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(11) | EP 1 662 638 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
| published in accordance with Art. 158(3) EPC |
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| (54) | CARBON BRUSH |
| (57) The particle size distribution calculated from measurement of graphite particles
forming a filler by a laser diffraction method is controlled so that the accumulated
value of graphite particles with a particle size of 5 µm or less is 10% or less and
preferably, 5% or less, the accumulated value of graphite particles with a particle
size of 100 µm or more is 10% or less, and the accumulated value of graphite particles
with a particle size of from 10 to 40 µm is 60% or more, and the graphite particles
with a particle size of from 12 to 20 µm is 40% or more of the whole. |
Technical Field
[0001] The present invention concerns a carbon brush which uses a graphite particle filler and which is for use in electric machines and, particularly, it relates to a carbon brush which prevents desorption of particles of the filler during use.
Background Art
[0002] Heretofore, carbon brushes have been known. For example, they include those disclosed in JP-A No. 2000-197315. Those in this document use artificial graphite particles or natural graphite particles, etc. as the filler. Then, since the artificial graphite particles, natural graphite particles, etc. used as the filler have been controlled loosely during use, for example, distinguishing between fine powder and coarse powder, the filler structures of the formed carbon brushes have not been uniform, but those not having uniform particle size have been predominant.
[0003] By the way, inputs to motors have been increased and also the usage conditions for carbon brushes have become severer in recent years. In the situation described above, the invention described in the document above sometimes has desorption of particles, etc. during use, which shortens the working life.
[0004] In view of the above, it is an object of the present invention to make the filler structure uniform for the graphite particle filler and provide a carbon brush using the graphite particle filler and which has long working life.
Disclosure of the Invention
[0005] In order to solve the foregoing subject, the present inventors have made an earnest study, as a result, have found that use of the graphite particles for forming a filler of a controlled grain size distribution is extremely important for extending the life of the carbon brush, and have accomplished the invention. That is, when graphite particles are measured forming the filler by a laser diffraction method, the carbon brush according to the invention has a grain size distribution in which the accumulated value of graphite particles with a grain size of 5 µm or less is 10% or less that of all the graphite particles.
Brief Explanation of the Drawings
[0006] Fig. 1 is a graph showing an example of a grain size distribution, Fig. 2 is a graph showing another example of the grain size distribution, and Fig. 3 is a table showing characteristics of examples of the invention and comparative examples.
Best Mode for Practicing the Invention
[0007] When measuring graphite particles forming a filler by a laser diffraction method, the distribution of particle diameters is controlled so that the accumulated value of graphite particles with a grain size of 5 µm or less is 10% or less and, preferably, 5% that of all the graphite particles or less, and further, the accumulated value of graphite particles with a particle size of 100 µm or more is 10% or less, that from 10 to 40 µm is 60% or more, and that from 12 to 20 µm is 40% or more of the whole. This makes the structure of the graphite particles for forming the filler uniform. Accordingly, in the carbon brush using the graphite particle filler, even when desorption of particles occurs during use, the amount of desorbed particles is small, which has the effect of extending the life of the brush.
[0008] The principle of the laser diffraction method will here be described. When a laser light (monochromatic light, parallel beam) is irradiated to particles as an object of measurement, a spatial distribution pattern of light intensity of diffracted and scattered lights is formed. The distribution pattern of light intensity is detected by a sensor. The distribution pattern of light intensity changes depending on the size of particles.
[0009] Since particles are actually measured as a group, and a plurality of particles of different sizes are present together, the distribution pattern of light intensity formed from the group of particles is an overlap of diffracted and scattered lights from respective particles.
[0010] Upon measurement by grain size distribution a measuring apparatus of laser diffraction type using the laser diffraction method, the overlapped distribution pattern of light intensity can be detected and the size of the particles and the ratio of them contained in the group of sample particles can be calculated from this data of the distribution pattern of light intensity. Thus, through calculation, distribution of the grain size can be obtained.
