JP2002174228A - Electrolytic corrosion prevention structure for rolling bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent electrolytic corrosion of a rolling bearing without generating points at issue such as generation of dust, an increase in cost, an increase in noise and a temperature rise. SOLUTION: In this structure in which the rolling bearing B, a housing 13 mounted on an outer ring 1 of the rolling bearing B and a rotary shaft 16 fitted into an inner ring 2 of the rolling bearing B are provided and the rolling bearing B rotatably supports the rotary shaft 16 on the housing 13, an insulating layer 5 is interposed between the outer ring 1 and the housing 13 and the insulating layer 5 is made of resin composition containing syndiotactic polystyrene resin and a non-conductive filler.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure for preventing electrolytic corrosion of a rolling bearing, and more particularly to a structure for preventing electrolytic corrosion of a rolling bearing used in a fan motor whose speed is controlled by an inverter.

[0002]

2. Description of the Related Art Conventionally, a rolling bearing (hereinafter, also simply referred to as a bearing) incorporated in a fan motor is mounted by fitting an outer ring to a housing and an inner ring to a rotating shaft of the motor by a clearance fit or an interference fit. Was. Needless to say, in the case of an interference fit, in the case of a clearance fit, a preload is applied to the bearing by pressing the side surface of the inner ring or the outer ring through a spacer or the like for the purpose of increasing the rigidity of the bearing and preventing vibration. Can be hung. Therefore, the outer race and the housing, and the inner race and the rotating shaft are electrically connected to each other.

[0003] On the other hand, the number of fan motors whose air volume is controlled by changing the number of revolutions by an inverter is increasing. In this case, setting the carrier frequency of the inverter higher can reduce the noise of the fan motor due to switching, and the carrier frequency can be set higher by improving the performance of semiconductor elements and circuit technology. In addition, the carrier frequency of the inverter has been set to a high value.

Accordingly, the shaft voltage generated in the fan motor driven by the inverter increases, so that a potential difference occurs between the rotating shaft and the housing, and furthermore, between the inner and outer rings of the bearing. Then, an electric current flows into the bearing via the rolling elements, and as a result, there is a possibility that electrolytic corrosion occurs on the raceway surfaces of the inner and outer rings and the rolling surfaces of the rolling elements. As described above, in the fan motor driven by the inverter, the carrier frequency of the inverter is set to be high, so that the possibility of electric corrosion occurring in the rolling bearings incorporated in the fan motor is increasing. I have.

Conventionally, the following countermeasures have been mainly taken when there is a possibility that electric erosion may occur in a fan motor driven by an inverter. First, as a first method, when a brush can be installed, the brush is brought into contact with the rotating shaft to maintain an equipotential between the rotating shaft and the housing, so that a current flows in the bearing. There are ways to prevent it.

Next, as a second method, there is a method in which a conductive grease is sealed in a bearing to maintain an equipotential between an inner ring and an outer ring of the bearing and to prevent a current from flowing in the bearing. . Then, as a third method, grease having a high base oil viscosity is sealed in the bearing, the thickness of the oil film formed between the outer ring and the rolling element, and the thickness of the oil film formed between the inner ring and the rolling element. By increasing the thickness of each oil film,
There is a method of electrically insulating the inner and outer rings.

[0007]

However, each of these conventional countermeasures for preventing electrolytic corrosion has the following problems. First, a first method (a method of installing a brush) will be described. Since one end of the rotating shaft of the fan motor is usually housed in the housing, there is no space for installing the brush. Further, since a fan made of an insulating material such as a synthetic resin is attached to the other end of the rotating shaft, it is often difficult to bring the brush into contact with the rotating shaft. Therefore, it is often impossible to install a brush on a fan motor as a practical matter.

Further, even if the brush can be installed, since the abrasion powder is generated from the brush, there is a problem that the abrasion powder is released as dust from the fan motor into the air. This is a fatal defect when the fan motor provided with the brush is used, for example, in a clean room. As described above, when the brush is installed in the fan motor, there is a problem that the use range of the fan motor is limited.

