Timken - Thrust Bearings

ENGINEERING
Bearing reactions
BEARING REACTIONS
DYNAMIC EQUIVALENT
THRUST LOAD (P a )
To calculate the fatigue life of a thrust bearing, it is necessary
to calculate a dynamic equivalent thrust load, designated as P a.
The dynamic equivalent thrust load is defined as the single thrust
load that, if applied to the bearing, will result in the same life as
the combined radial and thrust loading under which the bearing
operates. For thrust ball, thrust spherical and thrust tapered
roller bearings, the existence of radial loads introduces complex
load calculations that must be carefully considered. If the radial
load (F r) is zero, the dynamic equivalent thrust load will be equal
to the applied thrust load (F a).
THRUST BALL, CYLINDRICAL AND TAPERED
ROLLER BEARINGS
Thrust cylindrical roller bearings, as well as most thrust ball and
thrust tapered roller bearings, are designed to carry thrust load
only. The dynamic equivalent thrust load is equal to the applied
thrust load (F a) for these pure thrust applications. For thrust ball
and thrust tapered roller bearing applications where radial load
is applied, load calculations become much more complex. Please
consult your Timken engineer for a review of bearing selection
and application.
Angular contact thrust BALL BEARINGS
For angular contact thrust ball bearings, the dynamic equivalent
thrust load is determined by:
P a = X F r + Y F a
For standard TVL and DTVL bearings having a 50° contact angle,
X = 0.76 and Y = 1.00. Minimim F a/F r ratio to maintain proper
operation for these applications is 1.56.
THRUST SPHERICAL ROLLER BEARINGS
Thrust spherical roller bearing dynamic loads are determined by:
P a = 1.2F r + F a
Radial load (F r) of a thrust spherical roller bearing is proportional
to the applied axial load (F a) such that F r≤ 0.55 F a. The steep
roller angle induces a thrust load (F ai = 1.2F r) when a radial load
is applied. This thrust load must be resisted by another thrust
bearing on the shaft or by an axial load greater than F ai.
STATIC AXIAL EQUIVALENT LOADS
To compare the load on a non-rotating bearing with the basic
static capacity, it is necessary to determine the static equivalent
load. In the case of thrust bearings, the static equivalent thrust
load is used. The static axial equivalent load is defined as the
pure thrust load that produces the same contact pressure in the
center of the most heavily stressed rolling element as the actual
combined load. The static axial equivalent load is dependent on
the bearing type selected. For bearings such as thrust cylindrical
roller bearings and most thrust tapered roller bearings that are
designed to accommodate thrust loading only, the static axial
equivalent load is equal to the applied load. For thrust tapered
roller bearings where a radial load or moment is applied, please
consult your Timken engineer.
THRUST BALL, CYLINDRICAL AND TAPERED
ROLLER BEARINGS
Thrust cylindrical roller bearings, as well as most thrust ball and
thrust tapered roller bearings, are designed to carry thrust load
only. The static axial equivalent load is equal to the applied thrust
load for these pure thrust applications. For thrust ball and thrust
tapered roller bearing applications where radial load is applied,
load calculations become much more complex. Please consult
your Timken engineer for these applications.
Angular contact THRUST BALL BEARINGS
Angular contact thrust ball bearings use the same equation for
equivalent static and dynamic loading.
P oa = X o F r + Y o F a
For standard TVL and DVL bearings having a 50° contact angle,
X = 0.76 and Y = 1.00.
THRUST SPHERICAL ROLLER BEARINGS
The following equation is used for thrust spherical roller bearings:
P oa = F a + 2.7 F r
Thrust spherical roller bearings require a minimum thrust load
for proper operation. P oa should not be greater than 0.5 C oa. If
conditions exceed this, consult your Timken engineer.
20 TIMKEN ® THRUST Bearing Catalog