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FAILURE OF A BEARING

BEARING FAILURES

The causes of the bearing failure must be identified and understood in order to apply proper corrective measures.

NORMAL FATIGUE

Normal
fatigue is evinced by flaking and spilling phenomena visible at the surface of the raceways which is natural for all bearing after certain time.
However, the causes or premature break- down can be identified as under:


(A) IMPROPER MOUNTING:
The most common causes of bearing rejection is brinell damage to the ball race. The conduction is common in installation where final assembly of units must be accomplished by inserting bearings, already assembled onto shafts, into housings. Damage occurs when axial pressure is applied to the shaft in order to slide the bearings into the housing. If the housing fit is too tight, or the bearing cocked on to the shaft, the load necessary to force the bearing into the housing pushes the balls high up on the raceway and creates a triangular shaped dent, or 'Brinell' spot at the juncture of the raceway with the shoulder.

(B) LOOSE FITS ON SHAFT:
Generally the shaft rotes and the inner ring is mounted with a firm press. If this fit is loose, damage within the inner ring can occur, producing small loose particles of metal. These eventually get into the bearing causing wear on the races which makes bearings noisy. This is easily identified by scoring or abrasion of the bore of inner ring.

(C) EXCESSIVELY TIGHT FITS:
Too tight a fit on the inner ring may cause it to crack. Usually this trouble shows up when the bearing is mounted or shortly thereafter. Too tight a fit on the outer ring occasionally causes it to crack, but usually, results in tightening the original fit-up of the bearing. This results in high operating temperatures, production of abnormal quantities of iron oxide from pressure on the inner raceways, and eventually bearing failure. The conduction can be spotted by initial high operating torque accompanied by high temperature. The bearing may emit a high pitched sound in operation.

(D) MISALIGNMENT:
Misalignment is a frequent source of trouble resulting in overheating of the bearing and separator failure. Misalignment is caused by a bent shaft, or when the inner ring is locked against an out-of-square with the bearing seat.

(E) ELECTRICAL DAMAGES:
When electrical current passes through the bearing, damage usually occurs at the contact between ball and raceway where fused spots resembling welds may appear. Actual tempering takes place under the race and hardened area is the surface. Subsequently the whole affected section separates from the raceway. The bearing becomes vary noisy. As such suitable insulation is very necessary.

(F) DIRT:
The conduction is usually detected by a gradual rise in operating noise. Most bearing failure are probably due to the introduction of foreign materials into the internal parts of the bearings.

(G) INADEQUATE LUBRICATION:
Inadequate lubrication shows up frequently as failure of the ball separator. Sometimes separator becomes discolored due to high temperature. This is an evidence of lack of lubrication between balls and separator.

(H) VIBRATION BRINELL:
A peculiar type of damage; it occurs as a result of vibration from outside the machine in with the bearing is mounted. Vibration causes rapid, imperceptible movements of the balls, either while in a static position of non use, or while the machine is operating. The conduction is identified by slight brinell marks giving a washboard affect in the ball raceway. In operation, the effect is characterized by excessively noisy operation on a low note.

 

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