Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to coins and similarly disc-
shaped articles, such as medals, or medallions.
The metallic composition of coins has varied over the
years owing to the escalating cost of the metals or alloys from
which coins have conventionally been made. For example, gold
coins are now virtually extinct, and silver coins may frequent-
ly contain copper ana/or other metals to reduce the metallic
value of the coin compared to its face value, while still giving
it a silver-like appearance. Another kind of coinage in fre-
quent use is copper coinage, which is made of copper or a copper
alloy. As compared to silver and gold coinage, of course, coppercoinage is usually used for coins of lower value in a monetary
system.
With the increasing cost of metals, the value of the
metal of which a coin is made may increase so much that it
approaches or even exceeds the face value of the coin, with
the result that it can be advantageous to melt down such coins
and obtain the current price of their contained metals. It is
primarily for this reason that, for example, coins made of silver
have now been replaced by coins made of other metals or alloys
of similar appearance and lower intrinsic values, such as nickel
or nickel alloys.
Until now, this problem has not become particularly
significant with respect to copper coinage, since the value of
the copper or copper alloy of which the coins are made has
remained small compared to the face value of the coins. How-
ever, with the escalating cost of copper and its alloys, this
problem has now become relevant with respect to copper coinage,
with the result that it is now desirable to find some alternative
composition or construction for copper coins. Because most
countries are reluctant to change the appearance of their coins,
it is at the same time necessary to preserve the copper-like
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appearance of such coins, as was done in the case of silver
coins, where the silver-like appearance of the coins was pre-
served by a suitable choice of metal or alloy for at least the
faces of the coin.
According to the present invention, blanks suitable
for minting into coins or similarly disc-shaped articles are
produced by loading a plurality of appropriately disc-shaped
steel cores into a perforated container, placing the container
i`n an intermediate metal electroplating bath, said intermediate
metal being selected from the group consisting of nickel and
zinc, electroplating an intermediate metal coating onto the
cores while moving the container angularly about a horizontal
axis unti`l the intermediate metal coating has a thickness of
at least about 0.005 mm on each opposed face of each core and a
th.ickness of the peripheral edge of each core measured radially
i`n the range of from about 2 to about 4 times the face thickness,
placi`ng the container in a copper electroplating bath, electro-
plating a copper coating onto the cores while moving the con-
tainer angularly about a horizontal axis until the copper
coating has a thickness of at least about 0.05 mm on each opposedface of each core and a thickness on the periPheral edge of each
core measured radially in the range of from about 2 to about 4
times the face thickness, the ratio of the two thicknesses being
adjusted by varying the ratio of the diameter of the core pieces
with the diameter of the electroplating container, the current
densi.ty and the number of blanks in the container, removing the
plated cores .from the contaïner, and heating the plated cores
to form a layer of interdiffused copper and intermediate metal
and a layer of interdiffused intermediate metal and steel with
consequent metallurgical bonding of the copper coating to the
intermediate metal coating and of the intermediate metal coat-
ing to each steel core and to decrease the hardness of each steel
core to less than about 65 on the Rockwell 30T hardness scale.
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The blank is subsequently minted by applying the
required insignia to one or both faces of the blank by means
of an appropriately designed die or dies. Where a coin is to
be produced, the size of the core and the thickness of the
copper coating will of course be such as to produce a blank
of the same size as a conventional copper coin which it
is intended the coin according to the present invention should
replace.
Steel is considerably less expensive than copper,
and the metallic value of a coin according to the present in-
vention is considerably less than the metallic value of a con-
ventional copper coin of the same size and made entirely of
copper and/or copper alloy. Also, the seigniorage of a coin
according to the invention, that is to say the difference
between the face value of the coin and the cost of producing
it (including the cost of raw materials~, is sufficient for
the present invention to constitute an attractive alternative
process for producing coins of copper-like appearance.
Further, since the exterior of the coin is copper, its appear-
ance will resemble that of a conventional copper coin, andwill not become substantially different therefrom over a
period of time. If desired, alloying elements may be in-
cluded in the copper coating to increase wear or corrosion
resistance.
In order to produce a coin of satisfactory hardness
and wear resistance for the usage which a coin experiences,
while at the same time permitting the blank to be readily
i~.printable with the required insignia by means of an
appropriately designed die or dies, the steel is preferably
a low carbon steel. Advantageously, the carbon content of
the steel is less than about 0.05%, a preferred value being
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of the order of 0.01%.
