Sintered alloy bearing

Abstract

To provide a sintered alloy bearing that is resistant to wear against a mating member (mating shaft) and can minimize adverse environmental effects during manufacturing.SOLUTION: A sintered alloy bearing is obtained by compressing raw material powder to form a green compact, and sintering the green compact. The sintered alloy contains Cu: 1.0-5.0 wt.%, SN: 0.4-2.0 wt.%, and C: 0.3-3.0 wt.% as free carbon, with the remainder: Fe and unavoidable impurities. An iron structure formed from iron powder has an area ratio of a ferrite structure of 90% or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a sintered alloy bearing.

Background Art

[0002] A sintered alloy bearing is a self-lubricating bearing in which lubricating oil is impregnated into pores existing in a sintered body. Such sintered alloy bearings can be used in transportation-related applications such as four-wheel and two-wheel vehicles, industrial machinery-related applications such as office machines and general machinery, and electromechanical-related applications such as IT devices, AV devices, and home appliances.

[0003] Conventionally, as a sintered alloy, there has been disclosed "a material suitable as a mechanical part that requires high wear resistance with relatively high hardness, having high strength and lubricity, and good machinability, in which graphite is not completely dissolved in iron and is dispersed in a partially free state" (Patent Document 1).

[0004] The iron-based sliding member (sintered alloy) described in Patent Document 1 has a network-like cementite in part. Here, the network-like structure is a mesh-like structure, and the mesh-like structure is generally a structure constructed by connecting bases with lines and is a structure in which they are combined like a three-dimensional network by chemical bridging. Also, a network consists of an autonomous whole and autonomous parts. In other words, a network is autonomous as a whole and also autonomous when viewed as a part. That is, in the case of the one described in Patent Document 1, when iron and graphite are mixed and sintered, graphite diffuses into iron and a pearlite structure is formed. However, when the graphite exceeds 0.8%, a linear cementite structure precipitates. As a result, a network-like cementite is formed. Cementite is a compound of iron and carbon, and its chemical formula is represented by Fe3C. It is a compound that appears in a pearlite structure or a tempered martensite structure in steel materials.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] By the way, among the metal structures, cementite tends to be hard, and when there is a lot of cementite, the aggressiveness to the other side (aggressiveness to the other-side member) increases. The aggressiveness to the other-side member refers to wear resistance, damageability, etc. to the other-side member. Therefore, if a sintered alloy bearing is formed of an iron-based sliding member (sintered alloy) as described in Patent Document 1, as a bearing, it tends to be hard, and when metal contact occurs during sliding, the aggressiveness to the shaft increases, and the mating material is likely to wear.

[0007] In addition, since it has a network-like cementite, in Patent Document 1, the sintering temperature is set to a relatively high temperature of 1000 to 1300 °C. However, when the sintering temperature is this high, the amount of carbon dioxide (CO2) generated in the manufacturing process increases, which has an adverse impact on the environment, and moreover, the amount of energy used increases, leading to cost increases. In addition, if the sintered alloy contains a large amount of Cu or Sn, it will lead to cost increases.

[0008] Therefore, in view of the above problems, the present invention provides a sintered alloy bearing that is difficult to wear against the other-side member (opposite shaft) and can suppress the adverse impact on the environment during manufacturing to a low level.

Means for Solving the Problems

[0009] The sintered alloy bearing of the present invention is a sintered alloy bearing obtained by compressing raw material powder to form a green compact and sintering this green compact. The sintered alloy contains, by weight ratio, Cu: 1.0 to 5.0 wt%, Sn: 0.4 to 2.0 wt%, and as free carbon, C: 0.3 to 3.0 wt%, and the balance: Fe and inevitable impurities. The iron structure formed of iron powder has a ferrite structure with an area ratio of 90% or more.

