Bearing Health

Lubrication of a Bearing

Lubrication
The fundamental principle of efficient lubricant is to make a store lubricant film which prevents metal to contact of the sliding parts of the bearing most effectively and economically, and thus prevent wear resulting from this under operating conditions .It also reduces the rolling frication by keeping the elements and tracks neat. It also minimizes the bearing noise and prevents corrosion. Ball and roller bearings can be lubricated with either oil or grease, depending on operating conditions.

Oil Lubrication
For high speed operations and in long horizontal steam engine bearings, oil lubrication is considered to be far better than grease since it possesses high tackiness and reduces the friction. The oil should be fed regularly in small amounts, in order to keep the bearing temperature down . For moderate and low speeds, oil pump lubrication system is adopted, in which housing is filled up to the level of the center of the lowest ball or roller. Only height grade non-aging mineral oils should be used, which are completely free from all mechanical impurities. Checking the oil viscosity that it is suitable for the working temperature is very essential

Grease Lubrication
On account of simplicity of maintenance and sealing of prevent entry of dirt, grease lubrication is widely used. The grease selected should have minimum possible adhesive properties so that it adheres well to metal. It is modern practice to use any lithium base or calcium base grease.

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.

Maintenance of a Bearing

Bearing Life
The life of a bearing is either defined as the number of revolutions, or the hours at some given constant speed; for which bearing runs before the first evidence of fatigue develops in the material of the races, rings or rolling elements.
Faulty methods of mounting, unsuitable fits, use of inferior lubricants, dirty surroundings etc. may result in the failure of the bearings before the calculated life. Such failure can be prevented by appropriated precaution during the design of the equipment (on which the bearing is to be fitted) by proper method of handling the bearing.
From the years of experience, it is observed that at least 90 % of the bearings, attain their calculated life, provided the bearing is properly fitted and maintained.

Cleanliness
Cleanliness is very important to bearing maintenance and longevity. Cleanliness doesn’t just mean clean bearings. It means clean housings and shafts, clean tools, clean solvents and flushing oils. It also means putting bearings on a clean surface and using clean rags to wipe bearings.
Use any cleaning solution such as kerosene or mineral spirits rather than steam or hot water to avoid corrosion. Never wash or clean bearings in an enclosed area. Solvent fumes are toxic and explosive. Make sure that there is adequate ventilation and no open flame, welding or smoking in the area. Use rubber gloves to protect skin and safety glasses to protect eyes from the solvents.

Storage
Packaging is designed to protect bearings against dirt and moisture during shipping and storage. Don't try to open the package early let the package do its job, and leave replacement bearings in their original containers. Store them in a clean, dry area until ready for use. Strictly avoid temperature changes in your storage area it may cause condensation and damage the bearing.

Sealing
Seals are vital to the performance of any bearing. Replace worn or damaged seals; they allow contaminants such as dirt and water to enter the bearing and they allow lubrication to escape. In most cases, it is good practice to replace all seals with new during tear-down. A film of lubricant should be applied to the seal lip contact surface at assembly. This will help prevent seal damage during installation and at initial start-up. It also will reduce rolling torque.

Handling
The less, the better. Fingerprints can cause rust, so handle bearings only when necessary. Never drop or handle these precision components roughly. Any sign of a bent cage renders replacement.

Communication
If you have any questions about the maintenance and handling of tapered roller bearings, contact to the service engineers of Bearings industry Technical team. They are experts in the use of bearing products, offering in-depth knowledge of bearing applications, design and operation, coupled with strict attention to the environments in which bearings will operate.

Bearing Maintenance
When handing bearings, Following are the right and wrong practices.

Right

1. Remove all outside dirt from housing before exposing bearing.
2. Treat a used bearing as carefully as you would a new one.
3. Work with clean tools in clean surroundings.
4. Handling with clean, dry hands or better, clean canvas gloves.
5. Use clean solvents and flushing oils.
6. lay bearings out on clean newspaper.
7. Protect dissembled bearings from rust and dirt.
8. Use clean rags to wipe bearings.
9. Keep bearings wrapped in oil poof paper when not in use.
10. Clean inside of housing before replacing bearing.

Wrong

1. Don't work in dirty surroundings.
2. Don't use dirty, brittle or chipped tools.
3. Don't use wooden mallers or work on wooden bench tops.
4. Don't handle with dirty, moist hands.
5. Don't use gasoline's containing tetra-ethyl lead, as they may be injurious to health.
6. Don't spin unclean bearings.
7. Don't spin bearings with compressed air.
8. Don't use cotton waste or dirty cloth to wipe bearings.
9. Don't expose bearings to rust or dirt.
10. Don't nick or scratch bearing surfaces.

Proper Handling Practice of Bearings