JP2020051506A - Holder for rolling bearing, and rolling bearing - Google Patents

Abstract

To provide a holder for a rolling bearing excellent in abrasion resistance and slide property while suppressing failure such as exfoliation, and a rolling bearing using the holder.SOLUTION: A holder 1 is a holder for a rolling bearing that has a sliding layer 2 on a surface of an iron-based metal material 3 and holds a rolling body of a rolling bearing. The sliding layer 2 has a fluororesin layer containing a fluororesin on at least its surface. The fluororesin layer is a crosslinked fluororesin layer 5 crosslinked from the surface of the sliding layer 2 to a boundary surface with another material. The cross-linked fluororesin layer 5 is a layer in which a crosslinking rate decreases continuously in a depth direction from the surface of the sliding layer 2. The crosslinking rate is within a range of 9 to 25%.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a cage for a rolling bearing and a rolling bearing, and more particularly to a cage for a rolling bearing which has excellent wear resistance on the surface of the cage and can maintain the excellent wear resistance for a long period of time, 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, there is known a method of irradiating a polytetrafluoroethylene (hereinafter, referred to as PTFE) coating formed on a sliding portion of a sliding member with radiation to improve abrasion resistance and adhesion to a base material ( 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 method for producing a modified fluororesin coating material that is irradiated with ionizing radiation is known (Patent Document 2).

  As a sliding member made of a fluororesin used for a non-lubricated bearing, a dynamic seal, etc., a fluororesin obtained by heating a fluororesin above its crystal melting point and irradiating ionizing radiation in the absence of oxygen is known. (Patent Document 3).

  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 4).

JP 2010-155443 A JP 2002-225204 A JP-A-9-278907 Japanese Patent No. 5189427

However, the production method disclosed in Patent Literature 1 is a method for improving adhesion to a substrate because it is used under a condition of low lubrication without lubrication, and is difficult to apply to a wide range of conditions.
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 material to rolling bearings used under a wider range of conditions.
In the silver-plated cage described in Patent Literature 4, 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 to address such problems, and a rolling bearing retainer excellent in wear resistance and slidability while suppressing defects such as peeling, and a rolling bearing using the retainer. The purpose is to provide.

  The cage for a rolling bearing of the present invention is a cage for a rolling bearing that has a sliding layer on a surface of a base material made of an iron-based metal material, and that holds a rolling element of a rolling bearing. A fluororesin layer containing a fluororesin on at least the surface, wherein the fluororesin layer is a crosslinked fluororesin layer crosslinked from the surface of the sliding layer to a boundary surface with another material, and the crosslinked fluororesin layer Is a layer in which the cross-linking rate decreases continuously from the surface of the sliding layer in the depth direction, and is characterized in that the cross-linking rate is 9 to 25%. Here, the “crosslinking ratio” refers to a crosslinking ratio at a predetermined depth from the outermost surface of the second fluororesin layer (the surface of the sliding layer).

  The sliding layer has an underlayer containing a heat-resistant resin and a first fluororesin formed on the surface of the iron-based metal material, and a second fluorine containing a second fluororesin formed on the surface of the underlayer. A resin layer, wherein 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; Is the crosslinked fluororesin layer.

  The sliding layer has a thickness of 10 μm or more and less than 40 μm, and the crosslinked fluororesin layer has a thickness of 5 to 11 μm.

  The fluorine resin contained in the crosslinked fluorine resin layer is a polytetrafluoroethylene (PTFE) resin.

  The cross-linking ratio at the deepest part of the cross-linked fluororesin layer is 9 to 12%. Further, the cross-linking ratio in the surface layer portion of the cross-linked fluororesin layer is 20 to 25%. Here, the “deepest part of the crosslinked fluororesin layer” refers to a portion within 1 μm from a boundary surface between the crosslinked fluororesin layer and another material (for example, an underlayer). Further, the “surface portion of the crosslinked fluororesin layer” refers to a portion within 1 μm from the outermost surface of the crosslinked fluororesin layer.

