JP2020051439A - Slide member, rolling bearing and holder - Google Patents

Abstract

To provide a slide member comprising a slide surface improved in slidability even under a condition of a high PV value (a high sliding velocity or a high surface pressure) in a lubricant, a rolling bearing and a holder.SOLUTION: A slide member 1 is used under an oil lubrication condition and a condition that a PV value of a product of a surface pressure (P) and a sliding velocity (V) ranges from 10 to 20 Pa m/min. A slide layer 2 comprises a ground layer 4 containing a heat resistant resin and a first fluororesin on a surface of an iron-based metal substrate 3, and fluororesin layer 5 containing a second fluororesin on a surface of the ground layer 4. The heat resistant resin is a resin including at least one atom of an oxygen atom, a nitrogen atom and a sulfur atom in at least a principal chain of a polymer structure together with a carbon atom. The fluororesin layer 5 is a crosslinked fluororesin layer in which at least the vicinity of its surface is crosslinked. Push-in hardness of the slide layer 2 measured by an ISO-14577 method is 85 to 146 MPa, and a fusing point in the vicinity of the surface of the slide layer 2 is 221 to 281°C.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a sliding member, a rolling bearing, and a cage used under conditions of high PV value, and particularly to a sliding member having excellent wear resistance on the surface of the sliding member and capable of maintaining the excellent wear resistance for a long time. For example, the present invention relates to a cage for a rolling bearing and a rolling bearing using the cage.

  Lubricating oil, lubricating grease, and the like are supplied to sliding surfaces such as rolling bearings and cages to reduce rolling friction or sliding friction. Further, a surface treatment for further improving the slidability is performed on the sliding surface. One of the surface treatments is a method of forming a fluorine-based resin film. For example, a method of irradiating a polytetrafluoroethylene (hereinafter, referred to as PTFE) film formed on a sliding portion of a sliding member with radiation of a dose of 50 to 250 kGy to improve abrasion resistance and adhesion to a substrate. Is known (Patent Document 1).

  Polyimide resin, metal materials such as copper, aluminum and their alloys, ceramics, and glass, selected from fluororesin coating on the surface of the substrate with excellent heat resistance, at a temperature above the melting point of the fluororesin A modified fluororesin coating material irradiated with ionizing radiation is known (Patent Document 2).

  As a sliding member made of fluororesin used for non-lubricated bearings and dynamic seals, etc., the fluororesin is heated above its crystal melting point, and ionizing radiation is irradiated in the range of 1 kGy to 10 MGy in the absence of oxygen. Irradiated fluororesins are known (Patent Document 3).

  A film or sheet-like product in which a film or sheet-like gradient material composed of PTFE and a substrate selected from the group consisting of aluminum, iron, stainless steel, polyimide and ceramics are laminated, The polymer present on one surface not in contact with the base material and the layer adjacent thereto has a three-dimensional structure, and the polymer present on the other surface in contact with the base material of the material and the adjacent layer has a two-dimensional structure. A film or sheet in which the content of the three-dimensional structure of the polymer present between the one side and the other side is continuously changing, and the thickness of the material is 5 to 500 μm A product is known (Patent Document 4).

  Further, as a fluorine-based resin film, a base layer containing a heat-resistant resin and a first fluorine-based resin was formed on the surface of an iron-based metal material, and a fluorine-containing resin layer containing a second fluorine-containing resin was formed on the base layer surface. One is known (Patent Document 5). This fluororesin layer is a crosslinked fluororesin layer in which at least the vicinity of the surface is crosslinked, and the fluororesin layer is crosslinked by irradiating radiation having an irradiation dose of 250 to 800 kGy.

  On the other hand, there are rolling bearings used for engines of automobiles, motorcycles and the like, in particular, needle roller bearings with a cage, and the surface of the cage is silver-plated to prevent seizure on the surface of the cage. This needle roller bearing with a retainer is composed of a press-made metal retainer that holds the needle rollers at equal intervals, and the entire surface of the retainer is silver-plated (Patent Document 6).

JP 2010-155443 A JP 2002-225204 A JP-A-9-278907 Japanese Patent No. 5454903 JP, 2017-32141, A Japanese Patent No. 5189427

However, the method disclosed in Patent Document 1 is a method for increasing the adhesion to a substrate because it is used without lubrication and under low surface pressure. In the case of high PV value (high sliding speed or high surface pressure), it is difficult to apply.
The fluororesin coating described in Patent Document 2 is intended to simultaneously cause a cross-linking reaction of the fluororesin and a chemical reaction between the fluororesin and the surface of the base material, thereby achieving a strong adhesion between the two. In the case of iron base materials such as irons and cages, it is difficult to generate a chemical reaction with the base material surface, and there is a problem that strong adhesion cannot be achieved.
The sliding member described in Patent Literature 3 is used for a non-lubricated bearing, a dynamic seal, and the like, and relates to a sliding member made of a fluororesin instead of a film. Therefore, the properties of the coating material are unknown, and it is difficult to apply the composition to rolling bearings that require a high PV value (high sliding speed or high surface pressure) in lubricating oil.
Similarly to the film produced by the method described in Patent Document 1, the coating described in Patent Document 4 is evaluated at low surface pressure, low sliding speed, and no lubrication, and has a high PV value (high sliding speed or high surface pressure). ), It is not known whether it can be used under oil lubrication.
The sliding member having a fluororesin coating described in Patent Document 5 is used under oil lubrication, but its wear resistance under conditions of high PV value (high sliding speed or high surface pressure) has been studied. Absent.
In the cage with silver plating described in Patent Document 6, a cage with less change over time in the wear amount of the sliding surface is required, and a sliding material instead of silver plating is required. . In addition, silver plating has a problem that it is sulfurized by a sulfur component contained in engine oil. When the silver plating applied to the surface of the cage is sulfurized, peeling or falling off occurs from the cage, and the base material of the cage is exposed.

  The present invention has been made in order to address such a problem, and provides a sliding surface having excellent slidability even under conditions of high PV value (high sliding speed or high surface pressure) in lubricating oil. It is an object of the present invention to provide a sliding member, a rolling bearing and a cage having the same.

