Retainer for rolling bearings, and rolling bearing

Abstract

The present invention provides: a retainer for rolling bearings, which has excellent heat resistance, is capable of achieving good moldability even in cases where the retainer is, for example, thick, and has excellent strength; and a rolling bearing which uses this retainer. This retainer 5 is a retainer for rolling bearings, which is formed by injection molding a resin composition and has a plurality of pockets 6 for holding rolling bodies. The resin composition contains the following components (A) to (C). (A) 30-89.9% by mass of a copolymerized polyamide resin which contains, as constituent units, a hexamethylene terephthalamide unit and a hexamethylene adipamide unit (B) 10-50% by mass of glass fibers or carbon fibers (C) 0.1-20% by mass of a plate-shaped filler

Description

Rolling bearing retainer and rolling bearing

[0001] The present invention relates to a cage for a rolling bearing and a rolling bearing using the cage.

[0002] In rolling bearings, resin cages are widely used as cages that hold rolling elements so that they can roll freely. Resin cages are superior to iron cages in terms of self-lubrication, low friction characteristics, light weight, etc. Aliphatic polyamide resins such as polyamide 6 (PA6), polyamide 66 (PA66), and polyamide 46 (PA46) are commonly used as synthetic resins for resin cages, and these are reinforced as needed by adding fibrous reinforcing materials such as glass fibers (see Patent Document 1).

[0003] In recent years, there has been a demand for bearings to operate at higher speeds, particularly in EV applications, and this has led to a demand for high heat resistance in resin cages. In response, aromatic polyamide resins, which offer superior heat resistance, are increasingly being considered as replacements for the commonly used aliphatic polyamide resins. For example, polyamide 9T (PA9T) and polyamide 10T (PA10T) have higher glass transition temperatures and melting points than aliphatic polyamide resins, and cages using these materials have been proposed (see Patent Documents 2, 3, and 4).

[0004] JP 2000-227120 A JP 2001-317554 A JP 2006-207684 A JP 2016-121735 A

[0005] When a rolling bearing incorporating a plastic cage rotates at high speeds, the centrifugal force generated by the high-speed rotation acts on the cage, which can cause the cage to deform. Deformation of the cage increases friction between the cage and the rolling elements held by the cage, causing the bearing to overheat. Deformation of the cage also brings the cage into contact with the bearing outer ring, and the resulting frictional heat can melt the resin, preventing the rolling bearing from rotating. Therefore, plastic cages incorporated into rolling bearings used at such high speeds must be resistant to deformation due to mechanical and / or thermal stress.

[0006] In contrast, aromatic polyamide resins have high melting points and glass transition temperatures, and are therefore excellent in high-temperature strength, making them suitable for conditions such as high-speed rotation. However, due to their high melting points and viscosity, aromatic polyamide resins tend to be less moldable than aliphatic polyamide resins. Specifically, aromatic polyamide resins are more prone to internal defects (such as voids and cracks) than aliphatic polyamide resins due to factors such as their high melt viscosity during injection molding and their different volumetric shrinkage behavior upon solidification compared to aliphatic polyamide resins. In particular, when the cage has a complex shape and is thick, differences in volumetric shrinkage behavior between the inside and outside are likely to occur, raising concerns about reduced strength due to the occurrence of internal defects.

[0007] Furthermore, aromatic polyamide resins have lower water absorption than aliphatic polyamide resins. However, resin cages manufactured by injection molding always have welds formed in areas where resin compositions join during molding. Because aromatic polyamide resins have a high elastic modulus and low toughness, stress concentration occurs at the welds during use, making them more susceptible to cracking and potentially reducing the strength of the cage.

[0008] The present invention has been made in view of the above circumstances, and aims to provide a retainer for a rolling bearing that has excellent heat resistance, can be easily formed even when the retainer is thick, and has excellent retainer strength, and a rolling bearing that uses the retainer.

[0009] The cage for a rolling bearing of the present invention is a cage for a rolling bearing having a plurality of pockets for holding rolling elements, which is formed by injection molding a resin composition, characterized in that the resin composition contains the following (A) to (C): (A) 30% by mass to 89.9% by mass of a copolymer polyamide resin containing hexamethylene terephthalamide units and hexamethylene adipamide units as constituent units, (B) 10% by mass to 50% by mass of glass fiber or carbon fiber, and (C) 0.1% by mass to 20% by mass of a plate-shaped filler.

[0010] The resin composition is characterized in that (C) is a plate-like filler of at least one of talc, mica, kaolin, and glass flakes, and its content relative to the entire resin composition is 0.1% by mass to 10% by mass.

[0011] The resin composition is characterized in that the mass ratio (B / C) of (B) to (C) is 99 / 1 to 60 / 40.

[0012] The above (A) is characterized by being a copolymer polyamide resin having a glass transition temperature of 80°C to 110°C and a melting point of 300°C or higher.

[0013] The resin composition is characterized in that it contains, as (B), 10% by mass to 35% by mass of the glass fiber, or 15% by mass to 30% by mass of the carbon fiber.

