JP2004218846A - Galvanic corrosion preventing rolling bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a galvanic corrosion preventing rolling bearing which is capable of displaying a high galvanic corrosion preventing effect, and has heat radiation characteristic against high-temperature operation over a long time by selecting a material of an insulation film, and high creep resistance with improved moldability and an excellent insulation film. <P>SOLUTION: The insulation film 2 formed into at least one of an outer ring 11 and an inner ring 12 of the galvanic corrosion preventing rolling bearing 1A is formed out of a resin composition containing 30 to 50 wt% of the sum of a fibrous material A of a glass fiber or the like and a filler B of which heat conductivity is at least 10 W/m × K and resistivity is at least 10<SP>10</SP>Ωcm. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to an anti-corrosion rolling bearing used for electric motors for railway vehicles and the like, and in particular, to prevent a phenomenon in which deterioration of grease is promoted due to an increase in heat generation of the bearing due to an increase in speed of the vehicle, thereby shortening a bearing life. The present invention relates to an anti-corrosion rolling bearing that is effective in performing rolling.

Conventionally, in anti-corrosion rolling bearings used for electric motors for railway vehicles, in order to prevent a phenomenon in which leakage current from a housing or a shaft flows between a rolling element of a bearing and a bearing ring to cause electrolytic corrosion. An electric insulating film (insulating film) is provided on at least one surface of a housing or a shaft to which an outer ring or an inner ring is fitted, to cut off an external current.
As an insulating film of a conventional anti-corrosion rolling bearing, for example, JP-A-3-277818 discloses an insulating film formed of a polyphenylene sulfide resin containing glass fibers (hereinafter referred to as PPS resin).

Japanese Patent Application Laid-Open No. 5-240255 discloses an insulating film formed of a PPS resin containing glass fibers and a non-fibrous insulating inorganic filler such as calcium carbonate.
The former is intended to obtain a stable anti-corrosion performance by forming an insulating film having excellent creep resistance by reinforcing a PPS resin with glass fibers.

In the latter case, not only glass fiber but also non-fibrous inorganic filler is used in combination to strengthen the PPS resin. It is intended to obtain a good formability.
By the way, high creep resistance is required for the insulating coating in the anti-corrosion rolling bearing because the insulating coating is formed on at least one of the inner and outer rings of the bearing, which is incorporated with an interference between the rotating shaft and the housing. This is because if the creep resistance is low, the thickness of the insulating film decreases with the passage of time, so that the interference of the bearing cannot be kept constant.
JP-A-3-277818 JP-A-5-240255

  However, recently, there is an increasing demand for higher speed of railway vehicles, and accordingly, the tendency of the heat generation of bearings during shaft rotation to increase has become remarkable. However, in the above-described conventional anti-corrosion rolling bearing, any of the materials used for the insulating coating has a low thermal conductivity and a large heat insulating effect. For example, the thermal conductivity of the resin is about 0.4 to 1 W / m · K, and the added glass fiber is only about 2 to 6 W / m · K. Therefore, when this insulating film is used as a bearing covering material, heat generated by rotation of the bearing is difficult to escape, and the temperature of the bearing increases. Then, there is a problem in that deterioration of grease in the bearing and the like are promoted due to the rise in the bearing temperature, which causes problems such as a reduction in the life of the bearing.

  Accordingly, the present invention has been made in view of such a conventional problem, and the thermal conductivity of an insulating film is improved by adding a filler having high thermal conductivity to improve the bearing of a motor for a railway vehicle. Even when used in applications such as bearings, it has a heat radiation property that quickly releases the heat generated during high-speed rotation to the outside of the system via the housing, shaft, etc. It is an object of the present invention to provide an anti-corrosion rolling bearing applicable to high-speed rotation capable of preventing a reduction.

  Further, another object of the present invention is to provide an excellent heat dissipation property and an excellent electrical insulation property, which can effectively prevent electric erosion due to discharge and conduction between the rolling element and the outer and inner raceways due to leakage current from the housing and the shaft. It also has excellent creep resistance and prevents the mating force and clearance between the housing and shaft from changing over a long period of operation to prevent co-rotation. Further, it has excellent moldability and prevents electrolytic corrosion. It is to provide a rolling bearing.

In order to achieve the above object, the present invention provides an anti-corrosion rolling bearing having an insulating coating on at least one of the outer and inner rings, wherein the insulating coating has a fiber material [A] contributing to the reinforcement of the matrix resin and a thermal conductivity of 10 W / M · K or more and a filler [B] having a specific resistance of 10 ¹⁰ Ω · cm or more, and the total [A + B] of both is 30 to 50% by weight.
In addition, the sum [A + B] of both can be 20% by weight or more and less than 60% by weight. The content of the filler [B] can be 10 to 40% by weight.

