Page 13 - NSK_CAT_E1102m_A7-141

SELECTION OF BEARING SIZE

The average speed nm may be calculated as follows: 5.4 Equivalent Load 5.4.1 Calculation of Equivalent Loads center for each bearing is listed in the bearing tables.
When radial loads are applied to these types of
nm = n1t1+ n2t2+ ...+ nntn ........................(5.19) In some cases, the loads applied on bearings are The equivalent load on radial bearings may be bearings, a component of load is produced in the axial
t1+ t2+ .........+ tn purely radial or axial loads; however, in most cases, calculated using the following equation: direction. In order to balance this component load,
the loads are a combination of both. In addition, such bearings of the same type are used in pairs, placed
(2) When the load fluctuates almost linearly (Fig. 5.8), loads usually fluctuate in both magnitude and direction. P = XFr + YFa ........................................(5.25) face to face or back to back. These axial loads can be
the average load may be calculated as follows: In such cases, the loads actually applied on bearings calculated using the following equation:
cannot be used for bearing life calculations; therefore, where P : Equivalent Load (N), {kgf}
a hypothetical load that has a constant magnitude and
FmH 1 (Fmin + 2Fmax) .........................(5.20) passes through the center of the bearing, and will give Fr : Radial load (N), {kgf}
3 the same bearing life that the bearing would attain Fa : Axial load (N), {kgf}
under actual conditions of load and rotation should X : Radial load factor Fa i = 0.6 Fr ...................................(5.27)
where Fmin : Minimum value of fluctuating load be estimated. Such a hypothetical load is called the Y
(N), {kgf} equivalent load.
Y : Axial load factor where Fa i : Component load in the axial direction
Fmax : Maximum value of fluctuating load (N), {kgf}
(N), {kgf} The values of X and Y are listed in the bearing tables.
Fr : Radial load (N), {kgf}
(3) When the load fluctuation is similar to a sine wave The equivalent radial load for radial roller bearings with Y : Axial load factor
(Fig. 5.9), an approximate value for the average
load Fm may be calculated from the following α = 0° is Assume that radial loads Fr1 and Fr2 are applied
equation: on bearings1and 2 (Fig. 5.12) respectively, and an
Fmax P = Fr external axial load Fae is applied as shown. If the axial
In the case of Fig. 5.9 (a) load factors are Y1, Y2 and the radial load factor is X,
Fm In general, thrust ball bearings cannot take radial then the equivalent loads P1 , P2 may be calculated as
FmH0.65 Fmax ........................................(5.21) F loads, but spherical thrust roller bearings can take follows:
some radial loads. In this case, the equivalent load may
In the case of Fig. 5.9 (b) be calculated using the following equation:

FmH0.75 Fmax ........................................(5.22) P = Fa + 1.2Fr ..................................(5.26)

where Fr ≤0.55 where Fae + 0.6 Fr2≥ 0.6 Fr1
Fa Y2 Y1
(4) When both a rotating load and a stationary load are
applied (Fig. 5.10). 0 ∑ niti 5.4.2 Axial Load Components in Angular Contact ( ) }P1 = XFr1 + Y1 Fae + 0.6 Fr2
Ball Bearings and Tapered Roller Bearings Y2
FR : Rotating load (N), {kgf} (a) ..............(5.28)
The effective load center of both angular contact
FS : Stationary load (N), {kgf} ball bearings and tapered roller bearings is at the P2 = Fr2
point of intersection of the shaft center line and a line
An approximate value for the average load Fm may representing the load applied on the rolling element by where Fae + 0.6 Fr2< 0.6 Fr1
be calculated as follows: the outer ring as shown in Fig. 5.11. This effective load Y2 Y1
F max
a) Where FR≥FS
FmHFR + 0.3FS FS2 Fm ( )}P1 = Fr1
+ 0.2 FR ..........................(5.23) F P2 = XFr2 + Y2 0.6 Fr1 − Fae ...............(5.29)
Y1
b) Where FR<FS
FmHFS + 0.3FR FR2
+ 0.2 FS ..........................(5.24)

0 ∑ niti Bearing I Bearing 2 Bearing I Bearing 2

(b)

Fig. 5.9 Sinusoidal Load Variation

F1 Fmax Fs αα Fa e Fr2 FrI Fae Fr2
F F2 Fm Fr I (b)
Fm FR aa
F Fig. 5.10 Rotating Load and Fig. 5.11 Effective Load Centers (a)

Stationary Load Fig. 5.12 Loads in Opposed Duplex Arrangement

Fn Fmin
0
0 n1 t1 n2 t2 nn tn ∑ niti

Fig. 5.7 Incremental Load Variation Fig. 5.8 Simple Load Fluctuation

A 30 A 31