The spring driven movement is one of mankind’s oldest machines and if we were to believe the famous sociologist Lewis Mumford, then the decisive machine of the modern industrial age was not the steam engine. It was the clock, a piece of power-machinery whose ‘product’ is seconds and minutes. The essential nature of the clock separated time from mankind’s own experience. It contributed to a belief in a separate world of mathematically measurable consequences, resulting to more precise and generalized time synchronization. It’s imposition on working discipline carried essential changes in the perception of time. This effect can be read about in Mumford’s Book: Technics and Civilization (1934).
In order to make mechanical clocks portable, an alternative way was required to replace the weights that used gravity as the source of power for the timepiece. A simple elastic strip was able to take on this role. Opinions about its origin are debatable among the researchers and historians. But it seems likely that its development was derived from the mechanism that locksmiths used in doors and weapons. The mainsprings debuted in France in late 15th century and first spring powered timepieces dates from early 16th century.
The mainspring (fig.1) can only drive the gear train when it is tightly coiled. This can occur either by manually winding it with the help of a crown or by the means of a rotor found automatic watches. The energy is transmitted through gears and pinions to the spring barrel. The larger of the two wheels (#1) is connected to the barrel arbor to which the inner end of the mainspring is attached; (fig.2) outer end of the mainspring is connected to spring barrel’s wall. A click (#2) assures that the mainspring can release its force in one direction of the gear train by blocking the pathway towards the winding system. Elasticity of the tightly compressed mainspring releases the tension by expanding. Therefore, the spring will continue to push the mainspring barrel resulting it to rotate on its axis. Hence, it acts as a power source for the mechanical watch.
In recent years, the focus on new materials and technology concerning the mainspring has evolved from being made of steel to Niva-flex and now of silicon or fiber glass. Primarily because of their desirable properties such as thermal and magnetic stability, break resistance, elasticity and need for little or no lubrication. Long ignored mainspring is emerging from the shadows in the light of the attention. Many watch manufacturers now consider it to be a strategic component.
The mainsprings endurance determines the power reserve of the watch. Power reserve has become the major issue among the manufacturers especially since the escalation of complications has boosted the energy demand. To increase power, watchmakers either improve the energy yield from power source or simply increase the number of mainspring barrels. Most of the new calibers from the maisons such as Jaeger-LeCoultre, Cartier, Panerai or Omega have twin barrels. Triple and quadruple barrels can also be found in modern watches. This results in increase of power reserve from traditional 30 – 48 hours to six days or more.
A Lange and Sohne of Saxony with their Lange 31 model claims a record of 31-day power reserve, The German brand was able to achieve this feat by using two superimposed spring barrels. With diameter of 25mm it takes up 3 quarter of the movement and it is 10 times longer than the conventional mainspring. However, to deliver power reserve of this magnitude, the strength of these springs requires them to be wound with an external key.
Increasing power of the barrels imposed considerable challenges on the engineers. The major obstacle was to prevent the energy loss. It is known that only 30% of the barrel’s energy gets to the escapement at the other end of the gear train. Thus it was important for the watchmakers to find a way to increase the efficiency. One of the interesting dimension of research in this area is pursued by Eterna. The Brand is remembered for using micro-ball bearings in the caliber. Mainspring is subject to the greatest pressure, friction and wear in the movement. As it unwinds, it puts considerable pressure on the arbor, where a fully wound spring exerts a force of around one kilogram per square millimeter. Which leads in the wearing of the barrel drum and its system.
Eterna got rid of these problems with their Spherodrive system. The barrel and arbor are mounted on small ball bearing which significantly reduces friction and energy loss while needing no oil. Thus power reserve is increased by around 30% or making standard mainspring capable of powering a watch for 56 hours.
The other challenge was of Constant Force leading to various innovative solutions for the problem which will be covered in next article.