[0011] For example, a graph as shown in Fig. 1 can be obtained. In the graph of Fig. 1, the abscissa indicates the particle size (µm) (logarithmic expression) and the ordinate indicates relative amount of particles (%). In this case, "the accumulated value of graphite particles with the particle size from 10 to 40 µm in the particle size distribution resulting from measurement of graphite particles by a laser diffraction method" in Fig. 1 means the ratio of the area of the hatched portion (portion corresponding to the particle size of from 10 to 40 µm) to the area surrounded by the particle size distribution line and the abscissa.
[0012] For the graphite particles used in the invention, graphite particles of artificial graphite or natural graphite can be used. Further, they may be a mixture thereof.
[0013] As the resin for bonding the particles of the graphite particles, epoxy resin, phenol resin and various thermosetting resin obtained by modifying them, etc. can be used. For use as a binder component, the amount of resin used is preferably from 10 to 40%.
[0014] Then, after mixing the thermosetting resin for use as the binder of the graphite particles, the mixture was molded into a predetermined shape and heat treated at a temperature of 150 to 250°C at which the resin is cured to prepare a carbon brush.
[0015] In the carbon brush according to the invention, a solid lubricant such as molybdenum disulfide, tungsten disulfide or boron nitride can also be added in addition to the filler. Further, the invention can be applied not only to the thermosetting carbon brush described above but also to various kinds of carbon brushes referred to as a carbon graphite type or metallic graphite type, formed by kneading with a phenol resin or pitch and firing, whereby similar effects can be obtained.
(Example 1)
[0017] As a grain size distribution measuring apparatus of laser diffraction type, SALD-2000A manufactured by Shimazu Seisakusho Co. was used. This was used also in the subsequent examples and comparative examples.
[0018] To 75% by weight of an artificial graphite powder having a mode diameter of 57 µm with a standard deviation value of 0.25 controlled so as to form a graphite particle filler (average particle size of 62 µm) in which the accumulated value of graphite particles with a particle size of 5 µm or less (ratio of the area of the hatched portion on the left to the area surrounded by the particle size distribution line and the abscissa (a portion for 5 µm or less on the abscissa in Fig. 2)) was 10% as calculated from measurement of the graphite particles forming a filler by a laser diffraction method, 25% by weight of an epoxy resin as a binder was blended and kneaded. After pulverizing the kneaded product so that particles of 63 µm or less were about 50%, they were molded at 100 MPa to obtain a carbon brush.
(Example 2)
[0019] To 75% by weight of an artificial graphite powder adjusted so as to form a graphite particle filler in which the accumulated value of graphite particles with a particle size of 5 µm or less was 5%, and the accumulated value of graphite particles with a particle size of 100 µm or more (ratio of the area of the hatched portion on the right to the area surrounded by the particle size distribution line and the abscissa (values of 100 µm or more on the abscissa)) was 10% as calculated from measurement of the graphite particles forming a filler by a laser diffraction method, 25% by weight of an epoxy resin as a binder was blended. This mixture was pulverized so that particles of 63 µm or less were about 50%, and then molded at 100 MPa to obtain a carbon brush.
(Example 3)
[0020] To 75% by weight of an artificial graphite powder adjusted so as to form a graphite particle filler in which the accumulated value of graphite particles with a particle size of 5 µm or less was 3%, the accumulated value of graphite particles with a particle size of 100 µm or more was 4%, and the accumulated value of graphite particles with a particle size of from 10 to 40 µm was 65% in the graphite particle in a particle size distribution as calculated from measurement of the graphite particles forming a filler by a laser diffraction method, 25% by weight of an epoxy resin as a binder was blended and kneaded. After pulverizing the kneaded product so that particles of 63 µm or less were about 50%, it was molded at 100 MPa to obtain a carbon brush.
