diagram showing the relationship between the compressed body and the core pin in the springback state.

[0045] Figure 3C The diagram shows a simplified cross-sectional view of the compressed body in the state of having the core pin pulled out during the compression forming process of the sintered bearing of the present invention.

[0046] Figure 4 This is a simplified cross-sectional view of the main part of the compressed body with the core pin pulled out.

[0047] Figure 5 This is a schematic diagram of the cross-sectional structure of the material.

[0048] Figure 6 This is a cross-sectional view of a fan motor using the sintered bearing of the present invention.

[0049] Figure 7 yes Figure 5 An enlarged cross-sectional view of the main part of the fan motor shown.

[0050] Figure 8 This is a simplified cross-sectional view of another sintered bearing of the present invention.

[0051] Figure 9 It was used Figure 8 An enlarged cross-sectional view of the main part of the fan motor with the sintered bearing shown.

[0052] Figure 10A It shows Figure 8 The compression forming process of the sintered bearing shown is a front view showing the state in which the concave and convex portions of the core pin are transferred onto the pressed powder.

[0053] Figure 10B It shows Figure 8 The compression forming process of the sintered bearing shown is a simplified diagram illustrating the relationship between the compressed body and the core pin in a springback state.

[0054] Figure 10C It shows Figure 8 The compression forming process of the fired bearing shown is a simplified cross-sectional view of the compressed body with the core pin pulled out.

[0055] Figure 11 This is a simplified cross-sectional view of the main part of the compressed body with the core pin pulled out.

[0056] Figure 12 This is a simplified cross-sectional view of the main parts of the fired bearing after the precision pressing process. Detailed Implementation

[0057] Figure 6A fan motor is shown. This fan motor includes a hydrodynamic bearing assembly 1, a motor base 5 constituting the stationary side of the motor, a rotor 3 fixed to a shaft assembly 2 of the hydrodynamic bearing assembly 1, blades 4 mounted on the rotor 3, and stator coils 6 and rotor magnets 7 arranged opposite each other with a radial clearance. The stator coils 6 are mounted on the housing 8 of the hydrodynamic bearing assembly 1, and the rotor magnets 7 are mounted on the rotor 3. In this fan motor configuration, when the stator coils 6 are energized, the rotor magnets 7 rotate due to the electromagnetic force between the stator coils 6 and the rotor magnets 7. Simultaneously, the shaft assembly 2 and the rotor 3 fixed to the shaft assembly 2 rotate as a unit. As the rotor 3 rotates, an axial or radially outward airflow is generated depending on the shape of the blades 4 mounted on the rotor 3.

[0058] like Figure 7 As shown, the hydrodynamic bearing device 1 is a so-called shaft rotation type bearing device with a shaft component 2 constituting the rotating side, a housing 8 constituting the stationary side, a bearing component 10 and a sealing component 9, and a lubricating oil (not shown) filling the internal space of the housing 8 as its main structure. The bearing component 10 adopts a fired bearing according to an embodiment of the present invention. Furthermore, for ease of explanation, the following will refer to... Figure 5 The upper side of the paper surface (the side where the sealing component 9 is located) is referred to as the "upper side". Additionally, Figure 2 The side below the paper is referred to as the "bottom side," but this is not intended to limit the posture when using the hydrodynamic bearing device 1.

[0059] The shaft component 2 is made of a high-rigidity metal material such as stainless steel. Its outer peripheral surface 2a is formed as a smooth cylindrical surface without any bumps or depressions, and its lower end surface 2b is formed as a convex spherical surface. A blade 4 and a rotor magnet 7 are fixedly mounted on the upper end of the shaft component 2 (see reference). Figure 1 Rotor 3.

[0060] The housing 8 is a bottomed cylindrical shape with a cylindrical portion 8a and a bottom 8b that closes the lower end opening of the cylindrical portion 8a. In the example shown, the cylindrical portion 8a and the bottom 8b are integrally formed from resin or metal. The inner circumferential surface 8a1 of the cylindrical portion 8a is formed as a cylindrical surface with a constant diameter, and an outer diameter end of an annular shoulder surface 8b2, which is formed as a flat surface perpendicular to the axial direction, is connected to its lower end. On the outer circumferential surface 8a2 of the cylindrical portion 8a, the stator coil 6 and the motor base 5 are fixed at intervals.

[0061] In the example shown, a thrust plate 11, formed of a material with superior sliding properties compared to the material used to form the housing 8, is mounted on the inner bottom surface (upper end surface of the bottom 8b) 8b1 of the housing 8. The upper end surface of the thrust plate 11 provides contact support to the lower end surface 2b of the shaft component 2 (providing contact support to the shaft component 2 in the thrust direction). However, the thrust plate 11 is not mandatory and can be omitted. When the thrust plate 11 is omitted, the lower end surface 2b of the shaft component 2 is contact supported by the inner bottom surface 8b1 of the housing 8.

[0062] The sealing member 9 is formed into a ring shape from resin or metal and is fixed to the upper end of the inner circumferential surface 8a1 of the cylindrical portion 8a of the housing 8, with its lower end face 9b abutting against the upper end face 10b of the bearing member 10. An annular sealing space S is formed between the inner circumferential surface 9a of the sealing member 9 and the outer circumferential surface 2a of the opposing shaft member 2. Through this sealing space S, the leakage of lubricating oil filled in the internal space of the housing 8 to the outside is restricted.

[0063] Furthermore, the hydrodynamic bearing device 1 can be used in a so-called fully filled state, where the entire internal space of the housing 8 is filled with lubricating oil, or in a so-called partially filled state, where a portion of the internal space of the housing 8 contains lubricating oil (a mixture of lubricating oil and air exists within the internal space of the housing 8). When the hydrodynamic bearing device 1 is used in a fully filled state, the volume of the sealing space S is determined such that even if the oil level changes axially with temperature variations, the oil level remains within the axial range of the sealing space S.

