Stock material or miscellaneous articles – All metal or with adjacent metals – Having metal particles
Patent
1996-06-21
1998-06-09
Mai, Ngoclan
Stock material or miscellaneous articles
All metal or with adjacent metals
Having metal particles
75247, 419 23, 419 32, 419 56, 252513, 252514, B22F 700
Patent
active
057631050
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a sintered contact material comprising silver and nickel, to a method for preparing it, and to contact facings made therefrom.
Good utility for switching currents in switchgear of power engineering has been shown in the past by contact materials comprising silver (Ag) and nickel (Ni). The preparation of such contact materials and the manufacture and testing of corresponding contact pieces is described in detail in Int. J. Powder Metallurgy and Powder Technology, Vol. 12 (1976), p. 219-228.
To prepare a contact material comprising silver and nickel, according to the prior art silver powder and nickel powder are customarily wet-mixed in a mixer, dried, pressure-moulded and sintered under a reducing atmosphere. The fineness of the microstructure essentially depends on the size of the starting powders used. Such relationships are described in detail in the monograph by H. Schreiner "Pulvermetallurgie elektrischer Kontakte", 105 to 140. In particular, an AgNi material prepared by means of precipitated powder and having average grain sizes of 1 .mu.m is specified.
It had previously been assumed that, in the case of contact materials comprising silver and nickel, the nickel particles must be present in the silver in as small and finely dispersed form as possible, in order for the contact to have good switching characteristics. A suitable way of achieving this, in principle, is the known method of mechanical alloying. As early a publication as JP-A 66/33090 discloses a method for preparing materials for electrical contacts on a silver basis, a further component being chosen in the form of a metal which is insoluble or only slightly soluble in silver.
This metal, in particular, is nickel, iron, tungsten or another metal which does not form a mixed crystal with silver or for which, on thermodynamical grounds, according to the state diagram there is the tendency towards segregation.
JP-A 66/33090 aims for a mixed crystal-like constitution of the material. To this end, electrolyte/silver powder and carbonyl-nickel powder are mixed in a ball mill with steel balls under so-called styrene gas for extended periods, for example up to 300 h, in order to obtain a mechanically alloyed powder. The aim is for the powder thus obtained to have grain sizes below 0.01 .mu.m. In an X-ray diffraction analysis, the disappearance of nickel reflections and thus the presence of an amorphous alloy was confirmed in this instance. When contacts are fabricated from an alloy powder thus prepared involving alternate sintering and pressing steps it should be possible for secondary segregations to be formed, but with the grain size of the nickel particles limited to 1 .mu.m.
It was found that when mechanically alloyed silver-nickel powders having the above-described amorphous character are used, undesirable side effects may occur which result in comparatively poor contact characteristics.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an appropriate remedy. A contact material comprising silver and nickel is to be provided which, compared with conventional silver-nickel materials, has improved contact properties. At the same time, the appropriate preparation method and corresponding contact facings are to be described.
The object is achieved, according to the invention, in the case of a sintered contact material comprising silver and nickel, by the mass fraction of nickel being between 5 and 50%, and by the nickel being present in the silver microstructure with average particle sizes 1 .mu.m<d<10 .mu.m in largely homogeneous dispersion.
Preferably, the average particle size of the nickel is a d<5 .mu.m, especially d<3 .mu.m. For the particle size distributions specified, the average distance D of the nickel particles should be between 5 and 10 .mu.m.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a photomicrograph of the material AgNi10 with a detailed view showing the average distance D between two nickel particles for particles having a particle size d of
REFERENCES:
patent: 4609525 (1986-09-01), Schreiner et al.
patent: 5198015 (1993-03-01), Tsuji et al.
patent: 5338505 (1994-08-01), Tsuji et al.
patent: 5422065 (1995-06-01), Hauner et al.
Schreiner, H. et al., "The Properties of P/M Electrical Contact Materials", The International Journal of Powder Metallurgy & Powder Technology, vol. 12 (1976), pp. 219-228.
Schreiner, H., "Pulvermetallurgie elektrischer Kontakte", Springer-Verlag, Berlin/Gottingen/Heidelberg (1964), pp. 105-140.
Mai Ngoclan
Siemens Aktiengesellschaft
LandOfFree
Sintered contact material, method for preparing it, and correspo does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Sintered contact material, method for preparing it, and correspo, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Sintered contact material, method for preparing it, and correspo will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2197138