THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

14.10 Ball and Roller Bearings 379load direction changing may result in temporary cessation of the lubricant film andin metal-to-metal contact. This calls for hydrostatic lubrication that introduces fluid(e.g., oil or air) to the bearing surface at a pressure sufficient to support the shaft,even when the bearing is stationary. A large increase in the noise level producedby a journal bearing is apt to indicate a failure of the lubrication system.14.10 Ball and Roller BearingsAn incipient failure of ball or roller bearing can be detected by noise and vibrationmeasurements. For the most part, bearing life can be predicted but premature failurecan and does occur. The occurrence of discrete tones in the noise spectrum for anoperating bearing may indicate manufacturing defects, and narrowband vibrationspectra can be utilized to detect wear and defects.A ball or roller bearing consists of the following elements: a set of balls orrollers are enclosed in a cage or separator sandwiched between an inner race(that is usually attached to the shaft) and the outer race (usually attached to thesupporting stationary structure). When the shaft turns, the balls (or rollers) rollalong the surface of the inner raceway, which allows for the rotational freedomof the shaft. The cage or separator follows the motion of the balls. The speedrelationships are as followsn O − n Cn I − n C=− D ID O(14.22a)andn B − n Cn I − n C=− D ID B(14.22b)wheren = rotational speed, rpmD = diameter, mm or in.and the subscripts denote the variables as follows:I = inner raceO = outer raceB = ball or rollerC = ball cage or separatorThe race diameters are measured at the point of contact with the balls or rollers.