Rolling bearing and use of rolling bearing

Abstract

In this rolling bearing, a material of a rolling element is silicon nitride, a material of an inner ring is a first steel material, a material of an outer ring is the first steel material, and the first steel material includes 0.3 mass%-0.5 mass% inclusive of carbon, 0.05 mass%-0.3 mass% inclusive of silicon, 0.05 mass%-0.5 mass % inclusive of manganese, more than 0 and 0.03 mass% or less of phosphorus, more than 0 and 0.03 mass% or less of sulfur, 13.0 mass%-16.0 mass% inclusive of chromium, 1.5 mass%-2.5 mass% of molybdenum, 0.1 mass%-0.5 mass% inclusive of vanadium, 0.1 mass%-0.2 mass% inclusive of nitrogen, and 0.0005 mass%-0.005 mass% inclusive of boron, with the balance being inevitable impurities and iron.

Description

Rolling bearings and their use

[0001] The present disclosure relates to rolling bearings and the use of rolling bearings.

[0002] As the use of hydrogen energy increases toward carbon neutrality, rolling bearings are increasingly being used in hydrogen atmospheres. When rolling bearings made of steel are used in hydrogen atmospheres, hydrogen can penetrate into the steel, causing hydrogen embrittlement in the steel. Therefore, there is a demand for rolling bearings that are highly durable against hydrogen gas. Patent Document 1 proposes a rolling bearing for use in hydrogen atmospheres.

[0003] Furthermore, rolling bearings used in hydrogen power generation (fuel cell power generation), one form of hydrogen energy utilization, may come into contact with water (water vapor) generated by the reaction between hydrogen and oxygen, and therefore rolling bearings used in hydrogen power generation must also be resistant to corrosion from water vapor and other contaminants.

[0004] JP 2010-249215 A

[0005] The rolling bearing described in Patent Document 1 sometimes fails to ensure sufficient durability when used in a hydrogen atmosphere. The present invention has been made in light of this situation, and has an object to provide a rolling bearing that has good corrosion resistance and excellent durability in a hydrogen atmosphere.

[0006] From the standpoint of ensuring the corrosion resistance and durability of the rolling bearing in a hydrogen atmosphere, it may be possible to consider making the outer ring, inner ring, and rolling elements from ceramics such as silicon nitride. However, a rolling bearing in which the outer ring, inner ring, and rolling elements are all made from silicon nitride is difficult to manufacture and requires significant manufacturing costs.

[0007] The rolling bearing of the present disclosure is a rolling bearing comprising a plurality of rolling elements, an inner ring, and an outer ring, wherein the rolling elements roll on an inner ring raceway of the inner ring and an outer ring raceway of the outer ring, wherein the material of the rolling elements is silicon nitride, wherein the material of the inner ring is a first steel material, wherein the material of the outer ring is a first steel material, wherein the first steel material contains: 0.3% by mass or more and 0.5% by mass of carbon, 0.05% by mass or more and 0.3% by mass of silicon, 0.05% by mass or more and 0.5% by mass of manganese, more than 0 to 0.03% by mass of phosphorus, more than 0 to 0.03% by mass of sulfur, 13.0% by mass or more and 16.0% by mass or less of chromium, 1.5% by mass or more and 2.5% by mass of molybdenum, 0.1% by mass or more and 0.5% by mass of vanadium, The alloy contains 0.1 mass % to 0.2 mass % nitrogen, 0.0005 mass % to 0.005 mass % boron, and the balance being inevitable impurities and iron.

[0008] The use of the present disclosure is a rolling bearing used in an environment where the hydrogen partial pressure is 0.05 MPa or more and 5 MPa or less.

[0009] The rolling bearing of the present disclosure has good corrosion resistance and excellent durability in a hydrogen atmosphere.

[0010] Fig. 1 is a cross-sectional view showing a deep groove ball bearing according to one embodiment of the present disclosure. Fig. 2 is a cross-sectional view showing a deep groove ball bearing according to another embodiment of the present disclosure. Fig. 3 is a diagram showing an apparatus for evaluating durability in a hydrogen atmosphere.

