# Root Cause Failure Analysis of Deep-Groove Ball Bearing Used in a Governor
[PERSON] [27] studied the effect of misalignment error on contact pressure of the roller and found that the maximum contact pressure increased to about 3.7% when misalignment error of the bearing was 0.05\({}^{\circ}\). [PERSON] [28] carried out failure analysis of a grease-lubricated cylindrical roller bearing and found that misalignments induced direct metal-to-metal contact between the cylindrical roller and inner ring raceway, then accelerated the wear rate of the cylindrical roller bearing. [PERSON] [29] conducted an experimental study on the wear of a roller bearing and mentioned that the misalignment between the shaft and the bearing caused most of the wear of the bearing. [PERSON] [30] investigated the harmful effect of misalignment on the skidding of angular contact ball bearings by employing a five degrees-of-freedom quasi-static model and found that angular misalignment can introduce skidding areas in angular contact ball bearings preloaded by the constant force method, and the skidding does not increase, owing to angular misalignment when using the constant displacement preload method, because an additional axial load is induced. From the above literature review, it can be concluded that most studies considered misalignment influence on bearings by numerical analysis. Little research has been performed in the investigation of ball bearing failure induced by misalignment. Failure modes and root causes of the bearing failure induced by misalignment need to be demonstrated. Therefore, in this paper, the failure of a deep-groove ball bearing of a governor caused by misalignment is analyzed. The deep-groove ball bearing was found to prematurely fail during service after operation for 1400 h. The maximum axial load of the bearing was 128 N. The rotational speed of the bearing was 6400 rpm. The assembly structure of the failed deep-groove ball bearing is shown in Figure 1. The inner ring is assembled on the centrifugal block shaft and subjected to axial pressure from the centrifugal block shaft. The outer ring is assembled on the bearing seat and supported by the axial pressure of the spring through spring housing. For the bearing, the axial pressure from the centrifugal block shaft and the axial pressure from the spring are a pair of balance forces. Failure modes and root causes of the bearing failure are obtained by macroscopic and microscopic examination, metallographic analysis, hardness test, calculation of contact stress of the raceways and L\({}_{10}\) life of the bearing, flatness measurement and comparative experiment. It is found that the failure mode of the inner ring raceway and steel balls is contact fatigue spalling, the failure mode of the cage is fatigue fracture, and the failure modes of the outer ring raceway are wear and contact fatigue spalling. The unqualified machining process was identified to be the root cause, leading to the greater flatness and high points in the spring end face, which induced misalignment of the bearing, thereby resulting in an unbalanced load on the bearing. This kind of fault can be prevented by adopting the refined grinding process and adding detection requirements of flatness.