Watch Case | Gasket System | Magnetic Field Protection | Patented Crown

Oil Free Escapement | Bezel Construction | Stainless Steel

The Watch Case

It has always been one of our major goals to design a watch case with superior resistance against scratches, knocks, and general wear, but the materials commonly available, including the rather soft titanium definitively do not feature the necessary characteristics. The term 316L describes the kind of steel which is predominantly used in the watch industry. It features good corrosion resistance but is also relatively soft. Occasional knocks with a watch made from this material will often lead to serious scratches or dents.

Although there is the possibility to harden the surface of 316L (1.4435) or 1.4301 up to 1200 Vickers by diffusing carbon into the top layers of the steel, there is no way to temper the material. Due to the austenitic structure of the alloy it is impossible to make sure that that steel remains its hardness throughout the body.

Various tests have proved that this kind of surface treatment is not suitable for our purposes because it only hardens the top layer of the metal. This leads to the so-called egg-shell effect. We were able to dent and scratch the “hardened” surface with an ordinary pair of tweezers (which are normally made from spring steel) because the material underneath the hard layer was not able to withstand the pressure.

Due to the reasons described above we searched extensively for better alternatives. In 1994 after five years of research we took out patents for 20 closely related martensitic sorts of stainless steel which highly exceeded our expectations. They are absolutely nickel-free, offer a good corrosion resistance, and can be tempered up to 64 HRC/800Vickers which is four times the hardness of every other steel currently used in the watch industry.

What makes this material so special is the fact that the molten steel is enriched with 0.35% nitrogen under high pressure. Nitrogen and carbon are responsible for the hardness of the alloy. Under normal circumstances it takes about 1% of carbon to temper a martensitic steel up to 60 Rockwell but the low nitrogen content of our steel only requires 0.35% of carbon to achieve this superior hardness and in addition to that leads to an excellent corrosion resistance which is many times higher compared to other temperable martensitic steels. Due to the special process of hardening we call this steel “ice-hardened, nickel-free stainless steel”. This material is patented for our applications and Damasko makes exclusive use of this pioneering material.

The entire watch case, including hardened crown and pushers is designed, engineered, and machined at our factory near Regensburg. Until the end of 2002 we supplied our cases to a well known German watch brand but from now on these cases will only be available through Damasko. After the special heat treatment mentioned above our steel reaches a maximum hardness of 62 Rockwell which makes it superbly scratch-resistant. You have to search hard to find a common household item ( apart from a sapphire nail-file or a brick) that is able to scratch the case.

Due to its superior performances this steel was mainly created for aeronautical use in:

- ball bearings for jet-engines
- rotor bearings for helicopters
- fuel pumps of the “Space Shuttle”
- high-speed bearings in CNC lathes
- dental and surgical instruments

The use of this steel in watch cases is patented for our company.

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The Gasket System

The main operating elements on a chronograph are the crown and the pushers. The crown is used to set the correct time, and in case of a mechanical wristwatch to wind the movement. The pushers are used for starting, stopping, and resetting the chronograph functions of the watch.

These operating elements basically consist of the visible piece of the crown and chronograph button and a shaft which connects them to the movement.

One of the major problems we had to face during the construction of our new crown and pusher system was to find a solution to seal the operating elements against the ingress of moisture and dust. Conventional systems make use of two O-ring gaskets made from an elastic material such as Nitril™. The longevity of these gaskets is to a large extend determined by the quality of the material and the friction between the stem and the O-ring. This friction factor increases the wear and ultimately leads to worn out and leaking sealing elements.

After extensive research we found a solution to the problem – our lubrication cell. Once again the concept for this unique element is a miniaturized design derived from industrial engineering. The lubrication cell is basically a tube made of our patented hardened stainless steel which is screwed into the drill holes for the crown and the pushers. The cell is filled with a synthetic viscous lubricant and sealed with two innovative Viton™ elements which prevent the filling from leaking or migrating.

The lubricant fills the microscopic surface roughness of the polished crown and pusher stem and eliminates friction and wear. Our lubricant system offers a longevity of gaskets and operating elements which is second to none.

Our gasket system and lubrication cell are patented.

