Sealing device and hub unit equipped with same

Abstract

To provide a sealing device having excellent followability under low-temperature environment.SOLUTION: A sealing device has an elastic member containing crosslinked nitrile rubber and grease, where the tip of the lip of the elastic member is in sliding contact with a seal contact surface via the grease. The elastic member containing the crosslinked nitrile rubber has a loss tangent peak of -35°C or less in a dynamic property test conforming to Japanese Industrial Standards K 6394:2007, and the grease has a pour point of an oil component of -25°C or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a sealing device and a hub unit including the same. [Background technology]

[0002] Nitrile rubber has excellent oil resistance, abrasion resistance, and tear strength, and is often used as a seal on the sliding surfaces of machines to prevent the inflow and outflow of fluids into and out of the machine. It is also known that by reducing the amount of bound acrylonitrile in nitrile rubber, the glass transition point (hereinafter referred to as "Tg") decreases, improving the cold resistance of nitrile rubber.

[0003] Patent Document 1 has an object to provide a hub unit bearing that can reduce friction and wear of the seal without compromising sealing performance, and discloses a hub unit bearing in which grease of a predetermined viscosity, whose base oil contains a synthetic hydrocarbon oil, is enclosed in the space surrounded by the seal lip of a seal made of nitrile rubber with an acrylonitrile content of 30 mass % or less and its sliding surface in order to improve durability at low temperatures. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2015-75180 A Summary of the Invention [Problem to be solved by the invention]

[0005] In extremely cold regions such as North America and Russia, cold-resistant nitrile rubber with a low content of bound acrylonitrile and a Tg of -40°C or less is used as an elastic member of a sealing device, which will be described later. However, even if a sealing device using an elastic member having cold-resistant nitrile rubber is used in a hub unit of an automobile, in extremely cold regions, the sealing ability of the sealing device decreases due to a decrease in the followability of the elastic member, and there are cases in which it is not possible to sufficiently prevent the inflow of liquids such as muddy water from the outside into the hub unit. [Means for solving the problem]

[0006] The present invention provides a sealing device having an elastic member containing crosslinked nitrile rubber and grease, wherein the elastic member containing crosslinked nitrile rubber has a peak loss tangent of -35°C or lower in a dynamic property test conforming to Japanese Industrial Standards K 6394:2007, and the grease has an oil component with a pour point of -25°C or lower. The sealing device and hub unit provided with the sealing device also provide a sealing device having an elastic member containing crosslinked nitrile rubber and grease. Effect of the Invention

[0007] According to the present invention, it is possible to provide a sealing device having excellent sealing properties in a low-temperature environment. Also, according to the present invention, it is possible to provide a hub unit having excellent properties for preventing the inflow of liquids, such as muddy water, from the outside in a low-temperature environment. [Brief description of the drawings]

[0008] [Figure 1] 1 is a schematic cross-sectional view of a hub unit equipped with a sealing device of the present embodiment. [Diagram 2] FIG. 2 is a schematic diagram of a mud / salt water testing machine used in the examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The present invention will be described in detail below based on preferred embodiments with reference to the accompanying drawings. Note that the present invention is not limited to these examples, but is indicated by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0010] (1) One embodiment of the present invention is a sealing device having an elastic member containing crosslinked nitrile rubber and grease, in which a lip tip of the elastic member is in sliding contact with a seal contact surface via the grease, The elastic member containing the crosslinked nitrile rubber has a peak loss tangent of -35°C or less in a dynamic property test in accordance with Japanese Industrial Standards K 6394:2007, The above grease is a sealing device in which the pour point of the oil component is -25°C or lower.

[0011] The sealing device of (1) above has excellent sealing properties even in low-temperature environments.

[0012] (2) In the sealing device described in (1) above, the elastic member containing the crosslinked nitrile rubber has a peak loss tangent of -60°C or higher.

[0013] (3) In the sealing device described in (1) or (2) above, the pour point of the oil component of the grease is -70°C or higher.