[0011] <Outline of Embodiments of the Invention of the Present Disclosure> Below, outlines of embodiments of the invention of the present disclosure will be listed and described. (1) A rolling bearing according to the present disclosure is a rolling bearing comprising a plurality of rolling elements, an inner ring, and an outer ring, wherein the rolling elements roll on an inner ring raceway of the inner ring and an outer ring raceway of the outer ring, wherein the material of the rolling elements is silicon nitride, wherein the material of the inner ring is a first steel material, wherein the material of the outer ring is a first steel material, wherein the first steel material contains: 0.3% by mass or more and 0.5% by mass of carbon, 0.05% by mass or more and 0.3% by mass of silicon, 0.05% by mass or more and 0.5% by mass of manganese, more than 0 to 0.03% by mass of phosphorus, more than 0 to 0.03% by mass of sulfur, 13.0% by mass or more and 16.0% by mass or less of chromium, 1.5% by mass or more and 2.5% by mass or less of molybdenum, 0.1% by mass or more and 0.5% by mass of vanadium, The alloy contains 0.1 mass % to 0.2 mass % nitrogen, 0.0005 mass % to 0.005 mass % boron, and the balance being inevitable impurities and iron.

[0012] In the above rolling bearing, the outer ring and inner ring are made of a first steel material having a specific composition. The rolling elements are made of silicon nitride. Therefore, the above rolling bearing has excellent durability even when used in a hydrogen atmosphere. In other words, the above rolling bearing has excellent durability against hydrogen gas. The reason why conventional rolling bearings have poor durability against hydrogen gas is thought to be as follows: Hydrogen easily penetrates conventional rolling bearings through the contact areas between the outer ring and rolling elements and the contact areas between the inner ring and rolling elements, making them susceptible to hydrogen embrittlement. Another reason why the outer ring, inner ring, and rolling elements that make up conventional rolling bearings have a high hydrogen content at the start of use is also thought to be one of the reasons why they are susceptible to hydrogen embrittlement.

[0013] In contrast, the rolling elements that make up the rolling bearing of the present disclosure are made of silicon nitride, and therefore do not suffer from the hydrogen embrittlement that is a problem with steel. Furthermore, the outer ring and inner ring that make up the rolling bearing of the present disclosure are made from the first steel material, and therefore contain a low amount of hydrogen at the start of use, and hydrogen is less likely to penetrate into the interior even after use has begun. Therefore, the rolling bearing of the present disclosure has excellent durability against hydrogen gas. Furthermore, the rolling bearing of the present disclosure has excellent corrosion resistance. Here, corrosion resistance refers to the ability to resist rust.

[0014] (2) The rolling bearing of (1) above further comprises a retainer, and the material of the retainer is a resin composition, and the resin composition preferably contains polyamide 66 and 15% by mass or more and 35% by mass or less of glass fiber.

[0015] (3) Preferably, the rolling bearing of (1) above further comprises a cage, the material of the cage is a second steel material, and the second steel material is stainless steel.

[0016] (4) In the rolling bearing of (3) above, the second steel material is preferably SUS304.

[0017] (5) Preferably, the rolling bearings of (1) to (4) above comprise two seals attached to axial ends of the outer ring and having elastic members in sliding contact with the inner ring, the seals comprising metal rings and elastic members fixed to the metal rings, the elastic members made of a first rubber composition containing fluororubber, and the portions of the seals attached to the outer ring and the portions in sliding contact with the inner ring are constituted by the elastic members.

[0018] (6) Preferably, the rolling bearing of any one of (1) to (4) above comprises two seals attached to axial ends of the outer ring and in sliding contact with the inner ring, the seals comprising a metal ring and an elastic member fixed to the metal ring, the elastic member made of a second rubber composition containing hydrogenated NBR, and the portion of the seal attached to the outer ring and the portion in sliding contact with the inner ring are constituted by the elastic member.

[0019] (7) It is preferable that the rolling bearing of (5) above is filled with grease, and the volume of the grease is 15% by volume or more and 45% by volume or less of the volume obtained by subtracting the volume of the plurality of rolling elements and the cage from the volume of the space surrounded by the inner ring, the outer ring, and the two seals.

[0020] (8) It is preferable that the rolling bearing of (6) above is filled with grease, and the volume of the grease is 15% by volume or more and 45% by volume or less of the volume obtained by subtracting the volume of the plurality of rolling elements and the cage from the volume of the space surrounded by the inner ring, the outer ring, and the two seals.

[0021] (9) Use of a rolling bearing according to any one of (1) to (8) above, in an environment where the hydrogen partial pressure is 0.05 MPa or more and 5 MPa or less.

