Making a Mint One of the UKs oldest money makers uses

a Mint
One of the UKs oldest
money makers uses
modern technology to
help supply the world
with affordable coins
By Stewart Hildred
When the Royal Mint in the UK
became a leading manufacturer of
affordable coin blanks, a feature
article by British journalist Stewart
Hildred described the modern,
automatic barrel plating process in
the June 1991 edition of P&SF. Here,
in a follow-up, Hildred tells how
circumstance has led a sister mint in
Birmingham, England, to become
even more producjive, in order to
meet the global demand for coin
blanks that cost less to make than
their face value.
US gallons of eleclrolyle solufion.
nal Birmingham order was increased to
Because of the success of the Royal
Mint, with its high performance and reliability, the manufacturer and designer of
the equipment received two additional
orders for similar installations. One was
for the IMI Mint and the other for the
famous BirminghamMint, both located in
Birmingham. Initially, both companies
hen the Royal Mint at Llantrisant wereset tospend about thesameamount
in Wales (UK) opened a new for similar equipment.
Within a short time, however, the Birplating shop in 1991,the design
and production capabilities of the equip- mingham Mint was the subject of a takement made it one of the largest and most over by the IMI Group. As a result, two
modern in the world. The automatic pro- different manufacturing lines in the same
duction line is a nickel barrel system for locationwere nolonger required. Instead,
plating mild steel coin blanks. The blanks the original specification for the Birmingare made of a metal worth less than its ham Mintwasupgradedbythenewownface value. They are used for coin mak- erssothattheoutputoftheproposedline
would bedoubled.Thevalue oftheorigiing around the world.
A new production structure was added
to the existing Birmingham Mint, a large
buildingdating backmore than 300years.
The plating line was delivered and installed on schedule. Plating trials began
in early August of 1992,followed by the
first production run about a month later.
The completed line at the Birmingham
Mintisvelysimllartothemintat Llantrisant
because the basic specification is about
the same. The line was built of standard
modular“ construction with coated steel
Improvements in computer software make it easierto monitor andmanage me completeplatlng
process at the Birmingham Mint.
‘Both the Birmingham and Royal Mint lines were designed,
builtand installed by Veralronlc Lld., Ayiesbury, Buck$. UK.
sbout 400 million coins a year.
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frames supporting the tanks, pipework
andfascia panels. Thisdesign allowsfor
easier construction, testing, and faster
installation. The line can also be extended or modified without difficulty.
The plating line is 40 meters long with
16 nickel stations and contains about
15,850 US gallons of electrolyte solution-the same used for coin production
by the Royal Mint.
Within the first year, the Royal Mint
completed 9,000hours of productionwithout a major breakdown. It was producing
at the rate of about 35,000 plated coin
blanks per hour.
The Four-Barrel Rig
The major difference between the Eirminghamandthe RoyalMint isthebarrel
system. The Royal Mint operates with
twin barrels on a single transporter. Eirmingham has a single transporter, but
with a four-barrel rig unit, designed to
carry 1.2 metric tons. This, with other
additions that enhance productioncapabilities, gives the unit a capacity of about
2,000 tons of blanks per year (about 400
million coins). That is about double the
Royal Mint output.
June 1993
Atfirstafour-barrel design wasconsidered to be fallible, but the potential problems associated with vertical pairs of
barrels were eliminated by the transporter control systemsoftware,designed
in-housebythe manufacturer.Oneofthe
common problems associated with plating coin blanks in the bottom pair of
barrels is the possibility of discontinuity
caused by silting up of the bottomsof the
anode baskets. A measuredreduction in
the lower barrel load, and additional software control, corrected this.
Particular attention was given to the
design of the plating barrels to prevent:
(1) blanks sticking to the sides of the
bariel; (2) blanks sticking together; and
(3)the entrapmentof blanksat lidapertures.
If there is a power outage during the
plating cycle, peculiar bipolar effects can
be experienced.This can cause one side
of the blank to dissolve, but the other side
to plate excessively, producing unusual
growth effects.
The line is fitted with a fully automatic
loadlunload system such as the one at
the Royal Mint. The operator station at
the loadend isdesigned forchecking the
dangler cathode contacts and cleanli-
ness of the barrels, as well as for replacing the barrel lids when the rig is back in
position. This operation has been made
fasterand more accessible by the use of
a light curtain rather than an interlocked
sliding mesh gate. A cross-transfer trolley enables the barrel rig to be loaded
automaticallyoff-line, so that the lids can
be refitted before the rig is placed back
into position.
Becausethe rating for rectificationon the
line needed to be 0-2Ov at 1500A, a
recently developed "D"series design of
air-cooled rectifiersbwas used as a basis
:or the system.
