WO2016147930A1

WO2016147930A1 - Composite sliding member and production process therefor

Info

Publication number: WO2016147930A1
Application number: PCT/JP2016/056970
Authority: WO
Inventors: 大平　晃也; 尚樹八代
Original assignee: Ntn株式会社
Priority date: 2015-03-19
Filing date: 2016-03-07
Publication date: 2016-09-22
Also published as: JP2016176515A

Abstract

A composite sliding member which comprises a metallic base 2, a resin layer 3 disposed on a surface of the metallic base 2, and a sliding surface disposed on the resin layer 3. The metallic base 2 is constituted of a powder compact in which metal-powder particles (iron particles 10) have been bonded to one another with an oxide coating 11 disposed thereamong. The oxide coating 11 in a region extending from the surface of the metallic base 2 to a depth of 50 µm therefrom has a maximum thickness of 2 µm or less. Some of the resin layer 4 has infiltrated into the surface openings 13 of the metallic base 2.

Description

Composite sliding member and manufacturing method thereof

The present invention relates to a composite sliding member in which a resin layer having a sliding surface is provided on the surface of a metal substrate, and a method for manufacturing the same.

For example, Patent Document 1 discloses a slide bearing in which a cylindrical metal substrate (bearing outer peripheral portion) is injection-molded with resin as an insert part to form a resin layer on the inner peripheral surface of the metal substrate. Thus, the linear expansion coefficient and the water absorption rate can be suppressed by forming the majority of the slide bearing with metal, and the slidability can be improved by providing the bearing surface on the resin layer. In addition, by forming the metal base with sintered metal, the resin enters the minute recesses formed on the inner peripheral surface of the metal base to exert an anchor effect, and the adhesion between the metal base and the resin layer is improved. .

JP 2003-239976 A Japanese Patent Publication No.51-43007

Sintered metal is usually manufactured through a compacting process, a sintering process, and a straightening (sizing) process. In the following description, a metal powder that has been compacted and not subjected to a sintering process at a high temperature is referred to as a green compact, and is further distinguished from a sintered body that has been subjected to a sintering process.

Among the above processes, the sintering process is generally performed in a high temperature range of 800 ° C. or more in the case of an iron-based material, and its cost accounts for 1/4 to 1/2 of the entire manufacturing cost. . Furthermore, since the green compact expands and contracts through a high-temperature sintering process, a correction process is indispensable in order to achieve a target dimension or accuracy.

In addition, the sintering process is generally performed in a non-oxidizing atmosphere such as an inert gas such as nitrogen or argon, a reducing gas such as hydrogen, a mixed gas thereof, or a vacuum. The purpose of this is to suppress the formation of an oxide film on the surface of the metal powder during sintering and to promote fusion between particles. Through such a sintering process, fusion and necking between metal particles occur, and the strength is improved. However, in addition to the high cost, the metal base of the slide bearing as described above may be of excessive quality. is there. Therefore, if sufficient strength as a metal base of the slide bearing is ensured by processing at a lower temperature, not only the manufacturing cost can be reduced, but also the dimensional change can be suppressed and the correction process can be omitted.

As a method for increasing the strength of a green compact without undergoing a sintering process at a high temperature as described above, for example, Patent Document 2 discloses that a green compact made of iron powder is heated to 400 to 700 ° C. in an oxidizing atmosphere. A technique is shown in which iron oxide is generated on the surface of each iron powder by heating and the iron powder is solidified by this iron oxide. Specifically, by heating the green compact, the surface of each iron powder is first oxidized to produce iron oxide, which fills the pores in the green compact and simultaneously forms a network. By connecting, individual particles are firmly bonded.

However, in the technique of Patent Document 2, by heating the green compact in an oxidizing atmosphere to generate an oxide, the internal pores of the green compact are filled with oxide. The surface aperture ratio is greatly reduced. When such a green compact is applied to the metal base of the composite sliding member, it becomes difficult for the resin to enter the recess provided on the surface of the metal base, and the adhesion between the metal base and the resin layer is reduced.

The above problems occur not only in the sliding bearing but also in the composite sliding member in which the resin layer is provided on the surface of the metal substrate by insert molding.

