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The “Spiralists” – Hairspring Production at A. Lange & Söhne

 

Tiny. Vital. The Balance Spring 

 

It weights slightly more than two milligrams. It is smaller than a thumbtack head and thinner than a human hair. And it is the pulsating heart of every wristwatch: the balance spring, or hairspring as it is also called. Perhaps only half a dozen watch companies in the whole world make them in-house. And A. Lange & Söhne is one of these chosen few.

Since 2003, the venerable Saxon manufactory has endowed a growing number of movements with its proprietary balance springs. Meanwhile, they oscillate in one out of two Lange movements.

Since the DOUBLE SPLIT, a spectacular double-rattrapante chronograph, was launched seven years ago, Lange has steadily increased the number of manufacture calibres with its proprietary hairsprings. At this year’s SIHH alone, the Saxons presented five new models with springs developed and manufactured in-house. So now, half of the 24 current Lange calibres are equipped with them. 

 

Lange’s balance spring manufacturing capability is based on an ingenious and elaborate system that Günter Blümlein began to develop in the 1990s. After all, hairsprings are part of the Lange heritage: the metal alloy still ubiquitously used today dates back to 1930 and to Richard Lange, Ferdinand A. Lange’s eldest son. The scientist in the family was the first to discover that the admixture of beryllium in steel-nickel alloys decisively improved their elasticity and thermal resistance.

Even today, the development and production of reliable balance springs is associated with nearly insurmountable technical obstacles. The slightest deviations from specified manufacturing tolerances or sequences in the multi-stage production process would have serious consequences with respect to the rate accuracy of the watch. This is why most watchmaking companies don’t even consider getting involved in such an intricate undertaking. 

 

The first difficulties are already encountered at the first stage during which the wire, made of a steel-nickel alloy, is drawn. Several times in succession, it is pulled through progressively smaller diamond dies until it has attained its final diameter of down to 0.05 millimetres. Then, between two extremely hard metal cylinders, it is rolled to a strip with a cross section measuring 0.018 by 0.09 millimetres. Uncompromising precision is absolutely crucial. This is because in the assembled watch, a deviation of just one ten-thousandth of a millimetre can cause a rate difference of about three minutes. The special rollers used by Lange are ground in the in-house toolmaking department. No outside supplier would be capable of delivering rolls to the required tolerances.

The next step involves measuring the strip after it has been rolled. A laser inside the roll mill measures the width, but it still lacks the precision to dependably measure the thickness of the strip. For this purpose, a defined section of strip has to be weighed. Then, using a special formula, the thickness can be determined with sufficient accuracy.

The rolled strip is now precisely cut into pieces of identical length. Three, four, or five of these pieces are pedantically coiled around each other by hand. This is how the hairsprings are ultimately formed. Up to 40 of these coiled packs are stacked in a metal ring. In a vacuum furnace, they are subject to a stabilising heat treatment at a temperature of several hundred degrees Celsius. The permissible temperature deviation during this phase is less than one degree. After the hairsprings are separated, collets are laser-welded to their inner ends. Finally, the hairsprings are cut to the desired number of windings. Now, they are ready to be connected to the balance.

But first, they have to be classified to assure that the balance spring and the balance truly constitute a harmonious pair. This is done with a method that accurately measures the moment of elasticity of the hairspring and assigns it to one of 20 classes. Then, the hairspring can be paired with a balance that has precisely the right moment of inertia. This eliminates pairings that would cause excessive rate deviations.

The process of bending the terminal curve calls for extreme sensitivity. It is decisive for the regularity of the hairspring’s oscillation behaviour. This applies in particular to the so-called “Breguet overcoil” for which the outer end of the spring is bent upwards and then folded inward on a second plane above the spring. For this critical procedure, which allows only one try, an experienced watchmaker spends about two to three hours. But if he succeeds, the balance spring will “breathe” about 200 million times a year with impeccable uniformity.

Lange’s technological know-how and in-depth experience in the domain of oscillation systems is in no way limited to the production of balance springs, by the way. Special springs like those that re-tension the constant-force escapements of the LANGE 31 and the LANGE ZEITWERK are also crafted in-house. And the balance wheels with eccentric poising weights, perfectly matched in their characteristics to Lange hairsprings, are produced on-site as well. Meanwhile, this lightweight and precisely adjustable system has been deployed in seven calibres. Thanks to the interaction of these two components, Lange watches are adjustable to a rate accuracy that is second to none. This achievement reflects a horological understanding with an ultimate goal that can be expressed in one word: precision.

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Written by kevin

August 31, 2010 at 1:45 am

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