I. The Essence of Lubrication: More Than Just Reducing Friction

The role of lubrication in rolling bearings goes far beyond "reducing friction resistance." During bearing operation, the lubricant performs at least five essential functions:

 

Isolating Metal Contact: Forming an oil film between rolling elements and raceways to separate the two metal surfaces and prevent direct contact. This is the most fundamental function of lubrication—and the most easily overlooked. When the oil film fails, direct metal-to-metal contact generates severe wear and temperature rise in an extremely short time.

 

Heat Dissipation and Cooling: Particularly in circulating oil lubrication, oil-mist lubrication or oil-jet lubrication, the lubricant can carry away most of the frictional heat generated inside the bearing, providing effective heat dissipation. The bearing's temperature rise curve is often the most direct reflection of lubrication condition.

 

Sealing and Protection: In grease lubrication, the grease forms a physical barrier inside the bearing, preventing external contaminants such as dust and moisture from entering. For equipment operating in dusty or humid environments, the value of this barrier is no less than that of mechanical seals.

 

Rust Prevention and Corrosion Protection: Rust inhibitors in the lubricant form an adsorption film on metal surfaces, preventing attack from moisture and oxygen.

 

Vibration Damping and Noise Reduction: The lubricant film has certain damping characteristics that can absorb some vibration energy and reduce noise levels during bearing operation.

 

Whether these five functions can be sustained depends on three core variables: whether the lubricant itself is correctly selected, whether the quantity is appropriate, and whether the supply is continuous. Deviation at any point can push a bearing from "stable operation" toward "accelerated failure."

 

II. Lubricant Selection: Not "Best," but "Best Matched"

Bearing lubricant selection is not about finding the "best" product, but the solution that "best matches" the operating conditions. Key factors to consider include: bearing type, speed, operating temperature, load, environmental conditions, mounting position, sealing requirements, impact and vibration.

 

Base Oil Viscosity: The Decisive Factor for Oil Film Thickness

 

Base oil viscosity is the most important indicator when selecting grease. It directly determines the load-carrying capacity and thickness of the oil film.

 

Heavy load or impact conditions: Higher viscosity oil should be selected to ensure the oil film is not squeezed out under high pressure.

 

High-speed conditions: Lower viscosity oil should be selected to reduce friction loss and churning heat generation.

 

High-temperature conditions: Higher viscosity oil should be selected, as viscosity decreases with rising temperature.

 

For bearings with line contact between rolling elements and raceways (such as cylindrical roller bearings and tapered roller bearings), the contact area is larger and sliding components are more significant, typically requiring grease with higher base oil viscosity (ISO VG 150 to 460 or higher). For point-contact ball bearings, ISO VG 68 to 100 is generally sufficient.

 

Thickeners: Determining the "Skeleton" of Grease

 

Thickeners are dispersed in the base oil, forming the structural skeleton of the grease that adsorbs and holds the base oil in place. The water resistance and heat resistance of grease are primarily determined by the thickener. Common thickener types include calcium-based, sodium-based, lithium-based, complex lithium-based, and polyurea-based. Different thickeners correspond to different operating temperature ranges and environmental adaptability.

 

Dropping Point and Operating Temperature

 

The dropping point is the primary indicator for evaluating the high-temperature performance of grease. The bearing's actual operating temperature should be 10-20°C below the dropping point. When selecting high-temperature greases, the dropping point and operating temperature range are among the most critical parameters to consider.

 

Consistency (NLGI Grade)

 

Consistency represents the "hardness" or "softness" of grease, expressed using the NLGI consistency number. Higher numbers indicate harder, thicker grease. Rolling bearings are typically suitable for NLGI grades 1, 2 or 3. For light-load high-speed conditions, greases with higher penetration (softer) are selected; for heavy-load conditions, greases with lower penetration (harder) are selected.

 

III. NMT's Lubrication Technology Practices

NMT's understanding of lubrication management is reflected across multiple levels of bearing design, material selection and manufacturing processes.

 

Precise Control of Roller End Face Roughness

 

Thrust cylindrical roller bearings face the risk of oil film rupture under low-speed heavy-load conditions. NMT precisely controls the roughness parameters of roller end faces, enabling lubricating oil to form a more stable elastohydrodynamic film in the contact zone. This design ensures that during prolonged pressure-holding operations, the bearing interior maintains reliable fluid lubrication, with virtually no direct contact between metal surfaces.

 

Embedded Oil Storage and Self-Replenishing Lubrication

 

In angular contact ball bearings, NMT embeds a porous oil-storage medium in the cage that slowly releases lubricant like a sponge. At the same time, micro-scale oil-retaining textures are designed on the raceway surface. This dual protection enables the bearing to maintain stable oil film thickness under low oil supply conditions—avoiding both early wear and the additional viscous resistance caused by excessive lubricant.

 

On the inner walls of cage pockets, NMT also embeds solid lubricant micro-pillars—when steel balls make slight contact with the cage,微量 solid lubricant is transferred to the ball surface and then carried to the raceway during rolling, forming a self-replenishing lubrication mechanism.

 

Micro-Protrusion Design on Roller End Faces

 

In full-complement roller bearings, friction between rollers is a potential issue. NMT introduces micro-spherical protrusions on roller end faces, converting line contact to point contact, while with specialized extreme-pressure grease to form a tough isolating oil film between rollers.

 

Logarithmic Crowning and Oil Film Uniformity

 

NMT introduces a logarithmic crowning only a few microns high on the roller generatrix. This design makes contact stress distribution between rollers and raceways more uniform, indirectly promoting uniform distribution of the lubricating oil film in the contact zone—avoiding early wear caused by localized oil film thinning.

 

PFPE Lubrication Adaptation and Surface Passivation

 

For extreme environments such as vacuum and cleanrooms, NMT has developed bearing solutions adapted for perfluoropolyether (PFPE) lubrication, while achieving extremely low outgassing rates on rollers and raceways through special surface passivation treatment—critical for semiconductor equipment, optical instruments and other applications with extreme cleanliness requirements.

 

IV. Lubrication Failure: The Most Common Bearing "Killer"

Analysis of bearing damage causes shows that approximately 40% of bearing damage is directly related to poor lubrication. Specific manifestations of lubrication failure include:

 

Excessive lubricant: Increases friction and heat generation, potentially causing seal damage.

 

Insufficient lubricant: Cannot form a complete oil film, leading to direct metal contact.

 

Incorrect lubricant type: Cannot form an effective load-carrying film under specific operating conditions.

 

Mixing incompatible lubricants: May cause thickener structure breakdown, base oil separation and other issues.

 

Incorrect lubrication intervals: Overly long intervals lead to lubricant depletion; overly short intervals increase costs and contamination risk.

 

Lubricant aging and degradation: Oxidation, thickening or moisture contamination lead to performance decline.

 

The consequences of lubrication failure are cascading: oil film rupture → direct metal contact → sharp friction increase → localized temperature rise → material discoloration and thermal damage → scoring and spalling → complete bearing seizure.

 

The damage caused by ineffective lubrication varies significantly in appearance and impact on bearing performance. In all cases, the grease quantity, type, grade, viscosity, additives and supply system must be correctly designed for the bearing system.

 

V. The Right Path for Lubrication Management: Systematic Thinking from Selection to Maintenance

Effective bearing lubrication management requires systematic control across five areas:

 

Correct Selection: Select the appropriate lubricant based on bearing type, speed, operating temperature, load and environmental conditions. Base oil viscosity, thickener type, NLGI consistency grade and additive formulation must all precisely match operating conditions.

 

Correct Fill Quantity: The amount of grease in a bearing should fill 1/2 to 1/3 of the bearing's internal space, reduced to 1/3 at high speeds. Excessive grease will increase temperature rise; insufficient grease cannot form a continuous oil film.

 

Correct Filling Method: Use clean tools and containers to avoid introducing contaminants during filling. For precision bearings,定量 grease filling equipment is recommended to ensure filling accuracy.

 

Regular Condition Monitoring: Regularly check bearing operating temperature, vibration and noise—these are the most direct indicators of lubrication condition. Abnormal temperature rise is often the first signal of lubrication failure.

 

Scientific Replacement Cycles: Establish grease change intervals based on operating conditions, runtime and lubricant condition, rather than mechanically applying fixed schedules. For bearings operating in high-temperature, heavy-load or humid environments, grease change intervals should be shortened accordingly.

 

In NMT's view, lubrication management is not an "ancillary service" for bearings, but a core component of bearing system engineering. Bearings provide precise geometric interfaces; lubricants are responsible for maintaining a stable load-carrying film on these interfaces. 

 

Precision begins with design and is perfected through lubrication. NMT proves with systematic lubrication management: a bearing's life depends not only on how precisely it is manufactured, but on how well it is lubricated.