coal commutator and a method for its manufacture

Abstract

Carbon commutator (2) comprising a plurality of segments (8) comprising a carbon layer (12) on a surface side of the segments and a metal-carbon layer (14) on a bottom side of the segments, wherein the metal-carbon layer of the segments is attached to a riser (4), wherein the carbon layer and the metal-carbon layer both contain at least one thermoplastic resin binder, and wherein the metal-carbon layer (14) contains electrolytic copper powder, where the thermoplastic resin binder has a melting point of 230°C to 400°C, and in which the metal-carbon layer contains 5 to 40 wt% electrolytic copper powder, 2 to 30 wt% tin and 20 to 83 wt% brass powder, wherein metal components constitute a total of 90 wt% or more and 95 wt% or less, and furthermore contains 0.3 to 1.5 wt% thermoplastic resin binder and as remaining wt% carbon.

Description

[0001] The present invention relates to a carbon commutator comprising a carbon layer and a metal-carbon layer, and a method for manufacturing the same.

[0002] Carbon commutators are used in fuel pump motors and the like, and carbon segments contact a brush, with the segments being attached to a riser as a metal clamp. Such carbon commutators have a problem in that the metal components contained in the segments are corroded by alcohol, sulfide, and the like contained in fuel. In this regard, JP 2002-369454 A discloses a carbon commutator in which the segment is formed of two layers: a carbon layer on a surface side and a metal-carbon layer on a riser side to insulate the metal-carbon layer from alcohol and the like. The metal-carbon layer is provided with protrusions, and the protrusions are press-fitted into holes in the riser to fix the segments, thereby eliminating the need for soldering and the like.For the metal-carbon layer, brass is used instead of copper to prevent metal corrosion, and tin is mixed with it to achieve liquid-phase sintering. Furthermore, phenolic resin is used as a binder for both the carbon layer and the metal-carbon layer.

[0003] WO 99 / 08367 A also discloses a carbon commutator comprising two layers, namely a carbon layer and a metal-carbon layer. The metal-carbon layer is formed by baking at 800 to 850°C using electrolytic copper powder, tin powder, and carbon with phenolic resin as a binder. As the tin powder is melted, liquid-phase sintering occurs, and the carbon in the carbon layer and the metal-carbon layer is sintered with the binder.

[0004] DE 102 24 738 A1 discloses a sulfidation-resistant current-carrying element, such as a commutator, suitable for a DC motor in a fuel pump. The current-carrying element for a DC motor in a fuel pump has a commutator consisting of a carbon layer, the main component of which is carbon, forming a sliding surface at one end, and a metal-carbon layer firmly bonded to the carbon layer at the other end, which comprises 55 to 90 wt.% of metal with brass as a main component and a remaining portion with carbon as a main component. By using brass as a main component in the metal-carbon layer, it is possible to obtain a commutator with improved sulfidation resistance.

[0005] DE 10 2008 004 378 A1 discloses a dual-component disk for a collector of an electric motor, in particular an electric motor of a fuel pump, comprising a graphite layer and a metal layer firmly bonded to the graphite layer. The metal layer can be produced from metal particles and a binder by means of which the metal particles can be firmly bonded to one another. Furthermore, the aforementioned document discloses a method for producing a dual-component disk, in particular for a collector of an electric motor, comprising the following steps: adding a binder to a metal powder and producing a metal layer, pressing the metal layer with a graphite layer, and firing the pressed-together layers at a temperature at which the binder of the metal layer melts.

[0006] EP 1 003 269 B1 discloses a carbon commutator having an insulating hub element and a plurality of segments arranged in a circumferential direction on the insulating hub element, wherein the segments are insulated from one another and each segment comprises: - a first end suitable for sliding a brush on the first end; - a second end opposite the first end; - a carbon layer adjacent to the first end;- a conductive terminal element adjacent to the second end and containing a first material or an alloy of the first material and - a metal layer integrally connected to the conductive terminal element, the commutator being characterized in that the metal layer is a sintered body containing a first material and a second material alloyed with the first material, the second material having a melting point lower than a melting point of the first material, and the first material being copper, the commutator being characterized in that a surface of the conductive terminal element is alloyed with the metal layer;

[0007] US 5 789 842 A discloses a rotating element of an electrical machine, rotating electrical contact parts and electrical machines incorporating these devices.

