Grease for High-Temperature Bearings
Lubricant selection for bearings operating above 120°C, including oven conveyor bearings, kiln equipment, and other elevated temperature applications.
High-temperature bearing applications require specialized lubricants that maintain their structure and lubricating properties at elevated temperatures where conventional greases would fail. Base oil evaporation, oxidation, and thickener breakdown are primary concerns.
Base Oil Selection by Temperature
| Temperature Range | Suitable Base Oils |
|---|---|
| 120-150°C | Synthetic PAO, ester |
| 150-200°C | PAO, ester, silicone |
| 200-250°C | PFPE, silicone |
| >250°C | PFPE only |
Thickener Considerations
Conventional soap thickeners have dropping points that limit high-temperature use. Alternative thickeners for extreme temperatures include:
- PTFE (Teflon): No melting point; excellent chemical resistance
- Bentonite (clay): No dropping point but can harden over time
- Silica: High temperature stability
PFPE Greases
Perfluoropolyether (PFPE) base oils provide the highest temperature capability and chemical resistance. They are commonly thickened with PTFE. These greases are expensive but necessary for extreme conditions.
Relubrication Frequency
High temperatures accelerate grease degradation, requiring more frequent relubrication than comparable ambient-temperature applications. Calculate relubrication intervals based on actual operating temperature, not ambient conditions.
Bearing Material Limits
Standard bearing steels have temperature limits independent of lubrication. AISI 52100 steel bearings are typically limited to 120-150°C continuous. Higher temperatures require special bearing materials (M50, ceramic hybrid) regardless of grease selection.
Operating Conditions
| Operating Parameter | Typical Range/Value |
|---|---|
| Operating Temperature | 120°C to 250°C continuous |
| Peak Temperature | May exceed 300°C for short periods |
| Speed | Typically low to moderate |
| Environment | Often oxidizing; may include thermal cycling |
| Bearing Types | Standard steel or special heat-resistant steels |
Required Lubricant Properties
| Required Property | Specification |
|---|---|
| NLGI Grade | NLGI 2 typical |
| Base Oil Type | Synthetic: PFPE, PAO, silicone, or ester |
| Base Oil Viscosity | ISO VG 100-460 depending on speed |
| Thickener Type | PTFE, bentonite (clay), or specialized synthetic |
| Dropping Point | >250°C (or no drop point for PFPE/PTFE) |
| Oxidation Stability | Excellent at operating temperature |
Compatibility Warnings
- -PFPE greases are incompatible with most other grease types
- -Silicone greases have limited load-carrying capacity
- -Clay-thickened greases have no dropping point but may harden with oxidation
- -Verify bearing steel and cage material ratings for high temperature
Availability
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Sources
- SKF High Temperature Bearing Solutions
- Kluber Lubrication High Temperature Guide
- NLGI High Temperature Grease Specifications
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