[0014] The above-mentioned rolling bearing cage is characterized in that the radial thickness at the axial end face of the cage is 3.0 mm or more. In the present invention, the "radial thickness at the axial end face of the cage (also simply referred to as the radial thickness)" refers to half the value of the difference between the inner diameter dimension and the outer diameter dimension at the axial end face of the cage, and if there are multiple values, it refers to the largest value among them.

[0015] In a plan development of the outer diameter surface of the cage, the diameter of the inscribed circle of the region surrounded by the adjacent pockets and the axial end surface is 5.0 mm or more.

[0016] The rolling bearing of the present invention is a rolling bearing comprising an inner ring, an outer ring, a plurality of rolling elements interposed between the inner and outer rings, and a retainer that holds the rolling elements, wherein the retainer is the rolling bearing retainer of the present invention.

[0017] The rolling bearing has a dm-n value of 80 x 10 ４ ~300 x 10 ４ The bearing is characterized by being used in a rotation range of

[0018] The rolling bearing retainer of the present invention is a resin retainer made by injection molding a resin composition. Depending on the structure of the retainer (for example, if it has thick-walled portions), there is a concern that internal defects may occur during injection molding. However, by using a copolymer polyamide (for example, PA6T / 66) containing hexamethylene terephthalamide units and hexamethylene adipamide units as constituent units as (A) polyamide resin for the base resin, it is possible to achieve both the heat resistance of aromatic polyamide resin and the high moldability of aliphatic polyamide resin. Furthermore, by combining (B) fibrous reinforcing material and (C) plate-shaped filler as fillers, the rigidity of the retainer is increased, and deformation of the retainer can be reduced even under high-speed rotation conditions, for example, while also suppressing the occurrence of internal defects during molding.

[0019] In particular, with regard to the occurrence of internal defects, the incorporation of (B) fibrous reinforcing material causes anisotropy in the shrinkage behavior during molding, making it more likely that internal defects will occur in cages with complex shapes, but by further incorporating (C) plate-shaped filler, the shrinkage behavior of the resin can be suppressed isotropically, thereby suppressing the occurrence of internal defects during molding. Furthermore, by inhibiting the fiber orientation in the welds with the plate-shaped filler, it is possible to suppress a decrease in strength at the welds, resulting in excellent cage strength.

[0020] The above (C) is a plate-like filler of at least one of talc, mica, kaolin, and glass flakes, and its content relative to the entire resin composition is 0.1 mass % to 10 mass %, so that deformation of the retainer can be suppressed even when used, for example, at higher rotational speeds.

[0021] The copolymer polyamide resin (A) has a melting point of 300°C or higher, and therefore has higher heat resistance than PA66 (melting point: approximately 260°C) and PA46 (melting point: approximately 295°C), which are commonly used as cage materials. It also has comparable heat resistance to PA9T (melting point: approximately 305°C) and PA10T (melting point: approximately 315°C). Furthermore, the copolymer polyamide resin (A) has a glass transition temperature of 80°C to 110°C, and therefore can suppress deformation of the cage, even when used under high-speed rotation conditions, for example.

[0022] By including the fibrous reinforcing material (B) above, the rigidity of the retainer can be increased, and for example, deformation of the retainer can be reduced even under high-speed rotation conditions. Furthermore, since the retainer includes 10% by mass to 35% by mass of glass fiber or 15% by mass to 30% by mass of carbon fiber, the weld strength can be further improved.

[0023] The rolling bearing of the present invention comprises an inner ring, an outer ring, a plurality of rolling elements interposed between the inner and outer rings, and a cage of the present invention that holds the rolling elements. For example, the dm·n value is 80×10 ４ ~300 x 10 ４ Even when used in a rotational range of 1000 rpm, deformation of the cage can be suppressed, resulting in a bearing with excellent durability.

[0024] Fig. 1 is an axial sectional view showing an example of a rolling bearing of the present invention; Fig. 2 is a perspective view showing an example of a cage for a rolling bearing of the present invention; Fig. 3 is a plan development view of the outer diameter surface of the cage; Fig. 4 is a partially enlarged perspective view showing another example of a cage for a rolling bearing of the present invention; Fig. 5 is a diagram showing measurement locations for evaluating internal defects in the examples; Fig. 6 is a diagram showing a neutral plane and a range to be binarized for evaluating internal defects; Fig. 7 is a diagram showing an outline of a cage tensile test;

[0025] The rolling bearing cage of the present invention is a resin cage formed by injection molding a resin composition. This cage is an annular member having a plurality of pockets for holding rolling elements. The resin composition used as the resin material is composed of (A) a predetermined polyamide resin as a base resin, to which predetermined amounts of (B) glass fiber or carbon fiber and (C) plate-shaped filler are blended. (A) to (C) are explained below.

[0026] [(A) Polyamide Resin] The present invention is characterized by using a copolymerized polyamide containing hexamethylene terephthalamide units and hexamethylene adipamide units as structural units as the polyamide resin for the cage. The hexamethylene terephthalamide units are structural units of PA6T, which is a polymer of terephthalic acid, a dicarboxylic acid, and 1,6-hexanediamine, a diamine. The hexamethylene adipamide units are structural units of PA66, which is a polymer of adipic acid, a dicarboxylic acid, and 1,6-hexanediamine, a diamine.

