Types of Bearings

What is the Purpose of Bearings?

Bearings are the basic component with great importance and can be found in all most every machine. Their sole purpose is prevention of direct contact between 2 parts of the machine that are in relative motion. Thereby preventing friction, heat generation hence preventing the wear and tear of parts. Energy consumption is also reduced as sliding motion is in turn replaced with low friction rolling. They also play an important role to transmit the load which may be radial, axial, or a combination of both. Depending on the application it can also restrict freedom of movement of different parts.

 Principle of Rolling Bearings: -

Rolling elements are in the form of balls or cylinders. We know that it’s easier to roll a wheel than slide it on the surface because the magnitude of rolling friction is less than friction. The same principle is in work here. Rolling element bearings make it possible to have free movement of parts in rotational motion. 

Classification: -

  

Ball Bearings: -

In Ball bearings the rolling elements are balls arranged in a row. They are trapped between two annulus-shaped metal pieces known as races. The inner race is free for rotation whereas the outer race is stationary. Ball bearings have the advantage of very low friction during rolling but have limited load-carrying capacity. The reason being the small area of contact between the balls and the races. They are known to support axial loads in two directions apart from radial loads. The main purpose of it is for controlling oscillatory and rotational motion. For example, if we consider electrical motors the shaft is free to rotate and the motor housing is not, ball bearings are used there to connect the shaft to the motor housing. We have different types of ball bearing which are application-specific.

 Advantages of ball bearings:

• Good resistance against wear
• No need for much lubrication
• Loss of energy is less because of low friction
• Long service life
• Easy to replace
• Comparatively cheap
• Can sustain thrust loads very well

Disadvantages of ball bearings:

• Limited load capacity
• Vulnerable to breakage due to shock
• Noise issues can occur

When can Ball Bearings be used?

1. If Thrust loads are present. They are capable of sustaining axial loads due to their design.
2. If no heavy loads are present. Heavy loads can result in early failure.
3. High-speed requirement. Their small point of contact means less friction means less resistance to overcome hence easier to achieve high speeds.

Now we will look further at the classification of ball bearings as per the above flowchart.

Deep Groove Ball Bearings: -

This is the most widely used ball-bearing type. The two races trap the ring of balls that transmit the load and permit rotational motion between the races. A retainer is used to keep balls in place. Very low rolling friction, low noise, low vibration, ease to install, low maintenance are its highlights. Hence often chosen for high-speed applications. Electric motors, compressors, fans, and conveyors are some of examples of where they're used. Note: During installation denting of the races should be taken care of as they have to be push-fit onto shafts. Single row and double row are two most common types available.

Self-Aligning Ball Bearings: -

As the name suggests it is immune to misalignment between the shaft and the housing which may happen due to shaft deflection or mounting errors. The inner ring has deep grooves followed by 2 rows of balls and finally the outer ring. The outer ring is concave shaped allowing the inner ring freedom to realign itself if there is any misalignment. Some of the benefits are as follows: Misalignment tolerance, extremely low friction & heat generation, low noise & vibration levels, environmentally friendly, high-speed efficiency, low lubricant use, high-speed performance, low lubricant use, low noise & vibration levels, Productivity is boosted by high-speed efficiency. It is used in cereal mills, magazine staple machines, refinery process pumps, thread twisting machines, and centrifugal separators.

 

Angular Contact Ball Bearings: -

In the needle bearing, the inner and outer races are being displaced with relevance to one another on the bearing axis. This kind of bearing is meant to handle larger amounts of axial loads in each of the two directions alongside radial load. Because of the shift within the inner and outer races, the axial load is transferred through the bearing to the housing. These find of bearings find their application in agricultural instruments, vehicles, pumps, gearboxes and different high-speed applications.

Thrust Ball Bearings: -

These are designed specifically for handling axial loads. They cannot sustain radial loads at all. Prominent features are very low noise, operation, and can be used for high-speed applications. They are classified broadly into two types single direction and double direction bearings. The process of selection depends on whether the load is of unidirectional type or of bidirectional type. Thrust bearings are used in cars because modern car gearboxes use helical gears in the forward gears, which produce axial forces that must be dealt with while improving smoothness and noise reduction. They're also found in the grips of RC (radio controlled) helicopters' main and tail rotor blades. The clutch "throw out" bearing (also known as the clutch release bearing) is a form of thrust bearing used in automobiles.

 

Roller Bearings: -

Roller bearings have cylindrical rolling elements instead of balls as load-carrying elements between the races. An element is said to be a roller if its length is longer than its diameter. Since they are in line contact with the inner and outer races hence, they can support greater loading. Roller bearings come in a variety of design types. The criterion for selection basically depends on the type and magnitude of loading, service conditions, the possibility of misalignment, etc.