[0010] If the content of Cu (copper) is less than 1.0 wt% or the content of Sn (tin) is less than 0.4 wt%, the strength will be low. If the content of Cu is more than 5.0 wt% or the content of Sn is more than 2.0 wt%, the price will be high. Also, the ferrite structure is soft and has excellent ductility. Since the iron structure has an area ratio of the ferrite structure of 90% or more, the aggressiveness to the counterpart member (for example, the counterpart shaft) can be suppressed low. Here, the area ratio refers to the ratio of the area of each structure in the observed area.

[0011] Also, when the content of C as free carbon is less than 0.3 wt%, the sliding characteristics deteriorate. When the content of C as free carbon is more than 3.0 wt%, the formability of the bearing deteriorates. Here, free carbon refers to carbon in an uncombined state, and the combined carbon is called fixed carbon.

[0012] The oil content is preferably 10 - 25 vol%. The oil content is a dimensionless % value obtained by dividing the volume of the impregnated oil by the volume of the bearing. If the oil content is less than 10 vol%, there is less lubricating oil, the bearing performance deteriorates, seizure etc. occur, and the bearing life becomes short. Also, if the oil content is more than 25 vol%, it is necessary to lower the density in order to increase the pores inside the bearing, and lowering the density will lead to a decrease in the strength of the bearing.

[0013] It is preferably configured so that there is no network-like cementite structure. The absence of the network-like cementite can reduce the aggressiveness to the counterpart (counterpart shaft), and the smooth rotational operation of the bearing is not impaired. Here, network-like means a mesh structure, and cementite is a compound of iron and carbon, and its chemical formula is shown as Fe3C. It is a compound that appears in the pearlite structure and the tempered martensite structure in steel materials.

[0014] By setting the sintering temperature to 700°C to 900°C, it is possible to configure such that a network-like cementite structure does not exist. If the sintering temperature is lower than 700°C, sintering does not proceed sufficiently. If the sintering temperature is higher than 900°C, C diffuses into Fe, and the pearlite structure and cementite structure increase, resulting in an increase in hardness. Here, the pearlite structure is a eutectic structure of ferrite (α-iron) and cementite (Fe3C). Ferrite and cementite are in a layered form. That is, by sintering at a temperature lower than the temperature at which graphite diffuses (700°C to 900°C), it is possible to suppress not only the precipitation of cementite but also the precipitation of pearlite, without increasing the hardness of the bearing and suppressing the aggressiveness to the mating shaft. Note that carbon can be in the state of free graphite, ensuring sliding characteristics.

Advantages of the Invention

[0015] In the present invention, it is possible to stably maintain strength, and moreover, suppress the aggressiveness to the mating member (for example, the mating shaft) to a low level, prevent damage and wear of the mating side, and stably exhibit the bearing function over a long period. Moreover, since the sintering process is performed at a relatively low temperature, it is possible to suppress the necessary energy during manufacturing, reduce the generation of carbon dioxide (CO2) in the manufacturing process, and suppress the adverse impact on the environment to a low level. In addition, by reducing the blending of copper (Cu) and performing the sintering process at a low temperature, it is possible to reduce costs.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0017] Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 5.

[0018] FIG. 1 shows a sintered alloy bearing 1, which is composed of a cylindrical body having a bearing surface 1a on its inner circumference. A shaft 2 made of stainless steel or the like is inserted into the inner circumference of the sintered alloy bearing 1. By rotating the shaft 2 or rotating the sintered alloy bearing 1, the outer peripheral surface of the shaft 2 is rotatably supported by the bearing surface 1a of the sintered alloy bearing 1.

[0019] The sintered oil-impregnated bearing 1 is manufactured by the process shown in FIG. 2. That is, this manufacturing process is manufactured through a powder mixing process S1, a powder compacting process S2, a sintering process S3, a sizing process (dimension sizing process) S4, and an impregnation process S5 in this order. As the raw material powder in the powder mixing process S1, for example, copper powder, tin powder, iron powder, etc. are mixed to form a mixed powder.

