JP2000110841A - Rolling bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a roller bearing whose life can hardly be shortened even when moisture is mixed in a lubricant from outside. SOLUTION: In case of a roller bearing made of a steel used in an environment wherein moisture is mixed in a lubricant, a stress corrosion crack starting from an oxide non-metal inclusion occurs to a rolling surface (the raceway surface of a race on the fixed side) where moisture is most easy to stow and life is apt to be shortened. In this case, it is previously ensured through non- destructive inspection that no oxide non-metallic inclusion with an average diameter exceeding 100 μm is present on the raceway surface of the race on the fixed side through which moisture is apt to enter a gap between the race and ground, and shortened life due to a stress collision crack is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling bearing and, more particularly, to a steel rolling bearing capable of suppressing a reduction in life in an environment where moisture is mixed in a lubricant.

[0002]

2. Description of the Related Art It is generally known that the durability of a rolling bearing is greatly reduced when moisture is mixed in a lubricant. For example, it has been reported that when 6% of water is mixed in the lubricant, the rolling fatigue life of the bearing is reduced from several times to about one twentieth as compared with the case where no water is mixed ( Kyozaburo Furumura, Shinichi Shirota, Kiyoshi Hirakawa:
"Rolling fatigue of surface origin and internal origin", N
SK BearingJournal, NO. 636
pp. 1-10, 1977: hereinafter referred to as “Document 1”).

[0003] The incorporation of water into a lubricant has a great effect on the life characteristics (durability) of a rolling bearing.
Various techniques for preventing the incorporation of moisture into the lubricant have been studied and developed in the past depending on the application of the rolling bearing.

As a rolling bearing used on the assumption that moisture enters the lubricant, there is, for example, a work roll bearing of a rolling mill made of a steel material. Conventionally, this work roll bearing is a chock (bearing box) with a built-in bearing.
A contact rubber seal was mounted on the bearing to prevent a large amount of rolling water from entering the chock, thereby preventing water from being mixed into the lubricant sealed inside the bearing. However, when the contact rubber seal is deteriorated or damaged, water infiltrates into the chock, and as a result, water may be mixed into the lubricant inside the bearing. For this reason, a technique has recently been proposed in which a contact rubber seal is also provided inside the bearing so as to avoid the entry of moisture into the lubricant (KY).
AMAMOTO, M .; YAMAZAK1, M. AKIY
AMA, K .; FURUMURA: "Introduci
ng of Sealed Bearings for
Work ROLL Necks in Rolli
ngMills ", Proceedings of
he JSLE international Tri
blogology Conference, pp. 146 609-
614, July 8-10, 1985, Tokyo, J
apan; hereinafter, referred to as “first prior art”).

According to the first prior art, the contact rubber seal attached to the chock outside the bearing and the contact rubber seal attached to the inside of the bearing are used in combination, so that only the rubber contact seal attached to the chock allows moisture to be removed. The water concentration in the lubricant is reduced from 40% to 10% as compared with the case where intrusion is prevented.
% And the consumption of lubricant can be reduced to 1%.
It has been reported that the bearing damage could be reduced to / 200 and that there were no bearing accidents that occurred several times a year.

In the above-mentioned work roll bearing, as another conventional technique for preventing moisture from being mixed into a lubricant, a technique of supplying a lubricant to a chock using compressed air as a carrier gas has been proposed (NSK Techni).
cal Journal No. 654 pp. 54-
56, 1992; hereinafter, referred to as "second prior art").

In the second prior art, by setting the air pressure in the chock high using compressed air, it is possible to suppress the entry of moisture into the lubricant.

[0008]

According to the first prior art, as described above, the water concentration in the lubricant can be reduced from 40% to less than 10%, and the consumption of the lubricant can be reduced. As a result of investigating the results of the use of work roll bearings afterwards, it was found that the seizure accident had been drastically reduced. However, the use time until the occurrence of peeling, that is, the bearing life L was significantly improved. It turned out not to be. This is because the decrease in the seizure accident is due to a decrease in the outflow of the lubricant due to the contact rubber seal built in the bearing. It is considered that the rolling fatigue strength is significantly reduced.

