EXPANSION

Expansion is the phenomenon by which a body sees its dimensions and volume increase mainly due to a rise in Temperature. In watchmaking, this behavior is decisive, as thermal variations alter the geometry of components and, consequently, the running of the Timepiece. The expansion of the Balance and the change in Stiffness (spring rate) of the Hairspring (balance spring) with temperature were long a major source of error, which watchmakers fought using the compensating Bimetallic balance, and then alloys with a low coefficient of expansion such as Invar and Elinvar. Each material has its own expansion coefficient, which requires particular attention when assembling parts of different natures, otherwise excessive set or jamming may occur. Mastery of expansion also plays a role in heat treatments, the fitting of jewels and the water resistance of cases. It remains a key parameter for chronometric stability.

Useful link:

– Steels (Invar, Elinvar)