02.coin manufacturing

8/6/2019 02.Coin Manufacturing

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MANUFACTURING

OF COINS

by,

SARAVANAN S

0205-PGTE



Coin Diagram with Terms and

Definitions



DEFINITIONS

� Device - a design element on the coin such as abust of a person, and eagle or any other element. Usually the devices are raised, but onsome coins they are below the coin surface(incused).

� Rim - A rim is where the edge and the obverseand reverse sides of the coin meet. On manycoins there is a raised rim as shown above. The

rim can be seen on both the reverse andobverse on this coin. The rim is used to helpprotect the coin from wear, by providing a raisedsurface right around the circumference of thecoin.



� Edge - The edge of the

coin is called the "third

side" by some. The edge

can be plain (smooth),reeded, ornamented, or

have letters embossed

into it. The edge is the

side around the

circumference of the coin,the edge is not the same

as the rim, the coin rolls

on its edge.



Obverse - The face or front of a

coin. "Heads." Usually has a

person, date on this side, but not

always

Reverse - The back of the coin. "Tails." Usually has secondary

design elements, the denomination, and other inscriptions. But

not always (look at some modern commems).

Fields - The open areas of the design, usually they

serve as the background and surround the devices.

Clean fields are desired in rare coins. Fields that do

not have bag marks and are mirror smooth can

raise the grade of a coin.

Denomination - The monetary value of the coin

Mint mark - the mint that produced the coin usually stamps a

mint mark for the coin. This shows what mint struck the coin.

Most common in the U.S. are S, P, D, CC, O, and WW.



Legend - The words on a coin are the legend or inscription.

Motto - an inscription that has special meaning in the country,such as "In God We Trust" -- the motto of the U.S.

Exergue - The area set off from the design for the date. Many times

this can be delineated with a line or depressed area. (See the buffalo

nickel.)

Dentils (aka Denticles) - the small serrated edge around the rim (tooth-like design around the circumference of the rim). Sometimes small dots

can be used, but often, just a gear-like design



Coin Dies

� Reverse and obverse

coin dies for the

spectacular 100 Escudo

gold piece, the largest

Spanish coin ever struck

at 76mm in diameter and

over 11 ounces in weight,

an exclusive issue

produced only at theRoyal Mill Mint of

Segovia. Click on picture

for full size photo



COMPOSITION OF

US COINS� standard alloy of 95 % Cu and 5 % Zn ie.,copper-plated zinc.

� Homogeneous alloy 75 %copper and 25 %

nickel (five-cent coin )� "clad" coins (ten-cent coin, quarter-dollar

coin, half-dollar coin and one-dollar coin)produced from three coin strips that are

bonded together and rolled to the requiredthickness.



MANUFACTURING

� Coin strip is fed into high-speed automatic

presses which cut the coin blanks, known

as planchets

� The cupronickel planchets are softened by

annealing in a special furnace

� then they are chemically cleaned in large

rotating barrels & dried



� Next, the planchets are put through anedge-rolling operation in the upsettingmachine

- edge hardens during this process

- It also removes any burrs

� Finally, the upset planchets are stamped

with the designs and inscriptions to makecoins



� Generally, the manufacturing process is

the same for all denominations

� The difference is the marking with tiny

ridges -"reeding´(a safety measure)

� After striking, each coin is inspected

� The coins are then counted and bagged

� Each bag is weighed before shipment to

ensure that it contains the correct number

of coins.



SOUTH AFRICAN MINT

ANNEALING� During the annealing process the coin

blanks are softened by heat treatment in

preparation for minting.

� All coin blanks are polished after heat

treatment to give them a high quality

surface finish and special anti tarnishing

chemicals are added to the polishingprocess.



BLANKING

� Blank circular discs are punched out of metal strip.

� Each of the four high-speed blankingpresses can produce 4000 coin blanks per minute. (At this stage unique edgemarking is applied to coins if required by

the client).� Each coin blank is rimmed before it is keptin the blank store for the next process.



COINING

� The prepared coin blanks are coined on

one of thirteen high-speed presses, each

producing 750 coins per minute.

� Finished coins are continuously subjected

to rigorous quality control inspections.

