Card – picture – or sign exhibiting – Check – label – or tag – Coin or token type
Patent
1984-10-30
1987-02-24
Rutledge, L. Dewayne
Card, picture, or sign exhibiting
Check, label, or tag
Coin or token type
420473, 420476, 428674, C22C 904
Patent
active
046446745
DESCRIPTION:
BRIEF SUMMARY
This invention relates to coins, coin blanks, metal for the production of coins or coin blanks and alloys for such uses. The term coin as used herein also covers tokens, medals and the like.
Over very many years numerous alloys have been used in the manufacture of coins. With the increasing tendency to produce high value coins--which may be utilised for vending machines and replace paper money which has a very short life--there has arisen a need to develop alloys which are attractive in color. Historically many high value coins were made from gold or gold alloys and the general public associates golden coins with high value coins. There is, therefore, a wish to develop coin alloys for high value coins which are golden in appearance.
Apart from gold itself the only yellow alloys contain copper, and brasses containing about 15% of zinc approach closest to the color of gold. Unfortunately brasses have inadequate tarnish resistance.
Although pure gold has a constant color it is impracticable to make coins from pure gold because pure gold is very soft. Gold coins have, therefore, to be made from a gold based alloy. The actual color of the alloy can depend on the actual alloying element added to the gold and the quantity of that element. Typically the addition of copper to gold will tend to make it redder whereas silver additions make gold appear whiter in color.
Because the existing gold alloys can have differing color it is possible that some countries would require alloys having a more red color whereas other countries would require alloys having a whiter color if they were to introduce coins which the public associates with high value currency.
Coin alloys have a number of requirements, some of which tend to be unique to coins. A coin alloy has to be such that it is fabricable into a coin, the alloy has to have sufficient ductility to enable it to be struck or minted as a coin, and after minting it has to be sufficiently hard to withstand normal everyday usage. The coins themselves have to be resistant to wear and have to be tarnish resistant. Because the alloys will tarnish to some extent the color of the tarnish is important and also the contrast between the original metal and the tarnish color is significant. In use tarnishing will be more evident in recesses in the coin whereas the high points of the coin tend to be kept fairly clean. It is undesirable, therefore, that the tarnish color should differ too significantly from the bulk alloy color.
The coin alloy has to be capable of being annealed and ideally should be such that it could be clad onto a base metal such as steel for further cheapening of the coin product.
Ideally the alloy should have a fine grained, homogeneous single phase structure, should be easily castable and should not work harden too greatly during manufacture. The alloy must be capable of being readily cleaned to remove any oxide film and be capable of being rimmed and minted.
It can be seen, therefore, that a coin alloy has a number of requirements, many of which are unique to coins. In many cases some of the properties are difficult to determine. Thus it is difficult to predict the type of tarnish an alloy will develop in normal use. Over a period of years a coin may develop a tarnish which is unattractive and which does not tend to show up in accelerated tarnishing tests.
These numerous requirements of a coin alloy tend to mean that prior art descriptions of alloys which make no reference to coins do not enable the man skilled in the art to determine from inspection whether an alloy is suitable for use as a coin, a coin blank, or for the production of coins or coin blanks.
By the present invention there is provided a coin, a coin blank or a strip of metal for the production of a coin or coin blank having as its surface a copper based alloy containing 15 to 30% zinc and 2 to 7% tin apart from incidental impurities.
The alloy may additionally contain up to 7% nickel. The nickel content may be in the range 2 to 7%.
Preferably the zinc content is in the range 20 to 25% and may be 20%
REFERENCES:
patent: 1988938 (1935-01-01), Corson
patent: 4436790 (1984-03-01), Prinz et al.
patent: 4579761 (1986-04-01), Ruscoe et al.
Chem. Abst., 95: 224093g, 1981.
Chem. Abst., 97: 149364g, 1982.
Chem. Abst., 98: 184216c, 1982.
Chem. Abst., 99: 26422h, 1983.
Burrows George R.
Scholes Ian R.
Rutledge L. Dewayne
The Deputy Master and Controller Royal Mint
Zimmerman John J.
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