JPH09177789A - Ball for ball bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent deterioration with the lapse of time of the precision of the front surface of a ball, so as to improve load resistance and impact resistance, by sequentially performing surface hardening and tempering to a steel in which the remaining austenite amount is the specified value or less. SOLUTION: When a ball for a ball bearing is manufactured, tempering is performed after surface hardening is applied to a steel ball 8 in which the remaining austenite amount is previously set to 6vol.% by thermal treatment. That is, impression resistance on a rolling surface is improved by restraining the remaining austenite amount, and also the front surface precision of the rolling surface can be prevented from being deteriorated with the lapse of time. Since the remaining austenite amount is small, deterioration of sound characteristics to be generated with decomposition of the remaining austenite, and deterioration of sound characteristics to be generated caused by deterioration of the surface precision are decreased. Remaining stress to be generated on the surface hardened layer of the ball, to be generated with the surface hardening is eliminated by performing tempering after surface hardening.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION A ball bearing ball according to the present invention is incorporated in, for example, a hard disk drive (HDD), a video tape recorder (VTR), a digital audio tape recorder (DAT) or the like, and has a spindle rotating at high speed. The present invention relates to a ball that constitutes a ball bearing to be supported.

[0002]

2. Description of the Related Art HD incorporated in a computer, for example
A spindle motor as shown in FIG. 1 is incorporated in D to rotate the hard disk drive spindle 1 at high speed. A pair of ball bearings 3, 3 are provided between the outer peripheral surface of the spindle 1 and the inner peripheral surface of the housing 2 to rotatably support the spindle 1 inside the housing 2. Each of the ball bearings 3, 3 has a steel inner ring 5, 5 having inner ring raceways 4, 4 on its outer peripheral surface, a steel outer ring 7, 7 having outer ring raceways 6, 6 on its inner peripheral surface, and the above inner ring. Between the tracks 4 and 4 and the outer ring tracks 6 and 6, a plurality of them,
It is composed of balls 8 made of steel that are provided so as to be rollable. Preload is applied to each ball 8 and 8 so that the spindle 1
No rattling occurs when the is rotated. The inner races 4, 4 may be formed directly on the outer peripheral surface of the spindle 1 and the inner races 5, 5 may be omitted.

In addition to the structure shown in FIG. 1 described above, HDD spindle motors having structures shown in FIGS. 2 to 3 are also known. Among them, the one shown in FIG. 2 has an outer ring 7a having double rows of outer ring raceways 6, 6 on the inner peripheral surface and an integrated hub, and also has inner ring raceways 4, 4
Are formed on the outer peripheral surface of the spindle 1 and the outer peripheral surface of the inner ring 5 fitted onto the spindle 1. Further, in the structure shown in FIG. 3, double rows of inner ring raceways 4, 4 are formed on the outer peripheral surface of the spindle 1 and double rows of outer ring raceways 6, 6 are formed on the inner peripheral surface of the outer ring 7b.

Conventionally, the balls 8, 8 constituting the ball bearings 3, 3 as described above have been manufactured by the following steps. That is, first,
Ordinary quenching (820-8
After 60 ° C.), a tempering process is performed at 120 to 180 ° C. Next, the balls are subjected to rough grinding and then subjected to a surface hardening treatment by a method described in Japanese Patent Publication No. 1-1812, for example. Further, after the surface hardening treatment, a second tempering treatment is performed under predetermined conditions in order to prevent deterioration of the surface shape of the ball with time, as described in, for example, Japanese Patent Laid-Open No. 6-264929. To do.
Then, after the second tempering treatment, the surface is subjected to finish grinding to complete a ball bearing ball.

[0005]

On the other hand, HDDs and VTRs
In the case of a high-precision small ball bearing used for, that is, a ball bearing whose dimensional accuracy or rotation accuracy is JIS Class 5 or higher and low torque is required, the required acoustic and noise performance is severe. In such a high-precision small ball bearing, the load defined by the basic static load rating C _O (maximum contact surface pressure, 4000
There was a problem that a very small permanent deformation was generated on the rolling surface of the ball due to a load much smaller than MPa) and an impact load, and this permanent deformation caused acoustic deterioration (noise increase).

