Eterna Spherodrive: ball bearing-mounted spring barrel design for higher quality and longevity
The watchmaker presents its elegant Madison gent's watch with Eterna Spherodrive
Eterna is presenting its Eterna Spherodrive innovation, as fitted to the Madison Three-Hands, at the Baselworld World Watch and Jewellery Show (26 March to 2 April 2009). The spring barrel's new bearing receives its first application in Eterna's own calibre 3505 movement. The core element of a mechanical watch, its energy source, is simple, lubricant-free and very efficiently mounted. Eterna has been setting new standards for quality and longevity ever since launching its legendary Eterna Matic rotor system, which first appeared in 1948.
The elegant Madison Three-Hands gent's watch will be available from specialist watch stores from autumn 2009. Back in 1948, Eterna astonished the watchmaking world with its ball bearing-mounted low-friction rotor system for self-winding movements, known as the “Eterna Matic”. A good sixty years later, Eterna is once again making news with the same principle, this time involving a ball bearing-mounted barrel. “This dual ball bearing represents a quantum leap in the quality of the gear train mechanism,” explains Eterna's Technical Director Patrick Kury. Aware of the efficiencies afforded by the use of ball bearings, Eterna has been focusing on the spring barrel, the component in the movement subject to the greatest pressure, the highest friction and the most intensive wear. Despite this, the barrel – where all the energy is stored – has remained unchanged for centuries. A team of engineers, designing engineers and watchmakers spent two years developing the prototype for a ball bearing-mounted spring barrel. First previewed in 2007, it is ready to go into production this year.
Greater efficiency for increased longevity
To understand the improvement, you have to picture the way a normal watch movement works: with a conventional winding mechanism, the barrel arbor is located in the middle of the spring barrel, where it rotates when wound and thereby tightens the spring. The movement runs on the basis that the barrel revolves around the static arbor to deliver a steady supply of energy to the gear train. This process exerts immense pressure on the arbor. “A fully wound spring barrel can generate torque in excess of 1000 gram/millimetres (10 Newton millimetres),” says Patrick Kury. This is where friction in the movement is at its highest; it is normally kept in check using viscous oil.
To improve the system, Eterna has separated the winding process from the gear train. The winding stem, mounted on two ball bearings, is integrated into the winding mechanism; it is not directly coupled to the spring barrel, which is mounted in an overhung position on a ball bearing incorporated in the gear train mechanism. The resulting rolling motion entails less friction and less loss of energy. The bearing's minuscule 0.3 millimetre-diameter balls are fashioned from zirconium oxide, a ceramic material which, like tempered steel, has self-lubricating properties. This invention is both simple and efficient: vertical play and canting are reduced by up to a factor of ten compared to conventional designs. As a result, the spring barrel is positioned far more precisely and affords a more efficient transmission of energy, which in turn leads to a longer service life of the entire system. Ageing tests have demonstrated the tremendous resilience of the bearing: 20 years of simulated service resulted in barely any wear, which means that the spring barrel no longer needs replacing after three to five years. Assembly and service are much simplified and less prone to error, since the bearing requires no adjustment or calibration.
Classic, elegant design
Aside from the advanced technology of the movement, the Madison Three-Hands is a compellingly attractive timepiece. Its polished stainless steel case bears a black sunray-brushed dial featuring rhodanised indices. The black alligator leather strap with folding clasp makes the watch look particularly elegant. Ticking away inside the Madison is Eterna's own calibre 3505 manual-winding movement, which incorporates the Eterna Spherodrive and provides 56 hours of power reserve. Thanks to the deliberately understated design of the watch, the Eterna Spherodrive innovation takes pride of place, with the individual balls of the bearing being visible through an aperture at 6 o'clock. The Eterna Spherodrive will feature in all the company's future innovative movements.
Accuracy, reliability and elegant discretion have been bringing life to Eterna Eterna watches for nearly 160 years.Find out more >
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