Coins in traditional alloys, electroplated

coins and bicolour coins are minted in thisdepartment



CAST-COINING

� The Chinese minted

coins by pouring molten

metal into molds - known

as casting - from before

the Christian era up until

the latter part of the

ninteenth century. The

molds and cast coins

shown above are fromMorocco, from the mid-

nineteenth century



SOUTH AFRICAN MINT

� The first step in the creation of amaster die is 3D modelling of thedesign in plasticine, followed byrefinement in fine plaster.

� An acrylic model of the

completed artwork is reducedand cut in steel by precision 3D reducing machines. The South

African Mint also uses computer controlled engraving machines

for high volume production items.� Cut steel dies are turned into

master dies from which theproduction dies are reproduced.



ELCTROPLATED COINS

� The manufacturing of bi-coloured coins bymeans of the electroplating process is oneof its more recent coin product

developments.Material Handling Devices

Material Handling Devices (MHDs) includestores, cranes, Automated Guided

Vehicles (AGVs), conveyors, drop-sections and automotors



Rolling Mill

� Coils are rolled on modern computer

controlled rolling mills to produce strip of

the correct thickness. Electronic

measuring equipment controls the rolling

gap and produces a product that is within

eleven microns of the required thickness.

These tolerances are essential indetermining the final mass of the product



Hammer-struck coining

� The hammer-struckmethod was used for minting coins ever

since they were firstinvented around theyear 700 B.C. inTurkey, up until thelatter part of the

nineteenth century insome countries suchas India



� Hammer-struck coins had very irregular

edges which inspired the illicit art of

clipping bits of gold and silver from them

before returning them one by one to

circulation. The roller-mills, as used in

Segovia, produced coins with almost

perfect edges, thwarting unscrupulousindividuals from performing their illicit

practice



Roller-mill coining

� The coin rolling-mill was firstconceived by Leonardo daVinci and became popular inEurope around the mid-sixteenth century. This was thetype of machine employed inthe Segovia Mint to "roll" (not"strike") coins from 1586through 1772 when screw-presses were finally installed.The rolling-mills (with smoothinstead of engraved roller surfaces) continued to be usedin Segovia however to preparethe metal strips, and aresimilar to machines used inmints today for the samepurpose



J APAN MINT PROCESS

� Silver plates are

mechanically

impressed with the

design of the master die. (IMPRESSING)

� Unneeded portions

are trimmed with a

fret saw. (TRIMMING)



� The blank is finished

by filing. (FILING)

� The impressed blank

is glazed withcloisonne enamels.

(GLAZING)



MELTING

� Coinage materials are melted in an electric

furnace, and ingots are produced by acontinuous casting machine



HOT & COLD ROLLING

� Ingots are heated in a soaking pit. While hot theyare rolled out and made into coil shape. This isfollowed by rough and finish rolling to completethe rolled plates having the thickness of thecoins to be produced.



BLANKING

� Blank discs are punched from the finished

plates. These are what we call "Engyo" (blanks).



EDGING

� To sharpen the images of coins, the peripheries

of the blanks are edged. This is followed byannealing to soften the blanks



COINING

� By means of a coining press fitted with a

coinage die, finished blanks are stamped withobverse (head) and reverse (tail) patterns and

milled at the same time if milling is required.



INSPECTION

� The patterns of each stamped coin are

inspected, and imperfect products are taken out.

Accepted coins are strictly counted and then

bagged.



EDM-CNC

� Coining dies can be made in cad-cam for cost savings in thesimpler designs, for the better, portrait-like designs the bestway is to sculpt a clay model at nine inches in diameter andcast it in epoxy resin. Then we use the finest machine availableto reduce the size and cut the die into steel. (the same reducingmachine that the U.S. Mint uses). We have two automaticJanvier die sinking machines with high speed precisionspindles used for this. The die can thenbe shot with glass bead(if a frosted look is desired) and polished to near proof quality.The sculptors we have available are among the best. We cancreate a sculpture from artwork, or this can be supplied.

�



Screw-press

� This screw-press was made inthe Seville Mint in 1735 andinstalled in the Segovia Mint tostrike a new series of copper coins which began in 1772.

After this date the roller-millswere only used to prepare themetal strips from which theblanks were cut, and not to rollthe coin designs onto the stripsas before. This press is

presently on display in the Alcazar castle of Segovia

02.coin manufacturing

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