EP4638038A1 - Method of producing a slip ring brush - Google Patents

Method of producing a slip ring brush

Info

Publication number
EP4638038A1
EP4638038A1 EP23833773.7A EP23833773A EP4638038A1 EP 4638038 A1 EP4638038 A1 EP 4638038A1 EP 23833773 A EP23833773 A EP 23833773A EP 4638038 A1 EP4638038 A1 EP 4638038A1
Authority
EP
European Patent Office
Prior art keywords
graphene
copper
slip ring
mixture
graphene mixture
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP23833773.7A
Other languages
German (de)
French (fr)
Inventor
Jian Qin
Su Zhao
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
ABB Schweiz AG
Original Assignee
ABB Schweiz AG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by ABB Schweiz AG filed Critical ABB Schweiz AG
Publication of EP4638038A1 publication Critical patent/EP4638038A1/en
Pending legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01R—ELECTRICALLY-CONDUCTIVE CONNECTIONS; STRUCTURAL ASSOCIATIONS OF A PLURALITY OF MUTUALLY-INSULATED ELECTRICAL CONNECTING ELEMENTS; COUPLING DEVICES; CURRENT COLLECTORS
    • H01R43/00—Apparatus or processes specially adapted for manufacturing, assembling, maintaining, or repairing of line connectors or current collectors or for joining electric conductors
    • H01R43/12—Manufacture of brushes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/05—Metallic powder characterised by the size or surface area of the particles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/10—Sintering only
    • B22F3/105—Sintering only by using electric current other than for infrared radiant energy, laser radiation or plasma ; by ultrasonic bonding
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/182—Graphene
    • C01B32/194—After-treatment
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C1/00—Making non-ferrous alloys
    • C22C1/04—Making non-ferrous alloys by powder metallurgy
    • C22C1/05—Mixtures of metal powder with non-metallic powder
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C1/00—Making non-ferrous alloys
    • C22C1/04—Making non-ferrous alloys by powder metallurgy
    • C22C1/05—Mixtures of metal powder with non-metallic powder
    • C22C1/059—Making alloys comprising less than 5% by weight of dispersed reinforcing phases
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C1/00—Making non-ferrous alloys
    • C22C1/10—Alloys containing non-metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C9/00—Alloys based on copper
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/10—Sintering only
    • B22F3/105—Sintering only by using electric current other than for infrared radiant energy, laser radiation or plasma ; by ultrasonic bonding
    • B22F2003/1051—Sintering only by using electric current other than for infrared radiant energy, laser radiation or plasma ; by ultrasonic bonding by electric discharge
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
    • B22F2998/10—Processes characterised by the sequence of their steps

