Bearing Lubrication Best Practices: Intervals, Quantities, and Mistakes to Avoid
Published 1 March 2025 · Drishti Powertech LLP
Approximately 36% of all premature bearing failures are caused by lubrication problems — wrong grease, too much grease, too little grease, or grease applied at the wrong interval. Yet proper lubrication is one of the simplest and cheapest forms of maintenance available. This guide explains how to get it right.
Choosing the Right Grease
Grease selection depends on operating speed, temperature, load, and environment. For most industrial electric motors and pumps operating at ambient temperature, a lithium-complex NLGI Grade 2 grease is the standard choice. For high-speed bearings (> 3,000 RPM), a softer NLGI 1 grade reduces churning losses. For high temperatures (100–150°C), use a polyurea or synthetic base oil grease. Never mix greases of different thickener types (e.g., lithium with polyurea) — incompatible greases can separate, leaving the bearing unlubricated.
Calculating the Correct Relubrication Interval
SKF's relubrication interval formula: tf = (14,000,000 / (n × √d)) − 4d. Where n = shaft speed (RPM), d = bearing bore diameter (mm), and tf = relubrication interval in operating hours. This formula gives a baseline for moderate-temperature (< 70°C), contamination-free conditions. For elevated temperatures, divide by 2 for every 15°C above 70°C. For contaminated environments, further reduce by 30–50%. Programme these intervals into your CMMS as a preventive maintenance task.
How Much Grease to Apply
Over-greasing is as damaging as under-greasing. Excess grease churns inside the housing, generating heat (it can raise bearing temperature by 10–15°C), increasing energy consumption, and causing the seals to blow out — admitting contamination. The correct fill quantity for a relubrication is: Gp = 0.005 × D × B (grams). Where D = bearing outer diameter (mm), B = bearing width (mm). For initial fill of a relubricated housing, fill to 30–50% of free space with grease — not 100%.
Common Lubrication Mistakes
The four most damaging mistakes: (1) Using a grease gun without a meter — this almost always over-greases. Invest in a metered grease gun. (2) Not purging old grease before re-greasing on open-drain bearings. (3) Cross-contamination from mixing grease types in the same gun. (4) Ignoring relubrication intervals during shutdowns, then rushing in a large quantity when the plant restarts — a shock dose of grease is almost as bad as no grease.
Automatic Lubrication Systems
For inaccessible bearings, high-speed applications, or large bearing counts, consider SKF's single-point automatic lubricators (LAGF/LAGE series) or multi-line systems (Lincoln or SKF ProFlex). These systems deliver precise grease quantities at precise intervals, eliminating human error entirely. The payback period through reduced bearing replacement, reduced downtime, and reduced labour is typically 12–18 months in a medium-to-large plant.
Conclusion
Correct lubrication is the single most cost-effective bearing maintenance activity. Define the correct grease type and quantity for each bearing point in your plant, programme relubrication intervals in your CMMS, and invest in metered tools or automatic systems for critical assets. As an authorised SKF partner, Drishti Powertech supplies the full SKF grease and automatic lubrication range, and provides relubrication interval calculations on request.
Frequently Asked Questions
How do I know if a bearing is properly lubricated?
A properly lubricated bearing runs at a stable, moderate temperature (typically 10–40°C above ambient). Rising temperature, rumbling noise, or visible grease weeping from seals are signs of over- or under-lubrication.
Can I use general-purpose grease for all bearings?
A general-purpose lithium-complex NLGI 2 grease is suitable for most standard industrial bearings. However, food-processing equipment requires NSF H1-certified grease, high-temperature applications require synthetic grease, and very high-speed applications need a low-viscosity, low-NLGI grade.
Drishti Powertech LLP
Need expert product support?
As an authorised channel partner for SKF, KITO, Rossi, Atlas Copco, JK Fenner, Regal Rexnord, and Tyrolit, we provide free technical selection support and genuine product supply across East India.
Send an Enquiry