Next, a second method (a method of sealing conductive grease in a bearing) will be described. Since the grease contains a good conductor such as carbon particles, the rotational noise of the bearing has to be larger than that of ordinary grease. Further, when such expensive special grease is used, there is also a problem that the cost of the bearing is increased.

Next, a third method (a method of sealing grease having a high base oil viscosity in a bearing) will be described. If the base oil viscosity of the grease is high, the bearing torque increases and the temperature tends to increase. Further, if the current passing between the inner and outer rings of the bearing is an alternating current having a high frequency, there is a problem that the current may be conducted in a gap having a thickness of about the oil film thickness. Further, since the formation state of the oil film fluctuates due to the deterioration of the grease with time or the invasion of foreign matter, the conductive state and the insulated state may alternately occur, and electrolytic corrosion may occur. .

As described above, the conventional measures for preventing electrolytic corrosion include:
There are various problems such as generation of dust, increase in cost, increase in noise, increase in temperature, incomplete effect of preventing electrolytic corrosion, and the like, and it cannot be said to be a complete measure. Therefore, the present invention solves such problems of the prior art and generates dust,
An object of the present invention is to provide an anti-corrosion structure for a rolling bearing which does not cause problems such as an increase in cost, an increase in noise, and an increase in temperature.

[0012]

In order to solve the above problems, the present invention has the following arrangement. That is, the anti-corrosion structure of a rolling bearing of the present invention includes a rolling bearing, a housing attached to an outer ring of the rolling bearing, and a shaft fitted to an inner ring of the rolling bearing, wherein the rolling is performed. In a structure in which the bearing rotatably supports the shaft in the housing, an insulating layer is interposed between at least one of the outer ring and the housing and between the inner ring and the shaft, and the insulating layer is It is characterized by comprising a resin composition containing a syndiotactic polystyrene resin and a non-conductive filler.

With such a configuration, the rolling bearing and the housing and the shaft are insulated by the insulating layer. Then, since a potential difference hardly occurs between the outer ring and the inner ring, the current flowing between the outer ring and the inner ring can be minimized, and the rolling bearing (the raceway surface of the inner and outer rings) can be suppressed. Or the rolling surface of the rolling element) can be prevented from generating electrolytic corrosion. In that case, dust generation, cost increase,
Problems such as noise rise and temperature rise do not occur.

In order to improve the insulating properties of the insulating layer, a resin having a low dielectric constant is optimal as the resin used in the resin composition constituting the insulating layer. Syndiotactic polystyrene resin has a dielectric constant of 1
Since the frequency is very low at 2.6 at MHz, the insulating effect can be sufficiently expected. In addition, since the syndiotactic polystyrene resin has a small water absorption, there is little possibility that the insulating property is reduced by water absorption.

Further, considering the working environment of the rolling bearing, since a certain level of heat resistance and oil resistance are required, a syndiotactic polystyrene resin satisfying both properties is optimal. As the non-conductive filler, a non-conductive reinforcing fiber material such as glass fiber is preferably used. It is preferable to use a non-conductive reinforcing fiber material because the mechanical properties (creep resistance and the like) of the insulating layer can be improved.

The content of the non-conductive reinforcing fiber material in the resin composition is preferably from 10 to 50% by weight. If it is less than 10% by weight, the effect of improving creep resistance and strength is small. On the other hand, if it exceeds 50% by weight, the formability of the insulating layer will be poor. That is, the melt viscosity of the resin composition becomes too high and the moldability decreases, and when the insulating layer is formed by the injection molding method, the strength of a portion (weld) where the molten resin meets is reduced. Not preferred.

When it is desired to impart thermal conductivity to the insulating layer, a filler having a thermal conductivity of 10 W / m · K or more and a specific resistance of 10 ¹⁰ Ω · cm or more (hereinafter referred to as “heat conductive material”) is used. Described below) can be used in combination with the non-conductive reinforcing fiber material. Specifically, alumina can be exemplified. If the insulating layer is made of a resin composition containing such a thermally conductive filler, it is possible to promote the heat generated in the rolling bearing to be radiated to the outside of the housing or the like, A reduction in bearing life can be prevented.

