GB2389358A

GB2389358A - Carbon brush

Info

Publication number: GB2389358A
Application number: GB0311986A
Authority: GB
Inventors: Takuji Fujimura; Kazuhiro Takahashi; Hidenori Shirakawa; Takashi Maeda; Yoshikazu Kagawa; Takahiro Sakota
Original assignee: TotanKako Co Ltd
Current assignee: TotanKako Co Ltd
Priority date: 2002-06-06
Filing date: 2003-05-23
Publication date: 2003-12-10
Anticipated expiration: 2023-05-23
Also published as: DE10324855B4; DE10324855A1; GB0311986D0; GB2389358B; CN1469514A; ITTO20030422A1; CN100375343C

Abstract

A carbon brush with improved radio interference restraining property that restrains generation of radio noise is provided. An additive made of a metal or an inorganic material is added to carbon base material which was formed by kneading graphite powder with a binder and carbonizing this binder component. The additive may be tungsten, tin, ZnO, ZnS or MoS2 and SiC, and may be used in amount 0.3 - 3 wt % of the carbon base material. The binder may be a thermosetting resin or pitch. The carbon base material may be impregnated with oil.

Description

CARBON BRUSH

This invention relates to a carbon brusl1 tor an electric machine, and particularly to a carbon brush for a commutator motor of an electric power tools a vacuum cleaner or the like causing less radio interference.

Conventionally a carbon brush for an electric machine of this type has been developed through restraint of temperature rise of the brush and maintenance of a stable commutation effect over a long period by adding a solid lubricant and an abrasive to a carbon base material and applying a good conductive metal on the entire circumferential surface except for the part of the brush contacting the commutator, as disclosed in JP-,\- 90001973] 5.

Recently, however, with respect to a carbon brush for a commutator motor of a vacuum cleaners an electric power tool or the like miniaturization, higher output and higher rotational speed have been particularly pursued. Therefore, a carbon brush having a small size but having a smaller resistance loss and less friction has been demanded. On the other hands a carbon inrush that satisfies such a demand easily generates radio noise. When radio noise is generated, it may have some effects on electric devices around the carbon brush and cause their malfunction. Thereiore' in various countries including Japan, particularly in the European countries and the United States. strict standards to cope with occurrence ot radio noise are provided and preventive measures are taken against occurrence of radio noise. lo lessen this radio

interference generation, oil impregnation of the brusl1 base material has been considered as disclosed in.TP-A--13()078.

However as the rotational speed is further increased, the oil impregnation alone is not enough to control radio interference. Moreover, the oil impregnation has a problem that loss of impregnation oil due to long-term storage prevents stable control of radio interference Thus, it is an object of the present invention to provide a carbon brush causing less radio interference that restrains generation of radio noise.

Tn Order to sol\'e the floreú'oirlg problem, the present inventors have found that addition of a small quantity of a specified metal or inorganic material to the carbon base material of a brush restrains generation of radio interference, and have completed this . mventon. Specifically. a carbon brush of this invention has its radio interference generating property improved by adding an additive made ol a metal or an inorganic material to a carbon base material formed by kneading graphite powder with a binder and heat-treating the binder component.

The additive preferably is made of at least one of the group consisting oftungsten. tin.

zinc oxide. and zinc sulfide.

Preferably. the additive is no more than 3% by weight and no less than 0. 3% of the

carbon base material.

Preferably, the additive is mo]ybJenum disulfide and silicon carbide.

Preferably, the molybdenum disulfide is no less than 0.5% and no more than 3% of the total quantity of the carbon base material and the binder, and the silicon carbide is no less than 0. 1% and no more than 0. 5% of the total quantity of the carbon base material and the binder.

The carbon base material is prcSerably impregnated with oil.

The hinder is nreferahly a thermosetting resin or pitch.

Fig.l is a view showing the result of terminal interference voltage measurement of carbon brushes according to embodiments of this invention.

Fig.2 is an enlarged view of a low-frequency region shown in Fi<T. 1.

Fig.3 is a view showing the result of interference voltage measurement of the carbon brushes according to the embodiments of this invention.

