Various types of sliding bearings possessing self-lubricating feature have been developed. However, the sliding bearings usually fail to long-term operate under severe conditions, such as shaft rotating at high speed, heavy load and strong vibration. Such failures are mainly caused by lacking of structural strength and exhausting of lubricating media resulting in decreasing contact pressure and velocity (PV) limits, thus shaft could be directly contacted with axial hole to induce high frequency impacts, excessive wear and heat generation. In addition, poor initial running-in characteristics, deficiency of thrust load capacity and axial back-and-forth movement of the shaft are the industry urgent issues yet to be solved.
Ball bearings are generally formed by using the inner and outer races each with a raceway inside so that plural balls are interposed. According to applied load, the clearance between raceways is reduced in different degrees. Such effect will be occurred on each ball along the raceways rotation and revolution which will induce local excessive wear, grease away from the balls, loss of fitness, and ultimately cause failure. Other disadvantages include ball loading difficulty, limited number of balls to be placed in, high price, limited thrust load capacity, and weak structure. Thus long-term operation under the aforesaid severe conditions will face tough challenges.