[0022] As described above, the rolling bearing has excellent durability against hydrogen gas. Therefore, the rolling bearing can be suitably used in an environment with the above hydrogen partial pressure. In the present disclosure, the hydrogen partial pressure is used in the sense of absolute pressure.

[0023] <Details of the Embodiments of the Invention of the Present Disclosure> Hereinafter, embodiments of the present disclosure will be described. Note that in this disclosure, the embodiments of the invention are to be considered as illustrative in all respects and not restrictive. The scope of the rights of the present invention is defined by the claims, and it is intended to include all modifications within the meaning and scope equivalent to the claims.

[0024] [Regarding the overall configuration of the rolling bearing] The overall configuration of the rolling bearing of the present disclosure will be described with reference to Figures 1 and 2. Figure 1 is a cross-sectional view showing a deep groove ball bearing according to one embodiment of the present disclosure. Figure 2 is a cross-sectional view showing a deep groove ball bearing according to another embodiment of the present disclosure. The deep groove ball bearing according to the embodiment shown in Figure 2 is the same as the deep groove ball bearing according to the embodiment shown in Figure 1, except for the cage.

[0025] Deep groove ball bearing 1 comprises an inner ring 2, an outer ring 3 provided radially outward of inner ring 2, a plurality of balls 4 as rolling elements provided between inner ring 2 and outer ring 3, and an annular cage 5 that holds these balls 4. Seals 6 are provided on both first and second axial sides of deep groove ball bearing 1. In deep groove ball bearing 1, grease G is sealed in the annular region between inner ring 2 and outer ring 3.

[0026] The inner ring 2 has an inner ring raceway 21 on its outer periphery in which the balls 4 roll. The inner ring raceway 21 is a raceway groove. The outer ring 3 has an outer ring raceway 31 on its inner periphery in which the balls 4 roll. The outer ring raceway 31 is a raceway groove. A plurality of balls 4 are interposed between the inner ring raceway 21 and the outer ring raceway 31, and roll on these inner ring raceway 21 and outer ring raceway 31.

[0027] The grease G sealed in the annular region between the inner ring 2 and the outer ring 3 is also present at the contact points between the balls 4 and the inner ring raceway 21 of the inner ring 2 and the contact points between the balls 4 and the outer ring raceway 31 of the outer ring 3. The volume of the sealed grease G is 15% by volume or more and 45% by volume or less of the volume obtained by subtracting the volume of the plurality of balls 4 and the cage 5 from the volume of the space surrounded by the inner ring 2, the outer ring 3, and the two seals 6. The cage 5 holds the plurality of balls 4 at equal intervals in the circumferential direction. The cage 5 shown in FIG. 1 is a crown-shaped cage made of resin. The cage 5 may also be made of corrosion-resistant steel. The cage 5 shown in FIG. 2 is a wave-shaped cage made of stainless steel.

[0028] The seal 6 is an annular member including an annular metal ring 6a and an elastic member 6b fixed to the metal ring 6a. The seal 6 has a radially outer portion fixed to the outer ring 3, and a lip tip of the radially inner portion, which is formed by the elastic member 6b, is attached so as to be able to slide against the inner ring 2. The seal 6 prevents the enclosed grease G from leaking to the outside. The seal 6 is fixed to a seal groove provided on the outer side of both axial ends of the outer ring raceway 31 of the outer ring 3. The lip tip of the seal 6 contacts seal contact surfaces provided on the outer side of both axial ends of the inner ring raceway 21 of the inner ring 2. The seal contact surfaces are planes perpendicular to the central axis of the inner ring 2. The outer periphery of the metal ring 6a is located radially outward of a shoulder adjacent to the outer ring raceway 31. The inner periphery of the metal ring 6a is located radially inward of the inner periphery of the cage 5. Because the metal ring 6a is less likely to deform than the elastic member 6b, the lip tip of the seal 6 sandwiched between the metal ring 6a and the seal contact surface is pressed against the seal contact surface and deforms, coming into annular contact in the circumferential direction with a width in the radial direction of the seal contact surface. Because the lip tip deforms, the contact area between the elastic member 6b of the seal 6 and the seal contact surface can be made larger, so hydrogen in the external space of the bearing is less likely to enter in large quantities into the internal space of the bearing surrounded by the inner ring 2, outer ring 3, and two seals 6 from the contact points between the elastic member 6b of the seal 6 and the seal contact surface.

