What are the most common failure modes of 69 series bearings

The 69 Series Deep Groove Ball Bearing, with its unique thin-section geometry, is widely used in precision equipment with stringent space and lightweight requirements. However, this design also causes the 69 Series to exhibit some failure modes different from those of standard thick-walled bearings under specific operating conditions. A professional understanding of these failure mechanisms is critical to ensuring long-term reliable operation of equipment.

1. Fatigue Spalling

Fatigue spalling is one of the most common and primary failure modes in bearings. It stems from material fatigue of the bearing raceways or rolling elements under repetitive stress.

Mechanism: Under operating loads, the raceway surface and subsurface are subjected to cyclical Hertzian contact stress. Over time, microscopic defects within the material (such as non-metallic inclusions) gradually expand into cracks. When cracks extend to the surface, small pieces of material break off, forming spall pits.

Characteristics of the 69 Series: While the spalling mechanism is directly related to load and life calculations (L10​), due to the relatively thin raceway wall thickness of 69 series bearings, their load capacity (Basic Dynamic Load Rating, C) is lower than that of standard series bearings of the same bore diameter. Therefore, if the design light load range is exceeded during selection, or if load fluctuations are large in actual application, fatigue life may be shortened beyond expectations, accelerating the onset of spalling.

Field Symptoms: Initial symptoms include gray spots or microcracks on the raceways or rolling elements. As the spalling area expands, bearing vibration and noise increase dramatically.

2. Wear - Abrasive Wear and Smearing

Wear is a major cause of reduced precision and increased clearance in 69 series bearings, primarily including abrasive wear and adhesive wear/smearing.

Abrasive Wear: Failure of the bearing seal allows external hard particles (such as dust and metal debris) to intrude into the raceways. These particles roll or slide between the raceways and rolling elements, causing scratches and abrasion on the raceway surfaces and altering the raceway geometry.

Sensitivity of the 69 series bearings: Because the 69 series bearings are primarily used in precision machinery, requiring high operating accuracy, even minor wear can significantly affect equipment performance. Furthermore, the thin-wall design has a low tolerance for clearance changes, and the increase in clearance caused by wear can quickly lead to vibration problems.

Scuffing: This typically occurs under poor or boundary lubrication conditions, particularly in high-speed, light-load, or frequent start-stop conditions. Direct contact between the raceways and rolling element surfaces generates localized high temperatures, leading to micro-welding and tearing of the metal surfaces, resulting in scuffing or galling. This directly threatens the bearing's limiting speed.

3. Electrical Corrosion/Fluting

Electrical corrosion is a serious failure mode unique to 69 series bearings (and all conductive bearings) in applications involving variable-frequency motors, generators, or those with stray currents.

Mechanism: When current passes through the contact surface between the rolling elements and the raceways, it forms discharge channels on the raceway surface, generating localized high temperatures that melt and vaporize the metal.

Damage Characteristics: In mild cases, dense, grayish-white pits (craters) form, known as electrical corrosion or pitting. In severe cases, numerous pits connect to form washboard-like grooves or ripples (fluting).

Risks of 69 Series Bearings: An increasing number of high-speed motors in modern industry use 69 series bearings. These motors are often driven by inverters, which are more prone to generating high-frequency shaft currents. Electrical corrosion can rapidly degrade the raceway surface quality, causing high-frequency vibration and noise, and accelerating fatigue spalling.

4. Failures Caused by Loose Fit and Clearance Change

Due to the thinner wall thickness of 69 series rings, their geometric stiffness is lower, making the bearings more sensitive to deformation induced by the fit and external loads.

Ring Creep: When a bearing fit is too loose, the inner or outer ring may rotate relative to the shaft or housing under load, a phenomenon known as creep. This can cause wear on the mating surfaces and form fatigue bands outside the raceway load zone, compromising bearing stability.

Load Deformation: Uneven axial preload or poorly sized housing bores can cause ovality or misalignment in thin-walled rings, altering the raceway contact angle and leading to load concentration. This concentrated edge stress can quickly lead to localized fatigue spalling.

Clearance Issues: Excessive interference fit during installation can excessively reduce or even eliminate radial clearance, resulting in excessive bearing preload during operation, causing severe heating, increased frictional torque, and premature failure.