JP2001119903A - Brush and motor fitted therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain brushes whose contact is likely to have few defect, and a motor fitted with the brushes by lowering their coefficient of friction, without having to increase their specific resistances. SOLUTION: A brush is composed of copper and graphite, and is obtained by performing sintering after compression molding. The brush is obtained by mixing copper-plated first graphite powder, and second graphite powder having particle diameter which is 10-50 times as large as that of the first graphite powder, thereafter performing compression molding, and performing sintering.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brush obtained by compressing and firing copper and graphite powders and a motor provided with the brush.

[0002]

2. Description of the Related Art It has been known that, in a brush made of copper powder and graphite powder used for a DC motor, a voltage drop occurs at a contact portion between the brush and a commutator.
This voltage drop is a contact resistance between the brush and the commutator and is known to be caused by a copper oxide film. To reduce this resistance, it is necessary to partially break through the oxide film. This can be achieved by increasing the copper content in the brush composition or by increasing the force pressing the brush against the commutator. Become.
The latter has a problem that even if the friction coefficient is the same, the friction force increases as a result. Therefore, there is a limit to the need to achieve both a frictional force and a voltage drop at a contact portion.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a brush which does not cause a voltage drop and does not increase frictional force, and a motor provided with the brush.

[0004]

According to a first aspect of the present invention, there is provided a first graphite powder having a metal-plated surface, and a first graphite powder having a particle diameter 10 to 50 times that of the first graphite powder. This is a brush which is obtained by mixing and compression molding with 2 graphite powders and then firing.

According to a second aspect of the present invention, in the brush according to the first aspect, the metal plating is copper plating.

A third invention is the brush according to the first aspect, wherein the second graphite powder has a cocoon shape and extends along the longitudinal direction of the brush.

Further, a fourth invention is a motor provided with the brush according to the first to third aspects.

[0008]

First, in the brush according to the first aspect of the present invention and the motor according to the fourth aspect, the first graphite powder, the second graphite powder, and the powder that is almost the material are provided with the graphite powder. The ratio is large enough. As a result, since the ratio of copper is not increased, the coefficient of friction is not increased, and the occurrence of poor contact of the brush is reduced. Further, since the first graphite powder is metal-plated on its surface, the first graphite powder is mixed with the second graphite powder inside the brush and the metal is uniformly distributed.
In addition, when firing in the longitudinal direction in which the current of the brush flows, the adjacent metal plating surfaces are connected and continuity is maintained, so that the specific resistance of the brush is not increased. Therefore, no voltage drop occurs. The second graphite powder is 10 to 10 of the first graphite powder.
It has 50 times the particle size. Here, based on the size of the particle size of the second graphite powder, the metal-plated first graphite powder is sufficiently smaller than the second graphite powder by 1/10 or less. The particles can reliably enter the gaps between the particles. In addition, the metal-plated first graphite powder maintains a certain size of 1/50 or more of the second graphite powder, so that the amount of metal in the first graphite powder is more than necessary for graphite. This eliminates the increase in frictional force during brush wear.

In the brush according to the second aspect of the present invention and the motor according to the fourth aspect, since the metal plating is copper plating, the conductivity of the brush main body is improved, and the adhesion is excellent when plating the graphite powder. Therefore, the first graphite powder is easily generated in advance.

In the brush according to the third aspect and the motor according to the fourth aspect, the second graphite powder, which is a main component of the brush main body, has a cocoon shape, so that it extends along the longitudinal direction in which the current of the second brush flows. The metal of the first graphite powder is disposed. Therefore, conductivity is improved. In addition, the longitudinal cross-section of the metal is reduced, so that the frictional force at the time of contact between the brush and the commutator is reduced.

[0011]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of a motor using the present invention, FIG. 2 is a detailed drawing of a brush of a first embodiment of the present invention, and FIG. 3 is a detailed drawing of a brush of a second embodiment of the present invention. FIG. 4 is a graph showing the resistance value and the frictional force value of the entire brush when the particle diameter ratio of the second graphite powder to the first graphite powder of the embodiment is gradually changed.

In FIG. 1, a brush 1 using the present invention is shown.
Are in contact with the commutator 2, and the DC motor 3 has the brush 1 and the commutator 2.

FIG. 2 shows a first embodiment. The first graphite powder 11 (open circle in FIG. 2) of the brush 1 is a material in which plated copper 112 is adhered to the surface of graphite powder 111 before compression firing, and is made of two materials, graphite and copper. It becomes. The particle size of the first graphite powder is about 10 μm. On the other hand, the second graphite powder 12 (black dot circle in FIG. 2) is formed from only the graphite powder 121 before the compression firing, and the particle diameter of the powder is about 100 μm to 500 μm. The particle size of the powder in the second graphite powder is about 10 to 50 times the particle size of the powder in the second graphite powder. As a method of forming the brush 1, first, a first graphite powder 11, which is a graphite powder whose surface is copper-plated, and a second graphite powder consisting of only graphite powder are mixed so as to be uniform. The mixed powder of the first graphite powder and the second graphite powder is put into a mold (not shown) having a brush-like rectangular parallelepiped groove. Then, the groove is pressurized by another mold, and the mixed powder is compressed. The result is a compression formed brush. This compression forming brush has a rectangular parallelepiped shape and is almost the same as the shape before completion.
By baking this compression-molded brush, the copper of the copper plating on the surface of the first graphite powder is melted and the adjacent copper is connected, so that the electrical conductivity of the brush in the axial direction is improved.

