JP2001037163A - Brushes for motor and motor provided with them - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the wear resistance of brushes for a motor and to reduce the driving noise of the motor by a method wherein sliding parts which come into contact with a commutator which is sandwiched between the brushes for the motor are formed of a silicon carbide sintered compact whose volume resistivity is at a specific value or lower and whose density is at a specific value or higher. SOLUTION: In the thrushes 7 for a motor at least sliding parts which come into contact with a commutator 6 are formed of a silicon carbide sintered compact which is at a volume resistivity of 1 Ω.cm or lower and which is at a density of 2.9 g/cm3 or higher. At this time, the silicon carbide sintered compact is manufactured in such a way that a resol-type phenolic resin containing an amine and a silicon carbide powder are mixed in an ethanol solvent, that the mixture is dried so as to be molded in a cylindrical shape and that its cylindrical body is sintered. The silicon carbide sintered compact is cut out in a desired shape, and the brushes 7 for the motor are obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor brush and a motor including the same, and more particularly, to a motor brush using a silicon carbide sintered body and a motor including the same.

[0002]

[Prior art]

Conventionally, small motors have been widely used in all other fields such as optical precision equipment, audio / video equipment, OA equipment, household electrical equipment, automobiles, toys and the like.

Such a small motor is usually provided with a permanent magnet mounted on the inner peripheral surface of a casing, a rotor provided inside the casing and rotatably supported and having an armature and a commutator, and a casing. And a brush slidably engaged with the commutator, and the rotor is rotated by being supplied with power from an external power supply to the armature via the brush and the commutator. However, in a small-sized motor that supplies power by such a brush, the brush and the commutator slide, so that, for example, friction (due to contact resistance or the like) in a sliding portion between the brush and the commutator, arc discharge, or the like. (Rectifying sparks, etc.) were generated, which caused heat, abrasion, deformation, film formation, radio interference, and the like, which resulted in poor contact, reduced performance, and reduced durability. In addition, there is another problem that a break-in operation is required to prevent generation of noise or chattering.

Therefore, it is important to select the material of the brush used for the small motor, particularly the material of the commutator and the sliding portion. Conventionally, a carbon brush has been used as the material, but a carbon brush containing a noble metal (for example, JP-A No. 11-4563), a metal brush, a noble metal (gold, platinum, rhodium, silver, palladium silver, etc.) Brushes (for example, Japanese Patent Application Laid-Open No. Hei 9-131023) and the like have been used, and further improvements have been made.

[0006] However, it is still insufficient to solve the above-mentioned problems, and the carbon brush has abrasion resistance due to generation of fine particles in a sliding portion, abrasion resistance that a film is formed, and large driving noise. Metal and noble metal brushes have a problem in that they have insufficient strength and heat resistance, causing significant wear and deformation, or corrosion due to oxidation and the like. In addition, there is a cost problem that a noble metal brush is particularly expensive. In addition, at present, neither the carbon brush nor the metal / noble metal brush has a problem that arc discharge occurs, abnormal wear, film formation, and radio interference occur.

On the other hand, in order to solve the problem in the sliding portion between the brush and the commutator, a motor for preventing an arc discharge by enclosing an atmosphere hardener made of diester carbonate in a casing (Japanese Patent Laid-Open No. 9-10766). Etc.), a motor (for example, JP-A-10-336984) for providing a rotor with a spark quenching element to prevent radio interference due to arc discharge, and a motor for providing a cooling fan to suppress heat generation (JP-A-10-2102)
No. 5719) have been proposed, but all of these factors have caused a decrease in productivity and an increase in cost, and there has been a strong demand for improving the brush material itself used for small motors.

[0008]

That is, an object of the present invention is to provide a low cost, excellent conductivity, strength, heat resistance, abrasion resistance, corrosion resistance (oxidation resistance, chemical resistance), and arc. Brush for motors that can prevent electric discharge (radio wave interference due to arc discharge, abnormal film formation, etc.) and drive noise, and low cost, durable, productive, and low drive noise equipped with it Is to provide a motor.

[0009]

Means for Solving the Problems The present inventors have conducted intensive studies on such objects and found that the heat resistance, abrasion resistance, corrosion resistance (oxidation resistance, chemical resistance, etc.) were obtained at low cost. It has been found that when electrical conductivity is imparted to a silicon carbide sintered body known as a ceramic excellent in (1), it is very suitable as a material for a motor brush. That is, the present invention

<1> At least a sliding portion of the brush for the motor, which is in contact with the commutator, is formed of a silicon carbide sintered body having a volume resistivity of 1 Ω · cm or less and a density of 2.9 g / cm ³ or more. It is a brush for a motor characterized by being performed.

<2> The silicon carbide sintered body has a conductivity variation index (β value) defined by the following equation (1) of 0.
The brush for a motor according to <1>, wherein the number is 8 or more.

Equation (1) ε _max = 1/2 (ε ₀ −ε∞) tan (βπ / 4) ε _max : maximum value of relative dielectric loss factor in the silicon carbide sintered body ε ₀ : silicon carbide sintered body Dielectric constant on the high frequency side of ε∞: dielectric constant on the low frequency side in silicon carbide sintered body

<3> A silicon carbide sintered body is obtained by mixing silicon carbide powder, a nonmetallic sintering aid, and a nitrogen compound.
The motor brush according to <1> or <2>, which is obtained by sintering at 000 to 2400 ° C.

<4> The silicon carbide powder is obtained by mixing at least one kind of a silicon compound and at least one kind of an organic compound which generates carbon by heating and baking the mixture. The motor brush according to <3>.