As a high precision small ball bearing as described above, generally, the diameter D _W (FIG. 1) of the plurality of balls 8, 8 incorporated between the inner ring raceway and the outer ring raceway is 3 mm or less, and The ball bearings 3, 3 having a pitch circle diameter D _PW (FIG. 1) in which a plurality of these balls 8, 8 are arranged are 11 mm or less are used.
However, with the recent miniaturization of HDDs, VTRs, and the like, smaller ball bearings 3 and 3 incorporated therein are being used, and the small ball bearings 3 and 3 described above are used. The acoustic deterioration caused by this is a big problem.

The ball bearing ball of the present invention was invented in view of the above-mentioned circumstances, and prevents deterioration of the surface accuracy of the ball over time, and also provides load resistance and impact resistance (pressure resistance mark). By improving impact resistance, it is possible to prevent harmful permanent deformation of the ball due to impact or the like.

[0008]

The balls for ball bearings of the present invention are
A steel having a retained austenite amount of 6% by volume or less is subjected to a surface hardening treatment and a tempering treatment in sequence. Further, preferably, the surface shape accuracy is less than 3 μm Rms.

When manufacturing the ball bearing ball of the present invention described above, the residual austenite amount is 6% by volume by heat treatment in advance.
The steel balls described below are subjected to a surface hardening treatment and then a tempering treatment.

Further, the ball bearing ball of the present invention can be used to form the following ball bearing. That is, this ball bearing comprises an inner ring or shaft having an inner ring raceway on the outer peripheral surface, an outer ring having an outer ring raceway on the inner peripheral surface, and a plurality of rollers rotatably provided between the inner ring raceway and the outer ring raceway. The ball bearing ball of the invention is provided.
In this case, the ball bearing ball of the present invention has a diameter of 3 mm or less, and a pitch circle diameter in which a plurality of these balls are arranged is 11 mm or less. Further, in this ball bearing, the amount of retained austenite in the steel forming at least one of the inner ring raceway and the outer ring raceway is set to 6% by volume or less.

[0011]

In the case of the ball bearing having the ball bearing ball of the present invention constructed as described above, harmful permanent deformation is unlikely to occur on the raceway surface due to the aforementioned load or impact load. That is, since austenite has a lower yield stress than martensite, the amount of retained austenite is 8 to 14% by volume.
In the case of a relatively large number of conventional balls, harmful permanent deformation is caused by a small load or the like. On the other hand, in the case of the ball of the present invention in which the amount of retained austenite is as small as 6% by volume or less, the indentation resistance of the rolling surface is improved (yield stress is increased), and depending on the above small load, it may be harmful. Permanent deformation is less likely to occur.

Further, in the case of the ball of the present invention, by suppressing the amount of retained austenite to be small, in addition to the effect of improving the scratch resistance of the rolling surface, the surface accuracy of the rolling surface deteriorates with time. It can also be prevented. That is, when the amount of retained austenite existing in the rolling surface portion is large, the retained austenite is decomposed by rolling stress repeatedly applied to the raceway surface of the ball bearing as the ball bearing is used. The surface accuracy of the rolling surface deteriorates with the disassembly. On the other hand, in the case of the present invention, since the amount of retained austenite is smaller than that of the conventional balls, deterioration of acoustic characteristics due to decomposition of retained austenite, and deterioration of acoustic characteristics due to such deterioration of surface accuracy Less. In particular, by suppressing the amount of retained austenite to be not more than 2% by volume, it is possible to almost eliminate the deterioration of acoustic characteristics due to the decomposition of retained austenite as described above.

Further, the amount of retained austenite is determined by increasing the tempering temperature or repeating the tempering.
It can be reduced by devising the tempering process. By the tempering treatment devised in this way, it is possible to prevent the deterioration of the acoustic characteristics due to the decomposition of the retained austenite as described above and stabilize the martensite of the matrix. Therefore, it is possible to prevent the deterioration of the surface accuracy due to the change of martensite with time. Therefore, the deterioration of the acoustic characteristics can be reduced as compared with the case where the deep-chill treatment and the normal tempering are performed.

In particular, in the case of the ball bearing ball of the present invention, by performing the tempering treatment after the surface hardening treatment, the residual stress generated in the surface hardened layer of the ball accompanying the surface hardening treatment is eliminated. As a result, the increase in the vibration acceleration of the ball component that occurs under a comparatively small impact load, as seen in conventional ball bearings incorporating balls, hardly occurs, and the surface accuracy deteriorates over time. There is no. Therefore, in the case of a ball bearing incorporating the ball of the present invention, impact resistance is improved and acoustic characteristics are not deteriorated with time.