In view of the above circumstances, the problem to be solved by the present invention is to firmly adhere the metal substrate and the resin layer in the composite sliding member in which the resin layer is provided on the surface of the metal substrate made of the green compact by insert molding. There is.

A composite sliding member according to the present invention made to solve the above-described problems includes a metal base, a resin layer provided on the surface of the metal base, and a sliding surface provided on the resin layer. The metal substrate is made of a green compact in which metal powder particles are bonded together through an oxide film. The maximum film thickness of the oxide film in a region within a depth of 50 μm from the surface of the metal substrate is 2 μm or less. A part of the resin layer enters the surface opening of the metal substrate.

In addition, the manufacturing method of the composite sliding member according to the present invention made to solve the above problems includes a step of compressing a metal powder to form a green compact, and heating the green compact in an oxidizing atmosphere. By processing, the metal powder particles are bonded to each other through an oxide film formed on the surface of each particle to form a metal base, and the metal base is used as an insert part to perform injection molding with a resin. And a step of forming a resin layer having a sliding surface on the surface of the metal substrate. Conditions for the heat treatment of the green compact are set so that the maximum film thickness of the oxide film in a region within a depth of 50 μm from the surface of the metal substrate is 2 μm or less.

Thus, by making the oxide film on the surface of the metal substrate (green compact) extremely thin (maximum film thickness of 2 μm or less), the ratio of filling the surface opening of the metal substrate with the oxide film is reduced, and the metal The porosity (surface aperture ratio) in the surface layer of the substrate is increased. By allowing the resin to enter the surface opening of the metal substrate, the metal substrate and the resin layer can be firmly fixed.

When the green compact is heat-treated in an oxidizing atmosphere, the oxidizing gas is less likely to enter the inside of the green compact (specifically, a region having a depth of 300 μm ± 10 μm from the surface) compared to the surface layer of the green compact. Therefore, it is difficult to form an oxide film. Therefore, as described above, when the oxide film formed on the surface layer of the metal substrate is thinned, the oxide film formed inside the metal substrate is further thinned. For example, the maximum film thickness of the oxide film in the surface layer May be less than or equal to 1/2. According to the verification by the present inventors, even with such an ultra-thin oxide film, it is possible to obtain the strength necessary for the metal base of the composite sliding member (specifically, the crushing strength is 100 MPa or more). found.

As the oxidizing atmosphere when the green compact is heat-treated, for example, a steam atmosphere is conceivable. However, when the green compact is heated in a water vapor atmosphere, an oxide film is likely to be formed on the surface of the metal powder, making it difficult to control the thickness of the oxide film on the surface of the metal substrate to 2 μm or less. In addition, in order to introduce a sufficient amount of water vapor into the furnace and keep the inside of the furnace at a high temperature and high pressure, the equipment becomes large and the cost increases. Therefore, the heat treatment of the green compact is performed in an oxidizing atmosphere in which the generation rate of the oxidizing film is slower than that in the water vapor atmosphere, specifically, an oxygen gas atmosphere in which an inert gas is mixed with oxygen or air. It is preferable to carry out in the inside. The air atmosphere includes an atmosphere in which pure air is supplied into the furnace and an air atmosphere in which the atmosphere is not controlled.

As described above, by reducing the thickness of the oxide film on the surface layer, the surface opening ratio of the metal substrate can be made 15% or more.

As described above, in the composite sliding member in which the resin layer is provided on the surface of the metal base made of green compact by insert molding, the maximum film thickness of the oxide film generated on the surface layer of the metal base is suppressed to 2 μm or less. Thus, the metal substrate and the resin layer can be firmly fixed.

It is sectional drawing of the slide bearing as a composite sliding member which concerns on one Embodiment of this invention. It is sectional drawing which shows typically the structure | tissue of the surface layer of the metal base | substrate of the said slide bearing. It is sectional drawing which shows typically the structure | tissue inside the metal base | substrate of the said slide bearing. It is a block diagram which shows the manufacturing method of the said slide bearing. It is an axial sectional view showing another example of a slide bearing. FIG. 4B is a cross-sectional view in the direction perpendicular to the axis of the plain bearing of FIG. 4A.

