Sliding contact material and method for producing same

Abstract

A sliding contact material that is used for a constituent material, particularly a brush, of a motor. The sliding contact material includes: Pd in an amount of 20.0% by mass or more and 50.0% by mass or less; Ni and/or Co in an amount of 0.6% by mass or more and 3.0% by mass or less in terms of a total concentration; and Ag and inevitable impurities as a balance. Preferably, the sliding contact material further contains an additive element M including at least one of Sn and In, and the total concentration of the additive element M is 0.1% by mass or more and 3.0% by mass or less. When containing the additive element M, the sliding contact material has material structures in which composite dispersed particles containing an intermetallic compound of Pd and the additive element M are dispersed in an Ag alloy matrix, and the ratio (K.sub.Pd/K.sub.M) of the content (% by mass) of Pd and the content (% by mass) of the additive element M in the composite dispersed particles is within a range of 2.4 or more and 3.6 or less.

Claims

1. A sliding contact material consisting of: Pd in an amount of 20.0% by mass or more and 50.0% by mass or less; Ni in an amount of 0.6% by mass or more and 3.0% by mass or less in terms of a total concentration; an additive element M in an amount of 0.1% by mass or more and 3.0% by mass or less; wherein the additive element M is Sn and/or In; and Ag and inevitable impurities as a balance; wherein the sliding contact material has material structures in which composite dispersed particles containing an intermetallic compound of Pd and the additive element M are dispersed in an Ag alloy matrix, and the ratio (K.sub.Pd/K.sub.M) of the content (% by mass) of Pd and the content (% by mass) of the additive element M in the composite dispersed particles is within a range of 2.4 or more and 3.6 or less.

2. The sliding contact material according to claim 1, wherein the average particle size of the composite dispersed particles is 1.0 μm or less.

3. The sliding contact material according to claim 2, wherein the sliding contact material contains at least Sn as the additive element M, and the content of Sn is 0.5% by mass or more and 1.0% by mass or less.

4. The sliding contact material according to claim 2, wherein the sliding contact material contains at least In as the additive element M, and the content of In is 1.0% by mass or more and 2.0% by mass or less.

5. The sliding contact material according to claim 2, wherein the sliding contact material contains both Sn and In as the additive element M, and the total content of Sn and In is 0.5% by mass or more and 3.0% by mass or less.

6. The sliding contact material according to claim 1, wherein the sliding contact material contains at least Sn as the additive element M, and the content of Sn is 0.5% by mass or more and 1.0% by mass or less.

7. The sliding contact material according to claim 6, wherein the sliding contact material contains at least In as the additive element M, and the content of In is 1.0% by mass or more and 2.0% by mass or less.

8. The sliding contact material according to claim 1, wherein the sliding contact material contains at least In as the additive element M, and the content of In is 1.0% by mass or more and 2.0% by mass or less.

9. The sliding contact material according to claim 1, wherein the sliding contact material contains both Sn and In as the additive element M, and the total content of Sn and In is 0.5% by mass or more and 3.0% by mass or less.

10. A motor in which the sliding contact material defined in claim 1 is applied to a brush.

11. A motor in which the sliding contact material defined in claim 2 is applied to a brush.

12. A motor in which the sliding contact material defined in claim 6 is applied to a brush.

13. A motor in which the sliding contact material defined in claim 8 is applied to a brush.

14. A method for producing the sliding contact material defined in claim 1, comprising a melting and casting step, the melting and casting step being a step of cooling a molten Ag alloy having a casting temperature, the molten Ag alloy consisting of Pd in an amount of 20.0% by mass or more and 50.0% by mass or less, Ni in an amount of 0.6% by mass or more and 3.0% by mass or less in terms of a total concentration, additive element M in an amount of 0.1% by mass or more and 3.0% by mass or less, and Ag and inevitable impurities as a balance, the casting temperature being set to a temperature higher by 100° C. or more than a liquidus temperature of an AgPd binary alloy having a Pd concentration equal to the Pd concentration of the Ag alloy, the molten Ag alloy being cooled at a cooling rate of 100° C./min or more.

