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  • Ball Bearing Speed Ratings...

    What is the limiting factor when it comes to ball bearing speeds? I have an unusual job that may require two telescoping shafts, each turning roughly 26000 rpm but in opposite directions. Presumably, I should be looking at bearings with 52k rpm rating, correct?

    Any recommendations for a high speed, reasonably priced bearing with something close to a 1/2" ID? OD should be as small as possible since it will be installed in another shaft that is rotating. I have some freedom there as far as size goes, but small would be good. I looked at McMaster-Carr for needle bearings and ball bearings. The only thing that was an obvious fit (12mm shaft, 28mm OD, 60k rpm) was an ABEC-7 bearing coming in at ~$200 - a little steep for the application. Looking for something in the $30-40 range.

    Thanks!

  • #2
    Originally posted by Fasttrack View Post
    What is the limiting factor when it comes to ball bearing speeds? ...
    .....Thanks!
    Very good question and one that I knew some of the answers to but certainly not all.
    Although I don't have a list of suitable bearing candidates for your project I did find a very interesting pdf file that perhaps will give you a better insight into the factors that limit bearing speeds. Hopefully this info will allow you to better make a prospective purchase decision.

    http://www.kaydonbearings.com/downlo...erformance.pdf

    Below a list from the pdf of the key factors that limit bearing speeds. I had not considered life requirement but In my opinion this is probably one of the most often overlooked elements in bearing choice.


    Bearing diameter
    Ratio of bearing diameter to cross-section
    Bearing type and internal configuration
    Ratio of ball groove radius to ball diameter
    Bearing internal fit-up (diametral clearance
    or preload)
    operating contact angle(s)
    Bearing precision (runouts)
    Ball separator material and design
    Precision of mount (roundness, flatness under load)
    Lubrication
    Ambient temperature and provision for
    Heat dissipation
    Seals
    Loads
    Life requirement
    Home, down in the valley behind the Red Angus
    Bad Decisions Make Good Stories​

    Location: British Columbia

    Comment


    • #3
      Ceramic ball bearings

      http://compturbo.com/spotlights/triplex-ceramic

      How's about ceramic ball bearings, fitted inside some pretty small turbochargers, spinning at 100K r's and better, almost red hot, very hot and thin lube, mile after mile after mile. Mass produced.

      Maybe the above people can help.

      --G

      Comment


      • #4
        I suspect that when you get into that speed range that there are no inexpensive bearings that will any sort of a reasonable life.

        Comment


        • #5
          Interesting question and I don't have the answer either. However, I believe that one of the main limiting factors for ball bearings is the strength of the cage and the centrifugal force acting on it. With both rings spinning in opposite directions the cage is standing still so that's not a problem anymore.
          You do have huge seal lip speed, so it's going to be hard to keep any contacting seal alive. Better to try a shielded bearing, or better, an open one with oil lubrication.

          Igor

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          • #6
            If you look up the bearings in something like a die grinder, you'll probably see that they're running way over their rated speed. You have to remember that bearings are usually specified at 100,000 hour operating life and you can exceed some of those specifications if you can accept a shorter life.

            A cheap die grinder might have a design life of 50 hours. That can equate to many years of hobby 'use'.
            Paul Compton
            www.morini-mania.co.uk
            http://www.youtube.com/user/EVguru

            Comment


            • #7
              Die grinder bearings also run in an air-oil mist which allows them to run at higher speed. That being said the bearing life in die grinders is pretty short compared to the same bearing in a "normal" speed application.

              I would probably go with a ceramic ball bearing. You can get them off ebay cheapish. They are used in the mini turbine jet engines which do 70-100k rpm and also turbo pumps which will do up to about 90krpm.

              Comment


              • #8
                I don't know whether you are able to try a bearing or whether it needs to be first time right, but I'd try this one:
                The energy efficient bearing E2.6002-2Z/C3 from SKF with a reference speed of 55000 and a limiting speed of 28000, bore = 15mm. They're pretty cheap, about five dollar for instance here:
                http://uk.rs-online.com/web/p/ball-bearings/7192036/
                Smaller sizes like 6001 and 6000 are rated for even higher speeds.

