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Preventative Maintenance - Brunswick All - Bearing Life


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  • Preventative Maintenance - Brunswick All - Bearing Life

    In relation to the recent “B Shaft” failure, I thought I would throw this subject on the table for discussion. I remember when I attended a “Bearing Life” seminar long ago, they showed us a bell curve for expected bearing life. Basically no matter how well bearings are taken care of, some will fail prematurely of their expected life. The calculations for the bearings on the pinsetter will give you a headache but I suspect the L10 and L50 calcs for these bearings have been far exceeded, especially on the very old machines. Another good argument for the Energy Savers. The bottom line here is, inspect often, keep bearings well lubed and clean, avoid contamination, practice good bearing mounting procedures and you will most likely avoid catastrophic failures and machine down time. The needle greaser is a great tool. Bearings can be greased easily in place with this tool. Here is a sample bell curve showing bearing life and a statement right from the Net where I did a search for “Bearing Life Expectancy”.

    "The bearing life statistic is a measure of the amount of time in revolutions where 90% of the ball bearings can be expected to have survived. This does not mean every bearing will fail as soon as this number has been exceeded, of course. The median life for ball bearings, also referred to as the Mean Time Before Failure, or MTMF, is about five times the basic life number for the bearing. This means that at 5 times the Basic Life Rating revolutions you should expect about half of your ball bearings to have failed. It’s important to remember that there may be some variation in your individual results with a ball bearing, and factors such as proper lubrication, care and handling of the bearing, and stress on the bearing can result in very significant fluctuations in the life of the ball bearing."

    Bearing Bell Curve.jpg
    Everything has to be Somewhere !!

  • #2
    Biggest cause of ball bearing failure that I have encountered on these machines is neglect closely followed by incorrect instalation causing stress to races.


    • #3
      Agreed HP. I also forgot to include: Every time a bearing turns, the bottom ball caries all the load for a split second. It is this constant stressing, compression and expansion that eventually causes the fatigue failure. When installing the jack shaft bearings, shaker shaft, etc., it is important to rap the shaft gently with a rubber mallet several times while rotating the shaft so that it "centers" or aligns the bearings on the shaft relieving any unnecessary pressure which will result in premature failure. Here is an article I found on the web, seems pretty informative:
      Everything has to be Somewhere !!


      • #4
        While it is very important to keep bearings well greased, use caution to Not Over-lubricate. This can cause overheating and premature failures. This probably won't effect the pinsetter bearings too much as many of them don't ever make a full rotation, run fairly slowly, and only run intermittently. Another good case for Power Savers!
        There also was a time when the Japanese bearings supplied from Brunswick were not properly machined. Inside and outside dimensions were not correct. Usually the ID. was too large. You typically need about 0.001 inch interference fit - that is, the shaft is 0.001 larger than bearing ID on small bearings. This will vary with shaft size, speed, etc. Micing these dimensions may save a lot of work and money due to shaft failure from a loose bearing. Looking at the Chines bearings that are coming through, I'm not getting a warm fuzzy feeling. If you can find a good bearing house that supplies US Bearings, really made in America, you may be better off.

        I attached the article here in case you don't want to go to the Net: Bearing Failures.pdf
        Attached Files
        Everything has to be Somewhere !!


        • #5
          Here's the real deal on bearing fatigue.

          Bearing life cycle.

          YMMV (your mileage may vary) but basically it comes down to operating conditions, load, temperature, and RPM. The one thing the calculator doesn't consider is preventive maintenance.

          The above page will take a little time to load, it's a bit complex.


          • #6
            Tried the Timken site. Looks like it only works for tapered roller bearings but it does work well unless I'm missing something. You need part numbers for both races which would indicate a tapered roller bearing ?? Calculated one small bearing at 200 RPM - L10 = 15,000 Hrs; 100 RPM = 30,000 Hrs; 1 RPM = Over 1,000,000 Hrs. Yikes
            Everything has to be Somewhere !!


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