WO2016140224A1 - Rolling bearing for use in extremely low-temperature environment - Google Patents

Abstract

A rolling bearing (A), wherein: a cage (4) for rotatably holding a ceramic rolling body (3) is provided between an inner race (1) and an outer race (2) which constitute part of the rolling bearing (A) and comprise a martensitic stainless steel or high-speed tool steel; the cage (4) comprises a resin material having polytetrafluoroethylene as the principal component thereof; the substrate surface of the inner race (1) and the outer race (2) is provided with a hard anodic oxidation coating (5) having a diamond-like carbon with a Vickers hardness (Hv) of 1,000-4,000 as a principal component thereof; long-term use in an extremely low-temperature environment is possible; and there is no decrease in lubricity and wear resistance over time.

Description

Rolling bearing for cryogenic environment

The present invention relates to a rolling bearing for a cryogenic environment used at a cryogenic temperature, such as a bearing used in a submerged pump for transferring a liquefied gas in a cryogenic state such as liquefied natural gas.

In general, a rolling bearing used in a normal temperature environment requires a rolling element to be rotatably held between an inner ring and an outer ring and requires liquid lubrication with a lubricating oil or the like. In a rolling bearing used in an environment where such a cryogenic liquefied gas or the like exists, or in an environment where these gases are handled, liquid lubrication with a normal lubricating oil or the like cannot be expected. In addition, rolling bearings for cryogenic environments are liable to deteriorate in strength and durability due to shrinkage and deformation of parts, and are required to withstand such severe use conditions.

Incidentally, liquefied natural gas (LNG), which is a typical example of a cryogenic liquefied gas, has methane as a main component and has a physical property that does not liquefy unless it is below −161.5 ° C. (about −162 ° C.) under normal pressure. In addition to LNG, examples of liquefied gas used in a liquefied state such as a refrigerant, a heat medium, and a filling gas include nitrogen and helium.

When transporting or storing such a liquefied gas while maintaining a liquid state at a cryogenic temperature, it is necessary to use a dedicated pump at a cryogenic temperature. As a type of such a pump, a submerged pump is used. Are known.
Since this type of pump is used by immersing the entire pump device including the motor in liquefied gas, it does not require a mechanical seal to seal the main body from the outside air, and is excellent in that there is little loss due to dissipation of the vaporized gas. It is a thing.

However, since such a submerged pump is used in a state where the motor etc. is also in direct contact with the liquefied gas, the rolling bearing supporting the motor shaft etc. is also lubricated with LNG having poor lubricity at extremely low temperatures, It is required that the rotation state is stable and good over a long period of time.

As another example of the cryogenic environment, the environmental temperature is not only in the above-mentioned environment where liquid gas exists, but also in a high altitude space beyond the stratosphere far from the surface of the earth, and in a far away space. Since the temperature is about 50 to −270 ° C., similar characteristics are required for rolling bearings for cryogenic environments used in such artificial satellites and spacecraft.

As a known technique of a rolling bearing used in such a cryogenic environment, an outer ring and an inner ring are made of martensitic stainless steel, a rolling element is made of ceramic, and a cage is made of a fluororesin. (Patent Document 1 below).

In addition, a film treatment of diamond-like carbon (hereinafter abbreviated as DLC) that forms a hard film with excellent wear resistance used for a sliding surface of a bearing is well known, and is intended to enhance adhesion to a substrate. It is known that it is preferably formed via an intermediate layer (Patent Document 2 below).

Furthermore, a rolling bearing is known in which the inner and outer rings, the rolling elements and the cage are formed of an iron-based base material or cemented carbide material, and the DLC film is formed on the raceway surface of the inner ring or the outer ring to improve wear resistance. (Patent Document 3 below, FIG. 1).

JP 2014-20490 A JP 2011-68940 A International Publication No. 2013/042765

However, in the conventional rolling bearing for cryogenic environment as described in Patent Document 1 described above, since the ceramic rolling elements cause the inner ring and the outer ring to wear, dimensional changes are likely to occur in these parts, and There is a problem that it is not easy to obtain a stable rotational state.

Further, as described in Patent Documents 2 and 3, when a hard film such as diamond-like carbon (DLC) is formed on the surface of each base material of an inner ring, outer ring or rolling element made of an iron-based material, these are There is a high possibility that the contacted material will be worn, and wear is more likely to occur particularly at low temperatures, and even more likely to occur under conditions of use when lubricated by LNG having poor lubricity.

