Comment
Author: Admin | 2025-04-28
The copper blank and then punching out a small hole, and next inserting the silver plug, and finally striking the coins using the appropriate dies. Outer Rings Another type of bimetallic coin is where there is a large core of one metal with a ring (of another metal) around the core. This type of bimetallic coin has been increasing in use over the past decade. A few examples are: aluminium bronze centre in stainless steel ring - eg Australia 5 dollar (1996 Bradman) aluminium bronze centre in cupro-nickel ring - eg New Zealand 50 cent (1994) silver centre in gold ring - eg Austria 500 schilling (1995 Austrian membership of European Union) bronzital centre in acmonital ring - eg Italy 500 lire (1982-95) Clad Centre with an Outer Ring Another type of "bimetallic" coin is where there is a large clad core of three metals with a ring (of another metal) around the core. Although this is not actually a bimetallic coin, they appear to be, and are probably being considered (and collected) as bimetallic coins. nickel-brass clad nickel centre in cupro-nickel ring - eg European Union 2 euro (2002) cupro-nickel clad nickel centre in nickel-brass ring - eg European Union 1 euro (2002) Production of bimetallic coins The image to the right illustrates one method of joining the bi-metal blanks. The external ring is manufactured by a mulitple-die progressive tool, which pierces out the center hole prior to blanking from a strip. The raised outer edge of the blank, formed by "rimming" assists in reducing the coining pressure. The inner, or "dump" is made very much like an ordinary coin blank, except for the special milling applied to the edge. When the two components are struck by the assembling press, the outer ring deforms to flow inside the milled indentations, providing efficient anti-twist locking and increasing the strength of the bond. This method is used by Krupp VDM, a leading German coin blank manufacturer. There are other ways of joining bi-metal blanks, with each manufacturer having their own preferred method. The force required to expel the inner ring in the Krupp method would utterly destroy the coin. Krupp reports the force needed to expel a 17 mm inner from a 25 mm outer ring would be 450 to 510 kPa, or a pressure of approximately 68 to 72 pounds per square inch. If two or more sheets or strips of metal are laid on top of each other with a sheet of high explosive above and below them, and the explosive is detonated, the sheets or strips of metal are welded together and appear (from the edge) to look like a sandwich. The resultant metal sandwich is then referred to as a "clad" metal and it can be worked in similar ways to other metals, including the various processes to make coins. The Federal Republic of Germany (ie West Germany) used several clad metal combinations for their coinage. Bronze clad steel was used for 1 pfennig (1948-49) and 2
Add Comment