Everything you need to know about the watch balance spring: function, origins and materials
The balance spring is an important component in a mechanical watch movement. When combined with the balance wheel, the balance spring acts as a regulating organ. It acts like a spring for the balance wheel, returning it to its starting position with each oscillation. In other words, the balance spring keeps time. More specifically, the balance spring compresses to balance the force applied, then expands to return the balance wheel to its starting position. It therefore allows the automatic watch to have true precision. The spiral, together with the balance wheel, constitutes what is called the resonator of the mechanical watch, which is responsible for fixing, in the most stable way possible, an oscillation frequency.
- Physically, the spiral is a small spring wound in the plane
horizon The spiral is extremely thin; to give you an idea, it's thinner than a human hair, less than 0.03 mm thick, and weighs less than 2 mg. Spirals are often made of steel, but some watches are equipped with silicon balance springs. The balance spring is an essential component of the watch and one of the most complicated to design because of its thinness, fragility and length. - Once assembled with a balance wheel, the balance spring rotates in one direction, then the other, meaning it oscillates around its equilibrium position. If the balance spring does this regularly, it produces a recurring phenomenon and becomes a basis for counting, which the gears then convert into seconds, minutes, or hours. The balance spring receives the energy produced within the watch and calibrates it so that this energy is translated into information.
The origins of the watch spiral
The spiral was invented in antiquity. This type of spring was used, for example, to fasten fibulae, the ancestor of safety pins. It is also found in medieval locks, and later used to power the mechanisms of balance spring watches.
Its use as a watch regulator dates back to the 17th century. Three men, including two renowned scientists, disputed the first application: Abbé de Hautefeuille, Christian Huygens, and Robert Hooke. Around 1675, the Dutch physicist, mathematician, and astronomer Christian Huygens invented the use of a spiral spring combined with a flywheel to regulate watches. Huygens presented his first watch with a spiral spring in the "Journal des Savans," entrusting its production to Isaac Thuret, one of the best watchmakers in Paris. However, when he tried to register his discovery with Parliament, Abbé Hautefeuille opposed it, explaining that he had already conceived of the idea. Meanwhile, the Englishman Robert Hooke, also an astronomer and mathematician, made an identical proposal for the use of the spiral spring as a watch regulator. He then challenged Huygens to claim authorship of this invention.
A watch balance spring that sparks debate: metal or silicon balance spring?
The balance spring is a complex component, difficult to manufacture, and few companies produce them. For it to function correctly, the balance spring must maintain its shape. However, with the sustained oscillations it undergoes, always regaining the same shape is not easy. As mentioned earlier, the balance spring is made of metal. This material is sensitive to magnetism and temperature variations, which alter the shape of the spring. Indeed, heat expands the metal, and cold contracts it. Thus, for the balance spring to maintain its shape, several factors are necessary.
To address this problem, the metal in the balance spring is gradually replaced by silicon, an essential component of glass and also found in sand. A silicon balance spring has the unique characteristic of always retaining its shape. Unlike a metal balance spring, a silicon balance spring is molded and manufactured to the correct shape from the outset. Indeed, while metal can be worked and cut to adjust the shape of the spring, silicon cannot be worked because it breaks. A silicon balance spring is less sensitive to heat and therefore more precise, and it does not become magnetized. The silicon balance spring was first used in watchmaking in 2001, when watchmaker Ludwig Oechslin partnered with the brand Ulysse Nardin. The research required funding, and three companies decided to finance it: Patek Philippe, the Swatch Group, and Rolex. A patent on the use of the silicon balance spring and the results were filed by these groups. They were the only ones authorized to exploit them. These silicon-related patents will enter the public domain in 2022. Over the next few years, we will therefore witness the popularization of the silicon balance spring in mechanical watches.
The world of watchmaking evolves over the years with technological advancements. The balance spring is an example that demonstrates once again how far-reaching innovation remains possible by combining expertise, tradition, and technique, sometimes sparking debate, particularly at the intersection of watchmaking and new technologies.
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