The hardness of the first graphite powder may be higher than the hardness of the second graphite powder. For example, the adjustment may be made by increasing the grade of the graphite material or changing the material of the binder used at the time of graphite particle milling. As a result, when the amount of copper is reduced, the brush body 1 is not broken by an external force.

Next, the operation will be described. Since graphite works as a lubricant when the brush 1 and the commutator 2 are in sliding contact with each other,
If the sliding area of graphite is large and the graphite is uniformly dispersed on the entire sliding surface, the sliding property is improved. In the first embodiment of the present invention, copper plating is uniformly provided on the surface of the first graphite powder as shown in the detailed view of FIG. 2, and the first graphite powder is uniformly mixed with the second graphite powder. In this case, the concentration of copper is suppressed locally, the increase in the coefficient of friction is suppressed on average, and a brush having low friction and low specific resistance as a whole can be obtained. In addition, since copper is provided on the surface of the first graphite powder, a contact state between adjacent coppers is ensured. In this state, the brush is compressed and fired, so that the conductivity of the brush 1 is improved. Here, as a result of using copper as the metal plating, the conductivity is relatively high as compared with other metals, and the adhesion to graphite is high as the plating, so that the conductivity when a brush is formed is good.

FIG. 3 shows a second embodiment. In this example, the shape of the second graphite powder 12 (black spotted ellipse in the figure) has a cocoon shape, and the long direction of the cocoon shape matches the longitudinal direction in which the current of the brush flows. As a result, the inside of the brush 1 that has been compressed and fired is formed such that the copper 112 of the first graphite powder 11 (open circle in the figure) is continuously connected in the longitudinal direction, so that the electric current flows in the longitudinal direction. Since many copper conductive lines are formed, the conductivity is improved and the resistance is not reduced. In addition, the frequency at which copper is exposed on the brush surface viewed from the longitudinal direction due to wear of the brush 1 is suppressed.

The arrangement of the cocoon-shaped second graphite powder 12 is as follows:
When a mixed powder obtained by mixing the first graphite powder and the second graphite powder is put into a centrifugal separator in which a force is applied in one direction and a load is applied to the mixed powder for a long time, the orientation of the cocoon-shaped second graphite powder is changed. Can be aligned in one direction. The brush is completed by putting this mixed powder into a mold without breaking it, compressing and firing.

FIG. 4 is a graph showing the resistance value and the frictional force value of the entire brush when the ratio of the particle size of the second graphite powder to the first graphite powder of the first embodiment is changed. . As shown in this graph, the larger the second graphite powder, the more reliably the first graphite powder enters the gaps between the second graphite powders, so that the conductivity is improved and the resistance value is reduced,
As the copper holding ratio of the first graphite powder increases, the frictional force increases. On the other hand, as the second graphite powder approaches the first graphite powder, it becomes difficult for the first graphite powder to enter the gaps between the second graphite powders, so that the electrical conductivity decreases and the resistance value increases. As the copper holding ratio of the graphite powder decreases, the frictional force decreases. A value that satisfies these two contradictory parameters to some extent is defined as the second value with respect to the particle size of the first graphite powder.
It was determined that the size of the particles of the graphite powder was suitably 10 to 50 times.

[0019]

As apparent from the above description, according to the present invention, it is possible to obtain a brush with reduced friction coefficient and less contact failure without increasing the specific resistance, and a motor provided with the brush.

[Brief description of the drawings]

FIG. 1 is a sectional view of a motor according to an embodiment of the present invention.

FIG. 2 is a detailed view of a brush according to the first embodiment of the present invention.

FIG. 3 is a detailed view of a brush according to a second embodiment of the present invention.

FIG. 4 is a graph showing a resistance value and a frictional force value when the ratio of the particle diameter of the second graphite powder to the first graphite powder of the embodiment is changed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Brush, 11 ... 1st graphite powder 111 ... 1st graphite powder graphite 112 ... 1st graphite powder plating copper 12 ... 2nd graphite powder 121 ... 2nd graphite powder graphite 122 ... 2nd cocoon-shaped graphite Powdered graphite 2 ... commutator, 3 ... motor.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H605 BB05 BB09 CC07 5H613 AA03 BB04 BB15 GA09 GB01 GB05 GB06 GB08 GB09 GB12 GB13 KK02 KK13 QQ03

Claims (4)

[Claims] 1. A brush obtained by mixing and compression molding a first graphite powder whose surface is metal-plated and a second graphite powder having a particle size of 10 to 50 times that of the first graphite powder. 2. The brush according to claim 1, wherein said metal plating is copper plating. 3. The brush according to claim 1, wherein said second graphite powder has a cocoon shape and extends along a longitudinal direction of the brush. 4. A motor provided with the brush according to claim 1.