Duplex Bearing Arrangements - Back to Back, Face to Face and Tandem

Duplex-Bearing-Angular-Contact-Ball-Bearing

Duplex bearings are a set of two bearings on a shaft with the inner and outer rings clamped together with preload to attain greater axial and radial rigidity. Duplex bearings also used to achieve additional capacity when insufficient space radially for larger bearings.

Duplex bearings are machined as matched sets. The pairs are furnished with the race faces ground to provide preload when installed. To accomplish this, a gap is provided between the inner races or outer race of the pair. When the bearings are installed and clamped axially, the gap is closed producing a preload on the bearings. There are three types duplex bearing arrangements commonly used and they are Back to Back, Face to Face and Tandem bearing arrangement. Bearings that are normally duplexed are angular contact ball bearings and tapered roller bearings.

Back to Back Bearing Arrangement (DB, O)

back-to-back-o-bearing-arrangement

Back to back bearing arrangement, gap is provided between inner races

Back to Back bearing arrangement (also known as “DB arrangement”, “O arrangement”) is a type of duplex bearing arrangement where the two half are placed so that contact angle lines of the bearing diverge inwardly. And these contact angle lines form ‘O’ shape, hence called as “O arrangement”.

back-to-back-o-bearing-arrangement

Back to back bearing - preload animation

In back to back arrangement a gap is provided between inner races and when installed, this gap is closed and producing a preload on the bearings. DB arrangement has higher moment stiffness than the DF arrangement. Under the same preload, DB and DF have identical radial and axial stiffness.

Back to back bearing arrangement may used to carry

Heavy radial loads, combined radial and thrust loads, reversing thrust load, moment loads

Face to Face Bearing Arrangement (DF, X)

face-to-face-bearing-arrangement-pretension-animation[4]

Face to face bearing arrangement, gap is provided between outer races

Face to face bearing arrangement (also known as “DF arrangement”, “X arrangement”) is a type of duplex bearing arrangement where the two half are placed so that contact angle lines of the bearing converge inwardly. And these contact angle lines form ‘X’ shape, hence called as “X arrangement”.

In face to face arrangement a gap is provided between outer races and when installed, this gap is closed and producing a preload on the bearings. DF arrangement has lower moment stiffness, so they must be spaced sufficiently to provide resistance to moment load.

Face to face bearing arrangement may used to carry

Heavy radial loads, combined radial and thrust loads, reversing thrust load

Tandem Bearing Arrangement (DT)

Tandem bearing arrangement - Only accepts one directional thrust load

Tandem bearing arrangement (also known as “DT arrangement”) is a type of duplex bearing arrangement where the two half are placed so that contact angle lines are parallel. This arrangement makes a very heavy duty thrust bearing arrangement, but it will not carry any radial load and accepts thrust loading in only one direction. DT has the same radial stiffness with equal preload as the DB/DF arrangement, but its axial stiffness is twice that of DB/DF arrangement with the same preload.