JP2004265873A - Carbon brush for electric machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a brush having excellent durability, whereby current density can be heightened, because its abrasion is not much, its resistance loss is not much, and accordingly its temperature rise is small. <P>SOLUTION: In this carbon brush for electric machines, which contains carbon as at least one component, a metal layer 1 having electrically excellent conductivity is coated on the surface of a brush base material 2 throughout the entire peripheral surface except for the tip contact part of the surface, so that an electric resistance as an entire carbon brush is reduced, and a hole 5 for attaching a lead wire to the coated base material is formed to attach the lead wire 4 by embedding it in the hole 5 by copper powder. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a carbon brush for an electric machine, and more particularly to a carbon brush having low resistance loss and long durability.

  In recent years, electric motors using carbon brushes for electric machines (hereinafter referred to as brushes) have been reduced in size and capacity in particular, and the brushes used for the brushes have a small resistance loss and small wear. Came to be required.

  For brushes used in slip rings and low-voltage electric motors, metal graphite made by mixing and sintering graphite powder and metal powder has often been used, but in order to reduce the resistance loss of the brush, In addition, when the content of the metal is increased, the lubricating property and the anti-arc property deteriorate, and the amount of wear increases.

  Further, in the case of a motor for an AC commutator motor, if a material having a small resistance is used in order to reduce a resistance loss, there is a problem that commutation is deteriorated and wear is increased.

  Conversely, when a material having a large resistance is used, when a large current is applied, the temperature of the brush rises due to resistance heating. The brush is usually embedded with copper powder, compressing, joining, and supplying current.However, if the brush temperature is high, the copper powder and lead wires in the caulked portion will be oxidized and the current will deteriorate, eventually There is a possibility that a problem that the motor stops will occur.

  In addition, among AC commutator motors, a motor having a high rotation speed such as for a vacuum cleaner has good commutation even at a high rotation speed, and does not require brush replacement during use of the cleaner body. As described above, a resin-bonded material obtained by bonding graphite powder with a resin binder and hardening the resin is sometimes used because of the required characteristics of prolonging the life. However, in the case of a resin-bonded material, when used under conditions where the current density is high, there is also a problem that the temperature of the brush increases due to the large resistance of the brush body, and the resin used for the binder is thermally degraded.

  In order to solve these problems, there is known a brush formed by molding so-called plated graphite in which raw graphite powder is previously plated with copper. For example, JP-A-2-285951, JP-A-2-285952 and the like can be mentioned. However, such brushes can have low contact resistance, but copper is applied as plating on the sliding surfaces of the brushes during operation of the electric motor, damaging the mating slip ring and commutator and increasing the amount of wear on the contrary. There was a problem.

Further, for the purpose of improving the rectification performance, a brush formed by sandwiching a copper-plated expanded graphite sheet in a sandwich shape and molding and hardening has been proposed in JP-A-63-39441. However, also in this case, since the copper plating layer intervenes on the sliding surface of the brush, it damages and damages the sliding surface of the other brush, so that there is a problem that the lubricating property is deteriorated and the wear amount is increased.
JP-A-2-285951 JP-A-2-285952 JP-A-63-39441

  It is an object of the present invention to solve such problems of the prior art and to provide a brush which has a low wear, a long service life, a low resistance loss and therefore a small temperature rise and a high current density. It is in.

The above problems can be solved by coating the surface of a graphite brush base with a metal layer having good electrical conductivity.
That is, in the carbon brush for an electric machine containing carbon as at least one component, the electric conductivity of the entire surface of the brush base material except for the tip contact portion of the surface is reduced so that the electric resistance of the entire carbon brush is reduced. A conductive metal layer, a hole for mounting a lead wire is formed in the coated base material, and the lead wire is embedded and mounted in the hole with copper powder. is there.

According to the present invention, the apparent resistance of the brush is reduced, the resistance loss is reduced, and the efficiency can be increased. Also, it was possible to suppress the temperature rise of the brush.
Further, since the metal film is relatively thin, it is sequentially oxidized and peeled off from the portion near the sliding surface by the operation of the electric motor, so that the other surface such as the commutator or the slip ring is not damaged.