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The Magnetic Field Protection - The Case inside the Case

Every Damasko watch features an important technical detail which is not visible at first sight but has a major influence on its accuracy under harsh conditions – the anti-magnetic cage.

Only very few mechanical pilot’s watches are equipped with this feature. The unique inner case consists of the dial, the movement retaining ring, and a second back. These parts are made of a special material with anti-magnetic characteristics which is able to withstand magnetic fields with a strength up to 80,000 A/m. They are machined with maximum precision to ensure an exact fit and to prevent the escapement from being magnetically charged.

The magnetic field protection in combination with martensitic ice-hardened steel is patented.

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The Patented Crown

During the development of our new crown we had to face the fact that literally every current crown system that works on a basis of a decoupling screw-down crown has two major weak spots that may sooner or later result in a defect.

The reason for that is to be found in the positive-fit coupling elements of the crown. They often consist of a fairly weak hexagon bolt which with1mm width across flats. Another reason for a defective crown mechanism is the wrong choice of material. Most watch manufacturers still make use of brass, German silver, or rather soft stainless steel (see “The Watch Case”). this leads in many cases to chamfered corners of the hex bolt which makes a form fit almost impossible. In such a case you would neither be able to wind the movement by hand nor to set the correct time.

Many watch manufacturers seem to be aware of this problem and use an inferior coupling crown which is permanently connected to the movement. The wrong choice of materials described above also sometimes results in ruined and worn out threads of the crown mechanism which also impacts the water resistance of the watch.

After extensive research we developed a decoupling screw-down crown which is constructed according to standards derived from mechanical engineering. The use of a hex bolt with 2mm width across flats and the fact that the entire crown, including shaft, thread etc. is made from our patented hardened steel (60-62 HRC) results in a longevity which is second to none.

All gaskets of the new crown system are made of Viton™, a material with high chemical and mechanical resistance which is superior to every other gasket material (Nitril etc.) currently used in wrist watches.
Crown and pushers are also equipped with our patented lubrication cell which ensures a smooth action and lubricates the shaft and the gasket. The tubes of both crown and pushers are, according to industrial engineering, screwed into the case using a special key. Almost every other watch manufacturer makes use of an inferior press fit tube.

Our new crown system is patented.

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The Oil-Free Escapement

For over 100 years the Swiss Anchor Escapement has been the most precise and reliable escapement for wrist- and pocket watches. In order to work properly it needs to be oiled regularly on the palettes and on the teeth of the escape wheel and in addition to that, watch manufacturers recommend to service a mechanical movement every 2-3 years by disassembling, cleaning, and lubricating it. An insufficiently oiled or even dry escapement ultimately results in bad accuracy or even worse, in worn out parts.

Since 1998 Damasko has experimented with different kinds of coatings which should lower the friction coefficient between anchor and escape wheel. Latest technological achievements showed that coatings made of various layers of amorphous carbon (Diamond Like Carbon/ DLC) are probably the most advanced solutions to create a dry escapement. The process to generate such a layer is called Plasma Activated Chemical Vapour Deposition (PACVD). Apart from its black colour the coating features the following characteristics:

- Extreme hardness of approximately 1800 – 3000 Vickers
- Excellent wear resistance
- High chemical resistance
- Superior surface quality
- Extremely low friction coefficient. DLC – Steel: 0.07 (without lubricant)
- Movements parts can be coated at a temperature that does not affect the structure of the metal (< 200 degrees)

This coating process was originally designed to increase the wear resistance of moving engine parts, cutting tools, and even medical implants. In addition to the hardness and wear resistance of the layer, the extremely low boundary friction coefficient makes this method of coating so interesting for us.
We started by coating the escape wheel of the ubiquitous but reliable ETA 7750 with amorphous carbon. As mentioned above, the combination of the ultra-hard carbon layer and the polished synthetic rubies (AL203) of the anchor already lead to a very good boundary friction coefficient, which allowed us to construct an escapement which works fine without any lubricant at a daily accuracy of approximately +- 2 seconds. Furthermore the escapement delivered an amplitude of 290-325 degrees, which is already very good.