  The rolling bearing of the present invention is a rolling bearing that supports a crankshaft that outputs rotational motion and is provided at a large end of a connecting rod that converts linear reciprocating motion into rotary motion, or a rolling bearing that is attached to the crankshaft. Further, the cage for holding the rolling element of the rolling bearing is a cage for a rolling bearing of the present invention.

  The cage for a rolling bearing of the present invention has a sliding layer formed on a base material made of an iron-based metal material, and has a fluororesin layer on at least the surface of the sliding layer. Since it is a cross-linked fluororesin layer cross-linked from the surface of the sliding layer to the boundary surface with other materials, it has excellent resistance under a wide range of conditions (for example, in lubricating oil, high sliding speed, and high surface pressure). It exhibits abrasion and can maintain the life of the bearing for a long time. Further, the crosslinked fluororesin layer is a gradient layer in which the crosslink rate decreases continuously from the surface of the sliding layer in the depth direction, and the crosslink rate is in the range of 9 to 25%. The wear resistance at the deepest part of the fluororesin layer can be maintained at a level equivalent to that of the surface part. In addition, since excessive cross-linking of the surface layer is suppressed, peeling of the coating due to brittleness can be suppressed. As a result, even if the vicinity of the surface layer is worn due to initial abrasion or accidental overload, the newly developed surface that has been worn maintains the abrasion resistance, preventing the exposure of other materials (underlayer and base material). The wear of the sliding layer during operation can be prevented for a long period of time.

It is sectional drawing of the base material of a cage, and a sliding layer. 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. It is an enlarged view of an NMR chart of a crosslinked PTFE resin or the like.

  In the sliding layer formed on the base material surface of the rolling bearing retainer, the present inventors focused on the crosslinking ratio of the crosslinked fluororesin layer on the sliding layer surface in order to improve the wear resistance of the sliding layer. . If the cross-linking ratio of the cross-linked fluororesin layer becomes too large, it is considered that the coating becomes brittle and problems such as peeling occur. Therefore, the present inventors have intensively studied to obtain an abrasion resistance effect by crosslinking in the entire crosslinked fluororesin layer while suppressing peeling and the like. As a result, it has been found that by setting the cross-linking rate of the cross-linked fluororesin layer within the range of 9 to 25%, the abrasion resistance effect by cross-linking can be obtained even at the deepest part of the resin layer. The present invention is based on such findings.

The cage for a rolling bearing of the present invention has a sliding layer formed on an iron-based metal material, and has a crosslinked fluororesin layer on at least the surface of the sliding layer.
Examples of the iron-based metal material include bearing steel, carburized steel, carbon steel for machine structures, cold-rolled steel, and hot-rolled steel used for rolling bearings. After the iron-based metal material is processed into the shape of the cage, the surface hardness is adjusted to a predetermined surface by quenching and tempering. 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 material whose Hv value is adjusted to 484 to 595.

  FIG. 1 shows a cross-sectional view of the cage for a rolling bearing of the present invention. The sliding layer 2 constituting the cage 1 includes an underlayer 4 formed on the surface of the iron-based metal material 3 and a crosslinked fluororesin layer 5 formed on the surface of the underlayer 4. The fluororesin contained in the crosslinked fluororesin layer 5 is crosslinked from the surface of the sliding layer to the interface between the underlayer 4 and the crosslinked fluororesin layer 5 (hereinafter simply referred to as an interface). The cross-linking rate of the fluororesin present between the surface and the boundary surface decreases continuously from the surface of the sliding layer toward the boundary surface. That is, the crosslinked fluororesin layer 5 is an inclined layer in which the crosslink rate decreases from the outermost surface toward the depth direction.

