Copper carbon brush

Abstract

The ratio of copper to carbon in the carbon brush is 20-60% by mass of copper and 80-40% by mass of the total carbon containing graphite and carbon derived from a binder resin. When the brush surface in an unpolished state is imaged, the RGB value is 135-200 in terms of Red component, and the value delta obtained by subtracting the Blue component from the Red component of the RGB value is 35-100. Even if the copper content is low, the brush can obtain high conductivity.

Description

Technical Field

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

[0002] Copper carbon brushes are used in motors and generators. Graphite and other carbon materials improve sliding performance against commutators and slip rings, while copper enhances electrical conductivity. If brushes with high conductivity can be achieved with a low copper content, the carbon content can be increased to improve sliding performance. It should be noted that the copper in brushes exists in a near-powder form. If it comes into contact with copper from commutators, slip rings, and other components, it tends to adhere to them, reducing sliding performance.

[0003] Related prior art is shown below. Patent Document 1 (Japanese Patent Application Laid-Open No. 2020-5490) discloses a brush for a high-current DC motor. The brush comprises two layers: a high-resistance layer for suppressing spark discharge and a low-resistance layer for ensuring conductivity. 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] Patent Document 2 (Japanese Patent Application Laid-Open No. 2001-298913) discloses a copper-graphite brush containing, for example, 50 to 90% by mass of copper in order to improve conductivity and reduce friction. This brush ensures conductivity by containing a large amount of copper.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2020-5490

[0008] Patent Document 2: Japanese Patent Application Laid-Open No. 2001-298913 Summary of the Invention

[0009] Problems to be solved by the invention

[0010] An object of the present invention is to provide a copper-graphite brush having a low copper content and excellent electrical conductivity and sliding properties.

[0011] Means for solving problems

[0012] The present invention is characterized in that, in a copper carbon brush containing copper and graphite, the ratio of copper to carbon is 20 to 60% by mass of copper and 80 to 40% by mass of total carbon, including graphite and carbon derived from a binder resin. When photographing the brush surface in an unpolished state, the RGB value (Red component) is 135 to 200, and the value Δ (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 polishing has not been performed after press molding and sintering.

[0013] Preferably, the RGB value is 145 or more and 200 or less in terms of the Red component, 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.

[0014] More preferably, the RGB value is 150 or more and 200 or less in terms of 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.

[0015] As described above, the brush resistivity can be, for example, 500 μΩ·cm or less and 20 μΩ·cm or greater. More preferably, the brush resistivity is 200 μΩ·cm or less and 20 μΩ·cm or greater. Therefore, for example, the RGB value (Red component) can be 145 or greater and 200 or less, and the value Δ (subtracting the Blue component from the Red component of the RGB value) can be 40 or greater and 100 or less.

[0016] In the examples, experiments were conducted with copper at 40 mass % and total carbon at 60 mass %. Therefore, the ratio of copper to carbon was set to, for example, 30 to 50 mass % copper and 70 to 50 mass % total carbon.

[0017] Effects of the Invention

[0018] The inventors have discovered that even if the copper content of the brush is the same, when the value of the Red component of the RGB value is large and the value Δ obtained by subtracting the Blue value from the Red value is large, the conductivity of the brush becomes higher. For example, when the copper content is unified to 40% by mass, when the Red of the RGB value is set to 135 or more and Δ is set to 35 or more, the resistivity of the brush can be made less than 500μΩ·cm. When the Red of the RGB value is set to 145 or more and Δ is set to 40 or more, the resistivity of the brush can be made less than 300μΩ·cm. When the Red of the RGB value is set to 150 or more and Δ is set to 45 or more, the resistivity of the brush can be made less than 100μΩ·cm. When the copper content is low, the friction with the commutator, slip ring, etc. is reduced, and when the carbon content increases, the sliding performance of the brush is improved. In the present invention, a copper-carbon brush with high conductivity and high sliding performance can be obtained. This effect is shown in Table 1, Figure 2 .

[0019] The higher the Red component and Δ value of the RGB values, the better. The upper limit represents the upper limit of their achievable range. The lower the brush resistivity, the better. The lower limit represents the lower limit of their achievable range. High Red component values and high Δ values in the RGB values are associated with low Blue component values. Furthermore, a low Blue component value in the RGB values is preferred, particularly preferably 110 or less.

