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Seals for a rotating shaft? 30k+ RPM motor?

  1. Feb 23, 2008 #1
    Hi, everyone

    I am a long time reader but this might be my first post. I am currently in a Senior Design Project and doing research for my project.

    I am doing a rotating shaft with flow through the middle of the shaft to a exiting hole on the other side radially out the shaft. ( I can explain more later if needed ) One end of the shaft is enclosed, so it needs to be sealed so no leakage is allowed. It will then exit a meter on the enclosed section.

    The requirement that I am looking for is seals for 30k+ RPM. 50-100 psi. This is for the shaft.

    I have looked into labyrinth seals and carbon seals. Would this be a right assumption?
    Is there any other seals that would do?

    Does anyone have knowledge of motors that spin 30k+ RPM?

    I was think a gearing up a electric motor or use a air driven motor. The torque that is needed should not be that much since it is not driving anything but the shaft and bearing friction.

    Any hints or toward a direction is greatly appreciated.

    Thank you for your time.

    Last edited: Feb 23, 2008
  2. jcsd
  3. Feb 23, 2008 #2


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    Google on "Flexible Graphite Packing" and you'll find suppliers of this material, Teflon/Graphite hybrids, etc. These are made for very high-temperature applications, and some may be able to handle your speed requirements. These are easier/faster to install than mechanical seals.

    Note: You'll have to convert your RPM to shaft FPM to conform to the specs that these packing manufacturers publish.
  4. Feb 23, 2008 #3


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    I have pretty good experience with high speed rotating seals. However, I am not quite understanding your layout. I understand that one end of your shaft will have radially spaced holes which the fluid will flow from. However the rest is a bit fuzzy. You say that one end is enclosed, yet you also say this is the end that needs to be sealed?

    First off, can you post a picture? Secondly, do you need a face seal or a radial seal? Labby seals will have a characteristic leakage rate associated with them. They are not perfect seals. However, the leakage can be minimized by proper buffering and they can take any speed that you throw at them assuming proper design and material selection. Depending on the diameter of your shaft, I'll bet you that you will not find a radial lip seal that will handle the surface speeds you'll be seeing. Carbon seals are another good option, but your machining and design need to be precise.

    Let's get a better picture of what you are doing and go from there.
  5. Mar 14, 2008 #4

    here is a picture of the item. It is the red part of the picture. The shaft size will be 2.5 inches. Air would be entering the shaft in the middle and exiting out of the green cylinder (thru a venturi, not in pictured). The shaft would be rotating at 30K + rpm. There will be bearings on both sides so the red part is only needed for sealing. I was told that labyrinth seal would work and they are zero contact.

    Can I use a grease/crank type seal if possible?

    Where can I get more info on labyrinth seals?

    Info on 30k+ electric motor with to turn almost a 1-2 pounds at the most?

    Info on couplers that can can be connected to the end of this?

    It is needed so air can be directed in. So far I just found 2/3k rpm couplers.

    The motors that I have found was mostly rc car engines.

    Sorry for the newbie questions but my school has limited resources since it has been cutting back and engineering department is on first on the list.
    Last edited: Mar 14, 2008
  6. Mar 14, 2008 #5


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    They are zero contact. However, like I mentioned, they do have an inherent leakage rate associate with them because they are zero contact. If you can run a buffer air source to the labby cavity, that can help tremendously.

    You will never find a lip seal that will handle that surface speed, especially with a Ø2.5" shaft.

    Unfortunately, labby seals are in that black area that companies like to keep to themselves. There are a lot of technical papers out there on their analyses and influences on other components.

    Oy. You're in trouble. You're going to have to use something like a gear box or air turbine to get those speeds. You can't just slap an electric motor that turns 30 krpm, especially one that is cheap. In this speed range, nothing is cheap.

    See the response above. At these speeds, you're looking at custom designs. I would suggest starting to do some research with companies like Rexnord and Lovejoy for couplers. Honestly, I would be surprised if you found a large enough coupler to handle those speeds. I know Rexnord makes some nice flexible disc couplers that can do it (their instrumentation coupler line), but not at Ø2.5 ID. I'd sugest you figure out how you're going to turn it at that speed first and then move on the coupler. I am thinking you'll have to go with a splined shaft connecting the two. At least that way you could have a hollow shaft to inject the air through.

    I hope you have an adviser that has experience in this area. You're dealing with some serious rotational energy. Have you given any thought to what bearings you'll be using? How about the shaft dynamics of the rotating hardware? How are you going to lubricate this? There are a bunch of other things to look at. I hope your bases are covered.
  7. Mar 15, 2008 #6
    wow that is a lot of stuff but great information, I will have to get back to you on this stuff as mid terms are here.

    Thanks you for the help, I will update on this once I get all my research done.
  8. Apr 27, 2008 #7
    Here a quick update, We came to the conclusion that it is not within our budget to go 30k+.

    We were given a electric motor the is rated at 22k ( not sure of the voltage) and electric fan bearings that are sealed and almost matches the speed. The bearings so ceramic type bearings the ID is .47 inch.

    Do manufactures give leakage rates through the bearings assuming perfectly sealed on the ID and OD? (leakage rate at a certain pressure though the inside of it)

    And for the sealed bearing gurus, Does anyone know of a sealed ball bearing 2.5ID that can go 30k at room temp, for a 1 to 2 min, the loading is minimal? ( I am just asking again because there might be a item that could work under these conditions)

    Thank you
    Engineering in Training
  9. Apr 27, 2008 #8


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    With an ID of 2.5" and 30krpm, that's a dN of 1.9 million. That is way up there ESPECIALLY for a sealed, grease packed bearing. I hate to say it, but you are probably going to be out of luck for something off the shelf. I have used grease packed bearings at about 36 krpm, but the ID was much smaller. To get a proper answer you will have to talk to a bearing manufacturer. I would recommend talking to someone at Barden Bearings. We use them quite a lot in our engines.

    One thing to note, you will have to decide what kind of bearings you need, i.e. conrad, angular contact, needle, etc...If your loading is minimal, you may have to add something like a wave spring to provide preloading. Bearings, in general, do not like to rotate at high speeds without a minimal load. A real bearing engineer will be invaluable in helping you with this.
  10. Apr 28, 2008 #9
    Thank you for the heads up. I will talk to Barden.

    The funny thing is that the engineers at my sponsor gave me a set of Barden Precision Bearings. The ID is .5 inch but they are older bearings and I cannot find any information on that.

    Thank you again, back to hibernation to figure this thing out. I will be back cause I know I will have questions.
  11. Apr 28, 2008 #10


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    They should have a laser etched part number on them. If you can find it, post the number. I am sure we can find the information on them.
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