Therefore, the problem of the present invention is to solve the above-mentioned problems, and in a rolling bearing for a cryogenic environment used in a cryogenic environment such as the presence of a liquefied gas or a space environment, the raceway surface and the rolling element are extremely worn. Extremely low durability, especially in extremely low temperature environments that are lubricated and cooled by liquefied gas such as LNG, and the inner and outer rings and rolling elements can withstand long-term use and wear resistance and lubricity do not deteriorate It is to make a rolling bearing for a low temperature environment.

In order to solve the above problems, in the present invention, in a rolling bearing provided with a cage that rotatably holds a plurality of rolling elements between an inner ring and an outer ring made of martensitic stainless steel or high-speed tool steel, The rolling element is a ceramic rolling element, and the cage is made of a resin material mainly composed of polytetrafluoroethylene, and diamond having a Vickers hardness (Hv) of 1000 to 4000 is formed on the surface of the base material of the inner ring and the outer ring. This is a rolling bearing for a cryogenic environment provided with a hard coating mainly composed of like carbon.

The rolling bearing for the cryogenic environment of the present invention configured as described above is a material in which an inner ring and an outer ring made of martensitic stainless steel or high-speed tool steel are unlikely to undergo aging change at extremely low temperatures, In addition, a hard coating mainly composed of diamond-like carbon with a Vickers hardness (Hv) of 1000 to 4000 is provided on the surface of the base material of the inner ring and outer ring. It becomes difficult.

In addition, the rolling elements that are in frictional contact during rotation of the inner ring and the outer ring having a predetermined hard film are made of ceramics to which polytetrafluoroethylene is easily transferred, and are transferred from the cage at an appropriate frequency along with the rotation. Since tetrafluoroethylene stably exhibits excellent solid lubricity even at extremely low temperatures, when the hard coating on the inner and outer ring surfaces comes into contact with the rolling elements, the rolling elements are worn by solid lubrication. It functions stably in a state where is suppressed.

For this reason, even when the rolling bearing is used for a long period of time, the wear of the raceway surface and the rolling element is extremely reduced, and the inner and outer rings and the rolling element in an extremely low temperature environment that is lubricated and cooled by LNG can withstand long-term use. In addition, the rolling bearing is excellent in durability without deteriorating wear resistance and lubricity.

The hard coating is a hard coating provided on an intermediate layer whose hardness has been increased stepwise or continuously toward the surface, thereby improving the adhesion of the hard coating, that is, increasing the peel resistance of the layer. Therefore, it is preferable.

The reason why the hardness of the hard coating is in the range of Vickers hardness (Hv) 1000 to 4000 is that if the hardness is lower than this numerical range, the amount of carbon transferred from the hard coating of the inner ring and outer ring to the rolling element becomes too much. This is because it is not preferable because the durability is lowered, and a high hardness exceeding the above numerical range is not preferable because the hard film has low adhesion and is easily peeled off.

The ceramic rolling element is preferably a silicon nitride ceramic rolling element because of its high hardness and excellent wear resistance.
The rolling bearing for the cryogenic environment can be applied to a rolling bearing of a liquefied gas pump. The liquefied natural gas submerged pump, which is a liquefied gas pump, is an application example that can increase the practical utility value of the rolling bearing of the present invention.

The present invention comprises a ceramic rolling element and a resin cage mainly composed of polytetrafluoroethylene, and a hard film mainly composed of diamond-like carbon having a predetermined hardness is formed on the inner ring and outer ring base material surfaces. Since the rolling bearing for the cryogenic environment is provided, the wear of the raceway surface and rolling elements is extremely small, and especially in a cryogenic environment such as LNG or a space environment that is lubricated and cooled by a liquefied gas such as LNG. There is an advantage that it becomes a rolling bearing for a cryogenic environment that can withstand long-term use even in an environment and does not deteriorate wear resistance and lubricity over time.