  The underlayer 4 is a mixture layer containing a heat-resistant resin and a first fluororesin, and improves the adhesion between the iron-based metal material 3 and the crosslinked fluororesin layer 5. The crosslinking of the fluororesin contained in the base layer 4 is not particularly limited. For example, a structure in which the cross-linking rate of the fluororesin existing between the boundary surface and the surface of the iron-based metal material 3 is continuously reduced from the boundary surface toward the iron-based metal material may be employed. May be a structure in which only the fluororesin present in the polymer is crosslinked.

The heat-resistant resin is a resin that does not thermally decompose during firing of the underlayer and the upper layer film. Here, “not thermally decomposed” means a resin that does not start thermal decomposition within the temperature and time for baking the underlayer and the upper layer film. Further, the heat-resistant resin is preferably a resin having a functional group having excellent adhesion to an iron-based metal material and a functional group which also reacts with the first fluororesin 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.

  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.

  The crosslinked 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 crosslinked 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.

The thickness of each layer and the sliding layer will be described with reference to FIG. The layer thickness t ₁ of the crosslinked fluororesin layer 5 is 10 to 90%, preferably 25 to 90%, based on the total thickness t of the sliding layer, which is the total thickness of the underlayer 4 and the layer thickness t _2. 75%.

The thickness t ₁ of the crosslinked fluororesin layer 5 is in the range of 5 to 20 μm, preferably 5 to 11 μm. If the thickness is less than 5 μm, the underlying layer 4 may be exposed due to peeling due to poor adhesion of the coating and abrasion at initial abrasion. In particular, when the layer thickness t ₁ is in the range of 5 to 11 μm, exposure of the underlayer 4 due to initial wear can be prevented, and even at the deepest portion 5 a of the crosslinked fluororesin layer 5 (a portion within 1 μm from the boundary surface). Abrasion resistance can be exhibited.

The layer thickness t ₂ of the underlayer 4 is in the range of 5 to 20 μm, preferably 10 to 15 μm. If the thickness is less than 5 μm, the iron-based metal material 3 may be exposed due to peeling due to poor adhesion of the coating and abrasion at initial abrasion. If it exceeds 20 μm, 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 t2 is in the range of ₅ to 20 μm, it is possible to prevent the iron-based metal material 3 from being exposed due to initial wear, and to prevent peeling during operation for a long time.

  As described above, the layer thickness t of the sliding layer 2 is 10 μm or more and less than 40 μm, and preferably 15 μm to 26 μm. If the layer thickness t is less than 10 μm, the iron-based metal material 3 may be exposed due to peeling or initial wear due to poor adhesion of the coating. 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 t is in the range of 10 μm or more and less than 40 μm, exposure of the iron-based metal material 3 due to initial wear can be prevented, and peeling during operation can be prevented for a long time.

A method for forming the sliding layer on the surface of the iron-based metal material will be described below.
(1) Surface treatment of iron-based metal material The surface roughness (Ra) of the iron-based metal material is previously adjusted to 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 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.

(4) Coating of an aqueous coating solution for forming a second fluororesin layer Before the aqueous coating solution for forming a second fluororesin layer, a ball mill is used to improve the dispersibility of the aqueous dispersion. Rotate at 40 rpm for 1 hour to redisperse. The redispersed aqueous coating liquid is filtered using a 100-mesh wire net, and coated using a spray method.
(5) Drying of aqueous coating liquid for forming second fluororesin layer The aqueous coating liquid 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.
As a method for coating the undercoat layer and the second 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 the second fluororesin layer is dried, it is fired in a heating furnace in air in the range of (melting point (Tm) + 30 ° C.) to (melting point (Tm) + 100 ° C.) for 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.

