Bearings Industry: Online B2B Portal for Bearings

Before Mounting a Bearing

Every possible care must be taken for following factors, to ensure smooth and satisfactory bearing performance.

Before unwrapping a bearing a bearing, all designation and symbols on carton should be thoroughly checked to make sure that bearing is exactly to required specification.
The fitter, must have a proper knowledge of bearing of bearing Mounting procedure, various operations involved, knowledge of force to be applied and amount of lubrication enquired etc.
Generally, anti frication bearings are coated with rust primitive oil. Therefore bearings should never be washed or cleaned before mounting. Washing and cleaning of bearing means damaging the bearing.
Any packed bearing must be used as it is. No supplementary modifications should be done to a bearing, such as putting additional shield, groove on outer race, taper bore, slots, lubricating hole etc. Such modification may damage the bearing and reduce it's a normal life.
For bearing, DIRT means Damage. All bearings must be properly protected from dirt. Work-shape premises used for bearing mounting must be neat, clean, dust-free and absolutely dry.
All tools to be used for mounting operations, must be totally clean.
Care should be taken to see that bearing shaft, housing and other parts are absolutely clean and dry.
Dimensions and tolerances of shaft and housing must be checked for utmost accuracy. Inaccurate shaft or housing dimensions may misalignment and thereby invites premature break-down of the bearing.
Shaft and housing dimensions should be kept in such a way that bearing gets a tight fit, (not to tight) on shaft and housing. in case inner ring slips in housing, result will be premature failure.
Small size bearings are generally passed on to the shaft whereas large size bearings are heated in an oil bath ( around 80 degree c.) for easy placement of a bearing on to the shaft.

Bearing Lubrication

Lubrication is the single most important factor in how long a bearing lasts. The lubricant does far more than "make things slippery": it separates the rolling elements from the raceways with a thin film, reduces friction and wear, carries away heat, protects against corrosion, and helps keep contaminants out. Get the lubrication right and most bearings reach their design life; get it wrong and they fail early.

Grease or oil?

Most bearings are lubricated with grease; a minority use oil. The choice depends mainly on speed, temperature and how heat is managed.

	Grease	Oil
Best for	The majority of bearings — easy to retain and seal in	High speed or high temperature; where heat must be carried away
Advantages	Stays in place, helps seal against dirt, simple, low maintenance	Removes heat, can be filtered and circulated, suits very high speed
Watch-outs	Limited heat removal; needs correct quantity and re-greasing	Needs a sealed/circulating system; more complex

What grease is made of

Grease is a base oil held in a thickener (often a metallic soap), with additives for oxidation resistance, corrosion protection and load capacity. Its stiffness is graded by the NLGI consistency number — NLGI 2 is the typical general-purpose grade for bearings. The base oil viscosity matters as much as the thickener: it must suit the speed and temperature of the application.

Choosing the right lubricant

Match the lubricant to the duty by considering:

Speed — higher speed needs a lower base-oil viscosity; very high speed may need oil.
Temperature — both the operating range and any extremes; greases have a usable temperature band.
Load — heavy or shock loads may need extreme-pressure (EP) additives.
Environment — water, dust or chemicals call for a grease that resists wash-out and corrosion.

How much — and why more is not better

Quantity matters. As a general guide, the bearing and a portion of the surrounding free space are filled with grease — but the housing should not be packed full, especially at higher speeds.

Over-greasing is a common cause of overheating: excess grease churns as the bearing turns and generates heat. On a high-speed bearing, too much grease can be as damaging as too little. See why bearings run hot.

Relubrication

Grease does not last forever — it ages, loses oil and picks up contamination. Re-greasing intervals shorten with higher speed, higher temperature and dirtier or wetter environments. Many smaller bearings are "sealed for life" and never re-greased; larger and harder-working bearings are re-greased on a planned schedule. When re-greasing, add the right amount of the correct grease and, where possible, let old grease purge out.

Common lubrication mistakes

The wrong grease type or base-oil viscosity for the speed and temperature.
Too little or too much lubricant.
Mixing incompatible greases (different thickeners can react and break down).
Missed or over-long re-greasing intervals.
Contaminating the grease with dirt or water during application.

Each of these shows up later as heat, noise or premature wear — see the grease condition guide and the Failure Diagnosis Library.

Frequently asked questions

Should I use grease or oil for my bearing?

Grease suits most bearings and is simpler to retain and seal. Oil is used for high speed or high temperature, or where heat needs to be carried away by a circulating system.

Can I mix two different greases?

Avoid it unless they are known to be compatible. Different thickeners can react, soften or harden the grease and destroy its performance. If changing grease, purge the old one out.

How often should bearings be re-greased?

It depends on speed, temperature and environment — faster, hotter and dirtier conditions mean shorter intervals. Many small sealed bearings are never re-greased; larger ones follow a planned schedule.

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

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

Wrong

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

Warning:
Never spin a bearing with compressed air. The force of the compressed air may cause the rollers to be expelled with great velocity, creating a risk of serious bodily harm. Proper bearing maintenance and handling practices are critical. Failure to follow installation instructions and failure to maintain proper lubrication can result in equipment failure, creating a risk of serious bodily harm. If a hammer and mild steel bar are used for bearing removal, fragments from the hammer, bar or bearing can be released with sufficient velocity to create a risk of serious bodily harm, including damage to your eyes.

Proper Handling Practice of Bearings

Bearing Health