[0027] Here, internal defects such as cracks and voids in injection-molded resin parts arise due to differences in shrinkage behavior between the inside and outside due to the temperature difference between the inside and outside during the cooling and solidification process. For example, aromatic polyamide resins PA9T and PA10T have a PVT diagram showing the volumetric shrinkage behavior of resins during cooling and solidification, whereby their shrinkage behavior at high pressure is significantly different from that at low pressure, making them prone to differences in shrinkage behavior between the inside and outside. On the other hand, aliphatic polyamide resins have a low pressure dependency of their shrinkage behavior, so there tends to be less difference between their inside and outside shrinkage behavior. The polyamide resin used in the present invention ensures heat resistance through the aromatic polyamide resin PA6T, while the aliphatic polyamide resin PA66 makes the difference in shrinkage behavior between the inside and outside less noticeable than aromatic polyamide resin materials, making it less prone to internal defects and deformation due to shrinkage.

[0028] The polyamide resin used in the present invention may be, for example, a two-component copolymer polyamide substantially composed of PA6T units and PA66 units.

[0029] The polyamide resin may also contain other monomer units, such as a terpolymer polyamide composed of three types of monomer units including PA6T units and PA66 units, or a quaternary copolymer polyamide composed of four types of monomer units including PA6T units and PA66 units.

[0030] Examples of dicarboxylic acid components used in the other monomer units include aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, and dodecanedioic acid, alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid, and aromatic dicarboxylic acids such as phthalic acid, isophthalic acid terephthalic acid, and naphthalenedicarboxylic acid. Examples of diamine components used in the other monomer units include aliphatic diamines such as 1,2-ethanediamine, 1,3-propanediamine, 1,4-butanediamine, 1,5-pentanediamine, 1,6-hexanediamine, 1,7-heptanediamine, 1,8-octanediamine, 1,9-nonanediamine, 1,10-decanediamine, 1,11-undecanediamine, and 1,12-dodecanediamine, alicyclic diamines such as cyclohexanediamine, and aromatic diamines such as xylylenediamine. The polyamide resin may be copolymerized with lactams such as caprolactam.

[0031] Examples of terpolymer polyamides include copolymer polyamides (PA4T / 6T / 66) of PA6T units, PA66 units, and tetramethylene terephthalamide units (constituent units of PA4T), and copolymer polyamides (PA6T / 6I / 66) of PA6T units, PA66 units, and hexamethylene isophthalamide units (constituent units of PA6I).

[0032] The polyamide resin preferably has a melting point of 300° C. or higher, more preferably 300° C. to 330° C., and even more preferably 300° C. to 320° C. It has a higher melting point and is more heat resistant than the PA66 resin and PA46 resin generally used as cage materials, and is therefore suitable for use in high-temperature environments and when the dm·n value is, for example, 80×10 ４ Even when used at such high speeds, deformation of the cage can be prevented. The melting point can be measured using a differential scanning calorimeter (DSC) as the temperature of an endothermic peak (Tm) that appears when the polyamide resin is cooled from a molten state to 25°C at a rate of 20°C / min in an inert gas atmosphere and then heated at a rate of 20°C / min.

[0033] The polyamide resin preferably has a glass transition temperature of 80°C to 110°C, and more preferably 90°C to 110°C. Because the glass transition temperature is higher than that of PA66 resin (glass transition temperature: approximately 60°C) and PA46 resin (glass transition temperature: approximately 78°C), which are commonly used as cage materials, deformation of the cage can be suppressed, even when used at high speeds, and heat generation due to sliding friction between the rolling elements and the cage can be reduced. The glass transition temperature can be measured using a differential scanning calorimeter (DSC) as the midpoint temperature (Tg) of a stepwise endothermic peak that appears when the polyamide resin is quenched in an inert gas atmosphere and then heated at a heating rate of 20°C / min (JIS K7121).

[0034] The water absorption of the polyamide resin is, for example, 3.0% to 5.0%. This water absorption is measured after 100 hours of exposure at a constant temperature and humidity of 80°C and 95% relative humidity. Because this water absorption is higher than that of PA9T or PA10T (approximately 1.6%), stress concentration at welds due to low toughness caused by excessively low water absorption can be suppressed. On the other hand, because this water absorption is lower than that of PA66 (approximately 5.6%) or PA46 (approximately 9.5%), dimensional changes and deterioration of physical properties due to excessive water absorption can be suppressed.

[0035] The polyamide resin used in the present invention can be produced by various polycondensation methods such as melt polymerization, solid-phase polymerization, bulk polymerization, solution polymerization, or a combination of these methods.

[0036] The content of the polyamide resin is 30% by mass to 89.9% by mass, preferably 50% by mass to 89.9% by mass, based on the total mass of the resin composition. The content may be 60% by mass or more, 65% by mass or more, or 80% by mass or less, or 75% by mass or less.