[0029] [Regarding Rolling Bearing Components] In a deep groove ball bearing 1, the inner ring 2 is made of a first steel material, and the outer ring 2 is made of a first steel material. The first steel material contains 0.3% to 0.5% by mass of carbon, 0.05% to 0.3% by mass of silicon, 0.05% to 0.5% by mass of manganese, more than 0% to 0.03% by mass of phosphorus, more than 0% to 0.03% by mass of sulfur, 13.0% to 16.0% by mass of chromium, 1.5% to 2.5% by mass of molybdenum, 0.1% to 0.5% by mass of vanadium, 0.1% to 0.2% by mass of nitrogen, and 0.0005% to 0.005% by mass of boron, with the remainder being inevitable impurities and iron. The first steel material is martensitic stainless steel.

[0030] One of the features of the first steel material is that it contains 0.1% by mass or more and 0.2% by mass or less of nitrogen. Since the first steel material contains 0.1% by mass or more and 0.2% by mass or less of nitrogen and 0.3% by mass or more and 0.5% by mass or less of carbon, it has good corrosion resistance.

[0031] Furthermore, because the first steel material contains 0.1% by mass or more and 0.2% by mass or less of nitrogen, hydrogen is less likely to penetrate during heat treatment. Therefore, the inner ring and outer ring made from the first steel material have a low hydrogen content at the start of use. Furthermore, because the first steel material contains 0.1% by mass or more and 0.2% by mass or less of nitrogen and 0.3% by mass or more and 0.5% by mass or less of carbon, hydrogen is less likely to penetrate into the inner ring and outer ring made from the first steel material during use. Therefore, the inner ring 2 and the outer ring 3 have excellent durability against hydrogen gas.

[0032] The inner ring 2 and the outer ring 3 are members obtained by subjecting the first steel material to heat treatment. The heat treatment includes quenching, subzero treatment, and tempering. The quenching is performed, for example, by heating the material at 1020°C to 1080°C for 20 to 90 minutes, followed by gas cooling using an inert gas such as nitrogen gas or argon gas.

[0033] The sub-zero treatment is carried out, for example, at −90° C. to −50° C. and for 30 to 90 minutes by cooling, while the tempering treatment is carried out, for example, at 160° C. to 230° C. and for 60 to 150 minutes by heating.

[0034] The first steel material that is the material for the inner ring 2 and the first steel material that is the material for the outer ring 3 may have the same composition or different compositions as long as they satisfy the composition of the first steel material described above. Each of the inner ring 2 and the outer ring 3 is manufactured by a known method, for example, by forging and cutting a steel bar to form a workpiece, subjecting it to the above-mentioned heat treatment, polishing, and superfinishing the raceway.

[0035] In the deep groove ball bearing 1, the material of the balls 4 is silicon nitride. When silicon nitride balls 4 are used, unlike when steel balls are used, the problem of hydrogen embrittlement does not occur in the balls 4. The silicon nitride balls 4 are manufactured by a known method.

[0036] In the deep groove ball bearing 1, the material of the cage 5 is, for example, a resin composition. The resin composition contains polyamide 66 and glass fiber. The preferred content of the glass fiber is 15 mass % or more and 35 mass % or less with respect to the entire resin composition. A cage made of the resin composition is resistant to moisture absorption and swelling even when in contact with water (water vapor). In addition to polyamide 66 and glass fiber, the resin composition may contain other additives as needed. When the material of the cage 5 is a resin composition, a preferred cage 5 is a crown cage as shown in FIG. 1.

[0037] In the deep groove ball bearing 1, the material of the cage 5 may be, for example, a second steel material. The second steel material is stainless steel. A cage made of stainless steel has higher corrosion resistance than a normal cage made of iron. A preferred stainless steel is SUS304. A cage made of SUS304 is easily available and has good corrosion resistance. When the material of the cage 5 is stainless steel, a preferred cage 5 is a wave cage shown in FIG. 2.

[0038] In the deep groove ball bearing 1, the seal 6 is an annular member including an annular metal ring 6a and an annular elastic member 6b fixed to the metal ring 6a. Examples of materials for the metal ring 6a include SPCC. The surface of the metal ring 6a is coated with an adhesive layer (also called a primer layer) to ensure adhesion to the elastic member.

