ROLLING BEARINGS AND USE OF ROLLING BEARINGS

Abstract

In the rolling bearing, the material of the rolling elements consists of silicon nitride, the material of an inner ring of a first steel material, and the material of an outer ring of the first steel material. The first steel material contains 0.3 wt% or more and 0.5 wt% or less carbon, 0.05 wt% or more and 0.3 wt% or less silicon, 0.05 wt% or more and 0.5 wt% or less manganese, more than 0 and 0.03 wt% or less phosphorus, more than 0 and 0.03 wt% or less sulfur, 13.0 wt% or more and 16.0 wt% or less chromium, 1.5 wt% or more and 2.5 wt% or less molybdenum, 0.1 wt% or more and 0.5 wt% or less vanadium, 0.1 wt% or more and 0.2 wt% or less nitrogen and 0.0005 wt% or more and 0.005 wt% or less boron, the remainder being unavoidable impurities and iron.

Description

Technical field

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

[0002] In the pursuit of CO2 neutrality, the use of hydrogen energy is increasing, and there are more and more cases where rolling bearings are used in a hydrogen atmosphere. A rolling bearing made of steel can allow hydrogen to penetrate the steel when used in a hydrogen atmosphere, leading to hydrogen embrittlement. Therefore, there is a demand for rolling bearings with high resistance to hydrogen gas. Patent document 1 proposes a rolling bearing for use in a hydrogen atmosphere.

[0003] A rolling bearing used in hydrogen energy generation (fuel cell energy generation), a form of hydrogen energy utilization, can come into contact with water (steam) produced by the reaction between hydrogen and oxygen. Therefore, it is desirable that a rolling bearing used in hydrogen energy generation also be corrosion-resistant to steam, etc. Documents on the state of the art Patent specifications

[0004] Patent document 1: Japanese unpublished patent application no. 2010-249215 (JP 2010 - 249 215 A) Summary of the invention Problem to be solved by the invention

[0005] The rolling bearing described in patent document 1 sometimes failed to provide sufficient durability when used in a hydrogen atmosphere. In light of these circumstances, an objective of the present invention is to provide a rolling bearing that exhibits good corrosion resistance and excellent durability in a hydrogen atmosphere.

[0006] From the perspective of ensuring both the corrosion resistance of the rolling bearing and its durability in a hydrogen atmosphere, it might be possible to use a ceramic such as silicon nitride for the outer ring, the inner ring, and the rolling elements. However, a rolling bearing in which the entire outer ring, inner ring, and rolling elements are made of silicon nitride is difficult to manufacture and involves high production costs. Means to solve the problem

[0007] A 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 are configured to roll on an inner ring raceway and an outer ring raceway; the material of the rolling elements is silicon nitride; the material of the inner ring is a first steel material; the material of the outer ring is the first steel material;and the first steel material 0.3 wt% or more and 0.5 wt% or less carbon, 0.05 wt% or more and 0.3 wt% or less silicon, 0.05 wt% or more and 0.5 wt% or less manganese, more than 0 and 0.03 wt% or less phosphorus, more than 0 and 0.03 wt% or less sulfur, 13.0 wt% or more and 16.0 wt% or less chromium, 1.5 wt% or more and 2.5 wt% or less molybdenum, 0.1 wt% or more and 0.5 wt% or less vanadium, 0.1 wt% or more and 0.2 wt% or less nitrogen and 0.0005 wt% or more and 0.005 wt% or less boron, the remainder being unavoidable impurities and iron.

[0008] The use according to the present disclosure is the use of the rolling bearing in an environment in which the hydrogen partial pressure is 0.05 MPa or more and 5 MPa or less. Effects of the invention

[0009] The rolling bearing of the present disclosure exhibits good corrosion resistance and excellent durability in a hydrogen atmosphere. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a sectional view showing a deep groove ball bearing according to an embodiment of the present disclosure. Fig. Figure 2 is a sectional view showing a deep groove ball bearing according to a further embodiment of the present disclosure. Fig. Figure 3 is a diagram showing a device for assessing durability against a hydrogen atmosphere. MODES FOR IMPLEMENTING THE INVENTION<Overview of embodiments of the invention of the present disclosure>

[0010] The following is an overview of embodiments of the invention of the present disclosure.

