JP2002250349A - Rolling bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rolling bearing capable of preventing the occurrence of hydrogen embrittlement flaking even if it is used under such an environment that water is mixed in lubricant, and having a long service life. SOLUTION: In the self-aligning rolling bearing 1 provided with an inner ring 2 having two rows of raceway track faces 2a, 2a, an outer ring 3 having a two-row integrated spherical face raceway track 3a, and two rows of spherical rollers 4 arranged between the inner ring 2 and the outer ring 3 so as to roll freely, a contact angle θ is 8 to 11 deg., and at least one of the inner ring 2, outer ring 3, and barrel shaped roller 4 is made of a steel having a C concentration of 0.80 to 1.10 wt.%, Cu concentration of 0.05 to 0.60 wt.%, Nb concentration of 0.02 to 0.20 wt.%, and V concentration of 0.02 to 0.20 wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a long-life rolling bearing, and in particular, has a long life even in an environment where water is mixed into a lubricant inside the bearing, and is suitably used as a bearing for a calender roll of a paper machine. It relates to a rolling bearing that can be used.

[0002]

2. Description of the Related Art Generally, the life of a rolling bearing tends to be extremely reduced when moisture is mixed in a lubricant. For example, it has been reported that when only 100 ppm of water is mixed into a lubricant in a rolling bearing, the life is reduced by 32 to 48% (Reference: Schatzberg, P. and Felsen, IM: E
ffects of water and oxygen during rolling contact
lubrication, Wear, 12 (1968), pp. 331-342, and Schatzbe
rg, P.and Felsen, IM: Influence of water on fatigue
failure lo-cation and surface alteration during r
olling contact lubrication, Journal of Lubrication
Technology, ASME Trans. F, 91, 2 (1969), pp. 301-307).

Therefore, rolling mills, water pumps,
Rolling bearings used in environments that come into contact with water, such as rolling bearings used in paper machine calender rolls, have measures to prevent water intrusion (sealing devices, etc.) to prevent a reduction in service life. ) Is given.

[0004]

However, in a rolling bearing used in such an environment as described above, for example, a self-aligning roller bearing used in a calender roll of a paper machine, water such as a sealing device is provided. Even if measures are taken to prevent intrusion, it is difficult to completely prevent intrusion of water, and some water will inevitably enter the lubricant.

[0005] Then, the steel constituting the bearing ring and the rolling elements is corroded by water, and hydrogen is generated by the corrosion reaction. The generated hydrogen penetrates and diffuses into the steel, causing cracks in the steel and eventually causing flaking (hereinafter, flaking generated by such a mechanism is referred to as "hydrogen embrittlement flaking"). As a result, the life of the bearing is reduced.

Accordingly, the present invention solves such problems of the conventional rolling bearing, and even when used in an environment where water is mixed into a lubricant, hydrogen-brittle flaking is unlikely to occur and a long life is obtained. It is an object to provide a rolling bearing.

[0007]

In order to solve the above problems, the present invention has the following arrangement. That is, the rolling bearing according to claim 1 of the present invention is a rolling bearing including an inner ring, an outer ring, and a plurality of rolling elements rotatably disposed between the inner ring and the outer ring. 8 to
11 °, and at least one of the inner ring, the outer ring, and the rolling element has a C concentration of 0.80 to 0.80.
1.10% by weight, Cu concentration of 0.05 to 0.60% by weight, Nb concentration of 0.02 to 0.20% by weight, and V concentration of 0.02 to 0.20% by weight. It is characterized by the following.

According to a second aspect of the present invention, there is provided a rolling bearing comprising an inner ring, an outer ring, and a plurality of rolling elements rotatably disposed between the inner ring and the outer ring. In the above, the contact angle is set to 8 to 11 °, and at least one of the inner ring and the outer ring is set to C of 0.80 to
1.10% by weight, 0.05 to 0.60% by weight of Cu, N
b or V is made of steel containing 0.20% by weight or less, the rolling element is made of bearing steel, and the surface of the rolling element has a hardness H.
It is characterized in that a nitrided layer of v800 or more is provided, and the surface roughness Ra of the rolling element is 0.1 μm or less.