[0014] (4) In the sealing device according to any one of (1) to (3) above, The elastic member containing the crosslinked nitrile rubber is A nitrile rubber having a bound acrylonitrile content of 18 to 22 mass%; Two or more types of carbon filler are contained, The total content of the two or more types of carbon fillers is 60 to 150 parts by mass relative to 100 parts by mass of the nitrile rubber, and the vulcanizate of the nitrile rubber composition is thus obtained.

[0015] (5) In the sealing device described in (4) above, the two or more types of carbon fillers are selected from carbon black, graphite, carbon fiber, carbon nanotubes, and graphene.

[0016] (6) In the sealing device described above in (5), the two or more types of carbon fillers include carbon black.

[0017] (7) In the sealing device described above in (6), the two or more types of carbon fillers include graphite.

[0018] (8) In the sealing device according to any one of the above (4) to (6), the total content of the two or more kinds of carbon fillers is 100 to 130 parts by mass with respect to 100 parts by mass of the nitrile rubber.

[0019] The sealing devices (2) to (8) above are even more excellent in sealing performance in low temperature environments.

[0020] (9) The sealing device according to any one of (1) to (8) above is for a hub unit.

[0021] (10) A hub unit comprising the sealing device described in (9) above.

[0022] The hub unit described in (9) above is excellent in preventing the inflow of liquid from the outside in a low-temperature environment.

[0023] The sealing device of this embodiment has an elastic member containing cross-linked nitrile rubber and grease. That is, the sealing device of this embodiment includes the concept of a state in which, for example, the elastic member containing cross-linked nitrile rubber before the grease is applied and the grease to be applied are set, in addition to the state in which the grease is applied to the elastic member containing cross-linked nitrile rubber.

[0024] The elastic member containing the crosslinked nitrile rubber has a peak loss tangent (hereinafter referred to as "tanδ") in a dynamic property test conforming to the Japanese Industrial Standards K 6394:2007. PEAK The test frequency is 10 Hz. tan δ is a value indicating the viscoelasticity of an elastic member containing crosslinked nitrile rubber. If the tan δ value of an elastic member containing crosslinked nitrile rubber is large, it means that the elastic member containing the crosslinked nitrile rubber has a strong viscous property and high followability. In other words, the elastic member containing the above-mentioned crosslinked nitrile rubber has a tan δ value of -35°C or less.PEAK Therefore, the sealing device of the present embodiment has excellent sealing properties, particularly on the sliding surfaces of machines, in low-temperature environments. From the viewpoint of maintaining the elasticity of the elastic member containing the crosslinked nitrile rubber at room temperature (15 to 25°C), tan δ PEAK The temperature is preferably −60° C. or higher.

[0025] tan δ PEAK The elastic member containing crosslinked nitrile rubber having a viscosity of −35° C. or less is not particularly limited, but is preferably a vulcanizate of a nitrile rubber composition containing nitrile rubber and two or more kinds of carbon fillers.

[0026] The nitrile rubber (NBR) is also called acrylonitrile-butadiene rubber, and is a copolymer containing acrylonitrile and butadiene as monomer components. In the present invention, the nitrile rubber may be a copolymer containing acrylonitrile and butadiene as main components, as well as other monomers as monomer components, or may be hydrogenated nitrile rubber (HNBR) in which the remaining double bonds in the main chain are hydrogenated. The bound acrylonitrile amount of the nitrile rubber is preferably less than 25%, particularly 18 to 22% by mass. The lower the bound acrylonitrile amount of the nitrile rubber, the better the cold resistance. Therefore, in a low-temperature environment, a low-nitrile nitrile rubber having a bound acrylonitrile amount of less than 25% by mass is used. This improves the sealing performance of the sealing device of this embodiment in a low-temperature environment. The higher the bound acrylonitrile amount of the nitrile rubber, the better the oil resistance. Therefore, the bound acrylonitrile amount of the nitrile rubber is preferably 18% or more.

