Causes of Raceway Spalling in Crossed Roller Bearings and Corresponding Mitigation Measures

Raceway spalling is one of the failure modes of crossed roller bearings, characterized by flaky or localized loss of bearing material from the raceway surface. This type of failure not only directly compromises the bearing’s geometric integrity—leading to increased equipment vibration, elevated noise levels, and reduced precision—but can also trigger cascading equipment malfunctions. Understanding the root causes of raceway spalling in crossed roller bearings and implementing proactive preventive and corrective measures is essential for ensuring the reliable operation of high‑precision machinery and extending the service life of the bearings.

I. Causes of Raceway Spalling in Crossed Roller Bearings
1. Internal Fatigue and Overload Impact in Materials
Subsurface crack initiation under cyclic stress: this is the classic mechanism of spalling. During operation, the maximum shear stress occurs at a certain depth beneath the raceway surface, corresponding to the Hertzian contact stress distribution. After an extremely large number of stress cycles, the material at this location develops microscopic cracks due to fatigue. Under alternating stresses, these cracks gradually propagate and extend toward the surface, resulting in flaky spallation of the surface layer. Even when the applied load remains within the rated range, such spalling will inevitably occur once a specified number of stress cycles—i.e., the fatigue life—is reached.

Direct effects of static or dynamic overload: Instantaneous impact loads that far exceed the bearing’s rated load capacity—such as accidental equipment collisions or abrupt stops—or prolonged operation under sustained overloads can sharply increase contact stresses. This may lead to two outcomes: first, it can directly induce pitting on the raceway surface (plastic deformation), with the edges of these pits becoming stress concentration points during subsequent operation and rapidly triggering premature spalling; second, it can alter the depth of shear stresses, accelerating the initiation and propagation of fatigue cracks.

2. Lubrication Failure and Contamination Ingress
Direct metal-to-metal contact caused by inadequate lubrication: In crossed roller bearings, a continuous lubricant film must be maintained between the rollers and raceways to separate them. When the lubricant is insufficient, improperly selected, severely degraded, or has reduced viscosity due to high temperatures, the oil film can be disrupted, leading to direct contact between microscopic asperities on the metal surfaces. This generates localized stresses and frictional heat, accelerating surface fatigue and wear and potentially triggering premature spalling.

The “indentation effect” of hard particulate contaminants: When hard particles such as dust or metal debris enter the bearing and are rolled into the raceway–rolling element interface, they carve out minute pits or scratches on the raceway surface. These pits not only serve as stress concentration sites, but their edges, subjected to repeated rolling contact, undergo plastic deformation and bulge, thereby initiating microscopic spalling that can rapidly propagate.

Misalignment and Eccentric Loading: Misalignment of the shaft axis—caused by installation errors, shaft bending, or deformation of the bearing housing—prevents the load from being evenly distributed across the entire raceway contact area, concentrating it instead on a localized region along one side of the raceway. This eccentric loading results in local stresses far exceeding design limits, markedly accelerating fatigue in that area and leading to premature spalling.

Unreasonable interference fits: Excessively large interference fits—particularly between the outer ring and the bearing housing—can eliminate the bearing’s required radial clearance and even introduce additional preload. This leads to a significant increase in contact stresses between the rolling elements and the raceways, while also potentially causing microscopic distortions in the raceway geometry of the rings. All these factors can serve as precursors to spalling.

Crossed roller bearing

II. Solutions and Preventive Measures for Raceway Spalling in Crossed Roller Bearings
1. Optimized selection and standardized installation
Scientific Selection and Precision Matching: Based on actual operating conditions—such as load magnitude and direction, and rotational speed—accurately calculate and select bearing models with adequate rated dynamic load capacity and service life. For applications subject to impact loads, choose materials with superior toughness or incorporate special design considerations. Ensure that the bearing’s precision grade is compatible with the equipment’s requirements.

Ensure proper installation: Strictly adhere to installation specifications, use specialized tools, and maintain precise alignment of the bearing’s axis with both the shaft and the housing. Carefully control the interference fit to prevent installation forces from being transmitted through the rolling elements. After installation, verify that rotation is smooth and free of binding.

2. Implement lean lubrication and rigorous sealing
Establish a lubrication management system: Select the appropriate type and viscosity of lubricant based on the manufacturer’s recommendations and the equipment’s operating conditions. Determine reasonable lubrication intervals and fill volumes; consider using a metered automatic lubrication system to ensure consistent and reliable performance. Regularly monitor the condition of the grease and replace it on schedule.

Establish a multi‑layered sealing and protection system: Depending on the severity of the operating environment—such as dust, moisture, or other contaminants—equip bearings with contact seals, non‑contact labyrinth seals, or a combination of both, and ensure that all seals remain in good condition. In challenging environments, consider implementing measures such as positive‑pressure clean‑air protection to fundamentally prevent the ingress of contaminants.

3. Strengthen condition monitoring and failure analysis
Conduct regular monitoring and trend management: Employ vibration analysis, noise monitoring, temperature recording, and other methods to periodically assess bearing operating conditions. In particular, vibration spectrum analysis can detect characteristic frequencies associated with micro‑flaking at an early stage, enabling proactive fault detection and early warning.

Conduct root cause analysis of failures: Once spalling failure occurs, the failed component should be preserved and analyzed. Examine the spalling morphology and location, and, in conjunction with the operating history, determine whether the failure was caused by fatigue overload, inadequate lubrication, or contamination. Such analysis provides a basis for equipment improvement and optimization of maintenance strategies, helping to prevent recurrence of similar issues.

The causes of raceway spalling in crossed roller bearings may result from the complex interplay of mechanical stresses, material properties, environmental factors, and human operational practices. To address this challenge, it is essential to move beyond the simplistic replacement approach that follows failure and adopt a lifecycle‑wide management mindset. Starting with computationally driven selection and installation, implementing lean‑based lubrication and sealing management for process control, and leveraging condition monitoring to enable early warning and closed‑loop optimization,