[0020] Brushes are made of powdered copper and graphite bound together with a resin binder. Polishing the brushes causes the graphite structure within the brushes to collapse, resulting in the appearance of ground graphite powder on the brush surface. This darkens the brush's color. Therefore, the RGB values for the brushes covered by this invention are those in the unpolished state. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a front view of the copper carbon brush of an embodiment.

[0022] Figure 2 This is a characteristic diagram showing the relationship between the RGB value R and the difference ΔRed-Blue between the RGB values and the resistivity of the brush in the copper carbon brushes of the Example and the Comparative Example.

[0023] Figure 3 This is a flowchart showing a method for measuring RGB values. DETAILED DESCRIPTION

[0024] The best embodiment for carrying out the present invention is shown below. The present invention is not limited to the embodiment, but can be defined based on the claims, and can be modified by adding matters known to those skilled in the art to the embodiment.

[0025] Example

[0026] Brush manufacturing

[0027] Copper powder is mixed with graphite powder and phenolic resin binder to make a mixed powder. The mixed powder is filled into a mold, pressed and sintered after forming to make a brush with a lead wire. The copper graphite brush 2 manufactured is shown in FIG. Figure 1 4 is the brush body, 6 is the sliding surface, and 8 is the lead. The manufactured brush 2 has a length of 20 mm, a width of 10 mm, and a thickness of 5 mm, but the size is arbitrary. The adhesive can be a thermoplastic resin, and the types of graphite powder and copper powder are arbitrary. In addition to copper powder, graphite powder, and adhesive, the brush 2 can also contain solid lubricants such as molybdenum disulfide powder and grinding materials such as aluminum oxide powder. The presence or absence of the lead 8 is arbitrary. The use of the brush of the present invention is arbitrary, and the brush has high conductivity, so it is suitable for uses such as the main motor of EV (electric vehicle) and wind turbines where high voltage and large current flow.

[0028] The ratio of copper to carbon was varied so that copper was 10 to 60% by mass and carbon was 90 to 40% by mass. The average particle size of the carbon was varied within a range of 80 μm to 200 μm.

[0029] Determination

[0030] The method for measuring RGB values is shown in Figure 3Measure the RGB value of the manufactured brush (an object that has not been polished, etc.). As a color sample, the "Standard Color for Paints Isoseki Mimotocho" (Standard Color Single-Color Sample Book for Paints) (2021 edition) of the Japan Paint Industry Association is used, and a color sample corresponding to 10R5 / 14 (JIS-W-8301) of the Munsell color system is used. In JIS, the RGB value of the color sample is specified as R value 212, G value 66, and B value 10. Adjust the illumination of the color sample and the brush so that the illumination is 500lx±10 (step 1). Adjust the image analysis software (Image-J) built into the digital camera as needed (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 calculate the RGB value (step 4). If the RGB values of the color sample are within the ranges of 212±20 for R, 66±10 for G, and 15±10 for B, the image is considered within the imaging conditions. If they are outside these ranges, the image is considered outside the imaging conditions. If the image is outside the imaging conditions, repeat steps 2 to 4 to bring the RGB values of the color sample within the conditions. After adjusting the image analysis software (Image-J) within the imaging conditions, use the same digital camera to photograph the brush sample at the same illumination (step 5). The RGB values of the copper carbon brush are then measured using the adjusted image analysis software (step 6).

[0031] The resistivity of the copper carbon brush is measured in the direction of pressure using the four-terminal method. The resistivity in the direction perpendicular to the pressure direction is lower. The copper content in the brush body, excluding the lead wire, is determined by chelate titration after the brush body is crushed and dissolved in, for example, an aqueous nitric acid solution. The carbon content in the brush is determined by weighing the insoluble components in the aqueous solution of nitric acid or the like.

