Nominal Life

Static Safety Factor

The basic static load rating C₀ refers to the static load with constant direction and magnitude, under which the calculated contact stress in the center of the contact area between the roller and the raceway under the maximum load is 4000 MPa. (If the contact stress exceeds this level, it will affect the rotation.) This value is indicated as "C₀" in the specification tables. When a load is statically or dynamically applied, it is necessary to consider the static safety factor as shown below.

fS	Static safety factor (see Table1 )
C0	Basic static load rating (kN)
P0	Radial load (kN)

Table1 Static Safety Factor (f_S )

Load conditions	Lower limit of fS
Normal load	1 to 3
Impact load	3 to 5

• * The minimum value for the static safety factor is based on the presumption of appropriate lubrication and optimal conditions for mounting and assembly. It is not possible to calculate the effect on internal loads that may be caused by improper mounting, deformation of mounting components, or the like. Please take all necessary action to ensure safety.

Calculating the Modified Nominal Life

The nominal life (L₁₀) is obtained from the following formula using the basic dynamic load rating (C) and the load acting on the roller follower (P_C ).

L10	Nominal life (rev.)
C	Basic dynamic load rating * (kN)
PC	Radial load (kN)

Calculating the Modified Nominal Life

During use, a roller follower may be subjected to vibrations and shocks as well as fluctuating loads, which are difficult to detect. In addition, the operating temperature will have a decisive impact on the service life. Taking these factors into account, the modified nominal life (L_10m) can be calculated according to the following formula (2).

Modifi ed factor α

α	Modified factor
fT	Temperature factor (see Fig.1)
fW	Load factor (see Table2)

Modified nominal life L_10m

L10m	Modified nominal life (rev.)
C	Basic dynamic load rating * (kN)
PC	Radial load (kN)

• * The basic dynamic load rating (C) of the roller follower shows the radial load under which the nominal life (L) is 1 million revolutions when a group of identical roller follower units independently operate, assuming a constant direction and magnitude of the load. This value is indicated in the specification tables.

Calculating the Service Life Time

When the nominal life (L₁₀) has been obtained, the service life time (L_h) is obtained from the following equation.

For Linear Motion

Lh	Service life time (h)
L	Nominal life
D	Bearing outer diameter (mm)
ℓS	Stroke length (mm)
n1	Number of reciprocations per minute (min-1)

• Note) The normal service temperature is 80°C or below. If the product is to be used at a higher temperature, contact THK.

For Rotary Motion

D1	Outer ring contact average diameter of the cam (mm)
n	Rotation speed per minute of the cam (min-1 )

Table2 Load Factor (f_W)

Service condition	fW
Smooth motion without impact	1 to 1.2
Normal motion	1.2 to 1.5
Motion with severe impact	1.5 to 3