Rolling bearing

Abstract

To provide a rolling bearing using a cage having high reliability capable of achieving dimensional stability required for the cage, particularly an outer ring guide cage, ductility required for a crown type cage, improvement of adhesion of grease using poly α - olefin oil or the like as base oil, and prevention of deformation at high speed.SOLUTION: In the rolling bearing comprising at least an outer ring 1, an inner ring 3, a rolling element 5 and a synthetic resin-made cage 7, the synthetic resin-made cage 7 is formed of a polyamide resin composition comprising a biomass polyamide 10T which is a polycondensate of a plant-derived 1,10-decanediamine and a petroleum-derived terephthalic acid, a PA10T in which a hard segment is a plant-derived 1,10-decanediamine and a petroleum-derived terephthalic acid, a PA10T-based thermoplastic elastomer in which a soft segment is a plant-derived dimer acid and a plant-derived dimer diamine, and a reinforcing fiber material.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a rolling bearing, and more particularly to an improvement in a synthetic resin cage to be incorporated in a rolling bearing. [Background technology]

[0002] There are many different types of rolling bearings, and they are used in a variety of environments, requiring different performance characteristics. Accordingly, the synthetic resin cages that are components of bearings are also made from a combination of various resin materials and reinforcing materials.

[0003] Conventionally, glass fiber reinforced 66 nylon resin has been the most commonly used synthetic resin cage for rolling bearings. Resin materials used in synthetic resin cages include nylon 66 resin, nylon 46 resin, polyphenylene sulfide resin, polyether ether ketone resin, etc., and reinforcing materials include glass fiber and carbon fiber.

[0004] Among rolling bearings, those used in machine tool spindles use an outer ring guide system in which the outer peripheral surface of the cage comes into contact with the inner peripheral surface of the outer ring during high-speed rotation, and the cage itself is required to have minimal dimensional change when it absorbs water. Accordingly, polyphenylene sulfide resin or polyether ether ketone resin, which have low water absorption, are generally used as the base resin for the cage. In addition, machined rings made of phenolic resin reinforced with cotton cloth, which also has minimal dimensional change when it absorbs water, are also used as cages for machine tool bearings. Furthermore, the lubrication method for these machine tool spindle bearings is selected and adopted from grease lubrication, oil-air lubrication, jet lubrication, etc., depending on the conditions of use and costs. Generally, grease lubrication is often used because it is low cost and easy to maintain. Furthermore, the crown cages most commonly used in ball bearings are usually made of nylon 66 or nylon 46 resin, since cracks will occur if the resin material is not ductile when the balls are pressed into it.

[0005] However, cages that use 66 nylon resin or 46 nylon resin as the base resin can change dimensions due to the ingress and egress of moisture, and in the worst case scenario, there is a risk that they may interfere with the inner and outer rings and rolling elements of the rolling bearing, causing adverse effects. Therefore, in the outer ring guide type cage described above, since dimensional change is important, it has been common to use polyphenylene sulfide resin or polyether ether ketone resin, which are expensive materials. The crown-type cages most commonly used in ball bearings use low-ductility polyphenylene sulfide resin or semi-aromatic polyamide resin (modified polyamide 6T, etc.) as the base resin (plus reinforcing fiber material). If the resin material is not ductile, cracks or chips will occur when the ball is pressed into the claws that hold the ball. Therefore, in reality, a resin composition containing glass fiber in 66 nylon or 46 nylon has been used.

[0006] Furthermore, the most commonly used greases for filling the internal spaces of rolling bearings are mineral oils and poly-α-olefin oils, which are primarily aliphatic hydrocarbons and have low polarity. However, these have poor wettability and insufficient adhesion to the cage due to the significant differences in molecular structure between nylon 66 and nylon 46 resins, which have many amide bonds in their molecular structure, and polyphenylene sulfide and polyether ether ketone resins, which have many aromatic rings in their molecular structure. The same is true for semi-aromatic polyamide resins such as modified polyamide 6T, which also have many amide bonds and aromatic rings in their molecular structure.

