JP2003239979A - Rolling bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rolling bearing provided with a rolling element having long service life while ensuring necessary electric conductivity and made of conductive ceramics. <P>SOLUTION: Volume resistance rate of the rolling element made of conductive ceramics is 10<SP>6</SP>Ω.cm or less, its flexural strength is at least 1000 MPa, and its fracture toughness value is at least 6.2 MPa.m<SP>1/2</SP>. <P>COPYRIGHT: (C)2003,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 used for a spindle motor or the like for rotating a magnetic recording medium in a magnetic recording device such as a hard disk drive or a floppy disk drive.

[0002]

2. Description of the Related Art In a magnetic recording device such as a hard disk drive or a floppy disk drive, a spindle motor that rotates a disk (magnetic recording medium) rotates at high speed, and therefore its bearing has a rotational / acoustic performance and an anti-fretting performance. Rolling elements made of excellent ceramic materials are sometimes used. Here, the usual ceramic material is an insulator, and therefore, the inner and outer rings of the bearing via the rolling elements are electrically insulated. Therefore, the electric charge on the disk rotating with the outer ring has no escape and is accumulated. As a result, there is a problem that the head is electrically attracted by the charged disk and crashes (contacts). Therefore, it is necessary to add an additive to the ceramic material to make the rolling element conductive.

[0003]

However, rolling elements made of conductive ceramics have a problem that the life is shortened as the conductivity is improved. Therefore, it is possible to secure necessary conductivity and long life at the same time. The actual situation was that no specific proposal was made. In view of the above conventional problems, the present invention has a long life while having the necessary conductivity,
An object of the present invention is to provide a rolling bearing provided with rolling elements made of conductive ceramics.

[0004]

The present invention provides a rolling bearing including an inner ring and an outer ring made of metal and a rolling element made of a conductive ceramic, wherein the conductive ceramic has a volume resistivity of 10 ⁶ Ω · cm. Bending strength of at least 1000 MPa and fracture toughness value of at least 6.
It is characterized by satisfying 2 MPa · m ^1/2 (claim 1). In such a rolling bearing, the conductivity required for the rolling element is secured by the volume resistivity of 10 ⁶ Ω · cm or less. Also, a bending strength of at least 1000 MPa,
With a fracture toughness value of 6.2 MPa · m ^1/2 , the rolling element can have the required mechanical strength.

The conductive ceramics may contain silicon nitride, 12 to 20% by weight of silicon carbide as a conductivity imparting material, and 2 to 8% by weight of titanium nitride (claim). Item 2). Here, the above-mentioned weight% is the ratio of the conductive ceramic constituent components to the whole.
By including the conductivity-imparting material in this way, the result is 1
A volume resistivity of 0 ⁶ Ω · cm or less is obtained, and the conductivity required for the rolling elements is secured. Further, by containing a predetermined amount of titanium nitride, the mechanical strength of the rolling element is improved as compared with the case of using silicon carbide alone.

Further, the conductive ceramic in the rolling bearing (claim 2) has a bending strength of at least 100.
0 MPa, fracture toughness value of at least 6.2 MPa · m
It is preferable to satisfy ^1/2 (claim 3). In this case, the rolling element has a required mechanical strength.

[0007]

1 is a sectional view showing a spindle motor using a rolling bearing according to an embodiment of the present invention. In the figure, a stator 1 includes a motor base 11 made of metal, a shaft portion 12 integrally provided in the center thereof, and a stator winding 13. On the other hand, the rotor 2 has a substantially tubular metal hub 21 on which a disc (not shown) is mounted.
And a magnet 22 attached to the hub 21 so as to face the stator winding 13. Two rows of rolling bearings 3 are mounted around the shaft portion 12 in the rotational axis direction of the hub 21, whereby the hub 21 is rotatably supported with respect to the shaft portion 12. As described above, the motor base 11 and the shaft portion 12 of the stator 1 and the hub 21 of the rotor 2 are all made of metal, that is, conductors. The inner ring 31 of the rolling bearing 3 is fixed to the shaft portion 12, and the outer ring 32 rotates together with the hub 21. The inner and outer rings 31, 32 are both made of metal, that is, a conductor, and the rolling elements 33 are made of a conductive ceramic material. Further, the rolling bearing 3 includes a cage 34 and a seal 35.

The above conductive ceramic material is based on silicon nitride Si ₃ N _{4 and} has silicon carbide SiC and titanium nitride TiN added thereto as substances for imparting conductivity. In addition, small amounts of other necessary known additives such as sintering aids are also added. In Table 1, for the samples A to G of the rolling elements 33 made of a ceramic material, the content of the conductivity-imparting material which is the main content, mechanical and electrical characteristics, and the evaluation results of the samples (electrical characteristics and durability)
Indicates. FIG. 2 is a graph showing the relationship between the test time (cumulative time) and the bearing vibration value (indicating the degree of bearing deterioration) for samples A to G.