 Advantages of roller bearings:

• Easy maintenance
• Low friction and vibrations
• Can take high radial loads and Tapered roller bearings can even sustain high axial loads
• Adjustment of the axial displacement is possible
• Accuracy is significant

Disadvantages of roller bearings:

• Noisy and expensive

Tapered Roller Bearings: -

As a load-carrying is the feature, these contain parts of a cone. Rollers fit between the two races which are also sections of a hollow cone. If the roller races and axes were to be extended, they would all meet at the same point. These bearings can handle higher axial loads besides radial loads. They can work as both thrust bearings and radial load bearings. In car and truck wheel bearings, pairs of tapered roller bearings are used to cope with strong vertical (radial) and horizontal (axial) forces at the same time. Agriculture, mining machinery, axle systems, gear boxes, railroad axle-box, and wind turbines are some examples of real-world applications.

Spherical Roller Bearings: -

The specialty of these bearings is that they can handle misalignment between shaft and housing very well. The major reason for misalignment is heavy radial and axial loads which makes the shaft vulnerable. Spherical roller bearings can also handle a heavy load. This lowers maintenance costs and extends the lifespan. Spherical roller bearings are used in a variety of scenarios. They are used where heavy loads, moderate to high speeds, and possible misalignment occur. Off-road military vehicles, generators, electric fans, underwater propulsion, wind turbines, and gearboxes are some examples of applications.

 

Cylindrical Roller Bearings: - 

These are the most basic of the roller bearings. Heavy radial loading and high speed are really no concern for these bearings. They have good stiffness, axial load transfer, low friction, and a long service life. The load capacity can be improved even further by removing the cages or retainers that are typically used to keep the cylindrical rollers in place. This allows for the installation of additional rollers to hold the load. They come in single row, double row, and four-row varieties. They're also available in split and sealed versions.

 

Needle Roller Bearings: -

The needle roller bearing is a type of roller bearing with cylindrical rollers that, due to their small diameter, resemble needles. In most roller bearings length of rollers is only slightly more than their diameter but in a needle bearing, the length is at least four times more than the diameter. Having a smaller diameter, more rollers can fit in the same space, increasing the surface area in contact with the races. As a result, they can handle heavy loads. Their small size proves helpful in applications with space restrictions. Gearboxes, automotive power transmission systems, two and four stroke motors, planetary gear sets, and air compressors are all popular uses for needle roller bearings.

 

When to Use Roller Bearings?

The most popular alternative to ball bearings is roller bearings. 

1. Roller bearings provide a larger area of contact, distributing the load more evenly. Thus, they are less prone to failure and can sustain the heavy load. 
2. Roller bearings provide a larger area of contact. Resulting in more friction in turn higher temperature generation and faster wear. Thus, they are suitable for low-speed applications only.

Some Other Important Types of Bearings: -

Plain Bearings: -

A plain bearing is the most basic type of bearing. It usually only consists of a bearing surface with no rolling elements. The bearing is a sleeve mounted on the shaft that fits into the bore. Plain bearings are cheap, compact, lightweight, easy to install, and have high load-carrying capacity. They can even handle some misalignment. Materials with low coefficients of friction are selected. The use of copper alloys is pretty common. Agriculture, vehicle, marine, also the construction industry all use it extensively. A plain bearing attaches the gudgeoned pin that connects the piston to the connecting rod in diesel engines.

 

Zero-Wear Bearings: -

Fluid Bearings: - 

 

This is a special purpose bearing that relies on pressurized gas or liquid to carry the load by eliminating friction. These bearings are used where they would have a short life and are exposed to high noise and vibration levels. An uptrend in their usage is observed to cut costs. Though initial costs are higher, the lifespan in harsh conditions balances it in the long run. When the machine is running, there is zero contact between the two elements (except during the start and stop), thus creating a near-zero wear scenario. There are two kinds of fluid bearings: hydrostatic and hydrodynamic bearings. Fluid bearings are widely used in high-load, high-speed, or high-precision applications where conventional ball bearings would have a limited life span or cause excessive noise and vibration. They're also being used more and more to cut costs.

Magnetic Bearings: -

Magnetic bearings are based on the principle of magnetic levitation to keep the shaft floating in mid-air. Magnetic bearings are zero-wear bearings since there is no physical touch. It also has no upper limit on the amount of relative speed it can bear. Since the shaft's location is automatically changed based on its center of mass, magnetic bearings can also tolerate certain irregularities in design of shaft. As a result, it can be shifted to one side and still work properly. Magnetic bearings are divided into two categories: active and passive. Compressors, centrifuges, high-speed generators, energy-storage flywheels, high-precision machine tools, and other commercial applications are examples. Magnetic bearings are an example of a mechatronic object.

Selection Of Bearing: -

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