PROCESS FOR PRODUCING COIN BLANKS

METHODE DE PRODUCTION D'EBAUCHES DE PIECES DE MONNAIE

English Abstract

ABSTRACT OF THE DISCLOSURE

A process for producing blanks suitable for
minting into coins includes providing a plurality of
appropriately disc-shaped metallic cores, heating the
cores to decrease their hardness to less than about
65 of the Rockwell 30T hardness scale, and cooling
the heated cores to provide cooled cores with a
hardness less than about 65 on the Rockwell 30T hard-
ness scale. A plurality of cooled cores are loaded
into an electrically non-conducting perforated con-
tainer, which is then placed in an electroplating bath.
A metallic cladding is electroplated onto the cores,
while moving the container angularly about a horizontal
axis, until a plating thickness of at least about
0.01 mm has been deposited on each face of each core
and a thickness of from about 2 to about 4 times the
face thickness has been deposited on the circumference
of each core. The cladded core pieces are then removed
from the container.

Claims

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:

1. A process for producing blanks suitable for
minting into coins, comprising providing a plurality
of appropriately disc-shaped metallic cores, heating
the cores to decrease their hardness to less than
about 65 on the Rockwell 30T hardness scale, cooling
the heated cores to provide cooled cores with a
hardness less than about 65 on the Rockwell 30T hard-
ness scale, loading a plurality of cooled cores into
an electrically non-conducting perforated container,
placing the container in an electroplating bath,
electroplating a metallic cladding onto the cores,
while moving the container angularly about a
horizontal axis, until a plating thickness of at least
about 0.01 mm has been deposited on each face of each
core and a thickness of from about 2 to about 4 times
the face thickness has been deposited on the circum-
ference of each core, and removing the cladded core
pieces from the container.
2. A process according to claim 1 wherein the
cores are of steel.
3. A process according to claim 1 wherein the
metallic cladding is selected from the group
consisting of nickel, nickel alloys, copper and copper
alloys.
4. A process according to claim 1 wherein the
steel has a carbon content in the range of from about
0.005 to about 0.1% by weight.
5. A process according to claim 4 wherein the
steel has a carbon content of less than about 0.01%
and the heated cores are cooled by immersion in water.
6. A process according to claim 4 wherein the
steel has a carbon content higher than about 0.01% and
the heated coxes are cooled at a rate to provide a
hardness of less than about 50 on the Rockwell 30T
hardness scale.

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7. A process according to claim 6 wherein
the heated cores are cooled at a rate of about
20°C/min.
8. A process according to claim 1 wherein
the cooled cores have a hardness less than about
45 of the Rockwell 30T hardness scale.
9. A process according to claim 1 wherein
the cores are of nickel.
10. A process according to claim 1 wherein
the cores are of cupronickel.
11. A process according to claim 1 wherein the
metallic cladding is bronze.
12. A process according to claim 1 wherein the
core is of zinc or zinc alloy.

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Description

PROCESS FOR PRODUCING COIN BLANKS

This invention relates to the production of coin
blanks suitable for minting into coins~ the term "coins"
being intended to cover not only coins used as currency
but also similar disc-like articles such as medals and
medallions upon which insignia is imprinted.
Because of the escalating cost of metals nor-
mally used for coins, attempts have been made to develop
satisfactory coins which are made of less expensive
material.s~ Prior proposals in this respect are disclosed
in United States patent No. 3~940r254 issued February
24, 1976, United States patent No. 4,089,7S3, issued
May 16, 1978, United States patent No. 4,176,014 issued
March 27, 1979 and United States patent No. 4,247,374
issued January 27, 1981. In these prior proposals,
a metal such as nickel or copper is electroplated onto
a disc-shaped steel core to produce a nickel or copper
cladding with a thickness of at least about 0.03 - 0.05 mm
on each opposed face of the core and a thickness on the
circumference of the core in the range of from about 2
to about 4 times the face thickness, and the cladded
core is heated to form a metallurgical bond between the
nickel or copper cladding and the core and to reduce
the hardness to less than about 65 on the Rockwell 30T
hardness scale. The resultant blanks are then imprinted
to form coins.