[0064] However, Figure 6 and Figure 7 The bearing component 10 used in the fan motor is the sintered bearing 10 of the present invention. The sintered bearing 10 is formed by containing lubricating oil in a sintered body made of sintered powder. Bearing surfaces 21 and 22 are provided at two locations axially separated along the inner circumferential surface (inner diameter surface) 10d. Between the bearing surfaces 21 and 22, there is a clearance portion 23 whose inner diameter is set to be larger than the inner diameter of the bearing surface. In addition, the bearing surface of 21 is sometimes referred to as the first bearing surface, and the bearing surface of 22 is referred to as the second bearing surface. In addition, sintering and firing are both processing methods for producing products by heating materials such as metals and ceramics. When the material is heated, the bonding between the raw material particles progresses. Sintering is mainly a process that uses metal-based powder materials to cause shrinkage by heating the powder particles to bond together. On the other hand, firing mostly uses ceramic-based materials and is a process that increases mechanical strength by heating to cause a chemical reaction at high temperature. Therefore, in this specification, it is referred to as sintering or firing.

[0065] In this case, the outer diameter surface 10a of the bearing component 10 is a straight cylindrical surface without steps, and is set to have the same inner diameter as the first bearing surface 21 and the second bearing surface 22. The inner diameter of the clearance portion 23 is 0.1% to 0.3% larger than the inner diameters of the two bearing surfaces 21 and 22. That is, when the inner diameter of the first bearing surface 21 is set to D1, the inner diameter of the second bearing surface 22 is set to D2, and the inner diameter of the clearance portion 23 is set to D3, D1 = D2 < D3, and D3 = (D1 + D1 / 1000) ~ (D1 + 3D1 / 1000) or D3 = (D2 + D2 / 1000) ~ (D2 + 3D2 / 1000). Here, the same dimension means within 0.001 mm.

[0066] Furthermore, when the axial length of the bearing component 10 is set as L, the axial length of the first bearing surface 21 is set as L1, the axial length of the second bearing surface 22 is set as L2, and the axial length of the clearance portion 23 is set as L3, L1 ≤ L2 < L3. Additionally, L3 is set to 1.0 × (L1 + L2) ~ 4.0 × (L1 + L2). When the axial length of the bearing component 10 is set as L, L = 2.0 × (L1 + L2) ~ 5.0 × (L1 + L2).

[0067] like Figure 7 As shown, the bearing component 10 is fixed to the inner circumference of the cylindrical portion 8a of the housing 8 with its lower end face 10c abutting against the shoulder surface 8b2 of the bottom 8b of the housing 8. In addition to being fixed to the inner circumferential surface 8a1 of the cylindrical portion 8a by pressing, bonding, or a combination of pressing and bonding, the bearing component 10 can also be fixed to the inner circumference of the cylindrical portion 8a by being clamped from both axial sides by the sealing component 9 and the shoulder surface 8b2 of the housing 8 after being fitted with a clearance fit to the inner circumference of the housing 8 (refer to JISB 0401-1). Particularly in the latter fixing method, the bearing component 10 can be fixed to the housing 8 simultaneously with the sealing component 9, thus reducing the effort required to assemble the components.

[0068] like Figure 2 As shown, the bearing component (fired bearing) 10 is formed by performing a powdering (mixing) process S1, a compression molding process S2, a firing process S3, and an oil-containing process S4.

[0069] In the powder preparation step S1, metal powder and resin powder are mixed and blended to produce raw material powder. In this case, the metal powder is not particularly limited, but in this embodiment, iron powder, which is widely used in powder metallurgy applications, is inexpensive, and readily available. That is, it is not limited to iron powder; stainless steel powder, copper powder, tin powder, etc., can also be used. Furthermore, the resin powder needs to be thermally cured during the sintering process; therefore, epoxy resin (EP) powder containing a potential curing agent is used. In addition to epoxy resin, phenolic resin (PF), polyurethane (PUR), and melamine resin (MF) can also be used.

[0070] The preferred composition of the mixture of metal powder and resin powder is 95 wt% to 99 wt% metal powder, with the remainder being resin powder.

[0071] Next, in the compression molding process S2, the compressed powder 31 is formed by stamping using a die device. This die device has upper and lower cylindrical punches (not shown) and a core pin 30 that shapes the internal form of the compressed powder 31 (see reference). Figure 3A The core pin 30 includes a first forming part 30a for forming one bearing surface (inner diameter surface 21a of the first bearing part 21), a second forming part 30b for forming another bearing surface (inner diameter surface 22a of the second bearing part 22), and a third forming part 30c between the first forming part 30a and the second forming part 30b. The third forming part 30c forms a clearance part 23, which is set to be larger than the outer diameter of the first and second forming parts 30a and 30b.

[0072] After the powder is formed, the process of removing the powder from the mold device involves opening the mold device to release the axial pressure applied to the formed powder 31. When this pressure is released, the elastic restoring force accumulated inside the powder is released, causing the powder 31 to spring back, such as... Figure 3B As shown, the inner circumferential surface (inner diameter surface) of the powder compactor 31 is enlarged. This enlargement allows the core pin 30 to be pulled out of the powder compactor 31. Thus, as... Figure 3C As shown, it is possible to form pressed powder 31 before firing.

[0073] By compressing a mixture of metal powder and resin powder as the main components, the strength of the pressed powder body 31 can be improved by utilizing the adhesiveness and flexibility of the resin, and the springback (inner diameter springback rate) can also be increased. Thus, by increasing the inner diameter springback rate, the core pin 30 can be pulled out from the inner diameter surface of the pressed powder body 31 formed by the uneven portion of the transfer core pin 30. Consequently, the cross-sectional shape of the clearance portion 23 can be formed into a rectangle.

[0074] That is, steps 30d and 30e are formed at the boundaries of the large-diameter third forming part 30c and the small-diameter first forming part 30a, and at the boundaries of the large-diameter third forming part 30c and the small-diameter second forming part 30b. These steps 30d and 30e are perpendicular to the axial direction. Specifically, step 30d is perpendicular to the outer diameter surface of the first forming part 30a, and step 30e is perpendicular to the outer diameter surface of the second forming part 30b.

