Cracks may form in
bearing rings for various reasons. The most common cause is rough treatment when the
bearings are being mounted or dismounted. Hammer blows, applied direct against the ring or
via a hardened chisel, may cause fine cracks to form, with the result that pieces of the
ring break off when the bearing is put into service. Excessive drive up on a tapered
seating or sleeve is another cause of ring cracking. The tensile stresses, arising in the
rings as a result of the excessive drive-up, produce cracks when the bearing is put into
operation. The same result may be obtained when bearings are heated and then mounted on
shafts manufactured to the wrong tolerances.
Figure 1 - Fractured outer ring of a self-aligning ball bearing. The indentations visible at the bottom edge of the ring were caused by rough treatment and the crack originated at one of these indentations.
Cracks caused by rough treatment
image : Cracked inner ring of a spherical roller bearing. One roller has been removed
to allow the raceway of the leff-hand of the photograph to be examined. The roller has
then been hammered back in place, causing part of the centre flange to break away. The
impacts have been transmitted via a roller in the other row and part of the outer flange
has broken off too. At the same time the ring has cracked right through.
Cracks caused by smearing
Left hand image :
Spherical roller bearing inner ring that has cracked right across following smearing of
one face. The ring has been mounted to a but spacer that has not been a sufficiently tight
fit on the shaft. Consequently the spacer has rotated relative to the shaft and the
Cracks caused by fretting corrosion