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Rolling Mill

Rolling Mill.  A machine with multiple rollers through which metal in plate or ingot form is rolled back and forth to reduce its thickness to a required size, creating strips

for blanking. Rolling mills have developed dramatically over their history but the concept remains constant, to reduceee metal thickness. The rollers – of solid steel – are often stacked and rotate in opposite directions so a second pass needs only to be fed into a set of rollers above or below the set previously used (with an operator on each side of the mill). The number of passes is dependent upon the desired thickness, the original thickness and the hardness of the metal. Rolling work hardens the strip, which must be annealed or softened before blanking and sometimes before additional rolling.

By this continuous rolling action a thick ingot can be reduced to long strips of controlled thickness in a manner of minutes. The mill can be set to control the width of the strip as well as the thickness, thus the length of the strip becomes elongated. The thickness difference between the in-going strip and the out-going strip is called the draft.

Formerly most strips for blanking coin and medal blanks were cold-rolled (in contrast to iron and steel mills which employ hot-rolling). Recently the hot rolling process has been adapted for rolling clad coinage strips. In addition to a desired thickness and width, rolling also provides a desired smooth surface of the metal from the polished surface of the rollers. Modern mills have gauges that continuously monitor the thickness and shut off when the desired gauge is reached. For coinage blanks, this prescribed thickness is called thickness strip and a different thickness strip is required for each denomination coin.

Parts of the rolling mill.  These include the housing of the rollers (as a three-high

blooming mill has three sets of rollers). The rollers are smooth steel drums and when stacked, say three high, the center roller is used with the adjacent roller. There are also straightening and cooling tables (where the strip extends between passes), slitters (where the strip is cut lengthwise), cutoff shears, coilers and decoilers (for rolling up and unwinding the strip); roll grinders and gauges. The rollers are run by heavy duty flexible direct current motors.

Today a typical clad coinage strip roll is 1,000 feet in length, and weighs between

3,000 and 7,000 pounds. Modern blanking presses accept this strip and with multiple blanking heads cut out as many as thirty blanks with each cycle of the press – the number of blanking dies determine the width of the strip and the number that can be blanked at one time.

History of the rolling mill.  Leonardo da Vinci was the inventor of a primitive rolling mill and published this in his sketchbooks in 1495. Thirty years later Renaissance artist Benvenuto Cellini used a rolling mill to roll lead for lead seals he struck for Pope Clemente VII (1523-34). Other goldsmiths in central Europe, like Cellini, used rolling mills and were the first to develop machines beyond these primitive mills. They needed thin strips of precious metal for their work (and even used rolling mills to make the first clad gold strips – rolled gold).

The first rolling mills for blanking of coins was developed by Max Schwab (1550) in Augsburg, Germany, along with an improved screw press he developed. The French ambassador at Augsburg learned of this equipment and was instructed to procure these for King Charles V's mint in Paris. A worker at the Lyons mint, Aubin Olivier, was sent to Augsburg, instructed to learn these machines and return with them to Paris. He arrived 31 January 1551 with a rolling mill, draw plates, a blanking press and the screw press that Schwab had improved and built.

These were placed into use at once, and by 1552 blanking was accomplished in France by Antoine Brulier. Attempts to improve the rolling mill in this period were mixed. Nicholas Briot, first at the Paris Mint (1606-25), then at the London Mint (1633) and finally at the Edinburg Mint (1635-39) worked on the rolling mill as part of his attempted coinage by roller die (taschenwerke). Despite these early attempts,

this form of coinage blank manufacture was in wide use with improved mills during the 1700s.

By 1787 Matthew Boulton was producing strips and blanking in quantity at his metal plants and Soho Mint in Birmingham. Joseph Bramah, also a manufacturer of Birmingham, had perfected his rolling mill and was supplying these to Boulton. Later, Henry Maudslay was manufacturing rolling mills following the establishment of his firm, Maudslay, Sons & Field (1810), along with other specialized mint tools, and later, counting machines.

By the mid 1800s Ralph Heaton was manufacturing rolling mills for coinage mints. Since then rolling mills have been manufactured in many industrialized countries by numerous firms (they are so widely used in the metalworking field).

In Boston Paul Revere built his own rolling mill about 1790, the first such rolling mill in America. He used this for his silversmith craft, but found it useful for other metals as well.

When coins were first produced by a blow to hand-held dies, this form of production was called hammered. With the introduction of the rolling mill and striking by the screw press, the process was called mill and screw, milled coinage, or simply milled. These terms were derived from the rolling of metal by the rolling mill prior to blanking. This form of metal processing has been in use from 1550 and every mint since then has required the use of a rolling mill if they do their own production of blanks. All struck coins since then have been milled. In truth, no struck coin or medal could have been made without the use of this equipment in the last 450 years!

Types of mills.  Early metalsmiths used only one rolling mill to reduce thick metal into thin (often in combination with drawing plates). In the 19th century, mills were created to accommodate ingots of virtually any thickness. These first-step mills were developed in England and called breaking-down mills. (Americans shortened the term to

break-down mill.

An ingot would be filed smooth on all sides (deburred) and swaged (flattened) on one end (the British called this step "topping.") The end that was flattened was fed between highly polished solid steel rollers; it would reduce the metal thickness and the newly stretched strip would emerge on the opposite side of the mill.

Perhaps three or four passes between these rollers could be accomplished before

the strip could become so work hardened further rolling would be pointless. Special heat treating ovens were developed with long canisters to contain the strips to heat and gradually cool the metal to soften it. The strips could then be rolled again or blanked as needed.

Ultimately a second type mill was developed, a finishing mill. These rolled the strip to a precise thickness and often had gauges attached to the mill to automatically measure the thickness; when a precise gauge was reached it would halt the rolling at a precise gauge. Thus thickness strip could be easily produced in the finishing mill, then taken to the blanking presses.


C43 {1966} Gilbert, rolling mill, #21, p 19-20, plate 4.

C66 {1988} Cooper, [early] p 88-93; [modern] 179-185.

excerpted with permission from

An Encyclopedia of Coin and Medal Technology

For Artists, Makers, Collectors and Curators


Roger W. Burdette, Editor

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