Sectional drawing of the principal part of the rolling bearing for cryogenic environments which shows 1st Embodiment The expanded sectional view which shows the principal part of 1st Embodiment and demonstrates the layer structure of a hard film Sectional drawing explaining the use condition of 1st Embodiment and showing schematic structure of the submerged pump for liquefied natural gas Sectional drawing of the principal part of the rolling bearing which shows 2nd Embodiment A perspective view of a spring washer used in the second embodiment Part disassembled perspective view for explaining the assembled state of the spring washer and the fastening pin by cutting out a part of the cage used in the second embodiment. Sectional drawing of the principal part of a rolling bearing which shows 3rd Embodiment The perspective view of the wave washer used for 3rd Embodiment

Embodiments of the present invention will be described below with reference to the accompanying drawings.
As shown in FIGS. 1 and 2, in the first embodiment, a cage 4 that rotatably holds a ceramic rolling element (ball) 3 between an inner ring 1 and an outer ring 2 made of a predetermined base material of a rolling bearing A. The retainer 4 is made of a resin material mainly composed of polytetrafluoroethylene, and has a hard film mainly composed of diamond-like carbon having a Vickers hardness (Hv) of 1000 to 4000 on the base material surfaces of the inner ring 1 and the outer ring 2. 5 is a rolling bearing for a cryogenic environment provided through an intermediate layer 7 whose hardness is increased stepwise or continuously toward the surface of a base material 6 (see FIG. 2).

The base material 6 of the inner ring 1 and the outer ring 2 described above is martensitic stainless steel or high-speed tool steel, and these are steel materials that are hard and have excellent wear resistance. Examples of martensitic stainless steel include SUS403, SUS420, and SUS440C. Examples of the high-speed tool steel include 50 high-speed steels according to the American Steel Association AISI standard and SKH4 of Japanese Industrial Standards.

The hard coating 5 mainly composed of diamond-like carbon (DLC) having a Vickers hardness (Hv) of 1000 to 4000 provided on the surface side of the substrate 6, at least on the raceway surface (or also referred to as a rolling surface), In order to improve the adhesiveness with the base material 6, it is preferably provided via the intermediate layer 7.

DLC has an intermediate structure in which diamond and graphite are mixed, and can be formed to have a hardness equivalent to that of diamond.
As a method for forming the DLC film, a known film forming method such as a physical vapor deposition method such as sputtering or ion plating, a chemical vapor deposition method, or an unbalanced magnetron sputtering (UBMS) method can be employed.

The intermediate layer 7 has increased hardness stepwise or continuously toward the surface, and can be formed by, for example, an “intermediate layer forming method” described later.
As an auxiliary method that can be added to improve the adhesion, the surface of the base material may be roughened to exert the anchor effect. The roughening can be performed by a known Ar ion bombardment treatment or the like so that the surface roughness Ra is 0.5 μm or less, preferably Ra is 0.05 μm or less.

[Formation of intermediate layer]
Referring to FIG. 2, the intermediate layer 7 first forms a first intermediate layer 7 a mainly composed of a metal-based material on the substrate 6 in order to increase adhesion with the substrate 6. It is preferable that the second intermediate layer 7b having a composition gradient in which the composition ratio of carbon is increased as the surface side is overlapped with the second intermediate layer 7b.

The metal material of the first intermediate layer 7a is selected from Cr, Al, W, Ta, Mo, Nb, Si, and Ti, which are compatible with the iron-based material in order to increase the adhesion with the base material 6. It is preferable that the material contains one or more kinds of metals. More preferred are Cr and W.
For example, it is preferable to form the first intermediate layer 7a mainly composed of Cr on the surface of the substrate 6, and to form the second intermediate layer 7b having a W-carbon composition gradient thereon.

In FIG. 2, an example of a two-layer structure is shown as the intermediate layer 7, but the intermediate layer 7 may be composed of one layer or three or more layers as necessary.
The composition gradient of the second intermediate layer 7b can be formed by tilting the metal-carbon composition by adjusting the sputtering power applied to the target metal used for sputtering and graphite.

In order to improve the adhesion between the substrate 6 and the intermediate layer 7, it is preferable to perform nitriding treatment on the surface of the substrate 6 before the intermediate layer forming step.
As the nitriding treatment, it is preferable to perform a plasma nitriding treatment in which an oxide layer that prevents adhesion is unlikely to be formed on the surface of the base material 6. Is preferable because it improves the adhesion to the intermediate layer 7.

