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The Spiromax®
balance springPatek Philippe

BASELNEWS 2006Patek Philippe presents the Spiromax® balance spring

A year after the launch of the first Swiss lever escapement with a silicon escape wheel (patent application No. EP05006186), Patek Philippe presents an additional fundamental innovation: the Spiromax® balance spring made of Silinvar™. It is an epochal step forward in the constant quest for isochronism in portable mechanical watches. On the occasion of Baselworld 2006, the Geneva workshops will showcase the first watch with this innovation in a second limited “Patek Philippe Advanced Research” edition: the Ref. 5350 with a Spiromax® spring and a silicon escape wheel.

Isochronism is the key to every measurement of time based on any form of vibration. The greater the regularity of the vibration, the better the movement can be adjusted to achieve a high rate accuracy. If the source of the vibration is perfect, it is called isochronous. The key factors that disrupt isochronism are:

- the asymmetry of the expansion and contraction of the balance spring
- changes of the elasticity of the spring in response to temperature changes
- magnetic fields
- the spring attachment points
- centrifugal forces and gravity
- inadequate balance-wheel poise
- the play between the curb pins

Ever since the spiral balance spring emerged, countless attempts have been made to eliminate its anisochronism. The history of the so-called hairspring is characterized by four milestones:

1675 – Invention of the balance spring by Christiaan Huygens: theoretically isochronous oscillator
1795 – Invention of the Breguet spring with overcoil: concentric development of the spring
1897 – Invention of Invar by Charles Edouard Guillaume: balance springs made of an alloy that offsets the influence of temperature changes
2005 – Invention of the Spiromax® balance spring by Patek Philippe: temperature compensation and concentric development of a flat spring

A new milestone: the Spiromax® spring by Patek Philippe

Spiromax® is a totally new type of balance spring made of Silinvar™, a revolutionary material based on monocrystalline silicon. It was developed jointly with two partners in the Swiss watch industry and a leading research institute. But it is not the material that prevents the asymmetric development of the spring. To make it breathe concentrically, the fundamental research department at Patek Philippe developed a new terminal “curve” design. The patented “Patek Philippe terminal curve” (patent application No. CH 20030749/03 & No. EP 03009603.6) exhibits a discernibly thicker region at the outer end, forcing a concentric development upon the Spiromax® spring. This causes the expansion and contraction of the spring to be symmetric relative to its center over the entire plane of oscillation. And because the “Patek Philippe terminal curve” lies within this plane, the Spiromax® spring can be crafted three times thinner than a spring with a Philips or Breguet overcoil, thus facilitating the construction of ultra-thin movements.

The Spiromax® spring exhibits additional important design features. In the center, it has an integral self-centering balance staff collet with which it is attached to the balance staff. At the outer end, it has an integral stud attachment geometry (patent application No. CH 01711/05 & No. EP 03020394.7) which precisely defines the active length of the spring.

With its revolutionary Spiromax® spring, Patek Philippe has created an oscillating element that unites several decisive advantages. The active length of the Spiromax® spring does not need to be painstakingly adjusted for each individual movement. The Spiromax® spring vibrates with ideal concentricity even without an overcoil. It is designed to be isochronous regardless of the temperature, the orientation of the movement, or the presence of magnetic fields.

Spiromax® springs: consistently identical quality

As is the case with the silicon escape wheel, the Spiromax® spring is manufactured with the photolithographic Deep Reactive Ion Etching (DRIE) process. The material exhibits a contiguously homogeneous monocrystalline structure and can be machined to tolerances in the micrometer range. Accordingly, all Spiromax® springs are of consistent, extremely high quality, a fact reflected by the remarkable rate accuracy of movements equipped with them.

The Patek Philippe Spiromax® spring at a glance

- Produced from monocrystalline silicon by deep reactive ion etching (DRIE)
- Concentric development thanks to patented geometry (Patek Philippe curve) for improved isochronism despite flat topology (patent application No. CH 20030749/03 & No. EP 03009603.6)
- Antimagnetic
- Temperature compensation based on the properties of Silinvar™
- Integral stud attachment end (patent application No. CH 01711/05 & No. EP 03020394.7)
- Integral self-centering balance staff collet
- No thermal or mechanical deformation at attachment points, contrary to conventional springs
- More homogeneous material structure than Invar alloys
- Less internal friction and greater elasticity than Invar alloys
- Insensitive to minor shocks
- Reduced sensitivity to centrifugal and gravitational forces because the Spiromax® is three times lighter than conventional springs
- No degradation of rate accuracy as a result of repetitive minor shocks in daily use
- Complies with NIHS standards on randomized shocks
- Fulfills the criteria of the Geneva Seal

The first Patek Philippe watch with a Spiromax® spring: the Ref. 5350 Annual Calendar in a limited “Patek Philippe Advanced Research” special edition

A pioneering invention like the Spiromax® spring deserves to be showcased. A second limited “Patek Philippe Advanced Research” edition of the self-winding Annual Calendar Ref. 5350 in 18K rose gold is therefore being launched on the occasion of Baselworld 2006.

Its caliber 324 S IRM QA LU is the first movement fitted with a Spiromax® spring made of Silinvar™. As a further exclusive feature, it is also equipped with a silicon escape wheel. To do justice to these technical innovations, the movement has a specially shaped balance cock that reveals a large portion of the Spiromax® spring and the going-train bridge is milled so that the mysterious blue-violet sheen of the nearly black silicon escape wheel is more readily visible. Additionally, the sapphire-crystal back has an integrated loupe and bears the inscription “Patek Philippe Advanced Research.” The solid 21K gold winding rotor features a zirconium ball bearing. Like the silicon escape wheel, the balls run dry and never need to be lubricated. The edition of this “Patek Philippe Advanced Research” model, the Ref. 5350R, is limited to three hundred watches.