[0011] (1) A 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 are configured to roll on an inner ring raceway of the inner ring and an outer ring raceway of the outer ring; the material of the rolling elements is silicon nitride; the material of the inner ring is a first steel material; the material of the outer ring is the first steel material;and the first steel material 0.3 wt% or more and 0.5 wt% or less carbon, 0.05 wt% or more and 0.3 wt% or less silicon, 0.05 wt% or more and 0.5 wt% or less manganese, more than 0 and 0.03 wt% or less phosphorus, more than 0 and 0.03 wt% or less sulfur, 13.0 wt% or more and 16.0 wt% or less chromium, 1.5 wt% or more and 2.5 wt% or less molybdenum, 0.1 wt% or more and 0.5 wt% or less vanadium, 0.1 wt% or more and 0.2 wt% or less nitrogen and 0.0005 wt% or more and 0.005 wt% or less boron, the remainder being unavoidable impurities and iron.

[0012] In this rolling bearing, the outer and inner rings are made of steel with a specific composition. The rolling elements are made of silicon nitride. Therefore, the rolling bearing exhibits excellent durability even when used in a hydrogen atmosphere. In other words, the rolling bearing has excellent resistance to hydrogen gas. The reasons why conventional rolling bearings are inferior in terms of durability against hydrogen gas are considered to be as follows. It is assumed that conventional rolling bearings are susceptible to hydrogen embrittlement because hydrogen can easily penetrate the bearing from the contact areas between the outer ring and the rolling elements, as well as from the contact areas between the inner ring and the rolling elements.In conventional rolling bearings, the outer ring, the inner ring and the rolling elements that make up the rolling bearing have a high hydrogen content at the beginning of use, which is considered a further reason for the likelihood of hydrogen embrittlement.

[0013] Since the rolling elements comprising the rolling bearing of the present disclosure are made of silicon nitride, hydrogen embrittlement, which occurs in steel materials, does not occur at all. Furthermore, since the outer and inner rings comprising the rolling bearing of the present disclosure are made of the first steel material, the outer and inner rings have a low hydrogen content at the beginning of use, and it is less likely that hydrogen will penetrate the outer and inner rings even after use has begun. Therefore, the rolling bearing of the present disclosure exhibits excellent resistance to hydrogen gas. In addition, the rolling bearing of the present disclosure exhibits excellent corrosion resistance. Corrosion resistance refers to the property of being less susceptible to rust.

[0014] (2) Preferably the rolling bearing according to (1) further comprises a cage, wherein the material of the cage is a resin composition and the resin composition contains polyamide 66 and 15 wt% or more and 35 wt% or less glass fibers.

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

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

[0017] (5) Preferably, the rolling bearing according to (1) to (4) preferably comprises two seals, each attached to the axial ends of the outer ring and each comprising an elastic element in sliding contact with the inner ring, wherein the seal comprises a metal ring and an elastic element attached to the metal ring, wherein the elastic element is made of a first rubber composition containing fluororubber, and wherein a section of the seal attached to the outer ring and a section of the seal in sliding contact with the inner ring are formed from the elastic element.

[0018] (6) Preferably, the rolling bearing according to (1) to (4) further comprises two seals, each attached to the axial ends of the outer ring and each in sliding contact with the inner ring, wherein the seal comprises a metal ring and an elastic element attached to the metal ring, wherein the elastic element is made of a second rubber composition containing hydrogenated NBR (hydrogenated acrylonitrile butadiene rubber), and wherein a section of the seal which is attached to the outer ring and a section of the seal which is in sliding contact with the inner ring are formed by the elastic element.

[0019] (7) Preferably, lubricant is enclosed in the rolling bearing according to (5), and the volume of the lubricant is 15% by volume or more and 45% by volume or less, based on the volume obtained by subtracting the total volume of the plurality of rolling elements and the cage from the volume of a space enclosed by the inner ring, the outer ring and the two seals.

[0020] (8) Preferably the rolling bearing according to (6) is surrounded with lubricant, and the volume of the lubricant is 15% by volume or more and 45% by volume or less, based on the volume obtained by subtracting the total volume of the plurality of rolling elements and the cage from the volume of a space surrounded by the inner ring, the outer ring and the two seals.

[0021] (9) Use of the rolling bearing in accordance with any of points (1) to (8) in an environment where the hydrogen partial pressure is 0.05 MPa or more and 5 MPa or less.

[0022] As already mentioned, the aforementioned rolling bearing exhibits excellent resistance to hydrogen gas. Therefore, the rolling bearing can be suitable for use in an environment where the hydrogen partial pressure lies within the aforementioned range. In this disclosure, the term "hydrogen partial pressure" is used in the sense of an absolute pressure. <details zu ausführungsformen der erfindung vorliegenden offenbarung>

[0023] The embodiments of the present disclosure are described below. In the present disclosure, the embodiments of the invention are to be considered in every respect illustrative and not limiting. The scope of the invention is defined by the claims, and it is intended that all modifications which correspond in meaning and scope to the claims are included in the scope of the invention. [Overall configuration of the rolling bearing]

[0024] The overall configuration of the rolling bearing of the present disclosure is described with reference to the Fig. 1 and Fig. 2 described. Fig. Figure 1 is a sectional view showing a deep groove ball bearing according to an embodiment of the present disclosure. Fig. Figure 2 is a sectional view showing a deep groove ball bearing according to another embodiment of the present disclosure. The deep groove ball bearing according to the one in Fig. The embodiment shown in Figure 2 is identical to the deep groove ball bearing according to the one shown in Figure 2, except for the cage. Fig. 1 embodiment shown.

