Specialized metallurgical processes – compositions for use therei – Compositions – Consolidated metal powder compositions
Reexamination Certificate
2003-03-25
2004-07-06
Mai, Ngoclan T. (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Consolidated metal powder compositions
C075S247000, C252S503000, C310S249000, C310S252000
Reexamination Certificate
active
06758881
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to metal-graphite brushes containing a metal sulfide solid lubricant, which are used in automobile motors, etc., and in particular, relates to make the metal-graphite brushes substantially free of Pb.
PRIOR ART
Metal-graphite brushes have been used as brushes for low-voltage operation, such as brushes for automobile motors. Metal-graphite brushes are produced by mixing graphite and metal powder such as Cu powder, molding, and sintering the mixture. As they are operated at low voltages, their resistivities are lowered by compounding metal powder of which resistance is lower than that of graphite. A metal sulfide solid lubricant such as molybdenum disulfide or tungsten disulfide and Pb are added to metal-graphite brushes for heavy loads in most of the cases.
In recent years, Pb has been attracting greater attention as one of materials damaging to the environment, and a demand for Pb-less brushes is grown. Of course, brushes containing no Pb have been available up to the present and they have been used in some motors other than starting motors. Even some brushes for starting motors may be used by simply eliminating Pb from them, provided that they are used under normal service environments. To improve the lubricating properties without Pb, Japanese Patent Opening Hei 5-226048 (U.S. Pat. No. 5,270,504) proposes that a metal having a melting point lower than that of Cu is mixed in such a way that Cu and the metal do not form an alloy.
The inventors found that in metal-graphite brushes wherein a metal sulfide solid lubricant is added to Cu and graphite, the elimination of Pb results in an increase in the brush resistivity or an increase in the lead connection resistance under high temperature or high humidity. The above-mentioned Patent Opening Hei 5-226048 does not disclose any increase in the brush resistivity or in the lead connection resistance under high temperature or high humidity.
SUMMARY OF THE INVENTION
A primary object of the invention is to control the increase in the connection resistance of an outer terminal in a Pb-less metal-graphite brush containing a metal sulfide solid lubricant at high temperature.
A secondary object of the invention is to provide a specific structure for that.
A secondary object of the invention is to control the increase in the connection resistance of the outer terminal in high humidity as well as controlling the increase in the connection resistance of the outer terminal at high temperature.
A secondary object of the invention is to control the increase in the brush body resistivity as well as the increase in the outer terminal connection resistance at high temperature or in high humidity.
A secondary object of the invention is to obtain advantages with a small addition of Ag.
Moreover, a secondary object of the invention is to provide a production method of a metal-graphite brush which may be controlled the increase in the connection resistance of an outer terminal at high temperature.
A secondary object of the invention is to provide a production method of a metal-graphite brush which may be controlled the increase in the connection resistance of an outer terminal in high humidity as well as at high temperature.
A secondary object of the invention is to provide a production method of a metal-graphite brush which may be controlled the increase in the connection resistance of an outer terminal and the increase in the brush body resistivity at high temperature and in high humidity.
Further, an object of the invention is to provide a production method of a metal-graphite brush which may be controlled the increase in the connection resistance of an outer terminal and the increase in the brush body resistivity at high temperature and in high humidity.
In the invention, a metal-graphite brush, comprises: a Cu-graphite brush body added with a metal sulfide solid lubricant; and an outer terminal connected to the brush body, characterized in that Ag particles having a mean particle size of not more than 5 &mgr;m are added to at least one of the brush body and a neighborhood of connecting interface between the brush body and the outer terminal. The added Ag particles control the increase in the resistance between the brush body and the outer terminal at high temperature.
The metal sulfide solid lubricant is, for example, molybdenum disulfide or tungsten disulfide, and its addition is, for example, 1-5 wt % of the brush body. As molybdenum disulfide and tungsten disulfide are equivalent to each other, while molybdenum disulfide is used in the embodiment, the results are identical when it is substituted with tungsten disulfide. As for the outer terminal, for example, a lead wire being molded in the brush body is used. The lead wire may be, for example, a stranded wire or a braided wire of nonplated Cu wires. In the invention, expression such as addition of Ag particles, addition of Zn powder, addition of a metal sulfide solid lubricant, or Pb-less does not refer to Ag, Zn, a metal sulfide solid lubricant, or Pb being contained as an impurity.
As it is difficult to obtain Ag particles having a mean particle size of 5 &mgr;m or under from electrolytic silver, Ag particles used here are produced by chemical reduction. In the case, Ag particles are prepared by adding a reducing agent such as Zn, formalin, or ferrous ions to, for example, an aqueous solution of silver nitrate to reduce it. The kind of the reducing agent is optional, and the solvent for the solution is also optional. By the chemical reduction, Ag particles having a mean particle size of 5 &mgr;m or under may be easily obtained, and the mean particle size is, for example, from 1 to 3 &mgr;m. When silver nitrate is reduced by ferrous ions in the presence of, for example, citric acid, Ag black having a mean particle size of about 3-10 nm may be produced and this Ag black may be used as well. Thus, the mean particle size of chemically reduced silver is normally 3 nm-5 &mgr;m, preferably 0.1-5 &mgr;m, and most preferably 1-3 &mgr;m. Ag particles prepared by the chemical reduction are granular, or flaky when such particles are crushed by a stamp mill. In contrast to them, the particles of electrolytic silver have normally tree-like structure. Hence, electrolytic silver particles may be distinguished from Ag particles produced by the chemical reduction by the particle structure. The mean particle size of electrolytic silver is, for example, about 30 &mgr;m.
Preferably, in addition to the Ag particles, Zn is added to at least one of the brush body and the neighborhood of the connecting interface between the brush body and the outer terminal. This is effective in controlling the increase in the connection resistance of the outer terminal both at high temperature and in high humidity.
In the addition of Ag particles or Zn at least in a neighborhood of the connecting interface between the brush body and the outer terminal, preferably, each amount of the addition of Ag particles or Zn powder is 0.05-3 wt % or 2-10 wt % of the brush body material.
When Ag particles of 0.05-3 wt % of the entirety of the brush body or Zn of 2-10 wt % of the entirety of the brush body is almost homogeneously added to, for example, the brush body, the increase in the resistivity of the brush body as well as the increase in the connection resistance of the outer terminal may be controlled.
Ag particles are a precious material, and the usage of silver may be reduced by adding Ag particles and Zn only to a neighborhood of the connecting interface between the brush body and the outer terminal.
According to the invention, a production method of a metal-graphite brush having a brush body and an outer terminal, comprising a step for producing the brush body by sintering a compounded powder including graphite powder, Cu powder, and a metal sulfide solid lubricant, is characterized in that the compounded powder, to be used at least in a neighborhood of a connecting interface between the brush body and the outer terminal, further includes Ag particles produced by chemical reduction
Honbo Ryochi
Ikeda Mitsuo
Inukai Kyoji
Morita Naoki
Murakami Youichi
Mai Ngoclan T.
Tris Inc.
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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