Grease selector for rolling bearings
Enter your bearing size, speed and running temperature. You get the type of thickener, the NLGI stiffness, the base oil viscosity and the additives to ask for, with the reason for each choice.
Worked example
Inputs: 40 mm bore, 90 mm outside diameter, 1,450 rpm, 70 °C, deep groove ball bearing, normal load, clean and dry, horizontal shaft, standard duty, grease gun.
- Thickener. The all-round standard for rolling bearings up to about 130 °C in normal conditions.
- Stiffness. NLGI 2 is the standard stiffness for rolling bearings.
- Base oil. At 1450 rpm on a 65 mm mean diameter the bearing needs about 14.6 mm²/s at running temperature. A base oil of about ISO VG 46 at 40 °C (one grade either side is fine) gives that at 70 °C. A mineral base oil is fine.
- Additives. A mild anti-wear or light EP grease is a safe choice. Look for rust inhibitor and oxidation inhibitor in all cases.
This is the live calculator output for the default values above.
How the selector chooses
- Thickener. Food areas need an H1-registered grease. Above about 180 °C only a PFPE oil with PTFE thickener lasts. Wet service or heavy and shock loads point to calcium sulfonate complex. Hot running, from about 130 °C, points to polyurea or lithium complex with a synthetic base oil. Quiet motors and sealed-for-life bearings suit polyurea. Everything else gets lithium complex.
- Stiffness (NLGI). NLGI 2 is the standard. Very cold starts and centralised systems move to NLGI 1. Vertical shafts and wet conditions move to NLGI 3.
- Base oil viscosity. The bearing needs a minimum oil viscosity at running temperature that depends on speed and mean diameter. The selector converts that to the ISO VG grade at 40 °C that will still meet it when the bearing is hot.
- Additives. Heavy or slow bearings need EP additives. Fast, lightly loaded ball bearings do not. Rust and oxidation inhibitors are always wanted.
Speed limit for grease: the n·dm number
Multiply speed in rpm by the mean diameter (bore plus outside diameter, divided by 2) in mm. Above about 450,000 plain grease starts to struggle, and above about 800,000 oil-air, oil jet or a special high-speed grease is normally needed. The selector warns you when you cross these lines.
Next steps
Once you have the grease type, work out how often to add it and how much with the regreasing interval calculator.
Related tools and guides
Questions
What grease should I use for an electric motor bearing?
For clean, normally loaded motor bearings the selector usually returns polyurea when low noise is the priority, or lithium complex for standard duty, at NLGI 2. Enter your own size, speed and temperature for the exact answer.
What does NLGI mean on grease?
NLGI is the stiffness grade of a grease. NLGI 2 is the standard for rolling bearings. Softer grades such as 1 suit cold starts and centralised systems, and firmer grade 3 suits vertical shafts and wet conditions.
Can I mix different greases?
Not casually. Different thickeners can be incompatible and soften or harden the mixture. PFPE greases must never be mixed with anything else. The Lubrication tab in the Rotec AI tool has a grease compatibility chart.
Results are starting points from standard engineering practice. Confirm critical selections with the bearing or lubricant maker.