  The sliding member according to the present invention is a sliding member having a sliding layer on the surface of an iron-based metal substrate, wherein the sliding member has an oil lubricating environment, a surface pressure (P) and a sliding speed. (V) is 10 to 20 GPa · m / min. The sliding layer is used under the following conditions, wherein the sliding layer has a base layer containing a heat-resistant resin and a first fluororesin on the surface of the iron-based metal substrate, and a second layer on the base layer surface. A fluororesin layer containing a fluororesin, wherein the heat-resistant resin is a resin containing, together with carbon atoms, at least one atom of an oxygen atom, a nitrogen atom and a sulfur atom in at least a main chain of a polymer structure, The fluororesin layer is a crosslinked fluororesin layer formed by crosslinking at least the vicinity of the surface, the indentation hardness of the sliding layer measured by the ISO14577 method is 85 to 146 MPa, and the vicinity of the surface of the sliding layer is Has a melting point of 221 to 281 ° C. The PV value in the present invention is the product of the surface pressure (P) under sliding and the sliding speed (V), and the high PV value is 10 to 20 GPa · m / min. Say.

  The sliding speed (V) is 0.1 to 1.0 m / s.

  The iron-based metal substrate, the underlayer, and the fluororesin layer are in close contact with each other without providing an adhesive layer.

  The sliding layer is characterized in that the cross-linking ratio of the first and second fluororesins decreases from the surface of the fluororesin layer toward the surface of the iron-based metal substrate.

The second fluororesin is a PTFE resin, and the vicinity of the surface of the second fluororesin appears on a solid ¹⁹ F Magic angle Spinning (MAS) nuclear magnetic resonance (NMR) chart as compared with the uncrosslinked PTFE resin. The chemical shift values (δ ppm) of the non-crosslinked PTFE resin are −68 ppm, −70 ppm, −77 ppm, −80 ppm, −109 ppm, −112 ppm, −152 ppm, and −186 ppm in addition to −82 ppm, −122 ppm, and −126 ppm of the PTFE resin. Wherein at least one chemical shift value selected from the group consisting of: or a signal intensity of a chemical shift value appearing at -82 ppm is increased as compared with the signal intensity of the uncrosslinked PTFE resin. .

  The heat-resistant resin is at least one aromatic resin selected from an aromatic amide imide resin and an aromatic imide resin.

  The sliding layer has a thickness of 5 μm or more and less than 40 μm.

  The ferrous metal cage of the present invention is a ferrous metal cage for holding a rolling element of a rolling bearing, wherein the ferrous metal cage is formed by the sliding member of the present invention. And

  The rolling bearing of the present invention is a rolling bearing having the iron-based metal cage of the present invention, wherein the rolling bearing is a rolling bearing for a large end of a connecting rod of an engine, a rolling bearing for a small end of a connecting rod, or for a crankshaft support shaft. It is a rolling bearing.

  The sliding member of the present invention has a PV value of 10 to 20 GPa · m / min. Used under high PV conditions, having a sliding layer on the surface of the iron-based metal substrate, the sliding layer consisting of an underlayer and a fluororesin layer, and at least the vicinity of the surface of the fluororesin layer being crosslinked. Since the indentation hardness of the sliding layer measured by the ISO 14577 method is 85 to 146 MPa and the melting point in the vicinity of the surface of the sliding layer is 221 to 281 ° C., the high PV value (high (Sliding speed or high surface pressure) can suppress abrasion and maintain the life of the sliding member for a long period of time.

  Since the iron-based metal cage of the present invention is formed of the sliding member of the present invention, it exhibits the same or better slidability as compared with the cage having the silver plating layer. Further, the rolling bearing of the present invention has the iron-based metal cage of the present invention, and the rolling bearing is a connecting rod rolling bearing used in lubricating oil and under high PV conditions. The slidability suitable for the characteristics can be exhibited.

It is sectional drawing of a sliding member. It is an enlarged view of the NMR chart of the irradiation dose of 0 kGy. It is an enlarged view of the NMR chart of an irradiation dose of 500 kGy. It is an enlarged view of the NMR chart of an irradiation dose of 1000 kGy. It is a normalized signal intensity ratio of -82 ppm due to crosslinking. It is a figure showing the relationship between indentation hardness and irradiation dose. It is a figure showing the relationship between a melting point and irradiation dose. It is a perspective view of a roller bearing retainer which uses a needle roller as a rolling element. It is a perspective view which shows a needle roller bearing. FIG. 2 is a longitudinal sectional view of a four-cycle engine.

  The present inventors have conducted intensive studies to obtain a sliding member having a sliding layer excellent in wear resistance even under conditions of high PV value in lubricating oil. A cross-linked fluororesin layer in which at least the vicinity of the surface of the fluororesin layer is crosslinked, and further, the indentation hardness of the slide layer is within a predetermined range, and It has been found that by setting the melting point near the surface within a predetermined range, the sliding member exhibits excellent wear resistance even under conditions of high PV value. In addition, it has been found that the above-mentioned sliding member can be obtained by irradiating an irradiation dose of 850 to 2500 kGy, preferably 1000 to 2000 kGy. The present invention is based on such findings.

  The sliding member of the present invention has a PV value of 10 to 20 GPa · m / min. Used under high PV conditions. As long as the PV value is within the above range, the surface pressure (P) and the sliding speed (V) are not particularly limited, but the sliding speed (V) is preferably 0.1 to 1.0 m / s, and the surface pressure Is preferably 0.17 to 3.3 GPa. In the use of the sliding member of the present invention, a more suitable PV value is 15 to 20 GPa · m / min. It is.

The sliding member of the present invention has a sliding layer formed on an iron-based metal substrate. The sliding layer includes an underlayer and a cross-linked fluororesin layer formed on the surface of the underlayer and having a cross-section in the vicinity of the surface layer.
Examples of the iron-based metal base material include bearing steel, carburized steel, carbon steel for machine structures, cold-rolled steel, and hot-rolled steel used for rolling bearings. The iron-based metal substrate is adjusted to a predetermined surface hardness by quenching and tempering after working into the shape of the sliding member. For example, in the case of an iron-based metal cage using chromium molybdenum steel (SCM415), it is preferable to use an iron-based metal base material whose Hv value is adjusted to 484 to 595.