[0008] The carbon commutators of JP 2002-369454 A and WO 99 / 08367 A use phenolic resin as a binder, and thus, baking is performed at a temperature greater than or equal to 700°C; at this temperature, the phenolic resin is carbonized to serve as a binder. However, excellent sliding characteristics can be obtained with a carbon layer baked at a lower temperature. The present inventors have found that when a metal-carbon layer is baked using phenolic resin as a binder at a low temperature, the metal-carbon layer has completely insufficient strength.Based on this finding, the inventors of the present invention have found a composition for a metal-carbon layer that can be baked at a low temperature and a method for manufacturing a carbon commutator, and thus the present invention has been accomplished.

[0009] An object of the present invention is to provide a carbon commutator using a metal carbon layer which can be obtained by baking (sintering) at low temperature and has sufficient electrical characteristics and mechanical characteristics, and a method for manufacturing the same.

[0010] This object is achieved by a carbon commutator according to claim 1. Advantageous further developments thereof can be found in the associated subclaims.

[0011] The present invention relates to a carbon commutator comprising a segment having a carbon layer on a surface side and a metal-carbon layer on a bottom side, the metal-carbon layer of the segment being attached to a riser, the carbon layer and the metal-carbon layer both containing a thermoplastic resin binder. The thermoplastic resin binder melts or softens to serve as a binder in each layer and bond the carbon layer and the metal-carbon layer. Accordingly, a carbon commutator having practical strength and conductivity can be obtained by low-temperature baking.

[0012] The metal-carbon layer contains electrolytic copper powder. The electrolytic copper powder has a dendritic shape and is thus entangled with other particles, which imparts strength and conductivity to the metal-carbon layer and also forms entanglements or irregularities at the interface between the carbon layer and the metal-carbon layer. More preferably, the metal-carbon layer also contains tin. The metal-carbon layer also preferably contains copper alloy powder such as brass powder, bronze powder, or copper / nickel alloy powder. More preferably, the metal-carbon layer contains brass powder with a zinc content of, for example, 10 to 40 mass%. Copper powder can be difficult to separate due to sulfur and the like contained in liquid fuel.are susceptible to corrosion, but copper alloy powder such as brass powder exhibits high corrosion resistance to sulfur and the like. More preferably, the metal carbon layer further contains tin. More preferably, the metal carbon layer contains electrolytic copper powder and brass powder. The electrolytic copper powder imparts conductivity and strength to the metal carbon layer and adhesion strength to the carbon layer, and the brass powder imparts corrosion resistance to sulfur and the like contained in liquid fuel. More preferably, the metal carbon layer further contains tin.

[0013] When tin is present in the metal-carbon layer, liquid-phase sintering of tin, which has a melting point of about 230°C, is used for sintering the metal-carbon layer. Since sintering is carried out at the melting point of tin or higher, it is preferable that the thermoplastic resin binder has a melting point of 230°C to 400°C, and for example, PPS (polyphenylene sulfide), PEEK (polyetheretherketone), nylon 66, polytetrafluoroethylene, or the like is used. In the case where tin is not used, polyethylene, which has a melting point of about 120°C, can be used as the binder. Electrolytic copper powder and other metal powders such as brass powder do not melt at 230 to 400°C and thus remain as powder in the metal-carbon layer and are bonded together by tin and the thermoplastic resin binder.In this specification, a range indication using "up to" such as 230 to 400°C or 5 to 40 mass% is to be understood as including a lower limit and an upper limit such as 230°C or more and 400°C or less, or 5 mass% or more and 40 mass% or less.

