How to Prevent Fretting in Bearing Houses

What Is Fretting Corrosion?

Fretting is a type of wear caused by repeated micro-movement between two metal surfaces in contact. In a bearing setup, this usually occurs between the shaft and the inner ring. These tiny movements may seem harmless, but over time they wear down surface material, which then oxidizes into a reddish-brown abrasive debris. This debris accelerates wear and can score the shaft surface, deform the bearing, and in extreme cases, seize the entire assembly.

What makes fretting dangerous is that it develops slowly and often silently. There's no obvious failure until the damage has progressed enough to affect performance. And by then, you're dealing with expensive downtime, replacement parts, and in some industries, the risk of product contamination.

The Role of Grease in Preventing Fretting

The most effective way to prevent fretting is to use a high-viscosity anti-fretting paste during installation. Even though NGI’s bearings don’t require lubrication in operation, that initial layer of grease at mounting acts as a cushion between the shaft and bearing. It fills microscopic surface imperfections and absorbs some of the vibration that would otherwise lead to wear.

We recommend using a product like SKF LGAF 3E Anti-Fretting Agent. This type of paste is formulated specifically to reduce micro-movement and is stable under high loads and temperatures. In field tests, it not only prevented fretting but also made disassembly easier, which is a major advantage during service intervals.
In one of our comparison tests, we installed two identical bearing setups: one dry and one lubricated. The dry-mounted bearing began to show signs of fretting in less than a week. The greased version showed no visible corrosion even after extended operation and deliberate removal of the paste for inspection.

Why Torque Settings Matter

Installation torque is just as critical as lubrication. If the set screws are under-torqued, even a greased bearing can begin to move on the shaft. In one lab simulation, we ran a bearing at 800 RPM under a 275 kg load. When installed without grease and with loose screws, fretting occurred in 95% of the test cycles. When grease was applied and set screws were torqued correctly, the failure rate dropped by more than 90%.
To ensure best results:

• Always clean the shaft before installation.
• Apply anti-fretting paste evenly inside the inner ring.
• Torque the set screws to the recommended spec using a calibrated tool
• Re-check torque settings after the first 24 hours of operation, as settling or vibration may loosen them slightly.

These steps are quick and inexpensive but make a significant difference in service life.