Radial rating (C_r) and life

The radial load ratings listed in this catalog are based on ABMA and ISO standards. The system establishes a common basis for calculating load ratings for all anti-friction bearings. For radial load rating this is denoted by C_r.

Bearing life is calculated by the equation L₁₀=(C_r/P)10/3, where : L₁₀ = expected life of 90% of similar bearings under similar operating conditions, C_r is the radial rating and P = equivalent radial load. The calculated life is given in millions of revolutions. When the equivalent radial load equals the C_r rating, the L₁₀ life will be 1 million revolutions. Average or L₅₀ life is five times the L₁₀ life. L₅₀ = expected life of 50% of similar bearings.

Axial ratings (C_a) of fixed bearings

The axial load on the fixed (GR) type bearings are considered independently from the radial loads as the effect of the axial load on the radial life of the bearing is small enough to discount at normal working loads and speeds.

The thrust or axial load is taken by the end face of the rollers and the flanged shoulders of the inner race assembly and outer race. The ability of the fixed (GR) unit to handle thrust loads is dependent upon specific pressure, velocity of contact areas and lubrication. It is essential that the rollers are maintained square to the shoulders at all times, consequently a very high degree of accuracy is required during manufacture.

Basic static load ratings (C_or)

The values of C_or given in this publication have been calculated in accordance with ISO and ABMA standards. The basic static load rating is defined as that static (radial) load which corresponds to a contact stress of 4,000 MPa (580,000 psi) at the center of the most heavily loaded roller/raceway contact and produces a permanent deformation of 0.0001 times the roller diameter.

Where rotation is very slow (less than 5 rpm) or intermittent, bearing size can be selected based on the static load carrying capacity. The requisite basic static loading rating can be determined from:

C_or =S_o.P where C_or = basis static load rating (radial) kN
P = effective bearing load kN
S_o = static safety factor

Bearing static safety factors, S_o

Speed and life factors (f_n, f_L)

The speed factor f_n = (rpm x 0.03)^0.3 can be found from the scale in the Life adjustment factors section. In case of variable speed, a mean speed over the time cycle should be taken. For rotation speed less than 5rpm, the speed scale may be extrapolated.

Bearing life requirements (L)

Suggested lives and factors for specific operating conditions are shown below.

f_L = (L₁₀ hours/500)^0.3 or find from scale in the Life adjustment factors section.
NOTE: The product of f_nf_L should not be less than 1.0.

Dynamic factor

Multiply by the appropriate dynamic factor f_d taken from the chart below.

Life adjustment factors for critical application

The basic L10 life obtained by using the equations or tables in this catalog are adequate for normal applications.