[0014] Regarding the composition, it is preferable that the metal-carbon layer contains 5 to 40 mass% of electrolytic copper powder, 2 to 30 mass% of tin powder, and 20 to 83 mass% of brass powder, with the total metal components accounting for 90 mass% or more, and further contains 0.3 to 4 mass% of thermoplastic resin binder and the remaining mass% of carbon. Metal-carbon layers obtained by low-temperature sintering have low conductivity. Accordingly, to ensure conductivity, a metal-carbon layer containing 5 to 40 mass% of electrolytic copper powder, 2 to 30 mass% of tin powder, and 20 to 83 mass% of brass powder, with the total metal component accounting for 90 mass% or more, is used.Furthermore, liquid-phase sintering with tin ensures interlocking with the electrolytic copper powder and strength by melting or softening the thermoplastic resin binder. The amount of the thermoplastic resin binder is preferably 0.3 to 4 mass%. Furthermore, the metal-carbon layer preferably contains a total of 90 mass% or more of metal components such as brass powder and tin, 0.3 to 4 mass% of the thermoplastic resin binder, and the remaining mass% of carbon. The carbon layer contains a thermoplastic resin binder with the same chemical formula as that of the metal-carbon layer in an amount of 3 to 15 mass%, and the remaining mass% of carbon.

[0015] It is preferable that the carbon layer contains a thermoplastic resin binder of the same chemical formula as that of the metal-carbon layer in an amount of 3 to 15 mass%, with carbon as the remaining mass%. Particularly, when the metal-carbon layer and the carbon layer have the same mass ratio of carbon to thermoplastic resin and contain thermoplastic resin binders of the same chemical formula, the same degree of bonding of carbon particles can be achieved between the metal-carbon layer and the carbon layer. As used herein, "the same chemical formula" means, for example, in the case of poly(phenylene sulfide) (PPS), the same chemical formula -[ø-S]- n , where ø is a phenylene group.

[0016] The present invention also relates to a method for producing a carbon commutator comprising a segment having a carbon layer on a surface side and a metal-carbon layer on a bottom side, the metal-carbon layer of the segment being fixed to a riser, in which a compression-molded article made of two layer materials, namely a metal-carbon layer material containing carbon, a thermoplastic resin binder, and metal powder, and a carbon layer material containing carbon and a thermoplastic resin binder, is baked at a temperature from a melting point of the thermoplastic resin binder to 500°C.

[0017] Compression molding and baking can be performed in the same mold, or baking can be performed separately after the molded article is removed from the mold. Since the firing temperature is low, any atmosphere can be used. To avoid thermal decomposition of the binder, the baking temperature is preferably set to not less than the melting point of the binder and not more than 400°C. In compression molding, the riser may be inserted into a mold, and at the same time, press-fitting and molding of the metal-carbon layer to the riser may be performed. In the working examples given below, compression molding, baking, press-fitting, and the like are performed separately.

[0018] Preferably, the metal-carbon layer material contains carbon, a thermoplastic resin binder, brass powder, and electrolytic copper powder. More preferably, the metal-carbon layer material contains carbon, a thermoplastic resin binder, brass powder, electrolytic copper powder, and tin powder, and the compression-molded article is baked at 230°C to 500°C. Particularly preferably, the metal-carbon layer material contains 5 to 40 mass% of electrolytic copper powder, 2 to 30 mass% of tin powder, and 20 to 83 mass% of brass powder, with the total metal components accounting for 90 mass% or more, and further contains 0.3 to 4 mass% of thermoplastic resin binder and the remaining mass% of carbon. In this specification, the descriptions regarding the carbon commutator apply to the method for manufacturing a carbon commutator.

[0019] According to the present invention, it is possible to obtain a carbon commutator using a metal carbon layer, which can be obtained by low-temperature baking and has sufficient electrical characteristics and mechanical characteristics due to the bonding by the thermoplastic resin binder. When the metal carbon layer contains electrolytic copper powder, even higher strength is obtained. When the metal carbon layer contains copper alloy powder such as brass powder, corrosion resistance to sulfur and the like contained in liquid fuel is improved. By incorporating tin, increased strength can be obtained by liquid-phase sintering of tin. The baking temperature can be adjusted by selecting the type of thermoplastic resin binder.