The carbon base material of this invention can be natural graphite. expansive graphite.

or artificial graphite. Of these. artificial graphite. which has relatively low crystallinity. is particularly preferred. Graphite particles made by mixing these graphite materials may also be used. Forms of graphite are not particularly limited.

aild may be for example scaly graphite or soil-like graphite. By using these carbon base materials and adjusting mixing conditions balking: conditions and the like at the preparation static. it is possible to realize desired rcsistivity of the brush base material.

As the binder for connecting these graphite particles. a generally used thermosetting resin can be used. Ior example, a solid or liquid epoxy resin, phenol resin, or various thermosetting resins prepared by modifying these epoxy and phenol resins can be used.

Preferably, these resins used for the binder are 10 to 40% of the composition.

To the carbon base material is added one or more of the group consisting of tungsten.

tin, zinc, oxides of these, and sulfides of these. Particularly, the additive is preferably made of at least one of the group consisting of tungsten; tint zinc oxide; and zinc sulfide. Moreover, tungsten is particularly preferred as the additive because only a small quantity of it exhibits stable radio interference restraining property in a broad frequency range.

The additive is 3% by weight or less of the carbon base material. snore preferably I % or less, and ().3% or more. If the quantity of the additive is less than 0.3% by weight.

the radio interference restraining effect is small. If the quantity of the additive exceeds the limit of 3% by weights or even the more preferable limit of 1%, the hardness of the brush base material increases and the low-friction property deteriorates. Alternatively molN hdenum disulfide and silicon carbide can be the additive.

Molybdenum disulfide as the additive. NAThen sinú1N mixed with a resin or the like.

easily flocculates under the inOuencc of static electricity and the like and cannot easily be dispersed evenly. In this intention. however. since molshdenum disulfide is mixed with electrically conductive graphite particles. less flocculation due to static electricity occurs. Moreover. the binder is added thereto and kneaded and then ground. 'I'herctore, molybdenum disulfde is completely dispersed by a mechanochemical effect and is firmly adhered and bonded with the binder and the graphite particles. Mixed powder containing the graphite powder prepared in this maimer as the principal component is molded and heat-treated to produce the brush base material.

However' the brush containing molybdenum disulfide. when in use. easily forms a coating on the s rface of the commutator As this coating gets too thicl;. exfoliation easily occurs. If partial exfoliation or the like occurs, a current concentrates in that part, deteriorating the commutation property. In some cases. the commutator itself is damaged and must be replaced 'I'herefore, the quantity of molybdenum disulfide to be added is preferably within a range of 0.5% and 3% of the total quantity of the carbon base material and the binder. more preferably. between 1.0% and 0.0%. This enables compliance w ith the radio noise standard. If the quantity of added molybdenum disulfde is less than 0.5%. the lubricant property with the commutator is lowered and radio noise occurs. If the quantity is more than 3%, the coating formed on the surface of the commutator becomes excessive and the commutation property deteriorates. As a result. radio noise occurs.

In order to reduce this coating formed on the surface of the commutator by molybdenum disulfide. silicon carbide. w-hic}1 functions as an abrasive. is added lo the

brush base material. Again, if the quantity of silicon carbide is too much or its grain size is too lar,e and silicon carbide flocculates instead of being evenly dispersed the surface ofthe commutator is damaged and this will cause radio noise. Therefore. the quantity of silicon carbide to be added is preferably within a range ot'O.]% and ().5 /o of the total quantity of the carbon base material and the binders more preferably.

between 0.1% and 0.3%. If the quantity is less than 0.1%. silicon carbide does not exhibit its desired effect. If the quantity is more than 0.5%, the surface of the commutator may be damaged and the temperature of the brush rises, burning, the commutator. If the grain size of silicon carbide is larger than 100 Em, its abrasion effect is too high. thereby, coarsening the surface of the commutator and increasing commutator friction. If the grain size is smaller than 5 m. effect to remove coating on the. surface of the e.ommtator is lowered. Therefore. the grain size is nreferahly within a range of S to 100 m. Since silicon carbide has high affinity with and dispersiveness in a resin or the like, silicon carbide and resin may be added and mixed together with the lubricant initially, or the silicon carbide and resin may be kneaded, ground and then added by mixing.