[Formation of hard film mainly composed of DLC]
The hard film 5 is a hard film mainly composed of diamond-like carbon (DLC) which is amorphous carbon.
In order to form the hard coating 5, a known technique called an unbalanced magnetron sputtering (UBMS) method can be employed. The UBMS method is sputtering in which the plasma irradiation to the substrate is enhanced by intentionally making the magnetic field of the sputter cathode non-equilibrium, and a close cured film can be formed by the ion assist effect.

The UBMS method will be specifically described. The degree of vacuum in the UBMS apparatus (Kobe Steel Works: UBMS202 / AIP combined apparatus) (inside the chamber) is 0.2 to 0.9 Pa, and the bias voltage applied to the substrate is Under the condition of 50 to 400 V, carbon atoms generated from a target serving as a carbon supply source are deposited on the intermediate layer 7 to form a hard film mainly composed of DLC.

At this time, if any of the degree of vacuum in the UBMS apparatus and the bias voltage applied to the substrate is out of the above range, the above physical properties cannot be obtained with certainty in the hard film, so the degree of vacuum in the UBMS apparatus is 0. More preferably, it is from 25 to 0.82 Pa. The bias voltage applied to the substrate is preferably 50 to 400V.

Since the hard coating 5 is a layer mainly composed of DLC, a graphite target is used as a carbon supply source during film formation. Moreover, the adhesiveness with respect to an intermediate | middle layer can also be improved by using together the said graphite target and hydrocarbon gas as a carbon supply source.

As the carbon-hydrogen gas, methane gas, acetylene gas, benzene and the like are not particularly specified, but methane gas is preferable from the viewpoint of cost and handleability.
When a graphite target and a carbon hydrogen gas are used in combination as a carbon supply source, the ratio of the introduction amount of the hydrocarbon gas is 100 with respect to the introduction amount 100 of argon gas into the UBMS apparatus (in the film formation chamber). It is preferably 1 or more and 5 or less. Within this range, the hardness of the hard coating can be maintained while improving the adhesion, and the specific wear amount can be reduced.
Note that the amount of Ar gas introduced as the sputtering gas is preferably 50 to 200 ml / min, for example.

The hard coating 5 gradually increases in hardness stepwise or continuously from the second intermediate layer 7b side to the outermost layer side so that the adhesion with the second intermediate layer 7b is improved. It is preferable to eliminate an abrupt hardness difference between the intermediate layer 7b and the hard coating 5 on the surface.
Specifically, the DLC gradient layer is obtained by forming the hard coating 5 while increasing the bias voltage with respect to the substrate 6 continuously or stepwise using a graphite target in the UBMS method.

The hardness of the DLC gradient layer increases continuously or stepwise because the composition ratio of the graphite structure (sp2) and the diamond structure (sp3) in the DLC structure is biased toward the latter as the bias voltage increases. It is.
Such a hard coating 5 is formed with a hardness adjusted to a Vickers hardness (Hv) of 1000 to 4000.

As described above, by increasing the bias voltage, the hardness can be adjusted by increasing the HV value within the above numerical range.
Regarding the wear resistance, the hardness of the hard film is more preferably (Hv) 1000 to 3000, and the hardness of the hard film is more preferably (Hv) 1000 to 1500 in terms of a low coefficient of friction.

Next, the rolling elements used in the present invention are made of ceramics, and the type of ceramics is not particularly limited, but silicon nitride, zirconia, silicon carbide, and alumina ceramics can be prepared. However, for example, a rolling element made of silicon nitride ceramics is preferable because it is particularly hard and excellent in wear resistance.

The cage 4 used in the present invention is made of a resin material mainly composed of polytetrafluoroethylene (PTFE). This is because it is preferable for exhibiting good and stable solid lubricity by transferring a solid lubricant to the surface of the rolling element even at an extremely low temperature.

The type of the cage 4 is not particularly limited and may be a known type, for example, a crown type, or an annular type in which pocket holes are formed at equal intervals in a cylindrical circumferential direction. Further, any of the types that can be divided into two in the annular axial direction and can be integrated by crimping with a pin may be used.

In the present invention, the type (model) of the rolling bearing is not particularly limited, and may be a deep groove ball bearing or a cylindrical roller bearing for a cryogenic environment.

The specific use of the rolling bearing for the cryogenic environment according to the present invention may be a rolling bearing of a pump for a liquefied gas, or a rolling bearing used for supporting or driving a satellite antenna. good.