[0009] The steel having the above composition is hardly corroded by water and generates a small amount of hydrogen on the steel surface. Further, since a steel film having a low hydrogen permeability is formed, the amount of hydrogen entering the steel is reduced. Few. Then, the occurrence of hydrogen embrittlement flaking is delayed, so that the rolling bearing has a long life. Therefore, the rolling bearing has a long life even in an environment where water is mixed into the lubricant inside the bearing, and can be suitably used as a bearing for a calender roll of a paper machine.

[0010] The steel is prepared by a vacuum arc remelting method (V
It is preferable to make steel using an AR method) or an electroslag remelting method (ESR method). When steel is made by the above method,
A steel having a uniform structure with less segregation can be obtained. In such steel, the amount of hydrogen generated on the steel surface is smaller since the local battery is small and corrosion is suppressed. Next, the reasons for limiting the above numerical values will be described.

[Contact angle: 8 to 11 °] For example, in the case of a self-aligning roller bearing or the like, since the outer diameter of the inner ring is different between the both ends and the central portion, the rolling elements (rollers) are arranged inclined with respect to the shaft. (The rollers have a contact angle). Therefore, a so-called skew is liable to occur at the time of roller rolling from pure rolling. When the contact angle is less than 8 °, the load weight in the axial direction becomes insufficient,
In addition, stable alignment cannot be sufficiently maintained. Also, 11 °
If it exceeds, the skew increases and heat is easily generated. Then, the lubricant is thermally decomposed and hydrogen is generated, and hydrogen embrittlement flaking occurs to easily shorten the life.

[C: 0.80 to 1.10% by weight] C (carbon) affects the surface hardness of steel. If the C concentration on the surface of the steel is less than 0.80% by weight, the surface hardness of the steel is insufficient, and the rolling fatigue life and wear resistance become insufficient.
On the other hand, if the content exceeds 1.10% by weight, giant carbides precipitate during the heat treatment, and the rolling fatigue life tends to decrease.

[Cu: 0.05 to 0.60% by weight] Cu
When (copper) is added, the steel tends to be less susceptible to corrosion by water, so that the amount of hydrogen generated on the steel surface is reduced. Furthermore, since a film through which hydrogen hardly permeates is formed, the amount of hydrogen penetrating into steel is reduced. As a result, the occurrence of hydrogen embrittlement flaking is delayed, so that the rolling bearing has a long life.

However, if the content is less than 0.05% by weight, the above-mentioned effect is hardly obtained, while 0.60% by weight
If it exceeds 300, the hot workability of the steel decreases. [Nb, V: 0.02 to 0.20% by weight] Nb (niobium) and V (vanadium) have an effect of refining old austenite crystal grains. When the austenite crystal grains are refined, many crystal grain boundaries through which hydrogen atoms pass are formed, so that hydrogen gas is dispersed in more inclusions and the generation of hydrogen embrittlement flaking is delayed.

The same effect can be obtained by containing elements such as Al and N. However, regarding the life of a rolling bearing used in an environment where water is mixed in a lubricant, the life of Nb And V contain more favorable results. However, if the content is less than 0.02% by weight, the effect is poor, and if it exceeds 0.20% by weight, the steel making cost increases.

In the rolling bearing of the second aspect,
The steel may contain any one of Nb and V, and may not contain any of them. [Surface hardness of nitrided layer: Hv 800 or more] Since the nitrided layer has corrosion resistance and is hardly corroded by water, the generation of hydrogen embrittlement flaking of rolling elements is delayed. Therefore, the rolling bearing has a long life even when used in an environment where water is mixed in the lubricant. In order to sufficiently improve the rolling fatigue life of the rolling bearing, the hardness of the nitrided layer must be Hv800 or more.