Definitions

  • the present disclosure generally relates to a composite material for a brush of a slip ring unit.
  • Slip ring units are used for conducting current to or from the rotating shaft of electrical machines.
  • Slip ring units comprise a slip ring, typically made of copper, bronze or stainless steel and a carbon brush as the counterpart, typically made of graphite or a metal-graphite blend.
  • the slip ring is mounted to the rotor shaft while the carbon brush is stationary.
  • the carbon brush is pressed to the slip ring surface by a spring to ensure good electrical contact.
  • the graphite has two functions. The first is to provide sufficient conductivity to transfer the needed current to the slip ring and the second is to act as a solid lubricant to provide low friction to keep the slip ring intact.
  • a common practice to prolong the lifetime of brushes is to limit the contact pressure between the brush and slip ring to a very low level, for example 20- 25 kPa. Because the contact resistance is inversely proportional to the contact pressure, the electrical losses at the contact region are relatively high.
  • CN112981159 B discloses a preparation method of a graphene-reinforced copper-based composite material.
  • the method comprises mixing copper powder and an organic metal carbon source and spark plasma sintering to obtain a three-dimensional graphene/ carbide or oxide co-enhanced copperbased composite material.
  • a general object of the present disclosure is to provide a method of producing a slip ring brush that solves or at least mitigates the problems of the prior art.
  • a method of producing a slip ring brush comprising: producing a composite material, including: a) mixing copper powder with a grain size of 10-500 pm with graphene to obtain a copper-graphene mixture, the content of graphene in the copper-graphene mixture being in a range of 0.5-5 wt.% of the total weight of the copper-graphene mixture, and b) sintering the copper-graphene mixture; and shaping the composite material as a slip ring brush in step b) or after step b).
  • the composite material exhibits superior tribological properties including low friction and high wear resistance in comparison with the commercial graphite containing electrical brushes.
  • the electrical contact resistance is 1 to 2 orders of magnitude lower than those of the commercial electrical brushes. Due to the low wear nature of the copper graphene composite produced by the method, the contact pressure between the brush and slip ring can be increased. This will further reduce contact resistance and voltage drop, so the electrical loss is minimized during application.
  • the composite material thus provides low friction, good electrical conductivity and additionally much less wear which leads to an extended lifetime of the brush part. Reduced voltage drop and contact resistance also opens up the possibility to increase the current carrying capacity. Unlike the graphite containing commercial brushes which are sensitive to humidity change, the present composite material is robust and can operate at a broad humidity and temperature range.
  • the present composite material has better electrical conductivity because it is free of oxides and carbides.
  • graphene is used collectively for carbon atoms in a 2D- honeycomb lattice in the form of mono-layer sheets, bi-layer sheets, few (3-5 layers)-layer sheets, or nano-platelets having a thickness of at most 50 nm, e.g., within the range of 1 to 50 nm.
  • the sintering is spark plasma sintering.
  • the high speed of the spark plasma sintering process ensures that it can densify powders with small particle size while avoiding coarsening which accompanies standard densification processes, such as non-spark plasma sintering techniques.
  • Samples of composite material produced by this method have shown to have a compact density between 80 to 99% of the theoretical density of pure copper.
  • the composite material retains the structure of the graphene material, and it is free from aggregation compared to other sintering techniques which take much longer time, causing the graphene sheets to oxidise or agglomerate, deteriorating the lubricating and electrical properties of graphene.
  • step b) is performed at a temperature of 650- 95O°C and under a pressure of 10-iooMPa.
  • step b) is performed under an inert atmosphere. This eliminates the risk of oxidation of the composite material. Oxidation reduces the electrical conductivity of materials. According to one embodiment step b) is performed for at most 20 minutes, such as at most 15 minutes, such as at most 10 minutes.
  • step b) is performed for at least 2 minutes, such as at least 3 minutes.
  • Step b) may for example be performed for 5 minutes.
  • the content of graphene in the copper- graphene mixture is in a range of 1-3 wt.% of the total weight of the copper- graphene mixture. It has been found that this range provides an optimal trade-off between cost, and lubrication and wear resistance properties, while accounting for the risk of graphene turning into graphite.
  • step a) in addition to mixing the copper powder with the graphene involves mixing additives with the copper powder and the graphene to obtain the copper-graphene mixture.
  • the additives include a stabilizer and a binder.
  • the additives consist of the stabilizer and the binder.
  • the content of the additives is below 5 wt.% of the total weight of the copper-graphene mixture.
  • the copper-graphene mixture consists of the copper powder, the graphene, and the additives.
  • the composite material consists of the sintered copper-graphene mixture.
  • the content of copper in the copper-graphene mixture is in a range of 90-99 wt.% of the total weight of the copper- graphene mixture.
  • the content of copper in the copper-graphene mixture is above 90 wt.% of the total weight of the copper-graphene mixture.
