All About Bearings

A bearing is a component used to decreasing of friction which could be caused from any elements related rotation, in order to reach the maximum efficiency of the power, which could have been converted from torque power into heat power, so the main function for the bearings is decreasing the "converted to heat" power.
A great variety of roller bearing types and designs are known, the manifolds of the bearings is justified by their various purpose of application.

Technical Information About Bearings:
Every form of antifriction Bearing consists of four basic parts:-

1. An Inner Ring
2. An Outer Ring
3. Rolling Elements
4. A Cage

1. An Inner Ring:-
The smaller of the two rings. It carries a precision-ground raceway on its outer surface, honed to a mirror-smooth finish held to very tight tolerances. The inner ring is mounted on the shaft and is usually the rotating element

2. An Outer Ring:-
The larger ring, with a matching raceway on its inner surface and the same high-precision finish. The outer ring normally seats in a housing and is usually held stationary.

3. Rolling Elements:-
These separate the two rings and let the bearing turn with minimal friction. In a ball bearing the ball radius is slightly smaller than the raceway groove, so contact is effectively at a single point. Rolling elements may be balls, cylindrical rollers, spherical rollers or tapered rollers (in plain journal bearings the “rolling element” is replaced by a film of oil). Their roundness, size and surface finish are controlled to the order of a millionth of an inch.

4. The Cage:-
The cage keeps the rolling elements evenly spaced, guides them around the raceways and stops them falling out. It may be made of steel, brass, bronze or a phenolic (polymer) composition, depending on the bearing type and application.

The parts of a Bearing in general is illustrated in the figure.

Bearings are designed in such a way that they offer following advantages:-

• Low Friction--Particularly low starting friction.
• The ability to support both radial and thrust load and high speeds of rotation.
• Accurate performance under changing load and speed.
• High Load Carrying capacity
• Operating ability under extreme conditions of speed and performance.
• Practically no wear in running.
• Simple methods of Lubrication.
• Inherently Precision Mechanisms.

The above advantages clearly justify the ubiquitous presence of Bearings in our life.

Bearing Selection

Choosing the right bearing for an installation depends mainly on five factors:

1. The load-carrying capacity required.
2. The shaft speed, in r.p.m.
3. The type of service and duty cycle.
4. The expected (design) life.
5. The ratio of thrust load to radial load.

As a first guide, the table below maps common bearing types to the duties they suit best:

Bearing type	Best suited to
Deep-groove ball	General-purpose radial and moderate axial loads at high speed; the default choice for electric motors, pumps and gearboxes.
Angular-contact ball	Combined radial and heavier one-direction axial load at high speed; usually mounted in pairs.
Self-aligning ball / spherical roller	Shafts subject to misalignment or deflection; spherical roller versions carry very heavy loads.
Cylindrical roller	Heavy radial loads where the shaft must be free to move axially within limits.
Tapered roller	Heavy combined radial and axial loads, such as automotive hubs and wheel ends; mounted in opposing pairs.
Thrust ball	Predominantly axial loads at lower speed.

Bearing Quality
Anti-friction bearings are precision-made: the rolling elements are hardened and the raceways are machined and finished to an extremely high degree of accuracy. That precision is what lets a small bearing absorb large forces — but it is also why even minor negligence in handling or fitting can damage it. Four essentials govern the quality of a standard ball or roller bearing:

1. Quality of steel — typically a high-carbon chromium bearing steel; AISI 52100 is generally preferred over EN31
2. Dimensional accuracy and surface finish of the raceways and rolling elements, measured in microns, with radial run-out kept within limits.
3. Careful selection and assembly — inner rings, outer rings and rolling elements are matched to the correct track dimensions.
4. Correct heat treatment — either through-hardening (in which the components are hardened throughout) or gas carburising / case hardening (in which a hard case is formed over a tougher core); balls are commonly hardened by oil-quench or salt-bath methods, depending on use. :-

Every quality bearing begins with testing of the raw material, and from raw material to finished product a bearing passes through many separate checks, tests and inspections on precision instruments. All of these factors together make a bearing perform as intended.

Frequently Asked Questions?

Q1. What is the difference between a shielded and a sealed bearing? Why stock both?

Ans: A shield is a metal disc fixed to the outer ring with a small clearance to the inner ring — it is non-contact, so it adds almost no friction and suits higher speeds and temperatures. A seal makes contact with the inner ring, giving far better protection against contamination and grease loss, but the rubbing contact raises friction, heat and starting torque and lowers the permissible speed. Because no single design wins on every count, both are stocked: shields for clean, high-speed duty and seals for dirty or wet environments where sealing matters more than speed.

Q2. A small amount of end-shake can be felt after a deep-groove ball bearing is mounted. Is it too loose?

Ans: No. A deep-groove ball bearing is designed with a small internal clearance, which is felt as slight axial and radial play before mounting. This running clearance is necessary — once the bearing reaches operating temperature, the inner ring expands and the clearance reduces. A bearing assembled with zero clearance would pre-load itself, run hot and fail early.

Q3. Are burrs on the shaft really a problem?

Ans: Yes. A burr on the shaft or housing shoulder prevents the bearing seating square and true. The ring is forced out of line, raising stress and causing premature failure. Time spent deburring and checking the shaft before mounting is always time well spent.

Q4. How much does lubrication really matter? Don’t bearings fail for many other reasons?

Ans: Lubrication is consistently the single largest cause of premature bearing failure. Industry maintenance studies repeatedly find that only a small fraction of bearings ever reach their natural fatigue life — the large majority are removed early, with lubrication problems and contamination leading the list, followed by mounting errors. Common lubrication faults include the wrong grease for the duty, using grease where oil is required, too little or too much lubricant, the wrong viscosity, missed re-lubrication intervals, and contamination of the lubricant

Q5. Our high-speed bearings run unusually hot, yet we are sure they are well lubricated. What is wrong?

Ans: Over-lubrication is a likely cause. Too much grease in a high-speed bearing churns, which increases friction and torque and drives the temperature up. In high-speed applications, over-greasing can be as harmful as under-greasing — the fact that the bearings are “well lubricated” may be the source of the heat.

Q6. Is there a right and wrong way to store bearings?

Ans: Yes. Keep bearings in their original packaging, in a clean, dry, vibration-free place, and use the oldest stock first. Handle them as little as possible — fingerprints can cause rusting — and avoid large swings in temperature, which let condensation form. Treat them as the precision components they are: never drop them or handle them roughly.

Q7. What are the most common mounting and installation mistakes?

Ans: Contaminating the bearing during fitting, and applying force to the wrong ring. Always press on the ring that has the interference (press) fit — force transmitted through the rolling elements brinells the raceways and ruins the bearing.

Q8. What are the clearest signs that a bearing is failing?

Ans: Excess heat, abnormal noise and increased vibration are the three reliable early indicators that a bearing has begun to fail.

Q9. Why does some new equipment arrive with bearings that are already noisy or fail early?

Ans: Damage can occur before the equipment is ever switched on. The bearing may have been dropped or had force applied to the wrong ring during assembly (denting or brinelling the raceway), or it may have suffered false brinelling from vibration during transit or while standing idle. If the shaft and housing dimensions check out, replacing the affected bearings usually resolves it.

Q10. What is the single most important aspect of bearing care?

Ans: Cleanliness. A large share of bearing trouble can be traced to contaminants that enter during handling, mounting or service. Even very small hard particles are crushed under the extreme contact pressures between the rolling elements and raceways, indenting the surfaces and starting wear. Keep the work area, tools, hands and clothing clean, and protect the bearing from dust and moisture at every step.