[0007] Additionally, aliphatic polyamide-based materials such as polyamide 11 (melting point 187°C) and polyamide 12 (melting point 176°C) are low-water-absorbent materials with few amide bonds in their molecular structure. However, because of their low melting points, they soften when the bearing temperature rises during high-speed rotation, which can cause deformation of the cage, and so these materials have not been used in practice. Polyamide 10T is a semi-aromatic polyamide that uses a relatively long-chain diamine as a constituent component. Compared to the polyamide 6T described above, it has higher wettability with mineral oils and poly-α-olefin oils, which have low polarity. However, because it is rigid, it is not easy to assemble when used as a retainer for rolling bearings. Therefore, in order to improve this assemblability, modified polyolefins have been added to polyamide 10T as a flexibility improver (Patent Document 1). However, since this modified polyolefin has low heat resistance, although adding it improves flexibility, it also reduces the heat resistance of the entire resin composition, and there is a risk that the modified polyolefin will gradually deteriorate and lose flexibility (ductility) when used at high temperatures. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2022-175033 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made to solve such problems associated with the prior art, and its object is to provide a rolling bearing using a highly reliable cage that can achieve the dimensional stability required of a cage, particularly an outer ring guide cage, the ductility required of a crown type cage, improved adhesion of grease based on poly-α-olefin oil or the like, and prevention of deformation at high speeds. [Means for solving the problem]

[0010] To achieve this object, the first aspect of the present invention provides a rolling bearing comprising at least an inner ring, an outer ring, a synthetic resin cage, and rolling elements, The synthetic resin cage is made of biomass polyamide 10T, which is a polycondensation product of plant-derived 1,10-decanediamine and petroleum-derived terephthalic acid, PA10T, whose hard segments are made of plant-derived 1,10-decanediamine and petroleum-derived terephthalic acid, A PA10T-based thermoplastic elastomer whose soft segments consist of plant-derived dimer acid and plant-derived dimer diamine; Reinforcement material (reinforced fiber material), The rolling bearing is characterized in that it is formed from a polyamide resin composition containing

[0011] A second aspect of the present invention is the rolling bearing according to the first aspect of the present invention, characterized in that the rolling bearing is an outer ring guide.

[0012] A third aspect of the present invention is the rolling bearing according to the first aspect of the present invention, characterized in that the cage of the rolling bearing is a crown cage having claws.

[0013] The fourth aspect of the present invention is the rolling bearing according to any one of the first to third aspects of the present invention, wherein a sealing device is disposed on an end face of the rolling bearing, The sealing device is made of biomass polyamide 10T, which is a polycondensate of plant-derived 1,10-decanediamine and petroleum-derived terephthalic acid, PA10T, whose hard segments are made of plant-derived 1,10-decanediamine and petroleum-derived terephthalic acid, A PA10T-based thermoplastic elastomer whose soft segments consist of plant-derived dimer acid and plant-derived dimer diamine; Reinforcement material (reinforced fiber material), The rolling bearing is characterized in that it is formed from a polyamide resin composition containing

[0014] The fifth aspect of the present invention is the rolling bearing according to the fourth aspect of the present invention, wherein grease is filled into the internal space of the rolling bearing, The rolling bearing is characterized in that the main component of the base oil of the grease is poly-α-olefin oil. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a rolling bearing using a highly reliable cage that can achieve the dimensional stability required for a cage, particularly an outer ring guide cage, the ductility required for a crown type cage, improved adhesion of grease based on poly-α-olefin oil or the like, and prevention of deformation at high speeds. By forming a synthetic resin cage from a resin material that uses biomass polyamide 10T, a semi-aromatic polyamide with excellent heat resistance and low water absorption, and a biomass polyamide 10T-based thermoplastic elastomer, which has excellent heat resistance and flexibility (ductility), as a flexibility enhancer, we are able to provide a rolling bearing that is environmentally friendly, has little thermal degradation, and can be used in a variety of environments, combining high reliability and low cost. Furthermore, because there is a C10 portion derived from 1,10-decanediamine, which has a long-chain hydrocarbon portion between the amide groups, by applying a grease made from a base oil whose main component is poly-alpha-olefin oil, which has a similar molecular structure, it maintains good wettability to resin materials, effectively prevents wear on the resin parts, and enables the rolling bearing to have a longer life. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic cross-sectional view, with some parts omitted, showing a cylindrical roller bearing to which the rolling bearing of the present invention is applied. [Figure 2] 2 is a perspective view showing a synthetic resin cage incorporated in the cylindrical roller bearing shown in FIG. 1. FIG. [Figure 3] 1 is a schematic cross-sectional view, with some parts omitted, of an angular contact ball bearing to which the rolling bearing of the present invention is applied. [Figure 4] 4 is a perspective view showing a synthetic resin cage incorporated in the angular contact ball bearing shown in FIG. 3. FIG. [Figure 5] 1 is a schematic cross-sectional view, with some parts omitted, of a deep groove rolling ball bearing to which the rolling bearing of the present invention is applied. [Figure 6] FIG. 6 is a perspective view of a synthetic resin cage incorporated into the deep groove rolling ball bearing shown in FIG. 5. [Figure 7] 1 is a schematic cross-sectional view of a hub bearing to which the rolling bearing of the present invention is applied. [Figure 8]1 is a schematic cross-sectional view of a hub bearing to which the rolling bearing of the present invention is applied. DETAILED DESCRIPTION OF THE INVENTION