[0020] Preferred embodiments of the present invention are explained in more detail below with reference to the accompanying drawings. They show: Fig. 1 is a plan view of a carbon commutator according to an embodiment of the present invention; Fig. 2 a cross-sectional view of the carbon commutator shown in the line II-II of the Fig. 1 indicated direction; Fig. 3 is a bottom view of a carbon plate according to the embodiment; Fig. 4 a cross-sectional view of the carbon plate shown in the diagram IV-IV of Fig. 3 indicated direction; Fig. 5 is a graph showing a relationship between baking temperature and resistivity of the metal-carbon layer in working examples and comparative examples; Fig.6 is a graph showing a relationship between baking temperature and bending strength of the metal-carbon layer in working examples and comparative examples; and Fig. 7 is a map showing tensile strengths between metal-carbon layer and carbon layer in working examples and comparative examples.

[0021] A preferred embodiment for carrying out the present invention will be described below. The present invention is not limited to the embodiment described herein and is defined based on the claims. It may be modified by adding material known to those skilled in the art to the embodiment.

[0022] Fig. 1 to 7 show an embodiment and characteristics thereof. Fig.1 to 4 show a structure of a carbon commutator 2 in which segments 8 obtained by cutting a carbon plate 6 are attached to metal risers 4 by press fitting or the like. Reference numeral 10 indicates a shaft hole. Each segment 8 is formed of two layers, namely a carbon layer 12 on one surface side and a metal carbon layer 14 press-fitted to the riser 4. The segments 8 are separated from each other by slits 16, which also separate the risers 4 from each other. Reference numeral 18 indicates a resin portion formed to countersink the riser 4. A projection 20 of the metal carbon layer 14 is press-fitted into a hole of the riser 4. The carbon commutator 2 can have any structure. Working exampleStep 1

[0023] Brass powder (water-atomized powder containing 30 mass% Zn with an average particle size of 40 µm) in an amount of 60 mass%, 20 mass% electrolytic copper powder (an average particle size of 40 µm), and 10 mass% tin powder were uniformly mixed using a mixer with 10 mass% natural graphite mixed powder (an average particle size of 30 µm) previously mixed with 8 mass% PPS (poly(phenylene sulfide)) resin powder (an average particle size of 15 µm) to obtain a mixed powder for a metal-carbon layer (metal-carbon layer material). As used herein, the natural graphite mixed powder mixed with 8 mass% PPS resin powder refers to a mixed powder containing 8 mass% PPS and 92 mass% natural graphite. Instead of pre-mixing PPS resin powder with natural graphite powder, PPS powder and natural graphite powder can be mixed with metal powder.Furthermore, the type of carbon is not limited to natural graphite, and artificial graphite such as electrographite, amorphous carbon, or the like can be used. The powders can have any average particle size. The metal-carbon layer material contains a metal component in an amount of at least 85 mass% or more and 95 mass% or less, preferably 90 mass% or more and 95 mass% or less, and the remaining mass% graphite and thermoplastic resin such as PPS. The metal component contains 5 to 40 mass% of electrolytic copper powder, 2 to 30 mass% of tin powder, and 20 to 83 mass% of brass powder, the total amount being 85 mass% or more, preferably 90 mass% or more and 95 mass% or less. The amount of the thermoplastic resin binder is preferably 0.3 to 4 mass%, and more preferably 0.3 to 1.5 mass%. Step 2

[0024] The metal-carbon film material obtained above was placed in a predetermined mold, and a separately blended carbon film material for a slide member was placed thereon. The carbon film material was then subjected to compression molding using an upper punch and a lower punch to obtain a green carbon sheet. It is preferable that the carbon film material be composed of 92 mass% natural graphite with an average particle size of 30 μm and 8 mass% PPS, and that the mass ratio of carbon to thermoplastic resin in the carbon film material be equal to the mass ratio of carbon to thermoplastic resin binder in the metal-carbon film material.The carbon layer material contains, for example, the same thermoplastic resin binder as that used in the metal-carbon layer in an amount of 3 to 15 mass%, and the remaining mass% carbon, such as natural graphite, artificial graphite, or amorphous carbon. The metal-carbon layer and the carbon layer can contain different types of carbon. The metal-carbon layer can be formed from a relatively metal-rich lower layer and a relatively carbon-rich upper layer, so that the composition at the interface between the metal-carbon layer and the carbon layer varies smoothly. Step 3

