# Experimental Investigation of Clearance Influences on Cage Motion and Wear in Ball Bearings
## 1 Introduction  
A cage is a key component in rolling bearings to ensure stable running [1]. The cage clearance is one of the important parameters influences on bearing properties, such as lubrication [2], oil film [3], and heating [4], and especially cage motion and instability [5]. Meanwhile, the cage motion plays a decisive role in the dynamic performance and service life of the bearing, even leading to abnormal operation of the bearing and occasionally premature bearing failure [6; 7]. Thus, the investigation of cage clearance on its complicated motions and wear is of great importance for the design, optimization, and evaluation of cages and has become an important research topic. Some theoretical investigations of cage motion affected by cage clearances have been carried out by scholars. [PERSON] [8] and [PERSON] [9] discussed the effects of the ratio of pocket clearance to guiding clearance on the cage motion in a cylindrical roller bearing and ball bearing, respectively, and indicated that cage motion stability is strongly dependent on the roller-cage pocket clearance. Further, the cage motion are evaluated as a function of clearances both in the ball pockets and at the guiding lands by [PERSON] [5; 10], with the well-known computer code ADORE (Advanced Dynamics Of Rolling Elements) and demonstrated that cage instability has a definite correlation to cage pocket and guidingland clearances. [PERSON] [11] analyzed the cage motion and forces affected by varying cage clearances and found that if a bearing has a larger ball pocket clearance compared with the guiding clearance, this may result in cage nonsynchronous motion and lower ball forces. Besides the theoretical literature above, several experimental studies of bearing properties with respect to cage clearances have also been conducted. [PERSON] [12] indicated that the geometry of the cage was a major contributor to the instability of the bearings. [PERSON] [13] experimentally investigated the cage instability with respect to ball-pocket clearances by measuring the friction coefficient of bearing and sound vibration and found larger ball-pocket clearance to be more stable. [PERSON] [14] compared the frictional torque under circular pocket to square pocket retainers and pointed out that the circular pocket showed low frictional torque and was more prone to instability compared to the square pocket. As for the cage motion measurements in rolling bearings, [PERSON] [15] checked a certain shaft speed at which the cage can run into a whirling pattern. [PERSON] [16] experimentally investigated the whirl amplitudes of the cage in a tapered roller bearing affected by inner-ring rotational speed and axial load. [PERSON] et al. [17] and [PERSON] et al. [18] experimentally investigated the rotating speeds and external loads on the cage motion in a ball bearing. [PERSON] et al. [19] experimental investigated the dynamic motions of a cage under various external radial loads during acceleration and deceleration for an angular ball bearing. [PERSON] et al. [20] experimentally studied the dynamic behavior of ball caused by cage guidance and pocket clearances in cryogenic environments. Although some studies on cage motion, as well as on how frictional torque and sound are affected by cage clearances or geometry, have been carried out, experimental investigations concerning the cage motion affected by its clearances and the relationship between cage motion and wear are also inadequate and unknown at present. In this paper, cage motion and the relationship between motion and wear in a ball bearing with different clearances were investigated experimentally. Firstly, a bearing test rig was specially developed to measure the spatial motions of the cage, and then six diverse pocket and guiding clearances of the cage were designed and carried out on the test rig at prescriptive operating conditions.