Reliability Engineering for Maintenance

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  • 1.  Bearing failure-root cause

    Posted 19 days ago

    Hi all 

    Recently had a bearing failure on a grinding/classifying mill. After taking the bearing assembly hub apart it became obvious why the mill had stopped working. However I'm trying to understand what would cause the bearing failure in the pictures.

    The assembly hub contains three bearings, two nu316 cylinderal roller bearing and one qj316 deep groved ball bearing with a spilt inner race. The bearing hub is located in a vertical position with with one bearing at the top end, and two bearings on the pulley end. The very bottom bearing is the  ball bearing. 

    Running speed:2600rpm

    Belt driven

    75kw motor

    What I believe has happened is that the outrace has been spinning inside the house,(the housing as been sleeved before) allowing for the ball bearings to impact the inner race as it turns. This has been generating enough heat to cause it to deform. 

    Any thoughts are most welcome.

    Also we have accelerometers attached to the bearing housing and readings were taken 3 days before this failed. The readings didn't indicate any defects or an increase in stress levels. 

    What could cause a bearing to fail so rapidly?

    James Peters

  • 2.  RE: Bearing failure-root cause

    Posted 18 days ago

    The damage to the split inner race bearing, axial or in/out movement of the shaft would create this pattern. If you put the split races in the correct orientation, this would mean the shaft had to be moving in and out at least .250" or more to dent both bearing races.

    The outer race, ball path is not in the center of the bearing, meaning the balls were not riding in the center of the outer race. Some how the outer race was not centered over the balls/inner race

    Cheap bearings that were not properly heat treated. Bearing overload can cause the bearing metal to deform.

    Your cage shows signs of elongated holes that hold the balls, also indicating in and out movement


    Dave Reynolds

  • 3.  RE: Bearing failure-root cause

    Posted 14 days ago

    Thank you Dave for your message. Really appreciate your insight on the bearing defects. I wasn't 100% sure what I seeing so it's good to get someone else's opinion who's clearly got a lot more knowledge and experience in this field. It will just help to identify what the root cause of this problem is and look at solutions.

    James Peters