[0017] An embodiment of the rolling bearing of the present invention will be described below. Note that this embodiment is merely one embodiment of the present invention and should not be construed as being limited in any way, and appropriate design modifications can be made within the scope of the present invention.

[0018] The rolling bearing of the present invention is configured to include at least an inner ring, an outer ring, a plurality of rolling elements installed between the inner ring and the outer ring, and a synthetic resin cage that holds the rolling elements at equal intervals. The present invention is technically characterized by the adoption of a configuration unique to synthetic resin cages. For example, in this embodiment, the rolling bearings shown in Figures 1 to 8 are disclosed as examples. The rolling bearing to which the present invention is applicable is not limited to the illustrated configuration, and well-known configurations may be adopted within the scope of the present invention. Note that the outer ring, inner ring, and rolling elements that constitute the rolling bearing have well-known structures, so they will be briefly described below, followed by a detailed description of the synthetic resin cage, which is a technical feature of the present invention. Rolling bearings

[0019] Figure 1 is a schematic cross-sectional view, with some parts omitted, of a cylindrical roller bearing that is one embodiment of the rolling bearing of the present invention. The cylindrical roller bearing comprises an outer ring 1 having an outer ring raceway surface 1a on its inner peripheral surface, an inner ring 3 having an inner ring raceway surface 3a on its outer peripheral surface, a plurality of cylindrical rollers (rolling elements) 5 disposed so as to be rollable between the outer ring raceway surface 1a and the inner ring raceway surface 3a, and a synthetic resin cage 7 that holds the plurality of cylindrical rollers 5 at approximately equal intervals in the circumferential direction. In this embodiment, an outer ring guided synthetic resin cage 7 is assumed.

[0020] As shown in Figure 2, the synthetic resin retainer 7 has a pair of annular portions 9 arranged coaxially and spaced apart in the axial direction, a plurality of column portions 11 arranged at approximately equal intervals in the circumferential direction to connect the pair of annular portions 9, and pocket portions 13 formed between each of the column portions 11 adjacent to each other in the circumferential direction and which hold the cylindrical rollers 5 in a rollable manner.

[0021] Another embodiment of the rolling bearing of the present invention is an angular contact ball bearing as shown in Fig. 3. The angular contact ball bearing comprises an outer ring 1 having an outer ring raceway surface 1a on its inner peripheral surface, an inner ring 3 having an inner ring raceway surface 3a on its outer peripheral surface, a plurality of balls (rolling elements) 5 rollably disposed between the outer ring raceway surface 1a and the inner ring raceway surface 3a, and a synthetic resin cage 7 that holds the plurality of balls 5 at approximately equal intervals in the circumferential direction. As shown in Figure 4, the synthetic resin retainer 7 that constitutes the rolling bearing of Figure 3 has a plate-shaped circular member 15 and a plurality of pocket portions 17 that are formed in this circular member 15 at approximately equal intervals in the circumferential direction and that hold the balls 5 in a rollable manner.

