Bearings. Can Outer Race rotatation in housing be acceptable? 1

[Swedishrigpig]

I am inspecting an Oilfield Triplex piston Mud pump and the Pinion shaft has two Self Aligning Roller Bearings (1 ea end).
Approx. diam 460mm. Max clearance as per spec is 0,040-0,1092mm between housing and Bearing OD, I.E. no interference fit. Max Pinion speed 417 RPM
During testing it was noticed that the outer bearing has turned a few degrees in the housing. The manufacturer states that there is an allowance for the shaft to float slightly to allow temperature expansion etc. and this might allow the outer race to rotate a few degrees.

My question is this:
Is it ever acceptable for the outer race to move (rotate)?
Will the clearance allow the outer race to spin or is this a normal clearance?

 

[JohnRBaker]

If the shaft is horizontal and the bearings are actually supporting the weight of the shaft (and whatever is attached to it), than I suspect there will be little chance of the bearing actually 'spinning'. Now if the shaft is vertical, well...

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[Swedishrigpig]

Yes it is a horizontal shaft that drives a bullgear, or like the Double Helical in:

http://en.wikipedia.org/wiki/Spur_gear#Spur

 

[Artisi]

I seem to recall from deep down in the grey-matter a discussion / lecture / idea from way way back in time that allowing the outer race to "creep" was actually beneficial, this ensured that any point load was not concentrated on only one part of the raceway.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[Artisi]

Having made the above statement, I decided to google bearing "creep" and it would seem that it's not such a good idea - Oh well, I'll just let the idea sink back to where it came from.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[MintJulep]

Common and expected on railroad axles.

 

[Swedishrigpig]

MintJulep (Mechanical)
27 Aug 12 23:11
Common and expected on railroad axles.

Interesting to hear about your similar experience.
Do you have any reference on this I can?
I personally don't think it is a problem but I need something to back it up with.

 

[Artisi]

I would agree, if it is "creep" and not rotation.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[Swedishrigpig]

Creep, the way I read it would be if it was, in this case on the shaft. This I will agree would be reason for consern.

 

[dhengr]

The backing ring, inner seal wear ring, inner cone & roller assembly, cone spacer, outer cone & roller assembly, outer seal wear ring and axle end cap do rotate with the axle, they should not (do not) move w.r.t. the axle they are on. Except for the end cap, all the parts above along with the bearing cup (outer ring), make up a complete bearing unit and are pressed onto the axle as a complete unit. Bearing pressing forces vary from 30 to 60 or 70 tons depending on the bearing size. So they probably don’t move much on the axle. The bearing lateral play when on the axle is btwn. .001 - .020", but the inner and outer cones are not moving on the axle. Finally, truck frame adapters support the bearing cup or outer ring, from above, and transfer the axle load to the truck frame.

 

[electricpete]

Sounds like op's question is already well covered. Fwiw, I'll provide my summary:

The important aspect as you know is which race is stationary with respect to applied load.
In original post, it appears the outer race is stationary with respect to applied load and loose fit selected accordingly between outer ring and housing. Should not be a problem at all to experience some movement at this interface (and as has been pointed out, often benefitical if bearing is required to float axially in the housing).

Double check that the seating surface is still smooth and round and meets your fit requirements before re-assembly, and you should be good to go.

Movement on the inner race on the other hand would likely advance quickly since rotating load with respect to an interface will encourage movement at that interface which can increase any loose clearance further.


=====================================
(2B)+(2B)' ?

 

[MotionGirl]

Just a point - if the outer race creeps then it can be summized that the housing is not supporting the outer ring. This means the outer ring will distort, or not be quite round. This is NOT good. Outer rings can afford to be 'thin' because it is usually expected that the housing supports the 'roundness' of it. Outer rings of cam-followers or not supported, and are therefore thicker than that of a typical bearing.

 

[IceStationZebra]

If you look at the fit recommondations from a bearing supplier like SKF or Timken you will see that this is a complicated subject with no one-size fits all answer. ISZ

 

[MintJulep]

See page 13

http://www.timken.com/en-us/solutions/rail/Documents/Trackside Inspection.pdf