                The raceways have a larger osculation reducing slip losses, non contacting shields, low friction grease and a low friction cage design. All of this is positive in your application. End of sales pitch :-)

                Igor
                Last edited by ikdor; 08-12-2014, 07:31 AM.

                Comment


                • #9
                  Originally posted by macona View Post
                  Die grinder bearings also run in an air-oil mist which allows them to run at higher speed.
                  Not in electric grinders!

                  I would probably go with a ceramic ball bearing. You can get them off ebay cheapish. They are used in the mini turbine jet engines which do 70-100k rpm and also turbo pumps which will do up to about 90krpm.
                  Having spoken to some model gas turbine builders, they rate the bearings at about 40 hours of full load running. That is quite a lot of flying between rebuilds though.
                  Paul Compton
                  www.morini-mania.co.uk
                  http://www.youtube.com/user/EVguru

                  Comment


                  • #10
                    Thanks guys. Lots of good suggestions. A 50-100 hour life would be more than sufficient at this point. The product in question is an early prototype and proof-of-concept. I think ceramic is the way to go and I would like to find one that would be used in a turbocharger for the "next generation", since we will eventually need longer lifetimes.

                    Igor, that looks like an interesting product to build the prototype around.

                    I have contacted SKF to get some more information about speed ratings and to see what they have to say about this particular problem.
                    Last edited by Fasttrack; 08-12-2014, 09:47 AM.

                    Comment


                    • #11
                      Originally posted by Guido View Post
                      http://compturbo.com/spotlights/triplex-ceramic

                      How's about ceramic ball bearings, fitted inside some pretty small turbochargers, spinning at 100K r's and better, almost red hot, very hot and thin lube, mile after mile after mile. Mass produced.

                      Maybe the above people can help.

                      --G

                      that's where my head went to too... that's some crazy RPM's and anything sealed or even shielded will most likely overheat and also pop it's cover off, I think @ 50,000 + you can forget about grease...

                      Comment


                      • #12
                        Originally posted by A.K. Boomer View Post
                        that's where my head went to too... that's some crazy RPM's and anything sealed or even shielded will most likely overheat and also pop it's cover off, I think @ 50,000 + you can forget about grease...
                        No grease, for sure. Since I don't require long lifetimes for the prototype, I have no problem removing seals and washing out grease, if a "standard" bearing will get me 100 hours or so at 50k rpm without blowing up. I used to do this for high mileage vehicles back in high school.

                        Comment


                        • #13
                          It won't be easy to find the turbo ones for sale as they are only produced for the turbo manufacturers. It is a cartridge with two raceways, special cages and it combines with the housing to make a fluid dynamic film damper.
                          Your requirements are not that dramatic, so there seems no need to go that exotic.

                          Igor
                          Last edited by ikdor; 08-12-2014, 10:03 AM.

                          Comment


                          • #14
                            Originally posted by Fasttrack View Post
                            ....................... if a "standard" bearing will get me 100 hours or so at 50k rpm without blowing up. I used to do this for high mileage vehicles back in high school.
                            I used to get what seemed at least like 50k rpm out of my vehicles in high school as well. But yeah not for long.
                            Home, down in the valley behind the Red Angus
                            Bad Decisions Make Good Stories​

                            Location: British Columbia

                            Comment


                            • #15
                              Originally posted by Fasttrack View Post
                              No grease, for sure. Since I don't require long lifetimes for the prototype, I have no problem removing seals and washing out grease, if a "standard" bearing will get me 100 hours or so at 50k rpm without blowing up. I used to do this for high mileage vehicles back in high school.

                              Iv done quite a bit of that too, some bearings feel great yet are running dry and the owner is on a budget so carefully remove seals and clean and re-pack, but you have to be careful, you have to leave all kinds of extra room, you can't pack them to the hilt or they will pop their seal covers off, found that out with a mitsu --- luckily it had timing belt change intervals of only 50,000 miles...

                              I generally leave about half space air,

                              @ 50,000 rpm's I don't know what id do, light oil - but your going to almost immediately toast your seal lips i would think, then there goes your oil...

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