[0037] [(B) Fibrous Reinforcing Material] The resin composition contains glass fiber or carbon fiber as a fibrous reinforcing material. ２ , B ２ O ３ , Al ２ O ３ , CaO, MgO, Na２ O.K. ２ O, Fe ２ O ３ It is obtained by spinning inorganic glass containing the following as its main component. Generally, alkali-free glass (E glass), alkali-containing glass (C glass, A glass), etc. can be used. Considering the effect on polyamide resin, alkali-free glass is preferred. Alkali-free glass is borosilicate glass that contains almost no alkali components in the composition. Since it contains almost no alkali components, it has almost no effect on polyamide resin and the properties of the resin composition do not change. Examples of glass fibers include 03JAFT692, MF03MB120, MF06MB120, etc. manufactured by Asahi Fiberglass Co., Ltd.

[0038] Carbon fibers can be used regardless of the type of raw material, such as polyacrylonitrile (PAN), pitch, rayon, and lignin-poval mixtures. Examples of pitch-based carbon fibers include Kureha Corporation's KUREKA M-101S, M-107S, M-101F, M-201S, M-207S, M-2007S, C-103S, C-106S, and C-203S. Examples of PAN-based carbon fibers include Toho Tenax Co., Ltd.'s Besfight HTA-CMF0160-0H, HTA-CMF0040-0H, HTA-C6, and HTA-C6-S, and Toray Industries, Inc.'s Torayca MLD-30, MLD-300, T008, and T010.

[0039] The content of the fibrous reinforcing material is 10% by mass to 50% by mass with respect to the entire resin composition. By setting the content of the fibrous reinforcing material within this range, molding flowability can be ensured, the rigidity of the cage can be increased, and deformation of the cage can be reduced, even when used at high speeds. Furthermore, when glass fiber is used as the fibrous reinforcing material, its content is preferably 10% by mass to 35% by mass with respect to the entire resin composition, and when carbon fiber is used, its content is preferably 15% by mass to 30% by mass with respect to the entire resin composition. Furthermore, in consideration of ensuring sufficient strength (tensile strength) of the weld portion during high speeds, the content of glass fiber is more preferably 25% by mass to 35% by mass with respect to the entire resin composition, and the content of carbon fiber is more preferably 20% by mass to 30% by mass with respect to the entire resin composition.

[0040] The average fiber diameter of the fibrous reinforcing material used in the present invention is not particularly limited, but is, for example, 5 to 20 μm, and preferably 5 to 15 μm. The average fiber diameter can be measured using an electron microscope or atomic force microscope commonly used in this field. The average fiber diameter can also be calculated as the number-average fiber diameter based on the above measurement.

[0041] [(C) Plate-like Filler] The resin composition contains a plate-like filler together with the (B) fibrous reinforcing material. Examples of the plate-like filler include, but are not limited to, talc, mica, kaolin, glass flakes, aluminum nitride, and aluminum oxide. The plate-like filler may be used alone or in combination of two or more. The plate-like filler may also be treated with a surface treatment agent.

[0042] The content of the platy filler is 0.1% by mass to 20% by mass of the entire resin composition. By setting the content of the platy filler within this range, the shrinkage behavior of the resin can be isotropically suppressed, the occurrence of internal defects during molding can be suppressed, and a decrease in strength at welds can also be easily suppressed. The content of the platy filler is preferably 0.1% by mass to 10% by mass, and may be 0.1% by mass to 5% by mass, of the entire resin composition.

[0043] Furthermore, from the viewpoint of preventing fiber orientation in the weld portion, the mass ratio (B / C) of the (B) fibrous reinforcing material to the (C) plate-like filler in the resin composition is preferably 99 / 1 to 60 / 40, and more preferably 90 / 10 to 60 / 40.

[0044] The average particle size of the plate-like filler is preferably 1 μm to 40 μm, more preferably 1 μm to 20 μm, and may be 1 μm to 10 μm, from the viewpoint of preventing fiber orientation in welds. The average particle size is the particle size (D50) at which the volume-based cumulative value reaches 50% when the particle size distribution is a cumulative distribution, and can be measured, for example, using a particle size distribution measuring device that utilizes laser light scattering. Furthermore, the average particle size of the plate-like filler is preferably smaller than the average fiber diameter of the fibrous reinforcing material.

[0045] Talc or mica is preferably used as the plate-like filler. Talc is a scale-like particle having a layered structure, and is composed of hydrated magnesium silicate, with the chemical formula Mg ３ (Si ４ O １０ ) (OH) ２ The average particle size of talc may be 1 μm to 4 μm. Mica is a scaly aluminum silicate mineral, and muscovite, phlogopite, biotite, artificial mica, etc. can be used.

[0046] The resin composition of the present invention may contain additives other than the fibrous reinforcing material and the plate-like filler, as needed, within the range that does not impair the cage function or injection moldability. Examples of other additives that can be added include solid lubricants, inorganic fillers, antioxidants, antistatic agents, and release agents.

