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    ROLLING BEARING FAILURE

    9.0 Manufacturing defects

    Click on photograph to enlarge 
    Figure 9a
    Inner race of double-row angular contact bearing with incorrectly machined filling slot
    Figure 9b Talyrond traces of track of inner race
    (a) Poor quality finish (magnification x2500)
    (b) normal quality finish (magnification x5000)
    Main CharacteristicsRolling bearings are manufactured in a highly competitive commercial market and are subject to rigorous inspection procedures. Nevertheless, the odd substandard bearing may get through and, although this is very uncommon, should not be discounted as a possible cause of failure.
    CauseThe following cases have been encountered.
    1. Wrong material One example concerns a single-row angular contact bearing in which, on removal from service, one of the balls was found to be scored, whereas all the others were in the as-new condition. Examination showed that the offending ball was of 13% Cr steel, not the standard 1% Cr, 1% C steel. This was by a chance examination; if this had not taken place, a premature failure would have occurred.
    2. Wrong heat treatment Races and rolling elements of normal rolling bearings are tempered at about 140°C to give a final hardness of 600-650 HV (62-63 HRc). Some large taper roller bearings may be manufactured of case-hardened steel. A soft bearing will fail prematurely. Incorrect heat treatment can be suspected if any of the components are soft and do not exhibit heat discolouration from the failure.
    3. Incorrect machining Very rarely bearings may be found to be outside the standardised external dimensions. This is usually obvious during fitting and should not cause a problem. A more serious error, however, was in a double-row angular contact bearing with a filling slot that had been machined right into the ball track (figure 9a).
    NoteFigure 9b shows comparative Talyrond tracings from the race of a normal quality bearing and the one that was removed because of excessive noise. This would probably have suffered a lubricant breakdown failure if it had not been removed because of the noise.
    Possible Confusion with
    Other Types of Damage    		 
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