Sliding contact material for motor brush, motor brush, and DC motor

Abstract

The present invention is a sliding contact material for a motor brush which is formed by dispersing a metal boride in a matrix made of pure Ag, wherein the content of the metal boride is 0.3 vol% to 12 vol%, inclusive. Specifically, a boride of Hf, Ta, Nb, Ti, Zr, Mo, Cr, and V is preferable for the metal boride that becomes dispersed particles. The matrix made of pure Ag may contain unavoidable impurity elements having a solid solubility limit with respect to Ag, but the content thereof is preferably 0.5 mass% or less. The sliding contact material according to the present invention is suitable as a constituent material for the motor brush of a small-sized DC motor. The sliding contact material of the present invention is excellent in mechanical abrasion resistance and spark wear resistance, and can be replaced with an Ag-Pd based alloy in terms of cost.

Description

Sliding contact material for motor brush, motor brush and DC motor

[0001] The present invention relates to a sliding contact material suitable for use as a constituent material for motor brushes of small DC motors. In particular, the present invention relates to a sliding contact material that is excellent in both abrasion resistance and spark erosion resistance, is Pd-free, and is also cost-effective, and to a motor brush using the same.

[0002] Small DC motors have been widely used in a variety of fields, including automobiles, various precision instruments, and household electrical appliances. For example, automobiles are equipped with numerous electrical components, such as audio equipment, air conditioning equipment (air conditioner dampers), power folding mirrors, steering lock pins, and door locks, and small DC motors are used to drive these components. Small DC motors are also used as key components in household electrical appliances such as shavers, electric toothbrushes, and small vacuum cleaners.

[0003] DC motors share a common basic structure and configuration, even though their applications vary. A typical DC motor has a casing, a permanent magnet installed inside the casing, and a rotor supported by a shaft in a rotatable state inside the casing. The rotor has an armature and a commutator, and brushes, which act as current collectors, are electrically connected to the commutator. The motor rotates by supplying electricity from an external power source to the rotor via the brushes and commutator. A key factor in ensuring stable operation of such DC motors is the durability of the contact materials that make up the brushes and commutator.

[0004] Brushes are components that work in pairs with the commutator inside a DC motor, and their contact materials must be more durable than the commutator's contact materials. Brushes are components that transmit current from the power supply to the commutator while constantly pressing against it when the motor is running, and are therefore exposed to a more severe environment. The contact material for motor brushes in small DC motors is selected based on the load determined by the correlation between the motor's stall torque and stall current. Specifically, contact materials for motor brushes in small DC motors are selected based on the following required characteristics:

[0005] (i) Brush materials for high-load small DC motors Motor brushes for high-load small DC motors, which have large stall torques and stall currents, are prone to spark discharges and arc discharges when the brushes separate from the commutator due to the large currents that flow through them. Therefore, high-load small DC motors require durability against spark wear in addition to durability against mechanical wear.

[0006] Carbon-based materials, which have a low coefficient of dynamic friction with metals and excellent mechanical wear resistance, are commonly used as contact materials for motor brushes in high-load, small-sized DC motors. Known carbon-based materials include carbon powder mixed with metal powders, such as precious metals and copper, or ceramic powders (see Patent Documents 1 and 2). To compensate for mechanical wear and spark wear, motor brushes for high-load, small-sized DC motors typically use brush materials made of large blocks of carbon-based material on the order of millimeters. Furthermore, motor brushes for high-load, small-sized DC motors typically employ a structure in which the block-shaped brush material is pressed against the commutator by a spring. High-load, small-sized DC motors employing such a structure are used in electrical equipment such as power folding mirrors, steering locks, and door locks in automobiles.

[0007] (ii) Brush materials for low-load small DC motors: Motor brushes for low-load small DC motors, which have relatively small stall torque and stall current, are less susceptible to spark wear due to discharge than high-load small DC motors. Therefore, brush materials for low-load small DC motors are more important to ensure durability against mechanical wear than against spark wear.

[0008] Precious metal materials, particularly Ag—Pd alloys, are used as contact materials for motor brushes in small, low-load DC motors. Examples of Ag—Pd alloys include an Ag-50% by mass Pd alloy and an Ag-30% by mass Pd alloy described in Patent Document 3. Ag—Pd alloys have extremely high durability against mechanical wear and also have excellent resistance to welding.