[0039] The elastic member 6b is made of a rubber composition. This rubber composition contains, for example, fluororubber (FKM), hydrogenated NBR, etc. as the rubber component. Here, fluororubber (FKM) and hydrogenated NBR both refer to crosslinked rubber. Because fluororubber (FKM) and hydrogenated NBR have excellent hydrogen resistance and heat resistance, rubber compositions containing these rubber components are suitable as materials for the elastic member 6a of the seal 6. Hydrogenated NBR has no or very few double bonds in its main chain. Rubber compositions using hydrogenated NBR are less likely to react with hydrogen in the environment, thereby suppressing changes in the physical properties of the elastic member 6a of the seal 6. Fluororubber (FKM) also has no or very few double bonds in its main chain, so it is less likely to react with hydrogen in the environment, thereby suppressing changes in the physical properties of the elastic member 6a of the seal 6. From the viewpoint of excellent hydrogen resistance and heat resistance, fluororubber is a more preferred rubber component. The elastic member 6b is vulcanization-bonded to the metal ring 6a. The elastic member 6b is bridged and bonded to the metal ring 6a.

[0040] In the deep groove ball bearing 1, the grease G is made of a grease composition containing a base oil and a thickener as essential components, and additives as optional components.

[0041] The deep groove ball bearing according to an embodiment of the present disclosure has excellent durability against hydrogen gas and is therefore suitable for use in environments where the hydrogen partial pressure is 0.05 MPa or more and 5 MPa or less. The rolling bearing according to an embodiment of the present disclosure is not limited to a deep groove ball bearing, and may be another rolling bearing such as an angular contact ball bearing or a tapered roller bearing.

[0042] Next, the present invention will be described in more detail based on examples. However, the present invention is not limited to the examples. In these examples, a deep groove ball bearing with a contact seal (bearing model number: 6000, inner diameter 10 mm, outer diameter 26 mm, resin cage) was manufactured using the bearing components described below, and the durability and corrosion resistance of the resulting deep groove ball bearing were evaluated.

[0043] (Inner ring, outer ring, balls) The inner ring, outer ring, and balls were manufactured by a known method using any of steel materials 1 to 3 and silicon nitride shown in Table 1. Table 1 shows the chemical components contained in steel materials 1 to 3, excluding iron and unavoidable impurities.

[0044] Table 1 also lists the pitting resistance equivalents (PRE) of Steels 1 to 3 calculated by the following formula (1): PRE=Cr+3.3(Mo+0.5W)+16N-Mn(mass%) (1) From the pitting resistance indices shown in Table 1, Steel 1 is considered to have superior corrosion resistance compared to SUS440C and SUJ2.

[0045]

[0046] When manufacturing the inner ring, outer ring and balls, the steel materials 1 to 3 were subjected to heat treatment under the conditions shown in Table 2.

[0047]

[0048] (Cage) The cage was manufactured by a known method using a resin composition (Ultramid A3HG5, manufactured by BASF) containing polyamide 66 and 25 mass % of glass fiber.

[0049] (Seal) The seal was manufactured by preparing a metal ring made of SPCC with an adhesive layer provided on the entire surface and an unvulcanized rubber composition for forming an elastic member made of fluororubber (FKM), and integrally molding the two in a mold.

[0050] (Grease) The grease is KVC grease, a standard grease for JTEKT bearings. The thickener of KVC grease is diurea, and the base oil is a mixed oil of polyalphaolefin and ester. The kinematic viscosity of the base oil at 40°C is 40mm. ２ / s or more 55mm ２ / s or less.

[0051] (Example 1 and Comparative Examples 1 to 4) Deep groove ball bearings with contact seals and filled with grease were manufactured using the combinations of inner rings, outer rings, and balls shown in Table 3. All of the balls were made of the materials shown in Table 3. The volume of the filled grease was 30% by volume of the volume of the space surrounded by the inner ring, outer ring, and two seals minus the volume of the balls and cage. The durability of the obtained deep groove ball bearings and the corrosion resistance of the inner ring of the deep groove ball bearings were evaluated using the following methods. The results are shown in Table 3.

[0052]

[0053] (Evaluation of durability against hydrogen gas) Using the rolling bearing testing device 101 described in WO 2020 / 250857, the durability against hydrogen gas of the deep groove ball bearings 6000 (test bearings) manufactured in Example 1 and Comparative Examples 1 to 4 was evaluated. In this evaluation, the time until the bearing broke was measured.

[0054] Figure 3 is a diagram showing the overall configuration of a bearing testing device 101. Note that a portion of Figure 3 is cut away for ease of understanding. As shown in Figure 3, the rolling bearing testing device 101 includes a sealed container 102, a bearing holding device 104 that is housed in the internal space of the sealed container 102 and holds a rolling bearing that is a test bearing, and a drive device 106.