[0025] A deep groove ball bearing 1 comprises an inner ring 2, an outer ring 3 arranged radially outside the inner ring 2, a plurality of balls 4 serving as rolling elements and arranged between the inner ring 2 and the outer ring 3, and an annular cage 5 that holds the plurality of balls 4. Seals 6 are provided on each of the first and second sides of the deep groove ball bearing 1 in the axial direction. Lubricant G is enclosed in the annular region between the inner ring 2 and the outer ring 3 of the deep groove ball bearing 1.

[0026] The inner ring 2 comprises an inner ring raceway 21 on its outer circumference, on which the balls 4 roll. The inner ring raceway 21 is a raceway groove. The outer ring 3 comprises an outer ring raceway 31 on its inner circumference, on which the balls 4 roll. The outer ring raceway 31 is a raceway groove. The plurality of balls 4 are arranged between the inner ring raceway 21 and the outer ring raceway 31 and roll on the inner ring raceway 21 and the outer ring raceway 31.

[0027] The lubricant G enclosed in the annular area between the inner ring 2 and the outer ring 3 is also present at contact sections between the balls 4 and the inner ring raceway 21 of the inner ring 2 and at contact sections between the balls 4 and the outer ring raceway 31 of the outer ring 3. The volume of the enclosed lubricant G is 15% by volume or more to 45% by volume or less, based on the volume obtained by subtracting the total volume of the plurality of balls 4 and the cage 5 from the volume of the space enclosed 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. Fig. Cage 5 shown is a snap-fit ​​cage made of plastic. Alternatively, cage 5 can be made of corrosion-resistant steel. The one shown in Fig. Cage 5 shown in 2 is a band cage made of stainless steel.

[0028] Each seal 6 is an annular element comprising an annular metal ring 6a and an elastic element 6b attached to the metal ring 6a. Each seal 6 has a radially outer section attached to the outer ring 3, and a lip tip of a radially inner section formed by the elastic element 6b is positioned such that the lip tip can be in sliding contact with the inner ring 2. The seals 6 prevent the enclosed lubricant G from escaping to the outside. The seals 6 are attached to corresponding sealing grooves provided on both sides in the axial direction of the outer ring raceway 31 of the outer ring 3. The lip tips of the seals 6 are in contact with corresponding sealing contact surfaces provided on both sides in the axial direction of the inner ring raceway 21 of the inner ring 2. The sealing contact surfaces are planes perpendicular to the central axis of the inner ring 2.The outer circumference of each metal ring 6a is located radially outside the corresponding shoulder adjacent to the outer ring raceway 31. The inner circumference of each metal ring 6a is located radially inside the inner circumference of the cage 5. Since the metal ring 6a is less deformable than the elastic element 6b, the lip tip of the seal 6, which is located between the metal ring 6a and the seal contact surface, is pressed against and deformed by the seal contact surface and comes into annular contact with the seal contact surface over a circumferential region with a width in the radial direction.Since the deformation of the lip tip can increase the contact area between the elastic element 6b of the seal 6 and the seal contact surface, it is less likely that hydrogen present in the outer space of the bearing will penetrate in large quantities through the contact section between the elastic element 6b of the seal 6 and the seal contact surface into the interior of the bearing, namely the space surrounded by the inner ring 2, the outer ring 3 and the two seals 6. [Components of the rolling bearing]

[0029] In the deep groove ball bearing 1, the material of the inner ring 2 consists of the first steel material and the material of the outer ring 2 consists of the first steel material. The first steel material contains 0.3 wt% or more and 0.5 wt% or less of carbon, 0.05 wt% or more and 0.3 wt% or less of silicon, 0.05 wt% or more and 0.5 wt% or less of manganese, more than 0 and 0.03 wt% or less of phosphorus, more than 0 and 0.03 wt% or less of sulfur, 13.0 wt% or more and 16.0 wt% or less of chromium, 1.5 wt% or more and 2.5 wt% or less of molybdenum, 0.1 wt% or more and 0.5 wt% or less of vanadium, 0.1 wt% or more and 0.2 wt% or less of nitrogen, and 0.0005 wt% or more and 0.005 wt% or less of boron, the remainder being unavoidable impurities and iron. The first steel material is a martensitic stainless steel.

