Introduction to Bearings

Structure & Function

NSK has made a vital contribution to the growth and advancement of the various industries that rely on machinery. As a comprehensive bearing manufacturer, NSK responds to needs in a wide variety of fields.

A surprisingly large number of bearings can be found all around us. Take automobiles, for example: there are 100 to 150 bearings in a typical car. Without bearings, the wheels would rattle, the transmission gear teeth wouldn't be able to mesh, and the car wouldn't run smoothly.

Bearings are not used only in cars, but in all kinds of machinery such as:

• trains
• airplanes
• washing machines
• refrigerators
• air conditioners
• vacuum cleaners
• photocopy machines
• computers
• satellites

Bearings enhance the functionality of machinery and help to save energy. Bearings do their work silently, in tough environments, hidden in machinery where we can't see them. Nevertheless, bearings are crucial for the stable operation of machinery and for ensuring its top performance.

The word “bearing” incorporates the meaning of “to bear,” in the sense of "to support," and "to carry a burden." This refers to the fact that bearings support and carry the burden of revolving axles.

The two pictures below show the most basic bearings, known as rolling bearings.

Rolling bearing

(Ball bearing)

Rolling bearing

(Roller bearing)

Rolling bearings are made up of four elements and have an extremely simple basic structure.

Outer ring:

The large ring of the outer race

Inner ring:

The small ring of the inner race

Rolling elements:

Several balls or rollers that are contained in the space between the outer race and inner race

Cage:

Used to fix the position of the rolling elements

History

The principle of bearings was known to the ancients, and they were used around B.C. 8 ^th century in ancient Mesopotamia.The illustration is a replica of a relief depicting construction in ancient Mesopotamia.

Later, that famous genius of the Renaissance, Leonardo da Vinci, came up with an idea for a structure that is remarkably similar to modern uses of bearings. The machine-based civilization that was born in the Industrial Revolution of the 18th century led to the development of modern bearings.

In 1916 NSK started up the first specialist production of bearings in Japan. However, it was not until after the end of the Second World War that Japan's bearings technology made substantial progress. 1955 marked the beginning of growth in demand for private automobiles, in addition to home appliances such as washing machines, refrigerators and air conditioners. In this environment, one of the key characteristics that the Japanese demanded of these home appliances was quietness. However, bearings manufacturers outside Japan didn't place much emphasis on the requirement for quietness; so Japanese manufacturers proceeded to build up know-how through research and development efforts based on the objective of developing the world's quietest bearings. Later, Japanese bearings renowned for their quietness were exported to the United States and Europe. Before long they also offered a high degree of durability.

Bearing specifications have been standardized in accordance with international ISO standards. Japanese-made bearings are admired around the world for their high performance and high quality. There are said to be around 3 billion bearings made annually in Japan, of which over 40% are for automobile use. Nearly 30% are exported.

Bearings have been developed and improved in a global environment, and results from research into further reducing friction are accumulating all the time, continually anticipating the needs of the times. The ongoing challenge remains. To:

• reduce weight
• increase compactness
• lengthen life
• reduce energy requirements
• reduce the impact on the environment

Types

Anything that can be called a machine will invariably incorporate bearings. Bearings must fulfill a great variety of needs, and they constantly evolve in response to this.

Deep groove ball bearing:

(1) This is the most widely used bearing in the world.

Angular contact thrust ball bearing:

(2) In this type, the rolling element meets the inner and outer ring raceways at a contact angle. This bearing can carry radial and axial loads.。

Thrust ball bearing:

(3) Thrust ball bearings are capable of handling loads in the axial direction (axial loads). They can support heavy loads.

Cylindrical roller bearing:

(4) The rolling elements are the cylindrical roller type.

Cylindrical roller bearing:

(5) Here too the rolling elements are the cylindrical roller type. However in this instance the shape of the cage differs from that in (4).

Tapered roller bearing:

(6) The rolling elements are of the tapered roller type. Because the rollers are tapered, this bearing is able to carry combined axial and radial loads.

Self-aligning roller bearing:

(7) This bearing has an automatic aligning function to compensate for minute misalignments between the inner and outer rings during operation.

