Definição

• Metal Stress.  The force on areas of a die where the metal cannot endure continued pressure, ultimately to cause some unstable area of the die to break. Metal stress is caused by the constant pounding of the die during striking. It usually occurs where the die has to move a relative large amount of surface metal into cavities by deformation during striking. There is a great deal of stress around the area of lettering in a legend, and from this area to the rim of a struck coin; this is the beginning location of so many diebreaks caused by stress.
  Another susceptible area of metal stress is in the loops of certain letters (as the center of an O or D, or the loops in A, R, P or figures 6, 8, 9). In the die this is a tall projection and is susceptible to breaking off. When this breaks it causes a filled letter. (The latter can be eliminated somewhat by the champs levée process.)
  There is no curing metal stress once a die is made. It is a natural function of steel in the die during striking on a press. The best prevention of breaking a die as a result of metal stress, however, is proper die design in the first place.
  In modern times, high quality die stock can be obtained from special steel firms (which can even supply vacuum melt steel – with no air pockets). Also die stock can be tested in advance to insure that the steel in which to make coining dies that can withstand the metal stress it will inevitably have to endure.
       

  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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