[0032] result

[0033] Even with the same copper content, if the R and Δ values of the RGB values of a brush differ, the brush's resistivity will vary. Furthermore, even with different copper contents, if the R and Δ values of the RGB values are similar, the brush's resistivity will be similar. Generally, brushes with high RGB R values and high Δ values have low resistivity, while brushes with low RGB R values and low Δ values have high resistivity. It should be noted that a brush with 10% copper by mass is difficult to achieve sufficient conductivity, so the weight ratio of copper to total carbon is set to 20:80 to 60:40. This ratio is preferably 30:70 to 50:50.

[0034] The results of Examples 1 to 6 and Comparative Examples 1 to 4 when the copper content was uniformly set to 40 mass % (the total of carbon and graphite derived from the binder was 60 mass %) are shown in FIG. Figure 2In Example 7, the copper content was set to 30% by mass (the total of carbon and graphite derived from the binder was 70% by mass), and in Example 8, the copper content was set to 50% by mass (the total of carbon and graphite derived from the binder was 50% by mass). These results are shown in detail in Table 1.

[0035] Table 1 RGB values and resistivity (copper 40 mass%)

[0036]

[0037] The copper content is the same in Examples 1 to 6 and the comparative example. The resistivity in the examples is 500 μΩ·cm or less, whereas it is 1000 μΩ·cm or more in the comparative example. According to Examples 1 to 8, if the R value of the RGB value is high and the Δ value is high, the resistivity of the brush becomes smaller. In particular, in Examples 1 to 4, the R value of the RGB value is 145 or more and the Δ value is 40 or more, and the resistivity of the brush is 200 μΩ·cm or less. In addition, in Examples 1 to 4, the Blue component of the RGB value is less than 110 (less than 105). Furthermore, when the R value of the RGB value is 150 or more and the Δ value is 45 or more (Examples 1, 2, 4), the resistivity of the brush is 100 μΩ·cm or less.

[0038] Comparative Examples 1 to 4 exhibited resistivities exceeding 1000 μΩ·cm. Comparative Examples 1 and 2, which exhibited both low Red values and low Δ values in the RGB values, exhibited resistivities exceeding 3000 μΩ·cm. Comparative Examples 3 and 4 exhibited high Red values in the RGB values but low Δ values, below 35, resulting in resistivities exceeding 1000 μΩ·cm. Furthermore, in all of these comparative examples, the Blue component of the RGB values exceeded 110.

[0039] Even with the same copper content, the differences in RGB values and resistivity on the brush surface are presumably indicative of differences in the dispersion of the graphite particles and copper powder. Specifically, a high R value and a large Δ value indicate a strong hue for the copper powder, suggesting that the copper powder particles are in contact with each other on the graphite particle surface, forming a low-resistance conductive path.

[0040] In addition to copper, graphite, and carbon derived from the binder, brushes may also contain metal sulfide solid lubricants such as molybdenum disulfide and grinding materials such as aluminum oxide. The proportion of materials other than copper, graphite, and carbon derived from the binder in the brush is, for example, 10% by mass or less, preferably 6% by mass or less. Within this range, the effects of metal sulfide solid lubricants and grinding materials on the brush's color and conductivity are minimal.

[0041] Description of Reference Numerals

[0042] 2 copper carbon brushes

[0043] 4Brush body

[0044] 6 Sliding surface

[0045] 8-lead

Claims

1. A copper carbon brush, characterized in that: It contains copper and graphite, among which, The ratio of copper to carbon is: copper is 20-60% by mass, and the total carbon including graphite and carbon derived from the binder resin is 80-40% by mass. The RGB value when the unpolished brush surface is photographed is 135 to 200 inclusive in terms of 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 inclusive.

2. The copper carbon brush according to claim 1, characterized in that The resistivity of the brush is 500 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 RGB value is 145 or more and 200 or less in terms of the Red component, and a value Δ obtained by subtracting the Blue component from the Red component of the RGB value is 40 or more and 100 or less.

4. The copper carbon brush according to claim 3, characterized in that The RGB value is 150 or more and 200 or less in terms of the Red component, and a value Δ obtained by subtracting the Blue component from the Red component of the RGB value is 45 or more and 100 or less.

5. The copper carbon brush according to claim 3, characterized in that: The electrical resistivity of the brush is 200 μΩ·cm or less and 20 μΩ·cm or more.

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

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