Bearing RCA

[Muhammad Mazher]

Hello everyone,

I need your guidance on an issue we are experiencing. In our industry, we encountered a bearing (Deep groove ball bearing 6319 ) failure in a motor driving a gear box. The motor is a 185 kw unit running at 1500 rpm. It is a non drive end bearing. We observed signs of electrical erosion (fluting) on the bearing, which is typically caused by current passing through them. This issue is often related to inadequate grounding in the motor. Additionally, the motor is operated by a variable frequency drive (VFD).

https://files.engineering.com/getfi...=WhatsApp_Image_2024-08-14_at_7.35.54_PM.jpeg

https://files.engineering.com/getfi...tsApp_Image_2024-08-14_at_7.35.53_PM_(3).jpeg

There are marks on the outer ring of the bearing that appear to be the result of burning or thermal stress. I have attached pictures for reference.

https://files.engineering.com/getfi...=WhatsApp_Image_2024-08-14_at_7.35.53_PM.jpeg

https://files.engineering.com/getfi...=WhatsApp_Image_2024-08-14_at_7.35.52_PM.jpeg

https://files.engineering.com/getfi...tsApp_Image_2024-08-14_at_7.35.53_PM_(2).jpeg

Could you please share your insights or reviews on this matter? your feedback will be valuable for conducting a root cause analysis.
Thank you!

 

[TugboatEng]

That's about as text book case of stray current wear as you're going to see. The discoloration on the back is 100% normal. It is caused by fretting, but at that level it is not detrimental.

There are quite a few options to resolve this issue ranging from shaft grounding, to bearing isolation, to modifying VFD parameters (lower switching frequency).