<5> A silicon carbide powder obtained by mixing and firing at least one silicon compound, at least one organic compound that generates carbon by heating, and a nitrogen compound, The motor brush according to <1> or <2>, wherein the brush is obtained by mixing a nonmetallic sintering aid and sintering at 2000 to 2400 ° C.

<6> A motor including the motor brush according to any one of <1> to <5>.

The motor brush of the present invention uses the above-mentioned specific silicon carbide sintered body as its material, and therefore has low cost, conductivity, strength, heat resistance, abrasion resistance, corrosion resistance (oxidation resistance). Excellent in chemical resistance), and can prevent the occurrence of arc discharge (e.g., radio interference due to arc discharge, abnormal film formation, etc.) and drive noise.

Since the motor of the present invention includes the motor brush of the present invention, it is low in cost, has excellent durability and productivity, and has low driving noise.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION In a motor brush according to the present invention, at least a sliding portion in contact with a commutator of the motor brush includes:
Volume resistivity is 1 Ω · cm or less and density is 2.9 g / c
It is formed of a silicon carbide sintered body having an m ³ or more.

(Silicon Carbide) The silicon carbide has a volume resistivity of ¹ Ω · cm or less, preferably 10 ⁻¹ Ω · cm or less. If the volume resistivity exceeds 1 Ω · cm, a normal electrical connection between the commutator and the brush cannot be obtained, resulting in significant heat generation, power loss, and impairment of the stability of the initial motor performance. , The durability deteriorates. Also, arc discharge is likely to occur.

The silicon carbide sintered body has a density of:
2.9 g / cm ³ or more, preferably 3.0 g / cm ³
cm ³ or more. If the density is less than 2.9 g / cm ³ , mechanical strength such as bending strength and breaking strength is reduced,
When the possibility of causing deformation or breakage increases and durability decreases, particles may further increase and abrasion resistance may deteriorate or a film may be formed. If the density is less than 2.9 g / cm ³ , the heat resistance is reduced, and remarkable abrasion and deformation may be caused. In addition, the oxidation resistance and the chemical resistance are also reduced, and corrosion is liable to occur.

The silicon carbide sintered body preferably contains nitrogen in order to maintain a low volume resistivity (high electric conductivity). The nitrogen content is preferably 150
ppm or more, more preferably 200 ppm or more.
If the nitrogen content is less than 150 ppm, a low volume resistivity (high conductivity) cannot be obtained, a normal electrical connection between the commutator and the brush cannot be obtained, and good conductivity, Not only remarkable heat generation, power loss, initial stability of the motor performance may be impaired, but also durability may be deteriorated, and arc discharge may be easily generated. From the viewpoint of stability, it is preferable that nitrogen is contained in a solid solution state.

The silicon carbide sintered body preferably has a total content of impurity elements of 10 ppm or less, preferably 5 pp.
m or less. As for the total content of impurity elements, the impurity content obtained by chemical analysis only serves as a reference value. Practically, if the impurities are evenly distributed,
Although the evaluation differs depending on whether the sample is locally unevenly distributed, in the present invention, the value measured by the solution ICP-MS method was used.

The above-mentioned impurity element is defined in IUPA 1989
C refers to an element belonging to Group 1 to Group 16 elements in the periodic table of the revised inorganic chemical nomenclature for C, having an atomic number of 3 or more, and excluding atomic numbers 6 to 8 and 14.

When the silicon carbide sintered body has a small variation in the electric conductivity in the sintered body, the silicon carbide sintered body has good electric conductivity and uniform electric conductivity, and the occurrence of arc discharge is more effectively prevented. From the viewpoint that it can be performed, the following formula (1)
Is preferably 0.8 or more.

Equation (1) ε _max = 1/2 (ε ₀ −ε∞) tan (βπ / 4) ε _max : maximum value of relative dielectric loss factor in the silicon carbide sintered body ε ₀ : silicon carbide sintered body Dielectric constant on the high frequency side of ε∞: dielectric constant on the low frequency side in silicon carbide sintered body

The conductivity variation index (β value) is determined by the relative permittivity (relative permittivity (ε ₀ ) on the high frequency side, relative permittivity (low permittivity) of the silicon carbide sintered body obtained by using an AC circuit, ε
∞)) and the maximum value of the relative dielectric loss factor (ε _max ) obtained from the measurement of the relative dielectric loss ratio are calculated using the above equation (1) (Maxwell-Wa).
gner equation). The β value takes a numerical value of 1 or less, and the closer the value is to 1, the more uniform the conductivity is. The relative dielectric loss factor and relative dielectric constant of the sintered body were measured using an impedance analyzer MAP1260 type (manufactured by Toyo Corporation).
Can be measured.

Considering other suitable physical properties of the silicon carbide sintered body, for example, the bending strength at room temperature is 50.0 to 65.0 kgf / mm ² , and the bending strength at 1500 ° C. is 55.0 to 80.0 kgf. / Mm ² , Young's modulus is 3.5 × 10 ^{4 to} 4.5 × 10 ⁴ , Vickers hardness is 2000 kgf / mm ² or more, and Poisson's ratio is 0.3.
14 to 0.21, thermal expansion coefficient: 3.8 × 10 ^{-6 to} 4.2
× 10 ⁻⁶ (° C. ⁻¹ ), thermal conductivity of 150 W / m · k or more,
The specific heat is 0.15 to 0.18 cal / g · ° C., and the thermal shock resistance is 500 to 700 ΔT ° C.

(Production Method of Silicon Carbide Sintered Body) The silicon carbide sintered body is preferably obtained by mixing and sintering a silicon carbide powder and a nonmetallic sintering aid.

