0—Bearing Basics (Uses, Types, and Components)

Let's first take a look at how bearings are used and the many types of bearings available. We'll also identify the main components found in rolling bearings and explore how they differ from plain bearings.

What Are Bearings and How Are They Used?

  1. Bearing benefits
    Bearings increase the efficiency of movement in machines by reducing friction.
    With less friction, equipment lasts longer.
    In this way, bearings are crucial machine components that keep equipment moving.
  2. Bearing types
    Plain bearings (or sliding bearings) use a liquid, solid, or gas to create sliding friction between the shaft and bearing whereas rolling bearings (or rolling-element bearings) move with efficient rolling friction through the use of balls or rollers. ​
Animation of plain bearing. A liquid, solid, or gas fills the space between the rotating shaft and stationary bearing.

Plain (sliding) bearing

Animation of rolling bearing in operation. One ring and the rolling elements (ball or element) move along with the rotation of the shaft while the other ring is stationary.

Rolling bearing

Types of Sliding Bearings

 

・Liquid-lubricated bearings: White metal, copper, lead alloys, etc.

・Oil-lubricated bearings (rolling bearings also utilize these lubrication methods):

  1. Forced lubrication: A pump forces pressurized oil into bearings
  2. Oil bath: A portion of the bearing is submerged in lubricating oil
  3. Splash lubrication: Gears or other rotating equipment splash droplets of lubricating oil onto the bearing
  4. Drip-feed lubrication: A lubricant container with a hole supplies a relatively constant amount of oil over time

・Water-lubricated bearings: Using water promises to be more environmentally friendly than oil.

・Gas bearings: High rotational accuracy and low friction bearings for applications unsupported by rolling bearings.
・Magnetic bearings: Magnetic forces support the shaft.
・Hydrostatic bearings: The shaft floats on a cushion of pressurized gas provided by a pump, etc. (used in ultra-precision machining tools/measuring instruments, etc.)
・Hydrodynamic bearings: The shaft is supported by an oil film created by the rotation of the lubricated shaft (typically grooved, used in video/information equipment, etc.)

Advantages of Rolling Bearings (vs. Plain Bearings)

Rolling bearings have six advantages over plain bearings:

1. In general, rolling bearings offer lower friction with high rigidity.

2. Dimensions, accuracy, markings, and so on are standardized internationally (ISO, ANSI/ABMA, JIS, etc.), making rolling bearings readily available and interchangeable.

3. Rolling bearings are easy to maintain, replace, and inspect.

4. Depending on the type, rolling bearings can take radial, axial (thrust), moment, or combined loads.

5. Rolling bearings can be used over a wide temperature range.

6. Certain types of rolling bearings, such as angular contact ball bearings and tapered roller bearings, can be preloaded for high rigidity.

Direction of forces imposed on a bearing and shaft under radial load.

Radial load

Direction of forces imposed on a bearing and shaft under axial (thrust) load.

Axial load
（Thrust load）

Forces acting on a bearing and shaft under combined loads (a mix of radial and axial load).

Combined load

(Both radial and axial load）

Forces acting on shaft and bearing under moment loads.

Moment load

Structure and Main Components

Rolling bearings (hereinafter, “bearings”) generally consist of raceway rings, rolling elements, and cages. A typical bearing appears as shown here:

Diagram listing the design and components of a typical ball bearing.

Structure and Main Components

Cross-sectional view of a typical single-row angular contact ball bearing showing important parts and dimensions.

Single-Row Angular Contact Ball Bearing

Cross-sectional view of a typical single-row deep groove ball bearing showing important parts and dimensions.

Single-Row Deep Groove Bearing

Cross-sectional view of a typical tapered roller bearing showing important parts and dimensions.

Tapered Roller Bearing

Cage Role and Types

Role of the cage

Many bearings feature cages. A cage maintains proper spacing between rolling elements and helps the rolling elements move smoothly, supporting bearing rotation.

  • Cages prevent the rolling elements (balls or rollers) from slipping or separating from the outer or inner ring.
  • Cages keep the rolling elements evenly spaced.
  • This prevents contact between rolling elements, suppressing additional friction and helping maintain smooth rotation.

Without a cage:

Animation of rolling elements rotating in a bearing without a cage. The elements are not spread evenly, so they crowd together and occasionally collide.

With a cage:

Animation of rolling elements in a bearing with a cage. The cage keeps the rollers evenly spaced so they move at a consistent speed and do not collide.

Cage Types

There are three broad categories of cages based on their materials.
Cages are typically determined by usage conditions, but options may be limited for some bearing types and sizes.

　High SpeedsRigidityHigh TemperaturesLow NoiseLubricant CompatibilityCost
Pressed-steel cage
(Pressed cage)		  〇 〇〇
Machined-brass cage〇〇〇 〇 
Synthetic-resin cage
(Injection-molded, Plastic)		〇 Varies by material〇Varies by material〇