15. A method for producing the sliding contact material defined in claim 2, comprising a melting and casting step, the melting and casting step being a step of cooling a molten Ag alloy having a casting temperature, the molten Ag alloy consisting of Pd in an amount of 20.0% by mass or more and 50.0% by mass or less, Ni in an amount of 0.6% by mass or more and 3.0% by mass or less in terms of a total concentration, additive element M in an amount of 0.1% by mass or more and 3.0% by mass or less, and Ag and inevitable impurities as a balance, the casting temperature being set to a temperature higher by 100° C. or more than a liquidus temperature of an AgPd binary alloy having a Pd concentration equal to the Pd concentration of the Ag alloy, the molten Ag alloy being cooled at a cooling rate of 100° C./min or more.

16. A method for producing the sliding contact material defined in claim 6, comprising a melting and casting step, the melting and casting step being a step of cooling a molten Ag alloy having a casting temperature, the molten Ag alloy consisting of Pd in an amount of 20.0% by mass or more and 50.0% by mass or less, Ni in an amount of 0.6% by mass or more and 3.0% by mass or less in terms of a total concentration, additive element M in an amount of 0.1% by mass or more and 3.0% by mass or less, and Ag and inevitable impurities as a balance, the casting temperature being set to a temperature higher by 100° C. or more than a liquidus temperature of an AgPd binary alloy having a Pd concentration equal to the Pd concentration of the Ag alloy, the molten Ag alloy being cooled at a cooling rate of 100° C./min or more.

17. A method for producing the sliding contact material defined in claim 8, comprising a melting and casting step, the melting and casting step being a step of cooling a molten Ag alloy having a casting temperature, the molten Ag alloy consisting of Pd in an amount of 20.0% by mass or more and 50.0% by mass or less, Ni in an amount of 0.6% by mass or more and 3.0% by mass or less in terms of a total concentration, additive element M in an amount of 0.1% by mass or more and 3.0% by mass or less, and Ag and inevitable impurities as a balance, the casting temperature being set to a temperature higher by 100° C. or more than a liquidus temperature of an AgPd binary alloy having a Pd concentration equal to the Pd concentration of the Ag alloy, the molten Ag alloy being cooled at a cooling rate of 100° C./min or more.

18. A method for producing the sliding contact material defined in claim 9, comprising a melting and casting step, the melting and casting step being a step of cooling a molten Ag alloy having a casting temperature, the molten Ag alloy consisting of Pd in an amount of 20.0% by mass or more and 50.0% by mass or less, Ni in an amount of 0.6% by mass or more and 3.0% by mass or less in terms of a total concentration, additive element M in an amount of 0.1% by mass or more and 3.0% by mass or less, and Ag and inevitable impurities as a balance, the casting temperature being set to a temperature higher by 100° C. or more than a liquidus temperature of an AgPd binary alloy having a Pd concentration equal to the Pd concentration of the Ag alloy, the molten Ag alloy being cooled at a cooling rate of 100° C./min or more.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a Pd—Sn system state diagram for illustrating an intermetallic compound that is generated in the present invention.

(2) FIG. 2 is a state diagram of an Ag—Pd binary alloy.

(3) FIG. 3 illustrates a test method for a sliding test conducted in a first embodiment.

(4) FIG. 4 shows results of structure observation by a SEM for a contact material produced in a second embodiment.

(5) FIG. 5 shows an enlarged picture illustrating analysis points in sample B2 (1% of Ni+1% of Sn), and EDX analysis results in the second embodiment.

(6) FIG. 6 shows an enlarged picture illustrating analysis points in sample B5 (1% of Ni+2% of In), and EDX analysis results in the second embodiment.

(7) FIG. 7 illustrates a configuration of a micromotor.

(8) FIG. 8 illustrates a structure of a coreless motor.

DESCRIPTION OF EMBODIMENTS

(9) First embodiment: Hereinafter, an embodiment of the present invention will be described. In this embodiment, a sliding contact material including an AgPd (Ni, Co) alloy was produced, and the properties of the sliding contact material were evaluated.