-Silicon Carbide Powder- Examples of the silicon carbide powder include α-type, β-type, amorphous, and mixtures thereof. Of these, β-type silicon carbide powder is particularly preferable. The proportion of β-type silicon carbide in the entire silicon carbide component is preferably 70% or more, more preferably 80% or more, and may be 100% β-type silicon carbide.

The amount of the β-type silicon carbide powder in the silicon carbide powder is preferably 60% by weight or more.
It is more preferably at least 65% by weight. If the amount is less than 60% by weight, the content of β-type silicon carbide in the silicon carbide component of the obtained silicon carbide sintered body may be outside the above-mentioned numerical range. The grade of the β-type silicon carbide powder is not particularly limited. Therefore,
Generally, commercially available β-type silicon carbide powder can be suitably used.

The average particle size of the silicon carbide powder is as follows:
From the viewpoint of obtaining a high-density silicon carbide sintered body, the particle size is preferably small, and specifically, 0.01 to 10 μm.
m is preferable, and 0.05 to 1 μm is more preferable. If the average particle size is less than 0.01 μm, it is difficult to handle at the time of processing such as measurement and mixing, and if it exceeds 10 μm, the specific surface area (the area where adjacent silicon carbide powders contact each other) ) Is small, it may be difficult to obtain a high-density silicon carbide sintered body.

The particle size distribution of the silicon carbide powder is as follows:
Although there is no particular limitation, from the viewpoint of improving the packing density of powder (such as silicon carbide powder) as a raw material and improving the reactivity of silicon carbide during the production of the silicon carbide sintered body, It is preferable that the distribution has two or more maximum values.

The silicon carbide powder has an average particle size of 0.05 to 1 μm, a specific surface area of 5 m ² / g or more,
Those having a free carbon content of 1% or less and an oxygen content of 1% or less are particularly preferred.

—Method for Producing Silicon Carbide Powder— The silicon carbide powder is preferably obtained by mixing a silicon compound and an organic compound that generates carbon by heating and baking the mixture.

--Silicon Compound (Silicon Source)-The silicon compound is not particularly limited as long as it is a compound that generates silicon by heating, and may be either a liquid silicon compound or a solid silicon compound. Good,
From the viewpoint of high purification and uniform dispersion, at least 1
Preferably, the seed is a liquid silicon compound.

Suitable examples of the liquid silicon compound include (mono-, di-, tri-, and tetra-) alkoxysilanes and polymers of tetraalkoxysilanes. Preferred examples of the (mono-, di-, tri-, and tetra-) alkoxysilanes include tetraalkoxysilanes. As the tetraalkoxysilane, specifically, tetramethoxysilane, tetraethoxysilane,
Tetrapropoxysilane, tetrabutoxysilane and the like are preferably exemplified, and tetraethoxysilane is particularly preferred from the viewpoint of excellent handleability. As the polymer of the tetraalkoxysilane, a low molecular weight polymer (oligomer) having a degree of polymerization of about 2 to 15 (for example, tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane,
Suitable examples include low molecular weight polymers (oligomers) such as tetrabutoxysilane) and liquid high-polymer silicate polymers.

As the solid silicon compound, silicon oxide and the like are preferably mentioned. Here, the silicon oxide in the present invention means, in addition to SiO, silica sol (colloidal ultrafine silica containing liquid, containing OH group or alkoxyl group inside), silicon dioxide (silica gel, fine silica, quartz powder) Body) and the like.

Among these silicon compounds, a low molecular weight polymer (oligomer) of tetraethoxysilane, and a low molecular weight polymer (oligomer) of tetraethoxysilane and fine powdered silica are excellent in homogeneity and handleability. And the like are particularly preferred. These silicon compounds may be used alone or in combination of two or more.

The total content of the impurity elements in the silicon compound is preferably 10 ppm or less, more preferably 5 ppm.
The following is more preferred. When the total content of the impurity elements is out of the numerical range, the purity of the obtained silicon carbide sintered body may be out of the numerical range. However,
The value is not necessarily limited to a value within the above numerical range as long as it is within an allowable range of purification during heating and sintering.

--Organic compound capable of generating carbon by heating (carbon source)-The organic compound capable of generating carbon by heating (hereinafter referred to as "organic compound" as appropriate) is not particularly limited. Any of liquid and solid organic compounds may be used, but it is preferable that at least one of them is a liquid organic compound.

The organic compound has a high residual carbon ratio,
Organic compounds that polymerize and crosslink by the presence of a catalyst and / or heating are preferred. For example, phenol resins, furan resins, polyimides, polyurethanes, polyvinyl alcohols, and other resin monomers and prepolymers, and liquid organic compounds such as cellulose, sucrose, pitch, and tar are preferably used. Among these, a phenol resin is preferable, and a resol-type phenol resin is particularly preferable. These organic compounds may be used alone or in combination of two or more.

The purity of the organic compound can be appropriately controlled and selected depending on the purpose. Particularly, in order to obtain a high-purity silicon carbide powder, the total content of the impurity elements must be
It is preferably not more than 5 ppm.

--Mixing-- In the mixing, the silicon compound and the organic compound which generates carbon by heating are uniformly mixed to form a mixture.

