US1969019A - Alloy - Google Patents

Description

Patented Aug. 7, 1934 1,969,019 ALLOY Robert 1!; beach, Fairfleld, Coma, assignor to Randy a Harman, New York, N. Y;, a corporation of New York No Drawing. Original application June 10, 1932,

Serial No. 616,498. Divided and this application March 1, 1934, Serial No. 713,524

4 Claims.

This invention relates to silver alloys and is concerned more particularly with a novel silver alloy which may be used to especial advantage inthe manufacture of table silver and hollow 5 ware and for various other purposes, because it has the property of strongly resisting tarnish and discoloration.

As is well known, silver alloys of ordinary composition and containing copper as the base in gredient are susceptible to tarnish. Such discoloration of the metal is brought about by numerous agents, the most active being sulphur which is present in various foods such as eggs, and is also present to some extent in the atmosphere in the form of gaseous compounds. Sulphur in bothforms causes tarnishing at a rate which depends on the length of contact or exposure of the metal, the concentration of the sulphur in the food or air, and the form in which 9 the sulphur is present. In any event, the necessity of frequent cleaning and polishing of silver articles to keep them in bright condition has led to numerous attempts in the past to produce silver alloys which are of good appearance, have the desired working characteristics, and have a better resistance to tarnish than ordinary silvercopper alloys, but upto the present, the proposed alloys with which I am familiar, have not proven entirely satisfactory.

The problem of producing a silver alloy which is resistant to tarnish is a diflicult one because investigation has shown that binary alloys offer little promise and the number of ternary and quartenary alloys is very large. When it is understood that small variations in the ingredients in these alloys have an important effect on the resistance to tarnish and the amounts of the alloying ingredients used are highly critical with respect to tarnish resistance, the magnitude and difiiculty of the problem will be appreciated.

' As a result of my investigations in this field, I have found that a silver alloy which has excellent resistance to tarnish produced by various agencies, may be made by using zinc and tin'as alloying metals, provided the amounts used are confined within rather narrow limits. The new alloys may be given a somewhat improved resistance to tarnish and, in some cases, better physical properties, if a small amount ofa fourth ingredient is added, which may be one or more of the metals nickel, silicon, magnesium, and antimony. In most instances, the fourth ingredient has a slight hardening eflfect, and I shall, therefore, refer to it as a hardener, although it is to be understood that, while all of the metals in the group mentioned increase the tarnish resistance to a greater or less degree, not all of those metals have a hardeningeifect. I prefer to use nickel for the purpose, since it offers certain advantages 0 over the others but for the purpose for which they are used in the new alloy, all four metals are substantial equivalents.

Silver alloys now in widest use are those of sterling fineness containing at least 925 parts of silver per thousand. In producing the new alloy in sterling fineness, I use approximately 92.5% silver, from about 3% to about 4% zinc, from' about 3% to about 4.5% tin, and'a' small amount of nickel, silicon, antimony or magnesium, nickel and silicon being especially suitable for the purpose. When one hardening metal is used, the amount present may vary from about 0.25% to about 1%, but when two or more hardeners are used, the total amount of the hardening ingredients is not to exceed about 1.5%.

Typical examples of the new alloy of sterling fineness have the following approximate analyses.

Example No. 1

. Percent Silver 92.5 Zinc -a 3.5 Tin--- 3.5 Nickel 0.5

Example No. 2

Percent Silver 92.5 Zinc--- a 3.5 Tin 3.0 Silicon 0.5 Nickel 0.5

Example No. 3

Percent Silver 92.5 Zinc 3.0 Tin 3.0 Nickel 0.5 .100 Magnesium 1.0

The new alloy can be made in flnenesses substantially less than sterling, and I have found that alloys of the new type as low as 800 fine can 5 An example or the new alloy of 800 fineness may have the following approximate analysis.

Example No; 4

Nickel. antimony, magnesium or silicon I am aware that it has been proposed heretofore to make silver alloys which contain zinc, antimony, tin and chromium, but after a large number of experiments involving the exposure of such alloys to various tarnishing agents, I have found that the ranges of 'zinc and tin and the relative proportions used are quite critical and any considerable departure from the ranges given results in a lowered tarnish resistance. My tests indicate further that increasing the zinc content improves the resistance to certain forms of tarnish while increasing the tin improves the resistance to certain other forms of tarnish. An alloy which has the best resistance to tarnish from all sources is one in which the zinc and tin are present in amounts within the ranges specified for an alloy 01 sterling fineness.

This application is a division or my copending application, Serial Number 616,498, filed June 10, 1932.

I claim:

1. A silver alloy which consists of silver ranging from about to about 92.5%, zinc ranging from about 14.5% to about 3%. tin ranging from about 5% to about 3%, and nickel ranging from about 0.25% to about 1%.

2. A silver alloy which consists of silver ranging from about 80% to about 92.5%, zinc ranging from about 14.5% to about 3%, tin ranging from about 5% to about 3%, and about 0.5% of nickel.

3. A silver alloy of sterling fineness which consists of about 92.5% of silver, from about 4% to about 3% of zinc, from about 4.5% to about 3% cl tin, and from about 0.25% to about 1% of nickel.

4. A silver alloy of sterling fineness which consists of about 92.5% of silver, about 3.5% of zinc, about 3.5% of tin, and about 0.5% of nickel.

ROBERT H. LEACH.