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

Copper Carbon Brush

[0001] The present invention relates to a copper-carbon brush having a low copper content and excellent conductivity.

[0002] Copper carbon brushes are used in motors, generators, etc., and the carbon, such as graphite, improves the sliding performance against commutators, slip rings, etc., while the copper improves conductivity. If a brush with high conductivity can be obtained with a low copper content, the carbon content can be increased to improve sliding performance. Note that the copper in the brush exists in a powder-like form, and when it comes into contact with the copper of the commutator, slip ring, etc., it tends to adhere to each other, reducing sliding performance.

[0003] Related prior art: Patent Document 1 (JP 2020-5490 A) 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 conductivity, with the low-resistance layer containing 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 (JP 2001-298913 A), a copper-graphite brush contains, for example, 50 to 90 mass% copper to improve conductivity and reduce friction. This brush ensures conductivity by containing a large amount of copper.

[0005] Patent Publication No. 2020-5490 Patent Publication No. 2001-298913

[0006] An object of the present invention is to provide a copper-graphite brush that has excellent conductivity and sliding properties with a small copper content.

[0007] This invention is a copper-carbon brush containing copper and graphite, characterized in that the copper to carbon ratio is 20 to 60 mass% copper and 80 to 40 mass% total carbon, including graphite and carbon derived from the binder resin, and the RGB value when the unpolished brush surface is imaged is 135 to 200 for the red component, and the value Δ obtained by subtracting the blue component from the red component of the RGB value is 35 to 100. The unpolished state refers to a state in which no polishing is performed after press molding and sintering.

[0008] Preferably, the red component of the RGB value is 145 or more and 200 or less, and the value Δ obtained by subtracting the blue component from the red component of the RGB value is 40 or more and 100 or less.

[0009] More preferably, the red component of the RGB value is 150 or more and 200 or less, and the value Δ obtained by subtracting the blue component from the red component of the RGB value is 45 or more and 100 or less.

[0010] By doing so, 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 red component of the RGB value should be 145 to 200, and the value Δ obtained by subtracting the blue component from the red component of the RGB value should be 40 to 100.

[0011] In the examples, experiments were conducted mainly with copper at 40 mass % and total carbon at 60 mass %, so the ratio of copper to carbon is, for example, 30 to 50 mass % copper and 70 to 50 mass % total carbon.

[0012] The inventors discovered that even with the same copper content in a brush, a larger red component (RGB value) and a larger Δ (red minus blue component) increase the brush's conductivity. For example, if the copper content is 40 mass%, a brush resistivity of 500 μΩ·cm or less can be achieved by setting the red component (RGB value) to 135 or greater and the Δ (red component) to 35 or greater. A brush resistivity of 300 μΩ·cm or less can be achieved by setting the red component (RGB value) to 145 or greater and the Δ (Δ) to 40 or greater. A brush resistivity of 100 μΩ·cm or less can be achieved by setting the red component (RGB value) to 150 or greater and the Δ (Δ) to 45 or greater. A lower copper content reduces friction with commutators, slip rings, etc., while an increased carbon content improves the brush's sliding performance. This invention produces a copper-carbon brush with both high conductivity and excellent sliding performance. These effects are shown in Table 1 and Figure 2.

[0013] Generally, the higher the value of the Red component of the RGB value and the Δ value, the better, with the upper limit indicating the upper limit of the range that these values ​​can reach. The lower the resistivity of the brush, the better, with the lower limit indicating the lower limit of the range that these values ​​can reach. A high value of the Red component of the RGB value and a high Δ value are related to a low value of the Blue component. A low value of the Blue component of the RGB value is preferable, and it is particularly preferable that the value is 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 inside the brush breaks down, and ground graphite powder appears on the brush surface. This causes the brush to darken in color. Therefore, the RGB values ​​of the brushes covered by this invention are those in an unpolished state.

[0015] A front view of the copper-carbon brush of the embodiment. A characteristic diagram showing the relationship between the RGB value R and the difference ΔRed-Blue between the RGB values ​​and the brush resistivity for the copper-carbon brushes of the embodiment and the comparative example. A flowchart showing the method for measuring the RGB values.

[0016] The best mode for carrying out the present invention will be described below. The present invention is not limited to the mode, but is defined by the claims, and can be modified by adding matters known to those skilled in the art to the mode.

[0017] Brush Manufacturing: Copper powder, graphite powder, and a phenolic resin binder were mixed to form a blended powder. The blended powder was filled into a mold, press-molded, and sintered to form a brush with lead wires. The manufactured copper-graphite brush 2 is shown in Figure 1. 4 is the brush body, 6 is the sliding surface, and 8 is the lead wire. The manufactured brush 2 was 20 mm long, 10 mm wide, and 5 mm thick, but the size is optional. The binder can be a thermoplastic resin, and the type of graphite powder and copper powder can be optional. In addition to copper powder, graphite powder, and binder, brush 2 can also contain a solid lubricant such as molybdenum disulfide powder or an abrasive such as alumina powder. The presence or absence of lead wires 8 is optional. The brush of this invention can be used for any purpose. Due to its high conductivity, it is suitable for applications where high voltages and large currents flow, such as the main motor of an electric vehicle (EV) or a wind turbine.

[0018] The ratio of copper to carbon was varied from 10 to 60 mass% copper and 90 to 40 mass% carbon, and the average particle size of the carbon was varied from 80 μm to 200 μm.