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

[0031] Since the first steel material contains 0.1% or more by mass and 0.2% or less by mass of nitrogen, hydrogen is less likely to penetrate it during heat treatment. Consequently, the inner and outer rings made from this first steel material have a low hydrogen content at the start of their service life. Furthermore, since the first steel material also contains 0.1% or more by mass and 0.2% by mass of nitrogen, and 0.3% or more by mass and 0.5% or less by mass of carbon, hydrogen is also less likely to penetrate the inner and outer rings produced from this material during service life. Therefore, inner ring 2 and outer ring 3 exhibit excellent resistance to hydrogen gas.

[0032] The inner ring 2 and the outer ring 3 are components obtained by heat treatment of the first steel material. This heat treatment includes quenching, cold treatment, and tempering. Quenching, for example, is carried out under conditions where heating occurs at 1020 °C to 1080 °C for 20 to 90 minutes, followed by gas quenching with an inert gas such as nitrogen or argon.

[0033] Cold treatment / subcooling / sub-zero treatment is carried out, for example, under conditions where cooling is performed at -90°C to -50°C for 30 to 90 minutes. Tempering / heating treatment is carried out, for example, under conditions where heating is performed at 160°C to 230°C for 60 to 150 minutes.

[0034] The first steel material used for the inner ring 2 and the first steel material used for the outer ring 3 can have the same or different compositions, as long as they meet the composition requirements of the first steel material described above. The inner ring 2 and the outer ring 3 are each manufactured by a known process, for example, by forging bar steel, machining the forged material into a workpiece, subjecting the workpiece to the heat treatment described above, grinding, and superfinishing the raceway.

[0035] In the deep groove ball bearing 1, the balls 4 are made of silicon nitride. When silicon nitride balls 4 are used, they are not subject to hydrogen embrittlement, unlike when steel balls are used. The silicon nitride balls 4 are manufactured using a known process.

[0036] In the deep groove ball bearing 1, the cage material 5 consists, for example, of a resin composition. The resin composition contains polyamide 66 and glass fibers. A preferred glass fiber content is 15% by mass or more and 35% by mass or less, based on the total resin composition. A cage made of this resin composition is less prone to absorbing moisture and swelling, even when in contact with water (steam). In addition to polyamide 66 and the glass fibers, the resin composition may contain further additives as required. If the cage material 5 is the resin composition, the cage 5 is preferably a snap-in cage, as shown in [reference to relevant figure]. Fig. 1 shown.

[0037] In deep groove ball bearing 1, the material of cage 5 can, for example, be the second steel material. The second steel material is stainless steel. A stainless steel cage has higher corrosion resistance than a conventional iron cage. The stainless steel is preferably SUS304. SUS304 steel is readily available, and a cage made of SUS304 has good corrosion resistance. If the material of cage 5 is stainless steel, cage 5 is preferably a strip cage, as shown in Fig. 2 shown.

[0038] In the deep groove ball bearing 1, each seal 6 is an annular element comprising the annular metal ring 6a and the annular elastic element 6b, which is attached to the metal ring 6a. An example of the material for the metal ring 6a is SPCC. The surface of the metal ring 6a is covered with an adhesive layer (also called a primer layer) to ensure adhesion to the elastic element.

[0039] The elastic element 6b consists of a rubber compound. This rubber compound contains, for example, fluororubber (FKM) or hydrogenated NBR as a rubber component. Fluororubber (FKM) and hydrogenated NBR each refer to a cross-linked rubber. Since fluororubber (FKM) and hydrogenated NBR exhibit excellent hydrogen and heat resistance, a rubber compound containing one of these substances as a rubber component is suitable as a material for the elastic element 6a of the seal 6. Hydrogenated NBR has no double bonds or an extremely low number of double bonds in its main chain. A rubber compound using hydrogenated NBR is therefore less likely to react with hydrogen in the environment, thus preventing a change in the physical properties of the elastic element 6a of the seal 6.Fluororubber (FKM) also has no double bonds or only an extremely small number of double bonds in its main chain and is less likely to react with hydrogen in the environment, thus suppressing any change in the physical properties of the elastic element 6a of the seal 6. Due to its superior hydrogen resistance and heat resistance, the rubber component is preferably fluororubber. The elastic element 6b is bonded to the metal ring 6a by vulcanization. The elastic element 6b is cross-linked and bonded to the metal ring 6a.

[0040] In the deep groove ball bearing 1, the lubricant G is a lubricant composition containing a base oil and a thickener as essential components and an additive as an optional component.