As molybdenum disulfde and silicon carbide are added at predetermined ratios to the carbon base material in this manner, the lubricant property of molybdenum disulfide and the coating adjustment function of silicon carbide on the surface of' the commutator interacts thus stabilizing the commutation property and restraining the occurrence of'radio noise.

These additives are added when the graphite powder is kneaded with the binder such as a thennosetting resin or pitch.

The brush base material. after kneading the graphite powder and the thermosettin resin binder and carbonizing or hardening the binder component, is impregnated with oil. This oil impregnation further facilitates improvement in the radio intert'erence restraining property. For this oil synthetic hydrocarbon oils ester oil, mineral oil, or petroleum hydrocarbon may be used. The oil impregnation rate is preferably 2% by weight or more of the brush base material, more preferably, 2 to 10%. It is particularly preferable that I to 0.5 /O of the oil is a silicon component.

As a metallic coating on an entire lateral surface of the brush extending in a direction in which the brush presses against the commutator, or on a part thereof. copper may be formed and applied by an electroless plating method. When this copper plating is performed, the above-described oil impregnation is carried out after the copper plating. ' If the copper plating film thus applied is too thick. it roughens the surface of a r counterpart brush holder sliding surface at the time of sliding and the friction between 1 the brush and the contacting commutator tends to increase. On the other hand, if the copper plating, film is extremely thin the brush base material coating effect is small and the resistance of the brush is not lowered enough. This makes it difficult to i restrain temperature rise of the brush. 'I'herefore, it is preferable that the thickness of the copper plating film is approximately 0.1 to 100 m.

Hereinafter. this invention will be described in detail using exanples. It should he noted that this invention is not limited to the following' examples.

Example 1

30 parts by mass of a phenol resin and 0.5 parts tungsten were added to 70 parts of a mixture of artificial graphite powder and natural graphite powder with an average grain size of 20 lam and an ash content of 1.0% or less' and the mixture was kneaded at 1 50 C for one hour. After that, the mixture was ground to a grain size of 40 mesh or less and pressed into a size of 6x9x1: mm at a pressure of 100 MI'a and the resin was heattreated at 700C, thus forming a brush base material. This brush base material was soaked with a mixture of synthetic hydrocarbon-based oil and ester oil with a kinematic viscosity of 68 (mm2/s) at 40 C measured according to DINS1561, and the brush base material was impregnated With oil so as to be 4.5% by weight of the whole.

Example

A brush base material was prepared by adding tin at 0.5% by weight in terms of the base material. instead of tungsten of Example 1. This brush base material was l impregnated with oil so as to be 3.8% by weight.

Example 3

A brush base material was prepared by adding zinc oxide (ZnO) so as to be 0.5% by weight of the base material, instead of tungsten of Example 1. This brush base material was impregnated with oil so as to be 3.7% by weight.

Example 4

A brush base material was prepared by adding zinc sulfide (ZrS) so as to he 0.% by weight of the base material, instead of tungsten of Example 1. This brush base

material was impregnated with oil so as to be 4.0% by weight.

Comparative Example 1 30 parts by mass of a phenol resin were added to 70 parts by mass of mixed powder of artificial graphite powder and natural graphite powder with an average grain size of 20 lam and an ash content of 1.0% or less. and the mixture was kneaded at 1 50 C for one hour. After that, the mixture was ground to a grain size of 40 mesh or less and pressed into a size of 6x9x15 mm at a pressure of 100 MPa, and the resin was heat-treated at 700 C, thus forming a brush base material. This brush base material I was soaked with the same of] as the oil used in Example 1 so as to be 4.5 /O by weight.