[0015]

EXAMPLES Next, in order to confirm the effects of the present invention, an experiment conducted by the present inventor will be described. The following table 1
As shown in FIG. 4, it is a comparative product which is out of the scope of the present invention.
Three types of balls (a to d) and seven types of balls (holes), which are examples of the present invention (product of the present invention), were prepared. As shown in Table 1, SUJ 2 (J
IS G 4805), SUS 440C (JIS G
4303) and 13Cr stainless steel. Each of these three types of steel has a predetermined shape (spherical shape)
After being processed into a sheet, it was heat-treated under the conditions shown in Table 1. That is, each sample was quenched at the temperature shown in Table 1 and then tempered (primary). Further, some of the samples were subjected to deep cooling treatment (subzero) between the quenching treatment and the primary tempering treatment. Next, each of these balls was subjected to rough grinding and then subjected to a surface hardening treatment. This surface hardening treatment was carried out by repeating the work of colliding the balls with the shielding plate by the jet air as described in JP-B-1-12812. Then, six kinds of samples belonging to the present invention (invention products 1 to 4 and 6 to 7) and 1 belonging to comparative products
A second tempering process (secondary) was performed on the sample of the type (Comparative product 2). Then, for these seven types of samples, after the secondary tempering treatment, lap finishing for adjusting the shape accuracy of the surface was performed to complete the ball bearing balls. The remaining one type of the present invention product and the three types of comparative products were subjected to lapping after the surface hardening treatment, and completed as balls.

[0016]

[Table 1]

For example, the comparative product 1 shown in column A of Table 1 above.
7A is the same as the step shown in the flowchart of FIG. 7A, the comparative product 2 shown in the column B is the same as the step of the flowchart shown in FIG. The product 6 of the present invention shown in the column (n) was manufactured by the steps shown in the flowchart of FIG. (C). As is clear from comparison between the comparative product of Table 1 and the product of the present invention, in the case of the present invention,
By increasing the temperature of the primary tempering treatment or by performing the sub-zero treatment, the amount of retained austenite in the steel forming the balls is reduced.

11 kinds of balls made as described above are
A ball bearing was assembled by incorporating it between the inner ring raceway on the outer peripheral surface of the inner ring and the outer raceway on the inner peripheral surface of the outer ring. In addition, both the inner ring and the outer ring,
It is made of SUJ 2 and is deep-cooled at -80 ° C and then tempered at 240 ° C, and the amount of retained austenite is 0% by volume. Then, this ball bearing was incorporated into a spindle motor as shown in FIG. 1 under a preload condition and dropped together with this spindle motor to apply an impact load. As impact load, 5, 10, 15, 20, 25,
Seven types of 30 and 35 (kgf) were added, and the degree of deterioration of the acoustic characteristics of the spindle motor (the increase in the ball component of vibration acceleration) was measured before and after the impact load was applied.
FIG. 4 shows the results of this test. Incidentally, this test was not conducted for Comparative product 4. Also, the letters I to I described in FIG. 4 and FIGS. 5 to 6 to be described later correspond to the letters I to I in Table 1 above, and I to D are comparative products 1 to 4, respectively. Each of the present invention products 1 to 7 is represented.

FIG. 5 shows changes in surface accuracy when the balls of the present invention product and the comparative product were kept at a constant temperature of 80 ° C.
Incidentally, the comparative product 4 indicated by reference numeral D in FIG. 5 is a ball that has been subjected to the same heat treatment as the comparative product 1 indicated by reference numeral a, and the change in the surface accuracy of the surface shape accuracy of which is 3 μm Rms was measured. It is a thing. This test was not conducted on the product 7 of the present invention.

FIG. 6 shows the results of measurement of changes in the Anderon value with time accompanying the rotation test. In order to carry out this rotation test, first, balls of the product of the present invention and a comparative product were assembled between the inner ring raceway of the inner ring outer peripheral surface and the outer ring raceway of the outer ring inner peripheral surface to form a ball bearing. Both the inner and outer rings are SUJ
It was manufactured by No. 2 and was deep-chilled at -80 ° C and then tempered at 240 ° C, and the amount of retained austenite was 0% by volume. Ten types of ball bearings obtained in this way, which differed only in the balls, were incorporated into a spindle motor as shown in FIG. 1 in a preloaded state. Then, with respect to each spindle motor, changes in the Anderon value with time were measured.
The comparative product 4 indicated by reference numeral D in FIG. 6 is a ball bearing that has been subjected to the same heat treatment as that of the comparative product 1 also indicated by a and has a surface shape accuracy of 3 μm Rms. It shows the change in value. The product of the present invention 7
I didn't do this test.