That is, it has been reported that the rolling fatigue strength of a bearing material is reduced by as much as 32 to 48% even when a trace amount of water of about 100 ppm is mixed into a lubricant (P. Schatzberg). , IM Fels
en: "Effects of water and
oxygen dur- ing rolling con
tact lubrication, wear, 12,
pp. 331-342, 1968: hereinafter referred to as "Reference 2"), when the contact rubber seal attached to the chock outside the bearing and the contact rubber seal incorporated in the bearing are used in combination, the water concentration in the lubricant becomes less than about 10%. Although it can be suppressed to a certain extent, it is not possible to completely prevent water from being mixed into the lubricant, and to avoid a decrease in the rolling fatigue strength of the bearing material as pointed out in Reference 2. Can not. That is, in the first prior art, since the water in the lubricant cannot be completely prevented, the rolling fatigue strength of the bearing material is reduced, and the bearing life L having a desired durability cannot be obtained. There is.

In the second prior art, since the infiltration of moisture is prevented by increasing the air pressure in the chock, the second prior art does not depend on the waterproof ability of the contact rubber seal as in the first prior art. 100p moisture concentration in lubricant
pm or less, it is difficult to prevent the ingress of moisture close to a nearly perfect wall.

The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a rolling bearing which has a short life even when moisture is mixed into a lubricant from the outside.

[0012]

In order to achieve the above object, the present invention relates to a steel rolling bearing used in an environment where water is mixed in a lubricant, at least a fixed-side race. The average diameter is 100 μm on the raceway
It has been characterized by nondestructive inspection that no oxide-based nonmetallic inclusions exceeding the above exist.

As described above, it has been pointed out that when water is mixed into the lubricant, the life of the rolling bearing is greatly reduced. The mechanism of the failure of the rolling bearing in the presence of water is described as follows.

As shown in FIG. 1, the rolling surface (track surface) K
Is the elastic displacement Δ in the depth direction under the load from the rolling element T.
h occurs, and a tensile stress f acts on the track surface near the contact point. Oxide-based nonmetallic inclusions W
Is present, and when water is present on the raceway surface K, a void S is formed around the oxide-based nonmetallic inclusion W by the action of the tensile stress f generated on the surface by rolling contact, and the void S is formed in the void S. Water seeps in. As a result, corrosion and dissolution of the metal base occurs, which grows into cracks (cracks) K and causes stress corrosion cracking starting from the oxide-based nonmetallic inclusions W,
This is a mechanism that eventually leads to peeling.

The inventors of the present application have studied this mechanism in detail, and have obtained the following findings to complete the present invention.

The oxide-based nonmetallic inclusion W is unlikely to be deformed even during the hot working of the bearing ring member and has inherently poor adhesion to the metal base material, so that a void S exists between the oxide base nonmetal inclusion W and the base material. . The void S plays a role as a pre-crack (pre-crack). In this case, it has been found that the size of the oxide-based nonmetallic inclusion existing on the track surface is a major factor. . That is, it has been found that reducing the size of the oxide-based nonmetallic inclusion W to 100 μm or less is effective for extending the life.

The reason is considered as follows.

During operation of the bearing, the gap S originally existing between the metal material and the oxide-based nonmetallic inclusion W is enlarged by the tensile stress f acting on the raceway surface in contact with the rolling elements. . At this time, if water exists on the raceway surface, the void S
, Water is first introduced into the base material, from which corrosion and dissolution of the base material occur, and grow into cracks K. The growth rate of crack K is
Basically, the longer the crack K is, the faster the crack K becomes. However, if the average diameter of the oxide-based nonmetallic inclusions W is 100 μm or less, the adhesion to the substrate is improved, so that water hardly enters the voids, and the crack growth rate is significantly reduced. Therefore, the size of the oxide-based nonmetallic inclusion W is set to 100
When the thickness is not more than μm, the progress of stress corrosion cracking starting from the oxide-based nonmetallic inclusion W is suppressed, and the life is extended.