When the application of the rolling bearing is a pump for liquefied gas, it may be a submerged pump for liquefied natural gas (LNG), but in that case, since the rolling bearing directly contacts the cryogenic LNG, The inner and outer rings and rolling elements of the present invention have a remarkable effect of becoming a rolling bearing for a cryogenic environment excellent in durability that withstands long-term use and does not deteriorate wear resistance and lubricity.

As shown in FIG. 3, the submerged pump for liquefied natural gas (LNG) exhibits airtightness in a pot (pressure vessel) 8 by immersing the entire pump in the liquid. Is a structure integrally connected to the motor shaft 10 coaxially.

The pot 8 is opened with the LNG suction port 11 facing outward, and has a discharge port 12 leading to an external pipe (not shown). The motor 13 mounted in the pot 8 supports the upper and lower sides of the motor shaft 10 rotated by an external power source with the ball bearing A of the embodiment shown in FIGS. A multi-stage impeller (impeller) 14 is attached to the pump shaft 9 that rotates integrally.

The flow path in the illustrated apparatus of the pump is such that the LNG flowing from the suction port 11 into the pot 8 along the inner surface of the pot 8 by the impeller 14 that rotates integrally with the pump shaft 9 by the driven motor 13. It flows downward and flows into the discharge port 12 from the pipe 16 inside the cylindrical inner wall 15 arranged around the impeller 14, and is sucked in from the lowermost portion of the multistage impeller 14. The other pipe 17 inside the cylindrical inner wall 15 flows in the motor 13 as a lubricating liquid, lubricates and cools the ball bearing A, joins the downward flow along the inner side surface of the pot 8, and again multistage. Is sucked from the tip of the impeller 14.

The ball bearing A used in this way holds ceramic balls with a PTFE cage, and a hard coating mainly composed of diamond-like carbon having a predetermined hardness is provided on the inner ring and outer ring base material surfaces. Therefore, it is used as a rolling bearing that can withstand long-term use in a cryogenic environment where it is lubricated and cooled by LNG, and wear resistance and lubricity do not deteriorate over time. Can withstand.

Further, as a second embodiment of the rolling bearing for the cryogenic environment according to the present invention, the structure of the cage in the above embodiment may be changed so that it can be divided in the annular axial direction.
That is, the second embodiment shown in FIGS. 4 to 6 is a pocket that rotatably holds the rolling elements 3 composed of a plurality of spheres in the annular space between the inner ring 1 and the outer ring 2 at intervals in the annular circumferential direction. A holder 19 having holes 18 formed at equal intervals is provided, and the holder 19 is a rolling for a cryogenic environment in which a pair of annular divided bodies 19a and 19b that can be divided in the annular axial direction are integrally coupled on a dividing surface 19c. Bearings are used.

A plurality of contact surfaces in a state where the pair of annular divided bodies 19a and 19b are abutted with each other are formed with through holes 20 penetrating in the axial direction of the annular divided bodies 19a and 19b, respectively. The pair of annular divided bodies 19a and 19b are fastened together by the fastening pin 21 that has been made.

The fastening pin 21 is made of a material having a lower coefficient of thermal expansion than the cage 19, and at least one of the head 21a at the base end and the crimped head 21b at the tip is provided with a spring washer 22 that is an elastic washer. The pair of annular divided bodies 19a and 19b are integrated by the elastic force of the spring washer 22 to form the cage 19 by being pressed against the end faces of the annular divided bodies 19a and 19b.
The thermal expansion coefficient under the above conditions may be either a linear thermal expansion coefficient or a volume thermal expansion coefficient (= linear expansion coefficient × 3).

The above-described cage 19 is a well-known cylinder (ring) shape such as a cylindrical body whose size is entirely accommodated in the annular space between the inner ring 1 and the outer ring 2, and is a pair of rings divided into two in the annular axial direction. The division surfaces 19c are brought into contact with each other so that the division bodies 19a and 19b are in a state before division.

The split surfaces 19c of the pair of annular divided bodies 19a, 19b are formed by projecting the inner peripheral side of one end face of the annular divided bodies 19a, 19b to be indented, and by recessing the other inner peripheral side. The joint form is adopted. A through hole 20 that penetrates in the axial direction of the retainer 19 is provided so as to penetrate such a split surface 19c, and a fastening pin 21 is inserted and fastened into the through hole 20 so as to integrate the pair of annular split bodies 19a and 19b. ing.