Further, since the nitriding treatment is usually performed at a relatively high treatment temperature of about 400 to 600 ° C., if the base material does not have sufficient heat resistance, the strength of the base supporting the nitrided layer is reduced. Insufficiently, the nitride layer on the surface is easily damaged. Therefore, in order to avoid such inconveniences, it is preferable that the hardness at a depth of 2% of the average diameter at the position where the maximum shear stress acts is Hv653 or more.

[Surface roughness Ra of rolling element: 0.1 μm or less] The surface roughness Ra of the rolling element after nitriding treatment is 0.5 to 2.
Since it is as large as about 0 μm, the nitride or oxide particles on the surface may fall off during rolling if the state is as it is, and the reliability of the device will be reduced. In addition, when the surface roughness of the rolling element is large, the aggressiveness to the counterpart material on the contact surface tends to increase, and, for example, the life tends to be short under boundary lubrication. Therefore, it is necessary to apply a finishing process to the rolling surface after the nitriding treatment, and in order to prevent the above-mentioned inconvenience, the surface roughness Ra of the rolling surface needs to be 0.1 μm or less.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a rolling bearing according to the present invention will be described in detail with reference to the drawings and tables. [First Embodiment] FIG. 1 is a partial longitudinal sectional view showing a configuration of a self-aligning roller bearing which is an embodiment of a rolling bearing according to the present invention.

This self-aligning roller bearing 1 is filled in an inner ring 2, an outer ring 3, two rows of spherical rollers 4, a cage 5, and a space formed between the inner ring 2 and the outer ring 3. And a lubricant (not shown). The outer peripheral surface of the inner ring 2 is the raceway surfaces 2a, 2a of the rollers 4 in two rows, and the outer diameter is formed larger at the center portion than at both ends in the width direction. The inner peripheral surface of the outer race 3 is a two-row integrated spherical raceway surface 3a.

The contact angle θ of the self-aligning roller bearing 1, that is, the contact point between the raceway surface 2 a and location 4 of the inner race 2, the contact point with the spherical raceway surface 3 a and location 4 of the outer race 3, and a line connecting the center of the bearing The angle formed by a plane (radial plane) perpendicular to the bearing center axis is 8 to 11 °. Also, inner ring 2,
The outer ring 3 and the rollers 4 have a C concentration of 0.80 to 1.10% by weight, a Cu concentration of 0.05 to 0.60% by weight, an Nb concentration of 0.02 to 0.20% by weight, and a V concentration of 0.02-0.
It is composed of 20% by weight of steel.

Such a self-aligning roller bearing 1 is suitably used, for example, in a paper machine calender roll 10 shown in FIG. The paper machine calender roll 10 introduces steam from the steam inlet 12 into the heating roll 11 to raise the temperature of the heating roll 11, and dries the paper adhered to the outer surface of the heating roll 11 while rotating the heating roll 11. Things. Note that the steam is discharged to the outside through the steam discharge port 13.

Since the self-aligning roller bearing 1 is disposed at both ends of the heating roll 11 so as to rotatably support the heating roll 11, steam flows from the steam inlet 12 to the steam outlet 13. Then, the water vapor contacts the spherical roller bearing 1. As can be seen from an enlarged view of the portion where the self-aligning roller bearing 1 is provided (FIG. 3), the self-aligning roller bearing 1 is placed in a steam atmosphere. Moisture is mixed into the lubricant filled in the lubricant.

However, this self-aligning roller bearing 1
Since the inner ring 2, the outer ring 3, and the rollers 4 are made of steel that is hardly corroded by water as described above, the amount of hydrogen generated on the steel surface is small. Further, since this steel forms a film through which hydrogen hardly permeates, a small amount of hydrogen penetrates into the steel. Therefore, the occurrence of hydrogen embrittlement flaking is delayed, so that the spherical roller bearing 1 has a long life even when used in an environment where water is mixed into such a lubricant.

The above effect can be obtained if at least one of the inner ring 2, the outer ring 3, and the rollers 4 is made of the above-mentioned steel. Excellent effects can be obtained. The self-aligning roller bearing of this embodiment has a long life even when used in an environment where water is mixed into a lubricant such as a paper machine calender roll, but is used in other environments. Of course, it also has an excellent life.