The mixing ratio (silicon compound / organic compound (hereinafter referred to as “C / Si ratio” as appropriate)) of the silicon compound and the organic compound at the time of the mixing is as follows. Defined by elemental analysis of a carbide intermediate obtained by carbonization, stoichiometrically, if the C / Si ratio is 3.0, the free carbon in the produced silicon carbide powder is 0%. However, in practice, the volatilization of the simultaneously generated SiO gas generates free carbon at a low C / Si ratio, so that the amount of free carbon in the generated silicon carbide powder depends on the amount of the silicon carbide sintered body or the like. It is necessary to determine the C / Si ratio in advance so as not to be unsuitable for production, use, etc. Usually, 1600 ° C. near 1 atm
In the case of firing as described above, the C / Si ratio is set to 2.0 to 2.5.
The generation of the free carbon can be suppressed. Further, when the C / Si ratio is set to 2.5 or more, the amount of generated free carbon significantly increases. However, since the free carbon has an effect of suppressing grain growth, it is appropriately selected according to the purpose of forming particles. You can also. However, when the atmosphere is fired at a low or high pressure, C to obtain pure silicon carbide is used.
/ Si ratio varies, so in this case, the C
The ratio is not limited to the range of the / Si ratio. In addition, since the action at the time of sintering of free carbon is very weak compared to the action by carbon derived from the nonmetallic sintering aid coated on the surface of the silicon carbide powder described below, basically, Can be ignored.

In the mixing, for the purpose of imparting conductivity to the silicon carbide sintered body, it is preferable to further mix a nitrogen compound with the silicon compound and the organic compound to form a mixture. However, in the present invention, as described later, a silicon carbide sintered body obtained by mixing the nitrogen compound together with the silicon carbide powder and the nonmetallic sintering aid when sintering the silicon carbide powder. It is also possible to impart conductivity to the material.

The mixing amount of the nitrogen compound is preferably 80 μg to 1000 μg with respect to 1 g of the silicon compound. When the mixing amount is less than 80 μg, the volume resistivity of the silicon carbide sintered body may not be able to be controlled within the numerical range, and when it exceeds 1000 μg,
Nitrogen evaporates and may exceed the target solid solution amount.

The nitrogen compound is preferably a compound which generates nitrogen when heated, and examples thereof include polyimide resins and precursors thereof, and various amines such as hexamethylenetetramine, ammonia and triethylamine.

In the mixing, if desired, a polymerization or cross-linking catalyst may be further added and cured to obtain a mixed solid, for the purpose of mixing the silicon compound and the organic compound more uniformly. Other curing methods are also available. Examples of the method include a method of crosslinking by heating, and a method using an electron beam or radiation.

The polymerization or cross-linking catalyst can be appropriately selected according to the type of the organic compound. For example, when the carbon compound is a phenol resin or a furan resin, toluenesulfonic acid, toluenecarboxylic acid, acetic acid, oxalic acid and the like are used. , Hydrochloric acid, sulfuric acid, acids such as maleic acid, and amines such as hexamine.

In the mixing, known mixing means such as a mixer and a planetary ball mill are used. or,
The mixing time is preferably 10 to 30 hours, and 16 to 30 hours.
24 hours is more preferred. As a material for the mixer, the planetary ball mill, and the like, a synthetic resin containing as little metal as possible is preferable from the viewpoint of obtaining high-purity silicon carbide powder.

The above-mentioned mixed solid material has improved handling properties,
For the purpose of removing volatile gas and moisture, heating and carbonization can be performed before firing, if desired. The heating and carbonizing are performed in a non-oxidizing atmosphere such as nitrogen or argon, for 50 hours.
It is preferably performed at 0 ° C. to 1000 ° C. for 30 to 120 minutes.

-Firing-In the firing, the mixture (or the solid mixture) is fired in a non-oxidizing atmosphere to produce silicon carbide powder. Conditions such as firing time and firing temperature in the firing,
Since it depends on the desired particle size of the silicon carbide powder and the like, it cannot be specified unconditionally, but it is preferably carried out at 1350 to 2000 ° C. in a non-oxidizing atmosphere such as argon.
More preferably, it is carried out at 00 to 1900 ° C. In order to further increase the purity of the silicon carbide powder, it is preferable to further perform a heat treatment at 2000 to 2100 ° C. for 5 to 20 minutes after the firing.

The method for producing the silicon carbide powder is as follows:
The method for producing a raw material powder described in the method for producing a single crystal previously filed by the applicant of the present invention as Japanese Patent Application No. 7-241856, that is, selected from high-purity tetraalkoxysilane and tetraalkoxysilane polymer A silicon carbide generating step of heating and firing a mixture obtained by homogeneously mixing one or more silicon compounds and a high-purity organic compound that generates carbon by heating under a non-oxidizing atmosphere to obtain a silicon carbide powder; And the obtained silicon carbide powder at 1700 ° C.
２０００2000 ° C., while maintaining the temperature, 20
Performing a heating treatment at a temperature of 00 ° C. to 2100 ° C. for 5 to 20 minutes at least once to obtain a silicon carbide powder having a content of each impurity element of 0.5 ppm or less; A method for producing a high-purity silicon carbide powder characterized by the following may also be used.

-Non-metallic sintering aid- The non-metallic sintering aid is not particularly limited as long as it is a substance that generates carbon by heating. For example, an organic compound that generates carbon by heating Alternatively, a silicon carbide powder (particle size: about 0.01 to 1 μm) whose surface is coated with an organic compound that generates carbon by the heating may be used. Among these, an organic compound that generates carbon by heating is preferable in that the effect can be more effectively exerted.

Examples of the organic compound which generates carbon by heating include coal tar pitch having a high residual carbon ratio,
Examples include various sugars such as pitch tar, phenolic resin, furan resin, epoxy resin, phenoxy resin, monosaccharides such as glucose, oligosaccharides such as sucrose, and polysaccharides such as cellulose and starch. Among these, from the point that the silicon carbide powder can be homogeneously mixed, a compound that is liquid at room temperature, a compound that dissolves in a solvent, has properties such as thermoplasticity or heat melting property, and becomes soft or liquid by heating. Are preferred. Among these, a phenol resin is particularly preferred in that a high-strength silicon carbide sintered body can be obtained, and a resole-type phenol resin is most preferred.