As described above, the stress corrosion cracking of a race in a rolling bearing originating from an oxide-based nonmetallic inclusion is a phenomenon that is observed when water is present at the time of rolling contact with a rolling element. It does not occur when only one of the physical nonmetallic inclusion W and water is present.

Under favorable lubricating conditions in which water is not mixed into the lubricant and an oil film is sufficiently formed, the starting point of peeling is also an oxide-based nonmetallic inclusion, but its existence position is It is below the track surface and does not cause stress corrosion cracking. The starting point of stress corrosion cracking is "oxide-based non-metallic inclusions present on the track surface". This is because water is not supplied even if inclusions are present.

As described above, the presence of water is essential for stress corrosion cracking of a raceway surface originating from oxide-based nonmetallic inclusions. Therefore, stress corrosion cracking is more likely to be promoted on the raceway surface of the fixed raceway, in which water tends to stay as compared with the raceway raceway surface, and thus peeling is more likely to occur. Since the rotating raceway and rolling elements are moving, water does not easily stay,
Low peeling frequency. Furthermore, since the rolling element has a rotation speed much higher than the rotation speed of the rotating raceway, water is easily blown off by centrifugal force, and stress corrosion cracking is further less likely to occur.
Therefore, the frequency of occurrence of peeling is the lowest.

Ultimately, it is most effective to extend the life of the bearing on the fixed-side trajectory, in which stress corrosion cracking and, consequently, peeling are most likely to occur. When it is necessary to extend the life of the bearing, the life of the bearing can be effectively extended by further extending the life of the rotation-side orbit theory.

From this point of view, in the present invention, the time until the occurrence of peeling in a lubricating environment in which water is mixed,
That is, in order to prolong the delamination life (hereinafter, simply referred to as life), stress corrosion cracking is less likely to occur particularly in the race including the fixed race and, if necessary, the rotating race.

Thus, in the rolling bearing according to the present invention, the presence of oxide-based nonmetallic inclusions having an average diameter exceeding 100 μm on at least the raceway surface of the fixed raceway is to be regulated. However, as a practical matter, it is a reality that large-sized oxide-based nonmetallic inclusions having a size exceeding 100 μm, which are called so-called ground flaws, are often present in the steel for bearings. It is difficult.

Therefore, as a next best measure, it is conceivable to sort bearing steel materials. 100μm in sorted steel
In order to ensure that no oxide-based non-metallic inclusions exceeding the maximum exist, it can be said that it is most effective to perform a 100% inspection by ultrasonic flaw detection. Since the detection limit of a defect due to an ultrasonic deep scratch is の of the wavelength of the ultrasonic wave, a high-frequency ultrasonic wave of 30 MHz or more may be used to detect a nonmetallic inclusion exceeding 100 μm. Incidentally, the acoustic velocity in steel of longitudinal waves used for general ultrasonic vertical flaw detection is 5900 m / s.
It is. However, since high-frequency ultrasonic waves of 30 MHz or more are significantly attenuated in the material, there is a problem that only the surface layer of the bearing steel material can be actually detected. After all, even if the material is selected, 100μ
There is no guarantee that there will be no more than m inclusions.

In order to solve such a practical problem, the present inventors have found that the starting point of peeling under water-mixed lubrication is nonmetallic inclusions on the raceway surface, and therefore, it should be guaranteed. Focused on the fact that it was the size of non-metallic inclusions on the track surface.