Hereinafter, the case where the composite sliding member according to the present invention is applied to a slide bearing having a bearing surface on the inner peripheral surface will be described.

1 includes a metal base 2 having a cylindrical shape (cylindrical in the illustrated example) and a resin layer 3 provided on an inner peripheral surface 2a of the metal base 2. The inner peripheral surface 3a of the resin layer 3 functions as a sliding surface (bearing surface) that supports the shaft 4 inserted in the inner periphery.

The metal substrate 2 is made of a green compact mainly composed of iron powder. As shown in FIGS. 2A and 2B, an iron oxide film 11 is formed on the surface of the iron particles 10. The iron particles 10 are bonded to each other through the oxide film 11. Not all the iron particles 10 are bonded to each other through the oxide film 11, and some of the iron particles 10 are directly in contact with each other without the oxide film 11 and fused. Yes.

The maximum film thickness of the iron oxide film 11 on the surface layer of the metal substrate 2 (region within a depth of 50 μm from the surface) is 2 μm or less. The “maximum” film thickness of the oxide film refers to the maximum film thickness in a portion of the oxide film excluding a locally thick part formed accidentally. Thus, by reducing the film thickness of the iron oxide film 11 on the surface layer of the metal substrate 2, the surface opening 13 of the metal substrate 2 is less likely to be filled with the iron oxide film 11. A large number of surface openings 13 communicating with the internal holes 12 are formed. Specifically, the surface opening ratio of the metal substrate 2 is 15% or more, preferably 20% or more. The surface opening ratio is the ratio (area ratio) of the total area to be tightened per unit area of the holes opened on the surface of the metal substrate 2. In addition, the surface area ratio of the metal substrate 2 is preferably measured on the contact surface with the resin layer 3 (in this embodiment, the inner peripheral surface 2a). In this embodiment, the green compact constituting the metal substrate 2 is used. Is not subjected to correction (sizing) and the surface aperture ratio of the entire surface is estimated to be substantially constant. Therefore, even if the aperture ratio of the surface other than the inner peripheral surface 2a (for example, the outer peripheral surface 2b) is measured. Good.

Also, if the surface opening ratio is too large, the internal porosity increases, and the strength of the metal substrate 2 may be insufficient. Therefore, it is desirable that the surface aperture ratio of the metal substrate 2 is 50% or less, preferably 40% or less.

The film thickness of the iron oxide film 11 inside the metal substrate 2 shown in FIG. 2B is thinner than the film thickness of the iron oxide film 11 on the surface layer of the metal substrate 2 shown in FIG. 2A. Specifically, the maximum film thickness of the iron oxide film 11 inside the metal substrate 2 (region having a depth of 300 μm ± 10 μm from the surface) is at least the maximum film thickness of the iron oxide film 11 on the surface layer of the metal substrate 2. It is 1/2 or less, or 1/5 or less, and further 1/10 or less. Thus, even if the film thickness of the oxide film inside is minimal, it has the strength required as a composite sliding part such as a slide bearing, specifically, the crushing strength is 100 MPa or more. .

The resin layer 3 is formed by resin injection molding using the metal substrate 2 as an insert part. The outer peripheral surface 3 b of the resin layer 3 is in close contact with the inner peripheral surface 2 a of the metal substrate 2. Specifically, a part of the resin layer 3 enters a myriad of minute surface openings 13 provided on the inner peripheral surface 2 a of the metal base 2. Thereby, an anchor effect is exhibited and the inner peripheral surface 2a of the metal base 2 and the outer peripheral surface 3b of the resin layer 3 are firmly fixed.

