Single direction and double direction thrust ball bearings
In terms of construction the thrust ball bearings are divided into single direction and double direction thrust ball bearings.
Single Direction Thrust Ball Bearings
consist of two flat washers with raceways, balls and cage. The washers have a flat seating surface therefore they have to be embedded so that all balls are equally loaded.
Double Direction Thrust Ball Bearings
have two cages with balls between the central shaft washer and both housing washers with flat seating surface. The shaft washer has raceways on both sides and is fixed on a journal.
Single direction and double direction thrust ball bearings can accommodate large axial load, however they must not be subjected to radial load. During operation these bearings must be constantly subjected to a specific axial load.
Main dimensions of thrust ball bearings specified in the dimension tables are in accordance with the international standards ISO 104.
Designation of standard applications is specified in the dimension tables. Difference from basic application is marked by additional symbols.
Thrust ball bearings have as standard steel cage, where the material and application is not marked. Special construction requests should be discussed with the supplier in advance.
Thrust ball bearings are commonly produced in the tolerance class P0 that is not marked. For more demanding kinds of seating bearings with higher tolerance class P6 or P5 can be supplied.
The seating of thrust ball bearings requires as accurate alignment of seating surfaces as possible, because the misalignment of the seating surfaces causes increased stress in the contact of balls with the raceways. It is not recommended to use thrust ball bearings where the conditions of alignment cannot be met.
Axial equivalent dynamic load
Pa = Fa (kN)
Axial equivalent static load
Poa = Fa (kN)
Minimal axial load
When the axial load Fa falls under allowed value at higher rotation speed there is a danger of skidding of balls between the raceways of the washers because of the centrifugal force. Allowed value Fa is calculated::
Fa min – minimal axial load
nmax – limiting rotation speed
M – minimal load index
If the axial load is lower than Fa min or during the operation the bearing is relieved, e.g. one row of balls in a double direction thrust ball bearing or one bearing in the arrangement of a single direction bearing pair is relieved it is necessary to secure the minimal load, e.g. by means of springs.