US1628673A - Silver alloy - Google Patents

Description

Patented May 17, 1927.

UNITED STATES PATENT OFFICE.

ROBERT H. LEAiCH, OF BRIDGEPOBT, CONNECTICUT, ASSIGNOB TO HANDY 8a KABMEN,

A CORPORATION OI NEW YORK.

SILVER ALLOY.

Io Drawing.

This invention relates to an improvement in silver alloys, and the object of the inven tion is to provide a silver which has reat resistance to tarnishing or other disco oration, or more specifically the object em braces an alloy containing a preponderating amount of silver and also containing cadmium and antimony.

This alloy is to be made preferably of sterling fineness, and the term sterling is used to'designate a silver alloy which contains, per thousand parts, approximately 925 parts of silver and 75 parts of base metal, which is usually copper. Such silver is subject to discoloration and this may result either by reason of various substances contained in dilute form in the atmosphere, or, in the case of table ware, the discoloration or tarnish may result from the exposure of the metal to the action of fruit acids, foods containing sulphur in various forms, and other substances which contain elements which act on the silver.

As has reviously been stated, it is the object of tliis invention to provide a silver, preferably of sterling quality, which resists discoloration, and I accomplish this result by substituting for the copper ordinarily used in such an alloy, cadmium and antimony. Such an alloy not only resists tarnishing but by the proper selection oi the proportions of these metals an alloy may be roduced which has varying mechanical qua ities.

It has been found that when cadmium is added to silver there is produced a very ductile white alloy which can be worked by rolling, spinning, and the like, to a greater extent than the standard silver-copper alloy, without becoming hard. The cadmium appears to form a homogeneous alloy which is of uniform quality and which is satisfactory in many respects as, for instance, having tarnish resisting properties, but such an alloy is usually so soft that an article made from it, provided little work is done on the metal during the manufacture, will be comparatively soft and will not offer sufiicient resistance to ordinary use. Such an article will, therefore, become dented or bent readily, and is objectionable for that reason.

On the other hand, the addition of antimon to a silver alloy increases the resistance of t e metal to tarnish, and in addition makes it quite brittle and difficult to work.

Serial No. 659,394.

However, by combining the three ingredients above mentioned, namely, silver, antimony and cadmium, in proper proportions, it is possible to secure an alloy which has the desired tarnish-resisting qualities and which has the ductility, and malleability which ma be required for any particular use.

11 alloy which fulfills the above requirements will contain a preponderating amount of silver, for instance, about 92.5%, when the alloy is to be of sterling fineness, and an amount of cadmium varying between 1% and 7%, and antimony between (3.5% and 0.5%. An alloy in which the cadmium approaches the upper limit will be comparatively soft and ductile, and will be used for the production of articles in which considerable working of the metal is required, while where little working is carried on during the manufacture, the alloy will contain cadmium approaching the lower limit. For what may be called a general'purpose alloy, the proportions will be approximately 2.5% of cadmium and 5% of antimony, the remainder of the alloy being made up of 92.5% of silver, when the alloy is to be of sterling quality.

From a scientific viewpoint a silver alloy which is designated as solid may contain as low as 66 of silver, the remainder being made up of various base metals with copper usually employed heretofore.

Silver which is used for manufacturing purposes may also run as high as 95% pure silver, in which event it is, of course, liner than sterling. That silver which is in greatest demand is sterling silver, and I have previously described the proportions of the ingredients which will be present in my non-tarnishing alloy of that fineness, but it is to be understood that by following the principles of the invention here set forth, it is possible to make alloys of other than sterling fineness which will have qualities which will be required by the purposes to which the alloy'is to be put. As I have stated, cadmium with silver produces a ductile alloy which has tarnish-resisting properties, but this alloy is so soft that unless some hardening ingredient is employed an article made from such a combination would be easily dented and bent. Accordingly, antimony is employed and the addition of the antimony makes it possible to control the malleability and ductility. The amount of antimony which will be included will naturally be selected in accordance with the purpose to which the alloy is to be put, but it may he said, in general, that the cadmium present will rangeifrom about 13% to about 93% of the combined amount of cadmium and antimony present, while the antimony will consequently range from about 87% to about 7% of this combined amount. The skilled metallurgist will be able to determine without difliculty the amount of antimony which is to be included in order to secure a metal of the desired mechanical qualities.

In producing such an alloy various methods may be used, but one convenient method consists in first making up an alloy of silver and cadmium which contains approximately 60% of silver and of cadmium. The cadmium is first melted in a reducing atmosphere under a heavy )rotective cover such as charcoal, then the si ver separately melted and preferably under a cover, is'added thereto and the two metals thoroughly mixed. A sample of this mixture which is found to be ver homogeneous, is taken and analyzed and on the basis of this analysis there is computed the necessar amount of fine silver and antimony whic is required to make the final mixture. The silver which is to be added is then melted and after it is thoroughly liquid the required amount of antimony is added thereto to form a silverantimony mixture. To this molten mixture the pro or weight of the silver-cadmium alloy 1s a ded, and with this method the metals are found to be mingled in the final product in a uniform manner. These several melting and mixing steps should be carried on in a reducing atmosphere to secure the best results.