FIG. 1 shows a sectional view of the sliding member of the present invention. The sliding layer 2 constituting the sliding member 1 includes an underlayer 4 formed on the surface of the iron-based metal base material 3 and a fluororesin layer 5 formed on the surface of the underlayer 4. The underlayer 4 is formed on the surface of the iron-based metal base material 3 and is a mixed resin layer of a heat-resistant resin represented by a white circle in the drawing and a first fluororesin similarly represented by a black circle in the drawing. The fluororesin layer 5 contains a second fluororesin, and the fluororesin layer 5 is a crosslinked fluororesin layer in which at least the vicinity of the surface is crosslinked. The sliding layer 2 has a three-dimensional structure of the second fluororesin present in the surface layer and the layer near the surface layer. Further, the second fluororesin contained in the fluororesin layer 5 and the first fluororesin contained in the base layer 4 have a smaller crosslinking ratio from the surface of the fluororesin layer 5 toward the surface of the iron-based metal substrate 3. Graded material.
It should be noted that the fact that the fluororesin present on the surface of the sliding layer and its neighboring layers has a three-dimensional structure is not limited to that the entire part of the fluororesin layer is composed only of the fluororesin having the three-dimensional structure. A two-dimensional fluororesin may be partially contained.
The layer thickness t ₁ of the fluororesin layer 5 is 10 to 90%, preferably 25 to 75%, of the layer thickness t of the sliding layer, which is the total thickness of the under layer 4 and the layer thickness t _2. %.

  The layer thickness t of the sliding layer 2 is 5 μm or more and less than 40 μm, preferably 15 μm or more and less than 30 μm. If the layer thickness is less than 5 μm, the metal substrate may be exposed due to peeling due to poor adhesion of the coating and abrasion at initial abrasion. When the thickness is 40 μm or more, cracks may occur during the formation of the coating, or the coating may peel off during operation to deteriorate the lubrication state. When the layer thickness is in the range of 5 μm or more and less than 40 μm, exposure of the metal substrate due to initial wear can be prevented, and peeling during operation can be prevented for a long time.

  The heat-resistant resin is a resin containing at least one atom of an oxygen atom, a nitrogen atom and a sulfur atom together with a carbon atom in at least a main chain of a polymer structure. It is a resin that does not thermally decompose when forming the sliding layer by firing. Here, “not thermally decomposed” means a resin that does not start thermal decomposition within the temperature and time for baking the underlayer and the fluororesin layer. By using a heat-resistant resin containing at least one atom of an oxygen atom, a nitrogen atom and a sulfur atom in a main chain of a polymer structure together with a carbon atom, a functional group having excellent adhesion to an iron-based metal substrate and A functional group that also reacts with one fluororesin can be provided in the molecular main chain or at the molecular end.

Examples of the heat-resistant resin include an epoxy resin, a polyester resin, an amide imide resin, an imide resin, an ether imide resin, an imidazole resin, a polyether sulfone resin, a polysulfone resin, a polyether ether ketone resin, and a silicone resin. In addition, a urethane resin or an acrylic resin that prevents shrinkage of the fluororesin during the formation of the coating film can be used in combination.
Among heat-resistant resins, a resin mainly containing an aromatic ring is preferable because of its excellent heat resistance. Preferred heat-resistant resins include aromatic amide imide resins and aromatic imide resins.

  The first fluororesin can be used as long as it is a resin that can be dispersed in a particle form in an aqueous coating solution for forming an underlayer. Examples of the first fluororesin include PTFE particles, tetrafluoroethylene-perfluoro (alkyl vinyl ether) copolymer (hereinafter, referred to as PFA) particles, tetrafluoroethylene-hexafluoropropylene copolymer (hereinafter, referred to as FEP) particles, Alternatively, two or more of these can be preferably used.

In addition to the heat-resistant resin and the first fluororesin, non-ionic surfactants such as polyoxyethylene alkyl ether, inorganic pigments such as carbon black, and N-methyl-2-pyrrolidone Aprotic polar solvent arbitrarily mixed with water, and water as a main solvent. Further, an antifoaming agent, a desiccant, a thickener, a leveling agent, an anti-cissing agent and the like can be added. Examples of the water-based coating liquid for forming the undercoat layer include primer paints EK series and ED series manufactured by Daikin Industries, Ltd.
Instead of the aqueous coating solution, a solution type coating solution in which a fluororesin is dissolved in a resin solution in which the above heat-resistant resin is dissolved in an aprotic polar solvent, or a dispersion type coating solution in which fine particles of a fluororesin are dispersed is used. be able to.

  The fluororesin layer is a fluororesin layer formed on the surface of the underlayer and crosslinked by radiation. The first fluororesin and the second fluororesin may be the same or different, but it is preferable to use the same fluororesin. Examples of the second fluororesin include PTFE, PFA, FEP, ethylene / tetrafluoroethylene copolymer (ETFE) and the like. These resins can be used alone or as a mixture. Among these, PTFE having excellent heat resistance and slidability is preferable.

  The fluororesin layer is obtained by applying and drying an aqueous dispersion in which PTFE resin particles are dispersed. As the aqueous dispersion in which the PTFE resin particles are dispersed, for example, polyflon = PTFE enamel manufactured by Daikin Industries, Ltd. can be mentioned.

  In the sliding member of the present invention, the iron-based metal substrate, the underlayer, and the fluororesin layer are in close contact with each other without providing an adhesive layer. In the method of forming the sliding layer on the surface of the iron-based metal substrate, a method for making the sliding layers adhere to each other will be described below.

(1) Surface treatment of iron-based metal substrate The iron-based metal substrate has a surface roughness (Ra) of 1.0 to 2.0 μm using a shot blast or the like before forming a sliding layer. After that, it is preferable to immerse in an organic solvent such as petroleum benzine and to perform ultrasonic degreasing for about 5 minutes to 1 hour.
(2) Coating of an aqueous coating solution for forming an underlayer Before application of an aqueous coating solution for forming an underlayer, in order to improve the dispersibility of the aqueous dispersion, it is rotated for 1 hour at, for example, 40 rpm using a ball mill. Redistribute. The redispersed aqueous coating solution is filtered using a 100-mesh wire net and applied by a spray method.
(3) Drying of the aqueous coating liquid for forming the underlayer The aqueous coating liquid is dried after being applied. As the drying condition, for example, drying in a constant temperature bath at 90 ° C. for about 30 minutes is preferable. The thickness of the underlayer after drying is in the range of 2.5 to 20 μm, preferably 5 to 20 μm, more preferably 10 to 15 μm. When the thickness is 2.5 μm or less, the metal substrate may be exposed due to peeling or initial abrasion due to poor adhesion of the coating. If the thickness is 20 μm or more, cracks may occur during the formation of the coating, or the coating may peel off during operation to deteriorate the lubrication state. When the layer thickness is in the range of 2.5 to 20 μm, exposure of the metal substrate due to initial wear can be prevented, and peeling during operation can be prevented for a long period of time.