  • the graphene is in the form of graphene particles each having a surface area in a range of 100-750 m 2 /g.
  • the copper powder has a grain size of at least 15 pm, such as at least 30 pm, at least 50 pm, at least 100 pm, or at least 200 pm.
  • the grain size of the copper powder may be with quasi spherical morphology.
  • the mixing in step a) is a mechanical mixing.
  • the mechanical mixing is a dry mixing.
  • the mixing can be performed in a high-speed shaker, for example, with adequate results.
  • Other mixing methods such as ball milling may also be employed.
  • step b) is the only sintering step performed for producing the composite material.
  • the density of the composite material will be high enough to be used as a brush in a slip ring unit. If the density would be increased further by an additional primary sintering step followed by the spark plasma sintering, the hardness of the material would be increased, and this would provide too much wear on the slip ring.
  • the graphene is graphene nanoplatelets.
  • Graphene nanoplatelets is a low-cost material which suffices for the purpose of making the composite material.
  • the slip ring brush is free of graphite.
  • Fig. 1 is a flowchart of a method of producing a slip ring brush
  • Fig. 2 is a side view of a slip ring unit comprising a slip ring brush made by the method in Fig. 1.
  • Fig. 1 depicts a method of producing a slip ring brush.
  • the method generally comprises producing a composite material, which is shaped or formed as a slip ring brush.
  • a step a) copper powder with a grain size of 10-500 pm is mixed with graphene to obtain a copper-graphene mixture.
  • the grain size of the copper powder may according to some examples be at least 15 pm, such as at least 30 pm, at least 40 pm, at 50 pm, at least 100 pm, at least 200 pm, or at least 300 pm.
  • the content of graphene in the copper-graphene mixture is in a range of 0.5- graphene in the copper-graphene mixture may for example be in a range of i- 3 wt.% of the total weight of the copper-graphene mixture.
  • the graphene which is a 2D material, may be in the form of graphene particles each having a surface area in a range of 100-750 m 2 /g.
  • the content of copper in the copper-graphene mixture may be in a range of 90-99 wt.% of the total weight of the copper-graphene mixture, for example in a range >90 wt.%.
  • Step b) of mixing is preferably a mechanical mixing.
  • the copper powder and the graphene may be mixed vigorously, for example in a high-speed shaker.
  • the shaking speed may be 700 rpm and the mixing time maybe 150 seconds.
  • a paint shaker model SK35 from Fast & Fluid was used. The mixing time varies depending on the amount of material mixed.
  • the graphene may for example be graphene nanoplatelets, graphene nanopowder, or graphene flakes.
  • Step a) may also comprise mixing additives with the copper powder and the graphene.
  • the additives may for example include a stabilizer and a binder. According to one example, the additives consist of the stabilizer and the binder.
  • the content of the additives may be below 5 wt.% of the total weight of the copper-graphene mixture.
  • the copper-graphene mixture obtained in step a) may consist of the copper powder, the graphene, and the additives.
  • a step b) the copper-graphene mixture is sintered.
  • the composite material is thus obtained.
  • the sintering in step b) may be spark plasma sintering.
  • the sintering in step b) maybe carried out at a temperature of 65O-95O°C and under a pressure of 10-iooMPa, such as 10-75 MPa.
  • the composite material is shaped as a slip ring brush in step b), or it maybe shaped as a slip ring brush after step b).
  • the slip ring brush thus obtained is composed of the composite material obtained according to the method.
  • the composite material may consist of the sintered copper graphene mixture.
  • Step b) is preferably carried out under an inert atmosphere.
  • Step b) is preferably the only sintering step performed to obtain the composite material.
  • Step b) may typically be performed for at most 20 minutes, such as at most 15 minutes, such as at most 10 minutes.
  • Step b) may typically be performed for at least 2 minutes, such as at least 3 minutes.
  • step b) is performed in the range of 2-20 minutes, for example in the range of 3-15 minutes, or 3-10 minutes. According to one example, step b) is performed for 5 minutes.
  • the slip ring brush obtained by the method is preferably free of graphite.
  • Fig. 2 depicts a slip ring unit 1.
  • the slip ring unit 1 is mounted to a shaft 9.
  • the shaft 9 may for example be a rotor shaft of an electrical machine.
  • the slip ring unit 1 comprises a plurality of slip rings 3 arranged in a support 5.
  • the support is attached to the shaft 9.
  • the slip ring unit 1 comprises a plurality of slip ring brushes 7 made by means of the method described above.
  • Each slip ring brush 7 is arranged in mechanical and electrical contact with a respective slip ring 3.
  • the slip ring brushes 7 are pressed radially inwards towards a respective slip ring 3 by means of a force member 11, such as one or more mechanical springs.
  • the force may be higher than 25 kPa, such as 30 kPa or higher than 30 kPa, for example equal to or higher than 35 kPa or equal to or higher than 40 kPa, such as equal to or higher than 45 kPa.
  • the force maybe equal to or higher than 100 MPa, for example equal to or higher than 250 MPa.
  • slip ring brushes 7 are arranged stationarily and the slip rings 3 are rotated concurrently with rotation of the shaft 9.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Organic Chemistry (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Manufacturing & Machinery (AREA)
  • Nanotechnology (AREA)
  • Dispersion Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Inorganic Chemistry (AREA)
  • Powder Metallurgy (AREA)
  • Motor Or Generator Current Collectors (AREA)