[0055] The sealed container 102 includes a wall 103 made of stainless steel and a window 131 fitted with a glass plate. The body 102a is a cylindrical body with a bottom and an open top. The body 102a has the wall 103 and the window 131, and the lid 102b is the entire wall 103. The body 102a has a flange 102a1 around the periphery of the opening 102a2. The lid 102b also has a flange 102b1 corresponding to the flange 102a1. The flanges 102a1 and 102b1 are butted together via an O-ring and fastened together with bolts. This allows the lid 102b to be detachably fixed to the body 102a. When equipment necessary for testing, such as a bearing retaining device 104, is placed in the internal space of the sealed container 102, the equipment in the internal space of the sealed container 102 can be accessed through the opening 102a2 in the main body 102a when the lid 102b is removed.

[0056] An inlet pipe 102c for introducing hydrogen gas, a hydrogen-containing mixed gas, or other gas (atmospheric gas) into the internal space of the sealed container 102, and an exhaust pipe 102d for exhausting gas from the internal space of the sealed container 102 are provided on the lower side surface of the sealed container 102. Two holes are provided penetrating the wall 103 of the sealed container 102, with the inlet pipe 102c connected to the first hole and the exhaust pipe 102d connected to the second hole. The atmosphere in the internal space of the sealed container 102 is adjusted by introducing gas into the internal space of the sealed container 102 from the inlet pipe 102c and exhausting gas from the internal space of the sealed container 102 from the exhaust pipe 102d.

[0057] A heater 102e is provided on the side surface of the sealed container 102 to raise the temperature of the atmosphere in the internal space of the sealed container 102 from the outside. The heater 102e is in the shape of a strip having a heating wire or the like, and is wrapped around the side surface of the sealed container 102 to heat the atmosphere in the sealed container 102 from the outside. This allows the heater 102e to raise the temperature of the atmosphere in the internal space of the sealed container 102, and ultimately to raise and adjust the temperature of the rolling bearings 200 (201, 202, 203, 204). The heater 102e can raise the temperature of the atmosphere in the internal space of the sealed container 102 to, for example, about 150 degrees.

[0058] A cooling device 102h is also provided on the side of the sealed container 102. The cooling device 102h is strip-shaped and has a flow path for circulating a refrigerant. The cooling device 102h is wrapped around the side of the sealed container 102 and cools the atmosphere of the sealed container 102 from the outside by the refrigerant flowing through the flow path. This allows the cooling device 102h to lower the temperature of the atmosphere in the internal space of the sealed container 102, and ultimately lower and adjust the temperature of the rolling bearings 200 (201, 202, 203, 204). The cooling device 102h can lower the temperature of the atmosphere in the internal space of the sealed container 102 to, for example, about -30 degrees. By providing the heater 102e and the cooling device 102h, the testing apparatus 101 can set a wide range of ambient temperatures.

[0059] A rotary fan 102g is provided at a bottom 102f of the sealed container 102. The rotary fan 102g agitates the atmosphere in the internal space of the sealed container 102 in order to maintain the temperature and atmosphere of the atmosphere in the internal space of the sealed container 102 uniform.

[0060] The bearing retaining device 104 includes a test section 110 that holds a plurality of rolling bearings 200 (201, 202, 203, 204) to be tested, a rotating shaft 111, a first load applying mechanism 112 that applies an axial load to the plurality of rolling bearings 200, and a second load applying mechanism 113 that applies a radial load to the plurality of rolling bearings 200. The bearing retaining device 104 is fixed on a pedestal 114 that is fixedly provided in the internal space of the sealed container 102.

[0061] The test section 110 is divided into three parts and includes a first side housing 140 arranged on the first axial side, which is the tip side of the rotating shaft 111, a second side housing 141 arranged on the second axial side of the rotating shaft 111, and a central housing 142 arranged between the first side housing 140 and the second side housing 141.

[0062] Four inner rings of rolling bearings 200 (201, 202, 203, 204) are fitted onto the rotating shaft 111. The outer ring of rolling bearing 201, which is arranged at the end of the rotating shaft 111 on a first axial side, is held in a first side housing 140. The outer ring of rolling bearing 204, which is arranged at the end of the rotating shaft 111 on a second axial side, is held in a second side housing 141. The outer rings of rolling bearings 202 and 203, which are arranged between rolling bearing 201 and rolling bearing 204, are held in a central housing 142.