[0009]

[Table 1]

The three-point bending strength in Table 1 is JI
It is obtained by measuring the three-point bending strength of S, R1601, “Testing method for bending strength of fine ceramics”. The fracture toughness is measured according to JIS R160.
7. I of "Fracture toughness test method for fine ceramics"
According to the F (Indention Fracture) method. However, the formula is J
Not according to IS, but according to the following formula known as Niihara's formula. Fracture toughness value ^{= 0.0114E 0. 4 P 0.} 6 a -0. 7 (C
/ ^{A-1) -0 5} where, ^P:. Load [kgf] d: diagonal length of the Vickers indentation [mm] E: Young's modulus [kgf / ^mm 2] C: crack length from the center point of the Vickers indentation [Mm] a: 1/2 [mm] of diagonal length of Vickers indentation The volume resistivity was in accordance with the volume resistivity measuring method described in JIS, K6911, "General Test Method for Thermosetting Plastics". It was measured by the method.

On the other hand, as a method of evaluating durability, two samples (rolling bearings) were assembled in a spindle motor as shown in FIG. 1, which was placed in a constant temperature bath, and the following test conditions were given. Lubrication condition: 1 mg of oil dropped, grease 15 to 16% Rotation speed: Outer ring 7200 rpm Ambient temperature: 70 ° C Preload: 1.5 kgf (combined with two) A vibration pickup is attached, the output signal is displayed as a bearing vibration value on a vibrometer, and this is read at predetermined intervals. When the bearing vibration value reaches a predetermined level, it can be determined that the bearing has deteriorated and has reached the end of its life.

In Table 1, first, the sample A is Si ₃ N.
_{No. 4} , which does not contain a conductivity-imparting material, is a rolling element made of a normal ceramic material instead of a conductive ceramic material. in this case,
Volume resistivity is infinite, of course electrical characteristics (conductivity)
Is very bad. On the other hand, it has excellent three-point bending strength and fracture toughness, and has excellent durability. That is, in FIG. 2, the bearing vibration value of the sample A does not change even when the test time exceeds 5000 hours. Next, sample B is based on Si ₃ N ₄ and contains 15 wt% of SiC as a conductivity-imparting material. In this case, the volume resistivity is 10
^It is as high as ⁷ Ω · cm, and its conductivity is still insufficient. The three-point bending strength is 980 MPa, which is reasonably good, but the fracture toughness drops to 6.0 MPa · m ^1/2 , and the durability deteriorates a little. That is, in FIG. 2, the bearing vibration value of the sample B increases when the test time exceeds 3000 hours. Next, sample C is based on Si ₃ N ₄ and contains 20% by weight of SiC. in this case,
The volume resistivity is reduced to 1/100 of that of sample B, and the electrical characteristics are improved, but on the contrary, the three-point bending strength is reduced to 900 MPa, resulting in poor durability. That is, in FIG. 2, the bearing vibration value of the sample C starts to increase before the test time reaches 1000 hours.

Evaluation results of the above samples A to C
Et al., Both SiC and SiC have both electrical characteristics and durability.
It is considered difficult to make them. Therefore, TiN
Let it be contained (Samples DG). Sample D is Si_ThreeN_Four
With SiC as the conductivity-imparting material.
It contains 2% by weight and 2% by weight of TiN. this
If the volume resistivity is 10 ⁶Ω · cm as electrical characteristics
Good value, 3-point bending strength of 1100 MPa,
Fracture toughness is 6.5 MPa ・ m^1/2With the highest level
Yes, it has excellent durability. That is, in FIG.
The bearing vibration value of sample D exceeds 5000 hours for the test time.
But it doesn't change.

Sample E is Si_ThreeN_FourBased on
20% by weight of SiC and TiN as a conductivity-imparting material
It contains 2% by weight. In this case, the volume resistivity is
10 ^FourIt is a value with excellent electrical characteristics in Ω · cm.
In addition, the three-point bending strength is 1050 MPa, and the fracture toughness is
6.5 MPa ・ m^1/2With high and excellent durability
It That is, in FIG. 2, the bearing vibration value of the sample E is
It does not change even when the test time exceeds 5000 hours. Sample F
Is Si_ThreeN_FourBased on
And contained 20% by weight of SiC and 8% by weight of TiN.
Of. In this case, the volume resistivity is 2 × 10^ThreeΩ · cm
It is an excellent level value in terms of electrical characteristics and has 3 points.
Bending strength is 1000MPa, fracture toughness is 6.2MPa.
m^1/2Although it is slightly lower than Sample E, the durability is
That's enough. That is, in FIG. 2, the bearing of the sample F
The vibration value does not change even if the test time exceeds 5000 hours.
Yes.

Finally, sample G is based on Si ₃ N ₄ and has 20 wt% of SiC as a conductivity-imparting material and T
It contains 15% by weight of iN. In this case, the volume resistivity is 2 Ω · cm, which is a value at a very excellent level as electric characteristics, while the three-point bending strength is 950 MPa,
The fracture toughness decreases to 5.8 MPa · m ^1/2, and the durability becomes insufficient. That is, in FIG. 2, the bearing vibration value of the sample G increases before the test time reaches 1000 hours.