The organic compound which forms carbon by heating generates an inorganic carbon-based compound such as carbon black or graphite on the particle surface (near) when heated. It is thought that it works effectively as a sintering aid for efficiently removing the oxide film. The effect cannot be obtained even if carbon black or graphite powder is added as a sintering aid.

The amount of the nonmetallic sintering additive added is
Since it varies depending on the type of the nonmetallic sintering aid used, it cannot be specified unconditionally, but generally, it is preferably 10% by weight or less, and preferably 2 to 8% by weight in terms of carbon to be generated. The following is more preferred. The addition amount is,
When the amount is too small, the density of the obtained silicon carbide sintered body cannot be increased, and when the amount is too large, the free carbon contained in the silicon carbide sintered body increases and the densification is hindered. Sometimes. Here, the amount of addition may be determined by previously quantifying the amount of silica (silicon oxide) on the surface of the silicon carbide powder using hydrofluoric acid and calculating the amount stoichiometrically sufficient for its reduction. it can. In addition, the amount of addition, silica determined by the above method, the carbon derived from the nonmetallic sintering aid, shall be reduced by the following chemical reaction formula, the nonmetallic sintering aid Residual carbon ratio after pyrolysis of carbon (Ratio of carbon formation in nonmetallic sintering aid)
It is a value obtained in consideration of the above.

SiO ₂ + 3C → SiC + 2CO

The purity of the nonmetallic sintering aid is preferably such that the total content of impurity elements is 10 ppm or less.
ppm or less is more preferable. If the total content of the impurity elements exceeds the above numerical range, the purity of the obtained silicon carbide sintered body may not be controlled within the above numerical range. However, the value is not necessarily limited to the numerical value within the above numerical range as long as it is within the allowable range of purification during heating and sintering.

When obtaining the mixture with the silicon carbide powder, the nonmetallic sintering aid is preferably dissolved and dispersed in a solvent and mixed. As the solvent, a suitable solvent can be appropriately selected in combination with the nonmetallic sintering aid. For example, as the nonmetallic sintering aid,
When using a phenolic resin, as the solvent,
Preferable examples include lower alcohols such as ethyl alcohol, ethyl ether and acetone.

-Mixing- In the mixing, the silicon carbide powder and the nonmetallic sintering aid (phenol resin or the like) are dissolved in a solvent (ethyl alcohol or the like), and the silicon carbide powder and the non-metallic sintering aid are mixed with each other. A metal-based sintering aid (a phenol resin or the like) is homogeneously mixed to obtain a mixture (a mixture containing silicon carbide powder).

In the mixing, as described in the section of the silicon carbide powder, it is preferable to mix a nitrogen compound together with the silicon carbide powder and the nonmetallic sintering aid. Dissolve and disperse in a solvent with the sintering aid and mix.

The mixing amount of the nitrogen compound is preferably from 200 to 2000 μg, more preferably from 1500 to 2000 μg, based on 1 g of the nonmetallic sintering aid. When the mixing amount is less than 200 μg, the conductivity of the obtained silicon carbide sintered body may be insufficient,
Even if it exceeds 0 μg, the amount of solid solution of nitrogen in the silicon carbide sintered body saturates, so that a large contribution to conductivity may not be expected.

If the mixture (mixture containing silicon carbide powder) contains at least 500 ppm of a nitrogen component, nitrogen is substantially uniformly contained at about 150 ppm and has a volume resistivity of 1 Ω · cm or less. A silicon carbide sintered body is obtained.

The mixing can be performed by a known mixing means, for example, a mixer, a planetary ball mill or the like. The mixing time is preferably 10 to 30 hours, more preferably 16 to 24 hours. After the mixing, an appropriate temperature according to the physical properties of the solvent (for example, 50 to 60 when ethyl alcohol is used as the solvent)
C) and the mixture is evaporated to dryness and then sieved. From the viewpoint of obtaining high-purity silicon carbide powder, a synthetic resin containing as little metal as possible is preferable as the material of the container or ball of the planetary ball mill. A granulating device such as a spray dryer may be used for the drying.

-Sintering- In the sintering, the mixture (silicon carbide powder-containing mixture) is sintered at 2000 to 2400 ° C. Prior to the sintering, it is preferable that the following heating and heating are performed to sufficiently remove impurities, and the nonmetallic sintering aid be completely carbonized.

--- Heating / heating-- If the heating / heating is difficult to control the temperature of the high-temperature furnace, heating and heating may be performed continuously. It is preferable to perform the first heating step and the second heating step in two stages.

In the first heating step, first, the inside of the furnace is heated to 10 ^-4 t.
Then, the temperature is gradually increased from room temperature to 200 ° C., and maintained at that temperature for a certain period of time. Thereafter, the temperature is further gradually increased to 700 ° C. and the temperature is maintained at a temperature of about 700 ° C. again for a certain time. In the first temperature raising step, adsorbed moisture and an organic solvent are desorbed, and further, carbonization is performed by thermal decomposition of a nonmetallic sintering aid. The holding time can be appropriately selected depending on the desired size of the silicon carbide sintered body. The determination as to whether or not the holding time is sufficient can be based on the point in time when the decrease in the degree of vacuum is reduced to some extent. In the first temperature raising step, if rapid heating is performed, impurities are not removed or the nonmetallic sintering aid is not sufficiently carbonized, and cracks and voids are generated in the obtained silicon carbide sintered body. Sometimes.

