View Full Version : centrifuge pics

03-18-2007, 01:25 AM
Here's the body of the device, otherwise known as the containment chamber, could otherwise be confused with Captain Fantastic's first intergalactic pickup truck-http://img.photobucket.com/albums/v136/heinrich/containmenthousing.jpg

A look down towards the warp drive, actually a breadmaker motor direct driving the reluctron beam cooler, er, the rotor shaft. http://img.photobucket.com/albums/v136/heinrich/lookinginside.jpg

Here's one of the dilithium cyclotrim gyros. Ok, it's just one of the cups where I put the mixtures to be de-aired. This pic illustrates the swinging motion of the cups when the rotor's turning. http://img.photobucket.com/albums/v136/heinrich/swingingcup.jpg

I demonstrated this for a friend the other day. As I plugged it in, he took a few steps backwards and somewhat behind a door frame. Talk about a self-preservation instinct :)

It works well enough, removing large bubbles quickly and leaving only the very smallest still in suspension. Crude but effective.

Just to add a couple things- the cups pop right out of the cyclotrim gyro rings, for easy cleaning and use of the material being de-aired. Also, a look at the top of the rotor seems to show at first glance that there's only one bolt holding each arm to the hub. That's not the case, each bolt passes through the hub and threads into the opposite arm. The two bolts on the top of the hub actually pinch the two halves of the hub together, tightly clamping the cross bolts between them. The two halves of the hub were bored to fit the shaft, then were mounted on a jig and tablesawn to size. This made sure that the center hole was indeed centered in each piece. After that, the halves were grooved (again on the table saw) to make channels for the cross bolts to fit through. This operation made these channels equidistant from the central axis, ensuring that the arms were also bolted up in a balanced position. No balancing was needed, though I did expect to have to do some.

03-18-2007, 07:00 AM
Cool! You might try slowing it down to see if you can get more of the small bubbles. If you recall in the previous discussion I suggested that too many gees will compress the small bubbles to the point where they are overwhelmed by fluid dynamics effects and don't rise.

Maybe a two stage action, first a short high speed phase and then a longer slow speed phase.

03-18-2007, 09:54 AM
If the motor is contained entirely within the containment vessel and the vessel is only pierced by the motors power leads, it'd be easy to seal that point, make a lid from part of another "pressurized flourocarbon vessel" and you'd be able to pull a vacuum on the whole affair, then spin it down.

Poor man's Beckman-Coulter...

03-18-2007, 10:01 AM
Looks like it'll fly to me! :)


03-18-2007, 10:02 AM
Nice work, but if Scotty saw your inertial dampers in that state, he'd have your guts for garters!

03-18-2007, 10:26 AM
If the motor is contained entirely within the containment vessel and the vessel is only pierced by the motors power leads, it'd be easy to seal that point, make a lid from part of another "pressurized flourocarbon vessel" and you'd be able to pull a vacuum on the whole affair, then spin it down.

The motor might have a conniption. Overall insulation resistance is greatly reduced at low pressures.

03-18-2007, 11:00 AM
Cool project.

A couple of questions:

- What exactly are we extracting bubbles from?

- Did you start with a new, unused propane tank? If not, how did you get the last remnants of flammability out before cutting it up so it didn't explode?



03-18-2007, 11:57 AM
Nice little project there. I dont know why I would need one but it would be fun to make one day.

And, yes indeed, what are you removing bubbles from? Plastic casting resin?

Or meth lab equipment?
:D Just kidding of course.


03-18-2007, 11:58 AM
I like it....Looks like the leg mounting points serve another purpose? The shaft bearing mounting plates?

Real nice, JRouche

03-18-2007, 12:44 PM
"If not, how did you get the last remnants of flammability out before cutting it up so it didn't explode?"

This is another furphy that should be laid to rest!

If you have filled the vessel with water, there is NO flammable gas left.
What you can smell is ethyl mercaptan, the agent added to LPG so you can smell leaks.

The ethyl mercaptan is not dangerous in itself (in these residual quantities)

So, let's do it again.......
Open the cylinder valve to ensure there is no gas pressure left.
Sit in the sun (outside, ok?) for a while to remove all traces of LPG.
Unscrew the cylinder valve.
Yes, this can be a problem cos of the protective collar.
Cut it off with a hacksaw (or other tool, your call).
OK, now you've removed the collar and unscrewed the (open) valve, you can fill the bottle with water.

Once you've filled the bottle with water, there can be NO flammable gas left. QED.

