A coiled heart: understanding the barrel spring

In a mechanical watch, the barrel spring is not just a component. It is the invisible muscle, coiled in a thin steel box – the barrel – which releases its energy with the patience of a metronome. We pull it up, it tenses; he relaxes, the watch lives. A centuries-old ballet, whose longevity fascinates as much as it questions.

So, how long does it last?

The short answer: a modern mainspring can last for decades. The honest answer: its longevity depends as much on the material as on the method — materials, rate of use, lubrication, movement design, environment. In practice, watchmakers recommend replacing it at each complete service (every 5 to 10 years) not because it “dies” so quickly, but because it costs little compared to the benefits of regular torque and newfound reliability.

From blued steel to modern alloys

The 20th century saw the abandonment of traditional blued steel, known for “taking a bend” (the spring “settles” and loses its strength), in favor of high-performance alloys: cobalt-nickel, iron-chromium-cobalt, families such as Nivaflex or Spron. These “white” springs offer greater elasticity, better corrosion resistance and more constant stability over time. Result: less risk of breakage, a more stable power reserve and an increased probability of crossing the decades without weakening — provided that the rest follows.

The 5 factors that make the difference

• Use and winding cycles : a manual watch experiences complete daily cycles (tense → relaxed), whereas an automatic watch lives in continuous micro-cycles. Both are taxing in different ways, but modern alloys tolerate these efforts without distress.
• Barrel lubrication : fats and oils (including the famous wall grease for sliding flange) age, thicken or evaporate. A dry barrel erodes the smoothness of the torque, tires the spring and can cause jerks.
• Architecture of movement : long power reserves, demanding complications (chronographs, large dates), or high torques place greater demands on the spring. Multi-barrel calibers distribute the effort better.
• Environment : shocks, humidity, large thermal amplitudes damage the barrel/spring assembly. Modern alloys are more resistant to magnetism, but corrosion remains the enemy of any metal.
• Assembly and adjustment : a poorly inserted spring, a sliding flange that is too “fat” or insufficiently braked, and it is the performance that suffers.

Automatic vs manual: which wears the spring more?

The manual watch is disciplined: you wind it all the way up, then let it go back down, once a day. The automatic lives to the rhythm of your movements, with a sliding flange which slides on the wall of the barrel to avoid any overvoltage. In theory, the manual imposes greater amplitudes of flexion; in practice, modern springs will withstand both for years. The weak link, more often than not, is not the metal but the grease that serves it.

Signs it's time to change the spring

• Power reserve at half mast : the watch lasts much shorter than advertised, despite complete winding.
• Rough winding or unusual noises : cracks, jerks, sensation of “sand” — often synonymous with exhausted lubrication, sometimes with a damaged spring.
• Amplitude variations : if on the chronocomparator the amplitude collapses too quickly after full winding, the torque delivered is no longer healthy.
• Sudden stops : especially on a manual, after an effort. The spring may be broken or the flange faulty.
• Old watch left idle for years : on vintage, the old steel may have taken a “set”; the restart deserves a fresh start.

Best practices to prolong your life

• Respect the services : 5 to 7 years of regular use is a good base. We open, we clean, we relubricate, we replace the spring.
• Avoid extremes : heat, humidity or violent shocks alter the barrel and lubricants before reaching the spring.
• Measured winding : on an automatic, 15 to 25 turns of the crown are enough after rest; no need for persistence.
• Storage : for prolonged rest, let the watch discharge naturally rather than leaving it constantly armed in the safe.
• Confidence in the test bench : measured amplitude, drift and power reserve are better than impressions by ear.

And what about vintage?

The charm of a caliber from the 40s and 60s is also the reality of its metals. Period springs, made of blued steel, break more easily and lose their nerve. Replacing them with a modern alloy restores breath and power reserve, often without betraying the aesthetics or integrity of the piece. For purists, keeping the original is a matter of collecting; for wearers, the security of a new spring is a discreet but decisive luxury.

How much does it cost, and is it systematic?

On a current movement, a new spring remains one of the most accessible parts in the workshop: a few dozen euros per part, included in the quote for a complete service. On rare, old or proprietary calibers, availability determines the price. Systematic? Let's say reasonably systematic: the difference in torque stability and power reserve justifies, in itself, the preventive replacement.

Verdict: a marathoner, not a sprinter

A modern barrel spring, well maintained, will survive many bracelets and many fashions. Factor in decades of potential service, but keep in mind that maintenance dictates the music. Watchmaking, after all, is not just a matter of seconds: it is a discipline of consistency. And the discreet spring is its most faithful artisan.