While the above process is entirely satisfactory I do not desire to limit myself to this exact rocedure. In any process, however, for tie production of this alloy, care should be taken in the manner in which the cadmium is added, inasmuch as it is readily oxidized at the temperature at which the melting is carried on.

An alloy containing the ingredients above referred to is found to resist corrosion or discoloration to a much greater extent than is the case with ordinary alloys containing copper as the base metal. The new alloy, aside from its non-tarnishing qualities, may he made with varying mechanical properties such as hardness, brittleness, and the like, b the proper selection of the amounts of ca mium and antimony used. The antimony combined with the silver not only serves to give the silver a tarnish-resisting quality but also serves to harden the alloy. In view of the properties possessed by the new alloy, it will be apparent that it is capable of wide use in the production of various metallic articles and is desirable for the manufacture of table ware or hollow ware.

I claim:

1. An alloy containing a preponderating amount of silver and about 7.5% of cadmium and antimony, the cadmium ranging from about 1% to 7% and the antimony from about 6.5% to 0.5%.

2. An alloy containing about 92.5% of silver and about 7.5% of cadmium and antimony, the cadmium rangin from about 1% to 7%, and the antimony r to 0.5%.

3. An alloy containing about 925 parts of silver, about 50 parts of antimony, and about 25 parts of cadmium.

In testimony whereof I aflix my signature.

ROBERT H. LEACH.

om about 6.5%

antimony which will be included will naturally be selected in accordance with the purpose to which the alloy is to be put, but it may be said, in general, that the cadmium present will range from about 13% to about 93% of the combined amount of cadmium and antimony present, while the antimony will consequently range from about 87% to about 7% of this combined amount. The skilled metallurgist will be able to determine without difliculty the amount of antimony which is to be included in order to secure a metal of the desired mechanical qualities.

In producing such an alloy various methods may be used, but one convenient method consists in first making up an alloy of silver and cadmium which contains approximately 60% of silver and of cadmium. The cadmium is first melted in a reducing atmosphere under a heavy protective cover such as charcoal, then the silver separately melted and preferably under a cover, isadded thereto and the two metals thoroughly mixed. A sample of this mixture which is found to be ver homogeneous, is taken and analyzed an on the basis of this analysis there is computed the necessary amount of line silver and antimony which is required to make the final mixture. The silver which is to be added is then melted and after it is thoroughly liquid the required amount of antimony is added thereto to form a silverantimony mixture. To this molten mixture the proper weight of the silver-cadmium alloy is added, and with this method the metals are found to be mingled in the final product in a uniform manner. These several melting and mixing steps should be carried on in a reducing atmosphere to secure the best results.

While the above process is entirely satisfactory I do not desire to limit myself to this exact procedure. In any process, however, for the production of this alloy, care should be taken in the manner in which the cadmium is added, inasmuch as it is readily oxidized at the temperature at which the melting is carried on.

An alloy containing the ingredients above referred to is found to resist corrosion or discoloration to a much greater extent than is the case with ordinary alloys containing copper as the base metal. The new alloy, aside from its non-tarnishing qualities, may he made with varying mechanical properties such as hardness, brittleness, and the like, b the proper selection of the amounts of ca mium and antimony used. The antimony combined with the silver not only serves to give the silver a tarnish-resisting quality but also serves to harden the alloy. In view of the properties possessed by the new alloy, it will be apparent that it is capable of wide use in the production of various metallic articles and is desirable for the manufacture of table ware or hollow ware.

I claim:

1. An alloy containing a preponderating amount of silver and about 7.5% of cadmium and antimony, the cadmium ranging from about 2, to 7% and the antimony from about 6.5% to 0.5%.

2. An alloy containing about 92.5% of silver and about 7.5% of cadmium and antimony, the cadmium ranging from about 1% to 7%, and the antimony from about 6.5%-

3. An alloy containing about 925 parts of silver, about 50 parts of antimony, and about 25 parts of cadmium.

In testimony whereof I aflix my signature.

ROBERT H. LEACH.

CERTIFICATE OF CORRECTION.

Patent No. 1,628,673.

Granted May 17, 1927, to

ROBERT H. LEACH.

lt is hereby certified that the name of the second mentioned assignee in the above numbered patent was erroneously written and printed as "Harmon" where" said name should have been written and printed as "Harman", as shown by the records of assignments in this office; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 7th day of June, A. D. 1927.

Sea]

M. J. Moore, 7 Acting Commissioner of Pateuto.

CERTIFICATE OF CORRECTION.

Patent No. 1,628,673. Granted May 17, 1927, to

ROBERT H. LEACH.

It is hereby certified that the name of the second mentioned assignee in the above numbered patent was erroneously written and printed as "Harmen" where" said name shouid have been written and printed as "Harman", as shown by the records of assignments in this office; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 7th day of June, A. D. 1927.

M. J. Moore, Seal. Acting Commissioner of Patents.