Specialized metallurgical processes – compositions for use therei – Compositions – Consolidated metal powder compositions
Reexamination Certificate
2002-07-01
2003-10-28
Mai, Ngoclan (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Consolidated metal powder compositions
C075S235000, C075S247000, C428S553000, C200S266000
Reexamination Certificate
active
06638334
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a sliding contact material that is used in a sliding part electrically switching on and off by a mechanical sliding action, particularly to a sliding contact material that is used in a commutator for a small direct-current motor which is used for loading of taking a CD in and out in a CD player or used for sending a pick to move a lens for reading signals of a CD, and further used in a commutator for a small direct-current motor which is used in household electrical appliances that are driven with a rechargeable battery (and others, including an earth ring and a rotary switch).
BACKGROUND ART
Recently, in the technical field mentioned above, studies have been energetically carried out to develop new sliding contact materials. Concerning these sliding contact materials, it may be stated that the most important subject to be developed is to make abrasion ideal when the contact is used and to realize low contact resistance. Originally, realizing the low contact resistance of a sliding contact material can be attained by surely contacting or adhering both materials to be contacted each other, as well as their conductivities. However, when the material slides, the higher the degree of the contact or adhesion of both materials to be contacted is, the larger the frictional resistance becomes, and sliding the materials against the friction produces remarkable abrasion phenomena. That is, in a sliding contact material, it is difficult to obtain more ideal properties unless the above-mentioned phenomena that are contrary to each other are controlled. Further, there are many scientifically unsolved points in the abrasion phenomena of this sliding contact, and it is also stated that controlling the abrasion phenomena by improving a sliding contact material is very difficult.
The abrasion in sliding contact materials is divided broadly into cohesion abrasion and scratch abrasion. Generally, even if the surface of a sliding contact material is finished to be considerably smooth, it is not a complete plane surface from the microstructural point of view and there are many micro uneven parts. When such metal surfaces are made contacted each other, though it seems that they are apparently contacted over the wide range of areas, they are practically in the state that projected sections out of the micro uneven parts existing in the surfaces are contacted, so that the true contact area is smaller than the apparent one. Consequently, high pressure will be applied on this true contact area, i.e., the projected sections that are contacted, to generate the deposition of contacted metals. As a result, cohesion abrasion is produced by which the soft metal is torn off and moved to the hard metal. Further, in the case where materials of different hardness are contacted, or in the case where hard particles are contained in one side even when soft metals are contacted, the soft metal is mechanically sheared by the hard metal to produce scratch abrasion.
Such abrasion phenomena depend heavily on the hardness of each metal material to be contacted, the bonding abilities of those metals and others, and abrasion phenomena of sliding contact materials also become remarkable basically in proportion to the contact pressure, so the abrasion phenomena can be reduced by the hardening of materials. However, abrasion phenomena also greatly change according to the change of temperature and humidity and the existence of any corrosive component, organic vapor, dust and the like when the materials are contacted. And since this change of abrasion phenomena is the change of the contacting states at the contact part, it will cause increasing in contact resistance to affect greatly the stable maintenance of contact resistance.
Abrasion phenomena mentioned above are concretely induced between a commutator and a brush when a cladding composite material using a sliding contact material is built into a small direct-current motor as a commutator and the motor is driven at high speed rotation. That is, the sliding contact material constituting the commutator is subjected to contact friction for a long stretch of time and frictional heat is also added, resulting in inducing cohesion abrasion and scratch abrasion as mentioned above in the combined state. Consequently, the surface of the sliding contact material is shaved by the abrasion phenomena to produce abrasion powder, which powder causes to increase contact resistance, make conduction short by filling up gaps between commutators with the abrasion powder or be attributable to generate noise.
Moreover, if the abrasion phenomena proceed further, in a cladding composite material using a sliding contact material, the metal, i.e., the sliding contact material that is provided on the surface layer of the cladding composite material is broken by abrasion and the abrasion will reach to the base material under the composite material. When such an abrasion state is made, because the base material, which is easily oxidized, is exposed, all sorts of electrical troubles may be caused by the metal oxide of the base material. Accordingly, when a so-called two-layer or three-layer cladding composite material is constituted and used as a commutator, it is an extremely important subject to improve an alloy material composing each layer.
Now, in recent years, as a sliding contact material that is used in a commutator for a small direct-current motor which is used for loading of taking a CD in and out in a CD player or used for sending a pick to move a lens for reading signals of a CD, and a sliding contact material that is further used in a commutator for a small direct-current motor which is used in household electrical appliances that are driven with a rechargeable battery, a two layer cladding composite material in which a Ag—Cd alloy containing 1 to 2 wt. % Cd and the balance of Ag is used in the surface layer, and Cu or a Cu alloy is used in the base layer (e.g., Ag 99-Cd 1/Cu), a two-layer cladding composite material in which a Ag—Cd—Ni alloy containing 1 to 2 wt. % Cd, 0.01 to 0.70 wt. % Ni and the balance of Ag is used in the surface layer, and Cu or a Cu alloy is used in the base layer (e.g., Ag 97.7-Cd 2-Ni 0.3/Cu) and others are used. The “alloy composition/Cu” described in the parentheses mentioned above means a cladding composite material constituting two layers and the “/” means the interface between the surface layer and the base layer. Further, the numerals described after the elements of alloy compositions mean the values in weight percent.
Such Ag—Cd alloy and Ag—Cd—Ni alloy are materials that are very excellent in electrical functions, hardness and low contact resistance properties, and are disclosed in, for example, Japanese Patent Publication No. Hei 2-60745 as a sliding contact material comprising a Ag alloy that contains at least one of Sn and Cd in 1 to 5 wt. % and the balance of Ag for a commutator in a small direct-current motor. However, considering environmental problems in these days, it is not desirable to produce and use sliding contact materials containing Cd that is considered to be a harmful substance.
As other typical alloys, Ag—Cu alloys, Ag—Cu—Cd alloys are also used. However, these sliding contact materials have low contact resistance at the initial stage of their usage, but the contact resistance is subject to secular change. Consequently, they have such a problem that the worth of a product using a rechargeable battery, including a shaver, is inferior. That is, in the case where a sliding contact material of these alloys is used in a motor, because the contact resistance becomes high with the passage of time, the starting voltage of the motor becomes high to lower the electromotive force of the battery, which cause a problem that the motor is not started up. As a result, the frequency of charging the battery is also increased and the battery itself shows a tendency of shortening its life.
Further, for example, in Japanese Patent Application Laid-open No. Sho 58-104140, a sliding contact material of Ag—Zn-based
Hashimoto Yasuhiro
Honma Takemasa
Nakamura Keiji
Sakaguchi Osamu
Taneichi Kengo
Mabuchi Motor Co. Ltd.
Mai Ngoclan
Rothwell Figg Ernst & Manbeck
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