JP2003307223A - Rolling bearing and method of manufacture - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rolling bearing and its manufacturing method hard to form an impression on a raceway surface even under a severe condition. <P>SOLUTION: A rocker arm bearing has an inner ring 2, a needle-like roller 3, and an outer ring 4. A nitriding layer formed by radical nitriding is formed on at least the raceway surface of the outer ring 4. The surface hardness of the raceway surface is set to HV 900 or more in Vickers hardness. The residual stress of the raceway surface is set to 500 MPa or more in compressive stress. <P>COPYRIGHT: (C)2004,JPO

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 a method for manufacturing the same, and more particularly to applications such as a rocker which is subjected to a high surface pressure cyclic load under impact or tensile stress. Arm, cam follower,
The present invention relates to a rolling bearing used for a roller follower and the like, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Among recent rolling bearings, for example, rocker arm bearings, cam followers, roller follower bearings are subject to impacts, or high surface pressure loads are momentarily or intermittently applied under the action of tensile stress. In many cases, it is used for the purpose of receiving it. In such a case, when the conditions are severe, Brinell indentation is formed on the raceway surface, which may deteriorate smooth rotation and quietness of the bearing, and in severe cases, cracking of the outer ring due to the indentation starting point may occur.

[0003]

In such a case, it has been customary in the past to lower the tempering temperature to increase the hardness of the bearing ring to increase the hardness, or to change the internal specifications to reduce the contact stress. It was correspondence. However, there is a limit to such measures, and lowering the tempering temperature also increases the susceptibility to cracking. Therefore, the effect of cracking is rather insufficient and the effect is insufficient.

Therefore, an object of the present invention is to provide a rolling bearing in which indentations are less likely to be formed on the raceway surface even under severe conditions.

Another object of the present invention is to provide a rolling bearing manufacturing method capable of manufacturing a rolling bearing in which an indentation is hard to be formed on a raceway surface even under severe conditions with a small number of steps.

[0006]

The rolling bearing of the present invention comprises:
A rolling bearing having a rolling element and a bearing ring is characterized in that a nitride layer formed by radical nitriding is formed on at least the bearing surface of the bearing ring.

The inventors of the present invention theoretically found that Brinell indentations are likely to be generated when a tensile stress other than hardness acts, and based on this, a surface treatment that provides high hardness and high compressive stress. By doing, it is difficult to crack even under severe conditions where impact, tensile stress and contact stress act simultaneously,
It has been found that a rolling bearing having a bearing ring that does not easily have an indentation can be obtained.

Concretely, M5 which originally has high crack fatigue strength
A high-alloy steel such as 0 has a high-strength cam follower or roller follower bearing that is hard to be indented by applying radical nitriding technology that does not cause formation of compound layer and decrease in surface roughness and has high hardness and large compressive stress. The present inventors have found that a bearing ring of

The above radical nitriding method and the conventional plasma nitriding method are different as follows.

In the conventional plasma nitriding method, first, plasma in a high energy state is generated by direct current glow discharge of a mixed gas of nitrogen and hydrogen. Ions such as nitrogen molecules thus obtained heat up the temperature of the object to be processed and simultaneously activate the surface, and the radicals formed in the plasma cause a nitriding reaction.

On the other hand, in the radical nitriding method, by precisely controlling the glow discharge of the mixed gas of ammonia and hydrogen, the ion density is low and highly active radicals (active species) are generated while generating plasma in a low energy state. ) Is effectively generated to perform the nitriding treatment. In addition,
In the radical nitriding method, an external heating furnace is used for heating and heating the processed material instead of electric discharge.

In this radical nitriding method, since the nitrogen compound layer (white layer) peculiar to nitriding treatment is not formed, the grinding process after the treatment, which has been a problem of conventional soft nitriding or gas soft nitriding, becomes unnecessary, and the cost can be reduced. It is possible to use a material that leaves an effective high hardness region. As a result, a rolling bearing having a raceway whose surface hardness of the raceway surface is HV900 or more in Vickers hardness and residual stress of the raceway surface is 500 MPa or more in compressive stress can be obtained.

