Path patterns

Not all patterns and marks are signs of bearing damage. Bearings will often show loading patterns from normal operation.

Interpreting path patterns

When a rolling bearing rotates under load, the contacting surfaces normally become dull in appearance. This is not an indication of wear in the usual sense of the word, and is of no significance to the bearing life. The dull surface in an inner or outer ring raceway forms a pattern called the path pattern. This pattern varies in appearance according to rotational and loading conditions. By examining the path patterns in a dismantled bearing that has been in service, it is possible to gain a good idea of the conditions under which the bearing has operated.
By learning to distinguish between normal and abnormal path patterns there is every prospect of being able to assess correctly whether the bearing has run under the proper conditions.
The following series figures illustrates normal path patterns under different rotational and loading conditions as well as typical patterns resulting from abnormal working conditions.
In the majority of cases the damage to the bearing originates within the confines of the path patterns and, once their significance has been learned, the appearance and location of the patterns prove to be useful aids in diagnosing the cause of the damage.
Deep groove ball bearings and thrust ball bearings have been used for illustrative purposes as they display such characteristic path patterns. However the figures are applicable, with some modifications, to other types of bearings as well.
Uni-directional radial load - Rotating inner ring / fixed outer ring
Inner ring: path pattern uniform in width, positioned in the centre and extended around the entire raceway.
Outer ring: path pattern widest in the load direction and tapered off towards the ends. With normal fits and normal internal clearance, the pattern extends around slightly less than half the circumference of the raceway.
(fig 1)
Uni-directional radial load- Fixed inner ring / rotating outer ring
Inner ring: path pattern widest in the load direction and tapered off towards the ends. With normal fits and normal internal clearance, the pattern extends around slightly less than half the circumference of the raceway
Outer ring: path pattern uniform in width, positioned in the centre and extended around the entire raceway.
(fig 2)
Radial load rotating in phase with the inner ring - Rotating inner ring / fixed outer ring
Inner ring: path pattern widest in the load direction and tapered off towards the ends. With normal fits and normal internal clearance, the pattern extends around slightly less than half the circumference of the raceway
Outer ring: path pattern uniform in width, positioned in the centre and extended around the entire raceway.
(fig 3)
Radial load rotating in phase with the outer ring - Fixed inner ring / rotating outer ring
Inner ring: path pattern uniform in width, positioned in the centre and extended around the entire raceway.
Outer ring: path pattern widest in the load direction and tapered off towards the ends. With normal fits and normal internal clearance, the pattern extends around slightly less than half the circumference of the raceway.
(fig 4)
Uni-directional axial load - Rotating inner or outer ring
Inner and outer rings: path pattern uniform in width, extended around the entire raceways of both rings and laterally displaced.
(fig 5)
Combination of unidirectional radial and axial loads - Rotating inner ring / fixed outer ring
Inner ring: path pattern uniform in width, positioned in the centre and extended around the entire raceway and laterally displaced.
Outer ring: path pattern extended around the entire raceway and laterally displaced. The pattern is widest in the direction of the radial loading.
(fig 6)
Uni-directional axial load - Rotating shaft washer / fixed housing washer
Shaft and housing washers: path pattern uniform in width, extended around the entire raceways of both washers.
(fig 7)
Uni-directional radial load + imbalance - Rotating inner ring / creeping outer ring
Inner and outer rings: path pattern uniform in width, extended around the entire circumference of the raceways of both rings.
(fig 8)
Fits too tight - preloading - Uni-directional radial load - Rotating inner ring / fixed outer ring
Inner ring: path pattern uniform in width, positioned in the centre and extended around the entire raceway.
Outer ring: path pattern positioned in the centre and extended around the entire circumference of the raceway and laterally displaced. The pattern is widest in the direction of the radial loading.
(fig 9)
Oval compression of outer ring - Rotating inner ring / fixed outer ring
Inner ring: path pattern uniform in width, positioned in the centre and extended around the entire raceway.
Outer ring: path pattern positioned in two diametrically opposed sections of the raceway.The pattern is widest where the pinching has occurred.
(fig 10)
Outer ring misaligned - Rotating inner ring / fixed outer ring
Inner ring: path pattern uniform in width, positioned in the centre and extended around the entire raceway.
Outer ring: path pattern in two diametrically opposed sections, displaced diagonally in relation to each other.
(fig 11)
Inner ring misaligned - Rotating inner ring / fixed outer ring
Inner ring: path pattern in two diametrically opposed sections, displaced diagonally in relation to each other.
Outer ring: path pattern widest in the load direction and tapered off towards the ends. The internal clearance is reduced on account of the misalignment of the inner ring; the length of the path pattern depends upon the magnitude of the internal clearance reduction.
(fig 12)
Housing washer positioned eccentrically relative to shaft washer - Rotating shaft washer / fixed housing washer
Shaft washer: path pattern uniform in width, positioned in the centre and extended around the entire raceway.
Housing washer: path pattern extended around the entire circumference of the raceway and off-centre relative to raceway.
(fig 13)
Housing washer misaligned - Rotating shaft washer / fixed housing washer
Shaft washer: path pattern uniform in width, positioned in the centre and extended around the entire raceway.
Housing washer: path pattern in the centre of the raceway but wider around part of the raceway.
(fig 14)
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