[0075] In this case, during the compression molding process S2, the steps 30d and 30e of the core pin 30 are directly transferred to the pressed powder 31, such as... Figure 4 As shown, steps 24A and 24B can be formed between the bearing face 21 and the clearance portion 23, and between the bearing face 22 and the clearance portion 23, respectively. Furthermore, for this pressed powder 31, after the resin powder is cured to form a sintered body in the sintering process S3, it is oiled in the oiling process S4, thereby forming a product (sintered bearing). Therefore, as... Figure 1 As shown, Figure 3A The bearing surfaces 21, 22, clearance portion 23, and steps 24A, 24B of the pressed powder 31 shown become the bearing surfaces 21, 22, clearance portion 23, and steps 24, 24 of the sintered bearing (bearing component) 10, respectively. Therefore, a conical surface will not be formed between the bearing surfaces 21, 22 and the clearance portion 23 in the sintered bearing 10.

[0076] In typical sintered bearings, the sintering process involves heating the pressed powder obtained in the pressing process (compression molding process) to the sintering temperature of the metal powder used to obtain a sintered body. That is, sintering is performed under specified atmosphere and temperature conditions. The specified atmosphere is typically a vacuum, a reducing gas, or an inactive gas, and can be selected from various options depending on the metal powder used. However, in the bearing component 10 of the sintered bearing of the present invention, since it is formed by compressing a mixture of metal powder and resin powder, it can be sintered at approximately 200°C under atmospheric pressure. Furthermore, approximately 200°C refers to 150°C to 250°C.

[0077] In the oil-impregnation process S4, lubricating oil is contained in the sintered body, thereby completing the bearing component 10, which contains lubricating oil in its internal pores. Alternatively, the lubricating oil into the internal pores of the bearing component 10 can be achieved, for example, by immersing the bearing component 10 in a lubricating oil bath filled with lubricating oil for a certain period of time under a specified reduced pressure environment. In this case, to reliably and quickly impregnate the bearing component, the oil-impregnation operation can also be performed while the lubricating oil is heated.

[0078] Figure 5This is a schematic diagram of the cross-sectional structure of the sintered bearing 10. The sintered bearing 10 is formed by compressing iron powder into physical pressure contact with each other or with resin powder, followed by thermal curing of the resin through sintering, resulting in a cross-sectional structure that bonds the iron powder together. Furthermore, by melting and softening the resin during curing, resin components are sandwiched and fixed at the contact points (neck) between the powder particles, thereby strengthening the bearing and achieving a material strength sufficient for use in bearings with relatively low loads.

[0079] In this invention, the average particle size of the iron powder is 50 μm to 200 μm. If the average particle size is less than 50 μm, it is difficult to form a resin film on the surface of the iron powder, resulting in reduced material strength. In addition, if the average particle size exceeds 200 μm, the powder particles are coarse, resulting in large pores, causing oil leakage, increasing the frequency of metal-to-metal contact between the bearing surface and the rotating shaft, and deteriorating the motor characteristics.

[0080] That is, by using coarse powder with an average particle size of 50μm to 200μm as the metal powder (iron powder), large pores are formed overall. In addition, for the part surrounded by the resin coating, micropores (fine pores) are formed. Furthermore, the spongy iron powder (reduced iron powder) has micropores that extend into the interior of the powder. The internal cavities formed by the coarse powder, i.e., the large pores (micropores), ensure smooth oil supply and reduce oil interruption, while the micropores formed by the resin coating inhibit oil leakage and have an oil retention effect. The micropores inside the iron powder have an oil retention effect and prevent outflow.

[0081] Therefore, in this invention, the ratio of coarse pores (average diameter: 10 μm or more) to micro pores (average diameter: less than 10 μm) surrounded by resin in the sliding surface (inner diameter surface) of the sliding part is set as follows: Area ratio of coarse pores to micro pores = 1:1 to 9:1 (area ratio of coarse pores = 50% to 90%).

[0082] If the area ratio of large pores is less than 50%, the oil supply cannot function smoothly, which may cause oil cut-off, especially in low-temperature environments. If the area ratio of large pores is more than 90%, it will cause oil leakage. In high-temperature environments, the frequency of metal-to-metal contact with the rotating shaft increases, which can easily lead to an increase in current and bearing wear.

[0083] According to the sintered bearing of the present invention, by compressing a composite powder mainly composed of iron powder and resin, the strength of the compressed powder body 31 can be improved and the inner diameter rebound rate can be increased by utilizing the adhesiveness and flexibility of the resin. Furthermore, when the core pin is pulled out of the compressed powder body during powder molding by increasing the rebound rate, the undercut portion formed by the unevenness of the bearing inner diameter surface, which is obtained by transferring the unevenness onto the core pin 30, can be forcibly pulled out. Thus, a rectangular clearance portion 23 can be easily formed at the center of the bearing inner diameter.

[0084] Since the sintered body is fired in an atmospheric atmosphere at around 200°C, it eliminates the need for a sintering furnace required in conventional sintering processes to maintain high temperatures of 700°C to 900°C, and it eliminates the need for hydrogen, nitrogen, or other similar gases as processing gases. Furthermore, during molding, the steps provided on the mold core pin are directly transferred to form the step 24 at the boundary between the sliding portion (bearing surface 21, 22) and the intermediate clearance portion 23. In other words, in this invention, the boundary between the sliding portion (bearing surface 21, 22) and the clearance portion 23 can be formed without precision pressing, thus preventing the formation of a conical surface between the sliding portion (bearing surface 21, 22) and the clearance portion 23 that would occur during precision pressing. Additionally, the bearing surfaces (the inner diameter surfaces of the bearing surfaces 21, 22) are formed through in-mold straightening during compression molding, and because it is fired at a low temperature, dimensional changes are reduced, and deviations in the axial length of the sliding surface are minimized. (For example, this deviation can be set to approximately ±0.1 mm.) Furthermore, if a fine pressing process is performed after the sintering process, a clearance portion is formed by narrowing, thus causing an axial length deviation in the bearing surface. However, in this invention, which does not perform a fine pressing process, a clearance portion is not formed by narrowing, thus reducing the axial length deviation of the bearing surfaces 21a and 22a. If the axial length L4 of the bearing surfaces 21a and 22a can be reduced (refer to...), Figure 4 )(Right now, Figure 1 If the deviation of L1 and L2 in the bearing is reduced, the sliding area between the shaft component 2 and the bearing surfaces 21a and 22a will be stable, and the bearing characteristics will be stable.

[0085] Furthermore, the sintered bearing of the present invention, after physically pressing iron powder into contact with each other or with resin powder through compression molding, undergoes thermal curing of the resin through sintering, forming a cross-sectional structure that bonds the iron powder together. Therefore, by melting and softening the resin during curing, and by clamping and fixing the resin components at the contact points (neck) between the powder particles, it is strengthened, resulting in a material strength level suitable for use as a bearing under relatively low loads. In particular, the sintered bearing of the present invention has a cross-sectional structure formed such that the iron powder particles are fixed by the adhesive force of the resin without sintering based on the interdiffusion between iron powder particles.

[0086] Therefore, in this invention, a sintering bearing can be obtained that can reduce the contact area with the rotating shaft, obtain stable rotation, suppress the current value to a low level, increase the rotation speed, and does not require a sintering furnace for high-temperature holding, a large amount of electrical energy, or hydrogen, nitrogen, or a mixture thereof as the processing gas.

[0087] In the above-mentioned mixed powder, to improve the resilience, it is preferable to make the metal powder 95wt% to 99wt%, with the remainder being resin powder. The metal powder in the mixed powder is iron powder, which can be set to be coarse powder with an average particle size of 50μm to 200μm. If the average particle size is less than 50μm, it is difficult to form a resin film on the surface of the iron powder, resulting in reduced material strength. If the average particle size exceeds 200μm, the powder particles are coarse, resulting in large pores, causing oil leakage, increasing the frequency of metal-to-metal contact between the bearing surface and the rotating shaft, and deteriorating the motor characteristics.

[0088] By using coarse iron powder with an average particle size of 50 μm to 200 μm, large pores can be formed integrally. Here, large pores refer to pores with an average diameter of 10 μm or more. In addition, metal powder (iron powder) is surrounded by resin powder, and micropores (average diameter less than 10 μm) are formed in the surrounded portion.

[0089] The iron powder is preferably a sponge-like iron powder that has pores inside the powder and is able to retain lubricating oil in the pores. Here, sponge-like iron powder refers to all of the porous iron powder (such as sponge iron powder) containing a large number of pores produced by reducing oxidized iron powder such as iron oxide with a gaseous or solid reducing agent. Therefore, this sponge-like iron powder has tiny pores that extend into the interior of the powder.

[0090] However, through this design, the internal cavities formed by the coarse powder, namely the large pores (micropores), ensure smooth oil supply and reduce oil interruption. The micropores formed by the resin coating inhibit oil leakage and have an oil accumulation effect. The micropores inside the iron powder have an oil retention effect and prevent outflow.

[0091] The resin powder may be an epoxy resin powder containing a thermosetting latent curing agent. Since the resin powder needs to be thermosetting during the firing process, a thermosetting epoxy resin is preferred.

[0092] Compressing the above-mentioned mixed powder under a molding pressure of 98MPa to 490MPa can result in a springback rate of over 0.2% in the inner diameter of the compressed powder. This setting allows for stable extraction of the core pin after compression molding.

[0093] Preferably, the inner diameter of the clearance portion 23 is 0.1% to 0.3% larger than the inner diameter of the bearing surfaces 21 and 22, and the cross-sectional shape of the clearance portion 23 is rectangular. By increasing the diameter by more than 0.1%, the clearance portion effectively functions to reduce the contact area with the rotating shaft. Because the cross-sectional shape of the clearance portion is rectangular, even if the bearing surfaces 21 and 22 wear, the area of ​​the bearing surfaces 21a and 22a will not change, minimizing changes in bearing characteristics. Furthermore, by increasing the diameter to less than 0.3%, the inner diameter of the clearance portion 23 will not become excessively larger than the inner diameter of the bearing surfaces 21 and 22, effectively preventing damage to the inner diameter surfaces of the bearing surfaces 21a and 22a when the core pin 30 is pulled out.

[0094] Preferably, the surface opening ratio (surface opening ratio) of the bearing surface is 40% to 80%. Surface opening ratio refers to the area ratio of all openings on the bearing surface, including not only openings that do not communicate with the internal vents, but also openings that do communicate with the internal vents. In this way, by increasing the surface opening ratio of the bearing surface, the contact area can be reduced, resulting in more stable rotation.

[0095] As a sintered bearing, it is preferably used as a bearing component in a motor. In this way, by using a bearing component for a motor, a high-quality motor (small motor) that can achieve stable rotation over a long period of time can be provided.

[0096] According to the method for manufacturing the sintered bearing of the present invention, a rectangular clearance portion can be easily formed at the center of the bearing's inner diameter, and hydrogen, nitrogen, or the like is not required as the processing gas. Furthermore, since it is sintered at a low temperature, dimensional changes can be reduced, and the deviation in the axial length of the bearing surfaces 21a and 22a can be minimized. Therefore, if the deviation in the axial length of the bearing surfaces 21a and 22a can be reduced, the sliding area between the shaft component 2 and the bearing surfaces 21a and 22a becomes stable, and the bearing characteristics become stable. By melting and softening the resin during curing, and by clamping and fixing the resin components at the contact points (neck) of the powders, a material strength of a level that is not problematic for use in bearings with relatively low loads can be obtained. In addition, during compression molding, the bearing surfaces 21 and 22 and the clearance portion 23 can be formed via a mandrel, resulting in excellent productivity.