But we thought that the combination of DLC on DLC should deliver even better results. We went one step further and designed an new one-piece anchor with a modified geometry and slightly different parameters. After polishing, tempering, and again polishing this anchor was also DLC coated and fitted to the movement. The result was absolutely amazing! Due to the extremely low friction coefficient of DLC on DLC the escapement delivered an amplitude of 300 – 347 degrees without any lubrication. Of course this was only a test run. In order to make sure that this result will also be achieved during serial production it is necessary to establish an effective quality control.

After two years of extensive testing on different movements, no signs of wear can be regarded and the escapements still deliver excellent amplitudes.

During our latest test run we replaced the synthetic rubies of the anchor by palettes made of silicon carbide and found out that this innovative material is another outstanding friction partner for the DLC coated escape wheel.

Boundary friction coefficients of the most important material combinations:

- DLC – Steel: 0.07
- DLC – Synthetic ruby: 0.05-0.06
- DLC – DLC: 0.04-0.05
- DLC – SiC:0.03-0.04
- For comparison the traditional, lubricated escapement:
Steel – Synthetic ruby (oiled): 0.05

The results of our research and the use of new materials for the escapement are patented.

All in all it is clearly visible that our efforts on this field have led to a major progress and for the near future we will put our main emphasis on the design of a completely oil-free movement.

Since the publication of our latest patent specifications there were several attempts to copy our technical solutions, this is the reason why these pages only contain very generic information on how our oil-free escapement works.

In 2001 our company started another test run with specially prepared movement plates. On these parts the drill holes that support the gears are DLC coated on their inner surface to eliminate friction. In addition to that we also decided to coat the inner surface of the main spring barrel. Although we are still in the middle of another extensive test phase the movements already work excellent and the treated parts show absolutely no signs of wear. We are confident to present a completely oil-free movement in a relatively short period of time.

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The Bezel Construction

In the following images we would like to give you a rare insight into our currently used bezel constructions (patent pending). We would like to illustrate how we achieve an ultra precise and reliable bezel action. CAD/CNC designed and engineered, hardened components guarantee that our bezels ratchets will never wear out, or become loose. Get a view on bezel parts that even Damasko owners will only hardly ever see.

	Click images to enlarge

No other bezel available offers that amount of precision and performance even under harshest conditions.

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The Stainless Steel

Due to the fact that we are well known experts on stainless steels and their metallurgical aspects, we are often approached by watch enthusiasts and customers from all over the world. And more or less all of them ask the same questions: Which steel used for watch cases offers the highest corrosion resistance, and which one features the greatest hardness? Which company offers the best choice?

Although it is possible to answer this question in one sentence, we feel that it might be of greater interest to compare the most commonly used stainless steels with each other, including one of our steels.

For our upcoming automatic pilot’s watch range (DA 36/46) we’ve chosen a highly corrosion resistant austenitic stainless steel alloy which can be fully hardened, leaving the surface with a key hardness of 1600 HV (Hardness Vickers). Just to give you an impression how hard this actually is: Titanium 180-210 HV, St. Steel AISI 316L 190-220 HV, Sapphire crystal 2000 HV.

In order to compare our new steel with other commonly used stainless steels, we’ve decided to measure the PRE-factor (Pitting Resistance Equivalent). This can be done by defining the ratio of three important alloy components, using the following formula:

PRE = %Cr (Chromium) + 3.3 x %Mo (Molybdenum) + 30 x %N (Nitrogen)

This leads to the following results:

1. Stainless steel AISI 304 (watch cases, not in common use): PRE-factor 20
2. Stainless steel AISI 316L (commonly used for quality watches): PRE-factor 26-30
3. Stainless steel AISI 904L (marine hardware, etc.): PRE-factor 35
4. Stainless steel used for latest strategic developments of the German Navy, e.g. 1.3964/1.4566: PRE-factor 38
5. Stainless steel DIN 1.4456 (high grade alloy used for medical implants): PRE-factor 52
6. New Damasko stainless steel used for the upcoming DA 36/46: PRE-factor 50-52

We think that this table perfectly illustrates the superior corrosion resistance of our new steel. Soon we will also discuss how we achieve the tremendous hardness of this pioneering material.

By the way: Since most quality watches are made from 316L they don’t offer real salt water resistance, so always make sure to rinse your sports/dive watch with fresh water after open water swimming or diving.

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