(4) Coating of an aqueous coating solution for forming a fluororesin layer Before applying an aqueous coating solution for forming a fluororesin layer, in order to improve the dispersibility of the aqueous dispersion, use a ball mill at 1 rpm, for example, at 40 rpm. Rotate for time and redisperse. Without firing the underlayer, the redispersed water-based coating solution is filtered on a dried underlayer surface using a 100-mesh wire net, and coated by a spray method.
(5) Drying of an aqueous coating solution for forming a fluororesin layer An aqueous coating solution is applied and dried. As the drying condition, for example, drying in a constant temperature bath at 90 ° C. for about 30 minutes is preferable. The layer thickness of the resin layer containing the fluororesin after drying is in the range of 2.5 to 20 μm, preferably 5 to 20 μm, more preferably 10 to 15 μm. When the thickness is 2.5 μm or less, the metal substrate may be exposed due to peeling due to poor adhesion of the coating and abrasion at initial abrasion. If the thickness is 20 μm or more, cracks may occur during the formation of the coating, or the coating may peel off during operation to deteriorate the lubrication state. When the layer thickness is in the range of 2.5 to 20 μm, exposure of the metal substrate due to initial wear can be prevented, and peeling during operation can be prevented for a long period of time.

  As a method for coating the underlayer and the fluororesin layer, any method can be used as long as a film can be formed, such as a dipping method or a brush coating method, in addition to the spray method. The spraying method is preferred in view of making the surface roughness and coating shape of the coating as small as possible and considering the uniformity of the layer thickness.

(6) Firing After drying the aqueous coating solution for forming the fluororesin layer, the temperature is higher than the melting point of the second fluororesin in the heating furnace and in air, preferably (melting point (Tm) + 30 ° C.) to (melting point (Tm) ) + 100 ° C.), and simultaneously baking the underlayer and the fluororesin layer within a range of 5 to 40 minutes. When the first and second fluororesins are PTFE, firing is preferably performed in a heating furnace at 380 ° C. for 30 minutes. By sintering both the first and second fluororesins simultaneously, rather than applying and drying them, the base layer and the fluororesin layer can adhere to each other without providing an adhesive layer.

(7) Crosslinking of fluororesin layer (crosslinking step)
The coating film after baking has an irradiation temperature of 30 ° C. lower than the melting point of the second fluororesin to 50 ° C. higher than the melting point or lower, preferably 20 ° C. lower than the melting point of the second fluororesin to 30 ° C. of the melting point. The fluororesin layer is cross-linked by irradiating radiation at a temperature of not higher than ℃ and an irradiation dose of 850 to 2500 kGy, preferably 1000 to 2000 kGy, more preferably 1000 to 1500 kGy. The radiation includes α-rays (particle beams of helium-4 nuclei emitted from radionuclides that perform α-decay), β-rays (negative electrons and positrons emitted from nuclei), and electron beams (almost constant kinetic energy. Particle beam such as electron beam having; generally, thermal electrons are accelerated in vacuum); gamma rays (emission and absorption due to transition between energy levels of nuclei and elementary particles, pair annihilation and pair generation of elementary particles) Ionizing radiation such as a short wavelength electromagnetic wave). Among these radiations, from the viewpoint of crosslinking efficiency and operability, an electron beam and a γ-ray are preferable, and an electron beam is more preferable. In particular, an electron beam has advantages such as easy availability of an electron beam irradiation apparatus, simple irradiation operation, and a continuous irradiation step.

If the irradiation temperature is outside the temperature range of 30 ° C. lower than the melting point of the second fluororesin to 50 ° C. higher than the melting point, crosslinking of the fluororesin layer does not proceed sufficiently. Hardening of the fluorine resin layer does not proceed sufficiently. Further, in the irradiation atmosphere, it is necessary to lower the oxygen concentration in the irradiation region by evacuation or injection of an inert gas in order to efficiently perform the crosslinking. The range of the oxygen concentration is preferably from 0 to 300 ppm. To maintain the oxygen concentration in the above concentration range, an inert atmosphere by nitrogen gas injection is preferable from the viewpoint of operability and cost.
Under the sliding condition with a high PV value, if the irradiation dose is less than 850 kGy, the crosslinking becomes insufficient, the abrasion amount is large, and the metal base material may be exposed. Further, when the irradiation dose is higher than 2500 kGy, crosslinking proceeds more than necessary, and the hardness of the coating increases, whereby the coating may become brittle and the coating may be easily damaged such as peeling.

  Irradiation is performed under the condition that the irradiation temperature is 30 ° C. lower than the melting point of the second fluororesin to 30 ° C. higher than the melting point of the second fluororesin and the irradiation dose is 850 to 2500 kGy to crosslink the fluororesin layer. Thereby, the surface hardness of the sliding layer represented by the indentation hardness can be made 85 to 146 MPa. Further, the melting point of the surface of the sliding layer can be lowered to 221 to 281 ° C.

  The acceleration voltage at the time of irradiation is 40 kV or more and less than 500 kV, preferably 40 kV or more and 300 kV or less, more preferably 50 kV or more and less than 100 kV. If it is less than 40 kV, the penetration of the electron beam into the vicinity of the surface layer of the fluororesin layer becomes shallow, and if it is more than 500 kV, the crosslinking proceeds to the underlayer and the whole fluororesin layer. When radiation is applied to a layer containing fluororesin, the intensity of the radiation is attenuated inside the fluororesin, so that the radiation reaches the vicinity of the irradiated surface sufficiently but does not reach other surfaces. Can crosslink the vicinity of the surface of the fluororesin layer.