In this case, the content of the non-conductive reinforcing fiber material in the resin composition is 10 to 40% by weight, and the content of the thermally conductive filler in the resin composition is 20 to 50% by weight. %, And the sum of the two is preferably 70% by weight or less. When the amount of the non-conductive reinforcing fiber material is less than 10% by weight, the effect of improving the creep resistance and strength is too small even in consideration of the presence of the thermally conductive filler used in combination. On the other hand, when the content exceeds 40% by weight, the formability of the insulating layer is deteriorated due to the influence of the thermally conductive filler used in combination.

On the other hand, the heat conductive filler is 20% by weight.
If it is less than 50%, the effect of improving the thermal conductivity of the insulating layer is small, and if it exceeds 50% by weight, the heat conductive filler has no reinforcing effect, so that the strength is reduced. Further, when the total of both exceeds 70% by weight, the resin content becomes too small, and the formability of the insulating layer deteriorates (the strength of the weld portion is insufficient).

In addition, as long as the insulating properties, mechanical properties (creep resistance and the like), and moldability of the insulating layer are not impaired, other fillers commonly used in ordinary resin compositions may be used, if desired. It may be used in combination with the non-conductive filler. Examples of the filler used include silica particles,
Aluminum hydroxide particles and the like.

[0021]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a rolling bearing according to an embodiment of the present invention; FIG. 1 is a partial sectional view showing the structure of a ball bearing B covered with an insulating layer, and FIG. 2 is a longitudinal sectional view showing the structure of a fan driving electric motor 12 incorporating the ball bearing B of FIG. .

The ball bearing B shown in FIG. 1 has an outer ring 1, an inner ring 2,
A plurality of balls 3 rotatably arranged between an outer ring 1 and an inner ring 2 and a retainer 4 for holding the balls 3 between the two wheels 1 and 2;
And Then, of the outer surface of the outer ring 1, a fitting surface with a housing 13 described later, that is, a bearing outer diameter surface 1
a and one side surface 1 b are covered with an insulating layer 5. That is, the shape of the insulating layer 5 is cup-shaped as a whole, and includes a cylindrical portion 5a and a bottom plate portion 5b having a hole at the center.
(Flat portion). The cylindrical portion 5a covers the bearing outer diameter surface 1a, and the bottom plate portion 5b covers the side surface 1b. Note that one side surface of the inner ring 2 is exposed from the hole and is not covered with the insulating layer 5.

The insulating layer 5 is composed of 90 to 50% by weight of syndiotactic polystyrene resin and 10 to 10% of non-conductive reinforcing fiber material (for example, glass fiber) which is a non-conductive filler.
50% by weight.
However, when the ball bearing B is used for an application that generates an extremely large amount of heat, if necessary, a syndiotactic polystyrene resin, a nonconductive reinforcing fiber material, and a heat conductive material such as alumina may be used. The insulating layer 5 may be composed of a resin composition comprising a conductive filler (which is also non-conductive).

The method of covering the outer surface of the outer ring 1 of the ball bearing B with the insulating layer 5 is not particularly limited, but may be a method of directly forming the insulating layer 5 on the outer surface of the outer ring 1 by injection molding or a method of separately manufacturing. The method of press-fitting the ball bearing B into the cup-shaped insulating layer 5 is preferable. Further, as in the above method, a ball bearing B in which the outer surface of the outer ring 1 is covered with the insulating layer 5 in advance is prepared.
It may be incorporated in an electric motor for driving a fan or the like.
A method of sequentially incorporating the ball bearings without the insulating layer 5 may be adopted.

In the present embodiment, the outer ring 1 has its outer surface fitted with a housing 13 to be described later, that is, the bearing outer diameter surface 1a and one side surface 1b covered by the insulating layer 5. The outer ring of the inner ring 2 may be covered with the insulating layer 5 on the fitting surface with the motor rotating shaft 16 described later, that is, the inner diameter surface of the bearing and one side surface. Further, both the outer surface of the outer race 1 and the fitting surface with the housing 13 to be described later, and the outer surface of the inner race 2 and the fitting surface with the motor rotation shaft 16 described later may be covered with the insulating layer 5.

Next, an electric motor 12 for driving a fan in which two ball bearings B of FIG. 1 are incorporated in a pair will be described with reference to FIG. The fan driving electric motor 12 includes a substantially cylindrical housing 13, a rotating shaft 16 passing through the center of the housing 13, and two ball bearings B, B for rotatably supporting the rotating shaft 16 on the housing 13. It is configured.

