Non-metallic Rotary Seal for High RPMs?

8,000 rpm.

carbide maybe, they are used for pump seals

phoenix911

Graphite may work

Ceramic? Maybe sleeve the shaft.

your solution may rest not in the shaft and seal materials but in a coating, I would try looking at a high lubricity coating such as boron nitride available from caswell plating, it is designed for internal combustion engine components and may well serve your purpose. Internal combustion engines present a very challenging environment for any material and friction reducing materials designed for them would be a good area to look for a solution, turbine engines also have a demanding set of requirements and make extensive use of high heat, chemical resistant seals.

GA from me. Babybear, good to see you again giving good answer

Hello gsuhas:

How are you my friend? I hope you are fine!

I thank you kindly for your GA. I have not been able to think straight for a while and seem to be getting back to my 'old' self now. Thank you once again!

Happy new year gsuhas.........

You mention that it is low pressure liquid... This is definitely not my area of expertise, but I am imagining a pressurised air system around the seal to force any liquids back into the process. Would this be viable? Is this the "labyrinth seal" that Garth proposed?

Hello Critcho:

This is a type of labyrinth seal.

In this cut-away you can see the helical groove which throw any oil back into the engine or whatever. In the OP case the liquid is acid. And from my point of view, there is bound to be some bypass of acid, which is extremely corrosive, through the labyrinthine 'seal'. Which as you can see makes no contact or seal with any moving part.

I hope this makes it a little easier to understand. There is so many different styles, with some including bristles.

Take care............Happy new year.................

Joining late. Not one of my favourite sections.

For this high speed I recommend labyrinth seal, since at this surface speed, it may be difficult to use contact seals.

In our machines of about 7000 RPM it is only labyrinth.

For this speed it is nit always required to go for the groove on the shaft and usually the seal will be sufficient.

As an additional precaution (I don't think it may be necessary, go for pressurised labyrinth (it is what we use in gas turbs)

(This is from the sketch of our regular seal ACAD converted)

At this high speed may be mechanical seals may work, but then you need stelliting or some other hard-facing.

Sorry Time ran out, so the socond part (converting from auto cad) -

The above seal is all aluminium

the other type of seal used is in a cast iron body with SS fins staked in (as in turbine sealing fins) and machined to the profile

Both are used for high speed machines

In either of these - any contact seal is strict no no for our high speed machines.

Upto 3000 rpm mech seal.

of course our machines being large, the diameters and hence surface speed are high.

Thank you all, for your insight. Priceless, as always.

I've considered all the suggestions. We are going to try a modification of the labyrinth idea. Since the shaft is vertical (which I hadn't mentioned) and the fluid is above the seal, we're going with a type of "umbrella" attached to the shaft which fits over and down around a collar on the lower section. This keeps the splash from seeping down the shaft and would necessitate the fluid to climb up the collar, between the umbrella and collar, before it could get down below, where we don't want it to be. This may work.

I appreciate your help.

Hello Out of Box Experience:

I really apreciate you letting me/other know. You did as you say leave out an important detail of the shaft being virtical, but, I hope what you try works.

There is another solution though........Drive the shaft from above which means the shaft will not have to go through the bottom of the case which is the bug-bear?

Tell me, what are you doing that necessitates the acid in there? You may have said but I can'r recall?

The top of the shaft has a vacuum port in the center of it. A disk sits on top of this, with the vacuum holding it in place. The 8000 RPM is used to spin this disk in order to shed the acid from it with centrifugal force, once the necessary reactions take place. So there really is no way to change the relationships or orientation from what I've stated. The challenge is to keep the acid from running down the shaft to the motor, and also to keep the acid fumes from getting to the motor... hence, the seal.

The modified vertical labyrinth that I described should do the trick if I keep the tolerances very small between the two barriers around the shaft and if I blow nitrogen up and out from the motor chamber, and also ventilate the upper chamber. The comments that I received from everyone confirmed that a contact seal wasn't needed, and that the desired results could be achieved through other means. So thanx to all!

If anyone is curious, the design we were discussing has come to fruition. I did, in fact, follow thru with the labyrinth concept. It may be interesting for you to see actual results that came from a discussion on this forum. This is rare, I know. Still some bugs to iron out. And actually I am getting suggestions for those bugs in another thread: Variables Related to High RPM Vibrations , if you would like to see what your suggestions have led to.

You have all been very helpful and are making my job a bit easier.

A design based on an international collaboration. I love it! :)

I gave a GA to garth for first suggesting a labyrinth seal, which is the direction I ended up going. And also a GA to Babybear, for all the effort put forth in researching all those excellent and useful websites, for me. They will prove useful.