WatchTime - August 2012

A
hairspring is minuscule, but its importance cannot be overestimated
– a mechanical timepiece simply won’t work without it. At just
3/100 of a millimeter thick, this tiny spring is thinner than a human
hair. It weighs only about 2.5 milligrams. But if you remove it from
a movement, the watch will grind to a halt instantly. Without the tiny
spring, the balance (the hairspring’s partner, to which it is attached)
will stop oscillating after just one beat. The gear train will also stop
dead in its tracks because it lacks the life-supporting energy the hairspring
provides. It’s no wonder that the hairspring is called the
“soul” of a mechanical watch.
Ambitious watchmakers and engineers have devoted themselves
to this tiny component for decades. Few secrets remain.
Contemporary hairsprings are made from an alloy known as
“Nivarox,” a name coined from the French acronym for “neither
variable nor oxidizing.” Reinhard Straumann (1892–1967)
perfected the process of hairspring manufacturing using Nivarox
in his Waldenburg, Switzerland, laboratory in 1932,
120 WatchTime August 2012
Four metal strips are wound into hairsprings at A. Lange & Söhne.
which greatly improved the accuracy of watches. Nivarox consists
primarily of iron, nickel and chrome, with additional mixtures
of very small amounts of beryllium and other ingredients.
Straumann’s patent from the 1930s specifies the formula for
the Nivarox alloy, but he never divulged all the details of his secret
blend. The exact formula is known only by a select few individuals
at Nivarox-FAR, a subsidiary of the Swatch Group.
These tiny springs function almost perfectly with
monometallic balances made from Glucydur, a blend of beryllium
bronze, brass and nickel. The theory on which the rate behavior
of mechanical watches is based is complex enough to fill
many volumes, but we’ll make a long story short: each semi-oscillation
of the balance and its hairspring should be as nearly
identical to every other beat as possible, regardless of shocks,
magnetic fields and fluctuations in air pressure and temperature.
When this is achieved, the device is said to oscillate with
perfect isochronism. Temperature fluctuations cause particularly
drastic changes in the length and elasticity of the metal strip
that forms the hairspring. In simple bronze hairsprings, an increase
or decrease of just 1 degree Celsius can cause a watch’s
daily rate to deviate by as much as 10 seconds. But thanks to the
negligible temperature coefficient of Nivarox, hairsprings made
from this alloy can reduce the daily deviation of rate to just half
a second.