(10) For production of a test material, high-purity raw materials of metal elements were mixed so as to have a predetermined composition, the mixture was melted at a high frequency to obtain a molten Ag alloy, and the molten Ag alloy was cast at 1300° C., and then rapidly cooled to produce an alloy ingot. The cooling rate was 100° C./min. After casting of the alloy, the alloy was rolled, annealed at 600° C., then rolled again, and cut to obtain a test piece (with a length of 45 mm, a width of 4 mm and a thickness of 1 mm).

(11) In this embodiment, sliding contact materials of various kinds of compositions were produced through the above-mentioned steps for test materials A1 to A5 in Table 1 below. In addition, for comparison with the conventional art, an AgPd alloy free from Ni and Co was produced (A6).

(12) Next, a sliding test for evaluation of wear resistance was conducted for each test piece. FIG. 3 schematically illustrates a sliding test method, and in this test, the test piece was processed into a movable contact assuming each test material brush, and the movable contact was slid on a fixed contact assuming a commutator. Here, the movable contact was slid by 50000 cycles (total sliding length: 1 km) with one cycle including moving the movable contact forward by 5 mm and backward by 5 mm from the starting point (over a distance of 10 mm) (total 20 mm) while a load of 40 g was applied with the movable contact constantly fed with electricity at 12 V and 100 mA. After this test, the wear depth (pmt) of a sliding portion of the movable contact was measured.

(13) In this sliding test, two kinds of materials for fixed contacts were used. The two kinds of fixed contact materials used include an AgCuNi alloy (92.5% by mass of Ag/6% by mass of Cu/1% by mass of Zn/0.5% by mass of Ni: hereinafter, referred to as “AgCuNi-1”) which is a conventional contact material for brushes; and an alloy with a rare earth metal (Sm) added to an AgCuNi-based alloy (89.6% by mass of Ag/8% by mass of Cu/1% by mass of Zn/1% by mass of Ni/0.4% by mass of Sm: hereinafter, referred to as “AgCuNi-2”) which is an improved contact material for brushes.

(14) In evaluation in the sliding test, the measured values of wear depth of the AgPd alloy (A6) free from Ni and Co in the conventional art, with respect to two kinds of partner materials (AgCuNi-1 and AgCuNi-2) were set to references, and wear amounts equal to about 75% of these measured values (wear depth with respect to AgCuNi-1: 2500 μm.sup.2 and wear depth with respect to AgCuNi-2: 3500 μm.sup.2) were set to standard values. For each test material, it was determined that the test material was “acceptable” when the wear amount was smaller than the standard value. Results of wear tests for test materials produced in this embodiment are shown in Table 1.

(15) TABLE-US-00001 TABLE 1 Composition (% by mass) Additive Wear area (μm2) element M Partner material No. Ag Pd Ni Co Sn In Sn + In AgCuNi-1 AgCuNi-2 Evaluation*.sup.1 Remarks A1 Balance 30 1.0 — — — — 1395 3954 ∘ A2 2.0 1944 4070 ∘ A3 4.0 2834 4851 x Excessive amount of Ni A4 — 1.0 2396 4036 ∘ A5 1.0 1.0 2232 4010 ∘ A6 — — — — — 3188 5052 x Conventional art *.sup.1⊙ . . . Acceptable for both of two kinds of partner materials ∘ . . . Acceptable for one of two kinds of partner materials x . . . Unacceptable for both of two kinds of partner materials

(16) First, it is confirmed from table 1 that wear resistance can be improved by adding Ni and/or Co to the AgPd alloy (sample A6) which is a conventional sliding contact material for brushes. However, it is apparent that when Ni is added in an excessively amount of 4%, the effect is reduced with the wear area being close to that when Ni is not added (sample A3).

(17) Second embodiment: In this embodiment, various kinds of sliding contact materials each including an Ag alloy with Sn and In further added to an AgPd (Ni, Co) alloy were produced, and the properties of the sliding contact materials were evaluated.

