Almost every sealed bearing leaves the factory with nitrile (NBR) seals, and nitrile has a hard ceiling near 120 °C. Above that the rubber hardens, loses elasticity and stops following the inner ring, so the grease escapes and the bearing runs dry. High-temperature positions need a different elastomer — or no elastomer at all.
In most high-temperature failures we inspect, the seal is intact and the grease is carbonised. Lithium soap thickener oxidises above roughly 130 °C; the base oil then separates, runs out past a perfectly good lip and leaves hard soap behind. Replacing the seal without changing the grease simply moves the failure point. Temperature rating has to be checked for the whole system: seal, grease, cage and clearance.
Work upward from the measured running temperature, not the ambient figure.
Heat expands the shaft before the housing, which consumes internal clearance. A high-temperature position that keeps a CN bearing will run preloaded and fail by cage or raceway distress even if the seal survives. Pair any high-temperature seal with C4 or C5 clearance and a steel or brass cage — polyamide cages are limited to about 120 °C.
| NBR (nitrile) | −40 to +120 °C — the standard seal |
|---|---|
| FKM (fluorocarbon / Viton) | −20 to +200 °C, short peaks to 230 °C |
| PTFE | −70 to +260 °C, chemically inert |
| Silicone | −60 to +200 °C, low strength, rarely used in bearings |
| Grease limit (lithium) | Usually 120–130 °C — often the real ceiling |
| Grease limit (PFPE) | Up to 250–280 °C |
| Designation | No universal suffix; specified by material on the order |
| Speed penalty | FKM and PTFE lips run slower than NBR, not faster |
| Material | Temperature | Chemical resistance | Speed | Relative cost | Use |
|---|---|---|---|---|---|
| NBR | −40 to +120 °C | Good against oils and greases | Reference | 100% | Standard sealed bearing |
| FKM | −20 to +200 °C | Excellent, but not for ketones | −5 to −10% | 180–260% | Ovens, exhaust fans, hot pumps |
| PTFE | −70 to +260 °C | Near-universal | −5% | 250–400% | Chemical plant, kilns |
| Silicone | −60 to +200 °C | Moderate, poor against some oils | −10% | 150–220% | Static or low-speed heat |
| No seal | Limited by grease and cage | — | 100% | 90% | Above 250 °C, sealed housing |
Rubber contact seal on both sides — maximum protection
Read →Steel shield on both sides — high speed, coarse dust only
Read →Non-contact rubber seal — shield friction, better sealing
Read →No seal — maximum speed, relubrication access
Read →The brand crosswalk for contact rubber seals
Read →SKF's reinforced contact seal for larger bores
Read →About 120 °C for the standard NBR seal, and often lower for the grease. A lithium-greased 2RS bearing is realistically limited to 110–120 °C continuous.
Yes, but only with a grease rated for that temperature. A PFPE grease is normally required above 180 °C, and clearance must be increased to C4 to absorb thermal expansion.
Sustained operation above the elastomer's limit. Nitrile oxidises and takes a permanent set, so the lip stops following the inner ring. The fix is a higher-temperature elastomer plus the matching grease — not a different brand of the same seal.
Not a universal one. Manufacturers specify it by material code on the order, and availability is limited to certain sizes. State the temperature and the size and the seal material will be quoted explicitly.
Send the designation, the three dimensions and the quantity — we reply with price, brand options and lead time within 30 minutes on working days.