In the above rolling bearing, preferably, the nitrogen compound is not present in the nitride layer, and the nitride layer is substantially composed of the nitrogen diffusion layer.

When radical nitriding is performed in this way, the nitride layer does not have a brittle nitrogen compound and is composed of a nitrogen diffusion layer, so that cracking can be suppressed and the surface roughness does not decrease. It is possible to omit the grinding step for improving the surface roughness.

In the above rolling bearing, preferably, the surface hardness of the raceway surface is HV900 or more in Vickers hardness and the residual stress of the raceway surface is 500 M in compressive stress.
Pa or higher.

As a result, even under severe conditions, it is possible to obtain a rolling bearing in which indentations are less likely to be formed on the raceway surface.

In the above rolling bearing, preferably, the depth of the surface hardened layer having a Vickers hardness of HV900 or more is 5 μm or more from the raceway surface.

Since the depth of the indentation is usually several μm, the indentation can be prevented if the depth of the hardened surface layer is 5 μm or more from the raceway surface. In addition, since cracks originate from the surface, cracks can be prevented by the presence of a surface-hardened layer having a Vickers hardness of HV900 or higher.

In the above rolling bearing, preferably, the rolling bearing is used for rotatably supporting the roller in a rocker arm having a roller that abuts on the cam.

As a result, the life of the roller support portion of the rocker arm can be extended. A method for manufacturing a rolling bearing according to the present invention is a method for manufacturing a rolling bearing having a rolling element and a bearing ring, in which at least the raceway surface of the bearing ring is subjected to radical nitriding by glow discharge of a mixed gas of ammonia and nitrogen. It is a feature.

As a result, as described above, the radical nitriding technique which does not cause the formation of the compound layer and the reduction of the surface roughness, and has the high hardness and the large compressive stress in the high alloy steel such as M50 which originally has the high crack fatigue strength. By applying the above, it is possible to manufacture a high-strength cam follower or roller follower bearing bearing ring that is hard to be indented.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic front view showing the structure of a rocker arm according to an embodiment of the present invention, and FIG. 2 is shown in FIG.
11 is a view corresponding to a cross section taken along line II-II of FIG. Referring to FIGS. 1 and 2, the cam follower body 1 is rotatably supported by the cam follower shaft 5 at the center through a bearing metal or the like.

At one end of the cam follower body 1,
The adjusting screw 7 is screwed. The adjusting screw 7 is fixed by a lock nut 8, and its lower end is in contact with the upper end of a protruding rod 9 of the air supply valve or the exhaust valve of the internal combustion engine. The projection rod 9 is biased by the elastic force of the spring 10.

The cam follower main body 1 integrally has a roller supporting portion 14 formed in a bifurcated shape at the other end. Both ends of the roller shaft 2 are fixed to the bifurcated roller support portion 14 by press fitting or snap rings. A roller 4 is rotatably supported at the center of the outer peripheral surface of the roller shaft 2 via a needle roller 3. The outer peripheral surface of the roller 4 is pressed against the cam surface of the cam 6 by the urging force of the spring 10.

Here, a rolling bearing composed of an inner ring composed of the roller shaft 2, a rolling element composed of the needle rollers 3, and an outer ring composed of the roller 4 is used as a rocker arm bearing. A nitride layer is formed by radical nitriding on at least the raceway surface of the outer race 4 among the inner race 2 and the outer race 4 which form the raceway of the rocker arm bearing. The surface hardness of the raceway surface is HV900 or more in Vickers hardness, and the residual stress of the raceway surface is 500 MPa in compressive stress.
That is all.

No nitrogen compound is present in the above-mentioned nitride layer, and the nitride layer is substantially composed of only the nitrogen diffusion layer.

