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Watch hairspring and method for making same

  • US 7,077,562 B2
  • Filed: 10/30/2003
  • Issued: 07/18/2006
  • Est. Priority Date: 11/25/2002
  • Status: Active Grant
First Claim
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1. A new hairspring intended to equip the balance wheel of a mechanical timepiece and in the form of a spiraled rod (10) cut from an {001} single-crystal silicon plate having a first thermal coefficient (C1) and a second thermal coefficient (C2) of its spring constant C, the turns of said hairspring having a width w and a thickness t, characterized in that said rod comprises a silicon core (12) and an external layer (14) of thickness ξ

  • formed around the silicon core and made of a material having a first thermal coefficient of the Young'"'"'s modulus of opposite sign to that of the silicon.

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