The humble bearing plays a vital role in almost every mechanical movement, keeping things on the move smoothly and efficiently, reducing friction between moving parts.
We know the Ancient Egyptians employed a form of a cylindrical roller bearing or bearings to move the massive stones used to build the pyramids. Today, you’ll find types of bearings in their many different shapes and sizes in use for both industrial and domestic applications.
What is a bearing and what’s their purpose?
Bearings are incorporated into mechanical design to make movement easier and smoother, and to reduce friction. They do this by transferring motion and force to support a load. Bearings may be contact or non-contact. Contact bearings make actual contact by sliding or rolling movements. Non-contact bearings may involve liquid, air and magnetic forces. Rolling element bearings are found in every corner of industry.
Main classification of bearings
Both ball bearings and roller bearings are mechanical devices used to reduce friction and defray radial forces and axial forces. They differ largely in terms of shape.
A ball bearing is usually made up of small spheres, reducing the point of contact made with a load. Roller bearings are primarily cylindrical in shape, which keeps their point of contact with the load in a linear way, giving them greater capacity.
A typical ball bearing contains spherical balls held within a ‘race’ or outer ring. These spheres move together with reduced points of contact resulting in reduced friction when compared with flat surfaces sliding against each other. The race is then connected to a rotating shaft or hub component.
Deep groove ball bearings
These are the most common types of ball bearing in use in industry today. They are versatile and suitable for radial load and axial load uses. Typical applications for deep groove ball bearings include:-
- Farm machinery
- Outboard motors
- Domestic appliance
- Automotive industry
- Office machinery
- Garden tools
Angular contact ball bearings
Angular contact bearings are produced to achieve contact with the outer ring and inner race at a variable contact angle, enabling them to handle both radial loads and axial loads.
Angular contact ball bearings are commonly used for high-speed applications such as gearboxes and electric motors in:-
- General industry
- Materials handling
- Agricultural machinery
- Chemical industry
- Wind power generation
Self-aligning ball bearings
Self-aligning ball bearings differ from other configurations because they are able to handle misalignment. Where shaft and/or housing alignment is challenging, this bearing provides a versatile solution. They are usually double-row bearings with the rolling elements able to rotate freely around the bearing axis to compensate for any deformation.
Self-aligning bearings are used across many types of bearings industry, including:-
- The rail industry
- General industry
Thrust ball bearings
Thrust ball bearings are designed to manage axial loads and are capable of rotating alongside parts of machinery, assisting with rotation. They are available in single or double-direction configurations.
Typical applications for thrust ball bearings include:
- Engines and gearboxes
- Power generation
- Heavy duty machinery
Just like ball bearings, cylindrical roller bearings work to carry loads and minimise friction. However, these roller bearings use cylindrical instead of spherical rolling elements, with an increased bearing surface they have a greater capacity for both radial and axial loads.
Spherical roller bearings
Designed for low-friction applications with the potential for angular misalignment, spherical roller bearings offer high load-carrying capacities and are capable of handling heavy radial and moderate axial loads well.
Applications for spherical roller bearings include:-
- Wind turbines
Tapered roller bearings
Tapered roller thrust bearings typically consist of a cup and cone assembly where the cup forms the outer rings and the cone contains an inner ring and rollers. This tapered roller bearing configuration is usually used to achieve reduced friction, increased performance and power density.
Applications for tapered roller bearings include:-
- Machinery shafts
- Fuel pumps for aircraft
- Wheel bearings
Needle roller bearings
In a needle roller bearing, the long and thin cylindrical rollers used are like needles in appearance. A standard roller bearing is usually just a little greater in length than the diameter, but rollers in needle bearings can be more than four times the length of their diameter, meaning a greater surface area is in contact with the race, allowing them to support higher loads.
Needle roller bearings are used in:-
- Drive transmissions
- Automotive components
- Steering gear
- Automatic transmissions
Thrust roller bearings
These compact bearings play an important role by rotating between parts to reduce levels of friction. Designed to handle high axial loads, they are similar to roller bearings but differ because the upper and lower sections need to rotate independently so the bearing races are not the same size.
Applications for thrust roller bearings include:-
- Heavy duty machinery
This is the simplest type of bearing, often also called a slide bearing. Plain bearings consist of a centre-drilled cylinder with no moving parts to handle oscillating movement and misalignment.
Applications for plain bearings include:-
- Machine tool spindles
- Drilling and milling
- Automotive crankshafts and camshafts
- Forklift trucks
Fluid bearings, as the name suggests, use a fine layer of liquid or gas to reduce sliding friction and to provide support for the rotating element. They can be either hydrostatic and hydrodynamic bearings, for static loading or dynamic loading, require minimal maintenance and provide a long service life.
Hydrostatic bearings use positive pressure to retain clearance between rotating and stationary elements, with the lubrication kept under pressure between the moving surfaces. These bearings are capable of supporting heavy loads at low speeds and can be used for linear or rotary motion with heavy radial loads.
- Space telescopes
- Precision measuring instruments
- Aircraft engines
- Machine tools
Hydrodynamic bearings are used for rotary applications, where the gap is generated dynamically by the motion of the bearing They are suitable for radial or thrust loads and use a film of oil or air. A typical example is the journal bearing.
Application environments include:
- Power generation plants
- Petrochemical plants
- Oil refineries
- Steam turbines
- Process equipment
Magnetic bearings are designed to support loads and moving parts without any physical contact by using magnetic levitation. They are capable of supporting extremely high rotating speeds with low friction and reduced mechanical wear.
These bearings are used in:-
- Electrical power generation
- Natural gas plants
- Machine tool handling
- Turbomolecular pumps to eliminate contamination
Active magnetic bearings
The most popular type is the active magnetic bearing, which offers all the advantages of low wear characteristics and reduced friction. They are both reliable and predictive, as well as having the capability to handle any irregularities in the distribution of mass.
Active magnetic bearings are commonly used in pumps and compressors.
Passive magnetic bearings
What factors dictate the choice of bearing for an application?
There are many different types of bearings operating at the heart of machinery and equipment. Making the right choice of types of bearings is dependent on a number of factors.
Load is an important consideration – axial load, radial load or axial and radial combined loads? Thrust loads? Heavy loads? High radial loads? Exceptionally low friction? Is the rotating speed high or low? Do you require high rotational accuracy? Is bearing rigidity important?
What is the environment like? A sleeve bearing can provide the best solution for areas subject to contamination.
Other things to consider when choosing a suitable bearing include material and construction, lubrication and sealing and required bearing life. Every application is different and will require careful specification to ensure the right fit.
From plain bearings to linear ball bearings and roller bearings, and even tapered roller bearings, thrust bearings and sleeve bearings, these mechanisms are found everywhere in modern life, from domestic appliances to electronic equipment.
Rolling element bearings may seem like a small consideration in machinery design and specification, but it’s a vital one. If your bearing fails, so does your process. Never underestimate the humble bearing – it’s working at the heart of your equipment.
Contact BE Power Transmission today for all your industrial bearing requirements.