[0097] then, Figure 8 Another sintered bearing 10 is shown. Figure 9 It was used Figure 8The enlarged cross-sectional view of the main part of the fan motor of the sintered bearing 10 shown is illustrated. The sintered bearing 10 has enlarged diameter portions 25 and 26 at its two outer axial ends on the inner diameter surface 10d, with the same inner diameter dimensions as the clearance portion 23. That is, when the inner diameter dimension of the enlarged diameter portion 25 is set to D5 and the inner diameter dimension of the enlarged diameter portion 26 is set to D6, in this embodiment, D3=D5 and D3=D6. Furthermore, Figure 8 Other structures of the sintered bearing 10 shown are similar to Figure 1 The sintered bearings shown are the same; for the same structure, the markings are the same. Figure 1 Labels that are identical in appearance are shown, and their descriptions are omitted. Additionally, Figure 9 The fan motor shown is Figure 7 The fan motor shown has a different sintered bearing 10 compared to the one shown. Figure 9 Other structures shown and Figure 7 The fan motor shown is the same; for the same structure, the labeling is the same. Figure 7 The same labels are shown, and their descriptions are omitted.

[0098] in addition, Figure 8 The dimensional relationships shown are also consistent with Figure 1 The dimensional relationships shown are the same. That is, when the axial length of the bearing component 10 is set as L, the axial length of the first bearing surface 21 is set as L1, the axial length of the second bearing surface 22 is set as L2, and the axial length of the clearance portion 23 is set as L3, L1 ≤ L2 < L3. Furthermore, L3 = 1.0 × (L1 + L2) to 4.0 × (L1 + L2). When the axial length of the bearing component 10 is set as L, L = 2.0 × (L1 + L2) to 5.0 × (L1 + L2).

[0099] When the axial length of the expanded diameter portion 25 is set to L5 and the axial length of the expanded diameter portion 26 is set to L6, the order is L1 > L5, L1 > L6, L2 > L5, and L2 > L6. Specifically, it is preferable to set L5 (L6) to 0.2 mm to 2.0 mm.

[0100] like Figure 9 As shown, in the case of bearing component 10 with enlarged diameter portions 25 and 26, the process is also performed... Figure 2 The process is as shown: powdering (mixing) step S1, compression molding step S2, firing step S3, and oil-containing step S4. Powdering (mixing) step S1, firing step S3, and oil-containing step S4 are... Figure 1 The bearing component 10 shown is molded in the same way, and the description of these processes is omitted.

[0101] Compression molding process S2 uses a Figure 10A and Figure 10BThe mold device for the core pin 30 shown. This mold device has cylindrical upper and lower punches (not shown), and a core pin 30 that shapes the internal shape of the pressed powder 31 (see reference). Figure 10A The core pin 30 includes a first forming part 30a for forming a bearing surface (inner diameter surface 21a of the first bearing surface 21), a second forming part 30b for forming another bearing surface (inner diameter surface 22a of the second bearing surface 22), a third forming part 30c between the first forming part 30a and the second forming part 30b, a fourth forming part 30d for forming an expanded diameter part 25, and a fifth forming part 30e for forming another expanded diameter part 26. The third forming part 30c forms a clearance part 23, the fourth forming part 30d forms an expanded diameter part 25, and the fifth forming part 30e forms an expanded diameter part 26, all of which are set to be larger than the outer diameters of the first and second forming parts 30a and 30b.

[0102] After the powder is formed, the process of removing the powder from the mold device involves opening the mold device to release the axial pressure applied to the formed powder 31. When this pressure is released, the elastic restoring force accumulated inside the powder is released, causing the powder 31 to spring back, such as... Figure 10B As shown, the inner circumferential surface (inner diameter surface) of the powder compactor 31 is enlarged. This enlargement allows the core pin 30 to be pulled out of the powder compactor 31. Thus, as... Figure 10C As shown, it is possible to form pressed powder 31 before firing.

[0103] By compressing a mixture of metal powder and resin powder as the main components, the strength of the pressed powder body 31 can be improved by utilizing the adhesiveness and flexibility of the resin, and the springback (inner diameter springback rate) can also be increased. Thus, by increasing the inner diameter springback rate, the core pin 30 can be pulled out from the inner diameter surface of the pressed powder body 31 formed by the uneven portion of the transfer core pin 30. Consequently, the cross-sectional shape of the clearance portion 23 can be formed into a rectangle.

[0104] Specifically, steps 30f and 30g are formed at the boundaries of the large-diameter third forming portion 30c and the small-diameter first forming portion 30a, and at the boundaries of the large-diameter third forming portion 30c and the small-diameter second forming portion 30b, respectively. These steps 30f and 30g are perpendicular to the axial direction. Steps 30h and 30i are formed at the boundaries of the large-diameter fourth forming portion 30d and the small-diameter first forming portion 30a, and at the boundaries of the large-diameter fifth forming portion 30e and the small-diameter second forming portion 30b, respectively. These steps 30h and 30i are perpendicular to the axial direction. Specifically, step 30f is perpendicular to the outer diameter surface of the first forming portion 30a, step 30g is perpendicular to the outer diameter surface of the second forming portion 30b, step 30h is perpendicular to the outer diameter surface of the first forming portion 30a, and step 30i is perpendicular to the outer diameter surface of the second forming portion 30b.

