Radial Load to Torque on Bearing 1

[Mandrill22]

I have a shaft with a radial load of 2300 N. I have two deep groove ball bearings on the shaft, pressed into rotating members. Is there an equation to calculate the amount of radial load the bearings absorb? I'm trying to figure out how much torque resistance there would be on the shaft's rotation. The shaft rotates with the long members. The drawing shown isn't fully representative of the system, but it gives you an idea.

 

[BrianE22]

My go-to for stuff like this is SKF. The following summarizes bearing moments:

https://www.skf.com/binary/77-121486/SKF-rolling-bearings-catalogue.pdf

Page 132 provides a link to a calculator. I'm guessing you are using seals? The seal friction will dominate the total bearing moment.

 

[Mandrill22]

I should've mentioned this, but didn't think to. The calculator can be a little finicky when it comes to low rotational speeds, particularly when the speed is unknown. Since the members will be turned by hand, we're looking at something like 30-50 RPM.

 

[Mandrill22]

The SKF calculator says no loss due to seals. I'm assuming because there is no axial load.

 

[Tmoose]

~ 600 lbs force on a 1/4"Ø 1.5" long shaft would induce a bit of deflection I'd guess, which might cause each of the a single row ball bearings to bind badly, even if the manufactured colinearity of the bearing bore in each of the legs was excellent, and maintained as excellent which seems highly questionable from the admittedly simplified model and scanty information provided.

 

[geesamand]

I once explored this question because hand-rotating a shaft with a torque wrench is a way to establish preload on a set of opposed bearings. Think pinion bearings on the rear axle of a vehicle.

I was unable to find any equations that worked with the low rotating speeds. I suspect it's because true rolling friction is less predictable. I used the SKF calculation anyway; I have no idea whether the actual torque was higher or lower than expected, but the equipment functions well for us.

I think you'll have to settle for a very rough estimate and measure the first few prototype units. Misalignment is another factor that could affect your real-world experience with frictional moment.

 

[Mandrill22]

@Tmoose, There is a block in the center that the pin runs through. The pin has some rigidity in the middle. I also considered using an 8mm shaft and self-aligning bearings from SKF. They are rated for 560N each and would allow for 3 degrees of misalignment.

The better option seems to be using needle roller bearings. Any ideas about what kind could work? The trick is how to keep them small. There's no axial load, so the roller kind could be the right fit.

 

[Mandrill22]

How about this one?
Link

 

[Mandrill22]

Or, even better, how about a Spherical Roller Bearing?

 

[BrianE22]

Needle bearings aren't good if the shaft is bending - you'll load up the edges of the rollers. Spherical bearings are good if the shaft is bending.

 

[dvd]

Your bearing has no seal losses because it has no seals (-2Z suffix denotes non-contact shields)