Making 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. f1.7million. 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 W Improvements in computer software make it easierto monitor andmanage me completeplatlng process at the Birmingham Mint. 16 ~ ~~ ‘Both the Birmingham and Royal Mint lines were designed, builtand installed by Veralronlc Lld., Ayiesbury, Buck$. UK. . ,. sbout 400 million coins a year. Plaling & Surface Finishing E N V I ~ ~ I ASYSTEMS'WITH T~~ AQUA-PORE'" You've followed expert advice. .. You've i d o l l e d an expensive wastewoter treatment system But you still aren't in compliance. .'.. A better way. A 199Os'technology far oheod of conventional treatment methods- becoming better known every day: lonics' new AQUA-PORE'" membrane. 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Combine innovotive chemistry with AQUA-PORE'" tubular membranes to precipitate and remove toxic metal compounds from wastewaters. Upgrade. Compact AQUA-PORE'" membrone filtration modules integrate into your existing system, preserving a good shore of your equipment investment. IDNICS, INCORPDRATED Telephone: (617) 926-2500 CORMORE INCORht&TIONABOUT AQUA-PORE'" AND ENVIROMIT'" SYSTEMB CALLTOLL CREE 1-800-338-9238. R e a DetallsClrcla 157011poslpald reader ssrvlcecard. 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. Rectifiers 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 17 ~ . ~~ 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 Heating 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. . 18 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 efficiemy. 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 StewatiHiidredisajournalistandphotographer whosetup hisownbusrness about 14 years ago, offering technical services to the electmnics industty He worked closely with thesurface iinishingindustrybefore 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