Masamasa Hirota, editor-in-chief of Chronos Japan, also known as "Watch Professor," will be publishing a six-part column on webChronos about masterpiece movements. In the third installment, he will explore the Caliber UN-250 from Ulysse Nardin, which introduced the world's first silicon escapement.
Text by Masayuki Hirota (Chronos Japan)
[Article featured in Movement Book 2023]
"Cal.UN-250" installed in Freak
The Cal. UN-250 used by Freak Vision was born from a concept model. The use of silicon further improved the performance of the escapement and automatic winding mechanism. The mass-produced version of this movement, the Cal. UN-240, was announced in 2023. 18,000 vph. 19 jewels. Power reserve of approximately 50 hours. 60-minute carousel. Free-sprung.
It's no exaggeration to say that the Ulysse Nardin Freak, released in 2001, changed the history of mechanical watches. This watch, in which the movement itself rotates to tell the time, was also equipped with the world's first silicon escapement. However, when you hear from the people involved, it makes sense. The original idea was conceived by Carol Cazapi, who later worked on numerous masterpiece movements for Cartier and Tag Heuer. Ludwig Oechslin, who created the Astronomical Trilogy, then gave it form. It was Pierre Gygax, who solidified the foundation of Ulysse Nardin, who added the silicon escapement.
Furthermore, the company continued to evolve this experimental watch every year, introducing new features such as the Diamondsil escapement, a diamond-coated silicon escapement, and a silicon balance wheel. The final product was the FreakVision, released in 2018, and the Caliber UN-250 it was equipped with. The design was based on the 2017 prototype, the InnoVision II. Although the dual constant escapement was not adopted, the shock-resistant, low-inertia silicon balance wheel and the grinder automatic winding mechanism, which winds the mainspring with a pawl, were reused in its entirety.
The Freak, which placed the mainspring on the back of the movement, did not have enough space to mount an automatic winding mechanism. However, the mainspring in the InnoVision 2 and FreakVision has been miniaturized, making it possible to mount an automatic winding mechanism. This grinder automatic winding can be considered the perfected version of the ratchet winding mechanism, which uses pawls to wind the movement. Four flexible silicon pawls are attached to the inside of the peripheral rotor, which directly wind the mainspring. Due to the simplicity of the mechanism, this automatic winding mechanism is approximately twice as efficient as a conventional system.
The escapement also takes advantage of the properties of silicon. The Ulysse Nardin anchor escapement, which has a silicon anchor, drives the balance wheel with the force of a bending spring, so it functions like a kind of constant force. In theory, its accuracy should undoubtedly be higher than that of a normal lever escapement.
In addition, the movement, which rotates once per hour, is fixed with ceramic ball bearings, which significantly reduces the resistance to the mechanism. The smooth feeling when turning the bezel to rotate the movement is quite unique.
While retaining its unique mechanism, the Cal. UN-250 has undergone significant evolution by taking advantage of the properties of silicon. Its particularly high-performance automatic winding and new escapement give this one-of-a-kind watch practicality beyond that of ordinary mechanical watches. The Freak, released in 2001, reached its perfection here.
