Bearings and their Applications

 Authors : Yash Gandhi, Gaurav Khadke, Shruti Gavare, Chaitanya Gawali, Shreyas Gaware

Bearings are used in a variety of light industrial equipment, from small shopping carts to large power plants.

bearings are an important part of a variety of machines and are available in a variety of sizes and shapes. Bearings are mechanical components that reduce friction between moving elements by limiting relative movement to what is intended.

Door-sliding is one of the example. You cannot push or lift the door to move it from its original position. You can open it just by sliding it. Bearings limit possible movement. Why do we need Bearings?

The primary function of bearings is to prevent direct metal-to-metal contact between two moving parts. Friction, heat buildup, and, eventually, part wear and tear are avoided. It also saves energy since it replaces sliding motion with low-friction rolling.

They also transfer the rotating element's load to the housing. This load could be radial, axial, or a mix of the two. As previously mentioned, a bearing restricts the freedom of movement of moving parts to prescribed directions.

Classification of Bearings:

• Bearings are classified in general terms based on the type of operation, the allowed motions, or the directions of the loads (forces) applied to the parts.
• At least six different bearing types exist, each with its unique set of principles:
•  A rolling-element bearing decreases sliding friction by inserting rolling elements between the rotating and stationary races. The two most common types are ball bearings, which have spherical balls as rolling elements, and roller bearings, which have cylindrical rollers as rolling components.
• Gem bearing, a plain bearing in which one of the bearing surfaces is formed of an ultra-hard glassy gem material such as sapphire to reduce friction and wear;
• Roller bearing, a plain bearing in which the rolling elements are cylindrical, taper, or spherical rollers; Plain bearing, consisting of a shaft rotating in a hole. There are several specific styles: bushing, journal bearing, sleeve bearing, rifle bearing, composite bearing.

• A fluid bearing (sometimes referred to as an air bearing) is a noncontact bearing that supports the load with a gas or liquid.

• Magnetic bearing, in which the load is supported by a magnetic field;

• A flexure bearing is one that has a bending load component that supports the motion.

Motions:

Bearings provide for radial rotation, such as shaft rotation;

linear motion, such as drawer motion;

Spherical rotation, such as ball and socket joints;

And hinge motion, such as door, elbow, and knee motion.

Types of Bearings and their applications:

   1. Rolling Element Bearings:

Bearings with rolling elements in the shape of balls or cylinders are known as rolling element bearings. Because the magnitude of rolling friction is lower than that of sliding friction, we know that rolling a wheel is easier than sliding it on the ground. Here, too, the same principle is at work. Rolling element bearings are utilized in rotational motion to allow pieces to move freely.

Even in cases where linear motion is required, it is simple to transform rotating motion to sliding motion. Take an escalator or a conveyor for example. Despite the fact that the motion is linear, it is propelled by rollers driven by motors.

Another example is a reciprocating pump, which uses linkages to transmit rotational energy from a motor to translational motion. Ball bearings are utilized to support motor shafts as well as shafts of other rollers in the assembly in each of these applications.

Because sliding friction is replaced by rolling friction, rolling elements carry the load with less friction. Ball bearings and roller bearings are the two most popular types of rolling element bearings.

  2. Ball Bearings:

One of the most regularly occurring varieties of bearings the ball bearing. As rolling elements, it consists of a row of balls. They're wedged between two metal annulus shapes. Races are the name for these metal bits. While the inner race rotates freely, the outside race remains motionless.

Ball bearings have a low friction coefficient when rolling, but their load-carrying capability is restricted. Because of the narrow contact area between the balls and the races, this is the case. Apart from radial loads, they can support axial loads in two directions.

Oscillatory and rotational motion are controlled by ball bearings. Ball bearings, for example, are used to connect the shaft to the motor housing in electrical motors where the shaft is free to rotate but the motor housing is not.

Different varieties of ball bearings are available to pick from depending on the application.

Advantages of ball bearings:

• Good wear resistance

• Requires little lubrication

• Provides low friction, resulting in less energy loss

• Long service life

• Simple to repair

• Small general dimensions

• Relatively inexpensive

• Can handle thrust loads

Disadvantages of ball bearings:

• It's prone to breaking from shocks;

• It's fairly loud;

• It can't manage big loads

   2A. Deep Groove Ball Bearings:

This is the most common type of ball bearing. A ring of balls is trapped between the two races, transmitting the load and allowing rotating motion between them. A retainer holds the balls in place.