Generally, a resin or a fiber material such as a glass fiber has a low thermal conductivity, and thus the thermal conductivity of an insulating film formed from a resin composition in which only both are mixed is also low. Therefore, in addition to the fiber material, a resin composition to which a high thermal conductivity and high electrical insulating filler having a thermal conductivity of 10 W / m · K or more and a specific resistance of 10 ¹⁰ Ω · cm or more is used. Thereby, the thermal conductivity of the formed insulating film is increased, and the heat radiation characteristics are improved. Thus, heat resistance, insulation, and heat dissipation as well as creep resistance are excellent.

  Hereinafter, the present invention will be described in more detail. As the resin material used for forming the insulating film of the present invention, PPS resin, aromatic nylon (aromatic polyamide resin), and aliphatic polyamide resin such as 4,6 nylon are exemplified. It can be suitably used. Since the PPS resin has low water absorption and good moldability, an insulating film having excellent water absorption properties can be formed at low cost by injection molding. Aromatic nylon has a high melting point and high strength, and is preferable because the insulating performance can be maintained at a high temperature of 120 ° C. when the bearing rotates at high speed. On the other hand, aliphatic polyamide resins such as 4,6 nylon also have good electrical insulation properties and are suitable for insulating coatings.

However, the above resin cannot simultaneously satisfy a plurality of functions required for an insulating film for an anti-corrosion rolling bearing at the same time, and is used together with an additive material described below.
The fiber material [A] of the present invention used to reinforce the resin material is mainly used to improve the creep resistance of the matrix resin. In particular, glass fiber (GF) fiber is effective. Ceramic fibers, rock fibers, slug fibers and the like can also be used. The addition amount of the fiber material [A] mainly for improving the creep resistance is 10 to 60% by weight, preferably 30 to 50% by weight of the resin amount. If it exceeds 50% by weight, the moldability will be poor, and if it is less than 10% by weight, the creep resistance will be poor.

The filler [B] of the present invention is used to simultaneously improve the electrical insulation and the heat conductivity of the insulating film. The higher the thermal conductivity, the better, but at least 10 W / g higher than the glass fiber. m · K or more is required. On the other hand, it is necessary to have high electrical insulation, and the specific resistance is 10 ¹⁰ Ω · cm or more, and more preferably 10 ¹³ Ω · cm or more. Fillers that can satisfy such conditions include, for example, powders such as SiC (silicon carbide), AlN (aluminum nitride), BeO (berylia), BN (boron nitride), and Al ₂ O ₃ (alumina), fibers, or whiskers. Etc. Table 1 shows the thermal conductivity and specific resistance of these filler materials in comparison with Cu (copper) and SiO ₂ (silicon oxide).

In general, inorganic materials having high specific resistance have low thermal conductivity and poor heat dissipation, and conversely, those having high thermal conductivity have low specific resistance and poor electrical insulation. [B] satisfies both conditions of specific resistance and thermal conductivity.
The amount of the filler [B] to be added is 10 to 40% by weight of the resin amount, and is preferably selected in the range of 20 to 40% by weight. If it exceeds 40% by weight, it becomes difficult to satisfy the creep resistance and moldability. On the other hand, if it is less than 10% by weight, no improvement in heat conductivity can be expected. Therefore, the electrical insulation, heat transfer and creep resistance of the present invention are not improved. The effect of improving in three beats cannot be expected.

  The total amount [A] + [B] of the fiber material [A] and the filler [B] is preferably 30 to 50% by weight. If the content exceeds 50% by weight, the matrix resin becomes insufficient and the fluidity at the time of molding is reduced. As a result, the surface roughness of the formed insulating film is deteriorated and the weld strength is reduced. On the other hand, if it is less than 30% by weight, both the fiber material [A] and the filler [B] approach the minimum required amounts, or the required amounts of both cannot be secured, and it is difficult to achieve both heat transfer and creep resistance. .

  The graph of FIG. 1 shows the respective addition ratios of the fiber material [A] for improving the creep resistance and the filler [B] for improving the heat transfer property, and the creep resistance, heat transfer property and formability of the obtained insulating coating. The relationship between (surface roughness and weld strength) is shown. In the region [I] in the figure, the addition amount of the fiber material [A] and the filler [B] is 10 to 20% by weight, and the region [II] ] Is 20 to 30% by weight, and the region [III] is 30 to 40% by weight, all of which are within the scope of the present invention. When the temperature drop ΔT ° C. of the anti-corrosion rolling bearing using the insulating film formed at the addition ratio of each of these regions was measured and compared with the conventional product, ΔT ≧ 10 ° C. in the region [I], ] Was ΔT ≧ 12 to 13 ° C., and the region [III] was ΔT ≧ 15 ° C. From this, it is clear that the temperature lowering effect in each region becomes more reliable in the order of [I] ≦ [II] ≦ [III].