[0105] In this case, during the compression molding process S2, the steps 30f, 30e, 30h, and 30 on the core pin 30 are directly transferred to the pressed powder 31, such as... Figure 11 As shown, steps 24A and 24B can be formed between the bearing face 21 and the clearance portion 23, and between the bearing face 22 and the clearance portion 23, respectively; step 24C can be formed between the bearing face 21 and the diameter expansion portion 25; and step 24D can be formed between the bearing face 22 and the diameter expansion portion 26. Furthermore, for this pressed powder 31, after the resin powder is cured to form a sintered body in the sintering process S3, it is oiled in the oiling process S4, thereby forming a product (sintered bearing). Therefore, as... Figures 10A to 10C As shown, Figure 10A The bearing surfaces 21, 22, clearance portion 23, and steps 24A, 24B, 24C, and 24D of the pressed powder 31 shown become the bearing surfaces 21, 22, clearance portion 23, and steps 24A, 24B, 24C, and 24D of the fired bearing (bearing component) 10. Therefore, a conical surface will not be formed between the bearing surfaces 21, 22 and the clearance portion 23 in the fired bearing 10.

[0106] exist Figure 8 In the bearing component 10 shown, oil-retaining expanded diameter portions 25 and 26 are provided at the axially outer end edges of the bearing surfaces 21 and 22. Therefore, lubricating oil flows into the sliding portion between the inner diameter surfaces of the bearing surfaces 21 and 22 (i.e., bearing surfaces 21a and 22a) and the rotating shaft, ensuring a stable oil supply to the sliding portion. Furthermore, "axially outer" refers to the direction from the bearing surface 21 towards the upper end surface 10b and the direction from the bearing surface 22 towards the lower end surface 10c.

[0107] Therefore, in this bearing component 10, a sintered bearing can be obtained that: reduces the contact area with the rotating shaft, achieves stable rotation, suppresses current values ​​to a low level, increases rotational speed, and eliminates the need for a sintering furnace for high-temperature holding, large amounts of electrical energy, and does not require hydrogen, nitrogen, or mixtures thereof as the processing gas. This results in a sintered bearing with excellent lubrication performance / sliding characteristics by reducing the frequency of oil cut-off and metal-to-metal contact with the rotating shaft. In particular, even in motor bearings used at high speeds or in low-temperature environments, oil circulation and supply function smoothly, improving oil cut-off and achieving good sliding. As a result, it can improve the reduction of motor speed and speed instability, thereby improving motor characteristics. Furthermore, it can reduce the increase of current values, achieving a reduction in power consumption.

[0108] Preferably, the inner surfaces of the bearing facets 21 and 22, the inner surface of the clearance portion 23, and the inner surfaces of the expanded diameter portions 25 and 26 have approximately equal surface opening ratios. This setting ensures well-balanced rotation. Here, "approximately equal" implies that there may be some deviations due to design errors, manufacturing errors, assembly errors, etc. These deviations are included.

[0109] The axial lengths L5 and L6 of each enlarged section 25 and 26 are preferably set within the range of 0.2 mm to 2.0 mm. When the length is less than 0.2 mm, it is difficult to function as an oil retainer. If the length exceeds 2.0 mm, the bearing surface of the bearing face becomes smaller, making it difficult to stably and reliably pivot the rotating shaft.

[0110] In addition, it has Figure 8 The bearing components 10 of the expanded diameter portions 25 and 26 shown also serve the same function as... Figure 1 The bearing component 10 shown has the same effect.

[0111] The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments and various modifications can be made. For example, the axial length L1 of the first bearing surface 21 and the axial length L2 of the second bearing surface 22 can be set to L1≤L2, but they can also be different. That is, it can be set to L1≥L2, or L1<L2, or L1>L2. In addition, in the embodiments, the axial length of the expanded diameter portion 25 is the same as the axial length of the expanded diameter portion 26, but they can also be different. That is, when the axial length of the expanded diameter portion 25 is set to L5 and the axial length of the expanded diameter portion 26 is set to L6, it can be L5>L6 or L5<L6.

[0112] In addition, the sintered bearing of the present invention can be applied to bearings for fan motors used in home appliances, automobiles, OA equipment, etc.

[0113] Example 1

[0114] Implementations 1 to 6 (sintered bearings) and Comparative Implementations 1 to 3 (sintered bearings) as shown in Table 1 were fabricated, and motor characteristics were evaluated. Implementations 1 to 6 and Comparative Implementations 1 to 3 were fan motors with a side length of 120 mm and an axial length of 25 mm, and a rated current of DC 12V. As for the bearing composition, except for Comparative Implementation 3, the composition consisted of 97 wt% iron powder and 3 wt% epoxy resin powder. Comparative Implementation 3 used a mixed powder obtained by mixing a mixed powder with copper powder, iron powder, and tin powder. As for the bearing specifications, the inner diameter was set to Φ3.0, the outer diameter to Φ8.0, the width (axial length) to 12 mm, and the clearance between the bearing surface (inner diameter surface) and the shaft component was set to 4 μm.

[0115] As bearing specifications, the surface opening ratio, the diameter expansion of the clearance portion, and the average particle size of the iron powder are adopted. Furthermore, the surface opening ratio is set to 40% in Embodiment 1, 50% in Embodiment 2, 70% in Embodiment 3, 80% in Embodiment 4, 60% in Embodiment 5, 60% in Embodiment 6, 60% in Comparative Example 1, 60% in Comparative Example 2, and 40% in Comparative Example 3. The diameter expansion of the clearance portion is set to 6 μm in Embodiments 1-4, 3 μm in Embodiment 5, 9 μm in Embodiment 6, 0 μm in Comparative Example 1, 6 μm in Comparative Example 2, and 100 μm in Comparative Example 3. That is, Comparative Example 1 does not have a clearance portion, and the average particle size of the iron powder is 90 μm in Embodiments 1-6 and Comparative Example 1, and 60 μm in Comparative Example 2. Furthermore, Comparative Product 3 not only uses iron powder, but also a mixed powder made by mixing copper powder, iron powder, and tin powder, so the average particle size of the iron powder is not limited. However, the enlarged diameter of the clearance part in Table 1 refers to t = D3 - D1 (D2) when the enlarged diameter of the clearance part is set as t, the diameter of the bearing surface is set as D1 (D2), and the diameter of the clearance part 23 is set as D3.