[0041] The deep groove ball bearing according to the embodiment of the present disclosure exhibits excellent resistance to 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 the embodiment of the present disclosure is not limited to the deep groove ball bearing and can be another type of rolling bearing, such as an angular contact ball bearing or a tapered roller bearing. [Examples]

[0042] The invention of the present disclosure will now be described in more detail with reference to an example. However, the invention of the present disclosure is not limited to this example. In this example, a deep groove ball bearing with contact seals (bearing number: 6000, bore diameter: 10 mm, outer diameter: 26 mm, plastic cage) was manufactured using the bearing components described below, and the durability and corrosion resistance of the resulting deep groove ball bearing were evaluated. (Inner ring, outer ring and balls)

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

[0044] Table 1 also shows the pitting resistance or pitting resistance number (PRE) of steel materials 1 to 3, calculated according to the following formula (1). PRE=Cr+3.3(Mo+0.5W)+16N−Mn(mass%)

[0045] The pitting corrosion resistance values ​​given in Table 1 show that steel material 1 has superior corrosion resistance compared to SUS440C and SUJ2. [Table 1]

[0046] During the manufacture of the inner ring, the outer ring and the balls, the steel materials 1 to 3 were subjected to heat treatment under the conditions specified in Table 2. [Table 2] Deter Hypothermia Tempering Steel material 1 Heat vacuum oven to 1050°C for 30 minutes → Gas quench -60°C × 30 min 180°C × 120 min Steel material 2 Heat vacuum oven to 1050°C for 30 minutes → Gas quench -60°C × 30 min 180°C × 120 min Steel material 3 Heating in an atmosphere furnace at 830°C for 30 minutes → oil quenching - 180°C × 120 min (Cage)

[0047] The cage was manufactured using a known process with a resin composition (Ultramid A3HG5, manufactured by BASF) containing polyamide 66 and 25 wt% glass fibers. (Seal)

[0048] The seal was manufactured using a process in which a metal ring made of SPCC with an adhesive layer applied over its entire surface and an unvulcanized rubber composition to form an elastic element made of fluoroelastomer (FKM) were prepared and both were integrally formed in one mold. (Lubricant)

[0049] The lubricant was KVC lubricant, a standard bearing lubricant manufactured by JTEKT CORPORATION. The thickener in the KVC lubricant is diurea, and the base oil is a polyalphaolefin / ester blend with a base oil kinematic viscosity of 40 mm at 40 °C. 2 / s or more and 55 mm 2 / s or less. (Example 1 and comparative examples 1 to 4)

[0050] A deep groove ball bearing with contact seals, containing enclosed lubricant, was manufactured using the combinations of inner rings, outer rings, and balls shown in Table 3. All balls in the array were made from the materials shown in Table 3. The volume of enclosed lubricant was set at 30% by volume relative to the volume obtained by subtracting the total volume of the array of balls and the cage from the volume of the space enclosed by the inner ring, the outer ring, and the two seals. The durability of the resulting deep groove ball bearing and the corrosion resistance of the inner ring were evaluated using the following methods. The results are presented in Table 3. [Table 3] Example 1 Comparative example 1 Comparative example 2 Comparative example 3 Comparative example 4 Bearing components Inner and outer rings (bearing rings) Steel material 1 Steel material 1 Steel material 2 Steel material 3 Steel material 3 Balls (rolling elements) Silicon nitride Steel material 2 Silicon nitride Silicon nitride Steel material 3 Shelf life (hydrogen gas) Failover mode No outage Rolling element peels off Career path leaves off Career path leaves off Career path leaves off Living conditions (in relation to comparison example 4) 19 or more 1 5 1 1 Corrosion resistance (salt spray test) 0 hours (area%) 0 ND 0 ND ND 24 hours (area%) 0 ND 30-60 ND ND 48 hours (area%) 0-30 ND 60-100 ND ND (Assessment of durability against hydrogen gas)

[0051] The resistance to hydrogen gas of the deep groove ball bearing 6000 (test bearing) produced in Example 1 and Comparative Examples 1 to 4 was evaluated using a rolling bearing test apparatus 101 described in WO 2020 / 250 857 A1. In this evaluation, the time to bearing failure was measured.

[0052] Fig. Figure 3 is a diagram illustrating the overall configuration of the bearing test device 101. Fig. Figure 3 is shown partially cut away for better understanding. As in Fig. As shown in Figure 3, the rolling bearing test device 101 comprises: a sealed container 102; a bearing holding device 104, which is housed inside the sealed container 102 and holds the rolling bearing serving as the test bearing; and a drive device 106.