[0022] Another embodiment of the rolling bearing of the present invention is a deep groove ball bearing as shown in Fig. 5. The deep groove ball bearing comprises an outer ring 1 having an outer ring raceway surface 1a on its inner peripheral surface, an inner ring 3 having an inner ring raceway surface 3a on its outer peripheral surface, a plurality of balls (rolling elements) 5 arranged to roll between the outer ring raceway surface 1a and the inner ring raceway surface 3a, and a synthetic resin cage 7 that holds the plurality of balls 5 at approximately equal intervals in the circumferential direction. Also, reference numeral 23 in the figure denotes a sealing member (seal) that seals in grease arranged in the internal space of the rolling bearing. As shown in Fig. 6, the synthetic resin cage 7 constituting the rolling bearing of Fig. 5 is a crown-type cage in which a plurality of recesses (pockets) 71 for holding balls 5 are formed at regular intervals along the circumferential direction at one axial end of an annular body. The inner surface of the recess 71 is spherical, and a pair of open ends of the recess 71 are elastic pieces 72, 72, respectively.

[0023] Another embodiment of the rolling bearing of the present invention is a hub bearing (rolling bearing for a wheel) as shown in Figures 7 and 8. The hub bearing comprises a plurality of balls (rolling elements) 5 arranged in a space formed by raceway surfaces 1a, 1a of an outer ring (outer ring constituent member) 1, a raceway surface 19a formed on a hub ring 19, and a raceway surface 21a of an inner ring constituent member 21 fixed by crimping to the end of the hub ring 19, and a synthetic resin cage 7 that holds the plurality of balls 5 at approximately equal intervals in the circumferential direction. In the figures, reference numeral 23 denotes a sealing member (seal) that seals in grease arranged in the internal space of the rolling bearing. "Configuration of synthetic resin cage"

[0024] The synthetic resin cage 7 constituting the rolling bearing of the present invention is formed from a polyamide resin composition described below.

[0025] As the base resin for forming the synthetic resin cage 7, polyamide 10T, which is a polycondensation product of 1,10-decanediamine derived from plant-derived castor oil and petroleum-derived terephthalic acid, can be used.

[0026] Polyamide 10T is a polycondensation product of 1,10-decanediamine and terephthalic acid in a molar ratio of 1:1, so its bio content (bio ratio) is approximately 56%. 1,10-Decanediamine is a plant-derived straight-chain diamine obtained through a unique manufacturing process using sebacic acid, whose main ingredient is castor oil obtained from castor bean seeds, etc. The melting point of Polyamide 10T is 315°C. Polyamide 10T has a significantly lower saturated water absorption rate, approximately one-fifth that of Polyamide 66, the most commonly used material for rolling bearing cages. This significantly reduces dimensional change due to water absorption, resulting in excellent dimensional stability and extremely high reliability. The molecular weight of the polyamide resin should be within a range that allows injection molding with a reinforcing material such as glass fiber. Specifically, the number average molecular weight should be 13,000 to 28,000. Considering fatigue resistance and moldability, the number average molecular weight should preferably be in the range of 18,000 to 26,000. A number average molecular weight of less than 13,000 is too low, resulting in poor fatigue resistance and low practicality. On the other hand, a number average molecular weight of more than 28,000 is not preferable because the melt viscosity becomes too high when a practical amount of reinforcing material such as glass fiber is added (15 to 35 wt%), making it difficult to precisely manufacture cages by injection molding.

[0027] To give flexibility (ductility) to Polyamide 10T, PA10T, whose hard segments consist of plant-derived 1,10-decanediamine and petroleum-derived terephthalic acid, and a PA10T-based thermoplastic elastomer, whose soft segments consist of plant-derived dimer acid and plant-derived dimer diamine, are added.

[0028] The content of PA10T-based thermoplastic elastomer is in the range of 2 to 10% by weight of the entire resin component. If it is less than 2% by weight, the improvement in flexibility (ductility) is insufficient. If it exceeds 10% by weight, the flexibility (ductility) improves but the tensile strength decreases, which is not preferable. PA10T has the same molecular structure as the hard segment of polyamide 10T-based thermoplastic elastomer, so they are mutually compatible.