The material of the resin layer 3 can be arbitrarily determined according to the required characteristics of the resin layer. Examples of the synthetic resin as the main component of the resin material include polyamide (PA) resin, polycarbonate (PC) resin, polyacetal (POM) resin, wholly aromatic polyester resin, polyphenylene sulfide (PPS) resin, polyether ether ketone ( PEEK resin, polyamideimide (PAI) resin, polyetherimide (PEI) resin, injection moldable polyimide (PI) resin, polytetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA) resin, tetrafluoroethylene Olefin resins such as hexafluoropropylene copolymer (FEP) resin, ethylene-tetrafluoroethylene copolymer (ETFE) resin such as injection moldable fluororesin (polyfluorinated olefin resin), and injection moldable PE resin Etc., and the like. Each of these synthetic resins may be used alone or may be a polymer alloy in which two or more kinds are mixed.

Among these, it is preferable to use a material containing a filler that is mainly composed of injection-moldable PE resin and improves wear resistance. Examples of such a filler include polytetrafluoroethylene (PTFE) resin and non-injectable ultrahigh molecular weight polyethylene (UHMWPE) resin. Moreover, you may add the filler which improves a friction wear characteristic and makes a linear expansion coefficient small. Examples of such fillers include polytetrafluoroethylene (PTFE) resin, non-injectable ultra high molecular weight polyethylene (UHMWPE) resin, fibers such as glass fiber and carbon fiber, calcium carbonate, talc, silica, clay And minerals such as mica, inorganic whiskers such as aluminum borate whisker and potassium titanate whisker, and various heat resistant resins such as polyimide resin and polybenzimidazole. Furthermore, fillers such as antistatic agents (carbon nanofibers, carbon black, graphite, etc.), mold release agents, flame retardants, weather resistance improvers, antioxidants, and pigments may be added. The fillers as described above can be used in appropriate combination.

When the resin layer 3 expands or contracts as the temperature changes, the outer peripheral surface 3b of the resin layer 3 is constrained by the metal substrate 2, so that the inner peripheral surface 3a of the resin layer 3 is reduced or expanded. As a result, the clearance between the bearing surface and the shaft may be too small, resulting in an increase in torque, or the clearance may be excessive and the shaft may be rattled. For this reason, the linear expansion coefficient (1 / ° C.) × thickness (μm) of the resin layer 3 is preferably 0.15 or less, preferably 0.13 or less, and more preferably 0.10 or less. In consideration of moldability, the linear expansion coefficient × thickness of the resin layer 3 is 0.003 or more, preferably 0.01 or more, more preferably 0.015 or more.

The thickness of the resin layer 3 is preferably 100 to 500 μm. The “thickness of the resin layer 3” in the present invention is the thickness (diameter direction thickness) of the portion that does not enter the surface opening of the metal substrate 2. If the thickness of the resin layer 3 is less than 100 μm, the durability during long-term use may be poor. On the other hand, if the thickness of the resin layer 3 exceeds 500 μm, sink marks are generated and the dimensional accuracy is lowered. Heat due to friction is difficult to escape to the metal base 2 and the temperature of the sliding surface is increased. As a result, there is a problem that the contact area with the shaft on the sliding surface increases and the frictional force and the heat generated by friction increase.

Hereinafter, the manufacturing method of the slide bearing 1 will be described focusing on the manufacturing method of the metal base 2.

As shown in FIG. 3, the plain bearing 1 has a resin layer 3 formed by a step of forming a metal base 2 through a mixing step, a compacting step, a degreasing step, and an oxidation step, and insert molding using the metal base 2. It is manufactured through an insert molding process to be formed. Hereinafter, each process will be described in detail.

(1) Mixing process A mixing process is a process of mixing various metal powders and producing raw material powder. The raw material powder of this embodiment mainly contains iron powder. Iron powder can be used regardless of the production method (for example, atomization method, reduction method, stamp method, carbonyl method, etc.). Also, alloy powders whose main component is iron (for example, pre-alloyed pre-alloy powder, partially diffusion-alloyed partial diffusion alloy powder) or pre-mixed powders premixed with multiple types of metal powders are used. It is also possible to do. In addition, in order to improve lubricity, increase strength, etc., low melting point metal powders such as Sn and Zn, and carbon-based powders such as graphite and carbon black may be appropriately added to the raw material powder.