[0027] The carbon filler is not particularly limited as long as it can be used as a rubber filler. Examples of the carbon filler include carbon black, graphite, carbon fiber, carbon nanotubes, graphene, diamond, activated carbon, and fullerene. The carbon filler of this embodiment is preferably carbon black, graphite, carbon fiber, carbon nanotubes, and graphene. The two or more types of carbon fillers preferably include carbon black, and more preferably include carbon black and graphite. This further improves the sealing performance of the sealing device of this embodiment in a low-temperature environment.

[0028] Examples of the carbon black include furnace black, channel black, acetylene black, and thermal black. The carbon black used in the nitrile rubber composition of this embodiment is preferably furnace black. If furnace black is used as the carbon black, the rubber can be made highly elastic. The carbon black preferably has an average particle size of 18 to 43 nm. By using carbon black with an average particle size of 18 to 43 nm, the rubber can be made highly elastic appropriately. The average particle size of the carbon black is the median size (D50) in the volume-based particle size distribution measured using a disk centrifuge photosedimentation method (Japan Industrial Standards K 6217-6:2019).

[0029] Examples of the graphite include natural graphite and artificial graphite, with artificial graphite being preferred. Artificial graphite has high hardness and can improve the abrasion resistance of the crosslinked nitrile rubber member. The graphite preferably has an average particle size of 1 to 10 μm. Graphite with an average particle size of 1 μm or more is substantially easy to obtain and inexpensive. Graphite with an average particle size of 10 μm or less can improve rubber elasticity by suppressing deterioration of rubber properties. The average particle size of the graphite is the median size (D50) in a volume-based particle size distribution measured using a laser diffraction / scattering method.

[0030] In the nitrile rubber composition used for producing the elastic member containing the crosslinked nitrile rubber, the total content of the two or more kinds of carbon fillers is 60 to 150 parts by mass relative to 100 parts by mass of the nitrile rubber. Preferably, the total content of the two or more kinds of carbon fillers is 100 to 130 parts by mass relative to 100 parts by mass of the nitrile rubber. When carbon black is included as one of the two or more kinds of carbon fillers, the content of carbon black is particularly preferably 30 to 60 parts by mass relative to 100 parts by mass of the nitrile rubber. This further improves the sealing property of the sealing device of this embodiment in a low-temperature environment.

[0031] The nitrile rubber composition is vulcanized and molded to become the elastic member. Therefore, the nitrile rubber composition may contain a vulcanizing agent (crosslinking agent), and may further contain a vulcanization aid or a vulcanization accelerator. The vulcanizing agent is not particularly limited, and a conventionally known vulcanizing agent can be used. Specific examples of the vulcanizing agent include, for example, powdered sulfur, finely divided sulfur, precipitated sulfur, highly dispersible sulfur, sulfur flowers, and other sulfur-containing compounds capable of releasing sulfur, and peroxides. Among these, sulfur or sulfur-containing compounds are preferred because they are easy to handle.

[0032] As the vulcanization accelerator, a conventionally known vulcanization accelerator can be used. The vulcanization accelerator may be appropriately selected according to the type of the vulcanizing agent. Specific examples of the vulcanization accelerator include guanidine compounds, aldehyde-ammonia compounds, thiazole compounds, thiourea compounds, sulfenamide compounds, thiuram compounds, dithiocarbamate compounds, and xanthate compounds. These may be used alone or in combination of two or more.

[0033] As the vulcanization aid, a conventionally known vulcanization aid can be used. Specific examples of the vulcanization aid include metal oxides such as zinc oxide, metal carbonates, metal hydroxides, organic acids such as stearic acid and derivatives thereof, amines, etc. These may be used alone or in combination of two or more.

[0034] The amount of each of the vulcanizing agent, the vulcanization aid, and the vulcanization accelerator may be about 0.1 to 10 parts by mass relative to 100 parts by mass of the nitrile rubber.