[0009] In addition, motor brushes for low-load small DC motors use brush materials in which these precious metal materials are bonded to a base material made of a copper material such as beryllium copper or phosphor bronze. Applications of low-load small DC motors employing such a configuration include automotive applications such as HVAC systems (HVAC) for air conditioner dampers and audio equipment. Furthermore, low-load small DC motors are also used in general-purpose motors built into household electrical appliances such as shavers and toys.

[0010] Japanese Patent Application Laid-Open No. 11-4563 Japanese Patent Application Laid-Open No. 2005-176492 Japanese Patent Application Laid-Open No. 5-277762 Japanese Patent Application Laid-Open No. 2023-095274

[0011] The sliding contact materials for motor brushes used in the above-mentioned high-load and low-load small DC motors have been used without any problems until now in their respective applications. However, due to the trend in demand for small DC motors and the need to reduce product costs, a change in the contact materials for both motor brushes of these small DC motors is required.

[0012] Regarding the carbon-based materials used in motor brushes for small, high-load DC motors, the primary reason for the material change is to meet the demand for smaller motors. Carbon-based materials have a small minimum arc current, making them prone to spark and arc discharges during sliding. Until now, carbon-based materials have been used as block-shaped brush materials to compensate for spark wear and mechanical wear caused by discharge, but brush materials on the order of millimeters are difficult to accommodate for miniaturization.

[0013] Furthermore, spark discharges and arc discharges that tend to occur in carbon-based materials can cause noise and rotational noise. In recent years, the automotive industry has tended to avoid noise when motors are running, partly due to an increasing trend toward luxury. Therefore, for sliding contact materials in high-load small DC motors, there is a demand for materials that can replace carbon-based materials, have excellent wear resistance, are less likely to cause spark discharges, and have good spark wear resistance, meaning that they are less likely to be worn out even if spark discharges occur.

[0014] Meanwhile, the recent rise in the price of Pd has led to demands for a change in the material of Ag-Pd alloys, which are used as contact materials for motor brushes in small, low-load DC motors. While the price of Pd was once relatively low among precious metals, it has risen sharply over the past two to three years and is now at or above the price of gold (Au). Some Ag-Pd alloys used for motor brushes contain a high Pd content, reaching as much as 50% by mass, so the price of Pd directly impacts the material cost of motor brushes. For motor brushes used in general-purpose motors for household electrical appliances, rising material costs also impact product costs.

[0015] As described above, Ag—Pd alloys have extremely high resistance to mechanical wear and unparalleled properties as sliding contact materials. However, due to the problem of the sudden rise in Pd prices, there is a demand for Pd-free sliding contact materials that offer an excellent balance between cost and properties, even if they do not exhibit the durability of Ag—Pd alloys.

[0016] Although the need for material changes in both the high-load and low-load small DC motors described above has been recognized, there have been few concrete efforts to address this issue. In particular, the reality is that changing materials has been difficult when the above-mentioned material cost issue is also taken into account.

[0017] To address these issues, the present applicants have disclosed a Pd-free, low-cost contact material that is excellent in both mechanical wear resistance and spark erosion resistance (Patent Document 4). This contact material uses pure Ag as a matrix and ZnO particles and Ta particles as dispersed particles. ２ O ５ The contact material developed by the present applicant and others has excellent spark-wear resistance due to the application of a pure Ag matrix with spark-wear resistance and the selection of appropriate oxide particles. This contact material also has excellent mechanical wear resistance, although not as good as Ag-Pd alloys, and because it is Pd-free, it has an excellent balance of cost and wear resistance.

[0018] However, in the field of sliding contact materials, there is always a demand for improved durability. The contact material developed by the applicants of the present application has an excellent balance between mechanical wear resistance, spark erosion resistance, and material cost, but if the durability can be further improved, it will contribute to reducing the cost and size of small DC motors.