Abstract

A method of producing a composite material for a slip ring brush, the method comprising: a) mixing copper powder with a grain size of 10-500 μm with graphene to obtain a copper-graphene mixture, the content of graphene in the copper-graphene mixture being in a range of 0.5-5 wt.% of the total weight of the copper-graphene mixture, and b) sintering the copper-graphene mixture.

Description

METHOD OF PRODUCING A SLIP RING BRUSH
TECHNICAL FIELD
The present disclosure generally relates to a composite material for a brush of a slip ring unit.
BACKGROUND
Slip ring units are used for conducting current to or from the rotating shaft of electrical machines. Slip ring units comprise a slip ring, typically made of copper, bronze or stainless steel and a carbon brush as the counterpart, typically made of graphite or a metal-graphite blend.
The slip ring is mounted to the rotor shaft while the carbon brush is stationary. The carbon brush is pressed to the slip ring surface by a spring to ensure good electrical contact.
The graphite has two functions. The first is to provide sufficient conductivity to transfer the needed current to the slip ring and the second is to act as a solid lubricant to provide low friction to keep the slip ring intact.
The main drawback of existing carbon brushes is that they wear out over time and need to be replaced to ensure proper functionality. Depending on the application carbon brushes usually need to be replaced every 6 to 12 months, generating high maintenance costs during the entire lifetime of electrical machines.
Moreover, due to the wear of the carbon brush carbon, dust is created, which can lead to clogging or electrical bridging for example.
A common practice to prolong the lifetime of brushes is to limit the contact pressure between the brush and slip ring to a very low level, for example 20- 25 kPa. Because the contact resistance is inversely proportional to the contact pressure, the electrical losses at the contact region are relatively high.
Another limitation of the commercial graphite containing brushes is that the frictional performance is sensitive to humidity which limits the application in less humid environments.
CN112981159 B discloses a preparation method of a graphene-reinforced copper-based composite material. The method comprises mixing copper powder and an organic metal carbon source and spark plasma sintering to obtain a three-dimensional graphene/ carbide or oxide co-enhanced copperbased composite material.
SUMMARY
A general object of the present disclosure is to provide a method of producing a slip ring brush that solves or at least mitigates the problems of the prior art.
There is hence according to a first aspect of the present disclosure provided a method of producing a slip ring brush, comprising: producing a composite material, including: a) mixing copper powder with a grain size of 10-500 pm with graphene to obtain a copper-graphene mixture, the content of graphene in the copper-graphene mixture being in a range of 0.5-5 wt.% of the total weight of the copper-graphene mixture, and b) sintering the copper-graphene mixture; and shaping the composite material as a slip ring brush in step b) or after step b).
The composite material exhibits superior tribological properties including low friction and high wear resistance in comparison with the commercial graphite containing electrical brushes. The electrical contact resistance is 1 to 2 orders of magnitude lower than those of the commercial electrical brushes. Due to the low wear nature of the copper graphene composite produced by the method, the contact pressure between the brush and slip ring can be increased. This will further reduce contact resistance and voltage drop, so the electrical loss is minimized during application.
The composite material thus provides low friction, good electrical conductivity and additionally much less wear which leads to an extended lifetime of the brush part. Reduced voltage drop and contact resistance also opens up the possibility to increase the current carrying capacity. Unlike the graphite containing commercial brushes which are sensitive to humidity change, the present composite material is robust and can operate at a broad humidity and temperature range.
With regards to CN112981159 B, the present composite material has better electrical conductivity because it is free of oxides and carbides.
Herein the term graphene is used collectively for carbon atoms in a 2D- honeycomb lattice in the form of mono-layer sheets, bi-layer sheets, few (3-5 layers)-layer sheets, or nano-platelets having a thickness of at most 50 nm, e.g., within the range of 1 to 50 nm.