(Comparative Example 1)
[0021] The particle size distribution calculated from measurement of graphite particles forming a filler by a laser diffraction method, was adjusted so as to form a graphite particle filler in which the accumulated value of graphite particles with the particle size of 5 µm or less was 20%, and 25% by weight of an epoxy resin as a binder was blended and kneaded. After pulverizing the kneaded product so that particles of 63 µm or less were about 50%, it was molded at 100 MPa to obtain a carbon brush.
(Comparative Example 2)
[0022] The particle size distribution calculated from measurement of graphite particles forming a filler by a laser diffraction method was adjusted so as to form a graphite particle filler in which the accumulated value of graphite particles with the particle size of 5 µm or less was 30% and the accumulated value of graphite particles with the particle size of 100 µm or more was 10%, and 25% by weight of a general-purpose epoxy resin as a binder was blended and kneaded. After pulverizing the kneaded product so that particles of 63 µm or less were about 50%, it was molded at 100 MPa to obtain a carbon brush.
(Comparative Example 3)
[0023] The particle size distribution calculated from measurement of graphite particles forming a filler by a laser diffraction method was adjusted so as to form a graphite particle filler in which the accumulated value of graphite particles with the particle size of 5 µm or less was 40%, the accumulated value of graphite particles with the particle size of 100 µm or more was 15%, and the accumulated value of graphite particles with the particle size from 10 to 40 µm was 55%, and 25% by weight of a general-purpose epoxy resin as a binder was blended and kneaded. After pulverizing the kneaded product so that particles of 63 µm or less were about 50%, they were molded at 100 MPa to obtain a carbon brush.
[0024] Each of the carbon brushes described above was assembled into a motor for use in a vacuum cleaner and working life was investigated. Fig. 3 collectively shows the characteristics of each of the carbon brushes.
[0025] As can be seen from Fig. 3, as compared with the not controlled carbon brush of Comparative Example 1, it can be seen that the working life of the carbon brush of Example 1 with an adjusted particle size distribution as calculated from measuring graphite particles for forming the filler by a laser diffraction method such that the accumulated value of graphite particles with the particle size of 5 µm or less in the graphite particles was 10%, was 1.5 times that of Comparative Example 1.
[0026] Further, it can be seen that the working life of the carbon brush of Example 2, in which the accumulated value of graphite particles with a particle size of 5 µm or less was 5% and the accumulated value of graphite particles with a particle size of 100 µm or more was 10% in the particle size distribution calculated from measurement of the graphite particles forming a filler by a laser diffraction method is extended by about twice that of the not controlled carbon brush in Comparative Example 2.
[0027] Further, it can be seen that the working life of the carbon brush of Example 3 in which the accumulated value of graphite particles with a particle size of 5 µm or less was 3%, the accumulated value of graphite particles with a particle size of 100 µm or more was 4%, and the accumulated value of graphite particles with a particle size of from 10 to 40 µm was 65% in a particle size distribution calculated from measurement of the graphite particles forming a filler by a laser diffraction method, is extended by about 3 times as compared with the not controlled carbon brush in Comparative Example 3.
[0028] Accordingly, it could be confirmed that the invention can provide a carbon brush with greatly extended working life compared with existent products.
[0029] The invention can be changed in view of the design within a range not departing the scope of the patent and it is not restricted to the embodiments and examples described above.
Industrial Applicability
1. A carbon brush with graphite particle filler in which, in the particle size distribution,
the accumulated value of graphite particles having a particle size of 5 µm or less
is 10% or less as calculated from measurement of graphite particles forming a filler
by a laser diffraction method.
2. A carbon brush according to claim 1, wherein the accumulated value of graphite particles
with the particle size of 100 µm or more is 10% or less.
3. A carbon brush according to claim 2, wherein the accumulated value of graphite particles
with the particle size of from 10 to 40 µm is 60% or more.
4. A carbon brush according to claim 3, wherein the accumulated value of graphite particles
with the particle size of from 12 to 20 µm is 40% or more.
5. A carbon brush according to any one of claims 1 to 4, which is selected from a resin
bonded type carbon brush, a carbon graphite type carbon brush and a metallic graphite
type carbon brush.