KEVOS® MAKEOS · Maintenance
Lubricant Film Thickness Ratio (Lambda)
Is the lubricant film thick enough to separate these rolling surfaces?
Film thickness ratio lambda of a rolling bearing or gear contact: the working film thickness divided by the composite roughness of the two surfaces, from RMS or average roughness, with the lubrication regime it indicates.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Working film thickness | µm | Minimum film thickness at the operating temperature (from an EHL calculation or the bearing maker’s data). |
| Roughness entered as | choice | Whether the roughness values are RMS or arithmetic average. |
| Roughness of surface 1 | µm | Roughness of the first surface (for example the raceway). |
| Roughness of surface 2 | µm | Roughness of the second surface (for example the rolling element). |
Method and formulas
- λ = h ÷ √(R_q1² + R_q2²).
- Where only Ra is known, R_q ≈ 1.25 Ra for typical ground surfaces.
- Commonly λ < 1 indicates boundary lubrication, 1–3 mixed, and above about 3 full separation.
- Example: a 0.25 µm film on surfaces of 0.06 and 0.04 µm gives λ = 3.4669.
Limitations
- Film thickness must be calculated or supplied; this tool does not compute EHL film thickness.
- Contamination and debris dents defeat a good λ.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check whether a bearing runs in full-film lubrication
- Judge the effect of a different oil viscosity
- Explain short bearing life from surface distress
Who it is for
- Reliability engineers
- Lubrication engineers
- Maintenance engineers
What you get
- Composite roughness
- Film thickness ratio λ
- Lubrication regime
Interpreting the result
- Raising viscosity at the operating temperature or improving surface finish increases λ and bearing life.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2420–2422. Topic reference; no source tables or recommended settings are reproduced.
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