[0035] The nitrile rubber composition may contain a plasticizer that can be generally blended into the elastic member containing the crosslinked nitrile rubber. Examples of the plasticizer include phthalic acid esters, adipates, trimellitates, polyesters, phosphates, citrates, epoxidized vegetable oils, sebacic acid esters, azelates, maleates, and benzoates. The plasticizer blended into the nitrile rubber composition is preferably an adipate, and bis[2-(2-butoxyethoxy)ethyl]adipate (DBEEA) is particularly preferred. In recent years, the use of ester oils that maintain low viscosity even in low temperature environments has been proposed as base oils for lubricating oils and greases. However, ester oils tend to soften and swell rubber. Blending an adipic acid ester, particularly DBEEA, as a plasticizer for the nitrile rubber composition can suppress the softening and swelling of the elastic member containing the crosslinked nitrile rubber caused by the ester oil. The amount of the plasticizer to be mixed may be about 5 to 20 parts by mass with respect to 100 parts by mass of the nitrile rubber.

[0036] The nitrile rubber composition may further contain various additives that can be generally blended into the elastic member containing the crosslinked nitrile rubber, such as antioxidants, antiaging agents, processing aids such as higher fatty acid esters and metal salts thereof, and the like.

[0037] The method for preparing the nitrile rubber composition is not particularly limited, and may be prepared by a conventionally known method. For example, the nitrile rubber composition containing the above-mentioned uncrosslinked nitrile rubber, two or more kinds of carbon fillers, and a vulcanizing agent may be uniformly kneaded using a conventionally known rubber kneading device such as a rubber kneading roll or a Banbury mixer. At this time, the kneading conditions are not particularly limited, but kneading is usually performed at a temperature of 30 to 80°C for 5 to 60 minutes.

[0038] The method of producing the elastic member containing the crosslinked nitrile rubber by using the nitrile rubber composition is not particularly limited, and a conventionally known method may be adopted. For example, the unvulcanized nitrile rubber composition may be heated while being pressurized in a mold, and may be produced by a known rubber molding method such as compression molding, transfer molding, or injection molding. The molding conditions may be appropriately selected according to the composition of the nitrile rubber composition, and for example, pressure vulcanization may be performed at 120 to 200°C for about 30 seconds to 30 minutes. Furthermore, secondary vulcanization may be performed at 120 to 200°C for about 10 minutes to 10 hours, if necessary.

[0039] In the sealing device of this embodiment, the grease applied to the elastic member containing the crosslinked nitrile rubber has an oil component with a pour point of -25°C or lower. The pour point of the oil component is a temperature measured by the pour point and cloud point test method for crude oil and petroleum products (Japanese Industrial Standards K 2269:1987). Here, the oil component is a component obtained by recovering a component separated from the grease. The grease having an oil component pour point of -25°C or lower is not particularly limited, and for example, commercially available urea grease, lithium grease, etc. can be used. In addition, from the viewpoint of a decrease in heat resistance, the oil component of the grease preferably has a pour point of -70°C or higher.

[0040] As described above, the sealing device of the present embodiment has excellent sealing properties, particularly on the sliding surfaces of machines, in low-temperature environments. Therefore, the sealing device of the present embodiment can be suitably used in automobile hub units. A hub unit equipped with the sealing device of the present embodiment has excellent properties in preventing the inflow of liquid from the outside in low-temperature environments.

[0041] 1 is a schematic cross-sectional view of a hub unit H equipped with a sealing device of this embodiment. The hub unit H is attached to, for example, a suspension device (knuckle) on the vehicle body side of an automobile, and supports the automobile wheels so that they can rotate freely. The hub unit H includes a hub shaft 2, an inner ring 10, an outer ring 3, balls 4 which are multiple rolling elements, a cage 5, a sealing device 1 on the vehicle inner side, and a sealing device 6 on the vehicle outer side.

[0042] The hub axle 2 comprises a shaft body 9 and a mounting flange 8. The mounting flange 8 and the shaft body 9 are integrally manufactured from, for example, carbon steel for mechanical construction. The carbon steel for mechanical construction is, for example, any one of JISS45C, JISS48C, JISS50C, JISS53C, JISS55C, and JISS58C. The inner ring member 10 is manufactured from, for example, high carbon chromium bearing steel. The high carbon chromium bearing steel is, for example, JIS SUJ2.