That is, the point of the present invention is to inspect the raceway surface of the finished bearing raceway which has been processed, not the unprocessed bearing steel material. Because the inspection object of the finished product is used as it is as a product bearing,
It must be a non-destructive inspection that scans the entire track surface non-destructively, not partial sampling. If non-destructive inspection of the finished product can detect non-metallic inclusions of 100μm on the raceway surface, it will be possible to provide bearings that do not contain non-metallic inclusions exceeding 100μm on the raceway surface, and the bearing will have a long life under water contamination Becomes

As such an inspection method, oblique incidence ultrasonic inspection is one of the effective inspection methods and can be suitably used as a powerful nondestructive inspection means. However, in ultrasonic flaw detection by oblique incidence, a transverse wave is used and the detection limit of a defect is １ ／ of the wavelength. Therefore, in order to detect a nonmetallic inclusion exceeding 100 μm, the use frequency is 17 MHz.
(The sound speed of the shear wave used for oblique flaw detection is 3230 m / s, and the wavelength is given by dividing the sound speed by the frequency.) In high-frequency ultrasonic inspection, noise is likely to occur if the surface roughness of the steel material to be inspected is poor, but the raceway surface of the finished bearing race is constantly polished and has a surface roughness of 0.3 μRa. It is as follows. Therefore, 17M
No noise is generated even at a high-frequency oblique flaw detection at a frequency of Hz or higher.

Conventionally, there have been rolling bearings in which the size and the amount of non-metallic inclusions per unit area or unit volume are regulated to extend the service life, but none of them is based on a nondestructive test.

As a technique for utilizing oblique incidence ultrasonic testing for a bearing race, there is Japanese Patent Application No. 10-146180 previously filed by the present applicant. However, in this case, the frequency range is 30 MHz or less, up to 2 mm below the surface, which is deeper than the maximum shear stress position of the bearing ring as the test object.
By obliquely inspecting the entire cross-section of the bearing raceway at an incident angle of 10 to 30 °, preferably 25 to 30 °, defects from the surface to the inside of the bearing raceway surface, particularly large non-metallic inclusions inside the raceway, Presence is detected with high accuracy to prevent short-life delamination due to internal defects, thereby guaranteeing internal defects of the bearing.

On the other hand, in the present invention, the inspection means is not limited to the ultrasonic angle beam flaw detection, but the inspection means is an effective means for extending the life of a rolling bearing used in a water-mixed environment. We use as one of. The rolling bearing of the present invention only needs to inspect the finished bearing race, at least only the surface layer of the fixed race, and confirm that there is no oxide-based nonmetallic inclusion exceeding an average diameter of 100 μm. .
Therefore, the ultrasonic oblique flaw detection frequency used in the present invention does not need to consider attenuation, and is, for example, 100 MHz.
z, the incident angle is 30 °. Thus, it is possible to reliably detect an oxide-based nonmetallic inclusion exceeding 100 μm in average diameter on the raceway surface, and to provide a rolling bearing that guarantees a long life in a water-mixed environment.

[0032]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a schematic diagram of an ultrasonic inspection device for a bearing ring used in the nondestructive inspection of a rolling bearing according to the present invention. Reference numeral 1 in the figure denotes a water tank in which water as an ultrasonic transmission medium is stored. In this water tank 1, a bearing ring 2 and an ultrasonic deep scratch probe 3, which are finished outer rings of tapered roller type rolling bearings, are arranged in a state of being immersed in water, respectively. As the ultrasonic deep flaw probe 3, a focus probe having strong directivity and being hardly affected by the curvature of the bearing ring 2 is used.

The bearing ring 2 is mounted on two pulleys 4 which are horizontally separated from each other in the water tank 1.
A belt 7 is wound around each pulley 4 and a pulley 6 fixed to the motor shaft of the rotary drive motor 5 in a regular triangular shape.

The rotary drive motor 5 is controlled by a control device 9 via a motor drive control amplifier 8, and the bearing ring mounted on each pulley 4 by the drive of the rotary drive motor 5 2 rotates at a predetermined speed. The control device 9 is configured by a personal computer or the like having a display unit such as a CRT.

The ultrasonic probe for deep scratches 3 is connected to an XY stage 12 supported by a linear guide device 10 movably arranged in the axial direction of the bearing ring 2 via a probe attachment 13. The bearing ring 2 is opposed to the inner peripheral surface of the bearing ring 2 in the mounted state. The ultrasonic deep wound probe 3 transmits an ultrasonic pulse corresponding to the voltage signal from the ultrasonic deep wound device 14 toward the inner peripheral surface of the bearing ring 2 and receives the reflected echo, This is converted into a voltage signal and transmitted to the ultrasonic deep wound device 14.

