Coin mfr. from composite metal strip - prevents counterfeiting by showing colour differences of metals at coin edge

摘要

Coins which are difficult to counterfeit are made from a composite strip of metal. A strip of copper-nickel alloy containing 2.5% nickel is laid between two strips of copper nickel alloy containing 25% nickel. The strips are then heated to 1050 deg.C and rolled together to the required overall thickness. After cooling the strip, it passes under a press which stamps out coin blanks. The coin blanks are then reduced in dia. by about 0.1 mm by turning or gainding. This machining operation ensures that the edge of the inner layer of metal which is of a different colour to the outer layer, is visible even after long use making it easier to identify counterfeit coins.