  A sliding member in which an electron beam is irradiated in an inert atmosphere by nitrogen gas injection at an acceleration voltage of 40 kV or more and less than 500 kV during irradiation, whereby the electron beam is irradiated in a direction perpendicular to the irradiation surface. The irradiation dose on the surface can be increased, and a surface adjacent to the sliding member surface and parallel to the electron beam irradiation direction is also irradiated with the electron beam by scattering of the electron beam. The number of electron beam irradiations on parallel surfaces decreases as the irradiation distance increases. For example, the irradiation dose in a portion near the electron beam irradiation window on the parallel plane can be changed to 1000 kGy and 500 kGy as the distance from 2000 kGy increases.

In order to evaluate the wear resistance of the sliding layer obtained by the above-described method during oil lubrication, the specific wear amount was measured by a Savan-type friction wear test. The test conditions, such as a test piece and a partner material, are shown below.
(1) Preparation of test piece Test piece: A sliding layer was formed on a 30 mm x 30 mm, 2 mm thick metal flat plate made by SPCC. A primer paint (model number: EK-1909S21R) manufactured by Daikin Co., Ltd. was used for the base layer, and a top paint (model number: EK-3700C21R) manufactured by Daikin Co., Ltd. was used for the fluororesin layer. The drying time was 30 minutes in a thermostat at 90 ° C., respectively, and the base layer and the fluororesin layer were simultaneously baked in a heating furnace at 380 ° C. for 30 minutes.
Thereafter, the test piece was irradiated with an electron beam from the sliding layer surface side under the following conditions.
Device used: EB engine manufactured by Hamamatsu Photonics KK Irradiation dose: 1000 kGy in Example 1, 2000 kGy in Example 2, and 500 kGy in Comparative Example 1.
Accelerating voltage: 70 kV
Film temperature during irradiation: 340 ° C
Atmosphere in chamber during irradiation: heated nitrogen

(2) Test piece coating of Comparative Example and Example Comparative Example 1: PTFE coating (irradiation dose: 500 kGy, layer thickness: 20 μm)
Experimental Example 1: PTFE coating (irradiation dose: 1000 kGy, layer thickness: 20 μm)
Experimental Example 2: PTFE coating (irradiation dose: 2000 kGy, layer thickness: 20 μm)

(3) Conditions of Savan-type friction and wear test Counterpart material: Ring of SUJ2 φ40 mm × width 10 mm × sub-curvature R60 mm (surface roughness Ra = 0.006 to 0.013 μm) that has been quenched and tempered
Lubricating oil: Mobile velocity oil No. 3 (VG2) lubrication Sliding speed: 0.5 m / s
Load: 50N (0.5 GPa surface pressure)
PV value: 15 GPa · m / min
Sliding time: 3000 minutes (50 hours)

(4) Test results Table 1 shows the test results. The specific wear amount is a value obtained by dividing the wear volume by the sliding distance and the load, and the wear volume was calculated from the short diameter of the formed wear mark and the shape and dimension (φ40 mm and R60 mm) of the mating material. Table 1 shows the specific wear amounts of Experimental Examples 1 and 2 when the specific wear amount of Comparative Example 1 was 1.000.

  As shown in Table 1, as compared to Comparative Example 1, Examples 1 and 2 exhibited excellent specific wear under high PV conditions. The specific wear of Examples 1 and 2 was 5% or less of the specific wear of Comparative Example 1. For example, in the related art having the same fluorine-based resin film (Patent Document 5), the irradiation dose in the crosslinking step was 250 to 800 kGy, whereas in the present invention, the irradiation dose was increased to 850 kGy or more. It has been found that abrasion resistance suitable for use under PV conditions is obtained.

Next, the fact that the vicinity of the surface layer of the fluororesin layer of the sliding member used in the present invention has a crosslinked structure will be described. In general, fluororesins, especially PTFE resins, are chemically very stable and extremely stable to organic solvents and the like, and it is difficult to identify the molecular structure or molecular weight. However, the crosslinked structure of the sliding member of the present invention can be identified by measurement and analysis by ¹⁹ F Magic angle Spinning (MAS) nuclear magnetic resonance (NMR) method (High speed magic angle nuclear magnetic resonance).

The measurement was performed using NMR apparatus JNM-ECX400 manufactured by JEOL Ltd., using suitable measurement nuclide ( ¹⁹ F), resonance frequency (376.2 MHz), MAS (Magic Angle Spinning) rotation speed (15 and 12 kHz), sample amount. (Approximately 70 μL in a 4 mm solid NMR tube), recycle delay time (10 seconds) and measurement temperature (approximately 24 ° C.). The results are shown in FIGS. 2 shows an NMR of the surface layer at an irradiation dose of 0 kGy, and FIG. 3 shows an enlarged view of an NMR chart at an irradiation dose of 500 kGy. FIG. 4 shows the NMR of the surface layer at an irradiation dose of 1000 kGy. In FIG. 2 to FIG. 4, the upper part shows the MAS rotation speed of 15 kHz, and the lower part shows the MAS rotation speed of 12 kHz. FIG. 5 is a graph in which the signal intensity at −82 ppm, at which the intensity increases with crosslinking, is normalized by the signal intensity at −122 ppm, which is the main signal. In FIG. 5, the upper part shows measured values, and the lower part shows a graph. It is considered that the higher the signal intensity ratio, the more the degree of crosslinking has advanced.

When the fluororesin layer without irradiation (irradiation dose, 0 kGy) was measured under the above conditions, signals of -82 ppm, -122 ppm, and -162 ppm were observed at a MAS rotation speed of 15 kHz (the upper part of Fig. 2). At MAS rotation frequency of 12 kHz, signals of -58 ppm, -82 ppm, -90 ppm, -122 ppm, -154 ppm, and -186 ppm were also observed (lower part in FIG. 2). -122ppm is -CF ₂ -CF ₂ - is a signal of the F atoms in the binding, -82Ppm is known to be a signal of F atoms -CF ₃ in -CF ₂ -CF ₃ binding. From this, the signals at −82 ppm and −162 ppm at a MAS rotation frequency of 15 kHz and at −58 ppm, −90 ppm, −154 ppm, and −186 ppm at a MAS rotation speed of 12 kHz are spinning side bands (SSB). Note that in the region of -122 ppm to -130 ppm, a signal which is hidden behind a signal of -122 ppm and is broad has been observed. This signal -CF ₂ in -CF ₂ -CF ₃ binding should be observed -126Ppm - is a signal of the F atoms. Therefore, the fluororesin layer of uncrosslinked not performed Irradiation -CF ₂ -CF ₂ - -122ppm attributable to binding, by NMR chart having a signal of -82ppm and -126ppm attributable to -CF ₂ -CF ₃ expressed.

