JPH02285951A - Carbon brush in miniature motor and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve mechanical noise and commutation characteristic by employing a high purity process and reducing the content of ash in graphite powder below 0.05% before metal galvanization process is executed. CONSTITUTION:Graphite material 20 is thrown into a furnace 30, and a halogen gas pipe 32 is placed below the graphite material 20. Then the temperature of the furnace is risen and when the temperature reaches to about 1800 deg.C, inert gas saturated with CCl4 is fed through the halogen gas pipe 32. When the temperature exceeds over 1900 deg.C, CCl4 is switched to CCl2F2 and refining operation is continued for longer than 4 hours under the temperature higher than 2500 deg.C. Flashing is continued with inert gas even through cooling process thus preventing reverse diffusion of impurities and removing halogen. By such arrangement, graphite to be produced through the high purity process has purity higher than 99.95wt.%.

Description

[Detailed Description of the Invention] [Summary] This invention relates to a carbon brush used in a small motor having a permanent magnet field.

The purpose of this invention is to provide a carbon brush with improved mechanical noise and rectification characteristics.

As graphite powder used in metal-plated graphite brushes.

Constructed using refined material with an ash content of 0.05 wt% or less.

[Industrial application field]

The present invention relates to a carbon brush used in a small motor, and particularly to a carbon brush used in a small motor having a permanent magnet field.

[Conventional technology]

Conventionally, carbon brushes in small motors are
A binder is added to the graphite raw material refined to about 99% to 99.5%, and the solidified material is crushed and sieved to obtain the desired conductivity as necessary. The material used is manufactured by first carrying out a metal powder addition and mixing process to give the desired properties, followed by a pressure molding process, and then a sintering process.

Furthermore, there is a so-called tJ! that eliminates the use of the above binder. ! Copper graphite brushes are known. The copper-coated graphite brush is produced by copper plating on powder particles of graphite raw material that has been refined to about 99%, and by press-molding the copper-plated graphite powder as it is, that is, without adding a binder. , manufactured by performing a firing process.

[Problem to be solved by the invention]

In the former case described in the above-mentioned prior art, graphite powder (which also contains ash) is molded and fired together with a binder. For this reason, due in part to the presence of a binder, the compositional strength is high, and when a brush manufactured in this manner is used, mechanical noise tends to be large when it slides on the commutator surface.

On the other hand, in the case of the latter copper-plated graphite brush.

In other words, the surfaces of individual graphite powder particles are covered with a copper coating layer and are pressed into contact with each other to form a bond. For this reason, since no binder is used, the copper-plated graphite brush has less mechanical noise than the former carbon brush.

However, in the case of the conventional copper-plated graphite brush.

Since the graphite powder contains ash, its rectifying properties are not sufficient.

FIG. 7 shows the bonding mode of powder particles in a conventional copper-plated graphite brush. In FIG. 7, reference numeral 11 represents graphite particles, 12 represents a copper coating layer, and 13 represents ash particles.

In the case of conventional copper-coated graphite brushes, ash particles 13 in Figure 1
is in contact with the commutator surface.

The surface of the commutator may be damaged and sparks may easily occur during subsequent commutation, or the presence of the ash particles 13 may cause momentary conduction failure.

The present invention solves the above problems and aims to provide a carbon brush with improved mechanical noise and rectification characteristics.

[Means to solve the problem]

FIG. 1 shows a principle diagram of the present invention, FIG. 1 (^) shows a principle configuration diagram, and FIG. 1 (B) shows a manufacturing process explanatory diagram.

In the figure, the symbol 1 indicates the commutator 52, the commutator piece, 3 the rotating shaft, and 4
is a carbon brush, and 5 is a brush elastic body.

11 represents graphite particles, and 12' represents a metal plating layer such as a copper coating layer.

Further, in FIG. 1(B), 20 is a graphite raw material that has been purified to, for example, about 99%, 21 is a high purity treatment process according to the present invention, 22 is a metal plating process, and 23 is a pressure forming process. , 24 represent the firing process.

The carbon brush 4 is held between conductive brush elastic bodies 5 and supported so as to slide on the commutator pieces 2, 2.2. The carbon brush 4 is fired into a convex shape, for example, as shown in Figure A-1, which is a perspective view.
The convex-shaped head is held between the brush elastic bodies 5. A somewhat curved surface is formed on the surface corresponding to the base of the convex shape, and the curved surface slides on the commutator piece 2.