[0047] The materials constituting the resin composition can be mixed as needed using a Henschel mixer, ball mixer, ribbon blender, or the like, and then melt-kneaded in a melt extruder such as a twin-screw kneading extruder to obtain molding pellets. The fibrous reinforcing material may be added by side feeding during melt-kneading in a twin-screw extruder or the like. The molding pellets are then injection molded into a cage. During injection molding, the resin temperature is maintained at or above the melting point of the polyamide resin, and the mold temperature is maintained at or above the glass transition temperature of the polyamide resin.

[0048] The cage for a rolling bearing and the rolling bearing of the present invention will be described with reference to Figures 1 and 2. Figure 1 is an axial cross-sectional view of an angular contact ball bearing, which is an example of the rolling bearing of the present invention, and Figure 2 is a partially enlarged view of the cage (machined type) of the rolling bearing of Figure 1.

[0049] As shown in FIG. 1 , an angular contact ball bearing 1 includes an inner ring 2, an outer ring 3, a plurality of balls (rolling elements) 4 interposed between the inner ring 2 and the outer ring 3, and a cage 5 that holds the balls 4 at regular intervals in the circumferential direction. The cage 5 is the above-described rolling bearing cage of the present invention. The inner ring 2, the outer ring 3, and the balls 4 are in contact with each other at a predetermined angle θ (contact angle) relative to the radial centerline, allowing the bearing to bear radial loads and unidirectional axial loads. In FIG. 1 , the cage 5 is of an outer ring guide type, and a portion of the outer peripheral surface of the cage has an outer ring guide portion that is guided by the outer ring 3. The cage guide type is not limited to an outer ring guide type, and may be an inner ring guide type. If necessary, a lubricant such as grease may be sealed around the balls 4 for lubrication.

[0050] The rolling bearing of the present invention is particularly suitable for use under high temperature conditions and high speed rotation conditions. ４ ~300 x 10 ４ This dm・n value is 150×10 ４ or more, 200 × 10 ４ It may be more than that.

[0051] In Figure 1, the angular contact ball bearing 1 uses an injection-molded product of a resin composition for the cage 5, which is based on polyamide resin, a resin with a high melting point and excellent moldability. This prevents deformation of the cage, even under high-speed rotation conditions. In particular, as shown in the examples below, internal defects are suppressed even when the cage is thick, which is thought to prevent fracture of the cage under high-speed rotation loads and to provide excellent fatigue characteristics. Furthermore, the polyamide resin has excellent self-lubricating and low-friction properties, which reduces heat generation due to friction between the balls 4 and outer ring 3 and the cage 5, thereby suppressing temperature rise. This allows the bearing to operate for long periods of time, even under high-speed rotation conditions.

[0052] As shown in Figure 2(a), the cage 5 has a ring-shaped cage body with a plurality of pockets 6 for holding balls, spaced at regular intervals in the circumferential direction. Pillars 7 are formed between adjacent pockets 6 in the circumferential direction. The cage 5 can be obtained by forming the pockets in the injection molding stage using the resin composition described above in a mold having a slide core, or by forming a base material and then machining the pocket portions by cutting.

[0053] Because the cage 5 is an injection-molded article, as shown in Figure 2(b), welds W are formed in areas where the resin compositions meet during molding. The welds W are locations on the cage annulus that are prone to fracture due to stress concentration. The cage of the present invention is a molded article obtained by injection molding a resin composition that uses the above-mentioned polyamide resin as a base resin and blends this with a predetermined amount of fibrous reinforcing material (glass fiber or carbon fiber) and plate-shaped filler. In particular, the plate-shaped filler inhibits fiber orientation, resulting in even greater tensile strength at the welds W, and cracking at the welds can be prevented even during use at high speeds.

[0054] Furthermore, even if the cage of the present invention has a structure having thick portions, the occurrence of internal defects can be suppressed by using the above resin composition. Here, in the cage 5, the direction parallel to the central axis is referred to as the axial direction, the direction perpendicular to the central axis in a plan view seen from the axial direction is referred to as the radial direction, and the direction going around the central axis in the plan view is referred to as the circumferential direction.

[0055] In Figure 2, the axial end surface 5a of the cage 5 is formed as an annular flat surface, and has a certain thickness (constant in Figure 2) in the radial direction of the cage 5. This radial thickness d is not particularly limited, but is, for example, 2.0 mm or more, preferably 3.0 mm or more, and may be 5.0 mm or more. If this radial thickness is large, internal defects are likely to occur in aromatic polyamide resins such as PA9T and PA10T, so the cage of the present invention is particularly suitable for thick-walled cages. The radial thickness of the cage 5 is, for example, 20.0 mm or less, and may be 15.0 mm or less.

[0056] The radial thickness of the cage 5 at its axial end face 5a is calculated as half the difference between the inner diameter dimension r and the outer diameter dimension R of the axial end face 5a at any circumferential position. The inner diameter dimension and the outer diameter dimension of the cage at its axial end face can be measured using a ruler, calipers, or the like.