According to one embodiment the sintering is spark plasma sintering.
The high speed of the spark plasma sintering process ensures that it can densify powders with small particle size while avoiding coarsening which accompanies standard densification processes, such as non-spark plasma sintering techniques. Samples of composite material produced by this method have shown to have a compact density between 80 to 99% of the theoretical density of pure copper.
Due to the rapid nature of the spark plasma sintering process, which is characterised by a high heating rate and short sintering time, typically only a couple of minutes, the composite material retains the structure of the graphene material, and it is free from aggregation compared to other sintering techniques which take much longer time, causing the graphene sheets to oxidise or agglomerate, deteriorating the lubricating and electrical properties of graphene.
According to one embodiment step b) is performed at a temperature of 650- 95O°C and under a pressure of 10-iooMPa.
According to one embodiment step b) is performed under an inert atmosphere. This eliminates the risk of oxidation of the composite material. Oxidation reduces the electrical conductivity of materials. According to one embodiment step b) is performed for at most 20 minutes, such as at most 15 minutes, such as at most 10 minutes.
According to one embodiment step b) is performed for at least 2 minutes, such as at least 3 minutes. Step b) may for example be performed for 5 minutes.
According to one embodiment the content of graphene in the copper- graphene mixture is in a range of 1-3 wt.% of the total weight of the copper- graphene mixture. It has been found that this range provides an optimal trade-off between cost, and lubrication and wear resistance properties, while accounting for the risk of graphene turning into graphite.
According to one embodiment step a) in addition to mixing the copper powder with the graphene, involves mixing additives with the copper powder and the graphene to obtain the copper-graphene mixture.
According to one embodiment the additives include a stabilizer and a binder.
According to one embodiment the additives consist of the stabilizer and the binder.
According to one embodiment the content of the additives is below 5 wt.% of the total weight of the copper-graphene mixture.
According to one embodiment the copper-graphene mixture consists of the copper powder, the graphene, and the additives.
According to one embodiment the composite material consists of the sintered copper-graphene mixture.
According to one embodiment the content of copper in the copper-graphene mixture is in a range of 90-99 wt.% of the total weight of the copper- graphene mixture.
According to one embodiment the content of copper in the copper-graphene mixture is above 90 wt.% of the total weight of the copper-graphene mixture. According to one embodiment the graphene is in the form of graphene particles each having a surface area in a range of 100-750 m2/g.
According to one embodiment the copper powder has a grain size of at least 15 pm, such as at least 30 pm, at least 50 pm, at least 100 pm, or at least 200 pm.
The grain size of the copper powder may be with quasi spherical morphology.
According to one embodiment the mixing in step a) is a mechanical mixing. The mechanical mixing is a dry mixing. The mixing can be performed in a high-speed shaker, for example, with adequate results. Other mixing methods such as ball milling may also be employed.
According to one embodiment step b) is the only sintering step performed for producing the composite material.
By only performing spark plasma sintering, the density of the composite material will be high enough to be used as a brush in a slip ring unit. If the density would be increased further by an additional primary sintering step followed by the spark plasma sintering, the hardness of the material would be increased, and this would provide too much wear on the slip ring.
According to one embodiment the graphene is graphene nanoplatelets. Graphene nanoplatelets is a low-cost material which suffices for the purpose of making the composite material.
According to one embodiment the slip ring brush is free of graphite.
There is according to a second aspect obtainable by means of the method of the first aspect.
Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, apparatus, component, means, etc. are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, etc., unless explicitly stated otherwise.
BRIEF DESCRIPTION OF THE DRAWINGS
The specific embodiments of the inventive concept will now be described, by way of example, with reference to the accompanying drawings, in which:
Fig. 1 is a flowchart of a method of producing a slip ring brush; and
Fig. 2 is a side view of a slip ring unit comprising a slip ring brush made by the method in Fig. 1.
DETAILED DESCRIPTION
The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplifying embodiments are shown. The inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description.
Fig. 1 depicts a method of producing a slip ring brush.
The method generally comprises producing a composite material, which is shaped or formed as a slip ring brush.
In a step a) copper powder with a grain size of 10-500 pm is mixed with graphene to obtain a copper-graphene mixture.
The grain size of the copper powder may according to some examples be at least 15 pm, such as at least 30 pm, at least 40 pm, at 50 pm, at least 100 pm, at least 200 pm, or at least 300 pm.
The content of graphene in the copper-graphene mixture is in a range of 0.5- graphene in the copper-graphene mixture may for example be in a range of i- 3 wt.% of the total weight of the copper-graphene mixture.
The graphene, which is a 2D material, may be in the form of graphene particles each having a surface area in a range of 100-750 m2/g.
The content of copper in the copper-graphene mixture may be in a range of 90-99 wt.% of the total weight of the copper-graphene mixture, for example in a range >90 wt.%.
Step b) of mixing is preferably a mechanical mixing.
The copper powder and the graphene may be mixed vigorously, for example in a high-speed shaker. According to one example, the shaking speed may be 700 rpm and the mixing time maybe 150 seconds. In tests, a paint shaker model SK35 from Fast & Fluid was used. The mixing time varies depending on the amount of material mixed.
The graphene may for example be graphene nanoplatelets, graphene nanopowder, or graphene flakes.
Step a) may also comprise mixing additives with the copper powder and the graphene. The additives may for example include a stabilizer and a binder. According to one example, the additives consist of the stabilizer and the binder.
The content of the additives may be below 5 wt.% of the total weight of the copper-graphene mixture.
In one example, the copper-graphene mixture obtained in step a) may consist of the copper powder, the graphene, and the additives.
In a step b) the copper-graphene mixture is sintered. The composite material is thus obtained.
The sintering in step b) may be spark plasma sintering. The sintering in step b) maybe carried out at a temperature of 65O-95O°C and under a pressure of 10-iooMPa, such as 10-75 MPa.
The composite material is shaped as a slip ring brush in step b), or it maybe shaped as a slip ring brush after step b). The slip ring brush thus obtained is composed of the composite material obtained according to the method. The composite material may consist of the sintered copper graphene mixture.
Step b) is preferably carried out under an inert atmosphere.
Step b) is preferably the only sintering step performed to obtain the composite material.
Step b) may typically be performed for at most 20 minutes, such as at most 15 minutes, such as at most 10 minutes. Step b) may typically be performed for at least 2 minutes, such as at least 3 minutes. Thus, typically, step b) is performed in the range of 2-20 minutes, for example in the range of 3-15 minutes, or 3-10 minutes. According to one example, step b) is performed for 5 minutes.
The slip ring brush obtained by the method is preferably free of graphite.
Fig. 2 depicts a slip ring unit 1. The slip ring unit 1 is mounted to a shaft 9. The shaft 9 may for example be a rotor shaft of an electrical machine.
The slip ring unit 1 comprises a plurality of slip rings 3 arranged in a support 5. The support is attached to the shaft 9.
The slip ring unit 1 comprises a plurality of slip ring brushes 7 made by means of the method described above.
Each slip ring brush 7 is arranged in mechanical and electrical contact with a respective slip ring 3. The slip ring brushes 7 are pressed radially inwards towards a respective slip ring 3 by means of a force member 11, such as one or more mechanical springs. The force may be higher than 25 kPa, such as 30 kPa or higher than 30 kPa, for example equal to or higher than 35 kPa or equal to or higher than 40 kPa, such as equal to or higher than 45 kPa.
According to some examples, the force maybe equal to or higher than 100 MPa, for example equal to or higher than 250 MPa.
The slip ring brushes 7 are arranged stationarily and the slip rings 3 are rotated concurrently with rotation of the shaft 9.
The inventive concept has mainly been described above with reference to a few examples. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended claims.

