Ball bearing spin to roll ratio recommendation

[cuckooclock]

I am in the process of choosing hybrid ceramic ball bearings for a high speed alternator (turbo-generator) application and would like recommendations as to good spin to roll ratios. Various ball bearing design programs will predict the ball to spin ratio under specific loading and speed, but apart from a vague remark that lower is better there is no real discussion of the consequences.

For example if I have a 25 mm bore ABEC grade 7 bearing running at 56000 rpm I predict a ball to spin ratio of 0.36 This seems about the same as found in some Nasa publications but I need to know if this ball to spin ratio will cause a reduction in bearing life due to cage and or raceway/ball wear.

[Aside: I have failed to get support from the ball bearing suppliers in this -and other matters- because I am not at the point of being able to buy 100s of bearings. SKF will not even allow me to open an account and to pay for engineering support!].

Thanks for all constructive advice.

 

[MartinSr00]

You might want to contact someone in the turbomachinery group at United Technologies/Pratt-Whitney/Rocketdyne in Canoga Park CA.

They have lots of experience in this area. They make very high speed turbopumps. They make the ones for the space shuttle fuel and lox pumps. You need to also get the cages right.

At DN's this high (in your case 1.4 million), overall bearing life will be short. Of course, proper lubrication, perhaps oil mist or something like that will be crucial for significant life.