I recently missed a cage defect on a vertical mounted 10hp ac motor that had shielded 6308 bearings on both ends. Demodulation did show cage frequencies but my alarms were set to high to be triggered. I have adjusted my alarms but my questions are;
What caused this cage to fail? There was no visable damage to the balls or either race other than the bearing getting very hot. The cage was very distroyed and compressed with balls to one side of the bearing like it come to a sudden stop.
Are deep grove ball bearings the correct bearing for vertical applications?
Are there any special grease applications we should be using to ensure the grease is not running out?

IN MY EXPERIENCE FIRST CAUSE OF BEARING FAILURES IN VERTICAL MOTORS ARE REALTED TO THE FACT THAT HORIZONTAL ELECTRIC MOTORS ARE NOT DESIGNED TO WORK VERTICALLY. THE PROBLEM IS THAT ELECTRIC MOTORS DESIGNED TO WORK VERTICALLY ARE MORE EXPENSIVE. THE DESIGN YOU HAVE (6308 BOTH SIDES)SEMMS TO ME LIKE A TIPICAL HORIZONTAL MOTOR WITH CROSS LOCATING BEARINGS (THEY TIPICALLY HAVE A SPRING WAHSER)

SECOND REASON IS POOR LUBRICATION DUE TO GREASE LEAKAGE. A HIGHER LUBRICANT LEAKAGE RATE IS NORMAL IN VERTICAL APPLICATIONS DUE TO THE INFLUENCE OF GRAVITY.

IF THE DAMAGED BEARING WAS THE ONE AT THE BOTTOM, AND YOU SEE THAT DAMAGE IS WORSE AT ONE SIDE OF THE GROOVE OF THE OUTER RING, I WILL PROBABLY BE AXIAL OVERLOAD DUE TO VERTICLA MOUNTING OF THE MOTOR. WHEN AXIAL LOAD IS HIGH CAGE IS SUBJECTED TO ADDITONAL FORCES DUE TO THE LARGER CONTACT POINT. IF THIS IS THE CASE, USE C3 OR C4(VERY DIFFICULT TO FIND) BEARINGS. THEY COPE BETTER WITH AXIAL LOAD THAN NORMAL CLEARANCE BEARINGS.

IF THE FAILED BEAQRING DOES NOT LOOK LIKE DESCRIBED ABOVE, POOR LUBRICATION COULD BE THE ISSUE. POOR LUBRICATION COULD BE THE RESULT OF A MECHANICALLY UNSTABLE GREASE THAT LEAKS OR TOO LARGE RELUBRICATION INTERVALS. REMEMBER THAT RELUBRICATION INTERVALS SHOULD BE MULTIPLIED BY 0.3 (APPROX 3 TIMES SHORTER) FOR VERTICAL SHAFTS. A NLGI 2 OR 3 LITHIUM COMPLEX GREASE WITH PROPER BASE OIL AND ADDITIVES WOULD WORK. A NLGI 2 OR 3 POLYRUEA GREASE WITH GOOD MECHANCIAL STABILITY COULD DO THE TRICK TOO.

HOPE THIS HELPS.

We have some motors with vertically mounting (50 motors). They are using deep groove ball bearing (DE and NDE). Some of them without shielded/open type. We never got problem like you.

We are using Unirex N3 grease from Exxon Mobile with Lithium Complex for vertical motor

For Horizontal mounting, we are using Multemp SRL from Kyodo Yushi

What cause it? did you check your spectrum for your motor?

Very interesting posts. Thank you for sharing.
I find all of this very useful
Thank you,
Steve,
Atlantic City