[0057] Next, Fig. 3 shows a planar development of the outer diameter surface of the cage. Fig. 3 shows one unit of the repeating structure on the outer diameter surface. In the cage 5, half of the pockets 6, 6 are arranged on both sides of the pillar portion 7 in the center.

[0058] When injection molding a cage, the cooling and solidifying speed of the molten resin differs significantly between the area near the cavity surface that comes into contact with the mold and the area away from the surface. In the cage, the area near the base of the column is particularly likely to be the area farthest from the cavity surface, and is therefore more susceptible to internal defects. In the present invention, by using the above-mentioned polyamide resin and blending (B) a fibrous reinforcing material and (C) a plate-shaped filler, internal defects in such areas can be effectively suppressed.

[0059] Specifically, even if the diameter φ of the inscribed circle 8 of the region surrounded by the adjacent pockets 6, 6 and the axial end face 5a of the cage is 3.0 mm or more, internal defects in that portion can be suitably suppressed. The diameter φ of the inscribed circle 8 may be 5.0 mm or more. On the other hand, the diameter φ of the inscribed circle 8 may be, for example, 15.0 mm or less, or 10.0 mm or less. Note that when setting the inscribed circle 8, the shape of the recesses 7a formed around the pockets 6 is not taken into consideration, and the shape of the pockets 6 in the developed plan view is set as a circle. Note that the diameter φ of the inscribed circle 8 can be calculated using the following formula (1) when the pockets 6 are evenly spaced and the pocket centers are at the center of the width (axial length) L of the cage 5.

[0060]

[0061] In the above formula (1), W represents the unit width of the cage (peripheral length / number of pockets), L represents the width of the cage, and D represents the pocket diameter.

[0062] In the cage for a rolling bearing of the present invention, the width L of the cage is, for example, 5.0 mm to 40.0 mm, and preferably 10.0 mm to 35.0 mm. Furthermore, the ratio of the width L to the thickness d (L / d) is preferably 3.0 to 6.0, as this makes it easier to reduce the occurrence of voids and the like.

[0063] The pocket diameter D and unit width W (periphery length / number of pockets) of the cage are not particularly limited and can be set appropriately. For example, the pocket diameter D is 5.0 mm to 40.0 mm, and preferably 10.0 mm to 35.0 mm. For example, the unit width W is 10.0 mm to 40.0 mm, and preferably 10.0 mm to 30.0 mm.

[0064] In Figures 1 and 2, an angular contact ball bearing has been described as an example of the rolling bearing of the present invention, but the bearing type to which the present invention can be applied is not limited to this, and the present invention can also be applied to other ball bearings, tapered roller bearings, cylindrical roller bearings, self-aligning roller bearings, needle roller bearings, etc.

[0065] As another example of a cage for a rolling bearing according to the present invention, a crown-type cage will be described with reference to Fig. 4. Fig. 4 is a partially enlarged perspective view of a crown-type cage obtained by injection molding the above-described resin composition. As shown in Fig. 4, the cage 9 has a pair of opposing retaining claws 10 formed at a constant circumferential pitch on the upper surface of an annular cage body, the opposing retaining claws 10 being curved in a direction approaching each other, and pockets 11 for holding balls as rolling elements being formed between the retaining claws 10. In addition, a flat portion 12 serving as a rising reference surface for the retaining claws 10 is formed between the back surfaces of adjacent retaining claws 10 in adjacent pockets 11.

[0066] In the case of a crown-type cage, the radial thickness at the axial end face 9a opposite to the retention claws 10 may be thick (for example, 2.0 mm or more). The inscribed circle can be determined in the same manner as in the description of Fig. 3. This method can also be used for other cages.

[0067] The rolling bearing cage of the present invention uses a polyamide resin obtained by copolymerizing a specific aromatic polyamide resin with an aliphatic polyamide resin, and the plate-shaped filler material suppresses isotropic shrinkage, even in a relatively thick cage where internal defects tend to occur when using an aromatic polyamide resin. This makes it possible to effectively suppress internal defects. Furthermore, internal defects can be reduced compared to the aliphatic polyamide resins that have been widely used in the past.

[0068] In the past, in order to suppress internal defects and deformation caused by shrinkage behavior, thickness reductions have been provided in thick-walled portions, and a mold structure that reduces the temperature difference between the inside and outside has been adopted. However, depending on the shape of the cage, it may be difficult to provide thickness reductions or the thickness of the thickness reductions may need to be large. However, the present invention is effective in addressing internal defects and deformation without taking such measures.

[0069] The present invention will be further explained below with reference to examples, but the present invention is not limited thereto in any way.

