Definizione

• Metal Flow.  The movement of metal in a blank at the instant of striking as it flows into the cavities of the dies under pressure during striking in a press. Metal flow is this metal movement, the result is called displacement. Metal flow occurs throughout the mass of the blank, but is most severe at and near the surface. Surface displacement is the metal flow that creates the design, where the metal flows into all the contours and cavities of both dies. Metal flow can also (but not always) cause microscopic surface striations, parallel ridges and channels, generally from the outer rim inwards as the metal is displaced to the area of the greatest cavities of the dies. These striations, flow marks, are the cause of luster, and, very infrequently, cartwheel effect.
  The pressure at the instance of the blow to the blank is the power that generates metal flow. It is so strong during striking in a press that it can move metal deep within the mass of the blank. The surface metal that flows into the die cavities is replaced by adjacent metal, and this, in turn moves its adjacent metal. The movement continues until both surfaces of the blank fit the shape of both dies.
  Metal flow stops at the instant the dies are fully extended and there is no more pressure. However, in rare instances, as the dies retract some metal may spring back somewhat (by molecular memory) and cause die draw. This is cured in coining with a slightly stronger impression.  See also striking, suction.
      

  excerpted with permission from

  An Encyclopedia of Coin and Medal Technology

  For Artists, Makers, Collectors and Curators

  COMPILED AND WRITTEN BY D. WAYNE JOHNSON

  Roger W. Burdette, Editor

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