[0029] Dimer acid, a softening ingredient, is made from vegetable oils such as linoleic acid and oleic acid, and is primarily composed of dibasic C36 dicarboxylic acid produced by the dimerization of C18 unsaturated fatty acids, with trace amounts of monobasic and tribasic acids. Dimer diamine, another softening ingredient, is also manufactured from dimer acid.

[0030] The above-mentioned base resins alone exhibit a certain level of durability and are advantageous in preventing wear on the mating components (rolling elements and outer rings) with which the cage may come into contact, allowing the cage to function satisfactorily. Because cages for wheel rolling bearings require flexibility, unreinforced materials that do not contain reinforcing materials are usually used. However, if the cage is used under more severe conditions, it is expected that the cage may be damaged, deformed, or worn, so it is preferable to compound a reinforcing material to further improve reliability.

[0031] Preferred reinforcing materials include glass fiber, carbon fiber, aramid fiber, potassium titanate whisker, aluminum borate whisker, etc., and those surface-treated with a silane coupling agent or the like are more preferred in consideration of adhesion to the above-mentioned polyamide resins. Furthermore, a combination of multiple types of these reinforcing materials can be used. Considering impact strength, it is preferable to blend fibrous materials such as glass fiber or carbon fiber, and considering damage to the mating material, it is preferable to blend whisker-like materials in combination with fibrous materials. When mixed, the mixing ratio varies depending on the type of fibrous material and whisker-like material, and is selected appropriately in consideration of impact strength, damage to the mating material, etc. In addition, glass fibers with a general average fiber diameter of 10 to 13 μm are preferred, as well as those with an average fiber diameter of 5 to 7 μm, which can improve strength and abrasion resistance with a small content, or those with an irregular cross section.

[0032] Furthermore, if strength is a priority, PAN-based carbon fibers are preferred, but pitch-based carbon fibers are also usable because of their cost advantage. The average fiber diameter is preferably 5 to 15 μm. Carbon fibers have high strength and elastic modulus, making it possible to achieve higher strength and elastic modulus in the cage compared to glass fibers.

[0033] As the aramid fiber, it is possible to suitably use para-aramid fiber, which has excellent reinforcing properties. The average fiber diameter is preferably 5 to 15 μm. Unlike glass fiber and carbon fiber, aramid fiber does not damage steel materials and does not deteriorate the surface condition of the mating member with which the cage comes into contact, making it even more suitable when emphasis is placed on the acoustic characteristics of the bearing.

[0034] These reinforcing materials are preferably blended in a proportion of 10 to 40% by weight, particularly 15 to 30% by weight, based on the total weight. If the blending amount of the reinforcing material is less than 10% by weight, the improvement in mechanical strength is small, which is not preferred. If the blending amount of the reinforcing material exceeds 40% by weight, the moldability decreases and, depending on the type of reinforcing material, the likelihood of damaging the mating material increases, which is not preferred. Furthermore, it is preferable to add an iodide-based heat stabilizer or an amine-based antioxidant, either alone or in combination, to the resin as an additive to prevent deterioration due to heat during molding and use.

[0035] The following describes grease that keeps rolling bearings well lubricated. The grease used in the present invention is primarily composed of a thickener and a base oil. The base oil is primarily composed of a poly-α-olefin oil, taking into account its wettability with the polyamide 10T used in the present invention. The thickener is a urea compound composed of an amine and an isocyanate, Li soap, Li complex soap, Ba soap, Ba complex soap, etc. Among these thickeners, urea compounds with a urea bond similar in structure to polyamides are particularly preferred because of their excellent adsorption to polyamide resins. The base oil may be a mixture of a diester oil or an aromatic ester oil to improve the lubricity of the poly-α-olefin oil. The amount mixed is 30% by weight or less of the total base oil.

[0036] Compared to polyamide 66, which is commonly used in rolling bearing cages, the polyamide 10T used in this embodiment has excellent wettability with poly-α-olefin oils due to the presence of C10 moieties (derived from 1,10-decanediamine) with long hydrocarbon chains between amide groups. The polyamide 10T-based thermoplastic elastomer added as a flexibility improver also has long-chain hydrocarbon moieties derived from dimer acid and dimer diamine in addition to the C10 moieties, providing even better wettability with poly-α-olefin oils. Other additives can also be added to this grease. Examples include amine-based or phenol-based antioxidants, rust inhibitors such as calcium sulfonates, extreme-pressure additives such as MoDTC, Montan acid ester wax, partially saponified Montan acid ester wax, polyethylene wax, and oiliness improvers such as oleic acid.