[0019] The present invention has been made in light of the above-mentioned background, and relates to a contact material for motor brushes of small DC motors, and provides a sliding contact material for motor brushes that is useful in both high-load and low-load small DC motors. That is, for high-load small DC motors, the present invention provides a sliding contact material that is excellent in both durability against mechanical wear and spark wear resistance. And for low-load small DC motors, the present invention provides a Pd-free sliding contact material that can replace Ag-Pd alloys and has good wear resistance.

[0020] In the prior art (Patent Document 4) proposed by the present applicant and others, spark erosion resistance is ensured by using a pure Ag matrix. Ag is a metallic material that is less susceptible to electrical discharge than carbon-based materials and Ag alloys and has good spark discharge characteristics under high loads. Therefore, Ag can also overcome the noise generation problem associated with carbon-based materials. For the present inventors, who have identified the essential goal of improving spark erosion resistance as a motor brush contact material, using pure Ag as the matrix is ​​an ideal configuration. Therefore, the present inventors investigated dispersed particles that can exhibit mechanical wear resistance and spark erosion resistance superior to those of the prior art while using a pure Ag matrix. As a result, they discovered that the above-mentioned problems can be solved by using a metal boride, leading to the invention of the present invention.

[0021] That is, the present invention provides a sliding contact material for a motor brush, which comprises a matrix of pure Ag and a metal boride dispersed therein, and is characterized in that the content of the metal boride is 0.3% by volume or more and 12% by volume or less.

[0022] The sliding contact material for motor brushes according to the present invention is composed of a pure Ag matrix and a metal boride, and exhibits both excellent resistance to mechanical wear and resistance to spark erosion. Furthermore, the present invention is a contact material made of a Pd-free precious metal material that does not contain expensive Pd as a constituent metal. Therefore, the present invention is also useful as a sliding contact material for motor brushes that can replace Ag-Pd alloys. The sliding contact material for motor brushes according to the present invention will be described in more detail below.

[0023] (A) Structure and manufacturing method of the sliding contact material according to the present invention (I) Pure Ag matrix The matrix of the sliding contact material for a motor brush according to the present invention is made of pure Ag. When considering spark wear resistance, if the matrix contains metal elements other than Ag, i.e., if the matrix is ​​an Ag alloy, the spark characteristics will deteriorate. Using pure Ag as the matrix is ​​an essential condition for the contact material for a motor brush according to the present invention.

[0024] The matrix is ​​the base material or parent phase in which metal boride particles are dispersed, and a matrix made of pure Ag is a metal that does not contain any elements other than Ag and inevitable impurities, such as Fe, Cr, Pd, Cu, Ni, Mn, Al, Si, Mg, Zn, Sn, In, and Bi. These inevitable impurity elements are mixed in trace amounts into the Ag powder and metal boride powder that are the raw materials for the sliding contact material, or from the constituent materials of the manufacturing equipment (such as a grinder, mixer, and grinding media).

[0025] The aforementioned elements that constitute unavoidable impurities are classified according to whether they have a solid solubility limit in Ag. Examples of unavoidable impurity elements that have a solid solubility limit in Ag include Pd, Cu, Mn, Al, Mg, Zn, Sn, In, and Bi. Elements that have a solid solubility limit in Ag can be alloyed with Ag to form an Ag alloy in the matrix. The Ag alloy matrix can change the melting point and contact resistance of the contact material, potentially reducing spark erosion resistance. Therefore, elements that have a solid solubility limit in Ag are unavoidable impurities that should be particularly limited. Specifically, the total content of these elements in the matrix is ​​preferably 0.5% by mass or less, more preferably 0.3% by mass or less, even more preferably 0.2% by mass or less, and particularly preferably 0.1% by mass or less.

[0026] On the other hand, examples of inevitable impurity elements that do not have a solid solubility limit in Ag include Fe, Cr, Ni, and Si. These elements do not alloy with Ag, but rather form a matrix with pure Ag in the form of atoms or compounds such as oxides. Therefore, these elements are not as restricted as the elements that can dissolve in Ag, and may be included to the extent that they do not interfere with the effects of the metal boride particles that are a feature of the present invention. However, Fe, Cr, and Ni should not be actively included because they may form oxides, increasing contact resistance and promoting wear of the commutator, which is the mating material of the brush. The content of inevitable impurity elements that do not have a solid solubility limit in Ag is preferably 3% by mass or less, more preferably 1% by mass or less, even more preferably 0.5% by mass or less, and particularly preferably 0.3% by mass or less, in terms of metal.