(18) Test materials were produced basically in the same manner as in the first embodiment. High-purity raw materials of metal elements were mixed to obtain a molten Ag alloy, the molten Ag alloy was heated to a temperature higher by 100° C. or more than the liquidus temperature in the AgPd binary state diagram while the molten metal temperature was measured, and the molten Ag alloy was then rapidly cooled to produce an alloy ingot. The casting temperature is 1350° C. for the alloy with 30% by mass of Pd, and 1450° C. for the alloy with 40% by mass of Pd. The cooling rate was 100° C./min for both the alloys. After casting of the alloy, the alloy was rolled, annealed, and rolled again to obtain a test piece having the same size as in the first embodiment (with a length of 45 mm, a width of 4 mm and a thickness of 1 mm).

(19) In this embodiment, sliding contact materials of various kinds of compositions were produced through the above-mentioned production steps for test pieces B1 to B12 in Table 2 below. Further, in this embodiment, influences of alloy production conditions are examined. Here, an alloy (B13) obtained by setting the casting temperature to a temperature (1250° C.) higher by about 50° C. than the liquidus temperature in the AgPd binary state diagram, and rapidly decreasing the temperature from the casting temperature, and an alloy (B14) obtained by setting the molten metal temperature to a temperature (1350° C.) higher by 100° C. than the liquidus temperature in the AgPd binary state diagram, and decreasing the cooling rate to less than 100° C./min in slow cooling (furnace cooling) were also produced.

(20) In this embodiment, structure observation was first performed with a SEM to examine whether composite dispersed particles were precipitated for each prepared test material. 20 composite dispersed particles were randomly selected, the dispersed particles were qualitatively analyzed by EDX to measure the Pd content and the M content in the dispersed particles, and the ratio of the contents of these elements (K.sub.Pd/K.sub.M) was calculated. In addition, the average particle size of the dispersed particles was measured. For the average particle size, the major diameter (L1) and the minor diameter (L2) of a particle was measured on the basis of a SEM image of the dispersed particle at a high magnification (20000 times), the arithmetic average ((L1+L2)/2) of these diameters was calculated, and this value was defined as the particle size D of the dispersed particle. The particle sizes (Dn (n=1 to 20)) of the 20 dispersed particles were measured, and the average value of these particle sizes was defined as the average particle size of dispersed particles.

(21) FIG. 4 shows some of results of structure observation performed for the test pieces. In these material structures, matrixes and dispersed particles were more minutely analyzed. FIG. 5 shows an enlarged picture illustrating analysis points (three points) in sample B2 (containing 1% of Ni+1% of Sn), and analysis results. In addition, FIG. 6 shows an enlarged picture illustrating analysis points (three points) in sample B5 (containing 1% of Ni+2% of In), and analysis results. In this embodiment, structure observation and measurement of the composition and the average particle size of dispersed particles were performed for each test piece. In this embodiment, the ratio K.sub.Pd/K.sub.M was confirmed to fall within an appropriate range for all of measured composite dispersed particles in alloys of samples B1 to B8 and B10 to B12 in examples. In this embodiment, the average value of these ratios is calculated (Table 2).

(22) On the other hand, in test materials (B13 and B14) which were not appropriate to conditions for the casting step, there were dispersed particles containing Pd and the additive element M, but there were not dispersed particles in which the value of K.sub.Pd/K.sub.M fell within an appropriate range, and composite dispersed particles did not exist.

(23) Next, a sliding test for evaluation of wear resistance was conducted for each test piece. Test conditions for the sliding test were the same as in the first embodiment. In addition, here values of wear depth with respect to two kinds of partner materials (AgCuNi-1 and AgCuNi-2) were measured. For the sliding contact materials produced in this embodiment, results of structure observation and results of the sliding test are shown in Table 2.