When the solid-state ¹⁹ F MAS NMR of the surface layer (irradiation dose of 500 kGy) of the fluororesin irradiated with the radiation of 500 kGy under the same conditions as the uncrosslinked fluororesin layer, -68 ppm and -70 ppm excluding the spinning side band , -80 ppm, -82 ppm, -109 ppm, -112 ppm, -122 ppm, -126 ppm, -152 ppm, and -186 ppm (FIG. 3, upper part and FIG. 3, lower part). Signals at -68 ppm, -70 ppm, -80 ppm, -109 ppm, -112 ppm, -152 ppm, and -186 ppm newly appeared upon irradiation, and the intensity of the signal at -82 ppm was higher than that of non-irradiation.

When the solid-state ¹⁹ F MAS NMR of the surface layer (irradiation dose of 1000 kGy) of the fluororesin irradiated with a dose of 1000 kGy under the same conditions as that of the uncrosslinked fluororesin layer is -68 ppm, -70 ppm except for spinning side bands. , -77 ppm, -80 ppm, -82 ppm, -109 ppm, -112 ppm, -122 ppm, -126 ppm, -152 ppm, and -186 ppm (FIG. 4, upper row and FIG. 4, lower row). Signals at -68 ppm, -70 ppm, -77 ppm, -80 ppm, -109 ppm, -112 ppm, -152 ppm, and -186 ppm newly appear upon irradiation, and the signal intensity at -82 ppm increases from that at 500 kGy irradiation. I was

The above signals, if indicated imputed to F atom underlined, for example -70ppm is = CF-C F _3, -109ppm is _{-C F 2 -CF (CF 3)} -C F 2 -, - 152ppm is = C F -C F =, - 186ppm is known to be attributed to ≡C F (Beate Fuchs and Ulrich Scheler , Branching and Cross-Linking in Radiation-Modified Poly (tetrafluoroethylene):. a Solid-State NMR Investigation. Macromolecules, 33, 120-124. 2000).

These signals indicate the presence of chemically non-equivalent fluorine atoms and also indicate that the surface layer of the fluororesin layer has formed a three-dimensional structure by crosslinking. Further, according to the above-mentioned literature, it is known that the intensity of the observed signal is stronger at an irradiation dose of 1000 kGy than at an irradiation dose of 500 kGy, and at least up to an irradiation dose of 3000 kGy, the signal becomes stronger as the irradiation dose increases. Have been. Note that signals that have not been described in the literature, it is conceivable to have different structures of the fluororesin layer due to the difference in irradiation conditions of radiation, the crosslinking structure is formed, = CF-C F _{3, -C F 2 -CF (CF} 3) -C F 2 -, = = C F -C F, it is apparent from the presence of structures such ≡C F.

  As shown in FIG. 5, the normalized signal intensity ratio increases as the irradiation dose increases. It can be seen that a crosslinked structure clearly appears at an irradiation dose of 500 kGy.

  The water-based coating solution for forming the fluororesin layer used in the above example was applied in a thermostat at 90 ° C. for about 30 minutes under a drying condition, dried and then baked in a heating furnace at 380 ° C. for 30 minutes in air. And an uncrosslinked fluororesin film having a thickness of 4 μm was prepared. Five such films were laminated closely, and one side was irradiated with an electron beam under the above experimental conditions. After the irradiation, the fluororesin coating was separated, and each film was subjected to NMR measurement using an NMR apparatus JNM-ECX400 manufactured by JEOL Ltd. in accordance with the above experimental example. As a result of the measurement, it was found that the signal intensity accompanying the crosslinking decreased from the irradiated surface toward the film present on the surface opposite to the irradiated surface, and that the film had an inclined structure.

  Radiation irradiation crosslinks the surface of the fluororesin and increases the surface hardness. Here, the surface hardness at the irradiation dose of 0 kGy, 500 kGy, and 1000 kGy was measured, respectively. The surface hardness was determined by measuring the indentation hardness of a flat plate test piece using a nanoindenter (G200) manufactured by Agilent Technologies, Inc., according to a method based on ISO14577. In addition, the measured value shows the average value of the depth (the place where the hardness is stable) which is not affected by the surface roughness and the base material (SPCC), and was measured at 10 places for each test piece. The measurement conditions were as follows: the indenter shape was a Berkovich type, the indentation depth was a depth at which the load was 5 mN, the load application speed was 10 mN / min, and the measurement temperature was 25 ° C. The indentation hardness was calculated from the indentation load and the displacement (area). FIG. 6 shows the measurement results and graphs of the results.

  In the graph of FIG. 6, the vertical axis indicates the indentation hardness and the horizontal axis indicates the irradiation dose. Since the indentation hardness and the irradiation dose show a good correlation, it is possible to draw a regression line between them. From the regression line, the indentation hardness was calculated when the irradiation dose was 500 kGy, 850 kGy, 1000 kGy, 1500 kGy, 2000 kGy, and 2500 kGy, respectively. Table 2 shows the results.

As shown in Table 2 and FIG. 6, by cross-linking the surface of the fluororesin, and as the degree of cross-linking increases, the surface hardness expressed by indentation hardness increases. Under the high PV conditions targeted by the sliding member of the present invention, the indentation hardness of the sliding layer is from 85 to 146 MPa, preferably from 88 to 126 MPa, and more preferably from 92 to 108 MPa. The fluororesin layer is hardened by irradiating radiation so as to have an indentation hardness in the above numerical range. The irradiation dose is preferably 850 to 2500 kGy. The surface hardness of the sliding layer can be adjusted within this irradiation dose range.
As a result of the irradiation, if the indentation hardness is less than 85 MPa, the amount of abrasion is large under high PV conditions, and the metal substrate may be exposed. Further, when the indentation hardness is higher than 146 MPa, the hardness of the coating is extremely increased, thereby embrittlement and the coating may be easily damaged such as peeling.