Furthermore, a lubricant may be added to the raw material powder in order to ensure the lubrication between the raw material powder and the mold in the compacting step, which will be described later, or between the raw material powders. As the lubricant, metal soap or amide wax can be used. The lubricant is mixed with the raw material powder as a powder, and the lubricant listed above is dispersed in a solution, sprayed or immersed in the metal powder, and the solvent component is volatilized and removed to remove the lubricant on the surface of the metal powder. May be coated.

Also, in order to ensure moldability, a binder may be added to the raw material powder. Examples of the binder include hydrocarbon resins, waxes, polyvinyl alcohol, and the like. The binder is used by being added to and sprayed on the main raw material powder and plays a role of increasing the bonding force between the powders. However, since the density of a molded object falls by adding a binder, attention is required.

(2) Compacting step The compacting step is a step of obtaining a cylindrical compact by supplying the raw material powder produced in the mixing step to a mold and compacting it. The method of the compacting process is not particularly limited, and other than uniaxial pressure molding, molding by a multi-axis CNC press, injection molding (MIM), and the like are applicable.

Usually, in a sintered part, the higher the density, the higher the strength. However, as in this embodiment, in the case of increasing the strength by subjecting the green compact to oxidation treatment, if the density of the green compact is too high, an oxidizing gas such as air cannot penetrate into the green compact. In addition, since the formation of the oxide film is limited to the very surface layer of the green compact, the strength may be lowered. In view of this point, the green density should be 6.8 g / cm ³ or less, preferably 6.4 g / cm ³ or less. On the other hand, if the powder density is too low, chipping or cracking may occur during handling (large rattra value), and there is a concern that the interparticle distance is too long to form an oxide film between the particles. In view of this point, the green density should be 5.8 g / cm ³ or more, preferably 6.0 g / cm ³ or more. In addition, the measurement of a compacting density is based on the dimension measuring method.

(3) Degreasing process The degreasing process is a process in which the green compact is heated to remove (dewax) the lubricant component contained in the green compact. The degreasing process of this embodiment is performed at a temperature higher than the decomposition temperature of the lubricant and lower than the oxidation process described later, and is heated at 350 ° C. for 90 minutes, for example. In the conventional method, the lubricant component contained in the green compact is decomposed because it is kept at a high temperature in the sintering process, and is not contained in the sintered product. However, when the present invention is applied, the lubricant component may remain depending on the density, processing temperature, and holding time of the green compact. Therefore, it is desirable to take a technique in which a degreasing process for decomposing and removing the lubricant component is provided in advance prior to the oxidation process, and the oxidation process is continuously performed in the same atmosphere after the degreasing process. However, it has been confirmed that high strength can be achieved even if an oxidation treatment is carried out while containing a lubricant without providing a degreasing step. In addition, the degreasing step may be performed in an atmosphere (for example, an inert gas, a reducing gas, or in a vacuum) different from the oxidation step using a separate heating device.

(4) Oxidation step The oxidation step is a step of forming the metal substrate 2 by heating the green compact in an oxidizing atmosphere. Specifically, by heating the green compact, an oxide film is generated on the surface of each particle of the metal powder (particularly, iron powder as a main component), and the particles are bonded to each other through the oxide film. In this embodiment, the processing conditions (heating temperature, heating time, heating atmosphere) of the oxidation process are set so that the oxide film shown above is obtained. Specifically, the heating temperature in the oxidation step of the present embodiment is set to 350 ° C. or higher, preferably 450 ° C. or higher. Moreover, since the dimensional change of a green compact will become large when heating temperature is too high, it is preferable that heating temperature shall be 600 degrees C or less. The heating time is appropriately set in the range of 5 minutes to 2 hours. The heating atmosphere is an oxidizing atmosphere in order to promote positive oxidation. However, since the water vapor atmosphere has a high production rate of the oxide film and the film thickness on the surface layer easily exceeds 2 μm, it is preferable to use an oxidizing atmosphere in which the production rate of the oxide film is slower than this. Specifically, it is preferable to heat in an atmosphere of air or oxygen, or an oxidizing gas in which an inert gas such as nitrogen or argon is mixed.