They have a low rolling friction and are designed to be quiet and vibration-free. As a result, they're perfect for high-speed applications.

They are relatively simple to install and require little upkeep. Because the races must be pushed into shafts, care must be given during installation to avoid denting.

   2B. Angular Contact Ball Bearings:

In this ball bearing type, the internal and outer races are offset from each other alongside the bearing axis. This kind is designed to handle increasing amounts of axial loads in both directions in addition to radial loads.

Because of the displacement in the inner and outer races, the axial load can be transferred from the bearing to the housing. This bearing is suited for axial guiding applications that require rigidity.

Angular contact bearings are used in agricultural equipment, cars, gearboxes, pumps, and other high-speed applications.

   2C. Self-Aligning Ball Bearings

This type of ball bearing is resistant to shaft-to-housing misalignment, which can occur due to shaft deflection or mounting problems.

Deep grooves, comparable to deep groove ball bearings, are found on the inner ring, which is followed by two rows of balls and the outer ring. Because the outer ring is concave, the inner ring has some flexibility in rearranging itself based on the misalignment.

   2D. Thrust Ball Bearings:

Thrust ball bearings are a special form of ball bearing that can handle axial loads. They are completely incapable of withstanding radial loads.

Thrust ball bearings are smooth-running, low-noise bearings capable of handling high-speed applications.

Whether they are single direction or double direction bearings, it depends on whether the load is unidirectional or bidirectional.

When to Use Ball Bearings?

So, let's go over some of the situations where a ball bearing can be required.

1. There are thrust loads present. The design of ball bearings allows them to endure axial loads.

2. There are no hefty burdens. Because the bearings include ball-shaped rolling elements, all of the force is concentrated on a few points of contact. With large loads, this can lead to early failure.

3. Fast speeds The small point of contact of the ball bearing also means reduced friction. As a result, there is less resistance to overcome, making high speeds easier to reach with these bearings.

   3. Roller Bearings:

Roller bearings use cylindrical rolling elements rather than balls as load carrying elements between the races. A roller is defined as an element whose length surpasses its diameter (even if only slightly). Because they are in line with the inner and outer races, they can withstand higher loads (rather than point contact as with ball bearings).

Roller bearings are available in a wide range of forms and sizes. The right kind can be chosen after analysing the type and size of loading, service circumstances, and the risk of misalignment, among other factors.

Advantages of roller bearings:

•  Tapered roller bearings can withstand high axial loads and have low friction.
• Low vibrations
• Easy to maintain
• High precision
• Can be used to alter axial displacement

Disadvantages of roller bearings:

• Noisy
• Quite expensive

   3A. Cylindrical Roller Bearings:

These are the most basic of the roller bearings. Heavy radial loading and high speed are no match for these bearings. They have good stiffness, axial load transmission, reduced friction, and a long service life.

The load capacity can be raised even more 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 handle the weight.

They come in single row, double row, and four-row varieties. They are also available in split and sealed versions.

Split variations are employed for difficult-to-reach regions like engine crankshafts. Bearing contamination is eliminated and the lubrication is maintained in sealed variations, making it a maintenance-free choice.

   3B. Spherical Roller Bearings:

When the shaft is prone to misalignment, heavy radial and axial loads can be more difficult to handle.

Spherical roller bearings are well suited to this condition. They have great load carrying capacity and can handle shaft and housing misalignment. This lowers maintenance costs and extends the life of the equipment.

The raceways of spherical roller bearings are angled away from the bearing axis. The rollers feature spherical sides that fit onto the spherical raceways and accept slight misalignments instead of straight sides.

Spherical roller bearings can be used in a variety of applications. They're employed in situations where there are huge weights, moderate to high speeds, and the possibility of misalignment. Off-road vehicles, pumps, mechanical fans, naval propulsion, wind turbines, and gearboxes are some examples of applications.

   3C. Tapered Roller Bearings:

 

As a load-bearing device, tapered roller bearings contain cone parts. These rollers fit between the two laces, which are also hollow cone sections. The longer the roller truck and the axle, they all meet at the same point. Tapered roller bearings are designed to absorb increased axial loads in addition to radial loads. The greater the axial load that this typical cone can withstand, the larger the half-width. As a result, they act as both axial load bearings and radial load bearings.

   3D. Needle Roller Bearings:

Needle roller bearings are a type of roller bearing with cylindrical rollers that, due to their small diameter, resemble needles.

In most roller bearings, the rollers are only slightly longer than the diameter. In needle bearings, the length of the rollers must be at least four times the diameter.

