Rolling-Bearing Friction Torque and Power Loss Calculator

Content

Operating point and bearing data

Results update automatically. The example factors describe one 6204 calculation; replace every bearing-specific factor for another bearing.

SKF-factor method coefficients

Enter coefficients from an applicable bearing catalogue or verified engineering dataset. They are not universal material properties.

Friction and heat result

Total friction torque— N·m
Power loss / heat rate— W
Rolling torque— N·m
Sliding torque— N·m
Kinematic viscosity— mm²/s
Inlet-shear factor—
Replenishment factor—

Speed sensitivity

Equations used

Torque is evaluated in N·mm and converted to N·m. Loads Fa and Fr are positive magnitudes in N, speed n is in rpm, diameters d and D are in mm, η is dynamic viscosity in Pa·s, ρ is density in kg/m³, C₀ is the basic static load rating in N, and ν is kinematic viscosity in mm²/s. The bearing mean diameter is dm.

Stle
ν = 10⁶η/ρ; dm = (d + D)/2
αF = aF(Fa/C₀)bF
Grr = R₁dm1.96[Fr + R₂Fa/sin αF]0.54
Φrs = exp{−Krsνn(d+D)√[Kz/(2(D−d))]}
Φish = [1 + 1.84×10⁻⁹(ndm)1.28ν0.64]−1
Mrr = ΦishΦrsGrr(νn)0.6
Φbl = exp[−2.6×10⁻⁸(νn)1.4dm]; μsl = Φblμbl + (1−Φbl)μEHL
Gsl = S₁dm−0.145[Fr5 + S₂dm1.5Fa4/sin αF]1/3
Msl = Gslμsl; M = 10⁻³(Mrr+Msl)
P = 2πnM/60; heat-generation rate = P

Intermediate quantities: αF is the load-dependent contact angle: aF is entered in degrees, and the resulting angle is converted from degrees to radians before every sine operation. Grr is the rolling geometry/load factor and Gsl is the sliding geometry/load factor; each has the fitted model units required for Mrr and Msl to be N·mm. Φrs is the replenishment/starvation reduction factor, Φish is the inlet-shear-heating reduction factor, and Φbl is the boundary-lubrication weighting factor; all three are dimensionless and range from zero to one. μsl is the dimensionless blended sliding friction coefficient formed from the dimensionless boundary coefficient μbl and full-film coefficient μEHL. Mrr, Msl, M, and P are rolling torque, sliding torque, total torque, and power loss/steady heat rate.

Method coefficients: R₁ is the rolling load-factor scale, R₂ is axial-load weighting in the rolling factor, S₁ is the sliding load-factor scale, S₂ is axial-load weighting in the sliding factor, Krs is the replenishment/starvation coefficient, Kz is the replenishment geometry coefficient, aF is the contact-angle scale in degrees, and bF is the contact-angle load-ratio exponent. These eight fitted coefficients are dimensionless in this fitted equation set except for the implicit model-unit scaling carried by R₁ and S₁; they are bearing- and lubrication-system-specific and must be sourced and used together.

Interpretation: Φish and Φrs are multiplicative corrections to rolling torque, not separate additive heat sources. Their reported reductions are ΔMish = Mrr,0(1−Φish) and ΔMrs = Mrr,0Φish(1−Φrs), with Mrr,0 = Grr(νn)0.6.

Assumptions and limits: steady representative operating values; positive axial load; applicable verified coefficients; no seal, cage, churning, or external drivetrain losses unless represented by the supplied model. This is not a thermal balance, temperature prediction, limiting-speed check, or bearing-selection approval. Do not extrapolate factors to another bearing or lubrication system.

FunctionalProduct

Reference: SKF, Rolling bearings, PUB BU/P1 17000/1 EN, October 2018, section B.5, “Bearing friction, power loss and starting torque,” page 132. The catalogue defines total friction as rolling, sliding, seal, and drag contributions; this calculator implements only the explicitly displayed rolling and sliding factor terms.

How to use

  1. Use the single SKF-factor calculation mode for a bearing with a verified coefficient set; do not infer factors from designation alone.
  2. Enter positive axial and radial loads in N and rotational speed in rpm.
  3. Enter dynamic viscosity and density at the actual operating temperature; the calculator derives ν in mm²/s.
  4. Enter bore, outside diameter, and basic static load rating in the displayed units.
  5. Open SKF-factor method coefficients and replace every example coefficient with values applicable to the selected bearing and lubrication system.
  6. Select Calculate or edit any field to update automatically; Reset example restores the demonstrated 6204 operating point.
  7. Read total torque as the canonical result. Power loss is the steady mechanical heat-generation rate; rolling/sliding terms sum to total torque.
  8. Correct any red validation warning before using the result. A factor below one indicates a modeled reduction, not a negative heat contribution.
  9. Do not use this model for zero axial load, unknown catalogue factors, transient thermal prediction, limiting speed, bearing life, or acceptance decisions without a separate engineering review.