For the inrushes of F.xamnles 1 to 4 and (:omp.arative x.nmple 17 ternnin. ! interference voltage measurement and interference voltage measurement were carried out under the conditions of AC 230V, 60 Hz. and 15 minutes using an EMI (electromagnetic interference) test based on the CISPR (Comite International Special des Perturbations; Radioelectriques) 14 standard. Table I shows the result of the terminal interference voltage measurement. Table 2 shows the result of the interference Volta measurement

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TABLE PHYSICAL CHARAC I ERISTICS

BULK SPECIFIC i HARDNESS RE;SISTIVllY i STREDGTCH 1 I GRAVITY SHORE CTYPE m I IPa i ., I EXAMPLE] 1.61 35 720 1 0.0

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EXAMPLE j 1 60 35 1 6Y0 19.4 1 1 1 1

EXAMPLE 3 1 1.60 36 1 690 19.6

EXAMPLE L60 36 700 1 19.:

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COlvlPAR.\TIVE I 1.60,; 670 0.6

As shown in Table 3. the physical characteristics are satisfactorilymaintained even when tungsten. tin. zinc, zinc oxide or zinc sulfide is contained as an additive.

Next, examples of adding molybdenum disulfide powder and silicon carbide powder as additives will be described.

Example j

80 parts by mass of artificial graphite powder with an average grain size of 40 lam and an ash content of 0.1% or less, l part of molybdenum disulfide powder, and 0.] S parts silicon carbide with an average grain size of 50 Em \vere mixed. the sum of graphite powder and later-added binder being 100 parts. 2Q parts by mass of the general-purpose epoxy resin as the binder were added thereto and kneaded at a normal temperature for one hour. After that, the mixture divas ground to a grain size of 4()0 1lm or less and pressed into a size of 7x 1 I x30 mm at a pressure of 200 MPa. Next, this molded material was heat-treated at 1 80 C thus forming a carbon brush.

Example 6

80 parts by mass of artificial graphite powder with an average,rain size of 40 lam and an ash content of 0. % or less. I part of molybdenum disulfide powder, and 0.3 parts silicon carbide with an average grain size of SO 1lm were mixed. the sum of graphite powder and later-added binder being l DO parts. 90 parts by mass of the ,eneral-purpose epoxy resin were added thereto and l;neaded at a normal temperature for one hour. After that. the mixture was =round to a grain size of 400 Em or less and embossed to a size of 7xllx'0 mm at a pressure of 00 MPa. Next. this molded

material was heat-treated at 1 80 C. thus forming a carbon brush.

Example 7

80 parts by mass of artificial graphite powder with an average grain size of 40 Em and an ash content of 0.1% or less, parts of molybdenum disulfide powder, and 0.15 parts silicon carbide with an average grain size of 50 lam were mixed, the sum of graphite powder and later-added binder being 100 parts. 20 parts by mass of the general-purpose epoxy resin were added thereto and kneaded at a normal temperature for one hour. After that, the mixture was ground to a grain size of 400 Em or less and embossed to a size of 7x1 Ix30 mm at a pressure of 200 ME,a. Next, this molded material was heat-treated at 1 80 C, thus forming a carbon brush.

Example 8

80 parts by mass of artificial graphite powder with an average grain size of 40 hum and an ash content of 0.1% or less, O.S parts of molybdenum disulfide powder, and 0.15 parts silicon carbide with an average grain size of 50 1lm were mixed the sum of graphite powder and later-added binder being 100 parts. 20 parts by mass of the general-purpose epoxy resin were added thereto and kneaded at a normal temperature for one hour. After that, the mixture was ground to a grain size of 400 Am or less and embossed to a size of 7x1 Ix30 mm at a pressure of 200 MPa. Next this molded material \Nas heat-treated at 1 80 C thus forming a carbon brush.

Example 9

8() parts by mass of artificial graphite powder with an amperage grain size of 40 Em and an ash content of 0.1% or less, 3 parts of molybdenum disulfide powder, and 0.1:

parts silicon carbide with an aNcrage grain size of 50 1lm were mixed. the sum of Graphite powder and later-added binder heing 100 parts. 20 parts by mass of the general-purpose epoxy resin mere added thereto and kneaded at a normal temperature l'or one hour. At'tcr that. the mixture was ground to a grain size of 400 imp or less and embossed to a size of 7x] lx30 mm at a pressure of 900 MPa. Next, this molded material was heattreated at 1 80 C. thus forming a carbon brush.