[0027] The content of inevitable impurities in the Ag matrix of the sliding contact material can be easily measured by analytical methods using analytical instruments such as electron probe microanalysis (EPMA), energy dispersive X-ray analysis (EDX), wavelength dispersive X-ray analysis (WDX), and X-ray fluorescence analysis (XRF analysis). The sliding contact material according to the present invention may be bonded to a base material such as a Cu-based material to form a motor brush. When part or all of the contact material can be separated from the base material, the amount of impurities in the Ag matrix can be estimated by performing inductively coupled plasma (ICP) atomic emission spectroscopy on the separated contact material. In this case, the amount of impurities in the Ag matrix can be estimated by measuring the content of each metal component in the contact material and then taking into account the content of dispersed particles.

[0028] (II) Dispersed Particles (Metal Borides) In the sliding contact material for motor brushes according to the present invention, particles made of metal borides are dispersed in the pure Ag matrix. Metal borides are highly hard ceramic materials, and their use as dispersed particles contributes to improving the mechanical wear resistance of the contact material. Metal borides also have a high melting point and relatively high thermal and electrical conductivity. Dispersed particles with high melting points and good electrical conductivity can impart spark wear resistance to the contact material. In this regard, many conventional brush contact materials (e.g., Patent Document 4) use metal oxides as dispersed particles. In contrast, the present invention uses metal borides as dispersed particles, thereby demonstrating durability superior to that of conventional techniques.

[0029] In the present invention, the preferred metal borides to be dispersed particles are metal borides containing Hf, Ta, Nb, Ti, Zr, Mo, Cr, and V (HfB ２ , TaB ２ , NbB ２ , TiB ２ , ZrB ２ , MoB, CrB ２ , V.B. ２ These metal borides have high melting points and high electrical conductivity, and therefore can contribute to improving spark erosion resistance.

[0030] The content of metal boride (dispersed particles) in the sliding contact material according to the present invention is set to 0.3% by volume or more and 12.0% by volume or less. If it is less than 0.3% by volume, the above-mentioned effect cannot be expected, and if it exceeds 12.0% by volume, workability is significantly reduced. Since contact materials for motor brushes are manufactured through multiple plastic working processes, good workability is also important. The content of metal boride is preferably 0.5% by volume or more and 11.0% by volume or less, and more preferably 1.0% by volume or more and 11.0% by volume or less.

[0031] The content of metal borides in sliding contact materials can be measured by the above-mentioned analytical methods using various analytical instruments such as EPMA, etc. The content of metal borides can also be measured by directly analyzing the contact material by ICP emission spectroscopy or the like to measure the content of each metal component and boron.

[0032] The average particle size of the dispersed particles made of metal boride is preferably 1.0 μm or more and 100 μm or less. Dispersed particles with an excessively small average particle size are less effective in improving wear resistance. On the other hand, if the average particle size of the metal boride particles is too large, the dispersion state becomes sparse, and in this case too, they are less likely to contribute to wear resistance. The average particle size of the dispersed particles in the contact material can be measured by observing the metal structure using an SEM or the like, and measuring the particle size of the metal boride in the image using a biaxial method or the like to determine the average value.

[0033] The dispersed particles in the sliding contact material for a motor brush according to the present invention may be metal borides only, and do not need to contain dispersed particles of other compositions. However, other dispersed particles may be included as long as the effects of the present invention provided by the metal borides described above are not impaired. Examples of other dispersed particles include metal oxides, nitrides, and carbides. These other dispersed particles should be restricted in the same manner as the metals (e.g., Fe) that are not solid-soluble with Ag described above.

