Patek Philippe creates its own balance spring
Created just five years ago, the new Patek Philippe research department seems already to have reached a fast-paced and regular cadence while demonstrating technological inventiveness and creativity in its work. Patek Philippe now hands in its second “term paper”, stemming from its “Advanced Research” programme. After the escape-wheel (or pallet-wheel), this second project was based on the theme of the balance spring. Spiromax will undoubtedly earn the Geneva-based Manufacture top marks, and we will soon see why.

Historical reminder
For the past ten years, the balance spring has been the hot topic and chief cause of contention in the war among watchmakers, both from a strategic and economic standpoint, and for technical reasons. But let’s backtrack first in order to grasp the value of the Patek Philippe invention. In 1675, famous Dutch watchmaker Christiaan Huygens invented the balance spring. The role of the latter is to determine the timing or rating of a watch by using an oscillating with rotating vibrations. However, its development (meaning successive contraction and expansion phases or “breathing”) is asymmetrical, meaning not concentric with the balance-staff around which it is centred (when at rest). The resulting imbalance is therefore detrimental to the rating by creating non-axial forces that disturb the oscillating system. In around 1795, Breguet empirically developed the overcoiled balance spring named after him, characterised by an (external) terminal curve that bent inwards. The geometry of this inward-bent terminal curve was later calculated with great precision by the French mathematician Edouard Philllips. Despite the disadvantage of taking up more space than a classic flat balance spring, it definitely enhanced the concentric development of the spring. In 1897, Charles Edouard Guillaume invented invar, an alloy with a small coefficient of thermal expansion that made it far more stable with regard to temperature fluctuations, another major factor that is prejudicial to watch rating. Ever since, the balance spring has been made from this alloy. Nonetheless, the difficulty of working this alloy without reducing its physical and mechanical properties while complying with the most sophisticated tolerances, combined with the crisis that hit the watch industry in the 1970s, led to a situation where Nivarox became the sole producer of balance springs.

The breakthroughs embodied in Spiromax
The main quality one expects from a balance spring is isochronism (meaning that the duration of its oscillations must be constant, whatever its amplitude). The main factors influencing isochronism, and thus the quality of the rating of a watch, are differences in temperature, magnetic fields (that also affect Invar) and shocks. Spiromax, for which three patents have been filed, features significant improvements on all these points.

The silicon-based material chosen for Spiromax is monocrystalline silicon. Already used in watchmaking (such as in the escape-wheel presented by Patek Philippe in 2005, for example), it is endowed with mechanical, physical and chemical properties that are extremely valuable in horological applications. Nonetheless, to make a spring expected to display such high performances and meet such exacting demands, the monocrystalline silicon used to date was not elastic enough. A balance spring made from the existing type of material would not have yielded satisfactory results in terms of rating and would have proved brittle. The silicon used for Spiromax has been given a special treatment by a prestigious laboratory, a process that is still a closely guarded secret and is to be protected by the application for the first Spiromax patent. The choice of this material offers several key advantages. Firstly, its volumic mass is three times lower than traditionally used alloys. Due to its low mass, it thus reacts far less strongly to centrifugal forces, meaning that shocks have a correspondingly lesser influence on the rating. Moreover, it is a totally pure, amagnetic element. This is an extremely important characteristic, since the increasingly ever-present magnetic fields are enough to stop the running of even the best-protected watches. Finally, its expansion coefficient is very low, which means that differences in temperature have virtually no influence on the rating. In addition to the choice of materials, the innovations that justify referring to Spiromax as revolutionary relate to its technological development and its mode of production.

Innovative manufacturing
The production process chosen has enabled the engineers to create a form of balance spring able to achieve symmetrical or concentric development and thus apparently to reach the horological “holy grail” represented by isochronism. The technique is the same as that used in making microprocessors (also made of silicon). State-of-the-art DRIE (Deep Reactive Ion Etching) equipment makes it possible to “machine” parts a mere several hundred microns thick with absolute and constant precision, as well as resulting surface states that require no subsequent treatment (such as polishing). There is therefore no need for actual machining as such, nor rolling, making it possible to produce components of unlimited profile complexity.

The simulation software tools such as those used in the Advanced Research programme enabled the company engineers, by entering all the dimensional, physical and chemical parameters, to calculate the ideal shape that the Spiromax should have in order to attain the much coveted isochronism. The secret lies in its “thickened” terminal curve, for which a patent has also been filed. DRIE technology made it possible to make the balance spring and integral double balance staff collet (with bendable inner arms) in one piece, and to place a buffer on the outer end to which an integral clipped stud attachment has been fixed, an invention that will also be protected by patent.

With its Spiromax, Patek Philippe has indeed reached the supreme goal of the horological quest for isochronism. It will thus also be far simpler to assemble this system (hitherto an extremely delicate operation) without having to adjust its rating! Patek Philippe presented this watchmaking wonder in a first limited edition at Baselworld 2006. The watch naturally meets the criteria enabling it to bear the prestigious Geneva Seal.