In the world of rotating machinery, the rolling bearing is a cornerstone of reliability and efficiency. However, even the highest quality bearing will eventually face the realities of operational stress. According to industry studies, wear is one of the most common failure modes for rolling bearings, directly impacting equipment uptime and maintenance budgets . While wear is an inevitable part of a bearing’s life cycle, premature failure is not. By understanding the specific mechanisms of wear and making informed choices—particularly in lubrication—you can dramatically extend the service life of your bearings and machinery.
DUHUI will walk you through the common types of bearing wear, how to diagnose them, and the critical factors in selecting a grease to prevent them.
Common Types of Rolling Bearing Wear and Their Remedies
Identifying the type of wear on a failed bearing is the first step toward preventing future occurrences. Each type has distinct characteristics, causes, and solutions.
Abrasive Wear (Three-Body Wear)
Abrasive wear is perhaps the most common form of bearing damage. It occurs when hard particles—such as sand, fine metal debris from gears, or contaminants—enter the bearing and act as a grinding paste between the rolling elements and raceways .
- Signs to Look For: A dull, matte, or high-luster finish on the raceways, sometimes described as a “mirror-like” surface. In advanced stages, it leads to increased internal clearance and eventual misalignment .
- Root Causes: Inadequate sealing, contaminated lubricant during initial fill, or ineffective filtration in oil-lubricated systems .
- Prevention Strategies: The solution lies in exclusion and protection. Upgrade to better sealing solutions, ensure cleanliness during maintenance, and choose greases specifically formulated with anti-wear (AW) additives to create a protective barrier against particle abrasion.
Adhesive Wear (Smearing/Scuffing)
This type of wear, often referred to as “smearing,” results from direct metal-to-metal contact. When the lubricant film fails to fully separate the rolling elements from the raceways, microscopic welds form at contact points and are immediately torn apart, transferring material from one surface to another .
- Signs to Look For: Scoring, scuffing, or smearing marks in the direction of sliding. You might see material that looks like it has been “dragged” across the surface.
- Root Causes: Insufficient lubrication, sudden acceleration that causes sliding, or excessively high loads that squeeze out the lubricant film .
- Prevention Strategies: The primary defense is a robust lubricant film. This means selecting a grease with a higher base oil viscosity. For roller bearings, which are more prone to sliding, greases with Extreme Pressure (EP) additives are often necessary to prevent this type of damage.
Fretting Wear / Corrosion
Fretting wear is a form of damage that occurs at the interface of tightly fitted components (like the bearing bore and shaft) under conditions of small-amplitude oscillatory motion. This micro-motion produces wear debris that instantly oxidizes, leading to characteristic corrosion marks .
- Signs to Look For: Reddish-brown or black oxide deposits on the bearing’s outer diameter, bore, or faces.
- Root Causes: Microscopic movements caused by shaft deflection, housing deformation, or an improperly fitted (loose) bearing ring .
- Prevention Strategies: Unlike other wear forms, this is primarily a design and assembly issue. Solutions include specifying tighter interference fits, increasing shaft rigidity, and carefully following mounting instructions to ensure the bearing is properly seated.
False Brinelling
Despite its name, False Brinelling is not an indentation caused by overloading (true brinelling) but a form of fretting wear. It happens when a non-rotating bearing is subjected to vibration or small oscillatory movements. These vibrations prevent the formation of a protective oil film, allowing the rolling elements to wear shallow depressions into the raceways .
- Signs to Look For: Polished, wear-like depressions in the raceway, precisely spaced at the rolling element pitch. The bottoms of these depressions are worn smooth, unlike the “bruised” look of a true brinell mark .
- Root Causes: This is famously caused by transportation vibration, where machinery is shipped long distances. It can also occur in equipment that experiences vibration while stationary.
- Prevention Strategies: During transport, the shaft should be securely locked. For in-service prevention, selecting a grease with strong anti-wear properties can help provide a sacrificial layer that protects the raceway during these minor movements.
How to Identify Bearing Wear
Modern condition monitoring allows us to detect these wear mechanisms before a catastrophic failure occurs.
- Visual and Microscopic Analysis: This remains the definitive method for failure analysis. Close inspection of a damaged bearing reveals a “fingerprint” that points directly to the root cause .
- Vibration Analysis: As wear progresses, it alters the vibration signature of a machine. Specific frequencies and patterns can indicate the type and severity of wear, allowing maintenance teams to schedule repairs proactively .
- Lubricant / Wear Debris Analysis: Analyzing an oil sample can reveal the “health” of your bearings. The quantity, size, shape, and material of wear particles tell a story about what is wearing out and how fast .
How to Select Right Grease for Optimal Bearing Protection
The single most effective tool for combating the wear types listed above is a well-chosen lubricant. In most applications, grease is the preferred choice due to its simplicity and sealing properties . Selecting the right one, however, requires understanding a few key parameters.
Understanding Grease Composition
Grease is not just “thick oil.” It is a precisely engineered combination of three elements:
- Base Oil (70-95%): This is the actual lubricant. Its viscosity (measured in ISO VG) is the most important property, determining its ability to form a load-bearing film .
- Thickener: This acts as a sponge, holding the base oil in place. Common types include lithium complex and polyurea, each offering different properties like high-temperature resistance or water resistance .
- Additives: These are performance enhancers. Anti-wear (AW) and Extreme Pressure (EP) additives chemically protect metal surfaces. Corrosion inhibitors prevent rust, and oxidation inhibitors extend grease life .
- NLGI Grade: This measures the “stiffness” or consistency of the grease. NLGI 2 is the industry standard for most ball and roller bearings . NLGI 1 or 0 are used for centralized lubrication systems where the grease must flow easily through pipes .
Key Factors in Grease Selection
Choosing a grease is a balancing act. Here are the critical application factors you must consider:
- Bearing Type: Ball bearings have point contact and are less demanding on grease. Roller bearings, with their line contact, generate more sliding friction and require greases with higher base oil viscosity (ISO VG 150-460) and often EP additives to prevent adhesive wear .
- Operating Speed: High-speed operation generates heat. Greases with lower viscosity base oils and “channeling” properties (where the grease pushes aside and stays out of the rolling path) help reduce energy loss and overheating .
- Operating Temperature: For continuous operation above 80-100°C, synthetic oils (like PAO or Esters) are necessary to prevent thermal degradation and oxidation . The thickener must also have a high “dropping point.”
- Load: High loads or shock loads require high-viscosity oils to maintain the film and EP additives to prevent welding of surface asperities .
- Environmental Conditions: If your application involves water washout or high humidity, you need a thickener with excellent water resistance (like calcium sulfonate) and strong corrosion inhibitors . In food processing, you must use NSF H1-registered greases .
Conclusion
Navigating the complexities of wear and lubrication can be challenging, but you don’t have to do it alone. At DUHUI Bearing, our two decades of manufacturing experience have taught us that the best bearing is one that is perfectly matched to its application and maintenance plan. We design our products with the precision needed to support optimal lubrication and minimize initial wear factors. Whether you are specifying bearings for a new project or seeking to improve the uptime of existing equipment, our team is ready to help.