[0053] The sealed container 102 comprises a stainless steel wall 103 and a window 131 with a glass plate inserted therein, and includes a cylindrical main body 102a with a bottom, an open top, and a lid 102b that hermetically seals an opening 102a2 of the main body 102a and has gaskets. The main body 102a comprises the wall 103 and the window 131, and the lid 102b is formed entirely from the wall 103. The main body 102a has a flange 102a1 around the circumference of the opening 102a2. The lid 102b has a flange 102b1 corresponding to the flange 102a1. The flanges 102a1 and 102b1 are butted together with an interposed O-ring and connected to each other by bolts. The lid 102b is thus detachably attached to the main body 102a.When testing equipment, such as the storage holding device 104, is placed inside the sealed container 102, the equipment inside the sealed container 102 can be accessed by removing the cover 102b through the opening 102a2 of the main body 102a.

[0054] An inlet pipe 102c for introducing hydrogen gas, a hydrogen-containing mixed gas, or another gas (atmospheric gas) into the interior of the sealed container 102, and an outlet pipe 102d for removing gas from the interior of the sealed container 102, are provided on a lower side surface of the sealed container 102. Two holes are provided extending through the wall 103 of the sealed container 102, with the inlet pipe 102c being connected to a first hole and the outlet pipe 102d to a second hole. The atmosphere in the interior of the sealed container 102 is adjusted by introducing gas into the interior of the sealed container 102 through the inlet pipe 102c or by removing gas from the interior of the sealed container 102 through the outlet pipe 102d.

[0055] A heater 102e for increasing the temperature of the atmosphere inside the sealed container 102 from the outside is provided on a side surface of the sealed container 102. The heater 102e is ribbon-shaped and comprises an electric heating wire or the like. The heater 102e is wrapped around the side surface of the sealed container 102 and heats the atmosphere inside the sealed container 102 from the outside. The heater 102e can thus increase the temperature of the atmosphere inside the sealed container 102 and thereby increase and adjust the temperature of the rolling bearing 200 (201, 202, 203, 204). By using the heater 102e, the temperature of the atmosphere inside the sealed container 102 can, for example, be increased to approximately 150 °C.

[0056] A cooling device 102h is also provided on the side surface of the sealed container 102. The cooling device 102h is ribbon-shaped and has a flow channel for circulating a cooling medium. The cooling device 102h is wrapped around the side surface of the sealed container 102 and cools the atmosphere inside the sealed container 102 from the outside by the cooling medium flowing through the flow channel. The cooling device 102h can thus lower the temperature of the atmosphere inside the sealed container 102 and thereby lower and regulate the temperature of the rolling bearings 200 (201, 202, 203, 204). By using the cooling device 102h, the temperature of the atmosphere inside the sealed container 102 can, for example, be lowered to approximately -30 °C.Since the test device 101 is equipped with the heater 102e and the cooling device 102h, the test device 101 can adjust the temperature of the atmosphere over a wide range.

[0057] A radial fan 102g is provided at a base 102f of the sealed container 102. The radial fan 102g circulates the atmosphere inside the sealed container 102 to maintain a uniform temperature and atmosphere within the sealed container 102.

[0058] The bearing holding device 104 comprises: a test unit 110 in which the plurality of rolling bearings 200 (201, 202, 203, 204), serving as test objects, are held; a rotating shaft 111; a first loading mechanism 112, which exerts an axial load on the plurality of rolling bearings 200; and a second loading mechanism 113, which exerts a radial load on the plurality of rolling bearings 200. The bearing holding device 104 is attached to a base 114, which is fixedly provided in the interior of the sealed container 102.

[0059] The test unit 110 is divided into three parts and comprises a first-side housing 140, which is arranged on a first side in the axial direction, namely the distal end face, of the rotating shaft 111, a housing 141 arranged on a second side in the axial direction of the rotating shaft 111 and a middle housing 142 arranged between the housing 140 on the first side and the housing 141 on the second side.

[0060] Four inner rings of the rolling bearings 200 (201, 202, 203, 204) are mounted on the rotating shaft 111. The outer ring of the rolling bearing 201, which is located at the end on the first side in the axial direction of the rotating shaft 111, is held by the housing 140 on the first side. The outer ring of the rolling bearing 204, which is located at the end on the second side in the axial direction of the rotating shaft 111, is held by the housing 141 on the second side. The respective outer rings of the rolling bearings 202, 203, which are located between the rolling bearings 201, 204, are held by the central housing 142.

[0061] The base 114 is a plate-shaped element made of stamped metal. The base 114 is essentially horizontally oriented, extending across the interior of the sealed container 102. The stamped metal is a sheet material with a large number of through-holes, and even though the stamped metal is positioned across the interior of the sealed container 102, the atmosphere can move vertically (up and down) through the base 114. Because the atmosphere can move vertically through the base 114, the temperature and atmosphere inside the sealed container 102 are kept uniform even when the base 114 is present.

