Preloaded angular contact bearings lock in the precision axial displacement of the bearing’s outer rings relative to its inner rings. If the thrust load is bi-directional, use a duplex arrangement for optimum performance. The benefits of preloading an angular contact bearing (ACCB) in a duplex set include:
- Increased load capacity
- Stiffer assembly
- Positioning precision
- Optimized life
- Consistent and predictable torque
- High-speed kinematics
- Vibration and noise suppression
Principles of Preloading
Preloading an angular contact bearing is achieved through stick-out grinding of the bearing components at a fixed axial applied displacement. This causes the inner and outer ring faces to be flush with each other within a set axial force tolerance.
ACBB deflection is not linear, however. Rather, it has a “knee”, meaning that very light loads can deflect the bearing to a greater extent than changes in load at higher loads. Preloading takes up the play in the duplex set and pre-deflects the rolling element to raceway Hertzian contact regions, such that the initial knee to the force versus deflection curve is eliminated.
Preloading Levels
Typically, there are three levels for preloaded angular contact bearings.
- Light Preload (125,000 PSI Max. Hertzian Contact Stress)
- Normal Preload (175,000 PSI Max. Hertzian Contact Stress)
- Heavy Preload (225,000 PSI Max. Hertzian Contact Stress))
Hertzian Contact Stress refers to the localized stresses that develop as two contacting surfaces come in contact and deform slightly under the imposed loads.
Set Configurations for Preloaded Angular Contact Bearings
There are three set configurations for preloaded angular contact bearings that are implemented in a duplex bearing set.
- Face-to-face (DF)
- Back-to-back (DB)
- Tandem (DT)
Bearings can also have a universal or custom configuration.
Face-to-Face (DF)
Face-to-face, or DF, is a duplex arrangement where ACCB contact angles converge toward the bearing axis. DF bearing sets are less sensitive to misalignment, but they’re not as stiff under moment loading as back-to-back (DB) bearing sets. The permissible load directions are radial, axial (both directions), and moment. The stiffness is good for moment loads, and very good for radial and axial loads.
Back-to-Back (DB)
Back-to-back, or DB, is a duplex arrangement where ACCB contact angles diverge from the bearing axis. DB bearing sets are stiffer under moment loading than DF bearings sets but are more sensitive to misalignment. The permissible load directions are radial, axial (both), and moment. For all three types of loads, the stiffness is very good.
Tandem
Tandem, or DT, is a duplex arrangement where ACCB contact angles are in the same direction (parallel). DT bearing sets share radial and axial loads equally but can only carry axial loads in one direction. Their stiffness for axial loads in one direction is excellent. It’s very good for radial loads but only fair for moment loads.
Universal
Universal, or U, is a bearing arrangement where the ACCB is flush ground (inner ring face to outer ring face) on both sides of the bearing at a particular preload force. Universal bearings can be used in face-to-face, back-to-back, or tandem configurations. Permissible load directions and stiffness depend upon the arrangement.
Custom
Finally, preloaded angular contact bearings can use a custom configuration in any set configuration or combination of configurations. They can also be paired with spacer sets. Custom configurations can be designed to optimize performance for a specific application, and both the permissible load directions and the stiffness depend upon the arrangement.
Ask Schatz for Preloaded Angular Contact Bearings
Schatz Bearings of Poughkeepsie, New York is a Made in USA bearing manufacturer that can supply you with preloaded angular contact bearings in duplex or non-duplex configurations. Contact us to learn more about our capabilities and the angular contact bearings that we offer.
