pre-loaded bearings

[MTSfitter]

Just going through a trade school book and there is a question related to ball and roller bearings i cannot find the answer to anywhere!!-

why would a bearing be pre-loaded?
and
what's one way to check pre-load?

some help if anyone know would be great.

ta.
MTS.

 

[dinjin]

They preload bearings to ensure more of the rolling elements
support the loads. It also removes any wobble caused by bearings with internal clearances. Essentially a preloaded bearing has no radial play if a radial bearing. If you know how to check bearing clearances, the result would be zero. Some do this also to increase stiffness. Turning torques can be high however and will cause heat build up at higher speeds.

 

[yaoc]

1. what preload is:
- Preload is the nagtive bearing internal clearance, meaning certain press applied inside the bearing in the cold condition before the operation.

2. why preload:
- Preload can increase the bearing & shaft system stiffness, measning the less runout of the shaft.
- Also under certain situation, the preload can help the bearing achieve the higher service life.

3. how to measure/inspect preload:
- As you know, the bearing internal clearance, bearing setup torque is related. Since the preload means nagtive internal clearance, we can get the specific preload status, thru:
a. OE can do the check while mounting the bearing, from a positive position, and achie the negtive one;
b. Or, do the "Setup Torque vs Bearing Preload" relation, and find the answer thru the torque.


BR,
Steven

 

[Tmoose]

The shop manual for many cars will have procedures to set rear axle pinion and carrier bearings with preload. Also in the days when cars used steering boxes, before rack-and-pinion was so popular. Torque required to turn the shaft is a common measure of preload achieved.

 

[Eratosthenes]

preload may also be required for bearings seeing high acceleration to avoid slipping (and wear) of the rolling elements.

 

[EngineerErrant]

Exactly as yaoc said (negative clearance of rolling elements), as well as:

Higher preload -> Higher rigidity of the bearing -> Less deflection of the assembly under load.

You can probably think of a bunch of examples where accuracy of the assembly's position under load is important. Preload's often used in machine tools to maintain a certain tolerance on the parts produced.

Note that by increasing the preload, you will also be increasing the drag of the bearing, as you're basically continuously squishing the rolling elements while it's in motion.

To check preload, measure the rolling element diameter, measure the space it has to roll in, and figure out how "oversized" it is.

 

[JJPellin]

We would typically install a pre-loaded bearing to avoid ball-skid. With no load, a rolling element can skid rather than roll. If this was pair of back-to-back angular contact thrust bearings for example, you might see a skidding failure in the unloaded bearing. The new bearings would be ground by the manufacturer to have a light pre-load. The inspection to verify the pre-load could be a simple as the feel of the force required to counter-rotate the two outer races after the bearings are installed and clamped tight to the shaft.

Johnny Pellin

 

[dinjin]

Other than simple thrust bearings, skip is unavoidable since the circumference of the inner and outer are not
the same and something has to give, skip, slide or whatever. I know it does help to avoid fretting corrosion as it keeps the elements from vibrating under no load or alternating load conditions.