Fitting and clamping of bearing rings
Fitting and clamping of bearing rings
(OP)
Hello everyone,
I'd like to discuss with you about the bearing and end cap torque for different bearings. For angular contact bearings, I have seen different methods. When I looked in the SNFA book, which is to me the best reference for angular contact bearings, they explain how to calculate the tightening torque in fonction of the preload and other parameters whereas NSK gives a unique torque value which is in fonction of the threads.Which one is the best? I'd say SNFA but I'd like to have your opinion. Moreover, SNFA says that this is a rule of thumb and the preload should be verified during operation. What is the best way to do it? NSK talked about three methods which are starting torque method, thrust static rigidity and natural frequency method but they don't give enough details. Does it really work great?
A second point is the locknut and end cap torque needed for non preloaded bearings such as deep groove or double row angular contact bearings. I haven't found something that could tell more about that. I know, I should call the bearing manufacturer, but honestly, I'd rather have the opinion of users than builders!
Thanks,
I'd like to discuss with you about the bearing and end cap torque for different bearings. For angular contact bearings, I have seen different methods. When I looked in the SNFA book, which is to me the best reference for angular contact bearings, they explain how to calculate the tightening torque in fonction of the preload and other parameters whereas NSK gives a unique torque value which is in fonction of the threads.Which one is the best? I'd say SNFA but I'd like to have your opinion. Moreover, SNFA says that this is a rule of thumb and the preload should be verified during operation. What is the best way to do it? NSK talked about three methods which are starting torque method, thrust static rigidity and natural frequency method but they don't give enough details. Does it really work great?
A second point is the locknut and end cap torque needed for non preloaded bearings such as deep groove or double row angular contact bearings. I haven't found something that could tell more about that. I know, I should call the bearing manufacturer, but honestly, I'd rather have the opinion of users than builders!
Thanks,





RE: Fitting and clamping of bearing rings
advice unless you know all of the specifics
of the contact angles and conformity for the
ball bearings or the specifics of the tapered
roller bearings. They in turn offer you some
guideline for the life based on the preload.
Too much preload will result in greater stiffness,
higher turning torque,but very short life.
RE: Fitting and clamping of bearing rings
Attempting to set preload by tightening end covers or nuts is danged risky at all but the very lowest speeds.
Machine Design had an article Sept 19, 2002 "How retaining forces affect spindle bearings". The tests they made sounded pretty scientific. One of their results was "excessive" OD clamping in an <> arrangement compresses the spacer and reduces preload. The conclusions were kind of controversial in my mind,
(first) since their recommended clamping forces were initially derived from such general recommendations (cover gap + 0.001 inch)
(second) their derived clamp force is wildly exceeded by recommended nut torque clamp
I forwarded that article to folks I knew in a big bearing tech department and got NO reply.
RE: Fitting and clamping of bearing rings
Angular contact preloaded bearing
SNFA recommends a force relative to the preload and other parameters whereas NSK gives a unique value independant from the preload. It just doesn't make sens to me. The clamping force should varie according to the preload and number of bearings. For the end cap, nsk recommands 0.0004'' to 0.001'' clearance before tightening whereas SNFA still recommands a value according to the preload. I worked with a spindle repair companie which used to set the clearance at 0.003'' to 0.005'' which is what I used to do. Tmoose, I'm not sure to understand what ''danged risky'' means (is it good or not) and what do you mean by 'cover gap + 0.001'')? Do you want to say 0.001'' clearance between housing and cover before tightening? If I understand your second point about the article, the effect on the spacer should have been worst on the inner ring since the clamping force is higher? According to NSK, excessive end cap clamping force will cause the ring to deform. I think there is a way to see this effect on vibration analysis but I'm not sure. But the real question is ''what is the best way to preload a bearing and ensuring that it's well done?'' . Another question could be ''what is the optimal end cap clamping force (or clearance) in order to avoid excessive deformation while keeping the outer ring well rested?''
Standard bearing
My question was more about a deep groove bearing than a taper roller bearing. With standard bearing, mechanics used to torque the locknut as bad as they can. I'd like to have an optimal value that will minimize the ring deformations.
RE: Fitting and clamping of bearing rings
RE: Fitting and clamping of bearing rings
RE: Fitting and clamping of bearing rings
RE: Fitting and clamping of bearing rings
You are using "preload" and I think you
mean "interference fit". That is why the
replies are confusing. Interference
fit will reduce the clearances in the
bearings. Preload is generally defined such
that the bearings have no clearance
but actually a tight fit.
RE: Fitting and clamping of bearing rings
My comments were meant for
JeanMicheling. Sorry!
RE: Fitting and clamping of bearing rings
But what about the prelaod on angular contact bearing, I used to preload my bearings at full torque with no consideration of the preload needed. And for the end cap?
