Grease Thickener Types
Classification of grease thickener systems including simple soaps, complex soaps, and non-soap thickeners with their characteristics and applications.
Grease thickeners are the structural component that holds the base oil in place. The thickener type largely determines a grease’s temperature capability, water resistance, and compatibility with other greases.
Simple Soaps vs. Complex Soaps
Simple soaps are formed by reacting a fatty acid with a metal hydroxide:
- Lower dropping points
- Less expensive
- Adequate for moderate conditions
Complex soaps include an additional complexing agent (usually a short-chain acid):
- Higher dropping points
- Better high-temperature stability
- More expensive
Thickener Selection Factors
Temperature
- Below 120°C: Simple lithium or calcium adequate
- 120-180°C: Lithium complex, polyurea, or calcium sulfonate
- Above 180°C: Non-soap (clay, PTFE, silica)
Water Exposure
- Excellent: Calcium sulfonate, aluminum complex, calcium complex
- Good: Lithium, lithium complex, polyurea
- Poor: Sodium (do not use in wet conditions)
Speed
- High-speed: Polyurea, lithium, barium complex
- Moderate speed: Most thickener types acceptable
- Low-speed, high-load: Calcium sulfonate, lithium complex
Food Contact
If NSF H1 registration is required:
- Aluminum complex is most common
- Limited calcium soap options
- Polyurea becoming more common
Understanding Dropping Point
Dropping point is measured by heating grease until the first drop falls from the cup (ASTM D566 or D2265). Important notes:
- Dropping point is NOT the maximum use temperature
- Operating temperature should be 50-80°C below dropping point
- Some thickeners (clay, PTFE) have no dropping point—they don’t “melt”
- Dropping point doesn’t indicate performance at high temperature
Classification Table
| Thickener Type | Dropping Point | Water Resistance | Primary Applications |
|---|---|---|---|
| Lithium (simple) | 180-200°C | Good | General purpose, automotive |
| Lithium complex | 250-270°C | Good | High-temp bearings, multi-purpose |
| Calcium (simple) | 80-100°C | Excellent | Wet environments, low-temp |
| Calcium complex | 250-300°C | Excellent | Steel mills, wet environments |
| Calcium sulfonate | >300°C | Excellent | Heavy-duty, extreme conditions |
| Sodium | 150-175°C | Poor | Wheel bearings (legacy) |
| Aluminum complex | 250-270°C | Excellent | Food-grade, water exposure |
| Barium complex | 200-250°C | Good | High-speed, rolling bearings |
| Polyurea | 240-270°C | Good | Electric motors, sealed bearings |
| Clay (bentonite) | No drop point | Fair | High temperature, specialty |
| PTFE | No drop point | Excellent | Chemical resistance, extreme temp |
| Silica | No drop point | Fair | Extreme temperature applications |
Typical Applications
| Grade/Class | Common Applications |
|---|---|
| Lithium/Lithium Complex | Most general-purpose greases, automotive, industrial bearings |
| Calcium Types | Marine, steel mills, water pumps, wet environments |
| Polyurea | Electric motors, sealed-for-life bearings, constant velocity joints |
| Aluminum Complex | Food processing, pharmaceutical, water-exposed equipment |
| Non-soap (Clay, PTFE) | Extreme temperatures, chemical exposure |
Notes & Limitations
- - Dropping point is the temperature at which grease becomes fluid—not the maximum use temperature
- - Maximum operating temperature is typically 50-80°C below dropping point
- - Mixing incompatible thickeners can cause grease failure
- - Complex soaps contain additional complexing agent for improved high-temp performance
Sources
- NLGI Lubricating Grease Guide
- SKF Bearing Grease Selection Guide
- STLE Tribology & Lubrication Technology
Last updated: