Types Of Bearings [PDF]

In this article, I will explain the types of bearings. A PDF has been provided at the end.

Many types of machinery, from a small supermarket trolley to huge power plants, rely on bearings for their operation. Bearings, which are crucial tribological components, come in various shapes and forms, defining them as machine elements that permit only a specific type of motion in a system under static or dynamic loading.

For example, consider a sliding door. Bearings restrict its movement to sliding only, preventing it from being lifted or removed from its place.

Definition of Bearings

Bearings are mechanical components designed to facilitate smooth motion between two moving parts by providing support and reducing friction. They prevent direct contact between surfaces, minimizing wear and heat generation, and contribute to efficient energy transmission and load distribution in various types of machinery.

Purpose of Bearings

Bearings serve to prevent direct metal-to-metal contact between two elements in relative motion, aiming to avoid friction, heat generation, and the resulting wear and tear of parts. The utilization of bearings replaces sliding motion with low-friction rolling, reducing energy consumption.

In addition, bearings transmit the load of the rotating element to the housing, handling radial, axial, or combined loads. Furthermore, bearings restrict the freedom of movement of moving parts in predefined directions.

Types of Bearings

Here is a list of the different types of bearings.

Roller Element Bearings

Rolling Element Bearings, housing balls or cylinders, leverage lower rolling friction for efficient rotational motion. This principle extends to linear applications, where converting rotational to sliding motion is seamless—evident in escalators or pumps. Ball bearings, key in these scenarios, support motors and roller shafts. This design minimizes friction, which is crucial for load-bearing. The broader classification includes ball bearings and roller bearings.

This is divided into two main types of bearings:

• Roller Bearings
• Ball Bearings

Let’s first discuss the roller bearings, and then we’ll cover the ball bearings.

Roller Bearings

Roller bearings employ cylindrical rolling elements distinct from ball bearings, enhancing load-bearing capacity. Rollers, with longer length than diameter, ensure line contact with inner and outer races, accommodating greater loads than ball bearings. Available in various types, selection depends on factors like loading, service conditions, and misalignment.

Types of Roller Bearings

In our list of different types of bearings, Let us explore the Different types of roller bearings

• Cylindrical Roller Bearings
• Spherical roller bearings
• Tapered Roller Bearings
• Needle Roller Bearings

Cylindrical Roller Bearings

Cylindrical roller bearings, the simplest in their family, handle heavy radial loads and high speeds effectively. They ensure stiffness, transmit axial loads, maintain low friction, and boast an extended service life.

Eliminating cages or retainers increases load capacity by allowing more rollers. They come in single-row, double-row, and four-row types, including split and sealed variants. Split versions suit hard-to-reach areas like engine crankshafts. Sealed types prevent contamination and retain lubricant, offering a maintenance-free solution.

Spherical roller bearings

Spherical roller bearings effectively handle heavy radial and axial loads, particularly in situations prone to shaft misalignment. These bearings boast high load-carrying capacities, efficiently managing misalignment between the shaft and housing. This not only reduces maintenance costs but also enhances service life.

Their raceways, inclined at an angle to the bearing axis, feature spherical sides on the rollers that accommodate small misalignments. Widely applicable, they find use in scenarios with heavy loads, moderate to high speeds, and potential misalignment—examples include off-road vehicles, pumps, mechanical fans, marine propulsion, wind turbines, and gearboxes.

Tapered Roller Bearings

Tapered roller bearings utilize cone sections as load-carrying elements, fitting between two races forming sections of a hollow cone. Extending the races and roller axes would converge at a common point. These bearings handle higher axial and radial loads, with the common cone’s half-angle determining the axial load capacity. Functioning as both thrust and radial load bearings, they are often used in back-to-back pairs for balanced axial support in either direction.

Needle Roller Bearings

A needle roller bearing is a distinctive roller bearing type featuring cylindrical rollers resembling needles due to their small diameter. Unlike typical roller bearings, the length of these rollers exceeds their diameter by at least four times. This design allows for a higher number of rollers in the same space, increasing the contact surface with the races and enabling them to handle high loads.

Their compact size is advantageous in applications with limited space, requiring smaller clearances between the axle and housing. Needle bearings find application in automobile components like transmissions and rocker arm pivots, as well as in compressors and pumps.

Ball Bearings

Ball bearings represent a prevalent bearing class, featuring a row of balls as rolling elements confined between two annulus-shaped metal pieces known as races. The inner race rotates freely, while the outer race remains stationary. Despite providing minimal friction during rolling, ball bearings have a limited load-carrying capacity due to the small contact area between the balls and races.

They support axial loads in two directions and radial loads. Ball bearings find application in controlling oscillatory and rotational motion, such as in electrical motors connecting a free-rotating shaft to a stationary motor housing. Various types of ball bearings are available based on specific application requirements.

Types of Ball Bearings

In our list of different types of bearings, Let us explore the Different types of ball bearings

• Deep Grove Ball Bearings
• Angular Contact Ball Bearings
• Self-Aligning Ball Bearings
• Thrust Ball Bearings

Deep Grove Ball Bearings

Deep Groove Ball Bearings, the widely preferred type, comprise a ball ring nestled between races, allowing load transmission and rotation. A retainer secures the balls. Renowned for minimal rolling friction, they excel at low noise and vibration, making them ideal for high-speed use. Installation is straightforward, with low maintenance needs. Precise care prevents race denting during push-fit onto shafts.

Angular Contact Ball Bearings

This ball bearing type displaces the inner and outer races along the bearing axis. Angular contact roller bearings can handle substantial axial loads in both directions and radial loads. The design allows the transfer of axial loads through the bearing to the housing, making it suitable for applications requiring rigid axial guidance. Angular contact bearings find widespread use in agricultural equipment, automobiles, gearboxes, pumps, and high-speed applications like CNC machining tool spindles.

Self-Aligning Ball Bearings

Self-aligning ball bearings are resilient to misalignment caused by shaft deflection or mounting errors. The inner ring, resembling deep groove ball bearings, houses two rows of balls along with the outer ring. The outer ring’s concave shape allows the inner ring flexibility to adjust based on misalignment.

Thrust ball bearings

Thrust ball bearings, crafted for axial loads, excel in low noise, smooth operation, and high-speed applications. They eliminate radial load support entirely. The bearings come in single-direction or double-direction variants, chosen based on the nature of the load—unidirectional or bidirectional.

Other Types of Bearings

Apart from the two main types of roller bearings and ball bearings, The other types of bearings are as follows:

Plain Bearings

A plain bearing, the simplest type, typically comprises only a bearing surface without rolling elements. Referred to as a sleeve bearing, it’s a sleeve mounted on the shaft, fitting into the bore. These bearings, which are inexpensive, compact, and lightweight, boast a high load-carrying capacity.

Suitable for rotational, sliding, reciprocating, or oscillatory motion, plain bearings remain fixed while the journal slides on the inner surface. Material pairs with low coefficients of friction, often copper alloys, are chosen for smooth movement. Accommodating misalignment and multi-directional movements, they suit static and dynamic loads, finding extensive use in agriculture, automotive, marine, and construction industries. An example is the gudgeon pin connecting the piston to the connecting rod in diesel engines.

Fluid Bearings

Fluid bearings utilize pressurized gas or liquid to eliminate friction and support loads. These bearings replace metallic counterparts in applications with short lifespans, high noise, and vibration levels. They are increasingly adopted for cost savings. Applied in high-speed, high-load machines, their higher initial costs are offset by prolonged lifespan in challenging conditions.

During operation, there is zero contact between elements (except during start and stop), allowing near-zero wear with fluid bearings. Classifiable into hydrostatic and hydrodynamic types, fluid bearings find diverse applications, offering advantages in reduced friction, longer life, and minimal wear in operational conditions.

Hydrostatic Bearings

In hydrostatic bearings, an externally pressurized fluid is compelled between two elements in relative motion. The pressurized fluid establishes a wedge between the moving parts, preventing direct contact and wear. Despite the potential thinness of the fluid layer, its continuous circulation, facilitated by a pump, ensures no wear as long as direct contact is avoided.

To maintain pressure at all shaft speeds and loads, the exit orifice diameter, responsible for fluid circulation, is adjustable. This feature allows for precise control of the gap between the moving parts in hydrostatic bearings.

Hydrodynamic Bearings

Hydrodynamic bearings use the motion of the journal to propel fluid between the shaft and housing. The journal’s movement draws lubricating fluid between the moving parts, establishing a continuous wedge. However, during start-stop and at low loads and speeds, the wedge formation may be insufficient to prevent wear. The system functions optimally only at designed speeds.

Magnetic Bearings

Magnetic bearings employ magnetic levitation to suspend the shaft mid-air, resulting in zero-wear bearings due to the absence of physical contact. These bearings have no limitations on the maximum relative speed they can handle.

Accommodating irregularities in shaft design, magnetic bearings automatically adjust the shaft’s position based on its center of mass, allowing offset configurations without affecting functionality.

There are two main types of magnetic bearings

Active Magnetic Bearings: Utilize electromagnets around the shaft, adjusting the current based on sensor-detected position changes to return the rotor to its original position.

Passive Magnetic Bearings: Employ permanent magnets to maintain a magnetic field without requiring power input, though this design is challenging due to the technology’s early stage.

In some cases, both types may be used together, with permanent magnets handling static loading and electromagnets maintaining precise positioning.

Conclusion

In conclusion, Bearings are essential for machinery, with roller and ball bearings leading the types. Roller bearings (cylindrical, spherical, tapered, needle) excel in load capacity and versatility. Ball bearings (deep groove, angular) minimize friction for efficient motion. Each type has unique pros and cons, addressing specific needs.

Other types, like plain, fluid, hydrostatic, hydrodynamic, and magnetic bearings, offer alternatives for diverse conditions. Consideration of these types of bearings ensures optimal performance and longevity in mechanical systems.