Since the rocker arm bearing described above rotates while contacting with the cam 6, the outer ring 4 has the cam 6
The pressing force and the impact force may cause the formation of indentations and cracking due to repeated bending stress. In particular, due to the higher output of the engine, these forces increase as the rotation speed increases, and the risk of cracks and indentations increases further.

When a large force is applied to the bearing to form an indentation, usually the surface pressure between the inner ring and the rolling element is higher than the surface pressure between the outer ring and the rolling element, so the indentation is formed on the inner ring. Are easily formed. However, when a high surface pressure load acts while bending stress acts on the outer ring, such as a cam follower, an indentation is likely to be formed between the outer ring and the rolling element. The inventors of the present application have paid attention to this fact and found that it is effective to prevent the formation of indentations and cracks by giving a large compressive stress and high hardness to the outer ring.

There are various methods for giving a large compressive stress and high hardness, and, for example, shot peening can also be used. However, the nitriding treatment has a particularly remarkable effect. This is because the nitriding treatment can make the surface hardness of the raceway surface HV900 or more and the residual stress 500 MPa or more in compressive stress.

However, in the soft nitriding which has been conventionally used as the nitriding treatment, the hardness is increased, but since a nitrogen compound called a white layer is formed in the surface layer, the surface layer becomes brittle and an impact acts. It was not preferable because the application cracked.

On the other hand, radical nitriding does not involve the formation of a brittle compound layer by nitriding and does not lower the surface roughness. For this reason, it is possible to omit the re-grinding step for the purpose of improving the surface roughness, and there is an advantage that the effect remains even if the treatment is performed for a very short time. This is economical because the number of manufacturing steps can be reduced.

For radical nitriding, the processing temperature (about 5
It is necessary to use a material whose hardness does not decrease even at 00 ° C.
No. 50 material is suitable as a material for radical nitriding because the hardness does not decrease and the crack strength (particularly crack fatigue strength) is high at 550 ° C. or lower where the secondary hardening phenomenon is completed. As a result, it is possible to obtain a rolling bearing including a bearing ring having large crack fatigue strength and pressure resistance.

The depth of the surface hardened layer having a Vickers hardness of HV900 or more is preferably 5 μm or more from the raceway surface. Usually, the depth of the indentation is several μm, so that the surface hardened layer having the depth of the indentation or more (5 μm or more) is effective in preventing cracks originating from the surface.

Further, in the rolling bearing manufacturing method of the present embodiment, radical nitriding by glow discharge of a mixed gas of ammonia and nitrogen is carried out on at least the raceway surface of the bearing ring (especially the outer ring 4 among the inner ring 2 and the outer ring 4). Processing is performed.
As a result, it is possible to manufacture the rolling bearing including the bearing ring having the large crack fatigue strength and the dent resistance as described above.

[0036]

EXAMPLES Examples of the present invention will be described below.

(1) The heat-resistant bearing steel M50 of the present invention was prepared as a material to be treated. This M5
The composition of 0 is 0.77% to 0.85% C (carbon), 3.75% to 4.25% Cr (chrome), and 4.0 by mass%.
% -4.5% Mo (molybdenum), 0.5% -1.1%
V (vanadium) and the balance Fe (iron). The shape of the object to be processed has the shape of the outer ring of the needle bearing, and the dimensions are as follows: inner diameter φ18.64 × outer diameter φ24 × width 6.9 (m
m). Also, the needle roller of the other party is φ2 × 6.8.
26 mm (mm) dimensions, inner ring (shaft) outer diameter φ1
The dimensions were 4.64 × width 17.3 (mm). The basic dynamic load rating of the bearing of this structure is 8.6 kN and the basic static load rating is 12.9 kN.