Due to the smaller diameter of needle bearings, more rollers can be packed into the same space, increasing the surface area in contact with the races. As a result, they have the ability to bear large loads. The tiny size may be useful in applications where space is limited since fewer clearances between the axle and the housing are required.

Needle bearings are found in a variety of automotive components, including transmissions and rocker arm pivots. They're also found in pumps and compressors.

When to Use Roller Bearings?

The most frequent alternative to ball bearings is roller bearings. So, let's figure out what kind of working conditions this bearing is most suited for.

1. Massive loads. Roller bearings provide a far wider contact surface area, allowing for a more uniform distribution of weight. As a result, they have a reduced failure rate and are more resistant to extreme loads.

2. Go at a slower speed. It all comes down to the contact area once more. Friction is increased, leading to higher temperatures and faster wear.

   4. Plain Bearings:

A plain bearing is the most basic type of bearing. It usually only comprises of a bearing surface. In this game, there are no rolling elements.

The bearing is merely a sleeve that is installed on the shaft and fits into the bore. Plain bearings are inexpensive, compact, and light. They have the ability to carry a significant amount of weight.

Rotating, sliding, reciprocating, and oscillating motions are all transmitted by plain bearings. The bearing remains fixed while the journal glides on the bearing's inner surface. To aid smooth movement, material pairs with low coefficients of friction are chosen. Copper alloys, for instance, are available in a wide range of shapes and sizes.

The gudgeon pin that connects the piston to the connecting rod in diesel engines are connected by plain simple bearing.

 The spherical bearing, like the plain bearing, is made up of two parts: an inner ring and an outer ring. Although it initially resembles ball and roller bearings, there are no rolling parts between the two rings.

   5. Fluid Bearings:

A fluid bearing is a type of bearing that carries the load and eliminates friction by using pressurized gas or liquid. These bearings are used to replace metallic bearings in applications where there is a high amount of noise and vibration, as well as a limited life span.

They're also being used more and more to save money. Machines that operate at high speeds and loads employ fluid bearings. While the initial expenses are higher, the longer longevity in difficult conditions more than compensates.

Because there is no contact between the two elements when the machine is running (except during start and stop), fluid bearings can achieve near-zero wear.

There are two types of fluid bearings: hydrostatic and hydrodynamic bearings.

   6. Hydrostatic Bearings:

An externally pressurized fluid is driven between two pieces in relative motion in this type. The pressurized fluid acts as a wedge, keeping the moving pieces apart. Even if the fluid layer is very thin, there will be no wear if there is no direct contact.

A pump is used to circulate the fluid. The diameter of the exit aperture can be adjusted to keep the fluid under pressure at all shaft speeds and loads. Precision gap control is thus achievable.

    7. Hydrodynamic Bearings:

The journal motion is used to drive the fluid between the shaft and the housing in this type of bearing. The lubricating fluid is sucked between the moving elements by the journal motion, generating a continuous wedge.

This means that the wedge formation may not be good enough to prevent wear during start-stop operations, as well as at low loads and speeds. Only at the specified speeds can the system function properly.

   8. Magnetic Bearings:

Magnetic bearings use magnetic levitation to keep the shaft in mid-flight. Magnetic bearings are zero-wear bearings since there is no physical contact. It also has no upper limit on the amount of relative speed it can handle.

Because the shaft's position is automatically altered based on its centre of mass, magnetic bearings may handle some abnormalities in shaft design. As a result, it can be shifted to one side and still function properly.

Magnetic bearings are divided into two categories: active and passive.

  Active Magnetic Bearings

Electromagnets encircle the shaft in active magnetic bearings to keep it in place. If the system detects a change in position, it changes the amount of current provided to the system and returns the rotor to its original position.

  Passive Magnetic Bearing

Permanent magnets are used in passive magnetic bearings to maintain a magnetic field around the shaft. This means there is no requirement for a power supply. However, because this technology is still in its early phases, the system is challenging to build due to restrictions.

In many circumstances, the 2 kinds of magnetic bearings are utilised in tandem, with the everlasting magnets managing the static strain and the electromagnets retaining the location with excessive precision.

 

References:

1.    https://en.wikipedia.org/wiki/Bearing_(mechanical)

2.    https://fractory.com/types-of-bearings/

3.    https://insights.globalspec.com/article/12325/bearing-terms-and-calculations-every-design-engineer-should-know

4.    https://www.machinedesign.com/archive/article/21813866/basics-of-design-engineering-bearings