In the first temperature raising step, for example,
When the mixture (silicon carbide powder-containing mixture) is about 5 to 10 g, the inside of the furnace is set to 10 ^-4 torr, and the temperature is lowered from room temperature to 200 g.
℃ gently, hold at that temperature for about 30 minutes,
Thereafter, the temperature is further gradually increased and heated to 700 ° C. The time from room temperature to 700 ° C. is 4
10 to 10 hours is preferable, and about 8 hours is more preferable. Further, thereafter, it is particularly preferable to maintain the temperature at about 700 ° C. for about 1 to 5 hours.

In the second temperature raising step, for example,
The mixture (a mixture containing silicon carbide powder) is the same
In the case of about 10 g, in vacuum, further 700 ° C.
From 1500 to 1500 ° C over 3 to 9 hours, and then held at 1500 ° C for 1 to 5 hours. It is considered that in the second temperature raising step, a reduction reaction of silicon dioxide or silicon oxide is performed. In the second temperature raising step, it is necessary to sufficiently complete the reduction reaction in order to remove oxygen bonded to silicon. Therefore, 1
At a temperature of 500 ° C., the generation of by-products (carbon monoxide) by the reduction reaction is completed, that is, the decrease in the degree of vacuum is reduced, which is the temperature before the start of the reduction reaction.
It is necessary to maintain that temperature until the degree of vacuum at around 00 ° C. is restored. The reduction reaction in the second temperature raising step removes silicon dioxide that adheres to the surface of the silicon carbide powder, hinders densification, and causes large grain growth. The gas containing SiO and CO generated during this reduction reaction is accompanied by impurity elements, but these generated gases are constantly discharged and removed to the reaction furnace by a vacuum pump. From the point of purification,
It is preferable that the temperature is sufficiently maintained.

--Sintering-- The sintering is a so-called hot press, in which the inside of the furnace is pressurized to a constant pressure and the temperature is from 2000 to 2400 ° C.

Prior to the sintering, it is preferable to introduce an inert gas to make the inside of the furnace a non-oxidizing atmosphere. Examples of the inert gas include nitrogen and argon, but it is preferable to use an argon gas because it is non-reactive even at a high temperature. As the inert gas, from the viewpoint of obtaining a high-purity silicon carbide sintered body, one having a low total content of impurity elements is preferable, and specifically, the total content of the impurity elements is preferably 10 ppm or less. , 500
ppm or less is more preferable. However, as long as it is within the allowable range of purification in the heating / sintering step, it is not necessarily limited to the above numerical range.

In the sintering, the temperature is raised from 1500 ° C. to a maximum temperature of 2000 to 2400 ° C. over a period of 2 to 4 hours.
Hold at 0 ° C. for 1-3 hours to complete sintering. When the maximum temperature is less than 2000 ° C., the density of the silicon carbide sintered body is insufficiently increased, and when it exceeds 2400 ° C., the mixture (powder or raw material of the compact) is sublimated (decomposed). May be. The sintering itself was performed at a temperature of 1850.
It progresses rapidly when it reaches ~ 1900 ° C.

The pressing is performed for the purpose of preventing abnormal grain growth of the silicon carbide sintered body. As the pressure at the time of the pressurization,
It is preferably from 300 to 700 kgf / cm ² , and within this numerical range, it can be appropriately selected according to the particle size of the mixture (powder) as a raw material. Generally, when the raw material powder has a small particle size, a suitable sintered body can be obtained even when the pressure at the time of pressurization is relatively small. The pressure is 300 kgf / cm ²
If it is less than 700 kgf / cm ² , the density of the silicon carbide sintered body will be insufficient. If it exceeds 700 kgf / cm ² , it may cause breakage of a mold such as a graphite mold. Not preferred. The temperature inside the furnace is 1500 ° C.
Since the sintering (hot pressing) starts when the temperature rises to a higher temperature, it is necessary to simultaneously apply pressure at this time.

As a molding die used for the sintering, a molding die is preferable. As the molding die, from the viewpoint of obtaining a high-purity silicon carbide sintered body, a (silicon carbide sintered body) is formed so as to prevent direct contact between the molded body and a metal part of the molding die. It is preferable to use a high-purity graphite material for part or all. When a graphite mold is used as the molding die, it is preferable to use a high-purity graphite raw material from the viewpoint of obtaining a high-purity silicon carbide sintered body. As the graphite raw material, a high-purity processed material is used,
Specifically, it is preferable that the baking is sufficiently performed in advance at a temperature of 2500 ° C. or more and no impurities are generated at the sintering temperature. Similarly, the heat insulating material of the heating furnace is preferably high-purity treated from the viewpoint of obtaining a high-purity silicon carbide sintered body.

Although the details of the relationship between the conductivity development mechanism and the sintering temperature are not clear, it is considered as follows. That is, in the method of manufacturing a silicon carbide sintered body, the fusion of the raw material particles becomes active from about 1800 ° C., so that at a high temperature of 1800 ° C. or more, electrons flow across the grain boundaries and within the grains. It is considered that the conductivity controlled by the mechanism appears. In the region of 1800 ° C. or lower, that is, in a region where the fusion of the raw material particles has not progressed so much, the electrons when energized flow through the carbon surrounding the silicon carbide, so that the mechanism of exhibiting conductivity is considered to differ depending on the sintering temperature. .

The sintering provides a silicon carbide sintered body having excellent characteristics. From the viewpoint of increasing the density of the obtained silicon carbide sintered body, if necessary, prior to the sintering, Can be performed.

That is, the mixture of the silicon carbide powder is filled in a predetermined mold, and heated and pressurized at a constant temperature and a constant time,
This is a step of obtaining a molded body of a mixture containing silicon carbide powder in advance (hereinafter, may be appropriately referred to as a “molded body”). In the filling, from the viewpoint of obtaining a silicon carbide sintered body of higher density, a mixture containing the silicon carbide powder,
It is preferred to fill a given mold as tightly as possible. By performing the above-mentioned step, when filling the mixture containing the silicon carbide powder in the subsequent sintering, the bulky mixture (the mixture containing the silicon carbide powder) can be made into a compact shape in advance. A sintered body (for example, a large and thick one) can be efficiently manufactured.