[0034] The sliding contact material for a motor brush according to the present invention can be produced by powder metallurgy. In the powder metallurgy method, Ag powder as a matrix and metal boride powder (HfB ２ Powder, TaB ２ powder, NbB ２ Powder, TiB ２ powder, ZrB２ powder, MoB powder, CrB ２ powder, VB ２ A contact material can be obtained by sintering a mixed powder of Ag powder and metal boride powder. In this case, the Ag powder preferably has an average particle size of 1.0 μm or more and 15 μm or less, and the metal boride powder preferably has an average particle size of 1.0 μm or more and 100 μm or less. Before sintering, the mixed powder is preferably compressed under pressure to form a billet (compressed body). The billet is manufactured by sintering the mixed powder in a manner similar to that described above. ２ MPa or more 15 x 10 ２ It is preferable to apply pressure at a pressure of 700° C. to 950° C. during sintering. The contact material made of the sintered body obtained by this powder metallurgy method can be processed as appropriate.

[0035] (B) Form of the sliding contact material according to the present invention When the sliding contact material according to the present invention is used as a motor brush, there is no particular limitation on the form. It can be processed into a shape and dimensions that match the specifications of the motor to be installed. However, since the motor brush must maintain contact with the commutator with an appropriate contact pressure, springiness is required. Therefore, it is preferable to use the sliding contact material according to the present invention in the form of a composite material combined with a base material having springiness.

[0036] The base material is preferably a Cu-based material, such as pure Cu, nickel silver, beryllium copper, phosphor bronze, or a Cu-Ni alloy. A composite material for a motor brush can be obtained by joining a sliding contact material to at least a portion of the base material made of a Cu-based material.

[0037] The sliding contact material according to the present invention is less expensive than Ag-Pd alloys, but more expensive than Cu-based materials. Therefore, the use of composite materials also leads to reduced motor brush costs. Furthermore, motor brushes using composite materials can be made more compact by selecting an appropriate base material with spring properties. Conventional high-load, small DC motors using carbon-based materials use brushes that combine a block-shaped carbon-based material with a spring material. However, the present invention allows for a more compact motor.

[0038] There are no particular limitations on the dimensions of the composite material. A tape-, plate-, or chip-shaped sliding contact material is bonded to a portion or the entire surface of a tape- or plate-shaped base material. The sliding contact material and the base material can be bonded by pressure bonding (clad bonding), seam welding, brazing, or other bonding methods. This composite material can then be cut and processed appropriately to form a motor brush.

[0039] The motor brushes to which the contact material according to the present invention is applied can be used in the high-load and low-load small DC motors described above. The configuration of a small DC motor is as described above, and the motor brushes and commutator are essential components. The motor brushes supply power from a power source external to the motor to the commutator.

[0040] For motor brushes to which the sliding contact material according to the present invention is applied, Ag alloys are preferred as the constituent material of the commutator. Examples of Ag alloys include Ag alloys containing one or more of Pd, Cu, Zn, and Ni in a total amount of 1% by mass to 12% by mass. Specific examples include Ag-Cu alloys, Ag-Cu-Ni alloys, and Ag-Pd-Cu-Zn-Ni alloys.

[0041] In addition to the Ag alloy (solid solution alloy), oxide-dispersed Ag alloys are sometimes used as commutator materials. For example, there is an oxide-dispersed Ag alloy in which MgO and ZnO are dispersed in an AgCu alloy matrix. There is also an oxide-dispersed Ag alloy in which an Ag alloy (an Ag alloy containing one or more of Fe, Co, Ni, and Cu) is used as a matrix and Ta is dispersed in the Ag alloy. ２ O ５ There are also dispersed particles and oxide particles of Mg, Fe, Co, Ni, and Zn.

[0042] The composition of the commutator material made of the above-mentioned Ag alloy is applied depending on the specifications of the small DC motor, whether it is a low-load or high-load motor. Regardless of the application, the commutator of the small DC motor only needs to have the above-mentioned commutator material on the surface that comes into contact with the motor brush. Therefore, the commutator can also be made of a composite material in which the contact material is clad on a base material. The base material in this case can be the same Cu-based material as the composite material for the motor brush.

[0043] The sliding contact material of the present invention has high wear resistance and spark consumption resistance, so that it can be used in motor brushes that are subjected to severe operating environments with respect to mechanical wear, discharge, and spark generation. Furthermore, these properties can be achieved without using Pd as a constituent metal. The present invention, which offers improvements in both performance and cost, is expected to serve as a contact material to replace the carbon-based materials that have been used in motor brushes for small, high-load DC motors. The contact material of the present invention also exhibits durability and noise reduction effects.

[0044] Furthermore, the sliding contact material of the present invention can also be used for brush applications in small, low-load DC motors. Ag-Pd alloys have traditionally been used as motor brush materials in these DC motors, but the present invention is useful as a replacement material. Because the contact material of the present invention does not use Pd, it is possible to provide general-purpose motors and the like at low cost, given the recent trend toward rising Pd prices.

[0045] The contact material (Ag-7% by volume HfB ２ Measurement results of the initial and after-use starting voltage of a DC motor equipped with HfB ２ Photographs showing the results of observing the material structure of contact materials with different content.

[0046] First Embodiment: A preferred embodiment of the present invention will be described based on the following examples. In this embodiment, a pure Ag matrix is ​​mixed with 7% by volume of HfB. ２ The composite was then processed into a motor brush and incorporated into a small DC motor to evaluate its wear resistance and spark wear resistance.

[0047] [Production of Sliding Contact Material] In this embodiment, the sliding contact material was produced by powder metallurgy. Pure Ag powder (average particle size 7 μm, Ag concentration 99.95 mass %) was mixed with 7 volume % HfB ２ The powder mixture was packed into a cylindrical container and subjected to a pressure of 5×10 from the longitudinal direction. ２ The mixture was compressed by applying a pressure of 0.1 MPa to form a cylindrical billet with a diameter of 50 mm. This cylindrical billet was then heated in a vacuum at 850°C for 8 hours for sintering. This compression and sintering process was repeated three times to produce a sliding contact material. This sliding contact material was hot extruded to form a rough wire with a diameter of 6 mm, and then repeatedly drawn and annealed to form a wire with a diameter of 1 mm. This wire was then rolled in a rolling mill to obtain a tape-shaped sliding contact material.

[0048] [Manufacturing of a composite material for a motor brush] Next, the above-mentioned tape-shaped sliding contact material and a base material were clad-bonded (inlay-bonded) using a rolling mill to form a composite material. The base material was a copper alloy (C1741) for springs. This composite material, which will become a motor brush, had a sliding contact material thickness of 40 μm and a total thickness including the base material of 75 μm.

[0049] [Reference Example] A sliding contact material (Ag-7% by volume HfB ２To confirm the durability of the Ag-Pd alloy, a composite was manufactured using an Ag-50% by mass Pd alloy as a sliding contact material. The Ag-Pd alloy was used as a reference example to serve as the evaluation standard for the contact material of this embodiment because, as mentioned above, the Ag-Pd alloy has extremely good abrasion resistance. Furthermore, since the Ag-Pd alloy is a precious metal-based contact material with excellent spark erosion resistance, taking into account high-load use, it can also serve as a reference for evaluating spark erosion resistance. However, in this application, the thickness of the sliding contact material (Ag-50% by mass Pd alloy) for the motor brush in this reference example was set to 10 μm. This was done in consideration of the fact that one of the main issues to be addressed by this invention is to improve material costs and the rising price of Pd. In this embodiment, the material cost of the motor brush is set to the same level, and then durability is evaluated and the possibility of substitution is considered.

[0050] [Fabrication of a Small DC Motor and Durability Evaluation Test] The composite materials manufactured in the present embodiment and the reference example were processed into motor brushes, which were then assembled into actual small DC motors together with commutators to conduct durability evaluation tests of the sliding contact materials. Durability tests were conducted in three patterns: (a) a wear resistance life test to evaluate durability mainly against mechanical wear, (b) a wear resistance life test to evaluate durability mainly against spark wear, and (c) a storage test to evaluate startability after storage at high temperatures. The commutators of the small DC motors used in each evaluation test used contact materials appropriate for the test conditions. The commutators were manufactured from composites in which each contact material was clad on a base material made of a copper-based material.

[0051] (A) Abrasion Resistance Life Test (Mechanical Abrasion Resistance Evaluation) Evaluation was performed under the following two test conditions, A-1 and A-2. These test conditions simulate a low-load small DC motor used in a vehicle air conditioning system (HVAC), and as described above, are intended to evaluate durability against mechanical abrasion. In these durability tests, an operating mode combining counterclockwise rotation (CCW) and stop (OFF) with clockwise rotation (CW) and stop (OFF) was defined as one cycle, and the number of cycles until the motor stopped was evaluated. At this time, a target value of twice the standard value was set, and those that met this were judged as excellent (◎). Furthermore, those that were less than the target value but equal to or greater than the standard value were judged as good (◯). Those judged as excellent and good were judged to have passed.

[0052]

[0053] (B) Wear resistance life test (evaluation of spark wear resistance) Evaluation was carried out under the following two test conditions, B-1 and B-2. These test conditions simulate a high-load small DC motor used in an automobile's power folding mirror, and as described above, are intended to evaluate durability against spark wear.

[0054]

[0055] (C) Standing test (starting performance evaluation) The standing test for starting performance evaluation was carried out using the DC small motor (commutator: AgCuNi-Ta) used in test condition A-2. ２ O ５ The test was carried out on a DC small motor (+ZnO). The DC small motor was left at 85°C (without humidity control) and 85°C (with 95% RH) for a predetermined time (without humidity control: 500 hours, 95% humidity: 250 hours). After the specified time, the motor was driven and the starting voltage was measured. The starting voltage after leaving was compared with the starting voltage before leaving, and a starting voltage of DC 3.5V was used as the pass value for a pass / fail judgment.

[0056] Tables 3 and 4 show the results of the evaluation tests (A), (B), and (C) performed in this embodiment.

[0057]

[0058]

[0059] Regarding Table 3, the evaluation of the wear life, which is the test (A), shows that the contact material of this embodiment (Ag-7% by volume HfB ２ ) shows durability that clearly exceeds the target value under all temperature conditions. In addition, compared with the contact material of the reference example (Ag-50 mass % Pd alloy), the contact material of this embodiment is inferior at the low temperature (-40°C) of test condition A-1, but has higher durability than the reference example at other temperatures. In addition, looking at the evaluation of spark consumption life, which is test (B), the contact material of this embodiment (Ag-7 volume % HfB ２ ) showed durability that clearly exceeded the target value even under these test conditions. In addition, in comparison with the contact material of the reference example (Ag-50 mass % Pd alloy), the contact material of this embodiment (Ag-7 volume % HfB ２ ) showed comparable spark consumption resistance.

[0060] In the evaluation test (C) on starting performance in Table 4, the contact material of this embodiment (Ag-7% by volume HfB ２ ) cleared the pass criteria along with the contact material of the reference example (Ag-50 mass % Pd alloy). ２ ) and after being held at a predetermined time. The contact material of this embodiment shows no change in starting voltage even after being left at a high temperature, and can be said to have good starting properties.

[0061] From the results of the above evaluation tests, the Ag-HfB ２ It has been confirmed that the contact material exhibits suitable durability in both applications where mechanical wear is a major concern and applications where spark wear is a major concern. ２ It was also confirmed that the contact material could be replaced with an Ag--Pd alloy contact material.

[0062] Second embodiment: In this embodiment, HfB dispersed in an Ag matrix ２Motor brush materials were manufactured with different contents of Hf. In addition, motor brush materials were manufactured in which metal borides of metals other than Hf (Ta, Nb, Ti, Zr, Mo, Cr, V) were dispersed in an Ag matrix. Furthermore, for comparison with each example, Hf oxide / carbide (HfO ２ Motor brush materials containing dispersed particles of HfC and tungsten carbide (WC) were also produced. These motor brush materials were then evaluated for durability.

[0063] The manufacturing method of the contact material in this embodiment is basically the same as that of the first embodiment. A powder mixture of pure Ag powder and powders of metal boride and metal oxide that constitute the dispersed particles was compressed to produce a cylindrical billet, which was then sintered in a vacuum at 850°C. The obtained sliding contact material was then hot extruded and wiredrawn to form a wire, which was then made into a tape-shaped sliding contact material. As in the first embodiment, this was clad with a copper alloy material that served as the base material and incorporated into a small DC motor as a motor brush.

[0064] The evaluation test for this embodiment was conducted under the same test conditions as those A-1 in the first embodiment (Table 1), and the wear resistance at room temperature was evaluated. The evaluation results are shown in Table 5.