  Originally, as a brush base material, (a) graphite powder was kneaded with a binder such as a thermosetting resin and then cured (resin bond type); (b) graphite powder was used as a thermosetting resin or pitch. Kneaded with a binder and calcined at a low temperature to carbonize the binder component (CG system); (c) further calcined at a high temperature to graphitize at least a portion of the carbon component (EG system) There is.

  In the present invention, the resin-bonded base material (a) described above is a main object. In a resin-bonded base material, the resin used as a binder is used in a cured state, and is not carbonized or graphitized, and thus has relatively high electrical insulation. Therefore, there is an advantage that the resistance is large and the rectification is good. Conversely, a large resistance loss due to a large resistance results in a disadvantage that a large amount of heat is generated. As a result, a continuous use under a high temperature condition for a long time causes a disadvantage that the resin is deteriorated and the characteristics are changed.

  The requirement for such conflicting properties is that the outer surface around the brush base material is coated with a highly conductive metal such as nickel, copper, gold, silver, etc., so that the resistance of the inner base material is high. However, it is possible to compensate for all the drawbacks of resin-bonded base materials, such as lowering the apparent resistance, suppressing the temperature rise, and preventing the performance change due to continuous use of the brush by the action of the outer good conducting film. Thus, a very high-performance brush can be made.

  In the present invention, as a method for coating the surface of the brush substrate with good electrical conductivity, a method using plating can be considered. For this reason, as a plating method, a method using electrolytic plating and a method using chemical plating (electroless plating) were used. Metal coating could be applied by any of the methods.

  However, when the brush was actually mounted on a motor and tested, it was found that electroless plating was superior to electrolytic plating in terms of the difficulty in peeling the metal coating and the substrate.

  This is evident from the fact that electroless plating technology has made great strides with IC technology, and is also used for metal coating on printed circuit boards such as resin, which is an electrically defective conductor. As described above, in terms of surface coating on a substance in which a carbon component (good conductivity) and a resin component (defective conductor) are mixed, such as the base material of the brush of the present invention, electrolytic plating covered mainly with an electric good conductor Rather than the method, on the resin, also on the carbon, the electroless plating method in which the liquid impregnated through the pores and through the pores reaches the deep part of the brush base material and is chemically plated, The present inventor has found that a metal coating that does not easily peel off can be formed from the viewpoints of anchor effect, plating uniformity, and the like. The present invention has been completed based on this new finding.

  However, in the present invention, in addition to the above-described action of plating, in practice, in a brush of this kind in which a carbonaceous portion and a resinous portion are mixed, the electroless plating method can be used. It is based on the results of practical studies that a metal coating can be formed on the surface of the brush, the electrical resistance of the entire brush can be reduced, and the motor efficiency can be greatly improved.

  Such practical research results are also exhibited in the case of CG and EG systems other than the resin bond system.

  Further, in the case of a resin bond system, the surface of the base material before plating is generally smooth, so that the surface of the product after plating is relatively smooth, and it also has a feature that the appearance is good in terms of merchandise.

  In the present invention, as a method of electroless plating, a method known from literatures and the like is widely used. For example, it is described in detail in "Electroless Plating" [Maki Shoten, Tokuzo Kobe (1986)], and a robust film can be formed on the surface of the brush substrate according to the present invention. As described in the above literature, the principle of electroless plating is as follows. For example, when copper is exemplified, an alkali tartrate, EDTA or the like is added as a complexing agent to a copper salt aqueous solution to form a complexed state under weak alkalinity. And forming a copper film on the substrate by using a formaldehyde or hydrazine salt as a reducing agent. The reaction is represented by the following chemical formula 1.

  This reaction is convenient because a coating of a metallic film can be formed on the surface of the brush substrate by a pure chemical reduction method at room temperature.

  Of course, coating with a metal plating layer formed by a well-known electrolytic method has the same effect as the chemical plating method (electroless method).