Thrust needle bearing:

(8) This bearing is used in parts such as compressors that deliver the air in automobile air conditioning units.

Cage and roller:

(9) This is one of several kinds of bearing used in vehicles' manual transmissions. It is required to be highly durable.

Amazing World of Bearings

Size varies from 2 millimeters to 6 meters

Bearings come in all sizes: The world's smallest, "miniature bearings," have an inner diameter of 0.6 mm, an outer diameter of 2.0 mm and a width of 0.8 mm. They are used in ultra-compact motors. At the other extreme, there are bearings with an outer diameter of 6 meters that weigh over 15 tons. These are used in giant boring machines that dig tunnels, such as the Euro tunnel linking France and Britain under the Straits of Dover.

400,000 Revolutions in One Minute

Bearings that can revolve at ultra-high speeds are used in dental drills. These drills incorporate two ultra-high precision bearings with an inner diameter of 3.0 mm, an outer diameter of 6.0 mm and a width of 2.0 mm, and incorporating ball bearings with a diameter of 1.0 mm. The bearings revolve at the astounding speed of 400,000 revolutions per minute. This ultra-high speed, together with extremely accurate revolution, almost eliminates vibration in the dental drill, helping to provide safe, comfortable dental treatment.

Ball Revolves at a Speed of 160 Meters per Second

These bearings are used in the main shaft of a V2500 jet engine in an international passenger airplane. The rolling elements in this bearing revolve at a speed of 160 meters per second. This is equivalent to 580 km/h. Next time you fly you can relax as these high performance, high speed bearings support the fast, powerful and lengthy operation of jet engines.

Vibration of Less than 100 Nanometers

It is no exaggeration to say that the accuracy of machinery is determined by the accuracy of the revolution of the bearings. A bearing supports each end of the axis of rotation. If there is a large runout from the center of that axis, you could not expect the machine to operate with high performance. The deflection from the central axis of a computer's external memory device (hard disk drive) that uses ultra-high precision bearings is less than 100 nm (1 nm is one billionth of a meter). What determines this ultra-high precision is the accuracy of the rolling elements such as balls and rollers.

15 Years in Space

Bearings are also essential to space development. Such information as weather reports, satellite broadcast data and car navigation positioning data come to us from satellites orbiting the earth. These satellites have a piece of equipment known as a flywheel that maintains them in the correct position and orientation. This flywheel uses ultra-high precision bearings. Such bearings have been patiently revolving in space for the past 15 years!

From Minus 253 Degrees to Plus 500 Degrees

The bearings that are used in the coldest temperatures are those that are incorporated in the liquid fuel pumps of space rockets, and they rotate in liquid hydrogen at -253 degrees C. At the other extreme, bearings that operate in a very high temperature environment include the high performance bearings used in CT scanners in the medical service field. Even in a vacuum tube where X-rays are generated and temperatures reach 300 to 500 degrees C, the bearings continue to revolve, helping us to maintain our health.

Future of Bearings

Lastly, let us introduce some themes on the further evolution of bearings.

1.Greater energy savings. The smaller a machine becomes, the smaller its components. Further, the smaller a machine becomes, the greater the need for precision becomes, and this could mean that even a small amount of friction could lead to a breakdown. Moreover, no matter how small machines become, total energy consumption will be large when viewed on a global scale. In order to produce even greater energy savings, we should continue to seek out even better ways of reducing friction using bearings.

2.“Cleaner” credentials. Improving bearing technology can have beneficial effects on the environment: a reduction in vehicle exhaust gas emissions, for example. Additionally, the vast majority of bearings are made from steel that doesn't contain any harmful chemical substances. This steel can be recycled into new steel materials. Bearings offer excellent potential as products for recycling and reuse.

3.Comfort. Machines must be agreeable for both people and the environment. In the past, machines have supported improved production; in the future, there will be demands that machines help society and individuals enjoy more fulfilling lives, through education, medical services, welfare and entertainment. Also, the bearings that are used in those machines may be asked to fulfill functions and roles that differ from the old ones...

Based on the above three themes, NSK will continue to work on research and development "for people and the planet".