Christopher Ward C6 Kingfisher - liquid filled case by jp28800, on Flickr
I own a Sinn UX and like the look of its liquid filled case. It made me wish all my quartz watches were liquid filled. The only other watch available on the market with this feature is the Bell & Ross Hydromax, also ~$2000. Of course this concept only works with quartz, as the balance wheel of a mechanical watch cannot oscillate properly in a viscous fluid.
The thing I like most about a liquid filled case is the incredible visibility at extreme angles and underwater. The liquid has the same refractive index as sapphire, so the hands appear to float on the top surface of the crystal. Also, there is no possibility of moisture condensation on the inner crystal, and the tick noise of the quartz movement is almost entirely dampened. And since liquids are incompressible, my Sinn UX case is rated to 12000 meters.
There is just one problem -- the battery change on my UX must be done in Frankfurt every 7 years. Here is the notice on the US authorized dealer website.
So I took that as an engineering challenge. How hard could it be? What fluid do they use? They used to use a silicone oil, but it discolored over the course of a few years and created a lot of warranty issues. Then Sinn made the switch to an unnamed fluorinated liquid. Since the whole battery and movement are submerged, the liquid must be a dielectric (insulator). The only fluorinated dielectric fluids are made by 3M and Solvay, and are marketed as Fluorinert and Galden respectively. These are "perfluorinated" hydrocarbons, which means all the hydrogen is replaced by fluorine. This fluorine functionality makes a compound extremely inert. For example, Teflon is perfluorinated polyethylene plastic.Under no circumstances should anyone other than Sinn attempt to open the case on an oil filled watch. Only Sinn in Germany has the equipment to properly service the watch because of the oil filled case. Our US service center RGM (as well as other watch repair centers in North America) cannot provide service for this model or change the battery, and to attempt to do so will damage the watch.
There are several grades of 3M Fluorinert with differing viscosities and vapor pressures. I selected one grade with properties similar to water. The molecular structure is like octane (petrol/gasoline), but with all the hydrogen atoms replaced with fluorine atoms. It is odorless, crystal clear, and nontoxic for ingestion -- though not recommended to drink! It can hold back 35000 volts over a 0.1 inch gap, so you can immerse electronics directly. Price is on the order of $1000 per gallon which works out to a few dollars per watch case.
I purchased some Fluorinert and tested a spare Ronda 715 movement in the fluid and found that it runs great while fully submersed. The Ronda 715 in the C6 Kingfisher watch actually has more torque than the ETA 955.652 Thermoline in the Sinn.
Ronda 715 movement running submerged in 3M Fluorinert fluid by jp28800, on Flickr
Two other problems needed to be solved: how to case the watch in liquid without an air bubble, and how to accommodate thermal expansion of the liquid.
Many years ago I ran an R&D program on capacitor development for military applications. Capacitors are filled with electrolyte liquid and do not contain any air bubbles. They are filled by vacuum impregnation. So it's easy to replicate this at home with some parts from Amazon.com: a vacuum pump, manifold gauge, and vacuum chamber. Here is the setup.
Vacuum impregnation setup in my workshop by jp28800, on Flickr
I opened the caseback of the watch, submerged it in a small container, and put this container in the chamber. When I pulled a vacuum to 27 inHg, the air was sucked out of the watch completely. You can see the bubbles rising in the photo:
Vacuum chamber - bubbles rise from vacuum impregnation by jp28800, on Flickr
I released the vacuum, opened the chamber, then screwed on the case finger tight while still submerged. Then I removed the watch and was able to tighten all the way with a case wrench.
How do you accommodate for thermal expansion of the fluid? Out of curiosity I looked up patents from Sinn, and I found the one from Lothar Schmidt (Sinn CEO) for HYDRO technology. I think the title says it all: DE19647439 (A1) "Diver's watch used for serious underwater use"
The UX is rated to operate from -20 to 60°C. Over this wide temperature range, the fluid contained inside the case will change volume by 10% due to thermal expansion. Since liquids are incompressible, this would destroy a traditional watch case -- the crystal would blow out from any slight changes in liquid volume. On the UX, the case back has a large movable piston with an o-ring seal, just as described in the patent. The piston allows the fluid to expand and contract to adjust internal fluid volume and equalize with outside pressure. Here is the drawing from the patent. The red arrow shows the edge of the piston [14], the crystal is [4], caseback [1], case [2], movement [6], o-ring [20], fluid on dial [9], fluid behind movement [23].
UX Back by West Shore, on Flickr
And the red arrow on the photo below shows the same piston edge on the case back. I notice the piston has a very slight wobble due to the dimensional tolerance of the gap. So far I have exercised my UX from -10 to 30°C, and I notice the vertical travel in the piston when I look very closely.
UX back by West Shore, on Flickr
I came up with a different way to account for thermal expansion, a much more simple solution to implement. I won't reveal it here, as I am considering filing a patent application...
Here are some photos of the project and the finished watch.
Vacuum pump - Interdynamics VCP-10 by jp28800, on Flickr
Manifold Gauge by jp28800, on Flickr
Christopher Ward C6 Kingfisher - liquid filled case by jp28800, on Flickr
Christopher Ward C6 Kingfisher - liquid filled case by jp28800, on Flickr
Christopher Ward C6 Kingfisher - liquid filled case by jp28800, on Flickr