Copper carbon brush

Abstract

According to the present invention, the proportions of copper and carbon in a carbon brush are set such that the proportion of copper is 20-60 mass% and the total proportion of carbons including graphite and a carbon derived from a binder resin is 80-40 mass%. With respect to the RGB value obtained by taking an image of the brush surface in an unpolished state, the red component is 135 to 200 (inclusive), and the value ∆ obtained by subtracting the blue component from the red component of the RGB value is 35 to 100 (inclusive). This brush can achieve high conductivity even if the copper content is low.

Description

Technical Field

[0001] This invention relates to a copper carbon brush with a low copper content and excellent electrical conductivity.

Background Art

[0002] Copper carbon brushes are used in motors, generators, etc. Carbon such as graphite enhances the sliding performance against commutators, slip rings, etc., and copper enhances the electrical conductivity. If a brush with a high electrical conductivity can be obtained with a low copper content, the carbon content can be increased to enhance the sliding performance. Note that the copper in the brush exists in a shape close to powder, and when it comes into contact with copper such as in a commutator or slip ring, there is a tendency to adhere to each other, thus reducing the sliding property.

[0003] The related prior art is shown. Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2020-5490) discloses a brush for a high-current DC motor, which has two layers: a high-resistance layer for suppressing spark discharge and a low-resistance layer for ensuring electrical conductivity, and the low-resistance layer contains a large amount of copper. In the brush of Patent Document 1, the low-resistance layer contains a large amount of copper.

[0004] In Patent Document 2 (Japanese Unexamined Patent Application Publication No. 2001-298913), for example, 50 to 90 mass% of copper is contained in a copper graphite brush to improve electrical conductivity and reduce friction. This brush ensures electrical conductivity by containing a large amount of copper.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] The objective of this invention is to provide a copper graphite brush with excellent conductivity and sliding properties, even with a low copper content. [Means for solving the problem]

[0007] This invention relates to a copper-carbon brush containing copper and graphite, characterized in that the ratio of copper to carbon is 20-60 mass% for copper and 80-40 mass% for total carbon, including graphite and carbon derived from binder resin, and the RGB value when the brush surface in an unpolished state is imaged is 135 or more and 200 or less for the Red component, and the value Δ, obtained by subtracting the Blue component from the Red component of the RGB value, is 35 or more and 100 or less. The unpolished state refers to the state after press molding and sintering without polishing.

[0008] Preferably, the RGB value for the Red component is between 145 and 200, and the value Δ obtained by subtracting the Blue component from the Red component of the RGB value is between 40 and 100.

[0009] More preferably, the RGB value for the Red component is between 150 and 200, and the value Δ obtained by subtracting the Blue component from the Red component of the RGB value is between 45 and 100.

[0010] As described above, the brush resistivity can be set to, for example, 500 μΩ·cm or less and 20 μΩ·cm or more. More preferably, the brush resistivity can be set to 200 μΩ·cm or less and 20 μΩ·cm or more. To achieve this, for example, the RGB value should be 145 or more and 200 or less for the Red component, and the value Δ obtained by subtracting the Blue component from the Red component of the RGB value should be 40 or more and 100 or less.

[0011] In the example, experiments were mainly conducted with 40 mass% copper and 60 mass% total carbon. Therefore, the ratio of copper to carbon should be, for example, 30-50 mass% copper and 70-50 mass% total carbon. [Effects of the Invention]

[0012] The inventors discovered that even with the same copper content, a larger Red component in the RGB values, and a larger Δ (Red minus Blue), results in higher brush conductivity. For example, if the copper content is set to 40 mass%, setting the Red RGB value to 135 or higher and Δ to 35 or higher allows the brush resistivity to be 500 μΩ·cm or less. Setting the Red RGB value to 145 or higher and Δ to 40 or higher allows the brush resistivity to be 300 μΩ·cm or less. Setting the Red RGB value to 150 or higher and Δ to 45 or higher allows the brush resistivity to be 100 μΩ·cm or less. Lower copper content reduces friction with the commutator, slip ring, etc., while increasing carbon content improves the brush's sliding performance. This invention provides a copper-carbon brush with high conductivity and high sliding performance. This effect is shown in Table 1 and Figure 2.