[0062] Inside the sealed container 102, a connecting shaft 124 for connection to a contactless coupling 116 and a coupling 126, which connects the connecting shaft 124 and the rotating shaft 111 so that these shafts can rotate integrally, is provided at one end of the rotating shaft 111, extending from the test unit 110. The base 114 is provided with a connecting shaft support section 128, which rotatably supports the connecting shaft 124 with respect to the sealed container 102.

[0063] The rotary shaft 111 (connecting shaft 124) is driven and rotated by the drive device 106, which is located outside the sealed container 102. The drive device 106 comprises: a motor 106a, which generates a driving force to drive the rotary shaft 111; a drive shaft 106b, which is located outside the sealed container 102 and is held by a drive shaft support section 120; a deflection pulley 106c, which is provided on an output shaft 106a1 of the motor 106a; a deflection pulley 106d, which is provided on the drive shaft 106b; and an endless belt 106e, which is wound around the deflection pulleys 106c and 106d and transmits the driving force from the output shaft 106a1 to the drive shaft 106b. The drive shaft 106b is connected to the rotary shaft 111 (connecting shaft 124) so ​​that it is integrally rotatable with the rotary shaft 111 (connecting shaft 124) and drives the rotary shaft 111 (connecting shaft 124).The drive device 106 and the rotary shaft 111 (connecting shaft 124) are connected by the contactless coupling 116.

[0064] A test procedure using the rolling bearing test device 101 is now described. First, deep groove ball bearings, serving as test bearings for the rolling bearings 200, are mounted between the rotating shaft 111 and the first housing 140, the second housing 141, and the middle housing 142 of the test unit 110 of the bearing holding device 104. The test unit 110 is located inside the main body 102a of the sealed container 102 and is connected to the connecting shaft 124 and the connecting shaft support section 128. The rolling bearings 200 are subjected to an axial load by the first load application mechanism 112 and to a radial load by the second load application mechanism 113. Only one of the axial loads and one of the radial loads can be applied at a time. The lid 102b is attached to the main body 102a, and the interior of the sealed container 102 is hermetically sealed from the outside.

[0065] Subsequently, hydrogen gas is introduced as an atmosphere (gas) into the interior of the sealed container 102, the temperature of the atmosphere in the interior of the sealed container 102 is set to a predetermined temperature, and the drive device 106 is actuated to rotate the rotary shaft 111. Accordingly, the inner rings of the rolling bearings 200 rotate relative to their outer rings.

[0066] While the rotating shaft 111 is turned, an axial load is applied between the inner and outer rings of each rolling bearing 200 by the first load application mechanism 112, and simultaneously a radial load is applied between the inner and outer rings of each rolling bearing 200 by the second load application mechanism 113. In this way, both the axial load and the radial load are applied simultaneously to the rolling bearings 200 in a hydrogen gas atmosphere.

[0067] The specific test conditions are listed in Table 4. In this test, the number of test bearings is two for each of the deep groove ball bearings from Example 1 and comparison examples 1 to 4. The shorter time to failure between the two test bearings was used as the evaluation result. Table 3 shows the results (life ratio) as relative values ​​obtained when the failure time of the deep groove ball bearing from comparison example 4 is taken as 1. [Table 4] Theme Condition Test device Bearing test device Number of storage 6000 (equipped with seals on both sides, as in Fig. 1 shown) radial load 0.9 kN Axial load 0.0 kN speed 10000 / min lubrication lubricant Hydrogen concentration in the vicinity of the interior 100% by volume Hydrogen concentration in the vicinity of the interior (absolute pressure) 0.4 MPa Indoor ambient temperature 120°C Number of samples 2 for each example and comparison example (Assessment of corrosion resistance)

[0068] This evaluation was performed on the inner rings of the 6000 deep groove ball bearings from Example 1 and Comparative Example 2. The evaluation was carried out in accordance with JIS Z 2371 (2015): Methods for Salt Spray Tests. The specific test conditions are listed in Table 5. In this evaluation, the inner rings (test specimens) of the deep groove ball bearings were continuously sprayed with salt water for 48 hours. The amount of salt water spray in this evaluation was such that the average collection rate of the sprayed solution on a horizontal collection area of ​​approximately 80 cm² was sufficient. 2 The flow rate was 1.0 to 2.0 ml / h.

[0069] The apparatus used for the salt spray test corresponds to the apparatus described in Annex A “(Reference) Example of an apparatus with facilities for dispensing and draining the spray solution” in JIS Z 2371 (2015). The test specimens were placed on two parallel, horizontally arranged, cylindrical, rod-shaped glass specimen holders, as shown in “Fig. JA.1 - Arrangement and positions of the test specimens, b) Diagram of the angle of the test specimens and arrangement of the collection containers for the spray liquid” in Annex JA “(Reference) Arrangement and positions of the test specimens” in JIS Z 2371 (2015). Each test specimen was supported at two points on the outer circumferential surface on the underside in a vertical direction by two adjacent glass specimen holders.