(7) Electron Beam Irradiation of the Second Fluororesin Layer The baked film is irradiated with an irradiation temperature, an irradiation dose, and an accelerating voltage such that the crosslinking ratio of the second fluororesin layer is in the range of 9 to 25%. Irradiation is performed to crosslink the second fluororesin layer. 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 cross-linking rate of the second fluororesin layer is lower than 9%, the amount of abrasion is large and the underlying layer may be exposed. On the other hand, when the crosslinking ratio is higher than 25%, the time required for electron beam irradiation becomes longer, and mass productivity is reduced. Further, the crosslinking proceeds more than necessary, and the hardness of the second fluororesin layer is increased, whereby the second fluororesin layer may be embrittled and may easily be damaged such as peeling. Further, since the cross-linking rate of the second fluororesin layer decreases in the depth direction, the cross-linking rate of the deepest portion 5a is lower than that of the surface layer portion 5b (a portion within 1 μm from the outermost surface) (see FIG. 1). In the present invention, the cross-linking rate of the second fluororesin layer is set to 9 to 25%, and the cross-linking rate is set to 9% or more even in the deepest portion 5a, so that the abrasion resistance in this portion is also ensured. As a result, even if the surface layer is worn due to initial abrasion or accidental overload, the newly formed surface (e.g., the deepest part) has abrasion resistance, so that the underlayer can be prevented from being exposed and the peeling during operation can be prolonged. Can be prevented over a period of time.

  Regarding the crosslinking ratio of the second fluororesin layer, more preferably, the crosslinking ratio at the deepest portion is 9 to 12%, and the crosslinking ratio at the surface layer portion is 20 to 25%.

FIG. 2 shows an example of the structure of a cage for a rolling bearing having the sliding layer. FIG. 2 is a perspective view of a ferrous 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. This retainer is a method in which an annular ring is cut out from a cast material, and the pocket 7 is formed by punching by pressing. After pressing a flat plate, it is cut into an appropriate length, then rounded into an annular shape and joined by welding. And the like. The sliding layer 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. Further, the crosslinking ratio of the second fluororesin layer in the sliding layer formed on the entire surface more preferably satisfies the above numerical range.

  FIG. 3 is a perspective view showing a needle roller bearing which is an embodiment of the rolling bearing. As shown in FIG. 3, the needle roller bearing 11 includes a plurality of needle rollers 12 and a retainer 6 for holding 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. 4 is a longitudinal sectional view of a four-cycle engine using the needle roller bearing. FIG. 4 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 sucks a mixture of gasoline and air into the combustion chamber 15 through the intake pipe 13; 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. In addition, 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.

  FIG. 3 illustrates a needle roller bearing as an example of a bearing. However, the rolling bearing of the present invention is not limited to the above-described cylindrical roller bearing, tapered roller bearing, self-aligning roller bearing, needle roller bearing, thrust cylindrical roller bearing, and thrust tapered roller. It can also be used as roller bearings, thrust needle roller bearings, thrust self-aligning roller bearings, and the like. In particular, it can be suitably used for a rolling bearing which is used in an oil lubricating environment and uses an iron-based metal material cage.

  FIG. 1 illustrates a two-layer structure in which the sliding layer includes an underlayer and a crosslinked fluororesin layer. However, the present invention is not limited to this. For example, the sliding layer has a single-layer structure including only a crosslinked fluororesin layer. You may. Also in this case, the crosslinking rate of the crosslinked fluororesin layer is 9 to 25%. Therefore, the abrasion resistance is excellent even in the deepest part near the boundary surface with the base material, and the base material can be prevented from being exposed.

(1) Preparation of Sliding Member Sliding member: A sliding layer was formed on a 30 mm × 30 mm, 2 mm thick metal flat plate made by SPCC. The undercoat layer is made of Daikin's primer paint (model number: EK-1909S21R), and the second fluororesin layer is made of Daikin's top paint (model number: EK-3700C21R). Was 20 μm. The drying time was 30 minutes in a thermostat at 90 ° C., and baked in a heating furnace at 380 ° C. for 30 minutes.
Thereafter, electron beam irradiation was performed from the sliding layer side under the following conditions to obtain a sliding member.
Apparatus used: Hamamatsu Photonics EB engine Irradiation conditions: Acceleration voltage 70 kV
Dose 1652 kGy
Temperature 340 ° C
Atmosphere in chamber during irradiation Heated nitrogen