The formation position of the dividing surface 19c is in the middle of the cylindrical shape of the retainer 19, and forming the pocket hole 18 in a half position facilitates the workability of incorporating the rolling element 3 into the pocket hole 18. It is preferable for reasons such as good.

As the annular divided bodies 19a and 19b constituting the retainer 19, those made of a resin material mainly composed of polytetrafluoroethylene resin (PTFE) are adopted as in the first embodiment. Examples of the resin as an additive component other than PTFE include polyamide resins (for example, polyamide 46, polyamide 66, polyamide 9T, etc.), polycarbonate, polyether ketone resin, polyphenylene oxide (PPO), polyphenylene sulfide resin, and the like.

The through-hole 20 provided through the dividing surface is provided in a diameter and a shape through which the fastening pin 21 can be inserted, and is not particularly limited to a circular hole shape, and is a polygonal hole or other well-known hole. There may be.
The fastening pin 21 preferably has a head portion 21a having a diameter larger than the diameter of the through hole 20 at one end from the beginning before use, and the shape of the head portion 21a is a disc shape, a polygonal disc shape, or a hemispherical shape. The shape is a frustum shape and is not limited to the illustrated shape. For example, it is preferable to use a well-known fastening pin 21 for rivets because it is easy to assemble.
Further, the fastening pin 21 has an axial length that protrudes from the other end when inserted from one end of the through hole 20, and the portion protruding from the other end has a normal temperature or heating condition. By causing plastic deformation by pressurization, a head 21b crimped to the same large diameter as the above-described head 21a is formed.

The fastening pin 21 is made of a material such as stainless steel that can be plastically deformed by pressurization, other steel alloys, or a synthetic resin such as a thermoplastic resin so that a crimped head 21b can be formed. A material having a thermal expansion coefficient lower than that of the cage 5 is employed.
For example, when the material of the retainer 19 and the material of the fastening pin 21 are either metal or resin, the thermal expansion coefficient (linear expansion coefficient or volume expansion coefficient) of the fastening pin 21 is The one having a low thermal expansion coefficient equal to or lower than that of the cage 19 is employed.

When synthetic resin is used as the material of the cage 19, a material having the same or lower thermal expansion coefficient as that of the cage 19 is adopted if stainless steel or other steel alloy is used as the fastening pin 21. This means that the fastening pin 21 is used.

Furthermore, when a synthetic resin is used as the material of the cage 19 and a synthetic resin is also used as the material of the fastening pin 21, the coefficient of thermal expansion corresponding to the type of the synthetic resin is taken into account. It is preferable to selectively employ a brittle temperature at a low temperature of less than −100 ° C. as shown in FIG. In particular, PTFE is a material that can withstand low temperatures up to -267 ° C.

Further, the retainer 19 presses one or both of the heads 21a, 21b provided at both ends of the fastening pin 21 to the annular divided body via an elastic washer.
The elastic washer is made of metal made of spring steel or the like, or made of synthetic resin such as fluororesin or a composite material thereof, and has elasticity in the annular axial direction, and particularly its kind Without limiting the form, the spring washer (also referred to as a spring washer) shown in FIGS. 4 to 6 and an elastic washer such as a wave washer or a disc spring can be exemplified.

The spring washer has a spring action by cutting a part of the flat washer and twisting the cut portion. For example, the step of the cut portion is about 50% of the thickness of the cut portion (40 to 40%). 60%, preferably 45 to 55%) is preferable for obtaining moderate elasticity.

An elastic washer such as a spring washer can also be used in combination with a flat washer to protect the cage. In addition, a disc spring, a spherical washer, and a wave washer can be used as an elastic washer having a higher spring constant than the spring washer.

In the rolling bearing for the cryogenic environment configured as described above, the pair of annular divided bodies 19a and 19b constituting the cage 19 are integrated by the elastic force of the elastic washer, and the fastening pin 21 is the cage 19. Since the material has a low thermal expansion coefficient equal to or less than the thermal expansion coefficient, the annular divided bodies 19a and 19b, which are greatly heat-shrinked compared to the fastening pin 21 when the room temperature is changed to an extremely low temperature state, have the diameter of the through hole 20 reduced. It shrinks and contracts until it approaches or comes into contact with the outer peripheral surface of the fastening pin 21 to reduce the radial gap or closely contact to prevent the fastening pin 21 of the retainer 19 from vibrating in the radial direction and rattling.