A cup-shaped holding step 14 and a holding recess 15 are formed at both ends of the housing 13, and ball bearings B, B are fitted inside the holding step 14 and the holding recess 15. Ball bearing B,
A rotating shaft 16 is fitted to the inner ring 2 of B, and the rotating shaft 16 passes through the center of the housing 13. And the rotating shaft 16
Project out of the housing 13 from a hole provided in the center of the holding step portion 14.

The housing body 13a of the housing 13
A stator 18 is fixed inside the (cylindrical portion), and a driving motor is formed so as to face the rotor 17 at the center of the rotating shaft 16 via a gap, and a driving motor is formed by the driving motor. Are driven to rotate. Reference numeral 13b denotes a front cover of the housing, and reference numeral 13c denotes a rear cover of the housing.

In such an electric motor 12 for driving a fan, the outer rings 1, 1 of the ball bearings B, B and the housing 13
The above-mentioned insulating layer 5 made of a resin composition composed of a syndiotactic polystyrene resin and a non-conductive reinforcing fiber material is interposed therebetween. That is, the insulating layer 5
Has a cup shape as a whole, and includes a cylindrical portion 5a and a bottom plate portion 5b (flat plate portion) having a hole at the center. The bottom plate portion 5b is interposed between the side surface 1b of the outer race 1 and the flat plate portion 14a of the holding step portion 14 or the flat plate portion 15a of the holding recessed portion 15 to prevent these two portions from coming into contact with each other. Further, the cylindrical portion 5a is interposed between the bearing outer diameter surface 1a and the inner peripheral surface of the cylindrical portion of the holding step portion 14 or the inner peripheral surface of the cylindrical portion of the holding concave portion 15, so that these two surfaces are prevented from contacting each other. are doing. Since the other side surface of the outer race 1 is exposed to the air, it is not necessary to cover it with the insulating layer 5 (of course, there is no problem even if it is covered).

As described above, the ball bearings B, B and the housing 1
3, an insulating layer 5 is interposed between the
And the rotating shaft 16 are insulated from each other, so that even if an axial voltage is generated on the rotating shaft 16 based on a high-frequency current (high carrier frequency) applied to the stator 18 from an inverter (not shown), the rotating shaft 16 and the housing 13, that is, the flow of current between the outer ring 1 and the inner ring 2 of the ball bearing B is minimized. Therefore, the occurrence of electrolytic corrosion in the ball bearing B is reliably prevented, and the durability of the ball bearing B is improved.

Further, there are no problems such as dust generation, cost increase, noise rise, temperature rise, etc. which occur in the conventional measures for preventing electrolytic corrosion. Note that the present embodiment is an example of the present invention, and the present invention is not limited to the present embodiment. For example, in the present embodiment, a ball bearing has been described as an example of a rolling bearing. However, the present invention can be applied to various types of rolling bearings. For example, radial rolling bearings such as cylindrical roller bearings, tapered roller bearings, and angular ball bearings,
Thrust ball bearings, thrust roller bearings, and other thrust-type rolling bearings.

Further, in this embodiment, the example in which the ball bearing is incorporated in the electric motor for driving the fan has been described. However, the anti-corrosion structure of the rolling bearing of the present invention can be applied to various other devices. Of course. Next, the results of evaluating the insulation properties and creep resistance of the insulating layer using the ball bearing shown in FIG. 1 as a test object will be described.

A 6002 single row deep groove ball bearing (outer ring outer diameter: 32 mm, inner ring inner diameter: 15 mm, width: 9 mm) was used for the test piece. However, since the outer ring was covered with an insulating layer as described above, The dimensions were equivalent to a 6202 single row deep groove ball bearing. Since the bearing of Comparative Example 2 described below is an example in which the insulating layer is not covered, a 6202 single row deep groove ball bearing was used.

Each test object (Examples 1 and 2 and Comparative Examples 1 and 2)
The insulating layer of the ball bearing 2) is composed of a resin composition as shown in Table 1.