[0065]

[0066] When the evaluation results of this embodiment are examined, first, when the metal boride is HfB ２ Regarding the content of HfB, good durability was demonstrated in the range of 0.3% by volume to 11% by volume evaluated this time (No. 1 to No. 8). ２ We also attempted to manufacture a contact material containing 13% by volume of metal boride, but fracture occurred during the wire processing stage, so we confirmed that from the perspective of processability, the metal boride content should be limited to an upper limit of 12% by volume.

[0067] HfB produced in this embodiment ２The results of observing the material structure of the contact material containing dispersed particles are shown in Figure 2. The material structure in Figure 2 is the result of observing the cross section of the wire after processing. Figure 2 also shows the measurement results of the hardness value of each contact material. From Figure 2, it can be seen that the hardness of HfB ２ It was confirmed that the hardness of the contact material increased with the increase in the content of HfB. ２ As the content increases, the dispersed particles tend to aggregate.

[0068] In this embodiment, the dispersed particles are made of a metal boride other than Hf (TaB ２ , NbB ２ , TiB ２ , ZrB ２ , MoB, CrB ２ , V.B. ２ Contact materials containing 3.6% to 9.1% by volume of TaB (No. 9 to No. 16) were investigated. Table 5 shows that the contact materials containing these metal borides as dispersed particles also exceeded the standard values ​​and showed higher durability than the prior art (No. 20). ２ , NbB ２ , TiB ２ , V.B. ２ Since contact materials containing dispersed particles of Hf, Ta, Nb, Ti, and V exhibited excellent durability exceeding the target value (twice the standard value), borides of Hf, Ta, Nb, Ti, and V are considered to be particularly preferable dispersed particles.

[0069] In this embodiment, the dispersed particles are HfB ２ We are currently investigating contact materials, such as HfB ２ It was confirmed that all contact materials with an appropriate content of Hf exhibited good durability. From these results, it was confirmed that Hf is useful as a metal component of dispersed particles, but that Hf compounds are not always effective. ２ ) and carbide (HfC) dispersed contact materials are ２ ) are both less durable than the other (Nos. 17 and 18).

[0070] It should be noted that tungsten carbide (WC), which is generally known as a hard particle, also has little effect on improving durability (No. 19). In addition, in this embodiment, the contact material (Ag / TaO ２ +ZnO) was also evaluated (No. 20). Referring to this result, it can be seen that the contact material according to the present invention, in which metal borides are dispersed in an Ag matrix, has higher durability than the prior art. The prior art contact material (No. 20) falls below the target value, which is twice the standard value, but since it satisfies the standard value, its usability is not denied. However, it can be said that the contact material according to the present invention is a contact material with better durability than the prior art.

[0071] The present invention has suitable wear resistance and spark consumption resistance as a sliding contact material for brushes in small DC motors. Furthermore, the contact material of the present invention exhibits durability and noise reduction effects. The present invention is suitable for use in small DC motors in various fields, including automobiles, various precision instruments, and household electrical appliances. Examples of automotive applications include small DC motors in electrical equipment such as audio equipment, air conditioner dampers, power retractable mirrors, and door locks. Furthermore, the present invention is suitable for use in small motors in household electrical appliances such as shavers, electric toothbrushes, and small vacuum cleaners.

Claims

1. A sliding contact material for motor brushes, comprising a matrix of pure Ag with metal boride dispersed therein, characterized in that the content of the metal boride is 0.3% by volume or more and 12% by volume or less.

2. The sliding contact material for motor brushes according to claim 1, wherein the metal boride is a boride of Hf, Ta, Nb, Ti, Zr, Mo, Cr, or V.

3. A sliding contact material for motor brushes according to claim 1 or claim 2, wherein the matrix made of pure Ag contains Ag and unavoidable impurity elements that have a solid solubility limit in Ag, and the content of said unavoidable impurity elements is 0.5 mass% or less.

4. A composite material for a motor brush, comprising a base material made of a Cu-based material and a sliding contact material bonded to at least a portion of the base material, wherein the sliding contact material is the sliding contact material described in claim 1 or claim 2.

5. A motor brush for a DC motor comprising the composite material of claim 4.

6. A DC motor having motor brushes and a commutator, the motor having the motor brushes according to claim 5.

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