The following can be understood from FIGS. 4 to 6 showing the results of these series of tests. First, referring to FIG. 4, the conventional product (comparative product 1
~ 3) is that the ball component of the vibration acceleration starts to increase with an impact load of about 10 kgf, while the amount of retained austenite in the ball is set to 6% by volume or less, so that the ball with the vibration acceleration when the impact load is applied. Impact load is 20kg when the composition starts rising
I know that it becomes f. In particular, if the amount of retained austenite is set to 0% by volume, the impact load at which the ball component of the vibration acceleration starts to increase when an impact load is applied can be set to 25 kgf.

Next, it can be seen from FIG. 5 that the ball subjected to the tempering treatment after the surface hardening treatment has a small change in surface accuracy with time. However, if the initial surface shape accuracy is 3 μm Rms as in the case of the comparative product 4, the surface accuracy of the ball does not clearly change with time. In other words, the residual austenite amount is set to 6% by volume or less to prevent deterioration of the surface accuracy over time. In order to obtain the effect of the present invention, the shape accuracy of the initial surface is kept below 3 μmRms. There is a need.

Further, it can be seen from FIG. 6 that a ball bearing incorporating a ball that has been subjected to a tempering treatment after a surface hardening treatment has little deterioration in acoustic characteristics over time. Even in this case, if the initial surface shape accuracy is 3 μm Rms as in Comparative product 4, the change with time does not appear clearly. This experiment also shows that in order to obtain the effect of the present invention sufficiently, it is necessary to keep the shape accuracy of the initial surface to less than 3 μmRms.

Thus, in order to fully exert the effects of the present invention, it is desirable that the shape accuracy of the surface of the ball be less than 3 μm Rms. This is because the surface shape accuracy is poor (3μ
In the case of a ball (mRms or more), the surface accuracy does not deteriorate with time, but the original surface accuracy and acoustic characteristics are poor, and the effect of the present invention cannot be sufficiently obtained.

From the above experimental results, it is possible to obtain high impact resistance and to improve the surface accuracy with time by setting the amount of retained austenite in the ball to 6% by volume or less and further performing a predetermined tempering treatment after the surface hardening treatment. It turns out that you can create a ball that changes less dynamically. In particular, the ball of the present invention is made of SUJ 2,
After deep-cooling treatment at 0 ° C, tempering is performed at 240 ° C, and by incorporating it into a bearing ring with a retained austenite content of 0% by volume, it has high impact resistance, excellent burn-in characteristics, and deterioration of acoustic characteristics over time. Ball bearings with less

[0026]

Since the ball bearing ball of the present invention is constructed and operates as described above, the ball bearing ball formed by using the ball bearing ball of the present invention can be incorporated into an HDD, VTR, or other acoustic performance. It is possible to improve the performance of these HDDs, VTRs and the like.

[Brief description of the drawings]

FIG. 1 is an HDD incorporating a ball bearing which is the subject of the present invention.
Sectional view showing a first example of a spindle motor for a vehicle.

FIG. 2 is a sectional view showing the second example.

FIG. 3 is a sectional view showing a third example.

FIG. 4 is a diagram showing the relationship between the magnitude of impact load and the degree of deterioration of acoustic characteristics with respect to the amount of retained austenite of a ball.

FIG. 5 is a diagram showing a state in which the surface accuracy of the bearing ring changes with time.

FIG. 6 also shows a state in which the Anderon value changes with time, (A) shows the measured value of MEDIUM BAND, and (B) shows
Indicates the measured values of HIGH BAND.

FIG. 7 is a flowchart showing four examples of ball surface treatment steps.

[Explanation of symbols]

 1 spindle 2 housing 3 ball bearing 4 inner ring raceway 5 inner ring 6 outer ring raceway 7, 7a, 7b outer ring 8 ball

Claims (1)

[Claims] 1. A ball bearing ball formed by sequentially subjecting steel having a retained austenite amount of 6% by volume or less to a surface hardening treatment and a tempering treatment.