Further, when changing from the normal temperature state to the extremely low temperature state, the annular divided bodies 19 a and 19 b contracted greatly compared to the fastening pin 21 contract without being regulated in the axial direction of the fastening pin 21. At this time, since at least one of the heads 21a and 21b at both ends of the fastening pin 21 is pressed against the annular divided bodies 19a and 19b by elastic washers, the fastening pins 21 are also elastic to the contracted annular divided bodies 19a and 19b. The pressure contact force of the washer acts to maintain the elastically integrated state of the pair of annular divided bodies 19a, 19b in the retainer 19, and the pair of annular divided bodies 19a, 19b by the fastening pin 21 are kept at a cryogenic temperature. There will be no looseness or gaps in the joint surface in use. As a result, the rolling element 3 is smoothly rotated and stabilized in a state where the bearing performance at a very low temperature is good.
In addition, in order to solve only the technical problem about the above annular division bodies, the structure of the rolling bearing which abbreviate | omitted the hard film 5 in a figure is also employable.

The third embodiment shown in FIGS. 7 and 8 shows a configuration exactly the same except that the wave washer 23 is used instead of the spring washer in the second embodiment.
The wave washer 23 is formed by bending a flat washer made of spring steel into a corrugated shape, and exhibits elasticity in the axial direction by elastically deforming the corrugated shape.

In the retainer 19, heads 21a and 21b provided at both ends of the fastening pin 21 are integrated with elastic washers such as a spring washer 22 or a wave washer 23, and a pair of annular divided bodies 19a and 19b are integrated with the elastic force of the elastic washer. Therefore, the pressure contact force of the elastic washer acts on the annular divided bodies 19a and 19b contracted in a use state at an extremely low temperature, and the state where the pair of annular divided bodies 19a and 19b are elastically integrated is maintained. 21 does not cause looseness or gaps in the joint surfaces of the pair of annular divided bodies 19a and 19b in a use state at an extremely low temperature. As a result, the rolling element 3 is smoothly rotated and stabilized in a state where the bearing performance at a very low temperature is good.

In the second and third embodiments configured as described above, a pair of annular divided bodies 19a, 19b by a fastening pin 21 such as a steel rivet assembled at room temperature are abutting surfaces in a use state at a cryogenic temperature. Thus, a rolling bearing for a cryogenic environment is obtained in which no looseness or gap is generated, and the rolling element 3 is smoothly rotated to stabilize the bearing performance in a good state.

DESCRIPTION OF SYMBOLS 1 Inner ring 2 Outer ring 3 Rolling element 4 Cage 5 Hard film 6 Base material 7 Intermediate layer 7a First intermediate layer 7b Second intermediate layer 8 Pot 9 Pump shaft 10 Motor shaft 11 Suction port 12 Discharge port 13 Motor 14 Impeller 15 Tubular inner walls 16, 17 Piping 18 Pocket hole 19 Cage 19a, 19b Annular division 19c Dividing surface 20 Through hole 21 Fastening pins 21a, 21b Head 22 Spring washer 23 Wave washer

Claims (5)

1. In a rolling bearing provided with a cage that rotatably holds a plurality of rolling elements between an inner ring and an outer ring made of martensitic stainless steel or high-speed tool steel,
   The rolling element is a ceramic rolling element, and the cage is made of a resin material mainly composed of polytetrafluoroethylene, and diamond-like carbon having a Vickers hardness (Hv) of 1000 to 4000 is formed on the surfaces of the inner ring and the outer ring. A rolling bearing for a cryogenic environment characterized by providing a hard film mainly composed of
2. 2. The rolling bearing for a cryogenic environment according to claim 1, wherein the hard coating is a hard coating provided via an intermediate layer whose hardness is increased stepwise or continuously toward the surface.
3. The rolling bearing for a cryogenic environment according to claim 1 or 2, wherein the rolling element is a silicon nitride ceramic rolling element.
4. 4. The cryogenic environment pump rolling bearing according to claim 1, wherein the cryogenic environment rolling bearing is a liquefied gas pump rolling bearing.
5. The rolling bearing for a cryogenic environment according to claim 4, wherein the liquefied gas pump is a submerged pump for liquefied natural gas.

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