The iron oxide film formed on the surface of the iron powder of the metal substrate 2 is a mixed phase of two or more of Fe ₃ O ₄ , Fe ₂ O ₃ and FeO. The ratio of these oxides varies depending on the material and processing conditions (heating atmosphere, heating temperature, heating time).

By this oxidation process, the oxide film generated on the surface of each particle of the metal powder spreads between the particles of the iron powder to form a network, replacing the conventional bonding force by sintering at high temperature Thus, the green compact is strengthened. Further, in this embodiment, not all particles of iron powder as a main component are bonded through an oxide film, but some particles are directly in contact with each other without an oxide film and fused. is doing. The strength of the green compact that has undergone the oxidation step is the strength required for the metal substrate 2 of the slide bearing 1, specifically, the crushing strength is 100 MPa or more, preferably 150 MPa or more.

Since the above oxidation process has a lower processing temperature than the conventional high temperature sintering process, the dimensional change is small, and the subsequent sizing process is omitted depending on the material, processing conditions, product shape, dimensions, etc. It becomes possible. Accordingly, the manufacturing process is shortened, the cost can be reduced, and the product and the mold for compacting can be easily designed.

The above oxidation process can be applied regardless of the shape and size of the green compact. Further, since the surface of the green compact (metal substrate 2) subjected to the oxidation step is covered with an oxide film, the antirust effect is high, and in some cases, the antirust treatment is unnecessary. In addition, since the processing temperature of the oxidation process is relatively low, an additive that denatures and decomposes at a temperature exceeding this processing temperature (for example, a material having slidability and lubricity) is added to enhance the functionality of the product. It is also possible to plan.

(5) Insert molding process The resin layer 3 is formed by carrying out the injection molding of the metal base | substrate 2 formed in this way with resin as insert parts. Specifically, the metal base 2 is supplied as an insert part to the cavity of the injection mold. And after injecting molten resin from a gate to a cavity, the resin layer 3 is formed by cooling and solidifying molten resin. Thereafter, the mold is opened, and the integral product of the metal base 2 and the resin layer 3 is taken out, whereby the plain bearing 1 is completed.

The present invention is not limited to the above embodiment. For example, in the above embodiment, the case where the resin layer 3 is provided only on the inner peripheral surface 2a of the metal base 2 has been described, but the present invention is not limited thereto. For example, a resin layer may be provided on the end surface or the outer peripheral surface of the metal substrate 2 and a sliding surface may be provided on these resin layers. Further, the resin layer 3 may be provided at a plurality of locations on the inner peripheral surface, end surface, and outer peripheral surface of the metal base 2.

In the above embodiment, the case where the inner peripheral surface 3a (sliding surface) of the resin layer 3 is a cylindrical surface without unevenness is shown, but the present invention is not limited to this. For example, a groove may be provided on the inner peripheral surface 3 a of the resin layer 3. In the embodiment shown in FIG. 4, a plurality of (for example, six) grooves 5 parallel to the axial direction are provided on the inner peripheral surface 3 a of the resin layer 3. The groove 5 extends over the entire axial length of the inner peripheral surface 3 a of the resin layer 3. The plurality of grooves 5 are arranged at equal intervals in the circumferential direction. By providing the gate trace 6 on the bottom surface of the groove 5, post-processing of the gate trace 6 becomes unnecessary. If gate traces 6 are provided every other plurality (even number) of grooves 5 arranged at equal intervals in the circumferential direction, weld lines are formed in the grooves 5 where the gate traces 6 are not provided.

Further, the fluid dynamics in which the slide bearing 1 is supported in a non-contact manner by the dynamic pressure action of the lubricating fluid (for example, oil) in the radial bearing gap between the inner peripheral surface 3 a of the resin layer 3 and the outer peripheral surface of the shaft 4. It may be used as a pressure bearing. In this case, a dynamic pressure groove may be provided on the inner peripheral surface 3 a of the resin layer 3. The dynamic pressure grooves are arranged in a herringbone shape or a spiral shape, for example. This dynamic pressure groove can be formed by, for example, a compacting process.

Further, the metal substrate 2 is not limited to a cylindrical shape, and may be a rectangular parallelepiped or a spherical shape, for example.