[0037] The above-described synthetic resin composition can also be used as a synthetic resin composition for forming a sealing device (seal) 23 to be incorporated into the rolling bearing shown in FIGS. When a sealing device is formed from the above synthetic resin composition, it becomes an even more environmentally friendly rolling bearing, which is preferable. Note that the shape of the sealing device is not limited to the shape shown in the drawings, and well-known shapes can be adopted within the scope of the present invention.

[0038] (Example of embodiment) Cage composition: Table 1 Cage structure: Cage for angular contact ball bearing shown in Figure 4, Cage for deep groove ball bearing shown in Figure 6 [Cage manufacturing] Synthetic resin compositions (resin pellets) are prepared by blending the polyamide resin and reinforcing material shown in Table 1. Each resin pellet is used to produce a cage (Figure 4) for an angular contact ball bearing (NSK's "70BER20XDB"; inner diameter 70 mm, outer diameter 110 mm, width 24 mm, contact angle 25°, double-row combination) by injection molding. Additionally, the same resin pellets are used to produce a cage for a deep groove ball bearing (Fig. 6, outer diameter 47 mm, inner diameter 17 mm) by injection molding.

[0039] [Table 1]

[0040] We now consider the material-based performance of the example embodiment and the comparative example. Comparative Example 1, which is made of a conventional highly water-absorbent polyamide resin, is thought to have poor dimensional stability under harsh conditions of high temperature and high humidity, resulting in poor durability. Comparative Example 3 also has low ductility, and is therefore thought to have poor performance in terms of embeddability. Furthermore, comparative example 2, which uses polyamide 6T6I as the base resin, which has the same level of low water absorption as the polyamide resin used in the examples of this embodiment, and comparative example 3, which uses L-PPS, which has even lower water absorption, as the base resin, are thought to have no problems with dimensional stability, but because they have even worse wettability with grease based on poly-α-olefin oil (even compared to polyamide 66), they are thought to wear out faster and have inferior durability under high temperature conditions. [Industrial Applicability]

[0041] The present invention can be used in rolling bearings. [Explanation of symbols]

[0042] 1 outer ring 3. Inner circle 5 rolling elements 7 Cage 23 Sealing device

Claims

1. In a rolling bearing comprising at least an inner ring, an outer ring, a synthetic resin cage, and rolling elements, The synthetic resin cage is made of biomass polyamide 10T, which is a polycondensate of plant-derived 1,10-decanediamine and petroleum-derived terephthalic acid, PA10T, whose hard segments are composed of plant-derived 1,10-decanediamine and petroleum-derived terephthalic acid; a PA10T-based thermoplastic elastomer whose soft segment is composed of a plant-derived dimer acid and a plant-derived dimer diamine; A reinforcement material; A rolling bearing formed from a polyamide resin composition comprising:

2. 2. A rolling bearing according to claim 1, wherein the rolling bearing is an outer ring guide.

3. 2. The rolling bearing according to claim 1, wherein the cage of the rolling bearing is a crown-type cage having claws.

4. A sealing device is disposed on the end face of the rolling bearing, The sealing device is made of biomass polyamide 10T, which is a polycondensate of plant-derived 1,10-decanediamine and petroleum-derived terephthalic acid; PA10T, whose hard segments are composed of plant-derived 1,10-decanediamine and petroleum-derived terephthalic acid; a PA10T-based thermoplastic elastomer whose soft segment is composed of a plant-derived dimer acid and a plant-derived dimer diamine; A reinforcing material (reinforcing fiber material), 4. The rolling bearing according to claim 1, wherein the rolling bearing is formed from a polyamide resin composition containing:

5. The internal space of the rolling bearing is filled with grease, 5. The rolling bearing according to claim 4, wherein the main component of the base oil of the grease is poly-α-olefin oil.

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