(2) Calculation of Crosslinking Ratio In the sliding member obtained above, the second fluororesin layer was scraped off at a depth of 5 μm (0 to 5 μm, 5 to 10 μm, 10 to 15 μm, 15 to 20 μm), and The sample in the depth range was used as a measurement sample. The crosslinking ratio was calculated from the result of NMR measurement of each measurement sample.
The crosslink rate was measured and calculated by ¹⁹ F Magic angle Spinning (MAS) nuclear magnetic resonance (NMR) method (High speed magic angle nuclear magnetic resonance). References (Beat Fuchs and Ulrich Scheller., Branching and Cross-Linking in Radiation-Modified Poly (tetrafluoroethylene)): A. Solid-State NMR, 1989. The underlined F atoms described below can be assigned.
A: -70ppm: = CF-C F 3
_{B: -82ppm: -CF 2 -C F} 3
C: -186ppm: ≡C F

Here, FIG. 5 (a) shows the NMR spectrum of uncrosslinked PTFE which has not been irradiated with an electron beam, and FIG. 5 (b) shows the NMR spectrum of crosslinked PTFE which has been irradiated with 1000 kGy. As shown in FIG. 5, it can be seen that the intensity of the signal B increases by irradiating the electron beam, and the signals A and C appear.
Assuming that the area ratios of the signals A to C are S _A , S _B , and S _C , respectively, the crosslinking ratio can be calculated by the following equation.

The above formula is of the three molecular chains extending from each of the carbon atoms of the structure of all ≡CF, not in cross-linked structure = CF-CF ₃ and = CF- (CF ₂₎ the molecular chains of the m-CF ₃ subtracted, a _{= CF- (CF 2) n-} CF = proportion of a crosslinked chain is calculated as a cross-linking rate. Note that m and n are arbitrary integers. By comparing FIG. 5 and the above equation, it can be seen that irradiation with an electron beam increases the crosslinking ratio.

  Here, the crosslinking rate of each measurement sample was calculated as the crosslinking rate of each average depth. For example, the cross-linking rate in a measurement sample having a depth of 0 to 5 μm was a cross-linking rate of 2.5 μm in depth. The crosslinking rate in the measurement sample having a depth of 5 to 10 μm was determined to be 7.5 μm. The obtained four crosslinking ratios were plotted on a graph in which the vertical axis represents the crosslinking ratio (%) and the horizontal axis represents the depth (μm) from the surface of the sliding layer. As a result, a good correlation was shown between the crosslinking ratio and the depth from the surface of the sliding layer. An approximate expression was obtained from this graph, and the approximate ratio was used to extrapolate the crosslinking ratio at a depth of 5 μm, 10 μm, 10.7 μm, 11.8 μm, 12.9 μm, 14.3 μm, and 15 μm. Table 1 shows the crosslinking ratio at the depth of the second fluororesin layer. The cross-linking rate at a depth of 1.7 μm obtained by extrapolation using this approximate expression was 25%.

(3) Abrasion test The sliding member obtained in the above (1) was shaved by a predetermined depth from the surface of the sliding layer to obtain test pieces (Examples 1 to 4, Comparative Examples 1 to 3). In Comparative Example 4, a test piece in which the second fluororesin layer was not crosslinked was used. In order to evaluate the wear characteristics of each test piece, a calo test using a steel ball was performed. Table 2 shows the test conditions of the calotest.

  The diameter D of the wear mark formed by the steel ball was measured, and the wear depth T was determined by the following equation. Table 3 shows the wear depth of each test piece. Table 3 also shows the cross-linking rate of the surface of the second fluororesin layer after shaving. The crosslink rate shown in Table 3 is the same as the crosslink rate at the depth of the second fluororesin layer shown in Table 1.