Comparative Example 2 80 parts by mass of artificial graphite powder with an average grain size of 40 Em and an ash content of 0.2% or less, and (). 15 parts silicon carbide with an average grain size of 50 Am were mixed. the sum of graphite powder and later-added binder being 100 parts. 20 parts by mass of the _encral-purpose epoxy resin were added thereto and kneaded at a normal temperature for one hour. After that. the mixture was ground to a grain size of 400 Am or less and embossed to a size of 7x 1] x30 mm at a pressure of' 900 MPa. NText, this molded material Noms heattreated at 180 C thus forming a carbon brush.

Comparative Example 3 80 parts by mass of artificial graphite powder with an average grain size of 40 Em and awash content of 0.% or less. 1 part of molybdenum disulfide powder. and 1 part aluminum powder with an average grain size of 75 lam were mixed. the sum of graphite powder and later-added binder being 1()0 parts. 90 parts by mass of the generalpurpose epoxy resin were added thereto and kneaded at a normal temperature for one hour. After that the mixture was ground to a grain size of 400 firm or less and embossed to a size of 7x1 lx30 mm at a pressure of 900 MPa. Next. this molded

material was heat-treated at I SO C, thus forming a carbon inrush.

Comparative Example 4 80 parts by mass of artificial graphite powder with an average grain size of 40 1lm and an ash content of 0.2% or less. and 0. 5 parts of molybdenum disulfide powder, the sum of graphite powder and later-added binder being 100 parts. 20 parts by mass of the generalpurpose epoxy resin were added thereto and kneaded at a normal temperature for one hour. After that, the mixture was ground to a grain size of 400 lam or less and embossed to a size of 7x11 x30 Em at a pressure of 200 MPa. Next, this molded material was heat-treated at 1 80 C, thus forming a carbon inrush.

For the brushes of Examples 5 to 9 and Comparative Examples 2 to 4 terminal interference voltage measurement and interference voltage measurement were carried out under the conditions of AC 230V and SO Hz, using an EMI test based on the CISPR 14 standard. Table 4 and Figs.1 and 2 show the result of the terminal interference voltage measurement. Table S and Fig.3 show the result of the interference voltage measurement. Fig. 2 is an enlarged view of a low-frequency region shown in Fig.1.

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As shown in Tables 4 and 5 and 1:igs.l to 3, with the carbon brushes of Examples I to 5 produced by adding molybdenum disulfide lo the carbon base material so as to be no less than 0.% and no more than 3% of the total quantity of the carbon base material and the binder, and adding silicon so as to be no less than 0.5% and no more than 1% of the total quantity of the carbon base material and the binder, the generated radio noise is equal to or less than the radio noise standard in the European countries and the United States.

This invention is constructed as described above. By adding specified metal components or inorganic materials such as molybdenum disulfide and silicon carbide to the carbon base material at a predetermined rate. radio noise is reduced and the radio interference restraining property can be stably improved.

Claims

1. A carbon brush causing less radio interference. produced by adding an additive made of a metal or an inorganic material to a carbon base material formed by lneading graphite powder with a binder and heattreating the binder component.

2. The carbon brush causing less radio interference as claimed in claim 1, wherein the additive is made of at least one of the group consisting oi tungsten, tint zinc oxide, and zinc sulfide.

3. 'I'he carbon brush causing less radio interference as claimed in claim 1 or 2, wherein the additive is no more than 3% by weight and no less than 0.3% of the carbon base material.

4. The carbon brush causing less radio interference as claimed in claim 1, wherein the additive is molybdenum disulfide and silicon carbide.

5. The carbon brush causing less radio interference as claimed in claim 4, wherein the molybdenum disulfide is no less than 0.5% and no more than 3% of the total quantity of the carbon base material and the binder, and the silicon carbide is no less than 0.] % and no more than 0.S% of the total quantity of the carbon base material and the binder.

6. The carbon brush causing less radio interference as claimed in one of claims 1 to 5. wherein the carbon base material is impregnated with oil.

7. The carbon brush causing less radio interference as claimed in one of claims I to 6 wherein the binder is a thermosetting resin or pitch.

8. A carbon brush substantially as herein described with reference to any one of the examples.