The ultrasonic deep wound device 14 transmits a command signal composed of a voltage signal to the ultrasonic deep wound probe 3 based on a command from the control device 9 and also converts the transmitted signal and the received signal. The flaw detection information obtained on the basis is transmitted to the control device 9, and the control device 9 displays this on the CRT.

The linear guide device 10 connects the ultrasonic deep wound probe 3 to the bearing ring 2 via a servomotor (not shown) controlled by the linear guide controller 16.
To move in the axial direction. When the rotary encoder 15 installed on the outer peripheral surface of the bearing ring 2 detects that the bearing ring 2 has made one rotation (360 °), the linear guide controller 16 controls the servo motor based on a command from the control device 9. To move the ultrasonic flaw detection probe 3 in the axial direction of the bearing ring 2 by a predetermined dimension. Thereby, flaw detection of the entire raceway surface of the bearing ring 2 is performed.

Next, a specific example of the nondestructive inspection of the rolling bearing according to the present invention using the above ultrasonic inspection equipment will be described.

The outer ring of a tapered roller bearing having an inner diameter of 350 mm was used as the bearing ring 2. The bearing ring 2 is connected to a focus type probe (frequency 100 MH) which is a probe 3 for ultrasonic deep damage.
z, an incident angle of 30 °, and a vibrator diameter of 6 mm) with water in the water tank 1. In this state, while rotating the bearing ring 2 and moving the ultrasonic deep flaw probe 3 in the axial direction of the bearing ring 2, the entire surface of the outer ring raceway surface, which is the inner peripheral surface of the bearing ring 2, is deepened. You only have to hurt.

(Examples) Comparative tests performed to clarify the effects of the present invention will be described below.

Steel materials whose outer ring is manufactured by various refining methods (vacuum degassing method, vacuum arc remelting method (VAR method), electroslag remelting method (ESR method), vacuum induction melting method (VIM method), etc.) (Steel type: JIS G 4052 SCr4
20H) tapered roller bearing (Model number: HR
32017XJ) as a test body, and a life test was performed under lubrication mixed with water.

The outer race is a fixed race. The heat treatment of the outer ring was performed by carburizing and quenching. The surface hardness was HRC61. Bearing dimensions are 85mm inside diameter, 130mm outside diameter,
The assembly width is 29 mm. Basic dynamic load rating C is 143kN
It is. The inner ring and the rolling elements were made of bearing steel type 2 SUJ2. The test equipment and test conditions are as follows.

Test Apparatus FIG. 3 is a sectional view of a main part of the durability test apparatus used. While the outer ring 22 is incorporated in the housing 24, the inner ring 23 is fitted on the rotating shaft 25, and 10 cc of water is injected into the bearing per hour as shown in FIG.
a and a radial load Fr were applied to the bearing, and a durability life test was performed while rotating the rotating shaft 25.

The outer ring 22 and the housing 24 are assembled by loose fit, and the inner diameter of the housing 24 is formed to be larger than the outer diameter D of the outer ring 22 by 10 to 15 μm. The inner ring 23 and the rotating shaft 25 are fitted by a clearance fit, and the inner diameter d of the inner ring 23 is formed to be larger than the shaft diameter of the rotating shaft 25 by 8 to 15 μm.

Test conditions Radial load: 35.8 GPa Axial load: 15.7 GPa Rotation speed of rotating shaft: 2500 rpm Lubricant: lithium soap-based grease (kinematic viscosity of base oil 197)
mm ² / sec, mineral oil) 60 g used Water content to be injected into the bearing: 10 cc / h On the other hand, a rotating bending test piece quenched and tempered from the material used for manufacturing the bearing was prepared, and a rotating bending fatigue test was performed. The size of the non-metallic inclusion at the fracture origin that appeared on the fracture surface was measured. When measuring the size of each nonmetallic inclusion, the average value of the maximum diameter and the minimum diameter of each nonmetallic inclusion was defined as the size of the nonmetallic inclusion. The maximum size of the nonmetallic inclusion of each material was larger than 100 μm. As described above, it is generally difficult to ensure that there is no inclusion having a size exceeding 100 μm in the material itself.

