Question 1

How do you calculate the bearing speed factor (DN) for rolling element bearings?

Accepted Answer

The bearing speed factor (DN value) is calculated by multiplying the bearing bore diameter in millimeters by the shaft speed in RPM. In some advanced standards, the pitch diameter is used instead for a more precise speed factor (dmN) calculation.

Question 2

Why is the DN value bearing critical for choosing the right viscosity grade?

Accepted Answer

The DN value represents the peripheral speed of the bearing components, which directly dictates the shear stress and temperature within the lubrication zone. High DN values require lower-viscosity oil to minimize viscous drag; low DN values require higher-viscosity oils to maintain a sufficient EHL oil film.

Question 3

When should I select a PAG viscosity grade bearing over a mineral oil?

Accepted Answer

Select a PAG viscosity grade when your bearing operates in extreme temperatures, high-load conditions, or requires exceptional shear stability. PAG base oils possess a high viscosity index, outstanding thermal-oxidative stability, and lower traction coefficients than mineral oils.

Question 4

What are the standard methods for bearing lubrication viscosity selection?

Accepted Answer

Standard industry methods from SKF and FAG use reference charts plotting bearing speed factor against operating temperature to identify the minimum required kinematic viscosity (kappa value). DIN 51563 is also referenced for temperature-viscosity behavior.

Bearing DN Speed Factor Calculator for Greases