[0043] The shaft body 9 is a shaft-shaped member that is long in the axial direction. The mounting flange 8 is provided extending radially outward from the end of the shaft body 9 of the inner shaft 7 on the vehicle outer side, and has an annular shape. A plurality of holes 11 are formed in the mounting flange 8 along the circumferential direction, and bolts 12 for mounting wheels are attached to the holes 11. A wheel and a brake rotor (not shown) are attached to the shaft body 9.

[0044] The inner ring 10 is annular, and is attached by fitting to a step formed on the end of the shaft body 9 on the vehicle inner side. An inner ring raceway surface 2a is formed on the outer peripheral surface on the vehicle outer side of the shaft body 9, and an inner ring raceway surface 2b is formed on the outer peripheral surface of the inner ring 10. The outer peripheral surface of the step has a smaller diameter than the outer peripheral surface of the inner ring raceway surface 2a.

[0045] The outer ring 3 is a cylindrical member and is made of, for example, carbon steel for mechanical construction. The carbon steel for mechanical construction is, for example, any one of JISS45C, JISS48C, JISS50C, JISS53C, JISS55C, and JISS58C. The outer ring 3 has a cylindrical outer ring body 13 and a fixing flange portion 14 for fixing that extends radially outward from the outer ring body 13. The fixing flange portion 14 is fixed to a knuckle (not shown), which is a vehicle body member, and thereby the hub unit H including the outer ring 3 is fixed to the knuckle.

[0046] When the hub unit H is attached to the vehicle body, the mounting flange 8 of the hub axle 2 is on the outer side of the vehicle. In other words, the left side of Fig. 1 (the mounting flange 8 side) is the vehicle outer side, and the right side of Fig. 1 is the vehicle inner side. Additionally, the left-right direction in Fig. 1 is the axial direction of the hub unit H.

[0047] On the inner peripheral surface of the outer ring 3, an outer ring raceway surface 3a on the vehicle outer side and an outer ring raceway surface 3b on the vehicle inner side are formed.

[0048] The outer ring raceway surface 3a and the inner ring raceway surface 2a on the vehicle outer side face each other in the radial direction, and the outer ring raceway surface 3b and the inner ring raceway surface 2b on the vehicle inner side face each other in the radial direction, with a plurality of balls 4 disposed between each of the raceway surfaces on the vehicle outer side and the vehicle inner side. The plurality of balls 4 are arranged in two rows in the axial direction, and the plurality of balls 4 in each row are retained by an annular cage 5. By providing the plurality of balls 4 between the hub shaft 2 and the outer ring 3, the outer ring 3 is configured to be concentric with the hub shaft 2, radially outward of the shaft body portion 9 of the hub shaft 2.

[0049] The cage 5 on the vehicle outer side holds the multiple balls 4 in the row on the vehicle outer side at intervals in the circumferential direction. The cage 5 on the vehicle inner side holds the multiple balls 4 in the row on the vehicle inner side at intervals in the circumferential direction. The cage 5 can be made of, for example, synthetic resin.

[0050] The vehicle inner-side sealing device 1 and the vehicle outer-side sealing device 6 are provided at both axial ends of the annular space S, which is a space formed between the outer ring 3 and the hub shaft 2 and in which a number of balls 4 held in a cage 5 are disposed, to prevent liquids such as muddy water and foreign matter from entering from the outside into the annular space S, and to prevent the lubricant that lubricates the inside of the annular space S from leaking to the outside. The first sealing device 1 and the second sealing device 6 each define the annular space S and an external space.