The heating temperature varies depending on the characteristics of the nonmetallic sintering aid, and cannot be specified unconditionally, but is preferably from 80 to 300 ° C., and more preferably from 120 to 140 ° C.
C is more preferred. The pressure in the pressurization is 6
0 to 100 kgf / cm ² is preferable. The density of the filled raw material powder (silicon carbide powder-containing mixture) is preferably 1.5 g / cm ³ or more, and preferably 1.9 g / cm ^3.
Three or more is more preferable. Therefore, it is preferable that the pressure at the time of the pressurization is appropriately selected within a numerical range of 60 to 100 kgf / cm ² so that the density is a numerical value within the numerical range. The heating and pressurizing time is preferably 5 to 60 minutes, more preferably 20 to 40 minutes. Here, as the average particle size of the raw material powder (silicon carbide powder-containing mixture) becomes smaller, it becomes more difficult for the compact to become dense. In order to increase the density, it is preferable to perform vibration filling or the like when filling the predetermined mold with the raw material powder. Specifically, the average particle size of the raw material powder is 1 μm
In this case, the density is preferably 1.8 g / cm ³ or more, and the average particle size of the raw material powder is 0.5 μm
In this case, the density is more preferably 1.5 g / cm ³ or more. If the density is less than the above range, it may be difficult to increase the density of the finally obtained silicon carbide sintered body.

If necessary, the molded body may be subjected to a cutting process before the next sintering so as to be suitable for a molding die used for the sintering.

The production apparatus used for producing the silicon carbide sintered body is not particularly limited as long as the pressure resistance required for the sintering mold can be obtained. It can be suitably used.

In the silicon carbide sintered body obtained as described above, the total carbon atom content derived from the silicon carbide compound and the nonmetallic sintering aid is 30% of the silicon carbide sintered body. It is preferable that the content be more than 40% by weight and less than 40% by weight. When the content is 30% by weight or less, the proportion of impurities contained in the silicon carbide sintered body increases, and when the content exceeds 40% by weight, the carbon content increases. The density of the silicon sintered body may decrease, and various properties such as the strength and oxidation resistance of the silicon carbide sintered body may deteriorate.

(Motor Brush) The motor brush of the present invention is manufactured by processing the silicon carbide sintered body obtained as described above into a predetermined shape, polishing, washing and the like. As the machining method, electric discharge machining or the like is preferably used because the silicon carbide sintered body preferably has conductivity.

The brush for a motor according to the present invention is characterized in that the silicon carbide sintered body as a material is excellent in strength, conductivity, heat resistance, abrasion resistance, and corrosion resistance (oxidation resistance, chemical resistance). From the viewpoint of taking advantage of the above, at least the sliding portion in contact with the commutator of the motor brush may be formed of the silicon carbide sintered body, but may be entirely formed of the silicon carbide sintered body. .

Since the brush for a motor of the present invention uses the above-mentioned specific silicon carbide sintered body as its material, it is low-cost, and has low conductivity, strength, heat resistance, abrasion resistance, corrosion resistance (oxidation resistance). , Chemical resistance), and can prevent the occurrence of arc discharge (e.g., radio interference due to arc discharge, abnormal film formation, etc.) and noise.

The motor brush of the present invention can be used as a motor brush of any type and shape.
Also, for example, optical precision equipment such as a camera, audio / video equipment such as a CD player, OA equipment such as a copying machine, household electric equipment such as a microwave oven, automobile such as an electric mirror, and toys such as an electric doll. It can be equipped with motors of different types and shapes. This results in a motor that is low cost, has excellent durability and productivity, and has low drive noise.

(Motor) The motor of the present invention includes the motor brush of the present invention. Specifically, as shown in FIG. 1, a casing 1, a permanent magnet 2 fixed to an inner peripheral surface of the casing 1, and a rotating shaft 4 rotatably supported inside the casing 1 include an armature 5 and an armature 5. A rotor 3 having a commutator 6 electrically connected to the armature 5;
And a brush 7 that has been slid in contact with the small motor.

The motor of the present invention is a motor having excellent durability because the motor brush of the present invention is excellent in strength, abrasion resistance and the like and can prevent occurrence of arc discharge.

The motor of the present invention has an atmosphere structure inside the motor for the purpose of preventing, for example, arc discharge, from the viewpoint that the motor brush of the present invention has excellent corrosion resistance (oxidation resistance and chemical resistance). When enclosing the agent or the like, there is an advantage that the selection range of the type is widened, from the viewpoint of excellent heat resistance, an advantage that there is no need to provide a cooling means such as a cooling fan, and it is possible to prevent occurrence of arc discharge. From a possible viewpoint, there is an advantage that there is no need to provide a spark quenching element in the rotor, for example. For this reason, the motor of the present invention is a motor with excellent productivity and cost reduction.

In the motor of the present invention, since at least the sliding portion of the motor brush of the present invention, which is in contact with the commutator of the motor brush, is formed of the silicon carbide sintered body, the motor has low driving noise. It is.

The motor of the present invention is not limited to the above-described structure. The structure other than the motor brush of the present invention is the same as the structure of any conventionally known and any kind of motor.

