Grease life halves for every 15 °C above 70 °C, so a standard lithium grease is finished at 150 °C. High-temperature greases replace both the base oil and the thickener: polyurea holds to about 160 °C, and perfluorinated (PFPE) greases hold to 250–280 °C with almost no oxidation. Both cost several times a standard grease.
Perfluorinated polyether has no hydrogen in its backbone, so there is nothing for oxygen to attack. It does not form sludge or varnish, and its vapour pressure is low enough for vacuum use. What it lacks is load capacity: PFPE is a poor extreme-pressure lubricant, so heavily loaded high-temperature bearings often need a different solution entirely.
A PFPE grease in a bearing with an NBR seal and a polyamide cage will not solve the problem — the seal hardens at 120 °C and the cage softens at the same point. High-temperature duty is a system specification: PFPE grease, FKM or PTFE seal, steel or brass cage, C4 clearance, and often a heat-stabilised bearing. Change one element only and the weakest one still fails.
| Lithium soap | to 120 °C |
|---|---|
| Lithium complex | to 150 °C |
| Polyurea | to 160 °C |
| PFPE (perfluorinated) | 250–280 °C |
| Silicone grease | to 200 °C, poor load capacity |
| Cost | PFPE is 10–30 times a standard grease |
| Compatibility | PFPE must not be mixed with any other grease |
| Companion changes | C4 clearance, steel or brass cage, high-temp seal |
| Type | Max continuous | Load capacity | Cost | Note |
|---|---|---|---|---|
| Lithium soap | 120 °C | Good | 1× | The default |
| Lithium complex | 150 °C | Good | 1.2–1.5× | Good water resistance |
| Polyurea | 160 °C | Good | 1.5–2× | Motor grade, incompatible with lithium |
| Silicone | 200 °C | Poor | 4–8× | Low load only |
| PFPE | 250–280 °C | Moderate | 10–30× | Chemically inert, no mixing |
About 280 °C with PFPE, and about 120 °C with a standard lithium grease. The practical limit is usually set by the seal or the cage before the grease.
No. PFPE is incompatible with hydrocarbon grease and the mixture loses its properties. The bearing and housing must be completely degreased before changing.
It tolerates 200 °C but has poor load capacity and can cause electrical contact problems. It is used in low-load, high-temperature positions, not in motors.
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