An outer ring having the above-mentioned composition, shape and dimensions was manufactured and subjected to the prescribed quenching and tempering shown in FIG.
With reference to FIG. 3, specifically, the outer ring is 850 ° C.
Was preheated at a temperature of 1100 ° C., heated at a temperature of 1100 ° C. for 5 minutes, and then oil-quenched. After that, it is heated at a temperature of 540 ° C. for 120 minutes to perform a primary quenching, and is held at a temperature of −65 ° C. for 90 minutes to perform a sub-zero treatment.
Secondary tempering was performed by heating at a temperature of ℃ for 120 minutes. Two
After the subsequent tempering, the product subjected to the final polishing / superfinishing was subjected to radical nitriding treatment under the conditions shown in Table 1. Radical nitriding treatment temperature is 500 ° C., tempering temperature is 550
The temperature was set to ℃ or below. Further, as shown in Table 1, the time of performing the above radical nitriding treatment is changed to 3 levels (Sample Nos. 1 to 3),
The thickness of the treated layer was changed.

[0039]

[Table 1]

(2) Comparative product M50 material (sample No. 4) as heat-treated as shown in FIG.
Then, M50 material (Sample No. 5) gas-nitrogenated after the heat treatment shown in FIG. 3 and bearing steel SUJ2 were prepared.
The gas nitrocarburizing of the M50 material was performed under the conditions shown in Table 2.

[0041]

[Table 2]

Under the conditions shown in Table 2, a brittle high hardness compound (nitrogen compound) called a white layer is formed on the very surface layer. Therefore, the M50 material subjected to gas nitrocarburizing has a high hardness, but has a drawback of being easily cracked.

The heat treatment conditions for the bearing steel SUJ2 are as follows: oil quenching from 850 ° C., then 2 at 180 ° C.
It has been tempered for a period of time, and the hardness after tempering is H
It was RC62.

Table 3 shows the surface roughness and roundness of the bearing outer ring before and after radical nitriding.

[0045]

[Table 3]

In Table 3, the sample No. Sample Nos. 1 to 3 are the samples subjected to the radical nitriding described above. No. 4 is a standard treated product of M50 described above, which is not subjected to radical nitriding treatment. From Table 3, sample No. Sample No. The roundness and surface roughness of the radical nitriding products of 1 to 3 hardly changed, and it can be understood from this that the dimensional accuracy is not significantly reduced even if radical nitriding treatment is performed.

4 to 8 show the above sample No. The cross-sectional microstructure of 1-5 is shown. In addition, FIG. 1 and FIG. 2 and FIG. 3, Figure 7 is sample N
o. 4 and FIG. 5 shows the microstructures of the respective cross sections of Sample No. 5 shows the cross-sectional structure of the M50 tuftride product.

From FIGS. 4 to 8, the samples (Sample Nos. 1 to 3) radical-nitrided had Sample Nos. The fragile nitrogen compound layer called the white layer shown in No. 5 did not exist, and only the nitrogen diffusion layer which was black and easily corroded existed. From these, it can be said that it is not necessary to re-grind each part of the rolling bearing that has been radically nitrided.

FIG. 9 shows the change in cross-sectional hardness distribution with nitriding time. The “depth” on the horizontal axis of FIG. 9 indicates the depth from the sample surface, and the “hardness” on the vertical axis indicates the Vickers hardness. From FIG. 9, the sample that was radically nitrided (Sample N
o. In 1-3), as the nitriding treatment time becomes longer,
It can be seen that the surface hardness is increasing.

(3) Indentation formation test Static load 1 from the above outer ring outer diameter portion with an Amsla tester
1.9kN is applied and the depth of indentations formed on the inner and outer rings is measured when the rolling element is directly under the load point (rolling element top) and when the rolling element is in the load direction (rolling element bridge). did. The results are shown in Table 4.

[0051]

[Table 4]

From the results shown in Table 4, it can be seen that the indentation depth of the radical nitride product is very small and the indentation is hard to be formed. Further, the indentation depth tends to decrease as the nitriding time increases, which is because the surface hardness increases as the nitriding time increases. On the other hand, the tufftride product (Sample No. 5) had cracks at the periphery of the indentation. Also, SUJ
In No. 2, the indentation is larger than that of M50 radically nitrided.

In addition, in the item of "surface stress" in Table 4, "-(minus)" is added to the numerical value means that the stress is a compressive stress.

From Table 4, a radical nitriding product having a hardened layer of HV900 or more formed to 30 μm (Sample No. 1)
Has half the indentation depth compared to that without radical nitriding. When the treatment time is lengthened and the hardening depth is increased, the indentation depth becomes shallower. On the other hand, in the case of gas soft nitriding, cracks were generated from the indentation as it was (Sample No. 5 was not polished). This is because a hard and brittle compound layer is generated on the surface, and when additional polishing was performed on this, the indentation depth was about the same as that of the radical nitrided product. Therefore, radical nitriding is a conventional method (gas soft nitriding + finish polishing).
The same surface material as can be achieved without polishing.

(4) Rolling Test A ball bearing 6206 (JIS bearing number) was used to carry out a life test under clean oil lubrication conditions and foreign object mixed oil lubrication conditions. The test results are shown in Table 5 and Table 6.

In this life test, the outer ring of the ball bearing was 6.86.
It was carried out by rotating at a speed of 3000 rpm while applying a radial load of kN. It should be noted that under the clean oil condition of Table 5, the lubrication of the turbine oil VG56 circulation lubrication is used, and under the foreign matter mixed lubrication condition of Table 6, 40 ml of the turbine oil VG5 is used.
High-speed steel powder (particle size 100 μm-180 μ in the oil bath of No. 6)
m) was used at a rate of 0.4 g / l.

[0057]

[Table 5]

[0058]

[Table 6]

From the results shown in Tables 5 and 6, it can be seen that the product of the present invention (Sample Nos. 1 to 3) has a longer life than the untreated product (comparative product) not subjected to radical nitriding. Generally, M50 tends to have a short life under a large load condition or a condition in which foreign matter is mixed. This is because the presence of large carbides causes a stress concentration source. However, the radical-nitrided product does not have a short life even under severe loading conditions and foreign matter mixing conditions. By increasing the hardness of the surface layer, as a result of suppressing the occurrence of surface cracks and plastic deformation of the surface layer,
Although it can be said that the life becomes long, it is considered that the radical nitriding also contributes to the long life because a large compressive stress is generated in the surface layer.

(5) Crack strength The crack strength was examined. As shown in FIG. Cylindrical test piece 21 of φ60 × φ45 × L15 made of each material of 1 to 5 and SUJ2
Is performed by rotating the drive roll 22 at a rotation speed of 8000 revolutions / minute while applying a load (9.8 kN) between the drive roll 22 and the load roll 23, and measuring the life time at that time. It was At this time, lubricating oil was supplied from the supply unit 25 between the drive roll 22 and the test piece 21. The test piece 21 was arranged so that the guide roll 24 was in contact therewith. The crack starting point in this test is the ring inner diameter portion of the cylindrical test piece 21. The results of this ring rotation crack fatigue test are shown in Table 7.

[0061]

[Table 7]

From the results of Table 7, it can be seen that the radical nitriding products (Sample Nos. 1 to 3) have a cracking strength improved to 150% or more of that of the product without radical nitriding treatment (Sample No. 4). On the other hand, the crack strength of the tufftride product (Sample No. 5) is reduced to 50% of that of the untreated product (Sample No. 4). This is because the brittle white layer is likely to become a crack generation source. For tuftride products, if the surface layer is lightly polished,
The strength was improved to a level close to that of radical nitriding products.

As described above, the radical nitriding exhibits a pressure resistance equivalent to that of the conventional (gas soft nitriding + finish polishing), and the rolling life, foreign matter mixing life, and crack fatigue more than (gas soft nitriding + finish polishing). Indicates the lifespan.

