Engineering tools · Plain bearings

Plain Bearing Viscosity Selector

Running a hydrodynamic (sleeve/journal) bearing on the wrong oil viscosity leads to wiped bearings, excess friction and heat, or wasted energy from unnecessary drag. This tool gives a practical starting-point viscosity recommendation from the bearing's speed, load, and operating temperature.

Enter the bearing geometry and operating conditions, then check a proposed lubricant against the guideline.

PRACTICAL METHOD · DN / UNIT LOAD GUIDELINE
01 Bearing geometry
—
02 Operating conditions
03 Friction estimate inputs (optional)
Leave clearance blank to use a typical default of 0.15% of shaft diameter.
04 Lubricant
05 Equipment type (optional)
L / D RATIO
–
UNIT LOAD P
–
MPa
DN VALUE
–
RECOMMENDED ISO VG (GUIDELINE)
–
–
00.71.01.32.0+
Fill in the bearing geometry, operating conditions, and lubricant to see the guideline comparison.
FRICTION ESTIMATE (PETROFF, CONCENTRIC APPROXIMATION)
Radial clearance ratio, r/c–
Surface velocity, V–
Friction coefficient, f–
Estimated power loss–

Method: This tool uses a practical DN‑value (journal diameter × rpm) and unit‑load (radial load ÷ projected area) guideline to suggest a starting ISO VG grade — the same style of empirical, industry‑practice approach used for the SKF rolling‑bearing formula elsewhere in this toolset, not a full Sommerfeld number / Raimondi‑Boyd design‑chart analysis (DIN 31652 / ISO 7902 / ISO 6834). The friction estimate uses Petroff's equation, valid for the lightly‑loaded, concentric‑journal approximation — it indicates the order of magnitude of friction and heat generation, not a precise design value. For critical, heavily loaded, or high‑speed bearings, verify against the bearing manufacturer's recommendation or a full hydrodynamic (Sommerfeld/Raimondi‑Boyd) calculation.

© 2026 UNIQOL LTD. All rights reserved. This calculator, its formulas' implementation, and design are original work and may not be copied, redistributed, or claimed as another party's work without permission.