  From Table 3, it can be seen that when the crosslinking ratio is 9% or more, the abrasion resistance is excellent (Examples 1 to 4). On the other hand, in Comparative Examples 1 to 3 in which the crosslinking ratio was less than 9%, although the difference in the crosslinking ratio was small as compared with Example 4, the abrasion resistance was significantly reduced. Comparative Examples 1 to 3 were equivalent to Comparative Example 4 in which the second fluororesin layer was not crosslinked, and it was found that this degree of crosslinking did not contribute to abrasion resistance. As described above, if the crosslinking ratio at the deepest portion of the second fluororesin layer is at least 9% or more, excellent wear resistance can be imparted even at the deepest portion. That is, excellent wear resistance can be exhibited in the entire second fluororesin layer.

  In the case of low-energy electron beam irradiation conditions in the embodiment, the second fluororesin layer is used by shaving the surface so that the cross-linking rate of the second fluororesin layer is 9 to 25%. In the above case, for example, about 2 μm is shaved off before use. The electron beam irradiation conditions may be set so that the cross-linking rate is 9 to 25% from the outermost layer to the deepest part.

  Under the conditions of low-energy electron beam irradiation in the examples, if the layer thickness of the second fluororesin layer is 11 μm or less, the cross-linking rate at the deepest portion can be 9% or more, and the wear resistance is maintained. be able to.

  Since the cage for a rolling bearing of the present invention is excellent in wear resistance and slidability while suppressing defects such as peeling, it can be used under a wide range of conditions (for example, no lubrication, oil lubrication, high sliding speed, high surface pressure). , Etc.), and particularly in the field of cages used in lubricating oil using cages made of iron-based metal materials and in the field of rolling bearings using these cages.

DESCRIPTION OF SYMBOLS 1 Cage 2 Sliding layer 3 Iron-based metal material 4 Underlayer 5 Crosslinked 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 (7)

A rolling bearing retainer having a sliding layer on a surface of a base material made of an iron-based metal material and holding a rolling element of a rolling bearing,
The sliding layer has a fluororesin layer containing a fluororesin on at least the surface,
The fluororesin layer is a crosslinked fluororesin layer crosslinked from the surface of the sliding layer to a boundary surface with another material, and the crosslinked fluororesin layer extends in a depth direction from the surface of the sliding layer. A layer in which the cross-linking rate decreases continuously,
The cage for a rolling bearing, wherein the crosslinking ratio is 9 to 25%. The sliding layer includes a base layer including a heat-resistant resin and a first fluororesin formed on the surface of the iron-based metal material, and a second fluorine including a second fluororesin formed on the base layer surface. Consisting of a resin layer,
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 cage for a rolling bearing according to claim 1, wherein the second fluororesin layer is the crosslinked fluororesin layer.   3. The cage for a rolling bearing according to claim 2, wherein the thickness of the sliding layer is 10 μm or more and less than 40 μm, and the thickness of the crosslinked fluororesin layer is 5 to 11 μm.   The rolling bearing retainer according to any one of claims 1 to 3, wherein the fluororesin contained in the crosslinked fluororesin layer is a polytetrafluoroethylene resin.   The cage for a rolling bearing according to any one of claims 1 to 4, wherein the crosslinking ratio at the deepest part of the crosslinked fluororesin layer is 9 to 12%.   The retainer for a rolling bearing according to claim 5, wherein the cross-linking ratio in a surface portion of the cross-linked fluororesin layer is 20 to 25%. An engaging hole provided at a large end of a connecting rod that converts a linear reciprocating motion into a rotary motion, supporting a crankshaft that outputs a rotary motion, or a rolling bearing attached to the crankshaft,
7. A rolling bearing, wherein the cage for holding the rolling element of the rolling bearing is the cage for a rolling bearing according to any one of claims 1 to 6.

Images