[0020] In this case, it contains Cu (copper powder): 1.0 to 5.0 wt%, Sn (tin powder): 0.4 to 2.0 wt%, and C (carbon powder) as free carbon: 0.3 to 3.0 wt% by weight ratio, and the balance: Fe (iron powder) and inevitable impurities. Various molding aids, for example, lubricants (such as metal soaps, etc.) for improving mold release properties, are added to the mixed powder as necessary. Note that the raw material powder used is not limited to these, and those generally used for cylindrical sintered alloy bearings can be used. The maximum particle size of the copper powder is 106 μm, the maximum particle size of the tin powder is 75 μm, the maximum particle size of the iron powder is 212 μm, and the maximum particle size of the carbon powder is 75 μm.

[0021] The powder compacting process S2 is a process of compression molding the metal powder formed in the powder mixing process S1 into a cylindrical shape. The sintering process S3 is a process of sintering the powder compact obtained in the powder compacting process S2 at a predetermined sintering temperature. The sizing process S4 is a process of applying a compressive force to the sintered body obtained in the sintering process S3 to perform sizing to a predetermined dimension. The impregnation process S5 is a process of impregnating lubricating oil after performing washing or the like as necessary.

[0022] The compacting process S2 forms a green compact using a press machine. The press machine includes an upper and a lower punch, a core rod for forming the inner shape of the green compact, and a die for forming the outer shape of the green compact.

[0023] In the sintering process S3, the green compact obtained in the compacting process (compact forming process) S2 is heated to the sintering temperature of the used metal powder to obtain a sintered body. That is, sintering is performed under a predetermined atmosphere and predetermined temperature conditions. Examples of the predetermined atmosphere include vacuum, reducing gas, and inert gas, etc., and various selections can be made depending on the used metal powder. The predetermined temperature conditions in this case are set to 700°C to 900°C.

[0024] In the sizing process S4, the sintered body distorted by sintering is compressed for dimensional shaping. Specifically, a core rod is inserted into the inner circumference of the sintered body, and the sintered body is pushed in by the upper punch. These are integrally press-fitted into the inner circumference of the die, and the axial width of the sintered body is compressed to a predetermined dimension by the upper and lower punches. As a result, the outer peripheral surface of the sintered body is compressed and shaped by the die, and the inner peripheral surface of the sintered body is pressed against the outer peripheral surface of the core rod and shaped (in-die sizing). By this sizing process, the surface layer of the sintered body is compressed, and the density of the surface layer becomes larger than that of the interior. Also, since the amount of compression of the surface layer on the outer peripheral surface side of the sintered body is larger than that on the inner peripheral surface side, the density of the surface layer on the outer peripheral surface side becomes larger than that on the inner peripheral surface side. Note that after the sizing process, the inner circumference of the sintered body may be further subjected to rotary sizing to further reduce the pores opened on the inner circumference. In this case, the sizing process includes a first sizing process (in-die sizing process) and a second sizing process. The second sizing process includes a rotary sizing process and an in-die sizing process.

[0025] In the impregnation step S5, the sintered alloy bearing 1 formed into a predetermined shape through the sizing step is impregnated with lubricating oil, whereby the sintered alloy bearing 1 having lubricating oil (lubricating oil) impregnated in internal pores is completed. The impregnation of the lubricating oil into the internal pores of the sintered alloy bearing 1 is performed, for example, by immersing the sintered alloy bearing 1 in a lubricating oil bath filled with lubricating oil for a certain period of time under a predetermined reduced pressure environment. At this time, in order to perform the impregnation of the lubricating oil reliably and in a short time, the impregnation operation may be performed with the lubricating oil heated. It is preferable that the oil content is 10 to 25 vol%. The oil content is a % value obtained by dividing the volume of the impregnated oil by the volume of the bearing and making it dimensionless. If the oil content is less than 10 vol%, there is little lubricating oil, the bearing performance deteriorates, seizure or the like occurs, and the bearing life becomes short. On the other hand, if the oil content is more than 25 vol%, it is necessary to lower the density in order to increase the pores inside the bearing, and lowering the density will lead to a decrease in the strength of the bearing.