[0025] The unbaked carbon sheet was removed from the mold and then heated and baked in air at 300°C, for example, which is slightly higher than the melting point of PPS, to produce a carbon sheet. During this process, the tin powder melts to bond the metal component particles together, and the PPS particles melt to bond the metal carbon particles together. At the same time, the carbon particles in the carbon layer are bonded together by PPS, and the interface between the metal carbon layer and the carbon layer is also bonded. At the interface between the metal carbon layer and the carbon layer, the particles of electrolytic copper powder protrude to help bond these layers together.The baking temperature is set to the melting point of the thermoplastic resin or higher, preferably 230°C, which is close to the melting point of tin, or higher and 500°C or less, and more preferably 230°C or higher and 400°C or less. Step 4

[0026] The carbon plate was press-fitted into a riser before being cut into segments and inserted into a mold. A resin for a housing was injected into the mold. Next, the carbon plate and riser were cut to form slits, thus obtaining a carbon commutator. The carbon commutator thus obtained is referred to as Working Example 1. Comparison examplesComparison example 1

[0027] A batch powder for a metal carbon layer was prepared by uniformly mixing 80 mass% of the same brass powder used above, 10 mass% of the same tin powder, and 10 mass% of the same mixed powder. The mixed powder was a mixed powder containing 8 mass% of PPS resin powder (an average particle size of 15 μm) and 92 mass% of natural graphite powder with an average particle size of 30 μm. As in Working Example 1, the mixed powder was also used as the carbon layer material. Then, compression molding and baking in air at 300°C were performed as in Working Example 1, and the resultant was press-fitted into a riser to provide a carbon commutator, and this carbon commutator is referred to as Comparative Example 1. Comparison examples 2 and 3Step 1

[0028] A metal-carbon layer batch powder was obtained by uniformly mixing, using a mixer, 70 mass% of the same brass powder used above, 5 mass% of the same tin powder, and 25 mass% of the same natural graphite mixed powder (the graphite having an average particle size of 30 μm before being mixed) mixed with 20 mass% of phenolic resin. Step 2

[0029] The metal-carbon layer batch powder was placed in a predetermined mold, and the same natural graphite mixed powder previously mixed with 20 mass% phenolic resin was placed thereon, which was then subjected to compression molding to provide an unbaked carbon plate. Step 3

[0030] The unbaked carbon plate was heated and baked in a reducing gas atmosphere at 900°C or 300°C. Step 4

[0031] Carbon commutators were obtained using the baked carbon plates in the same manner as in the working example and comparative example 1. Hereinafter, the carbon commutator produced by baking at 300°C is referred to as comparative example 2, and the carbon commutator produced by baking at 900°C is referred to as comparative example 3.

[0032] Table 1 shows the manufacturing conditions and characteristics of Working Example 1 and Comparative Examples 1 to 3. The interface tensile strength shown in Table 1 indicates the tensile strength at the interface between the metal-carbon layer and the carbon layer. Table 1 Comparison example 1 Working example Comparison example 2 Comparison example 3 Brass 80% by mass 60 mass% 70 mass% 70 mass% electrolytic copper powder - 20 mass% - - tin 10 mass% 10 mass% 5 mass% 5 mass% graphite 9.2% by mass 9.2% by mass 20 mass% 20 mass% (Binder) PPS PPS phenol phenol 0.8 mass% 0.8 mass% 5 mass% 5 mass% Baking temperature 300°C 300°C 300°C 900°C specific resistance of the metal layer 1.400 700 80.000 200 (µΩ·cm) 16 28 5 18 Flexural strength of the metal layer (MPa) 4,0 4,4 3,2 1,8 Tensile strength of the interface (MPa)