These thyristor-controlled units, with
matched harmonic filters, also occupy
about half the spaceofconventionaltransformer regulators. The rectifier room at
the Birmingham Mint, however, is about
the same size as that at the Royal Mint.
The"D series incorporatestwosetsof
semiconductor devices. A three-Dhase
'Supplied by Electronic Power Sewices 01 Leeds. YorkShire, UK
thyristor stack, to provide the facility with
full, stepless, outputcontrol, isconnected
on the primary side of the transformer,
while a six-diode assembly is connected
into the secondary. Thyristorcontroland,
hence, output control, is provided by a
firing m o d u h well-triedand tested unit.
The main deviation of the rectifying
system from the standard design is in the
packaging of the units. The installationin
the special rectifier room comprises 36
units standing side by side. At the time of
installation, provision was made to bus
bar entry at the rear of each unit-with
access into the control circuitry at the
front. Valuable space was saved by employing this method and by using lowprofile rectifier cubicles. Each unit has its
own cooling fan because the cabinets
are so close to each other.
The 16-bit data driver interfaceEwas
designed and built specifically for the
Birmingham installation and has since
been used successfully with other comMultiplehandlingallowsmaximumplatputer-controlled automatic lines.
ing line utilizationwhen there are several
batches of work loaded on the system at
any one time, all at different stages of
Another important facet of the Birming- preparation and plating.
ham line is the heating, which is govAstandardtime-waywritingfacilityhas
erned by a low-pressure, closed-loop, been incorporated intothe computer systhermal fluid heating and monitoring tem, and libraries are generated so that
system.cThe low-pressure,closed-loop, job requirements can be manually enthermal fluid system is Smaller and more tered into the processor library. Thoucompact than conventional steam heat- sands of job types may be stored and
ing units of similar output.
retrieved easily with their appropriate
A natural gas boiler with a highllow parameters. Such elements as heating,
burner supplies heat to the degreasing filtration, pH measurement, solution dostanks, eight nickel tanks and three off- ing, manual control of all the transporter
line storage tanks (though these are movements, safety interlocks, temperaheated by a separate system). The de- tureandotheralarmsystems,etc., areall
signers produced a heating system using covered by the system and reloaded with
air-operated ball valves, instead of di- each job.
rect-acting temperature-type controls.
Process times can vary between 15
Visual temperature adjustment and minutes and 15 hours, depending on the
monitoring is by way of a computer video metal deposited and the plating specifidisplay unit. The method is designed to cation to beachieved. It is imperativethat
lower operating costs to about two-thirds all process parameters are monitored
of an equivalent electrical system. The throughoutthe platingcycle. Barrel loads
system is accurate to plus or minus one that do not receive correct plating curpercent of optimum.
rents, etc., are identified for a quality
check and then rejected or accepted.
Plant Control System
Continuing improvements by the designer, in computer software for overall
plant monitoring and management, have
assured that the use of thyristor rectification and the low-pressure heating
has been readily absorbed into the operating system.
-~_ _ _ _ _ ~ ~
'Jointly developed by VeP1~onIcand Wanson Company
Lld., Borehamwood, H e r l ~UK.
Other Features
The weighing and loading system has
been enhanced. A conveyor takes the
steel blanksuptothemainhopper,where
measured weights are deposited into a
weigh pan directly below, and then into
the barrel chutes. The same intrinsic
weighing accuracy has been retained.
Unloading is automatic after the barrel
lids are removed, The transporter re.
the rigfrom the load station and
emotiesthe barrels onto a stainless steel
The weighing an0I loading System is
automatic and de;signed for amuracyand
primary drainage tray. The plated blanks
are then fed into two off-line vibratory
driersfilledwithMaizeorb.Thedry blanks
are discharged into stillages for immediate removal by lift truck to the next process.
The plating line uses a conventional
filter system withcontinuouscarbontreatment. Fume scrubbing chambers are
used to remove exhaust gases at tank
level to an exterior stack.
The Systems Are Flexible
The comparisons made here between
the Royal Mint installationand that of the
Birmingham Mint serve only to illustrate
some of the design options incorporated
into each of the plating lines. It is important to note that no suggestion is made
that one system is better than the other
because each company has its own production requirements and installation
specifications. In both cases the equipmentsuppliedallowstheuserstoexpand
the system at a later date.
About the Author
whosetup hisownbusrness about 14 years
ago, offering technical
services to the electmnics industty He worked
closely with thesurface
specializingin this market, withan emphasis
onPCBproduction. Heworkswithsomeofthe
leading UK equipment and consumables
manufacturers. His address is Leadercross
Marketing & Public Relations, 177 Bideford
Green. Linsiade, LeightonBuzzam:BedsLU7
7TS, UK.
Plating & Surface Finishing