[0093]

EXAMPLES The present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

Example 1 6 g of resole type phenol resin containing amine (residual carbon ratio after pyrolysis: 50%), high purity β having an average particle size of 2.0 μm and one particle size distribution maximum value
-94 g of silicon carbide powder was mixed in a wet ball mill in 50 g of ethanol solvent, dried, and formed into a column having a diameter of 20 mm and a thickness of 10 mm. The amount of the phenol resin and the amount of the amine contained in the molded product were 6 wt% and 0.1 wt%, respectively. The formed body was sintered by a hot press method under a pressure of 700 kgf / cm ² under an argon gas atmosphere at a temperature of 2300 ° C. for 3 hours to obtain a silicon carbide sintered body.

The physical properties of the obtained silicon carbide sintered body were measured by the following methods. (Conductivity variation index (β value)) Relative permittivity (relative permittivity on high frequency side: ε _O , relative permittivity on low frequency side: ε∞) and relative permittivity of sintered body obtained using AC circuit The maximum value (ε _max ) of the relative dielectric loss factor obtained from the loss factor measurement is calculated using the above equation (Maxw).
(Wellner equation).

(Volume Resistivity) Resistivity Meter (Lorester A)
P, manufactured by Mitsubishi Chemical Corporation) and four deep needles for semiconductors (electrode spacing 1)
mm), the potential difference was measured by the four-deep needle method in which the potential difference was read by the inner electrode when 1 mA was applied between the electrodes at both ends.

(Nitrogen Analysis) In nitrogen analysis, 10 mg of a sintered body obtained by pulverizing an agate mortar was placed in a nickel capsule manufactured by Japan Analyst Co., Ltd., and analyzed by a LECO Co., Ltd. TC-436 oxygen-nitrogen analyzer. The sample was subjected to a dehydration treatment in a graphite crucible manufactured by LECO for 30 seconds, and then heated and burned at 2000 ° C. The gas generated at this time was once purified by a dust trap, and then analyzed using a thermal conductivity detector.

As a result of the measurement, the density of the obtained silicon carbide sintered body was 3.11 g / cm ³ , it contained 200 ppm of nitrogen, and had a volume resistivity of 10 ⁻¹ Ω · cm.
Met. The dispersion index β value of the conductivity was 0.998.

The obtained silicon carbide sintered body was cut into a desired shape to prepare a motor brush.

Using the obtained motor brush, FIG.
A motor as shown in FIG.

<Evaluation> The obtained motor was repeatedly applied with a voltage at an interval of 10 seconds, and tested for 6 hours (1080 cycles). As a result, the weight reduction of the motor brush was 0.1%. The driving noise near the motor when the voltage was applied was about 52 dB.

Comparative Example 1 A motor was prepared and evaluated in the same manner as in Example 1 except that a metal brush (made of beryllium copper) was used instead of the motor brush made of a silicon carbide sintered body. As a result, the weight reduction of the metal brush was 0.4%. In addition, the metal brush was deformed by heat, and abnormal wear and film formation due to arc discharge were slightly observed. Further, the driving noise near the motor when applying a voltage was about 52 dB.

(Comparative Example 2) In the same manner as in Example 1 except that a carbon brush (made of graphite powder hardened with a thermosetting resin) was used instead of the motor brush made of a silicon carbide sintered body. A motor was fabricated and evaluated. As a result, the weight reduction of the carbon brush was 0.1%. Also, the carbon brush was not deformed by heat,
Abnormal wear due to arc discharge or fine particles,
Film formation was observed. Furthermore, the driving noise near the motor when applying voltage was about 55 dB.

According to Example 1 and Comparative Examples 1 and 2, the motor provided with the brush for the motor using the specific silicon carbide sintered body has a small weight loss, excellent abrasion resistance, and no deformation due to heat. It turns out that it is excellent in intensity | strength and heat resistance, and there is no arc discharge and conductivity is favorable. Also, it can be seen that the driving noise is small.

[0105]

As described above, low cost, excellent conductivity, strength, heat resistance, abrasion resistance, corrosion resistance (oxidation resistance, chemical resistance), and arc discharge (radio interference due to arc discharge, abnormalities) A motor brush that can prevent the generation of driving noise, and a low-cost motor-equipped brush.
It is possible to provide a motor that has excellent durability and productivity and has low driving noise.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing one example of a motor of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Casing 2 Permanent magnet 3 Rotor 4 Rotating shaft 5 Armature 6 Commutator 7 Brush

Claims (6)

[Claims] At least a sliding portion of a brush for a motor, which is in contact with a commutator, has a volume resistivity of 1 Ω · cm or less,
A motor brush formed of a silicon carbide sintered body having a density of 2.9 g / cm ³ or more. 2. The motor brush according to claim 1, wherein the conductivity variation index (β value) defined by the following equation (1) of the silicon carbide sintered body is 0.8 or more. . Equation (1) ε _max = 1/2 (ε ₀ −ε∞) tan (βπ / 4) ε _max : maximum value of relative dielectric loss factor in the silicon carbide sintered body ε ₀ : high frequency side in the silicon carbide sintered body Ε∞: dielectric constant on the low frequency side in silicon carbide sintered body 3. A silicon carbide sintered body comprising: a mixture of silicon carbide powder, a nonmetallic sintering aid, and a nitrogen compound;
The motor brush according to claim 1, wherein the brush is obtained by sintering at 00 to 2400 ° C. 4. 4. The silicon carbide powder is obtained by mixing at least one kind of silicon compound and at least one kind of organic compound that generates carbon by heating and baking the mixture. Item 4. A motor brush according to item 3. 5. A silicon carbide sintered body obtained by mixing and firing at least one kind of a silicon compound, at least one kind of an organic compound which generates carbon by heating, and a nitrogen compound; The motor brush according to claim 1, wherein the brush is obtained by mixing a metal-based sintering aid and sintering at 2000 to 2400 ° C. 4. 6. A motor comprising the motor brush according to claim 1.