In addition, the radiation resin can crosslink the fluororesin to lower the melting point. The measurement of the melting point was performed using a differential scanning calorimeter (product name "DSC6220", manufactured by SII Nanotechnology Inc.). For the measurement sample from which only the irradiation surface layer was scraped, a fluororesin coating 10 to 15 mg sealed in a sealed aluminum sample container (hereinafter referred to as an aluminum pan) was used. A material in which aluminum oxide (Al ₂ O ₃ ) was sealed in an aluminum pan was used. Regarding the measurement conditions, in a nitrogen flow (200 mL / min) atmosphere, the temperature was raised from 30 ° C. to 370 ° C. at a rate of 2 ° C./min, and held at that temperature for 20 minutes, followed by 2 ° C./min. It is a numerical value measured by lowering the temperature from 370 ° C. to 40 ° C. at a temperature lowering rate. The peak top of the endothermic peak at the time of temperature rise was defined as the melting peak temperature and the melting point. FIG. 7 shows the measurement results and graphs of the results.

  The graph of FIG. 7 shows the melting point on the vertical axis and the irradiation dose on the horizontal axis. Since a good correlation is shown between the melting point and the irradiation dose, it is possible to draw a regression line between the two. From the regression line, melting points were calculated when the irradiation dose was 500 kGy, 850 kGy, 1000 kGy, 1500 kGy, 2000 kGy, and 2500 kGy. Table 3 shows the results.

  As shown in Table 3 and FIG. 7, the surface is crosslinked, and the higher the degree of crosslinking, the lower the melting point of the surface. In the present invention, the coating film after firing, the irradiation temperature is from 30 ° C. lower than the melting point of the second fluororesin before irradiation to 50 ° C. or higher than the melting point, the melting point of the coating is 221 to Radiation is applied at 281 ° C., preferably 241-281 ° C., more preferably 260-276 ° C. to lower the melting point of the fluororesin layer. The irradiation dose is preferably 850 to 2500 kGy. Under the high PV conditions targeted by the sliding member of the present invention, if the melting point is higher than 281 ° C., the abrasion loss is large, and the metal base may be exposed. Further, when the melting point is lower than 221 ° C., the hardness of the coating increases, thereby embrittlement, and the coating may be easily damaged such as peeling.

  The iron-based metal substrate having the above-mentioned sliding layer has the following characteristics: the sliding layer has excellent adhesion to the iron-based metal substrate, and the sliding surface has excellent wear resistance even in oil. It can be suitably used for a cage made and a rolling bearing having this cage. In particular, the present invention is suitable for a large connecting rod end bearing, a small connecting rod bearing, or a crankshaft support shaft of an engine which is used in oil and under high PV conditions and is a rolling bearing using a needle roller as a rolling element.

FIG. 8 shows the structure of the rolling bearing cage having the sliding layer. FIG. 8 is a perspective view of an iron-based metal cage for a rolling bearing using needle rollers as rolling elements.
The cage 6 is provided with pockets 7 for holding the needle rollers. Each of the needles 8 includes a column portion 8 located between the pockets and both annular portions 9 and 10 for fixing the column portion 8. Maintain the roller spacing. The column portion 8 has a complicated shape of a flat plate which is bent at the center of the column portion into a mountain fold and a valley fold in order to hold the needle rollers, and has a circular bulge in a plan view at a joint portion with the annular portions 9 and 10 on both sides. It has been. The method of manufacturing this cage is to cut out an annular ring from the shaped material and form the pocket 7 by punching, press a flat plate, cut it to an appropriate length, then round it into an annular shape and weld it. Can be employed. A sliding layer of a fluororesin film is formed on the surface of the cage 6. The surface part of the cage forming the sliding layer is a part that comes into contact with the lubricating oil or grease, and the sliding layer is formed on the entire surface of the cage 6 including the surface of the pocket 7 that comes into contact with the needle rollers. Is preferred.

  FIG. 9 is a perspective view showing a needle roller bearing which is one embodiment of the rolling bearing. As shown in FIG. 9, the needle roller bearing 11 includes a plurality of needle rollers 12 and a retainer 6 that holds the needle rollers 12 at regular intervals or at irregular intervals. In the case of the bearing for the connecting rod portion of the engine, the bearing inner ring and the bearing outer ring are not provided, and a shaft such as a crankshaft or a piston pin is directly inserted into the inner diameter side of the retainer 6, and the outer diameter side of the retainer 6 is a housing. It is used by being fitted into an engagement hole of a certain connecting rod. Since the needle rollers 12 having no inner and outer rings and having a smaller diameter than the length are used as rolling elements, the needle roller bearing 11 is more compact than a general rolling bearing having inner and outer rings. Become.

FIG. 10 is a longitudinal sectional view of a four-cycle engine using the needle roller bearing.
FIG. 10 is a longitudinal sectional view of a four-cycle engine using a needle roller bearing as an example of the rolling bearing of the present invention. The four-stroke engine opens the intake valve 13a, closes the exhaust valve 14a, and inhales a mixture of gasoline and air into the combustion chamber 15 through the intake pipe 13, and the piston 16 closes the intake valve 13a. To compress the air-fuel mixture by expelling the air-fuel mixture, an explosion process to explode the compressed air-fuel mixture, and an exhaust process to exhaust the exploded combustion gas through the exhaust pipe 14 by opening the exhaust valve 14a. A piston 16 that performs a linear reciprocating motion by combustion in these strokes, a crankshaft 17 that outputs a rotary motion, a connecting rod 18 that connects the piston 16 and the crankshaft 17 and converts the linear reciprocating motion into a rotary motion, Having. The crankshaft 17 rotates about a rotation center axis 19, and the rotation is balanced by a balance weight 20.

The connecting rod 18 has a large end 21 provided below the linear rod and a small end 22 provided above. The crankshaft 17 is rotatably supported via a needle roller bearing 11a attached to an engagement hole of the large end 21 of the connecting rod 18. A piston pin 23 connecting the piston 16 and the connecting rod 18 is rotatably supported via a needle roller bearing 11b attached to an engagement hole of the small end 22 of the connecting rod 18.
By using the needle roller bearing having excellent slidability, even a small-sized or high-output two-cycle engine or a four-cycle engine is excellent in durability.