[0063] The base 114 is a plate-like member formed using a perforated metal. The base 114 is disposed approximately horizontally across the internal space of the sealed container 102. The perforated metal is a metal plate with numerous through holes formed therein, and even though it is disposed across the internal space of the sealed container 102, the atmosphere can move in the vertical direction (up and down) of the base 114. Even with the base 114, the atmosphere and temperature in the internal space of the sealed container 102 can be maintained uniform because the atmosphere can move in the vertical direction of the base 114.

[0064] In the internal space of the sealed container 102, a connecting shaft 124 for connecting to the non-contact coupling 116 and a coupling 126 for connecting the connecting shaft 124 and the rotating shaft 111 so that they can rotate together are provided at the end of the rotating shaft 111 extending from the testing section 110. A connecting shaft support section 128 for supporting the connecting shaft 124 rotatably relative to the sealed container 102 is provided on the base 114.

[0065] The rotating shaft 111 (connecting shaft 124) is driven to rotate by a driving device 106 provided outside the sealed container 102. The driving device 106 includes a motor 106a that generates a driving force for driving the rotating shaft 111, a driving shaft 106b that is provided outside the sealed container 102 and supported by a driving shaft support portion 120, a pulley 106c provided on an output shaft 106a1 of the motor 106a, a pulley 106d provided on the driving shaft 106b, and an endless belt 106e that is wound around the pulleys 106c and 106d and transmits the driving force of the output shaft 106a1 to the driving shaft 106b. The driving shaft 106b is connected to the rotating shaft 111 (connecting shaft 124) so ​​as to be rotatable together with the rotating shaft 111 (connecting shaft 124) and drives the rotating shaft 111 (connecting shaft 124). The driving device 106 and the rotary shaft 111 (connection shaft 124 ) are connected by a non-contact coupling 116 .

[0066] Next, a testing method using the rolling bearing testing device 101 will be described. First, a deep groove ball bearing, which is a test bearing for the rolling bearing 200, is assembled to the rotating shaft 111 of the testing section 110 of the bearing retaining device 104, the first side housing 140, the second side housing 141, and the central housing 142. The testing section 110 is disposed in the internal space of the main body 102a of the sealed container 102, and is connected to the connecting shaft 124 and the connecting shaft support section 128. An axial load is applied to the rolling bearing 200 by the first load applying mechanism 112, and a radial load is applied by the second load applying mechanism 113. It is not necessary for one of the axial load and the radial load to be applied. The lid 102b is attached to the main body 102a, and the internal space of the sealed container 102 is sealed from the external space.

[0067] Next, hydrogen gas is introduced as the atmosphere (gas) into the internal space of the sealed container 102, the temperature of the atmosphere in the internal space of the sealed container 102 is set to a predetermined temperature, and the driving device 106 is operated to rotate the rotating shaft 111. In this way, the inner ring of the rolling bearing 200 rotates relative to the outer ring.

[0068] While the rotating shaft 111 is rotating, an axial load is applied between the inner and outer rings of the rolling bearing 200 by the first load application mechanism 112, and at the same time, a radial load is applied between the inner and outer rings of the rolling bearing 200 by the second load application mechanism 113, so that an axial load and a radial load are simultaneously applied to the rolling bearing 200 in a hydrogen gas atmosphere.

[0069] Specific test conditions are as shown in Table 4. In this test, two bearings were tested for each of the deep groove ball bearing of Example 1 and the deep groove ball bearings of Comparative Examples 1 to 4. The shortest time until the test bearing broke was used as the evaluation result. Table 3 shows the results (life ratio) relative to the time until the breakage of the deep groove ball bearing of Comparative Example 4, which is set to 1.

[0070]

[0071] (Evaluation of corrosion resistance) This evaluation was carried out on the inner rings of the deep groove ball bearings 6000 of Example 1 and Comparative Example 2. This evaluation was carried out with reference to JIS Z 2371 (2015): Salt spray test method. Specific test conditions are as shown in Table 5. In this evaluation, the inner rings of the deep groove ball bearings (test samples) were continuously sprayed with salt water for 48 hours. The amount of salt water sprayed in this evaluation was approximately 80 cm ２ This is the amount that results in an average collection amount of spray liquid of 1.0 to 2.0 mL / hr in the horizontal collection area.