[0116] Table 1

[0117] As for motor characteristics at -30℃, speed, current, and starting voltage are defined, and their related evaluations are categorized as double-coil, single-coil, delta, and cross (×). The speed is 820 rpm in Embodiment 1, 870 rpm in Embodiment 2, 890 rpm in Embodiment 3, 850 rpm in Embodiment 4, 800 rpm in Embodiment 5, 850 rpm in Embodiment 6, 650 rpm in Comparison 1, 720 rpm in Comparison 2, and 830 rpm in Comparison 3. The current is 65 mA in Embodiment 1, 62 mA in Embodiment 2, 61 mA in Embodiment 3, 64 mA in Embodiment 4, 66 mA in Embodiment 5, 63 mA in Embodiment 6, 72 mA in Comparison 1, 69 mA in Comparison 2, and 65 mA in Comparison 3. The starting voltage is 7.9V in embodiment 1, 7.6V in embodiment 2, 7.5V in embodiment 3, 7.7V in embodiment 4, 8.0V in embodiment 5, 7.7V in embodiment 6, 8.5V in comparison 1, 8.2V in comparison 2, and 7.8V in comparison 3.

[0118] Regarding the double-turn designation in Table 1, products with a rotational speed of 860 rpm or higher, a current value of 62 mA or lower, and a starting voltage of 7.6 V or lower are considered excellent; Items 2 and 3 meet this requirement. Regarding the single-turn designation in Table 1, products with a rotational speed of 800 rpm or higher, a current value of 66 mA or lower, and a starting voltage of 8.0 V or lower are considered good; Items 1, 4, 5, 6, and Comparative Item 3 meet this requirement. Regarding the triangle designation in Table 1, products with a rotational speed of 700 rpm or higher, a current value of 70 mA or lower, and a starting voltage of 8.6 V or lower are considered acceptable; Comparative Item 2 meets this requirement. Regarding the cross (×) designation in Table 1, products with a rotational speed less than 700 rpm, a current value exceeding 70 mA, and a starting voltage exceeding 8.5 V are considered unacceptable; Comparative Item 1 meets this requirement.

[0119] As shown in Embodiment 5, if the diameter expansion of the clearance portion is less than 3 μm (the case where the diameter expansion is 0.1% relative to the inner diameter of the bearing surface), the performance improvement effect brought about by providing the clearance portion is weakened. Furthermore, as shown in Embodiment 6, if the diameter expansion of the clearance portion exceeds 9 μm (the case where the diameter expansion is 0.3% relative to the inner diameter of the bearing surface), the large diameter portion 30c of the mandrel 30 is too large compared to the small diameter portion 30a (30b), and the inner diameter surface (bearing surface) of the bearing surface will be damaged when the mandrel 30 is pulled out. Comparative Embodiment 1 does not have a clearance portion and therefore does not exhibit any performance improvement effect brought about by providing the clearance portion.

[0120] Thus, products with a rotation speed of 800 rpm or higher, a current value of 66 mA or lower, and a starting voltage of 8.0 V or lower, such as embodiments 1, 4, 5, and 6, are preferred. Products with a rotation speed of 860 rpm or higher, a current value of 62 mA or lower, and a starting voltage of 7.6 V or lower, such as embodiments 2 and 3, are even more preferred. Furthermore, products with a rotation speed of 700 rpm or higher, a current value of 70 mA or lower, and a starting voltage of 8.6 V or lower, such as comparative embodiment 2, are not preferred. Products with a rotation speed of less than 700 rpm, a current value exceeding 70 mA, and a starting voltage exceeding 8.5 V, such as comparative embodiment 1, are even less preferred. Comparative embodiment 3 is preferred, but the compressed powder is not formed by compressing a mixture of metal powder and resin powder; instead, it is formed by compressing a mixture of copper-iron-tin powder, requiring a high-temperature sintering process followed by a precision pressing process.

[0121] Example 2

[0122] Sintered bearings of embodiments 7 to 9 (sintered bearings) and comparative embodiments 4 to 5, as shown in Table 2, were fabricated, and motor characteristics were evaluated. Each embodiment and each comparative embodiment (sintered bearing) was designed as a fan motor with a side length of 120 mm and an axial length of 25 mm, and a rated current of DC 12V. As bearing specifications, the inner diameter was set to Φ3.0, the outer diameter to Φ8.0, the width (axial length) to 14 mm, the sliding portion lengths of bearing faces 21 and 22 to 3.0 mm each, and the clearance between the bearing face (inner diameter face) and the shaft component to 4 μm. In embodiments 7 to 9, the clearance portion expansion dimension and the expansion dimension of the clearance portion were both 6 μm. Comparative embodiments 4 and 5 did not have expansion portions; the clearance portion expansion dimension was 6 μm in comparative embodiment 4 and 100 μm in comparative embodiment 5.

[0123] As bearing specifications, the following parameters are defined: the amount of metal powder (metal wt%), the amount of resin (epoxy resin) powder (resin wt%), the axial length of the two expansion sections (expansion section length), and the price. In embodiments 7-9 and comparative embodiment 4, the metal wt% is set to Fe 97%, while comparative embodiment 5 uses an Fe-Cu-Sn type sintered material. In embodiments 7-9 and comparative embodiment 4, the resin wt% is left as the remainder. Furthermore, in comparative embodiment 5, an Fe-Cu-Sn type sintered material is used, but resin powder is not used. The expansion section length is set to 0.2 mm in embodiment 7, 1.0 mm in embodiment 8, and 2.0 mm in embodiment 9. Additionally, comparative embodiments 4 and 5 do not have expansion sections at both ends, therefore the expansion section length is 0 mm. Regarding price, embodiments 7-9 and comparative embodiment 4, which do not use an Fe-Cu-Sn type sintered material, are cheaper, while comparative embodiment 2, which uses an Fe-Cu-Sn type sintered material, is more expensive. However, the expanded diameter length in Table 2 refers to the dimensions of L5 and L6, where L5 = L6.