  In FIG. 9, needle roller bearings are exemplified as the bearings. However, the rolling bearings of the present invention include cylindrical roller bearings, tapered roller bearings, self-aligning roller bearings, needle roller bearings, thrust cylindrical roller bearings, and thrust tapered rollers other than those described above. It can also be used as roller bearings, thrust needle roller bearings, thrust self-aligning roller bearings, and the like. In particular, it is used in an oil lubricating environment and under high PV conditions, and can be suitably used for a rolling bearing using a ferrous metal cage.

  Further, since the iron-based metal base material having the sliding layer is excellent in wear resistance even under grease lubrication composed of a base oil and a thickener, an iron-based metal cage, It can be suitably used for a rolling bearing having. The grease deteriorates due to a rise in the temperature of the bearing due to heat generated at the time of high-speed rotation, and the incorporation of metal wear powder generated by friction between the rolling elements made of steel and the retainer. On the other hand, by providing the sliding layer of the present invention on at least one of the iron-based metal base materials that slide with each other, the increase of the metal wear powder over time as compared with the case where iron slides with each other. The amount (the amount mixed into grease) can be suppressed. As a result, deterioration of the grease can be suppressed, and the lubrication life of the grease can be extended.

  As an example of a grease-lubricated bearing, a bearing for a main motor of a railway vehicle uses a ball bearing as a fixed-side bearing in order to cope with expansion and contraction of the main shaft in an axial direction due to a temperature change. As the free-side bearing, a cylindrical roller bearing capable of coping with expansion and contraction of the main shaft is used. The fixed-side ball bearing is, for example, a deep groove ball bearing, and includes a steel ball and an iron plate corrugated cage. The cylindrical roller bearing on the free side includes a steel cylindrical roller and a brass rubbing and holding device. When these main motor bearings are used under high temperature and high speed rotation, for example, grease containing lithium soap and mineral oil is used as a lubricant.

  Since the lubrication life of grease in such a main motor bearing of a railway vehicle is shorter than the rolling fatigue life of the bearing, at present, grease refilling work is performed in a disassembly inspection of a vehicle performed at a predetermined traveling distance. Maintenance) is performed. Also, even in the current maintenance cycle, the grease often deteriorates due to the above-described reasons. By applying the rolling bearing of the present invention as this bearing, the lubrication life of the grease can be extended, and the maintenance cycle can be extended.

  The present invention can provide a sliding material which can suppress wear even under conditions of high PV value (high sliding speed or high surface pressure) in lubricating oil. Can be used in the field of cages used therein and rolling bearings using the cages.

DESCRIPTION OF SYMBOLS 1 Sliding member 2 Sliding layer 3 Iron-based metal base material 4 Underlayer 5 Fluororesin layer 6 Cage 7 Pocket 8 Column part 9 Ring part 10 Ring part 11 Needle roller bearing 12 Needle roller 13 Intake pipe 14 Exhaust pipe 15 Combustion chamber 16 Piston 17 Crankshaft 18 Connecting rod 19 Rotation center axis 20 Balance weight 21 Large end 22 Small end 23 Piston pin

Claims (9)

A sliding member having a sliding layer on the surface of an iron-based metal substrate,
The sliding member has an oil lubricating environment and a PV value, which is a product of a surface pressure (P) and a sliding speed (V), of 10 to 20 GPa · m / min. A sliding member used under the following conditions:
The sliding layer has an underlayer containing a heat-resistant resin and a first fluororesin on the surface of the iron-based metal substrate, and a fluororesin layer containing a second fluororesin on the surface of the underlayer,
The heat-resistant resin is a resin containing at least one atom of an oxygen atom, a nitrogen atom, and a sulfur atom in at least a main chain of a polymer structure, together with a carbon atom,
The fluororesin layer is a crosslinked fluororesin layer formed by crosslinking at least the surface vicinity thereof,
A sliding member, wherein the sliding layer has an indentation hardness of 85 to 146 MPa as measured by an ISO 14577 method, and a melting point near the surface of the sliding layer is 221 to 281 ° C.   The sliding member according to claim 1, wherein the sliding speed (V) is 0.1 to 1.0 m / s.   The sliding member according to claim 1, wherein the iron-based metal substrate, the underlayer, and the fluororesin layer are in close contact with each other without providing an adhesive layer.   The sliding layer according to claim 1, wherein a cross-linking ratio of the first and second fluororesins decreases from a surface of the fluororesin layer toward a surface of the iron-based metal substrate. Item 4. The sliding member according to any one of Items 3 to 3. The second fluororesin is a polytetrafluoroethylene resin, and the vicinity of the surface of the second fluororesin is higher than that of an uncrosslinked polytetrafluoroethylene resin by solid-state ¹⁹ F Magic angle Spinning (MAS) nuclear magnetic resonance. (NMR) The chemical shift value (δ ppm) appearing in the chart is −68 ppm, −70 ppm, −77 ppm, −80 ppm, −109 ppm, in addition to −82 ppm, −122 ppm, and −126 ppm of the uncrosslinked polytetrafluoroethylene resin. At least one chemical shift value selected from -112 ppm, -152 ppm, and -186 ppm appears, or the signal intensity of the chemical shift value appearing at -82 ppm is compared to the signal intensity of the uncrosslinked polytetrafluoroethylene resin. And increase The sliding member according to any one of claims 1 to 4, characterized in that there.   The sliding member according to any one of claims 1 to 5, wherein the heat-resistant resin is at least one aromatic resin selected from an aromatic amide imide resin and an aromatic imide resin.   The sliding member according to claim 1, wherein a thickness of the sliding layer is 5 μm or more and less than 40 μm. A ferrous metal cage for holding a rolling element of a rolling bearing,
An iron-based metal cage, wherein the iron-based metal cage is formed by the sliding member according to any one of claims 1 to 7. A rolling bearing having the iron-based metal cage according to claim 8,
A rolling bearing, wherein the rolling bearing is a rolling bearing for a large end of a connecting rod of an engine, a rolling bearing for a small end of a connecting rod, or a rolling bearing for a crankshaft support shaft.

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