US1952082A - Alloy - Google Patents

Description

Patented Mar. 1934 UNITED STATES mm n. w... Fail-field, com, assigns! a Handy a Harman, New York, N. 1;. a corporation'ot blew 'York No. Drawing. Application June 10, 1032.

- Serial No. 610.49.

3 Claims.

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

.As is well known, silver alloys of ordinary composition and containingcopper as thebase ingredient are susceptible to tarnish. Such discoloration ofthe 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 iormoi gaseous compounds. Sulphur in both forms 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 the sulphur is present. In any event, the necessity of frequent cleaning and polishing silver articles to keep themin bright condition has led r so about 92.5%, tin rangin from tarnish and, in some instan to numerous attempts in the past to produce silver alloys which are '0! good appearance, have the desired working characteristics, and have a better resistance to. tarnish than ordinary silvercopper alloys, but up to 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 dimcult one because investigationhas shown that binary alloys oiier little promise and .the number of ternary and quarternary alloys is very large. When it is un-- 'derstood that small variations in the'ingredients in these alloys have an important eifect on the resistance to tarnish and the amounts of'the ailoying ingredients used is highly critical with respect to tarnish resistance, the magnitude and difllculty oi 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 causes may be made by using tin as an alloying metal, provided the amount of tin used be kept within relatively narrow limits. The new alloy may be given a somewhat improved resistance to properties, it a small amount of a third ingredient isused which is preferably chromium. although calcium may be substituted for chromium. This third ingredient has a slight hardenin eilect and, for convenience, it will be referred to as a better physical" 7.1%.and. as a hardening ingredient, chromium from about V4 up to about oi calcium replacing in an amount ranging or a similar amount wholly or calcium being substantially equivalent for the purposes mentioned.

Typical examples of the new alloys in sterling fineness have, the following approximate analyses: 7

Sample No. 1

- 7 Per cent Silver 92.5 Tin 7.1- Chromium 0.4

Example No. 2 Per cent Silve 92.5 Tln' 8.8 Calcium 0.! I have found that chromium is the most satisiactory of the hardening ingredients that might be used and ordinarily the chromium employed need not exceed 5; or 1%. Also, while I have specified that the silver content shall be about 92.5%, it is to be understood that the silver may be increased in amount impairinz the quality oi the new alloy.

, I am aware that it has been proposed tore to employ tin and nickel in silver alloys, but with which I am familiar hereto- .the alloys of this type in part, chromium and chromium, and tin andto some extent without have contained less tin.

than the amounts specified above. A large numher of experiments which I I this-field have demonstrated that the range of tin used in this alloy is quite critical and any departure from the 'range mentioned results in a lowering of the tarnish resistance. the specified range, the resistance is at its maximum.

What I claim: l'. A silver alloy which amount oi-about 92.5%. tin ranging from about 6% etc about 1.1%. and chromium in an amount ranging irom about 0.25% to about 1.5%.

2,. A silver alloy which consists of about 92.5% silver, about 1.1% tin, and about 0.4% chromium. 3. -A silver alloy which consists of silver in the mo t oi. about 92.5%. tin ranginz irom about 0% to mut 7.1%, and chromium in an amount from a t 0.25% to about 0.5%;

' ROBERT H. LEACH.

hardener'fiialthough it is. to be understood that 55 it also increases the tarnish resistance to a substantial extent. i silver alloys nowin widestuse are those of sterling fineness and the new alloy of that fineness contains silver in anamount not less than about 0% to about have conducted in' while within consists of silver in the