[0051] The sealing device 6 on the vehicle outer side has a metal ring 15 and an elastic member 16. The sealing device 6 is fitted and attached to the inner circumferential surface of the vehicle outer side end of the outer ring body 13 of the outer ring 3. The elastic member 16 is fixed to the metal ring 15 by vulcanization adhesion. The elastic member 16 has a lip tip 16a, a lip tip 16b, and a lip tip 16c. The lip tip 16a is in sliding contact with the mounting flange portion 8 of the shaft main body 9 at the seal contact surface SCS1 via the above-mentioned grease. The lip tip 16b is in sliding contact with the mounting flange portion 8 of the shaft main body 9 at the seal contact surface SCS2 via the above-mentioned grease. That is, the lip 16a and the lip tip 16b are in sliding contact with the mounting flange portion 8, which is a circular ring portion of the shaft main body 9. The lip tip 16c is in sliding contact with the shaft main body 9 at the seal contact surface SCS3 via the above-mentioned grease.

[0052] The vehicle inner side sealing device 1 is composed of an annular seal 17 and an annular slinger 18. The seal 17 has a metal ring 19 and an elastic member 20. The elastic member 20 is fixed to the metal ring 19 by vulcanization adhesion. The seal 17 is fitted and attached to the inner peripheral surface of the vehicle inner side end of the outer ring body 13 of the outer ring 3. The slinger 18 is fitted and attached in a tight fit state to the outer peripheral surface 10a of the vehicle inner side end of the inner ring member 10 constituting the inner shaft 7. The elastic member 20 has a lip tip 20a, a lip tip 20b, and a lip tip 20c. The lip tip 20a is in sliding contact with the annular portion of the slinger 18 at the seal contact surface SCS4 via the above-mentioned grease. The lip tip 20b is in sliding contact with the portion of the slinger 18 that is fitted to the outer peripheral surface 10a at the seal contact surface SCS5 via the above-mentioned grease. The lip tip 20c is in sliding contact with the portion of the slinger 18 that fits onto the outer circumferential surface 10a at the seal contact surface SCS6, via the above-mentioned grease.

[0053] The elastic member 16 and the elastic member 20 are elastic members including the crosslinked nitrile rubber of the sealing device of this embodiment. The elastic member 16 and the elastic member 20 are coated with the above-mentioned grease. That is, the grease is present on the seal contact surface where the lip tip of the elastic member 16 and the elastic member 20 slides against the above-mentioned annular portion, shaft portion, etc. As a result, as described above, the sealing device of this embodiment has excellent sealing properties in a low-temperature environment. Therefore, the hub unit H including the sealing device of this embodiment has excellent properties in preventing the inflow of liquid from the outside in a low-temperature environment. EXAMPLES

[0054] The present invention will be described in more detail below with reference to examples, but the embodiments of the present invention are not limited to the following examples.

[0055] A sealing device was produced using the elastic member containing the crosslinked nitrile rubber and the grease for application shown in Table 1 below, and then the performance was evaluated.

[0056] [Table 1]

[0057] Details of the elastic member containing crosslinked nitrile rubber and the grease used in the production of the sealing device are as follows.

[0058] <Crosslinked nitrile rubber> The nitrile rubber composition having the compounding composition shown in Table 2 below was prepared by kneading for 20 minutes at a temperature of 30 to 60°C using a rubber kneading roll. The prepared nitrile rubber composition was pressure-vulcanized at 170°C for 3 minutes to produce an elastic member containing crosslinked nitrile rubber for use in a sealing device.

[0059] [Table 2]

[0060] (Nitrile rubber) Nipol DN407 (22% acrylonitrile (AN) content): manufactured by Zeon Corporation Nipol DN401L (18% acrylonitrile (AN) content): manufactured by Zeon Corporation Nipol DN2850 (28% acrylonitrile (AN) content): manufactured by Zeon Corporation (Carbon Black) HAF-HS carbon (Seat 3■): Tokai Carbon Co., Ltd. (graphite) Artificial graphite (average particle size: 6 μm): SEC Carbon (Plasticizer) DBEEA (bis[2-(2-butoxyethoxy)ethyl] adipate): ADEKA Cizer RS-107

[0061] <Grease> Grease A (oil pour point = -15.5°C): Grease applied to the outer seal of the rear hub unit of the NHP10 / NHP10H Toyota Aqua. Grease B (oil pour point = -26.5°C): Grease applied to the outer seal of the AL20 Lexus RX, front hub unit. Grease C (oil pour point = -52.5°C): Bearing grease for AL20 type Lexus RX, front hub unit.