[0013] Generally, a higher value for the Red component and Δ value in the RGB values ​​is better, and the upper limit indicates the upper limit of the achievable range. A lower brush resistance is better, and the lower limit indicates the lower limit of the achievable range. A high Red component value and a high Δ value in the RGB values ​​are related to a low Blue component value. And a low Blue component value in the RGB values ​​is preferable, and it is particularly preferable that it be 110 or less.

[0014] The brush contains powdered copper and graphite, bound together with a resin binder. When the brush is polished, the graphite structure within the brush breaks down, and the ground graphite powder appears on the brush surface. As a result, the color of the brush darkens. Therefore, the RGB values ​​of the brush targeted by this invention are those in the unpolished state. [Brief explanation of the drawing]

[0015] [Figure 1] Front view of the copper carbon brush in the example. [Figure 2] Characteristic diagram showing the relationship between the RGB value R, the RGB value difference ΔRed-Blue, and the resistivity of the copper carbon brushes in the examples and comparative examples. [Figure 3] Flowchart showing how to measure RGB values

Best Mode for Carrying Out the Invention

[0016] The following shows the optimal embodiments for carrying out the present invention. The present invention is not limited to the embodiments, but is defined based on the claims and can be modified by adding matters known to those skilled in the art to the embodiments.

Embodiment

[0017] Brush manufacturing Copper powder, graphite powder, and a phenolic resin binder were mixed to obtain a blended powder. The blended powder was filled into a mold, sintered after press molding, and made into a brush with a lead wire. The manufactured copper-graphite brush 2 is shown in FIG. 1. 4 is the brush body, 6 is the sliding surface, and 8 is the lead wire. The manufactured brush 2 had a length of 20 mm, a width of 10 mm, and a thickness of 5 mm, but the size is arbitrary. The binder may be a thermoplastic resin, and the types of graphite powder and copper powder are arbitrary. In addition to copper powder, graphite powder, and the binder, the brush 2 may contain a solid lubricant such as molybdenum disulfide powder and an abrasive such as alumina powder. The presence or absence of the lead wire 8 is arbitrary. The use of the brush of this invention is arbitrary. Since the brush has high conductivity, it is suitable for applications where a high voltage and a large current flow, such as the main motor of an EV (electric vehicle) and a wind power generator.

[0018] The ratio of copper to carbon was changed so that copper was 10 to 60 mass% and carbon was 90 to 40 mass%. The average particle size of carbon was changed within the range of 80 μm to 200 μm.

[0019] measurement The method for measuring RGB values is shown in Fig. 3. Measure the RGB values of the brush after manufacturing (without any polishing, etc.). As a color sample, use the "Standard Color Chart for Paints" (2021 edition) of the Japan Paint Industry Association, and use the color sample corresponding to 10R5 / 14 (JIS-W-8301) in the Munsell color system. In JIS, the RGB values of this color sample are defined as R value 212, G value 66, and B value 10. Adjust the illuminance so that the illuminance on the color sample and the brush is 500 lx ± 10 (Step 1). If necessary, adjust the image analysis software (Image-J) built into the digital camera (Step 2), and take a picture of the color sample (Step 3). Process the captured image of the color sample with the image analysis software (Image-J) to obtain the RGB values (Step 4). If the RGB values of the color sample are within the range of R value 212 ± 20, G value 66 ± 10, and B value 15 ± 10, it is considered within the shooting conditions. If it is outside this range, it is considered outside the shooting conditions. In the case of outside the shooting conditions, repeat Steps 2 to 4 until the RGB values of the color sample are within the conditions. After adjusting the image analysis software (Image-J) within the shooting conditions, at the same illuminance, take a picture of the brush sample with the same digital camera (Step 5), and measure the RGB values of the copper carbon brush with the adjusted image analysis software (Step 6).

[0020] The resistivity in the pressing direction of the copper carbon brush was measured by the four-terminal method. Note that the resistivity in the direction perpendicular to the pressing direction is lower. The copper content in the brush body does not include the lead wire. The brush body was pulverized, dissolved in, for example, an aqueous nitric acid solution, and the copper content was measured by chelate titration. The carbon content in the brush was determined by weighing the insoluble matter in an aqueous solution such as the above-mentioned nitric acid.

[0021] result Even with the same copper content, the resistivity of the brush changed when the R and Δ values ​​of the RGB values ​​of the brush differed. Conversely, even with different copper content, the resistivity of the brushes was similar when the R and Δ values ​​of the RGB values ​​were similar. In general, brushes with high R and Δ values ​​had low resistivity, while brushes with low R and Δ values ​​had high resistivity. Since it was difficult to obtain a sufficiently conductive brush with 10 mass% copper, the weight ratio of copper to total carbon was set to 20:80 to 60:40. This ratio is preferably 30:70 to 50:50.