Next, using various bearings having substantially the same configuration as the above-mentioned spherical roller bearing 1, a life test was conducted in an environment where water is mixed in the lubricant. The test conditions are shown below.・ Testing machine: Spherical roller bearing life tester ・ P / C: 0.43 (P: dynamic equivalent load, C: basic dynamic rated load) ・ Rotational speed: 1000 rpm ・ Lubricant: Nisseki Mitsubishi Co., Ltd. turbine VG68 (forced circulation lubrication)-Water input: 5% by weight of water is mixed into the lubricating oil every 4 hours by an intermittent pump.

Twenty-one self-aligning roller bearings with various types of steel and various contact angles (Examples 1 to 13, Comparative Examples 1 to 8)
The bearings were prepared and a life test was performed for each bearing. Tables 1 and 2 show the composition of the steel, the magnitude of the contact angle, and the test results (life, parts where peeling occurred). In addition, the life test of five bearings was performed for one type of bearing, and the average time was taken as the life of the bearing.

[0028]

[Table 1]

[0029]

[Table 2]

First, the effect of the C concentration of steel on the life of the bearing will be examined. Examples 1 to 13 in which the C concentration was 0.80 to 1.10% by weight had an excellent life, whereas Comparative Examples 1 and 2 in which the C concentration was out of the above range had a significantly poor life. I was Next, the effect of the Cu concentration of the steel on the life of the bearing will be examined. Cu concentration 0.05 ~
Examples 1 to 13 at 0.60% by weight had an excellent life, whereas Comparative Examples 3 and 8 having a Cu concentration of less than 0.05% by weight had a significantly inferior life. This indicates that Cu is extremely effective in retarding hydrogen embrittlement flaking.

Next, the effects of the Nb concentration and V concentration of steel on the life of the bearing will be discussed. In Examples 1 to 13 in which the Nb concentration and the V concentration are 0.02 to 0.20% by weight,
Comparative Example 4 in which the Nb concentration was 0% by weight, Comparative Example 5 in which the V concentration was 0% by weight, and N
In Comparative Example 8 in which both the b concentration and the V concentration were 0% by weight, the life was significantly inferior. This indicates that Nb and V are extremely effective in retarding hydrogen embrittlement flaking.

Next, the effect of the contact angle on the life of the bearing will be discussed. Example 1 in which the contact angle is 8 to 11 °
No. 13 had an excellent life. In Comparative Example 7 in which the contact angle was 6 °, the occurrence of skew due to the inclination of the rollers was small, and the life of the conventional bearing steel was not significantly reduced. In contrast, Comparative Example 6, in which the contact angle was 12 °,
The occurrence of skew due to the inclination of the rollers was large, and a significant reduction in life was observed even when the steel of the present invention was employed.

As described above, in the self-aligning roller bearings of Examples 1 to 13, the inner ring, the outer ring, and the rollers are made of the steel of the present invention, and the contact angle is 8 to 11 °. Compared with the self-aligning roller bearings of Comparative Examples 1 to 8 in which the outer ring and the rollers are made of conventional bearing steel, they are less susceptible to corrosion by water and the generation of hydrogen embrittlement flaking is delayed. It has a long life even when used in an environment where it is mixed. [Second embodiment] Several types of spherical roller bearings (Nominal number:
22211, outer diameter: 100 mm, inner diameter: 55 mm, width:
25 mm, roller length: 9.45 mm, roller maximum diameter: 1
(1.84 mm, roller minimum diameter: 11.29 mm) was manufactured as follows, and a life test was performed in an environment where water was mixed into the lubricant by the same method as in the first embodiment. .

First, the spherical roller bearings of Examples 14 to 21 and Comparative Example 9 will be described with reference to Tables 3 and 4. The inner ring and the outer ring were made of the same steel as in Example 1 in Table 1, and were subjected to quenching (820 ° C./0.5 hours) and tempering (160 ° C./2 hours) to obtain a surface hardness HR of the raceway surface.
C was 62.5, and the surface roughness Ra of the raceway surface was 0.1 μm.