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In the heating step in such prior proposals,
care must be taken to ensure that the smooth external
surface appearance of the cladded core does not deteri-
orate. It is therefore an object of the invention to
provide a process which OverQOmes this problem.
The present invention is based on the
discovery that satisfactory coln blanks can be produced
by annealing a metal core to reduce its hardness to less
than about 65 on the Rockwell 30T hardness scale, and
electro-plating a metallic cladding onto -the annealed
core to produce a thickness of at least about 0.01 mm
on each opposed face of the core and a thickness on
the circumference of from about 2 to about 4 times the
face thickness. In other words, the metallurgical
bond formed between the cladding and the core in the
prior proposals can be omitted, and the annealing of
the core can be carried out before instead of after
the electroplating operation.
Accordingly, the present invention provides
a process for producing blanks suitable for minting
into coins, comprising providing a plurality of
appropriately disc-shaped metallic cores, heating the
cores to decrease their hardness to less than about 65
on the Rockwell 30T hardness-scale, cooling the
heated cores to provide cooled cores with a hardness
less than about 65 on the Rockwell 30T hardness
scale, loading a plurality of cooled cores into an
electrically non-conducting perforated container,
placing the container in an electroplating bath,
electroplating a metallic cladding onto the cores,
which moving the container angularly about a
horizontal axis, until a plating thickness of at least
about 0.0] mm has been deposited on each face of each
core and a thickness of from about 2 to about 4 times
the face thickness has been deposited on the circum-




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ference of each core, and removing the cladded corepieces from the container.
The metallic cladding may be nickel, a
nickel alloy, copper or a copper alloy, silver or
gold, and the cores may be of steel, nickel, zinc,
zinc alloys or other commercial coinage metals such
as cupronickel. The st~el may have a carbon content
in the range of from about 0.005 to about 0.1% by
weight. It has been found that, where the steel has
a carbon content of less than about 0~01~ the heated
cores may be cooled by immersion in water. However,
when the steel has a carbon content higher than about
0.01%, it has been found that the heated cores should
be cooled at a much slower rate, for example about
20 C/min, to provide the resultant required hardness.
Advantageously, the cooled cores have a
hardness less than about 50 on the Rockwell 30 T
hardness scale. The annealing step will usually be
carried out at a temperature of from about 800 to
about 1000C in a non-oxidizing atmosphere, for
example a reducing atmosphere such as hydrogen.
The metallic cladding may be applied in
the manner described in previously mentioned United
States patent No. 4,176,014, with a face thickness
of at least about 0.01 mm, preferably between about
0.01 mm and 0.1 mm.
Examples of the heating and cooling steps
will now be described.
Several disc-shaped steel cores of
different carbon content were heated to 900C and
retained at that temperature for 30 minutes in a
nitrogen atmosphere. After this heat treatment,
the cores were cooled by plunging them into water to
give an estimated cooling rate of more than 1000C/min.
The core hardness was then measured.

7~:~



A similar number of fresh cores were heated
as before, with the cooling in this test being slow
cooling effected by merely allowing the furnace to cool
down, the cooling rate in this case heing less than
1C/min. Other cores were then subjected to a further
test in which, after the heating step, the cores were
cooled under a nitrogen atmosphere at a rate of about
20C/min. The hardness of the cooled cores was
measured in each case.
The results of the tests are shown in the
following table, the hardness being measured on the
Rockwell 30 T scale.
Carbon Content Hardness Hardness HardnessO
(w/o) after water after slow after 20 C/min
cooling coolingcooling
0.0523 57 31 ~6
0.0758 63 31 4~
0.0814 66 32 46
0.10579 35 49
0.00832 31 23
It will be seen from the above table that,
where the carbon content was less than 0.008~, water
cooling ~as satisfactory but that, where the carbon
content was greater than 0.05%, the cooled cores had
a hardness which was too high. The very slow cooling
was satisfactory for the cores of high carbon content,
but such a cooling rate is rather slow for a
commercial operation. Cooling at a rate of about
20C/min is more satisfactory for the cores of higher
carbon content.
As mentioned earlier, the metallic cladding
may be of nickel, nickel alloys, copper, or copper
alloys. A nickel alloy may be nickel-iron and a
copper alloy may be copper-tin (i.e. bronze), with the
metallic c]adding of such an alloy being obtained by





co-depositing f,-om an electroplating solution
containing the -two alloy constituents. As also
mentioned, the core may be of zinc or zinc alloy, and
in the latter case an alloying element may for example
be cadmium, copper or magnesium.
Suitable metallic cladding and metallic core
combinations which can be used with the process of
the present invention are nickel on steel, silver on
nickel, copper on nickel, nickel on copper, nickel on
cupronickel, gold on copper on nickel, bronze on
steel, bronze on nickel, copper on steel and nickel-
iron on steel.
Other embodimen-ts and examples of the invention
will be readily apparent to a person skilled in the
art.