Raceways and rolling elements may become dented if the mounting pressure is applied to the wrong ring, so that it passes through the rolling elements, or if the bearing is subjected to abnormal loading while not running. Foreign particles in the bearing also cause indentations.
Indentations caused by faulty mounting or overloading
The distance between the dents is the same as the rolling element spacing. Ball bearings are prone to indentations if the pressure is applied in such a way that it passes through the balls during the mounting or dismounting operations. Self-aligning ball bearings are particularly susceptible to damage in such circumstances. In spherical roller bearings the damage originates as smearing, see section Smearing, and subsequently, if the pressure increases, develops into a dent. The same conditions apply in taper roller bearings that are unduly preloaded without being rotated.
Bearings that are mounted with excessively heavy interference fits, and bearings with tapered bore that are driven too far up the shaft seat or sleeve, also become dented.
|Indentations in the raceways of both rings with spacing equal to the distance between the rolling elements.||Mounting pressure applied the wrong ring.||Apply the mounting pressure to the ring with the interference fit.||Washer of a thrust ball bearing subjected to overloading while not running. The indentations are narrow and radially aligned, not sphered as in radial ball bearings (fig 1).
A roller in a double row cylindrical roller bearing has suffered impact (fig 2). A periphery camera view of the roller shows two diametrically opposed indentations (fig 3).
The roller has in turn dented the inner ring raceway (fig 4).
|Exessively hard drive-up on tapered seat.||Follow carefully the SKF instructions concerning mounting bearings on tapered seat.|
|Overloading while not running.||Avoid overloading or use bearings with higher static load rating.|
Indentation caused by foreign particles
Foreign particles, such as swarf and burrs, which have gained entry into the bearing cause indentations when rolled into the raceways by the rolling elements. The particles producing the indentations need not even be hard. Thin pieces of paper and thread from cotton waste and cloth used for drying may be mentioned as instances of this. Indentations caused by these particles are in most cases small and distributed all over the raceways.
|Small indentations distributed around the raceways of both rings and the rolling elements.||Ingress of foreign particles into the bearing||Cleanliness to be observed during the mounting operation.
|Indentations, caused by dirt, in one of the raceways of a roller bearing - 50× magnification (fig 5).|