Bearing margins of safety 1

[dlreed]

I have a question about standard methodology that bearing manufacturers use to grade bearings. I guess this is a Machine Design 101 (Shigley) question. I have been asked to specify a 'margin of safety' against static and dynamic loads. Is this accepted practice for a bearing, or are we only interested in L10 life for a given reliability level for a given load and rpm.

 

[willdo]

The static and dynamic load ratings listed in bearing catalogs are load values that cause permanent deformation on the bearing races. I've been told by NTN engineers you should try to design your bearings at 10% to 20% of these published load ratings.

 

[ChrisGW]

Bearing manufactures list Static Load Rating and Dynamic Load Rating. They are used for completely separate things.

You always use Static Load Rating to determine the factor of safety for an application. Find the worst case loading condition and use that for Factor of Safety calculations.

You use dynamic load rating to calculate the theoretical L10 life of a bearing.

For most applications, to get decent life out of bearing you end up with a factor of safety of 4-5. Depends though.

Your bearing manufacturer should be able to help you out. The calculations and defintions are ussually found in the manufacturers catalogs.

 

[AHRBearing]

Willdo is correct with what the NTN engineers advised. Once once the actual loads approch 50% of the BDR (basic dynamic load rating) most bearing manufacturers start to panic badly, hence NTN speek wise words here.


AHR International Ltd

http://www.ahrinternational.com