The following tests were conducted in order to confirm preferable conditions in the above-described method for manufacturing a metal substrate of a plain bearing. Table 1 shows the conditions of each test piece. In the following, a material satisfying a crushing strength of 100 MPa or more and a dimensional change rate of ± 0.1% or less is referred to as an “example”, and one not satisfying any of these is referred to as a “comparative example”.

Example 1
Commercially available reduced iron powder (manufactured by Höganäs / SC100.26) and molding lubricant (Accra wax C): 0.7% by weight were added and dry-mixed (40 min) with a V blender. Thereafter, the mixed powder was put into a powder molding die and compression molded at room temperature and 140 MPa to produce a ring-shaped green compact (outer diameter φ16 mm × inner diameter φ8.5 mm × thickness 5 mm). The green density was 5.8 g / cm ³ . The obtained ring-shaped green compact is put into a batch-type heating furnace, heated from room temperature to 350 ° C. at an air flow rate of 0.1 L / min, at a rate of temperature increase of 10 ° C./min, and then 350 The temperature was maintained at ℃ × 30 min, the temperature was increased to 400 ° C. at a rate of temperature increase of 10 ° C./min, held for 10 minutes, and then cooled to room temperature in the furnace example.

The outer diameter was measured before and after the treatment, and the dimensional change due to the heat treatment was measured. Further, the crushing strength of the green compact after the treatment was measured. The outer diameter dimensional change rate by the heat treatment was -0.04% (contraction side), and the green compaction strength of the green compact was 110 MPa.

The rate of dimensional change was determined according to the formula: ((outside diameter after processing−outside diameter before processing) / (outside diameter before processing)) × 100. The crushing strength conforms to JIS Z2507 “Sintered bearing-crushing strength test method”.

Examples 2-14
A powder mixture having a predetermined density was obtained by using the same mixed powder as in Example 1 and adjusting the molding pressure with the same mold. The obtained ring-shaped green compact was subjected to the same degreasing treatment as in the example, then heated to a predetermined temperature with the same temperature rising pattern, held for a predetermined time, and then air-cooled to room temperature in the furnace example. Various conditions are as shown in Table 1.

The outer diameter was measured before and after the treatment, and the dimensional change due to the heat treatment was measured. Further, the crushing strength of the green compact after the treatment was measured. The crushing strength and dimensional change rate are also shown in Table 1.

Examples 15 and 16
A powder mixture having a predetermined density was obtained by using the same mixed powder as in Example 1 and adjusting the molding pressure with the same mold. The obtained ring-shaped green compact was not degreased, and was heated as it was to a predetermined temperature with the same temperature rising pattern, held for a predetermined time, and then air-cooled to room temperature in the furnace example. Various conditions are as shown in Table 1.

Example 17
Water atomized powder MH28N manufactured by Kobe Steel, Ltd. was used as the iron powder, the same lubricant as in Example 1 was mixed, and the molding pressure was adjusted with the same mold to obtain a green compact with a predetermined density. The obtained ring-shaped green compact was subjected to the same degreasing treatment as in Example 1, and then heated to a predetermined temperature with the same temperature rising pattern, held for a predetermined time, and then air-cooled to room temperature in the furnace example. Various conditions are as shown in Table 1.

Comparative Examples 1-10
Molding and heat treatment were basically performed in the same manner as in Example 1. Various conditions are as shown in Table 1.

Since the comparative example 1 has a density as low as 5.6 g / cm ³ and a heating temperature as low as 400 ° C., the crushing strength is as low as 70 MPa.

In Comparative Example 2, the density is as low as 5.8 g / cm ³ , the heating temperature is 400 ° C., and the treatment time is as short as 1 minute, so the crushing strength is as low as 80 MPa.

Comparative Example 3 has a low density of 5.8 g / cm ³ , but has a high crushing strength of 170 MPa because the heating temperature is 600 ° C. and the treatment time is as long as 120 minutes. However, the dimensional change rate is as large as -0.2%.

Comparative Example 4 has a density of 6.2 g / cm ³ and a medium density, but since it is an untreated product, the crushing strength is as low as 20 MPa.

