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Bearing lubrication

Enter the bearing, speed, temperature and environment to see how often to regrease, how much grease to add and whether the grease base oil builds a sufficient film.

Pre-sizing and estimating tool: results do not replace design, calculations or reports signed by a licensed professional, nor verification against the applicable codes and standards.

Preliminary estimate
Bearing

Example: 6309 bearing (45 × 100 × 25 mm, 1.8 lb). Bearings follow metric ISO 15 sizes; the mass comes from the catalog and is used only to estimate free space for the initial fill.

Operation
Environment and mounting
Grease

General-purpose lithium greases (NLGI 2) usually have a base oil of 100 to 150 cSt at 40 °C (104 °F); EP greases for heavy loads, 220 to 460 cSt. Check the grease data sheet.

—Relubrication interval
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Relubrication interval versus speed

Base interval at 70 °C (158 °F) and interval corrected for the conditions entered, on a log scale.

Tap the chart to see the values.

Base oil viscosity and required viscosity

Grease base oil viscosity versus temperature, compared with ν1 (κ = 1) and 4·ν1 (κ = 4).

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Method, assumptions and references

Equations used

Base interval at 70 °C (Noria/SKF): tf = K · [14·10⁶ ÷ (n · √d) − 4 · d] (h; n in rpm, d in mm; K = 10 ball, 5 cylindrical and needle roller, 1 tapered, spherical and thrust)
Corrected interval: t = tf · fT · fC/P · fc · fm · fv · fp ≤ 30,000 h; fT = 0.5^((T − 70) ÷ 15) above 70 °C (grease life halves every 15 °C / 27 °F)
Speed factor: A = n · dm · bf, dm = (d + D) ÷ 2 (mm·rpm)
Replenishment: Gp = 0.005 · D · B (g, mm) = 0.114 · D · B (oz, in); initial fill = 0.9 g/cm³ × [π/4 · B · (D² − d²) − mass ÷ 7.85 g/cm³]
Required viscosity (ISO 281): ν1 = 45,000 · n^−0.83 · dm^−0.5 (n < 1000 rpm); ν1 = 4500 · n^−0.5 · dm^−0.5 (n ≥ 1000 rpm); κ = ν ÷ ν1, ν from the Walther equation (ASTM D341)

Assumptions and limits

  • Good-quality lithium-soap mineral oil grease, rotating shaft and stationary outer ring. Contamination, moisture, vibration and position factors per the table published by Noria; temperature and load per SKF.
  • Below 70 °C the interval is not extended (SKF allows up to 2 times). With a rotating outer ring, shock loads or very low speed, shorten the interval and consult the manufacturer.
  • Initial fill: fill the bearing free space completely and 30% to 50% of the housing free space; at high speed (A above 400,000) fill only about 30% of the bearing to avoid heating.

Standards and technical documents

  • ISO 281:2007: Rolling bearings — Dynamic load ratings and rating life
  • SKF: Rolling bearings catalogue (PUB BU/P1 17000), capítulo Lubrication — relubrication intervals, adjustments and quantities
  • Schaeffler: Lubrication of rolling bearings (TPI 176)
  • Wright, J. Calculating grease quantity and frequency. Machinery Lubrication (Noria)
  • ASTM D341: Viscosity-temperature equations for liquid petroleum products

U.S. regulations

  • OSHA 29 CFR 1910.147: control of hazardous energy (lockout/tagout) during lubrication
  • OSHA 29 CFR 1910.212: machine guarding
  • EPA 40 CFR Part 279: standards for the management of used oil

Frequently asked questions

How often should a bearing be regreased?

It depends on type, size, speed and temperature. A 6309 bearing at 1780 rpm and 167 °F needs grease about every 7,900 operating hours, roughly 16 months at 6,000 h per year. A spherical roller bearing of the same bore needs an interval 10 times shorter.

How much grease goes into a bearing?

By the SKF formula, Gp = 0.114 × D × B in ounces with inches (0.005 × D × B in grams with mm). For a 6309 (D = 3.94 in, B = 0.98 in), that is about 0.44 oz per relubrication. Too much grease overheats the bearing; pump it slowly, with the shaft turning when it is safe.

Why does temperature shorten the interval so much?

Grease oxidizes faster when hot: its life halves for every 27 °F (15 °C) above 158 °F (70 °C). At 212 °F the interval is only 25% of the value at 158 °F.

What is the κ ratio?

It is the base oil viscosity of the grease at operating temperature divided by the ISO 281 minimum viscosity ν1. With κ from 1 to 4 the film separates the raceways; below 1, use a more viscous base oil or an EP grease.