As shown in Figure A-2, which is an enlarged view of the carbon brush 4, the carbon brush 4 is made of, for example, copper-plated graphite powder particles that are pressure-molded and fired. As shown in Figure A-3, which is a micrograph of the graphite particles, a metal plating layer 12' is formed on each surface of the graphite particles 11. They are bonded by layer 12'.

The carbon brush 4 is as shown in FIG. 1CB),
The graphite raw material 20 is subjected to a high purity treatment process 21, a metal plating treatment process 22, a pressure forming process 23, and a firing process 2.
4.

[For production]

The coated graphite brush itself, which is manufactured by applying copper plating to graphite particles, is well known as described in the section of the prior art. In the state before step 22 is performed, the graphite powder has an ash content of 0.05 wt% or less.

Therefore, among all the metal-plated, pressure-formed and fired particles in the manufactured carbon brush 4, the particles corresponding to ash content are 0.05 wt% or less of the graphite particles.

Therefore, since the metal-plated graphite brushes are formed, there is less mechanical noise during motor operation compared to carbon brushes using conventional binders2, and the ash content is extremely low, resulting in excellent rectification characteristics. Become. That is, although the conventional copper-coated graphite brush was known in concept, it could not be used in reality.

The present invention has brought this to a practical level for the first time.

〔Example〕

FIG. 2 shows a conceptual diagram of a refining furnace used in the high purity treatment process according to the present invention. In the figure, reference numeral 20 represents a graphite raw material, 30 a furnace body, 31 a transformer, and 32 a halogen gas pipe.

The high-purity treatment process uses substances such as CC that easily release halogens at high temperatures in an inert gas such as nitrogen or argon.
It corresponds to the process of removing impurities from graphite raw materials using Z, CC1, F, etc.

That is, the graphite raw material 20 is put into the furnace body 30, and the graphite source i,
: A halogen gas pipe 32 is placed below +20.

When the temperature of the furnace reaches approximately 1800℃.

cce, is saturated with inert gas and the halogen gas pipe 3
Feed from 2. In this case, it may be considered that a first-order reaction takes place, ie.

CCZ4 → C+2 (1!.

3C+FezO3+3CR1-P 2 Fe Ctlz +3 C○ Then, when the temperature reaches 1900°C or higher, CCβ24 is switched to CCβ2 FK, and the purification treatment is continued for 4 hours or more at a temperature of 2500°C or higher. During the cooling process, flushing with an inert gas such as nitrogen or argon is continued to prevent back diffusion of impurities and remove halogen.

The purity of graphite obtained in this high purity treatment process is 99
．． It becomes 95 sit% or more. That is, 5 impurities are 0.05
wt% or less.

In addition, in order to increase the purity of graphite used in metal-plated graphite brushes, the inventors of the present invention have refined the graphite using the following method in addition to the above-mentioned high-precision treatment process. ! A copper graphite brush was manufactured and tested by applying it to a motor.

(i) Impurities and graphite are separated by utilizing physicochemical differences on the surface of solid particles using 11-point scouring flotation, and particles of approximately 300 μm or less are targeted. Because graphite can be sorted by air bubbles,
Graphite powder was placed in oil and bubbles and collected by floating on the bubbles. In this case, a purity of 98% or more and less than 99.5% can be obtained.

Therefore, about 0.5% or more and about 2.0% of impurities are contained.

(ii) Chemically treated impurities contained in graphite are melted with a highly concentrated acid or alkaline solution, and simultaneously heated (160” to 170°C) and pressurized (5 to 6°C).
atmospheric pressure) is added. This treatment method is called an autoclave method, and the reaction of the main components can be considered as follows.

Pe5os "6HCj- 2Fe C1x +3H10 2Si Ox +4Na OH= 2NamSj Os +2H Mushroom 0 In the case of this treatment, a purity of 99% or more and less than 99.9% can be obtained. Therefore, as an impurity, 0.05% or more1
．． It contains about 0%.

FIG. 3 is a diagram illustrating the brush test results. 11
611 is when a conventional carbon brush (containing a binder) is used, Nl11 is when a physically refined t11w4 graphite brush is used, Nnu is when a chemically treated 11m graphite brush is used, and Na is the high purity of the present invention. Each figure shows a case where a coated copper graphite brush obtained through the treatment process is used. 1 for each of the above Nil or NarV
0 brushes were manufactured and tested.