[0070] After 0 hours (before the start of the salt spray test), 24 hours, and 48 hours after the start of the salt spray test, the outer circumferential area of ​​the inner ring of each test sample, i.e., each deep groove ball bearing, was observed, and the ratio (area fraction in %) of the area on which red rust appeared to the total outer circumferential area of ​​the inner ring was calculated. The evaluation results were presented as a range from the minimum to the maximum value among the three test samples. [Table 5] Theme Condition Test procedure Neutral salt spray test saline solution concentration 5% by mass temperature 35°C moisture 98% RH Observation site Outer circumferential surface of the inner ring Object of observation Rust condition at each inspection time Review time 0 hours, 24 hours, 48 ​​hours Number of test samples 3 for each example and comparison example

[0071] As the results in Table 3 show, it was found that the rolling bearing according to the embodiment of the present disclosure has excellent durability against hydrogen gas and excellent corrosion resistance. Reference symbol list 1 deep groove ball bearing 2 inner ring 3 Outer ring 5 cage 6 Seal 6a Metal ring 6b Elastic element 21 Inner ring track 31 Outer Ring Track 101 Rolling bearing test device G Lubricants QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 2010 - 249 215 A

[0004] WO 2020 / 250 857 A1

[0051] < / details>

Claims

[1] Rolling bearing which features: a large number of rolling elements; an inner ring; and an outer ring, wherein: the rolling elements are configured so that they roll on an inner ring raceway of the inner ring and on an outer ring raceway of the outer ring; a material of the rolling elements is silicon nitride; one of the materials of the inner ring is a first steel material; The outer ring material is the first steel material; and The first steel material contains the following: 0.3% by mass or more and 0.5% by mass or less carbon, 0.05% by mass or more and 0.3% by mass or less silicon, 0.05% by mass or more and 0.5% by mass or less manganese, more than 0 and 0.03% by mass or less phosphorus, more than 0 and 0.03% by mass or less sulfur, 13.0% by mass or more and 16.0% by mass or less chromium, 1.5% by mass or more and 2.5% by mass or less molybdenum, 0.1 wt% or more and 0.5 wt% or less vanadium, 0.1% by mass or more and 0.2% by mass or less nitrogen and 0.0005% by mass or more and 0.005% by mass or less boron, the remainder being unavoidable impurities and iron. [2] Rolling bearing according to claim 1, further comprising a cage, wherein: one of the cage materials is a resin composition; and The resin composition contains polyamide 66 and 15% by mass or more and 35% by mass or less glass fibers. [3] Rolling bearing according to claim 1, further comprising a cage, wherein: one material of the cage is a second steel material; and The second steel material is stainless steel. [4] Rolling bearing according to claim 3, wherein the second steel material is SUS304. [5] Rolling bearing according to claim 1, further comprising two seals, each of which is attached to the axial ends of the outer ring and each of which comprises an elastic element in sliding contact with the inner ring, wherein: the seal comprises a metal ring and the elastic element attached to the metal ring; the elastic element is made from a first rubber composition containing fluoroelastomer; and a section of the seal that is attached to the outer ring and a section of the seal that is in sliding contact with the inner ring are formed by the elastic element. [6] Rolling bearing according to claim 1, further comprising two seals, each of which is attached to the axial ends of the outer ring and each of which is in sliding contact with the inner ring, wherein: the seal comprises a metal ring and an elastic element attached to the metal ring; the elastic element is made from a second rubber composition containing hydrogenated NBR; and a section of the seal that is attached to the outer ring and a section of the seal that is in sliding contact with the inner ring are formed by the elastic element. [7] Rolling bearings according to claim 6, wherein: a lubricant is included; and a volume of lubricant is 15 volume% or more and 45 volume% or less, based on a volume obtained by subtracting a total volume of the plurality of rolling elements and the cage from a volume of a space surrounded by the inner ring, the outer ring and the two seals. [8] Rolling bearings according to claim 7, wherein: a lubricant is included; and a volume of lubricant is 15 volume% or more and 45 volume% or less, based on a volume obtained by subtracting a total volume of the plurality of rolling elements and the cage from a volume of a space surrounded by the inner ring, the outer ring and the two seals. [9] Use of the rolling bearing according to any one of claims 1 to 8 in an environment where the hydrogen partial pressure is 0.05 MPa or more and 5 MPa or less.

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