Claims

1. Method of producing a slip ring brush (7), comprising: producing a composite material, including: a) mixing copper powder with a grain size of 10-500 pm with graphene to obtain a copper-graphene mixture, the content of graphene in the copper-graphene mixture being in a range of 0.5-5 wt.% of the total weight of the copper-graphene mixture, and b) sintering the copper-graphene mixture; and shaping the composite material as a slip ring brush (7) in step b) or after step b).
2. Method as claimed in claim 1, wherein the sintering is spark plasma sintering.
3. Method as claimed in claim 1 or 2, wherein step b) is performed at a temperature of 65O-95O°C and under a pressure of 10-iooMPa.
4. Method as claimed in any of the preceding claim, wherein step b) is performed under an inert atmosphere.
5 Method as claimed in any of the preceding claims, wherein step b) is performed for at most 20 minutes, such as at most 15 minutes, such as at most 10 minutes.
6. Method as claimed in any of the preceding claims, wherein step b) is performed for at least 2 minutes, such as at least 3 minutes.
7. Method as claimed in any of the preceding claims, wherein the content of graphene in the copper-graphene mixture is in a range of 1-3 wt.% of the total weight of the copper-graphene mixture.
8. Method as claimed in any of the preceding claims, wherein step a) in addition to mixing the copper powder with the graphene, involves mixing additives with the copper powder and the graphene to obtain the copper- graphene mixture.
9. Method as claimed in claim 8, wherein the additives include a stabilizer and a binder.
10. Method as claimed in claim 9, wherein the additives consist of the stabilizer and the binder.
11. Method as claimed in any of claims 8-10, wherein the content of the additives is below 5 wt.% of the total weight of the copper -graphene mixture.
12. Method as claimed in any of claims 8-11, wherein the copper-graphene mixture consists of the copper powder, the graphene, and the additives.
13. Method as claimed in claim 12, wherein the composite material consists of the sintered copper-graphene mixture.
14. Method as claimed in any of the preceding claims, wherein the content of copper in the copper-graphene mixture is in a range of 90-99 wt.% of the total weight of the copper-graphene mixture.
15. Method as claimed in any of the preceding claims, wherein the content of copper in the copper-graphene mixture is above 90 wt.% of the total weight of the copper-graphene mixture.
16. Method as claimed in any of the preceding claims, wherein the graphene is in the form of graphene particles each having a surface area in a range of 100-750 m2/g.
17. Method as claimed in any of the preceding claims, wherein the copper powder has a grain size of at least 15 pm, such as at least 30 pm, at least 50 pm, at least 100 pm, or at least 200 pm.
18. Method as claimed in any of the preceding claims, wherein the mixing in step a) is a mechanical mixing.
19- Method as claimed in any of the preceding claims, wherein step b) is the only sintering step performed for producing the slip ring brush (7).
20. Method as claimed in any of the preceding claims, wherein the graphene is graphene nanoplatelets.
21. Method as claimed in any of the preceding claims, wherein the slip ring brush (7) is free of graphite.
22. Slip ring brush (7) obtainable by means of the method of any of the preceding claims.
EP23833773.7A 2022-12-19 2023-12-18 Method of producing a slip ring brush Pending EP4638038A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP22214418.0A EP4389318A1 (en) 2022-12-19 2022-12-19 Method of producing a composite material for a slip ring brush
PCT/EP2023/086438 WO2024133128A1 (en) 2022-12-19 2023-12-18 Method of producing a slip ring brush

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EP23833773.7A Pending EP4638038A1 (en) 2022-12-19 2023-12-18 Method of producing a slip ring brush

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CN118763472B (en) * 2024-09-02 2024-11-19 佳木斯电机股份有限公司 A carbon brush for a wound motor and a method for preparing the same

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CN106636725A (en) * 2017-01-05 2017-05-10 江苏大学 Copper graphene-based electric contact material and preparation method thereof
CN109004380A (en) * 2018-07-18 2018-12-14 上海电机学院 A kind of EMU axle head grounding device carbon brush material and preparation method thereof
CN109338148B (en) * 2018-11-19 2020-11-06 西安建筑科技大学 Graphene-copper-chromium-zirconium alloy and preparation method thereof
CN112981159B (en) 2021-02-09 2022-03-22 中国科学院电工研究所 Preparation method of graphene reinforced copper-based composite material
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