Bearing FLAKING and its Causes.

Flaking (spawling)

Flaking occurs as a result of normal fatigue, i.e. the bearing has reached the end of its normal life span. However, this is not the commonest cause of bearing failure. The flaking detected in bearings can generally be attributed to other factors. If the flaking is discovered at an early stage, when the damage is not too extensive, it is frequently possible to diagnose its cause and take the requisite action to prevent a recurrence of the trouble. The path pattern of the bearing may prove to be useful, see path patterns and their interpretation.
When flaking has proceeded to a certain stage, it makes its presence known in the form of noise and vibrations, which serve as a warning that it is time to change the bearing. The causes of premature flaking may be heavier external loading than had been anticipated, preloading on account of incorrect fits or excessive drive-up on a tapered seating, oval distorsion owing to shaft or housing seating out-of-roundness, axial compression, for instance as a result of thermal expansion. Flaking may also be caused by other types of damage, such as indentations, deep seated rust, electric current damage or smearing.

Deep seated rust in the outer ring of a deep groove ball bearing.

Fig 1 - Flaked cone and rollers of taper roller bearing. Heavy loading and inadequate lubrication are the causes of this damage.

Flaking caused by preloading

Appearance	Heavily marked path pattern in raceways of both rings. Flaking usually in the most heavily loaded zone.
Cause	Preloading on account of fits being too tight. Excessive drive-up on a tapered seating. Single row angular contact ball bear- ings or taper roller bearings adjusted to give excessive preload. Temperature differential between inner and outer rings too great.
Action	Alter the fits or select bearing with larger internal clearance. Do not drive the bearing so far up its tapered seating. Re-adjust the bearings to obtain lighter preload. Select bearing with larger internal clearance.

Figure 2 - Outer ring of a self-aligning ball bearing that has been driven too far up its tapered seating. The bearing had only performed a few revolutions when the damage was detected. Flaking would soon have occurred if the bearing had been put into service.

Flaking caused by oval compression

Appearance	Heavily marked path pattern at two diametrically opposed sections of either bearing ring. Flaking in these sections.
Cause	Oval shaft or oval housing seating. The latter is a common defect in split housings and machine frames. The bore of plummer blocks mounted on an uneven base becomes oval when the base bolts are tightened.
Action	Usually it is necessary to manufacture a new shaft or a new housing to remedy this defect. One expedient is to spray metal on the components and then regrind. If it is a matter of an oval shaft with the bearing mounted on a sleeve, it is possible to adjust the shaft by grlnding, in certain cases. Adjust the base.

Figure 3 - Flaking in the outer ring of spherical roller bearing that has been mounted in a housing with oval bore.

Flaking caused by axial compression

Appearance	Deep groove ball bearings: heavily marked path pattem displaced to one side of both rings. Self-aligning ball bearings and spherical roller bearings: severely marked raceway path pattems from one row of rolling elements. Flaking in these areas. Single row angular contact ball bearings and taper roller bearings: same appearance as damage resuling from preloading, see flaking caused by preloading
Cause	Incorrect mounting, which results in axial loading, e.g. excessive preloading of angular contact ball bearings and taper roller bearings. The non-locating bearing has jammed. Axial freedom of movement has not been sufficient to accommodate the thermal expansion.
Action	Check adjustment when mounting the bearings. Check the fit and lubricate the surfaces. If temperature differential between shaft and housing cannot be reduced, provide greater freedom of movement.

Outer ring and inner ring.

Figure 4
Left hand image : Outer ring of a self-aligning ball bearing subjected to excessive axial loading. Flaking in the load zone.
Right hand image : Flaked inner ring of a spherical roller bearing. The extent of the flaking around one entire raceway indicates that the axial load has been very heavy in relation to the radial load.

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