[0062] (1) Dynamic property test The dynamic property test conforming to the Japanese Industrial Standard K 6394:2007 was used to measure tanδ. PEAK The temperature was calculated.

[0063] (2) Muddy saltwater test 2 is a schematic diagram of the mud / saltwater test machine M used in this embodiment. The mud / saltwater test machine T includes a sealing device 100, a drive shaft 200, a housing 300, an agitator blade 400, and a mud tank 500. The dashed line AC indicates the center of the drive shaft 200.

[0064] The sealing device 100 is provided to prevent the muddy salt water M contained in the muddy water tank 500 from entering the housing 300. When the drive shaft 200 rotates, the muddy salt water M contained in the muddy water tank 500 is agitated by the agitating blade 400.

[0065] The sealing device 100 has the same configuration as the sealing device 6 used in the above-mentioned hub unit H. The sealing device 100 has a metal ring 115 and an elastic member 116. The elastic member 116 is fixed to the metal ring 115 by vulcanization adhesion. The sealing device 100 is fitted and attached to the inner peripheral surface of the housing 300. The elastic member 116 has a lip tip 116a, a lip tip 116b, and a lip tip 116c. The lip tip 116a is in sliding contact with the flange portion of the inner ring 210 at the seal contact surface SCS7. The lip tip 116b is in sliding contact with the flange portion of the inner ring 210 at the seal contact surface SCS8. The lip tip 116c is in sliding contact with the portion of the inner ring 210 that fits with the outer peripheral surface of the drive shaft 200 at the seal contact surface SCS9.

[0066] The drive shaft 200 is configured so that the axial tilt degree can be adjusted at the axial point AP. By adjusting the axial tilt degree, axial runout can be generated on the sliding surface between the elastic member 120 of the sealing device 100 and the slinger 118.

[0067] The sealing cycle (cyc) was evaluated under the following test conditions using nine types of sealing devices 100 made with the elastic member 120 containing the crosslinked nitrile rubber and the grease for application shown in Table 1. The sealing cycle (cyc) is the value (number of cycles - 1) when the intrusion of muddy salt water M into the housing 300 was confirmed. <Test conditions> Test temperature: -40℃ Axis inclination: 0.05, 0.1 deg (sliding surface runout against elastic member 120) Mud water composition: Japanese Industrial Standard Z 8901:2006 8 types 10.5wt% + CaCl2219.6wt% Water amount: shaft center bath Cycle pattern (1 cycle): 500 min -1 ×3min+stop 27min

[0068] As shown in Table 1, tan δ PEAK In the sealing device 100 having the elastic member 120 using rubber A, which is a cross-linked nitrile rubber having a temperature of -28°C, leakage occurred at 0 cycles at an axial tilt of 0.05 deg, regardless of whether grease A, grease B, or grease C was applied.

[0069] tan δ PEAK A sealing device 100 having an elastic member 120 using rubber B, which is a cross-linked nitrile rubber with a flow point of -28°C, leaked at 0 cycles regardless of the axial tilt when grease A with an oil component flow point of -15.5°C was applied. On the other hand, it was confirmed that grease B with an oil component flow point of -26.5°C had a muddy saltwater sealability of 65 cycles at an axial tilt of 0.05°C. Also, it was confirmed that grease C with an oil component flow point of -52.5°C had a muddy saltwater sealability of 80 cycles at an axial tilt of 0.05°C.

