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Politics : Foreign Affairs Discussion Group -- Ignore unavailable to you. Want to Upgrade?

To: Sig who wrote (124112)	2/2/2004 11:54:21 PM
From: Bilow	Respond to of 281500

Hi Sig; Re: "But der centrifuges for isotope separation are far different than the ones you showed. They have to run for years without stopping and are criticaly balanced so the bearings do not fail because they contain deadly materials being separated and once started nobody vants to mess with the mechanisms. So the best tubes are none too good. A tube used for a rocket requires consistent material of high strength, but distortion or the thickness tolerance is not so critical as with a centrifuge." Nice German impersonation, but bad engineering. High speed centrifuges use gas or magnetic bearings, there are no contacting surfaces. There's a drive at the bottom, but it's not a contact drive so there is no wear. At the top, there's a magnetic bearing. These things have no parts that wear, the bearings last indefinitely. Here's a diagram: nanp.dubna.ru Low speed centrifuges have standard bearings with a motor and the centrifuge on a rigid axis. For that, you must have a very well balanced machine or you will get vibrations. High speed centrifuges instead let the apparatus find its own stable axis of rotation (i.e. a "principal axis"). That such an axis exists, and that rotations around it are stable against small perturbations is due to a law of physics that is described here: scienceworld.wolfram.com Here's another physics reference to why it is that long centrifuges don't have to be carefully balanced: Review of the gas centrifuge until 1962. Part II: Principles of high-speed rotation Three types of rotor can be identified, depending on the ratio of length to diameter. If the rotor is very short, length-diameter ratio less than one, it is gyroscopically stable and easy to spin. If the length-diameter ratio is in the region of 4 or 5, the rotor behaves as a rigid body and is relatively easy to accelerate to speed; however, it has a tendency at full speed to exhibit gyroscopic precessions. Finally, if the length-diameter ratio is very large, the rotor becomes easy to stabilize gyroscopically, but it is difficult to get it to speed because long rotors are very flexible and have resonant frequencies of flexure lower than the operating speed. ... These early principles are briefly reviewed, with particular reference to the work of De Laval, who invented the principle of self-balancing, Reynolds and Evershed, who developed hydrodynamic and magnetic bearing, respectively, and Chree, who did the most extensive early work on the stress analysis of tubes and discs. prola.aps.org Here's more information on self balancing rotors: The Laval rotor: resonance and self-centering ... wwwrz.rz.uni-karlsruhe.de ... The support for high speed rotors is provided typically by gas lubricated bearings. The reason is not only the low friction, but also a certain freedom for self-balancing. This freedom is given by the gap of the order of few tens of micrometers between the bearing surface and the rotor. The principle of self-balancing was established by De Laval in 1889. ... kbfi.ee Self-centering in supercritical rotation ... Since the end of last century such rotors are known to have an equilibrium position very close to the rotation axis, which is pivotal in reducing the otherwise destructive effects of centrifugal forces in high-speed machines such as turbines, centrifuges and ultra-vacuum pumps (see Whitley, S., 1984, Rev. Mod. Phys., 56, 67 for a review). ... eotvos.dm.unipi.it In short, small balancing errors in a (well designed) high speed centrifuge do not result in significant balance problems. They're designed to be self-correcting. As far as that goes, the technology required to balance a rotor is so ancient and simple that it's already been done to billions of wheels in the United States at small time garages. So if a rotor were severely out of balance one can trivially correct it by adding, as it were, little lead tire weights, LOL. The big problem with high speed gaseous diffusion centrifuges is not balance, but vibration and tensile strength. The accuracy of the machining of the tube doesn't enter into the equation. Here's what the experts say (buy your centrifuges here): "Materials particularly suitable for centrifuge rotors are those for which the ratio between tensile strength and material density is large: for example high strength steels or composites. Ultimate strength and density are not, however, the only material parameters which limit the development of higher separative powers: the length of centrifuge rotors is limited, long rotating tubes start to vibrate when they reach the so-called critical frequency. The critical frequency is a function of the length, of the crosssectional area and the polar moment of inertia of the rotor, the density and the modulus of the rotor material and boundary conditions determined by the bearings." urenco.de Note that accuracy of machining isn't listed as a parameter because the accuracy of any reasonably modern machine tool is enough. And contrary to common fuzzy headed liberal thinking, uranium is no more toxic than other heavy metals. But let's cut to the chase. The evidence that the tubes were associated with a nuclear program evaporated despite all the war heads going on and on about how no one would ever use high accuracy aluminum tubes for rockets. My own guess is that the Iraqis did what every engineer on the planet does and simply copied the most recent manufacturer's specs into their latest part specification. As time goes on, the manufacturers improve their specifications and the engineers ask for better stuff. -- Carl