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  • zaveri

    zaveri

    MemberOct 27, 2013

    Bearings And Lubrication

    Here are a few questions about bearings:

    1) how exactly does a ball bearing fail ?

    2) Consider a situation, where a ball bearing with its balls fully immeresed in grease is present in a machine. Now if this machine is made to run 24 x 7, when and how will the bearing fail and stall the rotating shaft ?
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  • Siddhant Mukherjee

    MemberOct 28, 2013

    Bearing generally fail when they are loaded in a way for what they are not designed. For example when a simple ball bearing is loaded axially, the bearing cage is likely to fail. The balls in a ball bearing also fail due to crushing and fatigue. Generally ball bearings rarely fail due to radial overloading due to high safety factor kept while designing them.
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  • zaveri

    MemberOct 28, 2013

    @#-Link-Snipped-# @#-Link-Snipped-#

    waiting for your expert opinions. especially to question number 2.
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  • Ramani Aswath

    MemberOct 29, 2013

    No bearing expertise. However, did have some bearing failures in high pressure/capacity chemical centrifugal pumps.
    1. Corrosion by spills leaks and immediate environment
    2. Abrasive failure by dust entrapment in the grease of bearing.
    3. Fatigue failure (poor preventive maintenance.

    This document gives a good overview of the situation. Not all issues will apply in all cases.

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  • Ramani Aswath

    MemberOct 30, 2013

    An update:
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  • CE Designer

    MemberOct 31, 2013

    I saw this topic on the day it was posted and wanted to reply then but work has been really busy lately. Good thing you tagged me in zaveri. It was a good reminder.
    Anyway:

    1. This is a very good question. There are four main reasons why a bearing would fail. Firstly, 'Poor Fitting'. During installation, if the right tools and method are not used you can end up damaging the bearing or even the shaft. This is evident where bearings are pressed unto a shaft where you should not press on the outer race of the bearing or you can risk damaging the balls even before the bearing is put into service. In this case a Bearing Induction Heater can be used. This heater expands the inner race of the bearing which can then be easily slipped unto the shaft. Furthermore to installation, the dimensional clearances of your shaft or bearing housing is critical to your bearing life. High interference fits can put too much strain on the bearing balls and this high pre-load can even damaging them in the process. So it is important also to design your shaft and housing with the proper clearance. Usually the bearing manufacturer would recommend the ideal tolerances. Then there is 'Poor Lubrication'. Wrong or poor lubrication can reduce the life of a bearing. Preventative Maintenance is important. Sadly most places you go don't take PM serious and therefore poor lubrication is a big reason why bearings fail prematurely. 'Contamination' is also another cause of bearing failures. It is important to seal your bearings from contamination. If you are using oil lubrication you should frequently filter or change your oil. Lastly there is 'Fatigue' which is caused by overloaded bearings or bearing that were not properly sized for the application.
    2. The answer to your second question is stated above. In this situation you described what can cause the bearing to seize is contamination from particles or water from the outside. Improper lubrication creates too much frictional resistance and since its in 24/7 service it can get very hot and thermal expansion can seize the bearing. Type of lubrication whether oil or grease should also be considered. In my experience I have found that bearings that are spinning at high rpm tend to push the grease away from itself due to the high centrifugal forces. You may want to consider oil in this application. If the bearing balls deform or wear out badly the shaft would seize since it is the balls that transfer the rotational motion.
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  • Sarathkumar Chandrasekaran

    MemberOct 31, 2013

    CE Designer
    I saw this topic on the day it was posted and wanted to reply then but work has been really busy lately. Good thing you tagged me in zaveri. It was a good reminder.
    Anyway:
    Thanks for your time and to you to give an understandable explanation.We are missing your contributions.
    I have a little doubt.Which "FIT" among the three fits were very efficient for power transmission purposes?
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  • Ankush Sharma

    MemberDec 18, 2013

    dear,
    about your second question, as you mentioned that bearing is fully immersed in grease. so its obvious that the chance of wear between internal and external race with ball bearing is less or too low.
    So now as you also mentioned that the machines is working 24 x 7, so its clear that we cannot consider static load carrying capacity.
    So this is the case of dynamic lad carrying capacity, means the bearing will fail only because of fatigue failure.
    So simply if the dynamic load carrying capacity of bearing is less or start decreasing because of fluctuating load as compared to the dynamic load acting on the bearing, then the bearing will fail.

    I hope its clear to you , if any doubt fell free to ask....
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