The materials of ordinary commemorative coins are gold, silver, platinum, palladium, two-color copper alloy, copper-zinc alloy, copper-nickel alloy, nickel-plated steel core, brass alloy, gold and silver inlaid, and copper alloy. The materials of commemorative banknotes are paper and plastic.
Currency theme
Roughly can be divided into 15 series, more than 240 sets.
Age of money
One set a year has been available since 1979.
Shape of money
Can be divided into circle, rectangle, plum shape, fan, polygon and so on.
Process of money
With the application of many new technologies in the coinage industry, the casting technology of metal commemorative coins is improving day by day and the technological level is constantly improving. The casting process mainly includes the following steps:
Material selection and identification
Silver coins are generally made of pure silver with the purity of 999, until they are made of silver-copper alloy containing silver 500. The most used in the world are the finished colors of 925 and 900. Gold coins are usually cast in gold or copper alloys such as 9999, 9999, 22K.
Melt-rolled strip plate
Molten metal from an electric furnace is passed through a continuous casting machine to form slabs of various sizes, the surface is mechanically milled to remove impurities, and then cold rolled under extremely demanding environmental conditions. A polished strip with a very small thickness tolerance is rolled out on a special finishing mill with an error of less than 0.005 mm.
Wash the cake and wash it
The minimum burr and optimum edge must be obtained when the strip is placed into the blank cake flushed out by the punch press. The surface of the billet is dried with a special cleaner, and each billet is weighed. The accuracy of the electronic scale is 0.0001 grams.
The mould
Mold design is a unique and important link in coin making process. After strict examination of the subject matter, patterns, through the mint's complex and superb engraving, combined with the use of modern precision equipment, the design of the chart mold.
embossed
Embossing is carried out in a purification chamber with air filtration. Any tiny dust is the root cause of coin scrap. Internationally, the scrap rate of embossing is usually 10%, and for coins with large diameter and large mirror area, the scrap rate is as high as 50%.
Protection and Packaging
In order to maintain the original color of the commemorative coins within a certain period of time, the surface of each coin should be treated and then sealed with plastic film.
In order to make the coin better and reflect its design theme, mint engineers have also developed a number of new processes during the coin minting process. For example:
1. On the basis of circular coins, special-shaped coins are added, which mainly include: rectangle, polygon, fan and plum shape.
2. On the basis of natural color coins, we developed a series of color coins. That is, we printed color patterns on the side of gold and silver coins by special process to increase the new artistic effect of gold and silver coins.
3. In casting, sandblasting, high relief and other processes are also widely used. The pattern part is sprayed into a very fine frosted surface, in the production of gold and silver coins, the pattern part appears a layer of beautiful silver; Or make the pattern higher than the currency surface, increase its three-dimensional and hierarchical sense.
4. On the basis of single metal coin, bimetallic coin and partial gold-plated silver coin are developed. One coin is made of two different colors of metal with inner and outer rings, such as gold core and silver outer ring; Partial gilding of silver coins refers to the partial inlaying of metal patterns on silver coins.