  The region [IV] is a range that satisfies either the creep resistance or the heat transfer property but the formability is poor. Region [0] is a range where the moldability is good but the creep resistance and the heat conductivity are both insufficient. Table 2 shows the quantitative combination of the glass fiber as the fiber material [A] and the AlN as the filler [B], and the creep resistance, heat transfer property, and the like of the insulating coating obtained by adding this to the PPS resin. The relationship between the moldability and the electrical insulation properties is shown for each of the above regions.

From this table, the range of the total additive amount of the additive material that can provide the insulating coating almost satisfying each of the above-mentioned properties is at most 20% by weight or more and less than 60% by weight, preferably in the range of regions [I] to [III] That is, the content of the fiber material [A] + the filler [B] is 30 to 50% by weight.
In addition, in the resin composition containing the fiber material [A] and the filler [B], a release agent, a coupling agent, and the like may be added as necessary.

  As described above, in the anti-corrosion rolling bearing of the present invention, the fiber material [A] having high creep resistance in the matrix resin and the filler [B] having a thermal conductivity and specific resistance of a certain value or more are used. And (A + B) were mixed in the total range of 30 to 50% by weight to form an insulating coating, so that an insulating coating excellent in creep resistance, heat transfer, moldability and electrical insulation was obtained. The present invention has the effect of providing an anti-corrosion rolling bearing capable of guaranteeing stable performance even under a use condition in which the bearing is exposed to a high temperature at a high rotation speed, such as a bearing for a motor for a vehicle.

In addition, the total [A + B] of the above two may be 20% by weight or more and less than 60% by weight.
Also, by adjusting the content of the filler [B] arbitrarily within the range of 10 to 40% by weight according to the type of the filler, the creep resistance, heat transfer property, moldability and electrical insulation of the insulating film are improved. By adjusting the balance of the various properties of the bearing, it is possible to give the product diversity according to the conditions of use of the bearing and the like.

  Hereinafter, the present invention will be described in detail with reference to examples. FIG. 2 is a cross-sectional view of a rolling bearing 1A according to one embodiment. The rolling bearing 1A uses a resin composition shown in each of Examples and Comparative Examples in Table 3 as a material of an insulating coating 2 covering the outer surface of an outer ring 11. The following characteristics were evaluated for each of the test samples. In this case, the inner ring 12 was not covered.

  The rolling bearing 1A of each DUT has grooves 11a and 11b formed on the outer periphery and the left and right end surfaces of the outer race 11, respectively, and an insulating coating 2 having a predetermined thickness is injection-molded to form an outer periphery of the outer race 11 (the housing is fitted). The surface was continuously attached to both end surfaces. That is, first, each material composition was previously mixed with a blender, a Henschel mixer, or the like, and supplied to an extruder such as a twin-screw extruder to obtain material pellets from the extruder. Next, a mold formed corresponding to the thickness of the insulating film 2 (here, about 1.0 mm) is placed outside the outer ring 11, and the pellet is melted in a space between the outer ring 11 and the mold. The molded material was injected, and after cooling for a predetermined time, a molded article having the outer ring 11 and the insulating coating 2 was obtained.

In the resins shown in Table 3, "Alen" (trade name) manufactured by Mitsui Petrochemical Co., Ltd. was used as the aromatic nylon resin (N), and "Fortron" manufactured by Kureha Chemical Industry Co., Ltd. was used as the polyphenylene sulfide resin (PPS). KPS "(trade name) was used.
The test method was as follows.
The anti-corrosion rolling bearing 1A (inner diameter 75 mm, outer diameter 160 mm, width 37 mm) manufactured as described above is pressed into a housing, and a predetermined amount (about 30% of the bearing space) of grease is sealed in the bearing. After performing the smoothing-out operation, rapid acceleration was performed up to 5000 rpm and held for about 30 minutes. During this time, the temperature T of the outer ring 11 was recorded.
Table 4 shows the results of the characteristic evaluation test.

Each evaluation item in Table 4 will be described.
(1) Evaluation of creep resistance The creep resistance is important to prevent the outer ring 11 fitted in the housing from rattling in the housing even after a long time has passed. That is, the anti-corrosion rolling bearing is often exposed to a relatively high temperature during use, in which case the resin material constituting the insulating coating 2 is creeped by the pressing force applied from the inner peripheral surface of the housing to escape to the side, The thickness dimension of the insulating coating 2 tends to decrease. When the thickness reduction amount increases, the outer ring 11 rattles inside the housing, and abnormal noise and vibration are generated in the rotation support portion in which the anti-corrosion rolling bearing is assembled. In addition, the outer ring 11 rotates with respect to the housing, and the outer peripheral surface of the insulating coating 2 is worn, resulting in a problem such that the backlash increases. Then, the above-mentioned specimen was pressed into the housing with a tightening margin of 30 μm, left in an atmosphere of 100 ° C. for 100 hours, and measured for dimensional change before and after the leaving to evaluate creep resistance. If the change amount was 8 μm or less, it was judged as acceptable (（), and if it exceeded 8 μm, it was judged as unacceptable (×).