03-18-2007, 04:01 PM
At one point, I was getting set up to make plastic model parts, so I started getting some time saving mechanisms together. That project did't fly, but from it I got to make the vacuum table, an epoxy mixing and dispensing machine, a vacuum/pressure molding vessel, and this centrifugal de-airing machine would have been not far behind that. It's been a few years since the project flopped, but I had awlays wanted to make this thing. Now it's done. I have lots of molding rubber and epoxy left over, so I want to use it up, and lately I've had a bit of a bend towards making some parts again.

If I was to do this project again, or develop a commercial use for a de-airing machine, I'd do it differently. I'd be spinning a tall cup shape, basically, and it would have a tight fitting cap so it could be evacuated just before and /or during spinning up. Whatever mixture was inside would spread up the sides of the container and try to escape from the top, except the lid would be on. There would be many advantages to doing it this way- one is that the mixture would spread out over a larger surface area than it does in my contraption, and the larger area means a thinner layer of the mixture, which means quicker de-airing. It would be smaller in overall size, use a standard speed motor, probably 3450 rpm, and could even be made to expel the de-aired mixture through a feed tube to the mold. Whatever, you always find better ways to do something after you've done it one way. This is just a hobby for me now anyway, so whatever.

You guys have raised a few interesting points. There may well be an optimum speed to de-air certain mixtures, and it might not always be the highest speed you can get away with. I like the idea of evacuating this chamber during operation, and I could set it up to do that, but I'm going to save that option for the next model if I have need of a better one. Interesting also that there would be less voltage standoff potential for magnet wire in a vacuum than in an air environment. I hadn't thought of that. I doubt it would be a problem for this motor to run it in a vacuum, but that's something to consider. There would be little cooling in a vacuum, but for short periods of operation this wouldn't be a problem either.

Preparation of the vessel- I did fill this old tank (has been used for years until the change to the newfangled valve) completely with water before cutting on it. I then left it outside and upside down for the water to drain, then brought it inside to work on it. I can imagine that lpg might outgas to some small extent from the pores of the metal, and that could give rise to a combustible mixture, but I don't know the truth of that. I do know that the ethyl mercapton has a staying power beyond belief. Once I had the top and bottom of the tank cut out, I sanded the entire inside, scrubbied it, and thoroughly washed it with soapy water, and even bleached it after that which is a no-no for the metal, but still it gives a smell. Everyone who's seen it remarks that it still smells like propane. Whatever.

Yes, the leg mounting points also fasten the three sheet metal plates inside, which hold the bearing blocks. You can see the curve cut out of these plates to allow room for the cups to swing without hitting them. I would have liked to make the leg mounting brackets a little nicer, but also- whatever. (that seems to be my word for the day :)). I could always upgrade those simple brackets for pieces of channel or similar. That would look a little better. If I get the urge to paint the thing, I'll neaten that up first. Maybe I'll print up some NASA decals to put on it :)

03-18-2007, 04:45 PM

The problem with insulation resistance isn't the actual insulation on the wires, it's any place the wire isn't insulated such as connectors, brushes etc. Things such as connectors are heavily derated when used at altitude. As an example a mil spec connector by Amphenol may have a 7000 volt flashover rating at sea level but that drops to 700 volts at 70,000 feet. In general a factor of ten is appropriate to determine derating.

BTW, the only way to get the mercaptans out of the micro-cracks in the metal is to bake it.

03-18-2007, 07:01 PM
Thanks, Evan, that makes sense. It would be easier for current to flow in a vacuum than in an obstructing environment, which is what air would be. Dry air, at least.

I did wonder how the motor would behave in a vacuum. Asiide from the lack of air cooling, there might be issues with the lube in the sealed ball bearings. What might be different about ball bearings used in a vacuum environment, or in space? Special lube, I presume, to start with. Maybe a full pressure seal- or conversely a shield instead of a seal- to allow air to escape without taking lube with it?

03-18-2007, 07:52 PM
I would expect the grease in a bearing to have a lot of entrained air in it so it would probably foam, at least the first time. Probably not good for the bearing or seal. In real space applications they have to worry a lot about outgassing and the contamination it produces as well as changing properties. You can buy vacuum rated greases and oils.

03-18-2007, 09:40 PM
You can buy vacuum rated greases and oils.

Haaa, thats HSM stuff.. :rolleyes: .. You can make vacuumed grease for prolly less....JRouche

03-18-2007, 11:07 PM
There isn't anything particularly unusual about vacuum greases and oils and they are widely available. They are used in refrigerant systems, any sort of vacuum pump and many other applications.


03-19-2007, 07:14 AM
Haaa, thats HSM stuff.. :rolleyes: .. You can make vacuumed grease for prolly less....JRouche

Bar oil is just as good.