  As described above, the present invention is intended to provide a coating (sheath) of a metal material having good electrical conductivity on the surface of the brush base material to reduce the electrical resistance of the entire brush and improve the power efficiency of the device. As the means for coating with a metal material, not only the particularly preferred electroless plating method exemplified above, but also an electrolytic plating method, a vacuum deposition method, an ion plating method, a cluster ion beam method and the like can be widely applied.

  Regarding the thickness of the coating layer by such means, if the thickness of the layer is too large, the sliding surface of the mating member tends to be roughened during sliding, and the abrasion of the brush and the mating material tends to increase, and conversely, extremely When it is thin, the effect of covering the brush substrate is small, in other words, the resistance of the brush does not decrease so much, the resistance loss is large, and the power effect is reduced. Usually, about 3 to 100 microns is preferable.

  Regarding the metal species used as the brush coating layer, any metal can be used as long as it is a good conductor of electricity and can be electrolessly plated or vapor-deposited, but from the viewpoint of manufacturing cost and ease of coating, copper, silver, nickel or Gold is generally preferred.

  As described above, the description has been given of the case where the base material is (a) a resin bond type, (b) a CG type, and (c) an EG type. The present invention can also be applied to a base material using as a raw material. In other words, in order to reduce the resistance due to the brush base material, a two-component system in which graphite powder is mixed with fine metal powder, for example, copper powder, silver powder, etc., and further consolidated, if necessary, further contains a resin component as a small amount of binder component. The present invention can also be applied to a mixed and consolidated three-component brush base material. However, when a metal powder is added, the electric resistance of the base material itself is smaller than that of a resin bond system, so the method of the present invention is used. Although the effect of forming the metallic outer coating by the above is recognized, the effect is relatively weakened.

Such a metallic coating (1) is not formed on the brush sliding surface (2) as shown in FIG. (Corresponding part) is removed, and the brush base material (3) is attached to an electric device via a lead wire (4) in a state where the brush base material (3) is exposed and used.
FIG. 2 is a cross-sectional view of FIG. 1. As shown in FIG. 2, a hole for attaching a lead wire is formed in the coated base material, and the lead wire (4) is embedded with copper powder (5). Install. Alternatively, after forming the lead wire mounting hole, a metal coating may be applied to cover the inside of the lead wire mounting portion, but the metal coating is preferably performed as shown in FIG.

[Example]
Hereinafter, embodiments of the present invention will be described. However, a comparative example which is a production example of the brush base material is also described. In these examples, parts indicate parts by weight.

[Comparative Example 1]
To 100 parts of artificial graphite having an average particle size of 40 microns, a two-part epoxy resin and 25 parts of a curing agent were added and kneaded. A commercially available bisphenol-based epoxy was used as the epoxy resin, and an acid anhydride was used as the curing agent. The kneaded material was pulverized and compression-molded, and then heated to 220 ° C. to advance the curing reaction, thereby obtaining a substrate (A) to be used in the present invention.

[Example 1]
The substrate (A) obtained by the method shown in Comparative Example 1 was cut into the shape of a test brush, immersed in an aqueous solution of copper sulfate, and then sodium hydroxide and potassium tartrate were added to the solution. A film of reduced copper was formed on the substrate surface. The thickness of the coating layer was about 3 to 10 microns.

[Comparative Example 2]
A phenolic resin was used as a resin component in the method of Comparative Example 1, and after molding in the same manner as above, the mixture was heated to 550 ° C. to 600 ° C. in a non-oxidizing atmosphere to carbonize the resin component, and a CG-based substrate (B ) Got.

[Example 2]
In the same manner as in Example 1, the surface of the substrate (B) was coated with copper by an electroless plating method.

[Comparative Example 3]
The pitch is added to the soot, and the mixture is heated and kneaded, cooled, pulverized, compression-molded, heated in a non-oxidizing atmosphere to carbonize the binder pitch, and then heated to 3000 ° C. in a graphitization furnace to form an EG-based substrate. (C) was obtained.

[Example 3]
In the same manner as in Example 1, the surface of the substrate (C) was coated with copper by an electroless plating method.