(2) Evaluation of Electrical Insulation Electrical insulation is important for preventing electric corrosion of each component of the rolling bearing. Therefore, after wiping off water adhering to the surface of the test object, a metal ring is attached to the outer peripheral surface of the insulating film 2 and the electric resistance value between the ring and the outer ring 11 is measured. Was used to evaluate the electrical insulation. A resistance value of 2000 MΩ or more was regarded as pass (○), and a resistance value of less than 2000 MΩ was rejected (×).

(3) Evaluation of heat transfer The heat transfer is such that when the temperature of the bearing rises because the heat generated by the rotation of the anti-corrosion rolling bearing hardly escapes, the deterioration of the grease in the bearing is promoted and the bearing life is shortened. This is particularly important in the case of high-speed rotation. Here, the heat conductivity was evaluated as follows based on the recorded temperature T of the outer race 11.
That is, when the temperature T after the operation of the outer race 11 recorded as described above is lower than the outer race temperature of the rolling bearings of the comparative examples 1 and 2 which are the conventional products by 10 ° C. or more, it is judged as pass (）). If the temperature exceeded 10 ° C., it was rejected (×).

(4) Evaluation of film formability If the film formability is good, the insulating film can be formed at low cost by injection molding, which is important for improving productivity and reducing costs. Therefore, the formability of the coating was evaluated by observing the presence or absence of voids, cracks, and the like in the welds, gates, and the like of the injection-molded test piece, and the surface state of the insulating coating 2. Those with no voids, cracks, etc. were judged as acceptable (O), and those with rough coating surfaces were judged as unacceptable (X).

From the results in Table 4, Examples 1 to 10 passed all of the creep resistance, insulation performance, heat conductivity, and moldability of the insulating film.
On the other hand, the filler [B] for improving the heat transfer property of Comparative Example 1 in which only glass fiber was filled in the PPS resin at 40% by weight and Comparative Example 2 in which only glass fiber was filled in the aromatic nylon in the same 40% by weight were used. In Comparative Example 3 in which the content of the filler [B] was as small as 5% by weight, the heat transfer was poor, and the rise in the outer ring temperature was remarkable.
Comparative Example 4, in which the total amount of the fiber material [A] and the filler [B] is 60% by weight, does not satisfy the conditions of the present invention and has poor moldability.
In particular, Comparative Example 5, in which the total amount of the fiber material [A] and the filler [B] was 65% by weight, could not be molded and could not be evaluated.

In Comparative Examples 6 to 8, the filler [B] of the present invention was replaced with SiO ₂ or Cu powder or both of them, but the SiO ₂ or Cu powder was added to the filler [B] of the present invention. Does not satisfy the condition that the thermal conductivity is 10 W / m · K or more and the specific resistance is 10 ¹⁰ Ω · cm or more. It passed.
In the above-described embodiment, the rolling bearing 1A has been described by way of example in which only the outer surface of the outer ring 11 is coated with the insulating coating 2. However, the inner ring 12 may be coated with the insulating coating 2, or alternatively, the outer ring 11 and the inner ring 12 may be coated. The same effect can be obtained by covering both of them with the insulating coating 2.

4 is a graph showing the relationship between the addition ratio of both fillers [A] and [B] in the electric insulating coating of the anti-corrosion rolling bearing of the present invention and the properties of the insulating coating. It is sectional drawing of one Example of the anti-corrosion rolling bearing of this invention.

Explanation of reference numerals

2 Insulation coating 11 Outer ring 12 Inner ring

Claims (2)

In an anti-corrosion rolling bearing having an insulating coating on at least one of the outer and inner rings, the insulating coating is made of a fiber material [A] contributing to the reinforcement of the matrix resin, and has a thermal conductivity of 10 W / m · K or more and a specific resistance of not less than 10 W / m · K. An anti-corrosion rolling bearing, comprising a filler [B] of 10 ¹⁰ Ω · cm or more, and the total [A + B] of both is 30 to 50% by weight. In an anti-corrosion rolling bearing having an insulating coating on at least one of the outer and inner rings, the insulating coating is made of a fiber material [A] contributing to the reinforcement of the matrix resin, and has a thermal conductivity of 10 W / m · K or more and a specific resistance of not less than 10 W / m · K. An anti-corrosion rolling bearing comprising a filler [B] of 10 ¹⁰ Ω · cm or more, and the total [A + B] of both is 20% by weight or more and less than 60% by weight.

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