Self-contained magnetic bearings

This is a very cool technology. The price is a bit steep...$45,000..., so it's not a hobbyist item. But it would be very, very cool to have some of these suckers.

Baldor is planning to use them in some new motors, for up to 30,000 rpm.

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Reply to
Ed Huntress
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I've seen them used in a15Kw semi-hermetic centrifugal refrigeration compressor. These things wizz around at about 30,000 RPM, and have an active control system that maintains the shaft in the centre of the bearing. I can't remember the name, but it was an Australian design that couldn't raise enough money to go into production ( Never ending storey, here in Auz) so managed to get a Canadian company involved. I saw an early production model set up in a test rig here in Melbourne. The big advantage that I saw, was that it was totally unlubricated, so no oil return systems were required. They only made the one size,as it was aimed at the commercial (not industrial ) sector. My first quetion was" What happens in a power failure?" They assured me that it maintained its centre untill it slowed down to about a thousand revs, then dropped onto some plastic wear blocks. They did not offer to demonstrate.

Reply to
Grumpy

air bearings are much cheaper and work if you don't need to operate in a vacuum

Reply to
Bill Noble

Not much good in a refrigeration compressor!

Reply to
Grumpy

Here's a stupid question. Suppose that your device is running happily on those magnetic bearings.

Then, wham, power to them goes out.

What will happen?

i
Reply to
Ignoramus7943

That's answered in the brief article linked to above.

Reply to
Ed Huntress

Ed, I did not see any answer.

i
Reply to
Ignoramus7943

This caught my eye too.

Here is the company's website: .

And the relevant patent application is US 2009/0265038 A1.

Joe Gwinn

Reply to
Joseph Gwinn

Oh, sorry, Iggy. I bounced all over with the links after I read that, and I see that I actually got the answer to that question at Synchrony's site.

Try this, and search down the page for this question: "What happens if the shaft contacts the auxiliary bearing due to a total loss of power?"

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Reply to
Ed Huntress

Similar to the concept of incorporating the amp and motion controller in the same package as a servo motor, for example...

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Reply to
Ned Simmons

Air bearings are certainly much cheaper, but they can have stability problems and tend to fail in spectacular fashion. I worked on a project a few years ago where we were considering magnetic bearings specifically for their ability to compensate for instability and load imbalance on the fly. SKF demo'ed a high speed spindle for us. The motor was barely audible as we sat in a conference room and the motor spun at 30,000 RPM in the middle of the table.

But it was godawful expensive, and we ultimately used conventional ceramic bearing spindles.

Reply to
Ned Simmons

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However, I think that the assumption is that if power fails to the bearing, it fails to everything else, too. If something else is providing the power to rotate the load (e.g. a steam or gas turbine), and it is not linked into the power failure sensors in the magnetic bearing with a fail-safe, things could get rather exciting.

Enjoy, DoN.

Reply to
DoN. Nichols

Been available for quite a few years in fans, I've been gradually replacing old computer fans with ones with mag-lev bearings as they gum up. No failures yet. They run about twice the price of ball bearing jobs. Mean time before failure is waaay out there. The trick is to scale the technology up so there's a payback within a reasonable time. Or use it where lube failure costs a lot more than just the failed motor, like a computer.

Stan

Reply to
stans4

The answer probably eventually should be:

"In that case we use the motor that's driving the shaft as a generator, and draw power from its rotational inertia in order to keep the bearing operational until speed is low enough not to matter. This enables us to have the auxiliary bearings last indefinitely, unlike the old versions of our bearings, in which the auxiliary bearings might only survive ten power losses, which meant that you really needed a UPS to keep them powered, as we still recommend if you have the old versions installed."

But they evidently haven't gotten around to implementing that feature yet... since that webpage, as it stands, only describes what I'm calling 'the old versions'.

Reply to
Norman Yarvin

Although those are nice, they aren't actually mag-lev bearings; instead they're just plain bearings (sleeve bearings) which are magnetically pre-loaded so that the thrust loads are in the opposite direction from what they would otherwise be. That is, the magnet's pull counters and overpowers the fan's aerodynamic thrust. I think the idea is that it's better to take the thrust load on the end of the shaft than it is to take it on a snap ring, since the end of the shaft has more surface area to bear the load.

Computer fan terminology seems to be driven more by marketing than by engineering precision; that same basic idea -- magnetic preload -- is called by a variety of names, including "fluid dynamic bearing" and "magnetic barometric bearing", depending on who is selling it. And if you really want to be amused, try guessing what an "air rifle bearing" is. (Can you shoot squirrels with it?)

Real mag-lev bearings can't be done by merely adding permanent magnets to a bearing; instead they require electromagnets driven by a controller that continually senses how far the shaft is from its desired position, and activates the electromagnets to push it back. Thus the high price.

Reply to
Norman Yarvin

(...)

OH!

I studied a cross - section drawing and tried to understand why the repulsion of the 'levitation' magnet wouldn't just push the blade assembly against the axial stop at the end of the sleeve bearing travel. Now I grok.

Thanks!

--Winston

Reply to
Winston

The answer is:

Regenerative braking.

Feedback loops have gotten pretty fast and they run either open or closed.

Reply to
John R. Carroll

One would think they would self power like a helicopter and auto gyro down.

It can be planned in the heavy stone wheels that spin through periods of time before a generator can come up if really bad. And if the wheel goes crazy the direction it blows through a building can be defined.

Mart> >> This is a very cool technology. The price is a bit steep...$45,000...,

Reply to
Martin H. Eastburn

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