[0035]

[Table 1]

That is, the resin composition of Example 1 was a resin composition ("Zarek C122" manufactured by Idemitsu Petrochemical Co., Ltd.) comprising 85% by weight of syndiotactic polystyrene resin and 15% by weight of glass fiber. The dielectric constant (catalog value) at 1 MHz is 2.8. The resin composition of Example 2 was a resin composition comprising 70% by weight of syndiotactic polystyrene resin and 30% by weight of glass fiber (“Zarek S13 manufactured by Idemitsu Petrochemical Co., Ltd.).
1 "), and its dielectric constant (catalog value) at 1 MHz is 2.9.

Further, the resin composition of Comparative Example 1 was a resin composition (“Zarek S100” manufactured by Idemitsu Petrochemical Co., Ltd.) consisting only of a syndiotactic polystyrene resin and containing no glass fiber. Is 2.6 (catalog value). Furthermore,
The ball bearing of Comparative Example 2 did not include an insulating layer.

With respect to such a test piece, the insulation and the dimensional stability were evaluated. First, a method for evaluating insulation properties will be described. After rotating at room temperature for 2000 hours in a state where a potential difference (20 V) is generated between the housing 13 of the electric motor 12 and the rotating shaft 16, the electric motor 12 is disassembled, and electrolytic corrosion occurs in the ball bearing B. (See FIG. 2).

When no electrolytic corrosion occurred, it was judged that the bearing (insulating layer) had good insulating properties, and was indicated by “○” in Table 1. On the other hand, if electrolytic corrosion has occurred, it is determined that the insulation of the bearing (insulating layer) is not good,
In Table 1, it is indicated by "x". Next, a method for evaluating dimensional stability will be described. If the creep resistance of the insulating layer is poor, the dimensions of the insulating layer change, and as a result, the dimensions of the bearing change. Then, the outer ring 1 attached to the housing 13 of the electric motor 12 rattles inside the housing 13 after a long time, which is a problem.

Therefore, the test object, which was pressed into the housing 13 with an interference of 10 μm, was placed
The bearing was left for a while, and the dimensional change of the bearing before and after the standing was measured to evaluate the creep resistance. When the dimensional change was 3 μm or less, it was judged that the creep resistance of the insulating layer was good, and in Table 1, it was indicated by “「 ”. On the other hand, when it exceeds 3 μm, it is judged that the creep resistance of the insulating layer is not good, and is indicated by “x” in Table 1.

As is clear from the test results shown in Table 1, Examples 1 and 2 were good in both insulating properties and dimensional stability (creep resistance). In contrast, Comparative Example 1
Although the insulating property was good, the creep resistance of the insulating layer was not good because it did not contain glass fiber, and the dimensional change was large. Further, Comparative Example 2 was not provided with an insulating layer and thus had poor insulating properties.

[0042]

As described above, according to the structure for preventing electrolytic corrosion of a rolling bearing according to the present invention, the insulation between the rolling bearing and the housing or shaft is insulated by the insulating layer. And there is almost no potential difference. Therefore, the current flowing between the outer ring and the inner ring can be minimized, and the occurrence of electrolytic corrosion in the rolling bearing can be prevented.

At that time, the conventional dust generation,
Problems such as cost increase, noise rise and temperature rise do not occur.

[Brief description of the drawings]

FIG. 1 is a partial sectional view showing the structure of a ball bearing provided with an insulating layer.

FIG. 2 is a longitudinal sectional view showing a structure of an electric motor for driving a fan, which is one embodiment of an anti-corrosion structure of a rolling bearing according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Outer ring 2 Inner ring 3 Ball 5 Insulating layer 13 Housing 16 Rotation axis B Ball bearing

Claims (1)

[Claims] 1. A rolling bearing, comprising: a housing attached to an outer ring of the rolling bearing; and a shaft fitted to an inner ring of the rolling bearing, wherein the rolling bearing rotates the shaft by the housing. In the structure which supports freely, an insulating layer is interposed between at least one of the outer ring and the housing and between the inner ring and the shaft, and the insulating layer is formed of a non-conductive material with a syndiotactic polystyrene resin. An electrolytic corrosion preventing structure for a rolling bearing, comprising a resin composition containing: