Metal treatment – Compositions – Heat treating
Patent
1989-11-03
1991-11-26
Dean, R.
Metal treatment
Compositions
Heat treating
75414, 75634, 148430, 148431, 423511, 423565, C22F 102
Patent
active
050679872
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing a material constituted by a blackened silver alloy, with the silver alloy being blackened throughout its bulk, the method including exposing the silver alloy to sulfur vapors.
2. Description of the Relevant Prior Art
French patent No. 2 516 548 describes a method of manufacturing silver blackened throughout its bulk by proposing several variants, one of which includes exposing a wire or a thin foil (about a few tenths of a millimeter thick) to sulfur vapors in order to blacken the silver by gas diffusion.
In order to speed up the blackening of the silver and to increase the efficiency of the method, said patent proposes increasing the pressure of the sulfur vapors, thereby enhancing sulfur/silver diffusion.
The object of the present invention in this new patent is to make the manufacturing method more effective with respect to production capacity while simultaneously also improving the quality and the microstructure of the final product.
SUMMARY OF THE INVENTION
According to the present invention, this object is achieved by a method which is characterized in that prior to being put into contact with the sulfur vapor, the silver alloy is heated to a temperature preferably lying between about 300.degree. C. and about 700.degree. C.
The temperature range 300.degree. C. to 700.degree. C. makes it possible to obtain a microstructure of satisfactory quality, with the optimum structure being obtained at a temperature lying in the range 450.degree. C. to 500.degree. c. Outside the range 300.degree. C. to 700.degree. C., the structure is not good enough for the material to be used in jewelry, it being observed that requirements for material quality are even more severe in watchmaking.
In one embodiment of the present invention, the silver alloy is used in the form of a wire which may be of various thicknesses, and the time for which said wire is put into contact with the sulfur vapors is a function of the wire gauge so as to ensure that the wire or wires are fully blackened throughout their bulk.
In another embodiment of the present invention, the silver alloy is used in the form of foil which may be of various thicknesses, with the time for which the foil is put into contact with the sulfur vapors likewise being a function of the thickness of said foil so as to ensure that it is completely blackened throughout its bulk.
The thicknesses of the silver alloy wires or foils suitable for use in a method of the present invention lie between about 0.1 mm to several mm. There is no lower limit on the thickness of the wires or the foils for implementing the method except with respect to ease of mechanical handling, and the upper limit of a few millimeters is likewise an imprecise limit since the interdiffusion between the silver alloy and the sulfur obeys a certain function with respect to time and high thickness in the base material merely extend the time required for exposure. In this way, the upper limit on the thickness of the silver alloy wire or wires or the foils is determined by questions of optimization rather than by technical constraints.
The silver alloy wires or foils are advantageously heated electrically, and electrical heating may be obtained by passing an electrical current through the alloy itself.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
A method of manufacturing a blackened silver alloy in accordance with the present invention is now described in greater detail. A silver alloy is formed into wires or foils having a thickness lying in the range 0.1 mm to a few millimeters. The wire or wires or foils are disposed in an enclosure and subjected to sulfur vapors. The silver alloy wire or wires or foils are electrically connected to a current source so as to be heated by the current flowing through the silver alloy itself and being heated by its electrical resistance, or alternatively the silver alloy may be heated by some other source of heat by conduction or radiation. The silver a
REFERENCES:
patent: 2091259 (1937-08-01), Fisher
patent: 4467856 (1984-08-01), Vachey
patent: 4676969 (1987-06-01), Smith
Gimelins Handbuch der anorganischen Chemie, p. 8.
Dean R.
Koehler Robert R.
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