[0026] By the way, as the impregnating oil (lubricating oil), generally ester-based synthetic oils and PAO-based synthetic oils are often used, but depending on the cost, the use environment temperature, etc., mineral oils and fluorine-based synthetic oils are also used. For automotive-related applications, ester oils, fluorine oils, and mineral oils, etc. are used, and for home appliance applications, PAO (polyalphaolefin) oils and mineral oils, etc. are used. Therefore, in the present invention, these impregnating oils can be selected according to the application or the like.

[0027] The iron structure formed of iron powder has a ferrite structure with an area ratio of 90% or more.

[0028] If Cu is less than 1.0 wt% or Sn is less than 0.4 wt%, the strength will be low, and if Cu is more than 5.0 wt% or Sn is more than 2.0 wt%, the price will be high. Also, the ferrite structure is soft and has excellent ductility, and since the iron structure has a ferrite structure area ratio of 90% or more, the aggressiveness to the mating member (for example, the mating shaft 2) can be suppressed low. Here, the area ratio is the ratio of the area of each structure to the observed area.

[0029] Therefore, the hardness of the inner peripheral surface, which is the bearing surface 1a of this sintered alloy bearing 1, is, for example, set to 40 HRH to 80 HRH. Also, when the hardness of the inner peripheral surface, which is the bearing surface 1a of the sintered alloy bearing 1, is defined as A, and the hardness of the outer peripheral surface with the mating member (mating shaft 2) is defined as B, A = B, A > B, or A < B may be acceptable.

[0030] When C as free carbon is less than 0.3 wt%, the sliding characteristics deteriorate, and when C as free carbon is more than 3.0 wt%, the formability of the bearing decreases. Here, free carbon refers to carbon in an uncombined state, and carbon in a combined state is referred to as fixed carbon.

[0031] By setting the sintering temperature to 700°C to 900°C, a network-like cementite structure can be prevented from existing. When the sintering temperature is lower than 700°C, sintering does not proceed sufficiently, and when the sintering temperature is higher than 900°C, C diffuses into Fe, increasing the pearlite structure and cementite structure, resulting in increased hardness. Here, the pearlite structure is a eutectoid structure of ferrite (α-iron) and cementite (Fe3C). Ferrite and cementite are layered.

[0032] Sintered machine parts can be classified into the following low-density parts at 6.2 g / cm 3 the following medium-density parts at 6.3 / cm 3 ~6.7 g / cm 3 and high-density parts at 6.8 g / cm 3 or higher. However, in this embodiment, the density of the sintered alloy bearing 1 is set to be 5.4 g / cm 3 to 7.4 g / cm 3 when dry.

[0033] The density ratio of the sintered alloy bearing 1 can be set to, for example, about 70% to 95%. Here, the density ratio is a relative value of the density of a porous material such as a sintered alloy, and is expressed as a percentage of the ratio of the density of the porous material to the density of a material having the same composition as the porous material but without voids inside the solid.

[0034] The surface opening ratio (porosity) of the inner peripheral surface, which is the bearing surface 1a of the sintered alloy bearing 1, is set to 5% to 50%. Here, the surface opening ratio refers to the ratio of the total area of each opening (total area) per unit area. When the surface opening ratio of the bearing 1 is increased, the supply of oil is promoted by the self-lubricating action, and oil starvation in the high rotational speed range can be prevented, improving the lubrication characteristics. On the other hand, if the surface opening ratio is decreased, the escape of oil can be prevented, enabling the formation of a stable oil film and improving the lubrication characteristics in the low rotational speed range. Therefore, it is preferable that the surface opening ratio be 5% to 50%.

[0035] According to the present invention, it is strong and stable, and can suppress the aggressiveness to the mating member (for example, the mating shaft) to a low level, prevent damage and wear of the mating side, and stably exhibit the bearing function over a long period. Moreover, since the sintering process is performed at a relatively low temperature, the necessary energy during manufacturing can be suppressed, the generation of carbon dioxide (CO2) in the manufacturing process can be reduced, and the adverse impact on the environment can be suppressed to a low level. In addition, since the blending of copper (Cu) is reduced and the sintering process is performed at a low temperature, cost reduction can be achieved.