The rollers are made of martensitic stainless steel having the composition shown in Table 3 and are turned and hardened (1060).
C./0.5 hours), sub-zero treatment (-80.degree. C.), tempering (160.degree. C./2 hours), rough grinding, nitriding, and lapping.

[0036]

[Table 3]

[0037]

[Table 4]

[0038] Before performing the nitriding treatment, to remove the chromium oxide that inhibits nitriding reaction, subjected to fluorination treatment (250 to 400 ° C.) using a fluorine-based gas such as NF _3, followed by NH ₃ Nitriding treatment (for example, Nv nitridation process of Daido Hokusan Co., Ltd.) was performed using gas. And
By varying the temperature of the nitriding treatment in the range of 400 to 480 ° C. and varying the treatment time in the range of 12 to 48 hours, the thickness of the nitrided layer on the roller surface is set to 0.1 to the average diameter of the roller. It was set to be from 0.5 to 2.5%.

The surface hardness of this nitrided layer is Hv 125
0, the hardness of the core of the roller was 59.5 HRC, and the surface roughness Ra of the roller was 0.1 μm. The carbide diameter is 1.0
μm. The surface hardness Hv of the nitrided layer is 0.49 load.
It was measured at a position 5 μm below the surface with N applied. The thickness of the nitrided layer is obtained by measuring the thickness of the white layer observed after etching with a ferric chloride solution (marble reagent) using an optical microscope. Surface hardness of nitrided layer H
Both v and the thickness of the nitrided layer are the average values of the results measured for 10 rollers.

Next, a self-aligning roller bearing of Comparative Example 10 will be described. The self-aligning roller bearing of Comparative Example 10 was not subjected to the nitriding treatment and did not include the nitrided layer. Other manufacturing methods and configurations are the same as those of the self-aligning roller bearings of Examples 14 to 21 and Comparative Example 9 described above. The self-aligning roller bearing of Comparative Example 11 had a SUS440 roller having the composition shown in Table 3.
C. And turning, quenching (1060
C./0.5 hours), sub-zero treatment (-80.degree. C.), tempering (160.degree. C./2 hours), finish grinding, and lapping, with a surface hardness of HRC 58.0 and a surface roughness Ra of 0.
It was 1 μm. The carbide diameter was 13.0 μm.

Further, in the self-aligning roller bearing of Comparative Example 12, the rollers are formed of M50 having the composition shown in Table 3.
Then, turning, quenching (1050 ° C./0.5 hours), tempering (550 ° C./2 hours), finish grinding and lapping are performed to obtain a surface hardness of HRC 63.5 and a surface roughness Ra of 0.1 μm. did. The carbide diameter was 8.3 μm.

Further, in the self-aligning roller bearing of Comparative Example 13, the rollers are made of SUJ2 having the composition shown in Table 3. And turning, quenching (820 ° C / 0.5 hour)
After tempering (160 ° C / 2 hours), finish grinding and lapping, the surface hardness is HRC 62.0 and the surface roughness Ra
Was set to 0.1 μm. The carbide diameter was 1.0 μm.

The inner and outer races of the spherical roller bearings of Comparative Examples 11 to 13 are the same as those of Embodiment 14. The result of performing a life test on such a self-aligning roller bearing in the same manner as in the first embodiment will be described with reference to FIG. 4 in which numerical values in Table 4 are graphed. The size of the contact angle during the life test was 8 ° 50 ′.
It is. Further, the lifespan in Table 4 and FIG. 4 is indicated by a relative value when the lifespan of Comparative Example 13 is set to 1.

As can be seen from the graph, when the thickness of the nitrided layer is 0.1% or more of the roller average diameter, hydrogen embrittlement flaking hardly occurs, so that the life is excellent. In particular, in Examples 14 to 14, the thickness of the nitrided layer was 1.0% or more of the average diameter of the rollers.
No. 17 has a very long life. Since the nitrided layer is dense and has corrosion resistance, the effect of preventing hydrogen embrittlement flaking under lubrication mixed with water is remarkable even when stress is applied to the interface (and below the interface) with the base material.