[0033] The characteristics of the working example and the comparative examples are shown in Table 1 and the Fig. 5 to 7 shown. Fig.5 shows the resistivity of the metal-carbon layer, and Fig. 6 shows the flexural strength of the metal-carbon layer. Fig. Figure 7 shows the tensile strength of the interface. When a metal-carbon layer material having a phenolic resin binder content of 5 mass% and a metal component content of 75 mass% was baked at 300°C (Comparative Example 2), a resistivity of 80,000 μΩ cm was obtained, which is 400 times that of Comparative Example 3 produced by baking at 900°C, and a flexural strength of 5 MPa was obtained, which is lower than one-third of that of Comparative Example 3 produced by baking at 900°C. From the above, it was found that baking at a low temperature such as 300°C using a phenolic resin binder does not produce a practical carbon commutator.

[0034] A comparison between the working example and comparative example 1 produced by baking at 300°C (using 0.8 mass% PPS binder) and comparative example 3 produced by baking at 900°C (using 5 mass% phenolic resin binder) shows that the resistivity of the working example and comparative example 1 was higher than that of comparative example 3, the flexural strength was approximately equal to or greater than that of comparative example 3, and the tensile strength of the interface between the metal-carbon layer and the carbon layer was higher than that of comparative example 3.From this, it can be seen that the working example and comparative example 1 provided equivalent performance to comparative example 3, which had a binder content of 5 mass% and was produced by baking at 900°C, although the working example and comparative example 1 had a lower binder content of 0.8 mass% and were produced by baking at a low temperature of 300°C.

[0035] The above effects were obtained by combining the thermoplastic resin binder in both the carbon layer and the metal-carbon layer, using the thermoplastic resin binder and liquid-phase sintering of tin, and increasing the metal content of the metal-carbon layer to 90 mass%. Incorporating electrolytic copper powder into the metal-carbon layer resulted in reduced resistivity of the metal layer and improved flexural strength of the metal layer and tensile strength of the interface. However, even Comparative Example 1, which did not include electrolytic copper powder, provided practical performance. List of reference symbols 2 carbon commutator 4 riser 6 Carbon plate 8 segments 10 shaft hole 12 Carbon layer 14 Metal-carbon layer 16 slots 18 Harz section 20 lead

Claims

[1] Carbon commutator (2) comprising a plurality of segments (8) comprising a carbon layer (12) on a surface side of the segments and a metal-carbon layer (14) on a bottom side of the segments, wherein the metal-carbon layer of the segments is attached to a riser (4), wherein the carbon layer and the metal-carbon layer both contain at least one thermoplastic resin binder, and wherein the metal-carbon layer (14) contains electrolytic copper powder, in which the thermoplastic resin binder has a melting point of 230°C to 400°C, and wherein the metal-carbon layer contains 5 to 40 mass% of electrolytic copper powder, 2 to 30 mass% of tin and 20 to 83 mass% of brass powder, with metal components in total accounting for 90 mass% or more and 95 mass% or less, and further contains 0.3 to 1.5 mass% of thermoplastic resin binder and the remaining mass% of carbon. [2] Carbon commutator (2) according to claim 1, wherein the carbon layer (12) contains a thermoplastic resin binder having the same chemical formula as that of the metal-carbon layer (14) in an amount of 3 to 15 mass% and carbon as the remaining mass%. [3] A method for producing a carbon commutator (2) comprising a plurality of segments (8) comprising a carbon layer (12) on a surface side of the segments and a metal-carbon layer (14) on a bottom side of the segments, wherein the metal-carbon layer of the segments is attached to a riser (4), wherein a compression-molded article made of two layer materials comprising a metal-carbon layer material containing carbon, a thermoplastic resin binder, electrolytic copper powder, brass powder, and tin powder, and a carbon layer material containing carbon and a thermoplastic resin binder is baked at a temperature not lower than a melting point of the thermoplastic resin binder at 230°C to 500°C, and wherein the metal-carbon layer contains 5 to 40 mass% of electrolytic copper powder, 2 to 30 mass% of tin powder and 20 to 83 mass% of brass powder, with metal components in total accounting for 90 mass% or more and 95 mass% or less, and further contains 0.3 to 1.5 mass% of thermoplastic resin binder and the remaining mass% of carbon.

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