[0070] The raw materials used in the examples and comparative examples are as follows: (A) Resin material PA6T / 66 PA66: Amilan CM3001 manufactured by Toray Industries, Inc. PA9T: Genestar N1000 manufactured by Kuraray Co., Ltd. (B) Fibre reinforcing material Glass fiber: 03JAFT692 manufactured by Asahi Fiberglass Co., Ltd. (average fiber diameter 10 μm, average fiber length 3 mm) Carbon fiber: HTA-C6 manufactured by Toho Tenax Co., Ltd. (average fiber diameter 7 μm, average fiber length 6 mm) (C) Plate-like filler Talc: Compressed fine powder talc UPN HS-T manufactured by Hayashi Kasei Co., Ltd. (plate-like, average particle size 2.7 μm) Mica: A21 manufactured by Yamaguchi Mica Kogyosho Co., Ltd. (plate-like, average particle size 6.2 μm)

[0071] These raw materials were blended in the proportions shown in Table 1 to produce resin compositions for angular contact ball bearing cages in Examples and Comparative Examples. Various tests were then conducted. A twin-screw extruder was used to produce the resin compositions. Glass and carbon fibers were fed using a constant-volume side feeder to prevent breakage, and extruded and granulated. The resulting pellets were molded using an inline screw injection molding machine to obtain the desired cage shape (outer diameter 93 mm × inner diameter 88 mm × width 13 mm; radial thickness at the axial end face 3.5 mm; and the diameter of the inscribed circle of the area enclosed by the adjacent pocket and the axial end face in the planar development of the outer diameter face was 6.0 mm). The radial thickness was calculated as half the difference between the inner and outer diameters at the axial end face. The diameter of the inscribed circle was calculated using the above formula (1). The cage shape was a machined mold shown in Figure 2.

[0072] [Internal Defect (Void / Crack) Observation] To identify internal defects in the cage, evaluation was performed based on CT cross-sectional images of the midplane of the thick-walled portion, where internal defects are most likely to occur. Cages with confirmed cracks were deemed non-compliant because they were considered susceptible to fracture when stresses such as lead-lag behavior increased due to changes in operating conditions (lubrication conditions). Figure 5 shows the measurement area (area A) of the cage 13 for internal defects. Cracks were evaluated based on the CT cross-sectional images (3: no cracks, 2: cracks present). Voids were evaluated by calculating the defect area ratio based on the CT cross-sectional images (3: no defects, 2: defect area ratio less than 10%, 1: defect area ratio 10% or more). The defect area ratio was calculated by extracting CT cross-sectional images of the midplane (see Figure 6(a)) for the thickness d, where voids and cracks are likely to form, within the observation range shown in Figure 6, and binarizing the area where voids were observed, as shown in Figure 6(b). The results are shown in Table 1.

[0073]

[0074] As shown in Table 1, cracks occurred in the aromatic polyamide resin PA9T (Comparative Example 2) due to its high melt viscosity and volumetric shrinkage behavior upon solidification that differs from that of aliphatic polyamide resins. No cracks occurred in the aliphatic polyamide resin PA66 (Comparative Example 1), but voids with a large defect area ratio were observed. In contrast, the cages of Examples 1 to 6 used PA6T / 66, and the plate-shaped filler suppressed shrinkage isotropically, so no internal defects occurred.

[0075] [Cage Tensile Test] A cage tensile test was conducted using the cage obtained above to confirm the cage's fracture strength. After molding, the cage was subjected to humidity conditioning in an atmosphere of 80°C and 95% relative humidity, and the test was conducted after water absorption. The water absorption rate of the obtained cage was measured using the following calculation formula from the masses before and after humidity conditioning. The results are shown in Table 1 above. The water absorption rates of the cages of Examples 1 to 6 under these conditions were 0.5% to 1.5%, more specifically, 0.6% to 1.2%. Water absorption rate (%) = (mass after humidity conditioning - mass before humidity conditioning) × 100 / mass before humidity conditioning (2). The cage tensile test was conducted by placing the cage 13 on the annular tensile jig 14 shown in Figure 7 so that its weld portion was horizontal, using a Shimadzu tensile tester (Autograph AG50KNX) at a tension speed of 10 mm / min. The results are shown in Table 1 above as cage fracture strength (N).

[0076] As shown in Table 1, the cages of Examples 1 to 6 exhibited higher strength than the cage of Comparative Example 1. The breaking strength of the cages of Examples 1 to 6 under the conditions was 2800 N or more, more specifically 3000 N to 3600 N. In the cages of Examples 1 to 6, the plate-shaped filler inhibited the fiber orientation in the weld area, thereby suppressing a decrease in strength in the weld area.

[0077] [High-speed durability test] Using an angular contact ball bearing using the cage obtained above, a dm·n value of 80×10 ４ , dm·n value 160×10 ４ , dm·n value 240×10 ４ , dm·n value 280×10 ４ Durability tests were carried out for 100 hours for each. Comparison tests were carried out using angular contact ball bearings that incorporated each of the cages from the example and comparative examples, filled with grease as a lubricant, and sealed with non-contact seals on both sides. A rating of "3" was given for cases where the test was completed without any damage to the cage, and a rating of "2" was given for cases where the test stopped due to melting of the cage, the maximum temperature limit, excessive motor output, etc. The results are shown in Table 1 above.

