Four bearings, eleven weeks each, for two years. The part number was right every time. The lubricant was not.
| Application | Hot strip mill, work-roll neck |
|---|---|
| Bearing | Four-row tapered roller, 52100 |
| Original life | ≈800 h (11 weeks) |
| Calculated L10 | >6,000 h |
| Failure mode | Adhesive wear — dry, hardened grease |
| Root cause | Grease rated 120 °C in a 145 °C housing |
| Change | High-temperature grease, reduced fill, seal check |
| Result | >14 months and running |
The plant was replacing the work-roll bearings on a fixed eleven-week cycle and had accepted it as normal. The bearings were genuine, the fits were checked, and the mounting procedure was followed. The maintenance team's assumption was that the duty was simply severe — a hot strip mill is a hard environment, and eleven weeks had become the planning assumption.
The returned bearing had no spalling. The raceways were polished and slightly torn, with material smeared along the direction of rolling, and the grease had carbonised into a hard brown varnish in the loaded zone. That is adhesive wear: the lubricant film was not there, the asperities touched, and the surfaces tore rather than fatigued.
That distinction matters. Fatigue says the bearing was too small or overloaded; adhesive wear says the lubricant was wrong. A bigger bearing would have failed in the same eleven weeks.
A thermocouple on the housing during a production run read 145 °C at steady state, and higher during a roll change. The grease in use was a lithium-complex product rated to 120 °C continuous. Above its rating the base oil oxidises, the thickener hardens, and the bearing runs on varnish — which is exactly what the damage showed.
| Parameter | Before | After |
|---|---|---|
| Grease rating | 120 °C lithium complex | 180 °C ester-based, high-temperature |
| Fill | ≈40% of free space | ≈25%, to reduce churning heat |
| Housing temperature | 145 °C measured | 138 °C measured |
| Replacement interval | 11 weeks | >14 months |
| Failure mode | Adhesive wear | None observed at inspection |
No. The steel was not the limit; the grease was. A stabilised ring would have survived 145 °C, but the bearing would still have run dry.
No spalling, and the wear was uniform across the loaded zone rather than concentrated. Overload produces fatigue; a missing film produces the polished, smeared surface we saw.
In a hot, fast bearing, excess grease is churned and shears, which generates heat and shortens life. A partial fill reaches the raceways without the churning penalty.
Send the model, the service hours and photographs of the damage. We will name the failure mode and what to change — not just quote the same part again.