KEVOS® MAKEOS · Maintenance
Journal Bearing Oil Check (Viscosity at Temperature, Film and Friction)
At its running temperature, how thick is this oil, does the journal bearing keep a safe film with it, and how much heat does the oil friction make?
Check of a plain journal bearing with a chosen oil grade: kinematic viscosity at the running temperature from the oil’s two catalogue viscosities by the ASTM D341 relation (as the oil viscosity–temperature tool), dynamic viscosity from the density, then the unit load, Sommerfeld number, Petroff friction torque and power loss (as the Petroff tool), with checks of viscosity against your minimum and of the Sommerfeld number against your limit.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Oil | ||
| First catalogue temperature | °C | Temperature of the first catalogue viscosity (usually 40 °C). |
| Viscosity at that temperature | cSt | Kinematic viscosity at that temperature (the ISO VG number at 40 °C). |
| Second catalogue temperature | °C | Temperature of the second catalogue viscosity (usually 100 °C). |
| Viscosity at that temperature | cSt | Kinematic viscosity at that temperature. |
| Running oil temperature | °C | Oil temperature in the bearing film when running. |
| Oil density at running temperature | kg/m³ | Density of the oil at the running temperature. |
| Least viscosity accepted | cSt | Least viscosity you accept for the bearing (from the bearing maker or your practice). |
| Bearing | ||
| Radial load | N | Radial load on the bearing. |
| Journal diameter | mm | Journal diameter. |
| Bearing length | mm | Bearing length. |
| Radial clearance | mm | Radial clearance. |
| Speed | rpm | Shaft speed. |
| Smallest Sommerfeld number | Smallest Sommerfeld number you accept for a safe film. | |
Method and formulas
- log log(ν + 0.7) = A − B log T (T in K) through the two catalogue points (as the oil viscosity–temperature tool).
- Dynamic viscosity μ (mPa·s) = ν (cSt) × ρ ÷ 1000.
- S = (r ÷ c)² μ N ÷ p; Petroff torque = 4π² r³ L μ N ÷ c; power loss = 2π N T (as the Petroff tool).
- Example: the oil thins to 20.623 cSt (17.942 mPa·s) at 60 °C, giving S = 0.087606 and 54.327 W of friction.
Limitations
- Viscosity relation is reliable between and slightly beyond the catalogue points.
- Petroff friction for a lightly loaded concentric journal.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Choose an oil grade for a plain bearing
- Check a bearing after its oil temperature rises
- Explain bearing distress after an oil change
Who it is for
- Maintenance engineers
- Lubrication engineers
- Design engineers
What you get
- Kinematic and dynamic viscosity at temperature
- Sommerfeld number and friction
- Viscosity and film checks
Interpreting the result
- Viscosity roughly halves for every 15–20 K rise in a mineral oil: cooling the oil is often better than a thicker grade.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2326–2345. Topic reference; no source tables or recommended settings are reproduced.
- ASTM D341 Viscosity–Temperature Charts for Liquid Petroleum Products
WORKOS tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Journal Bearing Oil Check (Viscosity at Temperature, Film and Friction) calculator