[0078] As shown in Table 1, PA66 (Comparative Example 1) has a low melting point and glass transition temperature, resulting in a decrease in durability under higher speed rotation conditions. On the other hand, the cage of Example 6 had no internal defects, and the polyamide resin had a high melting point and glass transition temperature, and showed higher high-speed durability than Comparative Example 1. However, the content of the plate-like filler was relatively high, and the plate-like filler was prone to falling off from the cage, so it was difficult to achieve high-speed durability under higher speed rotation conditions (dm·n value 280×10 ４ In Example 1, the plate-like fillers that fell off attacked the rolling elements and the rolling surfaces of the inner and outer rings, resulting in a decrease in durability. In contrast, the cages of Examples 1 to 5 showed sufficient durability even under test conditions of higher rotation speeds.

[0079] For example, in the case of a thick-walled cage, specifically, when the radial thickness is 3.0 mm or more and the diameter of the inscribed circle of the region enclosed by the adjacent pockets and the axial end face in a plan development of the outer diameter surface is 5.0 mm or more, there is a concern about the occurrence of internal defects during injection molding. However, as in the above example, by using a specific polyamide resin obtained by copolymerizing an aromatic polyamide resin and an aliphatic polyamide resin and blending a fibrous reinforcing material and a plate-shaped filler, it is possible to achieve a resin rolling bearing cage that combines the heat resistance of an aromatic polyamide resin with the high moldability of an aliphatic polyamide resin while suppressing the occurrence of internal defects and reducing the strength at the welds. As a result, even in the case of a thick-walled cage, for example, internal defects and deformation of the cage can be suppressed without providing a recess, and internal defects and deformation of the cage can be addressed without machining a complex mold shape.

[0080] The cage for a rolling bearing of the present invention is excellent in heat resistance, and can achieve good formability even when the cage is thick. The cage has excellent strength, and can particularly suppress the occurrence of internal defects such as cracks and voids. Therefore, it is possible to suppress the occurrence of internal defects such as cracks and voids in a high-temperature atmosphere (for example, at a high temperature of 80°C or higher) or under high-speed rotation conditions (for example, when the dm·n value is 80×10 ４ and can be used as retainers for various rolling bearings used in automobiles, motors, machine tools, etc.

[0081] REFERENCE SIGNS LIST 1 Angular contact ball bearing (rolling bearing) 2 Inner ring 3 Outer ring 4 Ball (rolling element) 5 Cage 6 Pocket 7 Column portion 8 Inscribed circle 9 Cage 10 Retaining claw 11 Pocket 12 Flat portion 13 Cage 14 Pulling jig

Claims

1. A cage for a rolling bearing having a plurality of pockets for holding rolling elements, which is formed by injection molding a resin composition, characterized in that the resin composition contains the following (A) to (C): (A) 30% by mass to 89.9% by mass of a copolymer polyamide resin containing hexamethylene terephthalamide units and hexamethylene adipamide units as constituent units, (B) 10% by mass to 50% by mass of glass fiber or carbon fiber, and (C) 0.1% by mass to 20% by mass of a plate-shaped filler.

2. A retainer for a rolling bearing as described in claim 1, characterized in that (C) is a plate-like filler selected from the group consisting of talc, mica, kaolin, and glass flakes, and its content in the entire resin composition is 0.1% by mass to 10% by mass.

3. A cage for a rolling bearing according to claim 1, characterized in that in the resin composition, the mass ratio (B / C) of said (B) to said (C) is 99 / 1 to 60 / 40.

4. A cage for a rolling bearing according to claim 1, characterized in that (A) is a copolymer polyamide resin having a glass transition temperature of 80°C to 110°C and a melting point of 300°C or higher.

5. A retainer for a rolling bearing as described in claim 1, characterized in that the resin composition contains as (B) 10 mass % to 35 mass % of the glass fiber, or 15 mass % to 30 mass % of the carbon fiber.

6. The rolling bearing retainer according to claim 1, characterized in that (C) is a plate-like filler of at least any one of talc, mica, kaolin, and glass flakes, the content of which in the entire resin composition is 0.1% by mass to 10% by mass, the average particle size of (C) is 1 μm to 20 μm, the mass ratio (B / C) of (B) to (C) in the resin composition is 99 / 1 to 60 / 40, and the resin composition contains, as (B), 10% by mass to 35% by mass of glass fiber or 15% by mass to 30% by mass of carbon fiber.

7. A cage for a rolling bearing according to claim 1, characterized in that the cage has a radial thickness at an axial end face thereof of 3.0 mm or more.

8. A cage for a rolling bearing as claimed in claim 1, characterized in that in a plan development of the outer diameter surface of the cage, the diameter of the inscribed circle of the area surrounded by adjacent pockets and the axial end face is 5.0 mm or more.

9. A rolling bearing comprising an inner ring, an outer ring, a plurality of rolling elements interposed between the inner and outer rings, and a retainer for retaining the rolling elements, wherein the retainer is the rolling bearing retainer described in claim 1.

10. The rolling bearing has a dm-n value of 80 x 10 ４ ~300 x 10 ４ 10. The rolling bearing according to claim 9, characterized in that it is a bearing used in a rotation range of 1000 to 2000 mm.

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