Compared to the normal M50 (surface layer hardness HV800, surface stress -400 MPa), the radical nitriding product was treated even for the shortest time (surface layer hardness HV900, surface stress-
Since it is 600 MPa), it is certain that these differences in surface layer hardness and surface stress result in differences in indentation resistance, rolling life, foreign matter life, and crack life. Furthermore, HV9
If the high hardness region of 00 or more and the surface stress of -500 MPa or more (that is, the surface stress is 500 MPa or more in compressive stress) is formed by radical nitriding, the indentation depth is half, and the rolling life is 4
-10 times, foreign material life is more than 20 times, crack fatigue life is 1.
Can be made into a material with long life and high strength of 5 times or more.

In this embodiment, M50 steel was used, but the present invention is not limited to this, and in the present invention, a steel whose hardness does not significantly decrease even at the radical nitridable temperature (300 ° C to 500 ° C) ( For example, high Si steel or carbonitriding steel) can be applied.

The radical nitriding treatment may be applied to the inner ring and rolling elements in addition to the outer ring. The embodiments and examples disclosed this time are to be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and is intended to include meanings equivalent to the claims and all modifications within the scope.

[0067]

As described above, according to the rolling bearing and the method for manufacturing the same of the present invention, by radical nitriding,
It is possible to obtain three effects, that is, improvement of the indentation resistance, improvement of rolling life, and improvement of crack fatigue life and crack fatigue strength.

[Brief description of drawings]

FIG. 1 is a schematic front view showing the structure of a rocker arm according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view taken along the line II-II of FIG.

FIG. 3 is a diagram showing a heat treatment pattern of an object to be processed (M50 material).

4] Sample No. It is a microscope picture which shows the metal structure of the cross section of No. 1.

5] Sample No. It is a microscope picture which shows the metal structure of the cross section of No. 2.

6 is a sample No. It is a microscope picture which shows the metal structure of the cross section of FIG.

7] Sample No. 4 is a micrograph showing the metal structure of the cross section of FIG.

8 is a sample No. 5 is a micrograph showing a metal structure of a cross section of No. 5.

FIG. 9 is a diagram showing a change in cross-sectional hardness distribution depending on the radical nitriding treatment time.

FIG. 10 is a diagram showing a state of a ring rotation crack fatigue test.

[Explanation of symbols]

1 cam follower body, 2 roller shaft (inner ring), 3 needle rollers (rolling body), 4 roller (outer ring), 5 cam follower shaft, 6 cam, 7 adjusting screw, 8 lock nut, 9 protruding rod, 10 spring, 14 roller Support section.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tadahisa Suzuki             Mie Prefecture Kuwana City Oogata Oyumi 3066 N             Inside Thien Co., Ltd. F term (reference) 3J101 AA14 AA24 AA42 AA52 AA62                       BA53 BA54 BA55 BA70 DA02                       FA15 GA21

Claims (6)

[Claims] 1. A rolling bearing having a rolling element and a bearing ring, wherein a nitride layer formed by radical nitriding is formed on at least a raceway surface of the bearing ring. 2. The nitride layer is free of nitrogen compounds,
The rolling bearing according to claim 1, wherein the nitride layer is substantially composed of a nitrogen diffusion layer. 3. The surface hardness of the raceway surface is HV900 or more in Vickers hardness, and the residual stress of the raceway surface is 500 MPa or more in compressive stress.
The rolling bearing according to claim 2. 4. The rolling bearing according to claim 3, wherein the depth of the surface-hardened layer having a Vickers hardness of HV900 or more is 5 μm or more from the raceway surface. 5. The rolling bearing according to claim 1, which is used to rotatably support the roller in a rocker arm having a roller that abuts on a cam. 6. A method of manufacturing a rolling bearing having a rolling element and a bearing ring, wherein at least a raceway surface of the bearing ring comprises:
A method for manufacturing a rolling bearing, which comprises subjecting a mixed gas of ammonia and nitrogen to radical nitriding by glow discharge.