Many coins have raised rims around the peripheries of
opposed faces, and these raised rims are preferably formed
on the steel cores before the electroplating step.
In one embodiment of the invention, a batch of coin-
age cores was made of low carbon steel, namely steel manu-
factured by Dofasco and sold by them as ASTM A424 type I, the
maximum carbon content of such steel being 0.01% by weight.
The circular steel cores of appropriate diameter were punched
out of steel strip of appropriate thickness, namely about
1.2 mm and were given a raised rim around the periphery of both
faces by an upsetting operation. The steel cores were loaded,
as a 60 kg batch, into a perforated barrel made of polypropylene
91 cm long and 46 cm in diameter. This 60 kg batch of cores
contained about 13,000 cores.
- The steel cores were than put through a cleaning
cycle by lowering the barrel into successive baths providing
rinses of 5% neutral detergent solution, hot water, cold water,
10% HCl and cold water respectively. In each instance, the
barrel was immersed in the bath with its longitudinal axis
horizontal, and was oscillated over nearly 180 about its
longitudinal axis at about six to and fro cycles per
minute. The barrel was then immersed in a nickel sulphamate
plating bath containing about 98 grams per litre nickel,
and oscillated as before. The temperature of the nickel
plating bath was maintained at about 55C and the pH was
maintained at about 2.1. Flexible cathode rods were mounted
within the barrel, and baskets containing nickel anode
pieces were supported in the plating bath externally of the
barrel. A voltage of 12V was applied, giving a current of
290A.
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After 1.5 h, a 2.8 kg sample of nickel-plated
cores was withdrawn from the barrel and rinsed in water.
The thickness of nickel coating on the faces of these
cores was found to be 0.003 mm. After a further 1.5 h, a
3.8 kg sample of nickel-plated cores was withdrawn from
the barrel, and the nickel coating thickness was found
to be 0.006 mm on the core faces and 0.02 mm on the
circumferential rims. Laboratory tests show that the
nickel coating thickness of 0.003 mm on the first sample
of cores was inadequate for subsequent copper plating.
The second sample of nickel plated cores was
then placed in a smaller barrel having a length of
30 cm and a diameter of 15 cm. The second barrel was then
immersed in an acid copper sulphate plating bath con-
taining 45 yrams per liire coppex and the barrel was
continuously rotated at 6 rpm. Flexible cathode rods
were mounted within the baxrel, and baskets containing
copper anode pieces were supported in the bath externally
of the barrel.
This plating bath was maintained at a tempera-
ture of 40C and a pH of 1. The ~ckel plated cores were
plated with copper for 13.5 h at a voltage of 3V and a
current of 40A and, after this time, a copper coating of
0.06 mm was deposited on the nickel-plated core faces,
with a copper coating of 0.14 mm having been deposited on
the circumferential rims. After the copper plating, the
resultant blanks were rinsed and dried.-
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The blank~ ~ere then annealed in a pure ~y~rogen atmos-
phere at a temperature of 800C for 30 min, and allowed to cool
in the same atmosphere, An analysis of the annealed blanks
is shown in Table 1.
TABLE 1
. F~ I _ _ . _ ~ Nickel Copper ~¦
Cu Ni (by dif- l~eight Diameter ~hickness l~a~dness Plate on Plate on 1
_ 7._ ~ fe~ence) (g) (~m). (mm) R-30T Face (mm) Face (m~) ~.
14.4 1.7 83.9 5.44 24.81 1.3S 42 0.006 0.060
. _ .i~
... . ~ . . . . . .......................... . . . . . . . :~
Metallography showed the plating of the cores to be
free from any significant defects, with there being good adhesion
between the copper and nickel coatings and between the nickel coat-
ing and the steel core.
Some of the blanks were minted, by applying appro-
priate insignia to both faces of the blanks by means of dies,
and excellent results were achieved. To provide a coin of high
lustre, it may be advantageous to burnish the blanks before mint-
ing, for example, by burnishing in a soap solution containing
metallic media.
The barrel in the copper plating bath may be oscillated,
as was the barrel in the nickel plating bath, rather then con-
tinuously rotated.
It will be understood that the invention is applicable
to the production of other disc-shaped articles, as well as
coin blanks. Medals and medallions are examples of other disc-
shaped articles to which the invention is applicable. Also, such
articles may not necessarily have a circular periphery and may
not necessarily be imperforate.
Other embodiments within the scope of the invention
will be apparent to a person skilled in the art, the scope of
the invention being defined in the appended claims.
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