Comparative Example 5 has a medium density of 6.2 g / cm ³ , but the heating temperature is as low as 350 ° C., so that the crushing strength is as low as 80 MPa even after treatment for 120 minutes.

Comparative Example 6 has a density of 6.2 g / cm ³ and a medium density. However, since the heating temperature is 400 ° C. and the treatment time is as short as 1 minute, the crushing strength is as low as 90 MPa.

Comparative Example 7 has a density of 6.2 g / cm ³ and a medium density, and a heating temperature of 500 ° C. and a relatively high temperature. For this reason, the crushing strength is as high as 190 MPa, but the dimensional change rate is as large as −0.14%.

Comparative Example 8 has a density of 6.2 g / cm ³ , a medium density, and a heating temperature as high as 700 ° C. Therefore, even if the treatment time is as short as 10 minutes, the crushing strength is as high as 220 MPa, but the dimensional change rate is −0. Increased to 4%.

Since Comparative Example 9 has a density of 7.0 g / cm ³ , the crushing strength is 120 MPa at a heating temperature of 400 ° C. and a processing time of 10 minutes, but the dimensional change rate is as large as −0.15%.

Since Comparative Example 10 has a density of 7.0 g / cm ³ and a high density, a heating temperature of 600 ° C. and a treatment time of 1 minute show a crushing strength of 160 MPa, but a dimensional change rate is as large as −0.20%.

From the above results, in order to obtain a green compact (metal substrate) having a crushing strength of 100 MPa or more and a dimensional change rate of ± 0.1% or less, the green density is 5.8 to 6.8 g / cm ^3. It can be said that it is preferable to set the heating temperature of the oxidation step to 400 to 600 ° C. and the heating time of the oxidation step to 5 to 120 minutes.

DESCRIPTION OF SYMBOLS 1 Sliding bearing 2 Metal base 3 Resin layer 4 Shaft 10 Iron particle 11 Iron oxide film 12 Internal hole 13 Surface opening

Claims

A composite sliding member comprising a metal substrate, a resin layer provided on the surface of the metal substrate, and a sliding surface provided on the resin layer,
The metal substrate is composed of a green compact in which metal powder particles are bonded together through an oxide film,
The maximum film thickness of the oxide film in a region within a depth of 50 μm from the surface of the metal substrate is 2 μm or less;
A composite sliding member in which a part of the resin layer enters a surface opening of the metal substrate.
The maximum film thickness of the oxide film in a region 300 μm ± 10 μm deep from the surface of the metal substrate is ½ or less of the maximum film thickness of the oxide film in a region within 50 μm depth from the surface of the metal substrate. The composite sliding member according to claim 1.
3. The composite sliding member according to claim 1 or 2, wherein the oxide film is formed by heating in an oxidizing gas atmosphere in which an inert gas is mixed with oxygen or air or an inert gas.
The composite sliding member according to any one of claims 1 to 3, wherein a surface opening ratio of the metal substrate is 15% or more.
Forming a green compact by compressing metal powder;
Heat treating the green compact in an oxidizing atmosphere to bond the metal powder particles together through an oxide film formed on the surface of each particle to form a metal substrate;
Forming a resin layer having a sliding surface on the surface of the metal base by injection molding with resin as the metal base as an insert part, and a method for producing a composite sliding member,
A method for producing a composite sliding member, wherein the conditions for the heat treatment are set so that the maximum film thickness of the oxide film in a region within a depth of 50 μm from the surface of the metal substrate is 2 μm or less.
The maximum film thickness of the oxide film in a region 300 μm ± 10 μm deep from the surface of the metal substrate is ½ or less of the maximum film thickness of the oxide film in a region within 50 μm depth from the surface of the metal substrate. The manufacturing method of the composite sliding member according to claim 5, wherein the conditions for the heat treatment are set so that
The method for producing a composite sliding member according to claim 5 or 6, wherein the heat treatment is performed in an oxidizing gas atmosphere in which oxygen or air or an inert gas is mixed with oxygen or air.
The composite sliding member according to any one of claims 5 to 7, wherein a surface opening ratio of the metal substrate is 15% or more.