From the characteristics of the above-mentioned samples E to G, when the content of TiN is increased, the volume resistivity is decreased and the electric characteristics are improved, but the three-point bending strength and the fracture toughness are decreased, and the mechanical strength is decreased. I understand that On the other hand, sample C and sample E or F
By comparing with, depending on the content of TiN,
It can be seen that the three-point bending strength and fracture toughness are improved as compared with the case of using SiC alone (Sample C).

From the above results, as the electrical characteristics, the samples C to G are suitable, and from the viewpoint of durability, the samples A and D to F are suitable. Therefore, the samples having both the electrical characteristics and the durability are DF. From this result, it was found that the preferable content of SiC is 12 to 20% by weight, and the preferable content of TiN is 2 to 8% by weight. Also,
On the contrary, considering the characteristics of these samples D to F, the volume resistivity is 10 ⁶ Ω · cm or less, the three-point bending strength is at least 1000 MPa, and the fracture toughness value is at least 6.
It can be considered that satisfying 2 MPa · m ^1/2 is a condition for achieving both electrical characteristics and durability.

In the above example, S is used as the wire-conductivity imparting material.
An example in which iC and TiN are added has been shown, but the conductivity-imparting material is not limited to these two types. In the sintering of silicon nitride, it is known that even if TiO ₂ is added, it is crystallized into TiN by a chemical reaction at the time of sintering. Therefore, not only TiN alone but also titanium dioxide TiO ₂ is used ( wt% of TiO ₂ + TiN) may be used so that 2 to 8. In addition, it is generally known that the conductivity-imparting material has better conductivity when the average particle size is smaller even if the content is the same. Therefore, the industrially available average particle size is preferably SiC 0.3 μm or less, TiO ₂ 0.5 μm or less, and TiN 1 μm or less.

In the above embodiment, the rolling bearing having the inner and outer rings made of steel has been described. However, the conductive ceramics shown in the above embodiment are used in other applications in which both electrical characteristics and durability are required. It is also applicable to.

[0020]

The present invention constructed as described above has the following effects. According to the rolling bearing of claim 1, 10 ⁶
The volume resistivity of Ω · cm or less ensures the conductivity required for the rolling element, and the bending strength of at least 1000 MPa and the fracture toughness value of 6.2 MPa · m ^{1/2 make} the machine necessary for the rolling element. Since a desired strength can be obtained, a long life can be secured. Therefore, it is possible to provide a rolling bearing having a rolling element made of a conductive ceramic, which has a required conductivity and a long life.

According to the rolling bearing of claim 2, as a result, a volume resistivity of 10 ⁶ Ω · cm or less is obtained, the conductivity required for the rolling element is secured, and a predetermined amount of titanium nitride is contained. As a result, the mechanical strength of the rolling element is improved as compared with the case of using silicon carbide alone, so that a long life can be secured. Therefore, it is possible to provide a rolling bearing having a rolling element made of a conductive ceramic, which has a required conductivity and a long life.

According to the rolling bearing of the third aspect, the required mechanical strength can be obtained, so that the rolling element can have a long life.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a spindle motor using a rolling bearing according to an embodiment of the present invention.

FIG. 2 Sample A of rolling element made of conductive ceramics
9 is a graph showing a relationship between a test time (cumulative time) and a bearing vibration value (indicating the degree of deterioration of the bearing) for G.

[Explanation of symbols]

3 Rolling bearing 31 inner ring 32 outer ring 33 rolling elements

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tomohiro Haruta             3-5-8 Minamisenba, Chuo-ku, Osaka Koyo             Within Seiko Co., Ltd. (72) Inventor Kazutoshi Horimoto             3-5-8 Minamisenba, Chuo-ku, Osaka Koyo             Within Seiko Co., Ltd. F term (reference) 3J101 AA02 AA62 BA10 EA44 EA72                       FA31 FA35 GA53                 5H605 BB05 BB10 CC04 EB01 EB04                       EB10 FF10 FF13 GG21

Claims (3)

[Claims] 1. A rolling bearing comprising an inner ring and an outer ring made of metal and a rolling element made of a conductive ceramic, wherein the conductive ceramic has a volume resistivity of 10 ⁶ Ω · cm.
And a flexural strength of at least 1000 MPa,
A rolling bearing having a fracture toughness value of at least 6.2 MPa · m ^1/2 . 2. A rolling bearing comprising an inner ring and an outer ring made of metal and a rolling element made of a conductive ceramic, wherein the conductive ceramic is silicon nitride and 12 to 20% by weight of carbonized as a conductivity imparting material. Silicon and 2 to 8% by weight
A rolling bearing characterized by containing titanium nitride. 3. The conductive ceramics has a bending strength of at least 1000 MPa and a fracture toughness value of at least 6.2.
The rolling bearing according to claim 2, which satisfies MPa · m ^1/2 .