[0070] tan δ PEAK A sealing device 100 having an elastic member 120 using rubber C, which is a cross-linked nitrile rubber with a flow point of -40°C, leaked at 0 cycles at an axial tilt of 0.1 deg when grease A with an oil component flow point of -15.5°C was applied. On the other hand, it was confirmed that grease B with an oil component flow point of -26.5°C at an axial tilt of 0.1 deg had a muddy / salty water sealability of 60 cycles. Also, it was confirmed that grease C with an oil component flow point of -52.5°C at an axial tilt of 0.1 deg had a muddy / salty water sealability of 170 cycles.

[0071] From Table 1, tan δ PEAK However, it was revealed that a hub unit equipped with a sealing device including an elastic member containing crosslinked nitrile rubber with a tan δPEAK of -35°C or lower and a coating grease with an oil component pour point of -25°C or lower has excellent resistance to the inflow of liquid from the outside in a low-temperature environment. This suggests that a sealing device including an elastic member containing crosslinked nitrile rubber with a tan δPEAK of -35°C or lower and a coating grease with an oil component pour point of -25°C or lower has excellent sealing properties. [Explanation of symbols]

[0072] 1 : Sealing device 2: Hub axle 2a: Inner ring raceway 2b: Inner ring raceway 3: Outer ring 3a: Outer ring raceway 3b: Outer ring raceway surface 4: Ball (rolling element) 5 : Retainer 6: Sealing device 7: Inner shaft 8: Mounting flange 9: Shaft body 10: Insider 10a: Outer surface 11 : Hole 12: Bolt 13: Outer ring body 14: Fixed flange 15 : Metal ring 16: Elastic material 16a: Lip tip 16b: Lip tip 16c: Lip tip 17: Seal 18: Slinger 19 : Metal ring 20: Elastic material 20a: Lip tip 20b: Lip tip 20c: Lip tip 100: Sealing device 115: Metal ring 116: Elastic member 116a: Lip tip 116b: Lip tip 116c: Lip tip 200: Drive shaft 210: Inner Circle 300: Housing 400: Stirring blade 500: Mud tank AC: Axis center AP : Axis point deg: Axial tilt H: Hub unit M: Muddy saltwater S: Annular space SCS1: Seal contact surface SCS2: Seal contact surface SCS3: Seal contact surface SCS4: Seal contact surface SCS5: Seal contact surface SCS6: Seal contact surface SCS7: Seal contact surface SCS8: Seal contact surface SCS9: Seal contact surface T: Muddy salt water tester

Claims

1. A sealing device having an elastic member containing crosslinked nitrile rubber and grease, wherein a lip tip of the elastic member is in sliding contact with a seal contact surface via the grease, The elastic member containing the crosslinked nitrile rubber has a peak loss tangent of −35° C. or less in a dynamic property test in accordance with Japanese Industrial Standards K 6394:2007, The grease is a sealing device in which the pour point of the oil component is -25°C or lower.

2. The sealing device according to claim 1, wherein the elastic member containing the crosslinked nitrile rubber has a peak loss tangent of -60°C or higher.

3. The sealing device according to claim 1 or 2, wherein the grease has an oil component with a pour point of -70°C or higher.

4. The elastic member containing the crosslinked nitrile rubber is A nitrile rubber having a bound acrylonitrile content of 18 to 22 mass%; Two or more types of carbon filler are contained, The sealing device according to any one of claims 1 to 3, which is a vulcanizate of a nitrile rubber composition, wherein the total content of the two or more types of carbon fillers is 60 to 150 parts by mass relative to 100 parts by mass of the nitrile rubber.

5. 5. The sealing device of claim 4, wherein the two or more types of carbon fillers are selected from carbon black, graphite, carbon fiber, carbon nanotubes, and graphene.

6. The sealing device of claim 5 , wherein the two or more types of carbon fillers include carbon black.

7. The sealing device of claim 6 , wherein the two or more types of carbon fillers include graphite.

8. The sealing device according to any one of claims 4 to 7, wherein a total content of the two or more types of carbon fillers is 100 to 130 parts by mass with respect to 100 parts by mass of the nitrile rubber.

9. The sealing device according to any one of claims 1 to 8, which is a sealing device for a hub unit.

10. A hub unit comprising the sealing device according to claim 9.

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