In the case of Nhl, the average value of one mechanical noise was 46 dB, and the results of examining the rectification characteristics using rectified waveforms showed that two out of ten were defective.

In the case of floor ■ and hm, 8! The average value of mechanical noise was 40 dB, but all of the 10 samples had poor rectified waveforms. In contrast to the above, in the case of mJV, the average value of Ia mechanical noise is 38 dB.

The rectified waveforms in all of the 10 brushes shown in Figure 4 (A), (B), (C) and CD) are typical when using the brushes shown in Figure 3. A photograph of an oscilloscope waveform representing a rectified waveform is shown. In addition.

The commutated waveform means the waveform of the motor current while the brush is sliding on the commutator piece.

When the brush of the present invention shown in FIG. 4(D) is used,
The waveform during commutation appears regularly.

This indicates good rectification characteristics.

On the other hand, the cover shown in Figure 4 (B) and Figure 4 (C)
In the case of km shown in , there is a disturbance in the waveform during commutation, and a non-door passing state also occurs at 1 o'clock.

In addition, in the case of 11 m1 shown in FIG. 4 (^), it is approximately regular and within a practical range.

No. 51ffl(a) and (B) are photographs showing the particle structure of the brush of the present invention. These are photographs of the brush of the present invention molded with resin and polished. Figure 5 (A
) is a photograph of a surface cut in the vertical direction in the drawing at A-1 in FIG. As shown in the photograph (5), a copper plating layer is present on the surface of each graphite powder particle.

FIG. 6(B) shows a photograph depicting the particle structure in a carbon brush using a conventional binder. FIG. 6(A) is a photograph corresponding to FIG. 5(A), and FIG. 6 CB) is a photograph corresponding to FIG. 5 CB). In the case of the photograph in FIG. 6, the binder is interposed between the graphite powder particles.

〔Effect of the invention〕

As explained above, according to the present invention, it has become possible to put into practical use a metal-plated graphite brush, which was previously thought to be impossible to put into practical use.

[Brief explanation of drawings]

Figure 1 is a diagram of the principle of the present invention, Figure 2 is a conceptual diagram of a refining furnace used in the high purity treatment process of the present invention, Figure 3 is a diagram explaining the brush test results, and Figure 4 (A) ( B) (C)
(D) is shown in Figure 3? Photographs of oscilloscope waveforms showing typical rectification waveforms when using the brushes shown in &lI to NarV, Figure 5 (A) (B) Photographs showing the particle structure in the brush of the present invention, Figure 6 (A ) (B) is a photograph showing the particle structure in a carbon brush using a conventional binder, and FIG. 7 shows the bonding mode of powder particles in a conventional 5mw4 graphite brush. In the figure, 1 is a commutator, 2 is a commutator piece, 3 is a rotating shaft 4 is a carbon brush, 5 is a brush elastic body, 11 is a graphite particle 91
2' is a metal plating layer, 20 is a graphite raw material, 21 is a high purity treatment process, and 22 is a metal plating process. 23 is a pressure molding process. 24 represents the firing process in FIG.

Claims (2)

[Claims] (1) Used in a small motor that is equipped with a permanent magnet as a field and rotated by commutation through a commutator, and is formed by bonding graphite powder and slides on the commutator. A carbon brush is a metal-plated graphite brush that is formed by covering powder particles of the above-mentioned graphite powder with a metal layer, then press-forming and firing, and the graphite powder used in the metal-plated graphite brush is ，
A carbon brush for a small motor, characterized in that the graphite powder has an ash content refined to 0.05 wt% or less. (2) Used in a small motor that is equipped with a permanent magnet as a field and rotated by commutation through a commutator, and is formed by bonding graphite powder and slides on the commutator. The method for manufacturing carbon brushes involves a high-purity treatment process in which a graphite raw material is purified using a substance that liberates halogens in a high-temperature inert gas atmosphere, and a metal layer is added to the graphite powder that has undergone the high-purity treatment process. A metal plating process for plating the powder, a pressure forming process for press-molding the metal-plated powder, and a firing process for firing the pressure-formed product to form metal-plated graphite. A method for manufacturing carbon brushes in a small motor, characterized by manufacturing a brush.