[0072] The equipment used for the salt spray test conforms to the equipment described in Appendix A of JIS Z 2371 (2015), "(Reference) Example of equipment with spray discharge and wastewater treatment equipment." The test sample was placed on two parallel, horizontally aligned cylindrical glass specimen holders on the upper vertical side, as described in "Figure JA.1 - Test specimen placement and position, b) Test specimen angle and spray liquid collection container layout diagram" in Appendix JA of JIS Z 2371 (2015), "(Reference) Test specimen placement and position." The test sample was supported at two circumferential points on the lower vertical side of the outer periphery by two adjacent glass specimen holders.

[0073] The outer peripheral surfaces of the inner rings of the test samples, deep groove ball bearings, were observed 0 hours (before the start of salt spraying), 24 hours, and 48 hours after the start of salt spraying, and the ratio (area %) of the area where red rust had formed to the entire outer peripheral surface of the inner ring was calculated. The evaluation results were shown as a range between the minimum and maximum values ​​of the three test samples.

[0074]

[0075] As the results shown in Table 3 show, it has become clear that the rolling bearing according to the embodiment of the present disclosure has excellent durability against hydrogen gas and corrosion resistance.

[0076] REFERENCE SIGNS LIST 1 deep groove ball bearing 2 inner ring 3 outer ring 5 cage 6 seal 6a metal ring 6b elastic member 21 inner ring raceway 31 outer ring raceway 101 rolling bearing test device G grease

Claims

1. A rolling bearing comprising a plurality of rolling elements, an inner ring, and an outer ring, wherein the rolling elements roll on an inner ring raceway of the inner ring and an outer ring raceway of the outer ring, wherein the material of the rolling elements is silicon nitride, wherein the material of the inner ring is a first steel material, wherein the material of the outer ring is a first steel material, wherein the first steel material has: 0.3% by mass or more and 0.5% by mass of carbon, 0.05% by mass or more and 0.3% by mass of silicon, 0.05% by mass or more and 0.5% by mass or less of manganese, more than 0 and 0.03% by mass of phosphorus, more than 0 and 0.03% by mass of sulfur, 13.0% by mass or more and 16.0% by mass or less of chromium, 1.5% by mass or more and 2.5% by mass or less of molybdenum, 0.1% by mass or more and 0.5% by mass or less of vanadium, A rolling bearing comprising: 0.1 mass % or more and 0.2 mass % or less of nitrogen; 0.0005 mass % or more and 0.005 mass % or less of boron; and the balance being unavoidable impurities and iron.

2. A rolling bearing according to claim 1, further comprising a retainer, the retainer being made of a resin composition, the resin composition containing polyamide 66 and 15% by mass or more and 35% by mass or less of glass fiber.

3. The rolling bearing according to claim 1, further comprising a cage, the material of said cage being a second steel material, and said second steel material being stainless steel.

4. The rolling bearing according to claim 3, wherein the second steel material is SUS304.

5. A rolling bearing as claimed in claim 1, comprising two seals each having an elastic member attached to an axial end of the outer ring and in sliding contact with the inner ring, wherein the seal comprises a metal ring and an elastic member fixed to the metal ring, the elastic member being made of a first rubber composition containing fluororubber, and the portion of the seal attached to the outer ring and the portion in sliding contact with the inner ring are constituted by the elastic member.

6. A rolling bearing as claimed in claim 1, comprising two seals attached to axial ends of the outer ring and in sliding contact with the inner ring, the seals comprising metal rings and elastic members fixed to the metal rings, the elastic members being made of a second rubber composition containing hydrogenated NBR, and the portions of the seals attached to the outer ring and the portions in sliding contact with the inner ring being composed of the elastic members.

7. A rolling bearing as described in claim 6, in which grease is enclosed, and the volume of said grease is 15 volume % or more and 45 volume % or less of the volume obtained by subtracting the volume of said plurality of rolling elements and said cage from the volume of the space surrounded by said inner ring, said outer ring, and said two seals.

8. A rolling bearing as described in claim 7, in which grease is enclosed, and the volume of said grease is 15 volume % or more and 45 volume % or less of the volume obtained by subtracting the volume of said plurality of rolling elements and said cage from the volume of the space surrounded by said inner ring, said outer ring, and said two seals.

9. Use of the rolling bearing according to any one of claims 1 to 8, which is used in an environment where the hydrogen partial pressure is 0.05 MPa or more and 5 MPa or less.

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