On standard bearing like deep groove, can tightening the locknut at the optimal torque can increase the bearing life? Is it negligible?
RE: Fitting and clamping of bearing rings
You are confusing me. If the bearing is preloaded,
by definition, it is preloaded axially and radially.
Isn't this true?
RE: Fitting and clamping of bearing rings
RE: Fitting and clamping of bearing rings
It is the confusion between preload which does
deal with the bearing internal conditions and that
interference deals with the outer envelope
dimensions ie bore and od or width.
RE: Fitting and clamping of bearing rings
RE: Fitting and clamping of bearing rings
I do not know if it is just semantics or not.
You can have a loose fit on shaft or housing
and still have a bearing preloaded or have
a bearing with clearance. The fit will affect
or reduce the clearance in a bearing. It will
increase the preload in an already preloaded
bearing, but I think you have already ruled out
using preloaded bearings for your application.
I think in some of your correspondence when you
are using "preload", you mean tight fit?
RE: Fitting and clamping of bearing rings
RE: Fitting and clamping of bearing rings
Tight fit is often used for the member that is
turning to assure that slippage does not occur.
Whether it affect the clearance is another issue.
Because you have a tight fit, does not mean that
you have any preload on the bearings. It will
diminish the clearance by a small amount. We
are in agreement that preload internally is not
a good thing for your application. So the bearing
manufacturer will recommend an initial clearance
that would exceed the effect that an interference
fit would cause to the internal workings of the
bearing to ensure that the bearing will have
clearance after being pressed on to the shaft
or into the housing.
RE: Fitting and clamping of bearing rings
RE: Fitting and clamping of bearing rings
RE: Fitting and clamping of bearing rings
So my assumption was wrong. You do want bearings
that have an internal preload to ensure that
fretting does not occur. I got confused by your
second point where you introduced angular contact
bearings with clearance. One of the beauties of
a nut is that you can tell by the amount of turn
of the nut and also dependant on the thread pitch
just how much axial preload you are applying to the bearings. Assuming that the contact angle is
45 degrees it then is a function of the sin of 45
degree contact angle that you are imposing on the balls.
The beauty of having preload on all of the balls in
the bearing is that more balls see part of the actual
loads imposed on the bearing.
I have not seen SNFA's book so I cannot comment on that.
How did you get a copy? I looked on the internet but
only found general information. Their literature that
I did see looks impressive. I assume you are from
Canada since the they are from France. I would think
any company supplying the aerospace industry would have
some very sophisticated equipment. The methods that
they suggest to determine the preload, can these be
done in house and at assembly?
RE: Fitting and clamping of bearing rings
Another way to distort an outer ring is to have extra gap between cover and housing, so the cover pilot diameter pinches inward or "oil cans" at each cover screw and distorts the race through face contact. That would only apply when the cover contacts and clamps the outer race, as is practically universal at one end of electric motors and machine tool spindles.
Limiting the cover gap (which usually requires adjustment at each overhaul) to 0.001 inch is intended to limit the oil can effect to a harmless level.
RE: Fitting and clamping of bearing rings
Torrington catalog 102-10M-998 wants a 75 mm bearing locknut tightened to 173-250 lb-ft, at which point it would exert between 3600 and 5200 pounds of clamping force on the inner races and spacers. Depending on bearing arrangement [ <> or >< } that would increase or decrease preload.
If the nut thread pitch is 1 mm then 0.002 inch of axial motion would require about 0.05 turn or 18 degrees to go from light to heavy preload, and cut the thermally limited speed about 50%.
The 1992 Machine Design article used a 7022 bearing. It says "CAP FORCE EFFECTS -
As the retaining cap clamps the assembly
into the bearing housing, the bearing
outer races, spacers, and joints between
them compress. This tends to reduce the
mounted preload and stiffness of the
bearing assembly." This cap is clamping bearing outer rings against precision spacers.
RE: Fitting and clamping of bearing rings
RE: Fitting and clamping of bearing rings
please list the url for the article where you found
the technical specs or information from SNFA. I did
find the SNFA website, but did not find any technical
data.
RE: Fitting and clamping of bearing rings
So, if I understand, methods for preloading the locknut may varie from one user ot another one. If you have ground bearings, one might want to torque the locknut enough to rest the rings together apart from the type of preload and other parameters. That's what NSK seems to believe. But another one might use the SNFA methods which will give you a specific torque for each type of bearing. The only difference, I guess, is the influence on the spacers and rings that could, by the way, affect the preload.
Can someone answer my question on the cover clamping load (Does the gap mentionned above must be set up before of after tightening the bolts?)
RE: Fitting and clamping of bearing rings
RE: Fitting and clamping of bearing rings
RE: Fitting and clamping of bearing rings
a pilot diameter.