[0022] Figure 2 shows the results for Examples 1-6 and Comparative Examples 1-4 when the copper content was standardized to 40 mass% (total of binder-derived carbon and graphite is 60 mass%). In Example 7, the copper content was set to 30 mass% (total of binder-derived carbon and graphite is 70 mass%), and in Example 8, the copper content was set to 50 mass% (total of binder-derived carbon and graphite is 50 mass%). These results are shown in detail in Table 1.

[0023] Table 1 RGB values ​​and resistivity (copper 40 mass%) Red Green Blue ΔRed-Blue Resistivity (μΩ cm) Example 1 152 110 98 54 98 Example 2 153 113 100 53 99 Example 3 145 117 103 42 169 Example 4 154 117 103 51 78 Example 5 150 120 113 37 355 Example 6 168 137 125 43 478 Example 7 168 137 125 43 455 Example 8 170 130 135 35 85 Comparison Example 1: 132 122 119 13 5824 Comparison Example 2: 138 124 121 17 3245 Comparison Example 3: 143 126 122 21 2588 Comparative Example 4: 158 133 125 33 1080

[0024] Examples 1-6 and the comparative example have the same copper content. The resistivity of the examples is 500 μΩ·cm or less, while that of the comparative example is 1000 μΩ·cm or more. From Examples 1-8, it can be seen that when the R value and Δ value of the RGB values ​​are high, the resistivity of the brush decreases. In particular, in Examples 1-4, when the R value of the RGB values ​​was 145 or higher and the Δ value was 40 or higher, the resistivity of the brush was 200 μΩ·cm or less. Also in Examples 1-4, the Blue component of the RGB values ​​was less than 110 (105 or less). Furthermore, when the R value of the RGB values ​​was 150 or higher and the Δ value was 45 or higher (Examples 1, 2, 4), the resistivity of the brush was 100 μΩ·cm or less.

[0025] In Comparative Examples 1-4, the resistivity exceeded 1000 μΩ·cm. In Comparative Examples 1 and 2, where the Red value of the RGB values ​​was low and the Δ value was also low, the resistivity was 3000 μΩ·cm or higher. In Comparative Examples 3 and 4, the Red value of the RGB values ​​was high, but the Δ value was low (less than 35), and the resistivity exceeded 1000 μΩ·cm. In addition, in all comparative examples, the Blue component value of the RGB values ​​exceeded 110.

[0026] The fact that the RGB values ​​and resistivity of the brush surface differ even with the same copper content suggests that this represents a difference in the dispersion state of the graphite particles and copper powder. In other words, a high R value and a large Δ value indicate that the color tone of the copper powder is strongly expressed, suggesting that the copper powder particles are in contact with each other on the surface of the graphite particles, forming a low-resistance conductive path.

[0027] The brush may contain copper, graphite, and carbon derived from the binder, as well as metal sulfide solid lubricants such as molybdenum disulfide or abrasive materials such as alumina. The proportion of materials other than copper, graphite, and carbon derived from the binder in the brush is, for example, 10 mass% or less, preferably 6 mass% or less. Within this range, the influence of metal sulfide solid lubricants and abrasive materials on the color tone of the brush and the conductivity of the brush are small. [Explanation of symbols]

[0028] 2 Copper carbon brushes 4. Brush body 6. Sliding surface 8 Lead wires

Claims

1. A copper carbon brush containing copper and graphite, The ratio of copper to carbon is 20-60 mass% copper and 80-40 mass% total carbon, including carbon derived from graphite and binder resin. A copper carbon brush characterized in that, when the surface of an unpolished copper carbon brush is imaged, the RGB value of the Red component is between 150 and 200, and the value Δ, obtained by subtracting the Blue component from the Red component of the RGB value, is between 45 and 100.

2. The copper carbon brush according to Claim 1, characterized in that the resistivity in the direction of pressure when the copper carbon brush is press-molded is 100 μΩ·cm or less and 20 μΩ·cm or more.

3. The copper-carbon brush according to claim 1 or 2, characterized in that the ratio of copper to carbon is 30 to 50 mass% copper and 70 to 50 mass% total carbon.

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