Electricity: circuit makers and breakers – Electric switch details – Contact
Patent
1990-12-21
1997-01-28
Fuller, Benjamin R.
Electricity: circuit makers and breakers
Electric switch details
Contact
200268, 428627, 428660, 428662, 428663, 428665, 428664, 428666, 427562, 427564, 427566, H01H 102
Patent
active
055970648
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to low-cost electric contact materials having high hardness and high melting point and being excellent in the wear resistance, environmental resistance and high rigidity, production methods thereof and electric contacts used these. In particular, these materials are used for lead relay, lead switch, relay for communication instruments, relay for control, microswitch, keyboard switch, oscillating contact, etc.
TECHNICAL BACKGROUND
So far, for the small and medium-sized electric contacts, contact materials with good electroconductivity comprising gold, gold alloy, silver and silver alloy have been used because of low contacting force. With these contact materials, however, when the number of works of switching-on and -off increases, the exhaustion reaches the substrate metal because of low hardness (Hv 100-200) and low melting point (900.degree.-1060.degree. C.) resulting in the scattering of exhausted powder onto the surface of contact. Hence, the contacting resistance etc. increased leading to the instability. Moreover, the time-lag (poor restoration) was caused due to the adherence and locking of the surface of contact leading to a drawback of remarkably short life of contact. On the other hand, in the cases of lead switch etc., if using W, Mo, etc. being metals with high melting point from the reasons of low contacting pressure and difficulty in providing thick layer of contact, the increase in the contacting resistance cannot be prevented. So, plated contacts with noble metals such as Rh, Ru, etc. are broadly used.
However, the Rh contact has a drawback that the contacting resistance increases with organic gases containing in the atmosphere and organic gases previously adsorbed onto the surface. Moreover, it is impossible to give the plating onto easily oxidizable contact strips or lead pieces of Fe, Ni, etc. and it is required to plate intervening plated layers of Au, Ag, Cu, etc. For this reason, effective plating thickness decreases and the process becomes complicated on production leading to a drawback of high-processing price for contact. Disclosure of the invention
As a result of extensive investigations in view of this situation, low-cost electric contact materials, wherein said drawbacks were solved and the life of contact and reliability were improved, production methods thereof and electric contacts used these have been developed according to the invention.
Namely, the first of the inventive materials is characterized in that a covering layer having at least one selected from carbides, nitrides, borides, silicides and aluminides of transition metals of groups IVa, Va and VIa as a major ingredient is formed on the substrate as an electric contact in a thickness of 0.03 to 100 .mu.m.
Moreover, the second of the inventive materials is characterized in that, in the middle of substrate and 0.03 to 100 .mu.m thick covering layer of electric contact being the outermost layer and having at least one selected from carbides, nitrides, borides, silicides and aluminides of transition metals of groups IVa, Va and VIa as a major ingredient, a not less than 0.1 .mu.m thick intermediate layer having a composition of ABx (A: transition metal of group IVa, Va or VIa, B: carbon, nitrogen, boron, silicon or aluminum) and having a gradient composition of X=0 on the side of substrate and X=1 in cases of carbon and nitrogen, X=2 in cases of boron and silicon and X=3 in case of aluminum on the side of covering layer of electric contact is formed.
Furthermore, the third of the inventive materials is characterized in that an intermediate layer comprising soft metal is covered on the substrate in a thickness of not less than 0.01 .mu.m and, thereon, a covering layer of electric contact having at least one selected from carbides, nitrides, borides, silicides and aluminides of transition metals of groups IVa, Va and VIa as a major ingredient is formed in a thickness of 0.03 to 100 .mu.m.
And, as said intermediate layer comprising soft metal, use of a metal having at least
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Mashimo Keiji
Ozaki Masanori
Fuller Benjamin R.
Lund Valerie Ann
The Furukawa Electric Co. Ltd.
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