On the other hand, in the bearing of Comparative Example 9, the thickness of the nitrided layer was as thin as 0.05% of the average diameter of the rollers. The effect of preventing hydrogen embrittlement flaking was insufficient. Since the bearings of Comparative Examples 10 to 13 were not provided with a nitrided layer, the life was inferior to those of the bearings of Examples 14 to 21. However, Comparative Example 10, in which the rollers were made of martensitic stainless steel, had the longest life in Comparative Examples because the carbon concentration in the steel was low and the diameter of the carbide was small. However, in Comparative Examples 12 and 13, although the surface hardness was high, the diameter of the carbide was large and the corrosion resistance was poor, so that the life was inferior.

The upper limit of the thickness of the nitrided layer is not particularly limited, but is preferably 2.5% or less, more preferably 2.0% or less of the roller average diameter, since the effect of improving the life is saturated. Is more preferred. Even if the nitride layer is made thicker than this, the nitridation processing time becomes longer and the cost becomes higher. As described above, such a spherical roller bearing of the second embodiment is
Since the inner and outer rings are made of steel as described above, and the rollers are provided with a nitrided layer, they are hardly corroded by water, and the generation of hydrogen embrittlement flaking is delayed, so that water is mixed into the lubricant. It has a long life even when used under such an environment.

The above embodiments are merely examples of the present invention, and the present invention is not limited to these embodiments. For example, in each of the above embodiments, the self-aligning roller bearing has been described as an example of the rolling bearing. However, the rolling bearing of the present invention can be applied to various other types of rolling bearings. For example, radial type rolling bearings such as deep groove ball bearings, angular ball bearings, cylindrical roller bearings, tapered roller bearings, and thrust type rolling bearings such as thrust ball bearings and thrust roller bearings.

Further, the type of grease is not limited to the one used in the above embodiment, and ordinary grease commonly used for rolling bearings can be used.

[0049]

As described above, the rolling bearing of the present invention has the following features.
Even when used in an environment where water is mixed into a lubricant, hydrogen embrittlement flaking is unlikely to occur and the life is long.

[Brief description of the drawings]

FIG. 1 is a partial longitudinal sectional view showing a configuration of a self-aligning roller bearing which is one embodiment of a rolling bearing according to the present invention.

FIG. 2 is a sectional view showing a structure of a calender roll of a paper machine.

FIG. 3 is an enlarged sectional view showing a structure of a peripheral portion of a self-aligning roller bearing in the calender roll of the paper machine of FIG.

FIG. 4 is a graph showing a correlation between a thickness of a nitride layer on a roller surface and a life of a bearing.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Self-aligning roller bearing 2 Inner ring 2a Raceway surface 3 Outer ring 3a Spherical raceway surface 4 Roller θ Contact angle

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) F16C 33/32 F16C 33/32 33/34 33/34

Claims (2)

[Claims] 1. A rolling bearing comprising an inner ring, an outer ring, and a plurality of rolling elements rotatably disposed between the inner ring and the outer ring, wherein a contact angle is set to 8 to 11 °. , At least one of the inner ring, the outer ring, and the rolling element has a C concentration of 0.80 to 1.10% by weight and a Cu concentration of 0.05 to 0.
60% by weight, Nb concentration of 0.02 to 0.20% by weight, V
A rolling bearing comprising a steel having a concentration of 0.02 to 0.20% by weight. 2. A rolling bearing comprising an inner ring, an outer ring, and a plurality of rolling elements rotatably disposed between the inner ring and the outer ring, wherein the contact angle is 8 to 11 °. , At least one of the inner ring and the outer ring, C is 0.8
0-1.10% by weight, Cu containing 0.05-0.60% by weight, Nb or V containing 0.20% by weight or less of steel, The rolling element is made of bearing steel, and the rolling element is made of A rolling bearing, wherein a nitrided layer having a hardness of Hv800 or more is provided on the surface of the rolling element, and the rolling element has a surface roughness Ra of 0.1 μm or less.