Coin blanks form 3C
|| Coin Blanks
Quality products ready for striking ||
Most of the properties demanded of a coin must already be present in the initial coin blank when it is ready for striking. The very narrow tolerances in the chemical composition of previous metals must also be applied to coin blanks as a security against fraud. Moreover,
the demand for minimum
deviations from the legally established piece weight must be established, since only a uniform coin blanks volume ensures a smooth operation of automatic minting presses, Whereas precious metals are
still classified by weight to guarantee the required tolerance, the production of nonprecious metals on an industrial scale must exclusively rely on suitable production processes. Weight deviations of cut blanks are mainly dependent on the variation in the thickness of the final strip used to make
the blank. Besides of the single piece-weight tolerance, the average weight deviation of a batch of coins plays a predominant role in transactions. Therefore, an even narrower mixed weight tolerance of, for instance, a lot of 300 pieces is regularly specified. During the final rolling operation of the coinage strip not only is it necessary to control variations within the strip, but it is also necessary to ensure consideration is given to the nominal weight tolerance to make sure the mixed lot tolerance is not exceeded.
In order to protect the coin design in everyday use the rim of the coin is lightly raised. With a view to facilitating the material flow under the pressure of the two coining dies, as the blanks leave the cutting press they are given an upsetting operation which produces a rim. Rim diameter and rim profile are exactly adapted to fit the coining tools. After the rimming operation the blanks are annealed and then are ready for striking. The anealing operation is controlled to give a uniformly low hardness without coarse grain formation as this is important for a perfect strike. However, even after an excellent bright-annealing, which can nowadays be applied, the blanks
are not still suited for mass coinage. They must first be subjected to a four stage surface treatment.
The stages are cleaning by washing (possibly pickling), wet burnishing, the application of lubricants and preservatives, and finally drying and dry polishing.
Coin blanks must be free from internal defects such as porosity, laminations, and, if applicable, cladding defects. Since even the most careful manufacture does not guarantee and absolute freedom from surface flaws such as scale, scratches, indentations and stains, a final visual inspection is carried out.
The stringent requirements as to precision and surface quality of coin blanks as mass produced products of high uniformity becomes understandable from the viewpoint of the mints. They are
equipped with high speed, electronically controlled machines and excessive dimensional deviations would result in stoppage and jamming with all the consequent cost of repairs.
Although minting presses are still working by the principle of knuckle-joint presses, they have been steadily improved and further developed. The initial performance of 40 strokes per minute has been raised up to 750 during the last few years. This means not only a high increase of the forming speed of the coinage material, but also of its running speed in contact with the coining dies. High-speed minting presses are only efficient and economical, if the relatively expensive coining tools have
a long and trouble-free service-life. This implies a growing demand for coinage blanks which are very accurate to size with a high surface finish. Increasingly faster and more complicated mechanisms have been developed for the transfer of blanks to the coining tools proper. This means that blanks of high precision and uniformity as well as with excellent anti-frictional properties are now demanded.
3C coin blanks meet these requirements.