Bearing Preload question. 2

[GrimRyan]

I am using 2 radial bearings, The inner race is stationary on a shaft, the outer race rotates with the bearing housing. I am using a tolerance ring to fit the outer race to the housing. I plan on using a wave spring washer to apply an axial force to hold them in the housing and to deal with manufacturing tolerances. My boss wanted me to see if the spring washer would apply enough force to pre load the bearings, but I did not think that pre load was a neccesity for radial bearings.

My questions are: Is it important to apply an axial pre load to the bearings, and if yes, how do I calculate the amount of force I need to apply.

 

[dinjin]

Contact the manufacturer of the bearings and fully
describe your application to them. They are paid to
do that by their company.

 

[GrimRyan]

Been contacting them for a couple days now. Keep getting the egineers voice mails. Kind of makes me want to reccomend another manufactuere to my company.

 

[dinjin]

Sorry to hear that. You would have to provide the full apllication data for two bearings on the same shaft and how they are mounted back to back or whatever. Some radial bearing are preloaded but often by controlling the the shaft or od sizes. Is your contact angle in the bearings Zero i.e. a true radial ball bearing, tapered roller bearing, or an angular contact bearing, or a radial roller bearing, a radial barrel roller type bearing. There are so many different answers to each of these.

 

[BobM3]

What bearings are you using? Most radial bearings don't need axial preload. Does your application require either axial location or axial stiffness? If so you would want enough preload to satisfy the application's requirements (but then make sure the bearings can handle that combination of radial and axial loading).

 

[Tmoose]

Even radial ball bearings benefit from light preload. Quieter running, less skidding, etc. Note electric motors often have a preload spring pushing axially on the floating bearing.

I think you'll find a desireable preload is ~ "light" preload on a similarly sized precision angular contact spindle bearing, or as provided by a standard bearing preload spring provided by Smalley and others. Of course the bearing manufacturer's spec prevails.

I question if it can push hard enough to slide the bearing in the "tolerance" ring

 

[electricpete]

What exactly is meant by a "tolerance ring" ?
Thanks

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[Tmoose]

I took it to be one of those corrugated sheet metal steel cylinder things.

http://www.usatolerancerings.com/

 

[electricpete]

Thanks Tmoose. I never heard of those... definitely learned somethign. I wonder if those allow a non-locating bearing to slide axially within the housing?

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[MikeHalloran]

The corrugations in a tolerance ring are fairly stiff; I wouldn't expect them to slide easily.



Mike Halloran
Pembroke Pines, FL, USA

 

[Tmoose]

I believe among the tolerance ring's claims are replacing press fits, so they can be quite grippy.

On principal I would not consider them for rotating machinery except maybe holding on a plastic cooling fan.
That is because I believe centering with flexible elements is imprecise, and I take reliable centering VERY seriously.

Nonetheless These guys use them for some big ball and roller bearing OD mounting in (aluminum ?) housings. Zoom 500% in on page 7 and see the thin dark rectangle on each of the bearing ODs.

http://www.voithturbo.com/applicati...22en_voith-tvvs-soft-start-fluid-coupling.pdf

Also that the bearing balls are marked with an X, like a cartoon character's eyes after being struck by a brick

 

[GrimRyan]

Exactly the tolerance ring allows a consistent press fit force with the expected tolerances of the machined housing.

I finally got in tough with the bearing manufacturers engineers, He said the bearings will run smoother and quieter with a light preload of 10-15lbs. He did say that not preloading the bearings will not affect the life of them as long as they are being pressfit into the outer housing and slip fit on the shaft. I dont know if preload changes for bearing size but I'm using 1" ID, 2.5" OD bearings.

 

[Tmoose]

How are you retaining and locating the device ( bearing inner rings) axially on the stationary shaft? If by a nut, or an inner shoulder, or practically any other way, the potential to preload the bearings hard against each other is real, and dangerous.
It is best if there is a way to keep the inner rings precisely separated at the same distance as the outer races.
One way is with an inner spacer

http://czmadness.net/techdata/Canada Parts/Parts101.jpg

Item #5 - disatanc collar
Or, shoulders machined on the shaft, necessitating assembling the bearings from each end

http://czmadness.net/techdata/Canada Parts/Parts103.jpg