[0124] Table 2

[0125] Assuming motor characteristics at -30°C, speed, current, and starting voltage are considered, and their associated evaluations are categorized as double-coil, single-coil, delta, and cross (×). The speed is 850 rpm in Embodiment 7, 880 rpm in Embodiment 8, 900 rpm in Embodiment 9, 820 rpm in Comparison 4, and 900 rpm in Comparison 5. The current is 63 mA in Embodiment 7, 61 mA in Embodiment 8, 60 mA in Embodiment 9, 65 mA in Comparison 4, and 60 mA in Comparison 5. The starting voltage is 7.7 V in Embodiment 7, 7.6 V in Embodiment 8, 7.5 V in Embodiment 9, 7.8 V in Comparison 4, and 7.5 V in Comparison 5.

[0126] Regarding the double-turn coil in Table 2, a speed of 880 rpm or higher, a current of 61 mA or lower, and a starting voltage of 7.6 V or lower are considered excellent products, and executors 8 and 9 meet these requirements. Regarding the single-turn coil in Table 2, a speed of 840 rpm or higher, a current of 64 mA or lower, and a starting voltage of 7.8 V or lower are considered good products, and executor 7 meets these requirements. Regarding the triangular coil in Table 2, a speed of 800 rpm or higher, a current of 67 mA or lower, and a starting voltage of 8.0 V or lower are considered acceptable products, and comparison item 4 meets these requirements. Regarding the cross (×), a speed less than 700 rpm, a current exceeding 70 mA, and a starting voltage exceeding 8.2 V are considered unacceptable products, and executors 7 through 9, as well as comparison items 4 and 5, do not meet these requirements. In other words, there are no crosses (×) in Table 2.

[0127] Compared to Comparative Example 4, which lacks the enlarged diameter portions 25 and 26 at both axial ends, Embodiment 7 exhibits improved motor characteristics, confirming an improvement in oil circulation. Compared to Embodiment 7, it is evident that by lengthening the axial length of the enlarged diameter portions 25 and 26 as in Embodiments 8 and 9, the oil retention effect and oil circulation to the bearing surface are further improved.

[0128] Furthermore, in Comparative Example 5, which uses Fe-Cu-Sn type sintered materials, a fine pressing process is required. During this process, the pores on the bearing surface tend to become denser, making it difficult to supply oil to the bearing sliding portion smoothly, especially at low temperatures and when the kinematic viscosity of the oil is high. However, in the sintered bearing of the present invention, as in Examples 7 to 9, the bearing face, the enlarged diameter portions at both ends, and the clearance portions are formed during powder pressing. Therefore, the bearing face and the enlarged diameter portions have approximately equal surface opening ratios and are coarser than those in conventional fine-pressed products. This promotes oil circulation from the bearing interior to the sliding surface. Therefore, even if the depth of the intermediate clearance portion is increased to approximately 3% of the inner diameter, as in Comparative Example 5, approximately 0.1% to 0.3% of the inner diameter is sufficient to obtain approximately the same sliding characteristics (motor characteristics).

[0129] Industrial availability

[0130] The sintered bearing of the present invention is a sintered bearing that can suppress the current value to a low level, increase the rotation speed, and does not require hydrogen, nitrogen or a mixture thereof as the processing gas. It can be applied to fan motors for household appliances, automobiles, OA equipment, etc.

[0131] Label Explanation

[0132] 10: Firing bearing (bearing component); 21, 22: Bearing face; 21a, 21a: Inner diameter face; 23: Clearance part; 24A, 24B, 24C, 24D: Step; 25, 26: Expanded diameter part; 30: Core pin; 30f: Step; 30g: Step; 30h: Step; 30i: Step; 31: Pressed powder.

Claims

1. A sintered bearing, comprising bearing surfaces separated axially on its inner circumferential surface, and a clearance portion between the bearing surfaces having an inner diameter larger than that of the bearing surfaces, the sintered bearing comprising metal powder and resin powder, characterized in that, The sintered bearing has a structure in which the metal powder is bonded together by means of resin powder sandwiched between the metal powders, the resin powder being an epoxy resin powder containing a thermosetting latent curing agent.

2. The sintered bearing according to claim 1, characterized in that, In the mixture of metal powder and resin powder, the metal powder accounts for 95 wt% to 99 wt%, and the remainder is resin powder.

3. The sintered bearing according to claim 1, characterized in that, The metal powder in the mixture of metal powder and resin powder is iron powder, which is coarse powder with an average particle size of 50μm to 200μm.

4. The sintered bearing according to claim 3, characterized in that, The iron powder is a sponge-like iron powder with cavities inside the powder and capable of retaining lubricating oil in the cavities.

5. The sintered bearing according to claim 1, characterized in that, The sintered bearing has a cross-sectional structure formed as follows: instead of sintering based on the mutual diffusion between iron powder particles, the iron powder particles are fixed by the adhesive force of the resin.

6. The sintered bearing according to claim 1, characterized in that, The mixture of metal powder and resin powder is compressed and molded in a mold, and the springback rate of the resulting compressed powder body is above 0.2%.

7. The sintered bearing according to claim 1, characterized in that, The inner diameter of the clearance portion is 0.1% to 0.3% larger than the inner diameter of the bearing surface, and the cross-sectional shape of the clearance portion is rectangular.

8. The sintered bearing according to claim 1, characterized in that, The inner diameter surface opening ratio of the bearing face is 40% to 80%.

9. The sintered bearing according to claim 1, characterized in that, An enlarged diameter portion with an axially outward opening is provided at the outer end edge of the bearing face.

10. The sintered bearing according to claim 9, characterized in that, The surface opening ratios of the inner surface of the bearing face, the inner surface of the clearance portion, and the inner surface of the enlarged diameter portion are approximately equal.

11. The sintered bearing according to claim 9, characterized in that, The axial length of each expanded section is set within the range of 0.2mm to 2.0mm.

12. The fired bearing according to any one of claims 1 to 11, characterized in that, This sintered bearing is used as a bearing component in a motor.

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