[0019] Measurement: The RGB value measurement method is shown in Figure 3. The RGB values ​​of the manufactured brush (unpolished) are measured. The color sample used is the Japan Paint Manufacturers Association's "Paint Standard Color Sample Book" (2021 edition), which corresponds to the Munsell color system 10R5 / 14 (JIS-W-8301). JIS specifies the RGB values ​​of this color sample as R 212, G 66, and B 10. The illuminance on the color sample and brush is adjusted to 500 lx ± 10 (Step 1). If necessary, adjust the image analysis software (Image-J) built into the digital camera (Step 2), and photograph the color sample (Step 3). The captured image of the color sample is processed using the image analysis software (Image-J) to determine 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 to be within the shooting conditions, and if they are outside this range, it is considered to be outside the shooting conditions.If it is outside the shooting conditions, perform steps 2 to 4 again to make the RGB values ​​of the color sample fall within the conditions.After adjusting the image analysis software (Image-J) to fit within the shooting conditions, photograph the brush sample with the same digital camera at the same illumination (step 5), and measure the RGB values ​​of the copper-carbon brush using the adjusted image analysis software (step 6).

[0020] The resistivity of the copper-carbon brush was measured in the pressure direction using a four-terminal method. The resistivity in the direction perpendicular to the pressure direction was lower. The copper content in the brush body, excluding the lead wires, was measured by crushing the brush body, dissolving it in, for example, a nitric acid solution, and then measuring the copper content by chelate titration. The carbon content in the brush was determined by weighing the insoluble matter in the above-mentioned nitric acid solution or other aqueous solution.

[0021] Results: Even with the same copper content, the brush resistivity changed when the R and Δ values ​​of the brush's RGB values ​​were different. Furthermore, even when the copper content was different, the brush resistivity was similar if the R and Δ values ​​of the RGB values ​​were similar. Generally, brushes with high R and Δ values ​​of the RGB values ​​had low resistivity, while brushes with low values ​​had high resistivity. Since it was difficult to obtain a brush with sufficient conductivity 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] The results for Examples 1 to 6 and Comparative Examples 1 to 4, where the copper content was uniformly set to 40 mass% (60 mass% total of carbon and graphite derived from the binder), are shown in Figure 2. In Example 7, the copper content was set to 30 mass% (70 mass% total of carbon and graphite derived from the binder), and in Example 8, the copper content was set to 50 mass% (50 mass% total of carbon and graphite derived from the binder). 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 Comparative Example 1 132 122 119 13 5824 Comparative Example 2 138 124 121 17 3245 Comparative Example 3 143 126 122 21 2588 Comparative Example 4 158 133 125 33 1080

[0024] The copper content of Examples 1 to 6 and the Comparative Example was the same. The resistivity in the Examples was 500 μΩ·cm or less, while in the Comparative Example it was 1000 μΩ·cm or more. Examples 1 to 8 demonstrate that a high R value and a high Δ value in the RGB values ​​reduces the brush resistivity. In particular, in Examples 1 to 4, when the R value of the RGB values ​​was 145 or more and the Δ value was 40 or more, the brush resistivity was 200 μΩ·cm or less. Furthermore, in Examples 1 to 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 more and the Δ value was 45 or more (Examples 1, 2, and 4), the brush resistivity was 100 μΩ·cm or less.

[0025] In Comparative Examples 1 to 4, the resistivity exceeded 1000 μΩ cm, and 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 at less than 35, and the resistivity exceeded 1000 μΩ cm. In addition, in the Comparative Examples, the values ​​of the Blue component of the RGB values ​​all exceeded 110.

[0026] Even if the copper content is the same, the difference in the RGB values ​​and resistivity of the brush surface is presumed to represent the difference in the dispersion state of the graphite particles and copper powder. In other words, a high R value and a large Δ value mean that the color tone of the copper powder is more pronounced, which suggests 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] In addition to copper, graphite, and binder-derived carbon, the brush may contain a metal sulfide solid lubricant such as molybdenum disulfide or an abrasive such as alumina. The proportion of materials other than copper, graphite, and binder-derived carbon in the brush is, for example, 10 mass% or less, preferably 6 mass% or less. Within this range, the metal sulfide solid lubricant and abrasive have little effect on the color tone and conductivity of the brush.

[0028] 2 Copper carbon brush 4 Brush body 6 Sliding surface 8 Lead wire

Claims

**Claim 1**: In a copper carbon brush containing copper and graphite, the ratio of copper to carbon is such that copper is 20 to 60 mass%, and the total carbon including graphite and carbon derived from the binder resin is 80 to 40 mass%, the RGB value when imaging the surface of the unpolished copper carbon brush is 150 or more and 200 or less in the Red component, and the value Δ obtained by subtracting the Blue component from the Red component of the RGB value is 45 or more and 100 or less. A copper carbon brush characterized by this. **Claim 2**: The copper carbon brush according to Claim 1, characterized in that the resistivity in the pressing direction when the copper carbon brush is press-molded is 100 μΩ·cm or less and 20 μΩ·cm or more. **Claim 3**: The copper carbon brush according to Claim 1 or 2, characterized in that the ratio of copper to carbon is such that copper is 30 to 50 mass%, and the total carbon is 70 to 50 mass%.