(24) TABLE-US-00002 TABLE 2 Composite dispersed Composition (% by mass) particles Additive Average Wear area (μm2) element M K.sub.Pd/ particle Partner material No. Ag Pd Ni Co Sn In Sn + IN K.sub.M size AgCuNi-1 AgCnNi-2 Evaluation*.sup.1 Remarks B1 Balance 30 1.0 — 0.5 — 0.5 3.52 0.5 μm 1216 3358 ⊙ B2 1.0 1.0 3.54 0.8 μm 1208 2908 ⊙ B3 2.0 2.0 3.37 1.3 μm 2654 3099 ∘ Dispersed particles coarsened (with a larger amount of Sn) B4 1.0 — — 1.0 1.0 3.22 0.6 μm 1302 2758 ⊙ B5 2.0 2.0 3.28 0.9 μm 1926 3496 ⊙ B6 3.0 3.0 3.15 1.7 μm 2772 3446 ∘ Dispersed particles coarsened (with a larger amount of In) B7 1.0 — 0.5 1.0 1.5 3.58 0.7 μm 1564 2413 ⊙ B8 1.0 2.0 3.0 2.83 0.8 μm 2315 3215 ⊙ B9 2.0 2.0 4.0 — 2.4 μm*.sup.2 2722 3932 x Dispersed particles coarsened B10 — 2.0 1.0 — 1.0 3.42 0.9 μm 1698 2857 ⊙ B11 1.0 — 2.0 2.0 3.12 0.9 μm 2012 2952 ⊙ B12 40 1.0 — 1.0 1.0 2.0 3.55 0.8 μm 1148 2269 ⊙ B13 30 1.0 — 1.0 — 1.0 — 3.4 μm*.sup.2 6291 6840 x Casting temperature low B14 1.0 1.0 1.0 — 5.2 μm*.sup.2 3890 4645 x Cooling rate low A6 — — — — — — — 3188 5052 x Conventional art *.sup.1⊙ . . . Acceptable for both of two kinds of partner materials ∘ . . . Acceptable for one of two kinds of partner materials x . . . Unacceptable for both of two kinds of partner materials *.sup.2The composition of dispersed particles is out of range, but the value of particle size is described for reference.

(25) It is apparent that by adding Sn and/or In to an AgPd (Ni, Co) alloy, an effect of further improving wear resistance is exhibited. The effect of improving wear resistance is remarkable particularly when AgCuNi-2, i.e. an improved material having high wear resistance, is applied as a partner material (commutator). Preferably, the concentration of Sn is 0.5% or more and 1.0% or less (B1 and B2), and the concentration of In is 1.0% by mass or more and 2.0% by mass or less (B4 and B5) as a composition that ensures excellent wear resistance in general. In the alloys having values above the appropriate value, dispersed particles were coarsened, and the wear area with respect to AgCuNi-1 exceeded the standard value. In addition, in the test material B9 which is an alloy containing Sn and In in a total amount of more than 3% by mass, there were dispersed particles containing Pd and the additive element M, but the value of K.sub.Pd/K.sub.M did not fall within an appropriate range. For the test material, only the particle size of dispersed particles was measured for reference. The particles had a large particle size, and wear resistance was insufficient.

(26) As in the case of B13 and B14, suitable composite dispersed particles were not generated when casting conditions were not appropriate in alloy production. In the test material, the wear resistance improving effect was not exhibited even though Sn and In were added, and an alloy inferior in wear resistance to the AgPd alloy was produced. It was confirmed that for the material according to the present invention, not only composition control should be performed, but also material structures should be made suitable by securing appropriate casting conditions.

(27) In addition, when consideration is also given to the results for AgPd (Ni, Co) alloys (A1 to A5) free from Sn and In in the first embodiment, the wear resistance improving effect of these alloys is not so high when the partner material is the AgCuNi alloy 2, but these alloys may be considerably effective for the AgCuNi alloy 1. Therefore, preferably, when applied to a brush, the sliding contact material according to the present invention is selected in consideration of the constituent material of a commutator as a partner material. When a commutator is formed from a conventional material such as the AgCuNi alloy 1, a contact structure with an AgPd (Ni, Co) alloy as a brush. Of course, for a material with Sn and In added to an AgPdNi alloy, it is not necessary that the material of a partner material be particularly limited.

INDUSTRIAL APPLICABILITY

(28) As described above, the sliding contact material according to the present invention has higher wear resistance in comparison with a conventional Ag-based sliding contact material. The present invention is particularly useful as a sliding contact material for brushes of small motors, such as micromotors and coreless motors, which have a reduced size and increased rotation speed.