[0036] As described above, the embodiments of the present invention have been described. However, the present invention is not limited to the above embodiments and can be variously modified. Although FIG. 2 is a block diagram showing a method for manufacturing a sintered alloy bearing, as a manufacturing method, steps other than the steps shown in FIG. 2 may be added. For example, a rotary sizing process may be added. In the rotary sizing process, a sizing pin having a substantially polygonal cross-section is press-fitted into the inner peripheral surface of the sintered body, and the sizing pin is rotated in this state (not shown). Among the sizing pins, the corner portions in contact with the inner peripheral surface of the sintered body are rounded to have a substantially arc-shaped cross-section. By this rotary sizing, the material on the surface layer of the inner peripheral surface of the sintered body is rolled by the sizing pin, the openings on the inner peripheral surface are crushed, and the surface opening ratio of the inner peripheral surface is reduced. In particular, since the hardness of the sintered body is low, the load on the sizing pin is also small.

[0037] In addition, the sintered alloy bearing according to the present invention can be incorporated not only into spindle motors for disk drive devices such as HDDs, but also into fan motors for cooling fans, polygon scanner motors for laser beam printers, and the like. Further, it can be suitable for bearings such as ventilation fans and air circulation fan motors used in extremely low temperature ranges such as household refrigerators, freezers, and industrial low-temperature storage warehouses.

Example

[0038] Image analysis of the metal structure was performed. As shown in FIG. 3, the measurement procedure of the image analysis includes an image reading step S10, a binarization step S11, and a shape feature measurement step S12. That is, the photograph to be measured (microscopic photograph) is converted into an electronic file, and then the image is read into publicly known and publicly used image analysis software for binarization (a process of converting a color image into black-and-white shades), and necessary measurement values are selected for this binarized image to perform shape feature measurement (including size measurement).

[0039] FIGS. 4 and 5 show binarized images of the sintered alloy formed in the process of FIG. 2. By the way, the area can be used to evaluate the size of the binarized region, and the area refers to the number of binarized pixels. Measuring the area means counting the number of pixels obtained by binarization. Therefore, the area ratio of each structure can be obtained.

[0040] In FIGS. 4 and 5, the horizontal side has 47 squares, the vertical side has 35 squares, for a total of 1645 squares, and the total area is 1645. As for the shooting conditions, the shooting magnification is ×500, and as the scale, it is a 2 μm grid. In FIG. 4, the gray grid indicates pores, with 258 squares, the white grid indicates the copper phase, with 110 squares, and the black grid indicates the pearlite structure, with 49 squares. Therefore, if the number of pixels obtained by subtracting the number of pixels of pores (258) and the number of images of the copper phase (110) from the total number of pixels (1645) is regarded as the iron structure, and the number of pixels obtained by subtracting the number of pixels of the pearlite structure (49) from this iron structure is regarded as the number of pixels of the ferrite structure (1228), it can be seen that the ferrite structure has an area ratio of 96%, which is 90% or more.

Description of Symbols

[0041] 1 Sintered alloy bearing

Claims

1. A sintered alloy bearing obtained by compressing a raw material powder to form a green compact and sintering the green compact, wherein the sintered alloy contains, by weight ratio, Cu: 1.0 to 5.0 wt%, Sn: 0.4 to 2.0 wt%, and C: 0.3 to 3.0 wt% as free carbon, with the balance being Fe and unavoidable impurities, and the iron structure formed of iron powder has a ferrite structure with an area ratio of 90% or more. The sintered alloy bearing is characterized by this.

2. The sintered alloy bearing according to claim 1, characterized in that the oil content is 10 to 25 vol%.

3. The sintered alloy bearing according to claim 1, characterized in that a network-like cementite structure does not exist.

4. The sintered alloy bearing according to claim 3, characterized in that the sintering temperature is set to 700°C to 900°C so that a network-like cementite structure does not exist.

Images