10-24-2025, 08:03 PM
Grease Is a Sponge Not a Sealant
Grease is often misunderstood as a simple sticky lubricant, but its internal structure is more like a sponge soaked in oil. The thickening agent—called the thickener—holds the base oil and additives in suspension. During operation, the oil seeps out to lubricate moving parts, and when the equipment cools, the sponge-like matrix can reabsorb the oil. This property is known as reversibility, and it’s critical for maintaining lubrication under fluctuating temperatures and loads.
Types of Thickeners and Their Roles
The thickener determines the grease’s water resistance, temperature stability, and compatibility with other greases. Common types include:
Molybdenum Disulfide and Its Controversies
Moly, or molybdenum disulfide, is a friction-reducing additive often included in grease for high-pressure applications. It plates onto metal surfaces, forming a protective layer that withstands pressures up to 500,000 psi. Moly is also negatively charged, repelling dirt and water—two major threats to bearing life.
However, moly is not universally beneficial. In needle and ball bearings, excessive moly content may interfere with rolling action or cause premature wear. Some manufacturers recommend moly only for friction bearings (e.g., bushings, pins) and advise against its use in non-friction bearings (e.g., ball or roller types). A safe compromise is using 3% moly, which balances protection without overloading the bearing surface. The older 5% moly specification was driven by legacy Caterpillar standards but is now considered excessive for many applications.
Grease Compatibility and Mixing Risks
Mixing greases with different thickeners can lead to fluid separation, loss of lubricating properties, and bearing failure. Compatibility charts vary, but general guidelines include:
Winter Greasing and NLGI Grades
Grease consistency is measured by the National Lubricating Grease Institute (NLGI) scale:
Conclusion
Choosing the right grease involves more than brand loyalty—it requires understanding thickeners, additives, compatibility, and operating conditions. Aluminum complex grease offers excellent all-around performance, especially in wet and high-heat environments. Moly additives provide superior protection in friction bearings but should be used cautiously in rolling applications. Switching grease types without testing can lead to failure, and seasonal adjustments must balance pumpability with durability. High-quality lubrication is one of the most cost-effective ways to extend equipment life, reduce downtime, and protect your investment.
Grease is often misunderstood as a simple sticky lubricant, but its internal structure is more like a sponge soaked in oil. The thickening agent—called the thickener—holds the base oil and additives in suspension. During operation, the oil seeps out to lubricate moving parts, and when the equipment cools, the sponge-like matrix can reabsorb the oil. This property is known as reversibility, and it’s critical for maintaining lubrication under fluctuating temperatures and loads.
Types of Thickeners and Their Roles
The thickener determines the grease’s water resistance, temperature stability, and compatibility with other greases. Common types include:
- Lithium Complex: Most widely used, offering good heat resistance and mechanical stability.
- Aluminum Complex: Highly water-resistant, excellent reversibility, and ideal for wet or high-temperature environments.
- Calcium 12 Hydroxy: Good water resistance, but less common in modern formulations.
- Polyurea: Used in sealed-for-life bearings, with high oxidation resistance.
- Clay-Based (Bentone): Rare, non-melting, used in extreme temperature applications.
Molybdenum Disulfide and Its Controversies
Moly, or molybdenum disulfide, is a friction-reducing additive often included in grease for high-pressure applications. It plates onto metal surfaces, forming a protective layer that withstands pressures up to 500,000 psi. Moly is also negatively charged, repelling dirt and water—two major threats to bearing life.
However, moly is not universally beneficial. In needle and ball bearings, excessive moly content may interfere with rolling action or cause premature wear. Some manufacturers recommend moly only for friction bearings (e.g., bushings, pins) and advise against its use in non-friction bearings (e.g., ball or roller types). A safe compromise is using 3% moly, which balances protection without overloading the bearing surface. The older 5% moly specification was driven by legacy Caterpillar standards but is now considered excessive for many applications.
Grease Compatibility and Mixing Risks
Mixing greases with different thickeners can lead to fluid separation, loss of lubricating properties, and bearing failure. Compatibility charts vary, but general guidelines include:
- Aluminum Complex: Compatible with calcium 12 hydroxy and borderline with lithium complex.
- Lithium Complex: Compatible with lithium 12 hydroxy and most other lithium-based greases.
- Polyurea: Often incompatible with other types; use caution when switching.
Winter Greasing and NLGI Grades
Grease consistency is measured by the National Lubricating Grease Institute (NLGI) scale:
- NLGI #2: Standard for most applications.
- NLGI #1: Softer, used in cold climates for better pumpability.
Conclusion
Choosing the right grease involves more than brand loyalty—it requires understanding thickeners, additives, compatibility, and operating conditions. Aluminum complex grease offers excellent all-around performance, especially in wet and high-heat environments. Moly additives provide superior protection in friction bearings but should be used cautiously in rolling applications. Switching grease types without testing can lead to failure, and seasonal adjustments must balance pumpability with durability. High-quality lubrication is one of the most cost-effective ways to extend equipment life, reduce downtime, and protect your investment.
