Micro Ball Bearing
From the beginning, ease of service and longevity were our primary concerns in the design of our new calibre A35. For this reason, we decided at an early stage already to place the complete winding mechanism on lubricant-free four-point micro ball bearings. As a result, the frictional losses are reduced to a minimum.
In establishing our rotor manufacture for different calibres, our goal was to make the rotor bearing lubricant-free, quiet and shock-proof, but also to keep the tilt angle as small as possible. But since a normal micro ball bearing leads to an excessive tilt due to the geometry of its raceways, these were unsuitable for our purposes.
The so-called four-point micro ball bearings already in use in the watch industry, whose inner race is divided and whose bearing clearance is adjusted by pressing or connecting on the second taper ring, were considered as well. But the attempts to precisely adjust the radial play and tilt by pressing the taper ring on a divided four-point bearing on the inner race turned out to be difficult due to the small outer diameter (<2.7 mm).
A bearing with a precisely defined play had to be developed, as our crown wheels only run on a one-sided inner bearing ring and a “tilting away” under stress had to be limited to a negligible minimum. We found the solution in a new raceway geometry for our micro ball bearings. Through this geometry, the required 4-point contact was also achieved. The advantage is that the bearing consists of a single-piece inner ring and outer ring. In production these can be machined with the closest work tolerances and subsequently the bearings are assembled using ceramic balls with a precisely defined size or dimension. Thus one can, for example, set radial plays of 5, 10 or 15 microns without any problem.
The thereby achievable very small radial play also permits only a so-called tilt in the μ-range, which is of major importance for rotor bearings.
It should be mentioned that our new bearings are made of non-corroding stainless steel and fully hardened, while it is quite common in the watch industry that the pressed-on taper ring on the inner race on multi-part four-point bearings is made of toxic copper beryllium bronze.
As the ceramic balls can be manufactured with a superfine surface structure and neither micro-bonding nor frictional corrosion occurs, a lubricant can be omitted completely. And as lubricants do not age this way, a high longevity ensues.