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SELECTION OF BEARING SIZE

5.5 Static Load Ratings and Static Equivalent where Po : Static equivalent load (N), {kgf} 5.6 Maximum Permissible Axial Loads for f : Load Factor k : Size Factor
Loads Fr : Radial load (N), {kgf} Cylindrical Roller Bearings
Fa : Axial load (N), {kgf} Diameter series Value of k
5.5.1 Static Load Ratings Xo : Static radial load factor Cylindrical roller bearings having inner and outer Loading Interval Value of f
Yo : Static axial load factor rings with ribs, loose ribs or thrust collars are capable 2 0.75
When subjected to an excessive load or a strong shock of sustaining radial loads and limited axial loads Continuous 1 31
load, rolling bearings may incur a local permanent (b)Static equivalent load on thrust bearings simultaneously. The maximum permissible axial load is Intermittent 2 4 1.2
deformation of the rolling elements and permanent limited by an abnormal temperature rise or heat seizure Short time only 3
deformation of the rolling elements and raceway Po = Xo Fr + Fa α =/ 90° .......................(5.32) due to sliding friction between the end faces of rollers
surface if the elastic limit is exceeded. The nonelastic and the rib face, or the rib strength.
deformation increases in area and depth as the load where Po : Static equivalent load (N), {kgf} The maximum permissible axial load (the load In the equations (5.34) and (5.35), the examination
increases, and when the load exceeds a certain limit, considered the heat generation between the end face of for the rib strength is excluded. Concerning the rib
the smooth running of the bearing is impeded. α : Contact angle rollers and the rib face) for bearings of diameter series strength, please consult with NSK.
The basic static load rating is defined as that static 3 that are continuously loaded and lubricated with In addition, for cylindrical roller bearings to have
load which produces the following calculated contact When Fa<Xo Fr , this equation becomes less accurate. grease or oil is shown in Fig. 5.13. a stable axial-load carrying capacity, the following
stress at the center of the contact area between the The values of Xo and Yo for Equations (5.30) and precautions are required for the bearings and their
rolling element subjected to the maximum stress and (5.32) are listed in the bearing tables. Grease lubrication (Empirical equation) surroundings:
the raceway surface. The static equivalent load for thrust roller bearings with
• Radial load must be applied and the magnitude
α = 90° is Po = Fa of radial load should be larger than that of axial
load by 2.5 times or more.
For self-aligning ball bearings 4 600MPa 900 (k⋅ d)2
{469kgf/mm2} 1 500 • Sufficient lubricant must exist between the roller
{ }CA = 9.8fn+ end faces and ribs.
5.5.3 Permissible Static Load Factor { } }= f − 0.023 × (k⋅ d)2.5 ...(N)
• Superior extreme-pressure grease must be used.
The permissible static equivalent load on bearings 900 (k⋅ d)2 .......(5.34)
varies depending on the basic static load rating and 1 500 • Sufficient running-in should be done.
For other ball bearings 4 200MPa also their application and operating conditions. n+ − 0.023 × (k⋅ d)2.5 .....{kgf}
{428kgf/mm2} • The mounting accuracy must be good.
The permissible static load factor fs is a safety factor
For roller bearings 4 000MPa Oil lubrication (Empirical equation) • The radial clearance should not be more than
{408kgf/mm2} that is applied to the basic static load rating, and it is necessary.
defined by the ratio in Equation (5.33). The generally 490 (k⋅d)2
In cases where the bearing speed is extremely slow, the
recommended values of fs are listed in Table 5.8. n + 1 000 speed exceeds the limiting speed by more than 50%, or
{ }CA = 9.8f the bore diameter is more than 200mm, careful study is
In this most heavily stressed contact area, the sum of Conforming to the modification of the static load rating, { } }= f − 0.000135 × (k⋅ d)3.4 ...(N) necessary for each case regarding lubrication, cooling,
etc. In such a case, please consult with NSK.
the permanent deformation of the rolling element and the values of fs were revised, especially for bearings for 490 (k⋅ d)2 ...(5.35)
1 000
that of the raceway is nearly 0.0001 times the rolling which the values of Co were increased, please keep this n+ − 0.000135 × (k⋅ d)3.4 .....{kgf}
in mind when selecting bearings.
element's diameter. The basic static load rating Co where CA : Permissible axial load (N), {kgf}
is written Cor for radial bearings and Coa for thrust d : Bearing bore diameter (mm)
bearings in the bearing tables. fs = Co ...............................................(5.33)
Po n : Speed (min–1)
In addition, following the modification of the criteria
for basic static load rating by ISO, the new Co values where Co : Basic static load rating (N), {kgf} kgf N d=101020 kgf N d=101020
for NSK's ball bearings became about 0.8 to 1.3 times 5,000 50,000 80 5,000 50,000 80
the past values and those for roller bearings about 1.5 Po : Static equivalent load (N), {kgf} 4,000 40,000 4,000 40,000
3,000 30,000 60 3,000 30,000 60
to 1.9 times. Consequently, the values of permissible For spherical thrust roller bearings, the values of fs 50 50
2,000 20,000 2,000 20,000 40
static load factor fs have also changed, so please pay should be greater than 4. 40

attention to this.

5.5.2 Static Equivalent Loads Table 5. 8 Values of Permissible Static Load Factor fs 1,000 10,000 1,000 10,000
800 8,000 800 8,000
The static equivalent load is a hypothetical load Lower Limit of fs 6,000 6,000
that produces a contact stress equal to the above CA 600 5,000 CA 600 5,000
maximum stress under actual conditions, while the Ball Bearings Roller Bearings 4,000 4,000
bearing is stationary (including very slow rotation or 500 3,000 500 3,000
oscillation), in the area of contact between the most 400 400
heavily stressed rolling element and bearing raceway. 300 2,000 300 2,000
The static radial load passing through the bearing
center is taken as the static equivalent load for radial 200 200
bearings, while the static axial load in the direction
coinciding with the central axis is taken as the static Operating Conditions
equivalent load for thrust bearings.
Low-noise applications 2.0 3.0 100 1,000 100 1,000
(a) Static equivalent load on radial bearings 1.5 2.0 80 800 80 800
Bearings subjected to vibration and 1.0 1.5
The greater of the two values calculated from the shock loads 60 600 60 600
following equations should be adopted as the static 50 500 50 500
equivalent load on radial bearings. Standard operating conditions 200 300 400 600 1,000 2,000 4,000 6,000 10,000 200 300 400 600 1,000 2,000 4,000 6,000 10,000

Po = Xo Fr + Yo Fa ...................................(5.30) Grease Lubrication n min–1 Oil Lubrication n min–1

Po = Fr ..................................................(5.31) Fig. 5.13 Permissible Axial Load for Cylindrical Roller Bearings
For Diameter Series 3 bearings (k=1.0) operating under a continuous load and lubricated with grease or oil.

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