Test Method Prior to the bearing life test of water-mixed lubrication, non-metallic inclusions existing on the raceway surface of the finished outer ring were subjected to ultrasonic flaw detection (oblique flaw detection, incident angle 30 °, frequency used). 100M
Hz), the detection position was inspected with a microscope to confirm whether it was an oxide type or a sulfide type, and the average diameter was measured. The outer ring raceway surface has a surface roughness of 0.1 mm.
05 to 0.15 μRa.

Thereafter, the test piece tapered roller bearing was set in the above-mentioned testing machine so that the oxide-based nonmetallic inclusion having the maximum average diameter confirmed on the raceway surface of the outer ring was located at the center of the stress load zone. A life test was performed under the above-mentioned water-mixed lubrication conditions.

Test Results FIG. 4 shows the relationship between the life value (hrs) of each bearing and the maximum average value (hereinafter abbreviated as Dmax; unit: μm) of oxide-based nonmetallic inclusions. The life value becomes longer as Dmax becomes smaller, but becomes saturated when it becomes 100 μm or less (this embodiment).

From this data, it can be concluded that the maximum value of the average diameter of the oxide-based nonmetallic inclusions existing on the raceway surface of a stationary ring of a rolling bearing used in a lubricating environment mixed with water should be 100 μm or less. It turns out that it is effective for extending the life.

In the present embodiment, the exfoliated portions are all outer rings, but in rare cases, the inner rings may be exfoliated. For such a case, the maximum value of the average diameter of the oxide-based nonmetallic inclusions existing on the raceway surface for the inner ring is also set to 100
It is more effective to reduce the length to μm or less for prolonging the service life.

In the present embodiment, case hardening steel (JIS
G 4052 SCr420H), but the present invention is applicable to any bearing steel. In order to reduce the maximum diameter of the oxide-based nonmetallic inclusion, it is desirable to use a vacuum arc remelting method or an electroslag remelting method in which the remelting rate of the material steel is sufficiently controlled. However, it is difficult to eliminate oxide-based nonmetallic inclusions exceeding 100 μm on the track surface by itself. Therefore, the nondestructive inspection method assures the absence of oxide-based nonmetallic inclusions exceeding 100 μm on the raceway surface, realizing a longer life of the rolling bearing used in a lubrication environment mixed with water. Is necessary for

[0053]

As described above, according to the first aspect of the present invention, no oxide-based nonmetallic inclusions having an average diameter exceeding 100 μm exist at least on the raceway surface of the fixed raceway. Is a rolling bearing that has been verified by non-destructive inspection, the adhesion between the non-metallic inclusions and the base material is improved, cracks are suppressed, and as a result, a long life is ensured in an environment where water is mixed. The effect that a rolling bearing can be provided is obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a phenomenon in which water existing on a rolling surface and tensile stress generated on the surface due to rolling contact cause stress corrosion cracking starting from an oxide-based nonmetallic inclusion.

FIG. 2 is a schematic diagram of an ultrasonic inspection device for bearing rings.

FIG. 3 is a sectional view of a main part of a durability test apparatus for a rolling bearing.

FIG. 4 is a graph showing the relationship between the bearing life under lubrication mixed with water and the maximum average diameter of oxide-based nonmetallic inclusions on the raceway surface of the fixed raceway.

Claims (1)

[Claims] In a steel rolling bearing used in an environment where water is mixed in a lubricant, at least on a raceway surface of a fixed-side race, an oxide-based nonmetallic inclusion having an average diameter of more than 100 μm is formed. A rolling bearing characterized in that its absence is verified by non-destructive inspection.