  (I) Brushes A ', B', and C 'each having a metal coating on brush substrates A, B, and C according to the present invention and, as comparative examples, the same substrates A, B, and C as raw materials thereof. A brush of the same shape was produced as it was without applying metal coating, and the effect of metal coating was compared and confirmed. However, each brush was unified to a size of 6 × 8 × 25 mm, and the lead wires were connected to the brush body by an embedding method using copper powder.

(II) Test measurement method.
(A) Measurement method of caulking resistance The caulking resistance is the electrical resistance of the connection between the brush lead wire and the brush body, and is calculated according to the method described in JIS-12-1968 (see FIG. 3). ]. However, d in FIG. 3 indicates a distance of 5 mm.

Here, E: voltage drop at the caulking (lead wire attachment) portion, I: measured current, R: caulking resistance, this time multiplied by 10 ^-6 and expressed in μΩ.

(B) Contact voltage drop measurement The contact voltage drop measures a voltage drop before and after the brush in a state where the brush is in contact with a rotating ring or a commutator. FIG. 4 shows a measurement principle diagram. However, 6 in FIG. 4 indicates a simulated commutator.

However, the measurement was performed at a diameter of a simulated commutator of φ25 mm, 24 bars, a rotation speed of 25,000 rpm, and a brush load of 400 g / cm ² .

(C) Brush Temperature Measurement A small hole was drilled from the lead wire mounting surface of the brush body to a depth of 3 mm from the sliding surface in contact with the commutator, and a thin thermocouple was inserted to measure the operation of the motor.

(III) Measurement results Table 1 shows the results measured by the above method.

(IV) Description of Measurement Results As is evident from the results in Table 1, in any case, by providing an electrically conductive coating layer around the substrate, the electrical resistance of the brush as a whole, that is, the lead wire and the main body, In each case, the apparent resistance including the caulking resistance, the resistance in the brush body, and the contact resistance between the brush and the commutator was reduced. The degree of the effect is greatest when a metal coating is applied to a resin bond system having a large electric resistance of the base material itself (Example 1), and is applied to a carbon-based or EG-based material having a small resistance of the base material itself. When the coating is applied, the degree of the effect appears to be relatively small.

  It is clear that as a result of the reduction in the resistance of the brush body, the resistance loss of the brush is reduced, and the efficiency of the motor and thus the efficiency of the electric equipment are improved.

  As a supplementary experiment, as a result of measuring the temperature rise of the brush main body using a thermocouple, the value of the current flowing through the brush was about 30 ° C. lower in the case of Example 1 than in the case of Comparative Example 1. It was confirmed that the temperature rise due to resistance heating was small.

  In addition, the result of the life test of the brush showed that the wear rate of Example 1 was almost the same as that of Comparative Example 1.

FIG. 1 is a perspective view of an example of the carbon brush of the present invention. FIG. 2 is an explanatory diagram for explaining the mounting of the lead wire of FIG. FIG. 3 is a diagram showing a circuit for measuring electric resistance according to JIS-12-1968. FIG. 4 is a drawing showing a circuit for measuring the contact voltage drop of the brush.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Metallic coating 2 Brush sliding surface 3 Brush base material 4 Lead wire 5 Copper powder

Claims (4)

  In an electromechanical carbon brush containing carbon as at least one component, an electrically conductive metal is provided on the surface of the brush base material, except for a contact portion at the tip of the surface, so that the electrical resistance of the entire carbon brush is reduced. A carbon brush for an electric machine, comprising: coating a layer; forming a hole for mounting a lead wire on the coated base material; and embedding the lead wire in the hole with copper powder.   2. The carbon brush for an electric machine according to claim 1, wherein the electrically conductive metal layer is formed by an electroless plating method, and the thickness of the electrically conductive metal layer is 3 to 100 μm. 3.   3. The carbon brush for an electric machine according to claim 1, wherein the brush base contains carbon as one component and further contains a resin component as another component, and the resin component remains in a cured state. 4.   3. The electric machine according to claim 1, wherein the brush base material contains carbon as one component and further contains a resin or a pitch component as another component, and the resin or the pitch component is baked and carbonized. 4. Carbon brush.

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