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METRIC Miniature Ball Bearings (Seals, Shielded or Open)
STAINLESS/CHROME/CERAMIC
ANGULAR
CONTACT/RADIAL

METRIC Flanged Bearings (Seals, Shielded , Open)
STAINLESS/CHROME/CERAMIC
ANGULAR
CONTACT/RADIAL

INCH Miniature Ball Bearings
(Flanged & Extended Inner)
STAINLESS/CHROME/CERAMIC
ANGULAR
CONTACT/RADIAL

METRIC Angular Contact Bearings
(Series 7000 to 7300)
STAINLESS, CERAMIC or CHROME

METRIC Deep Groove Radial Ball Bearings (Series 6000, 6200, 6300, 6700, 6800, 6900 and 16000) STAINLESS, CERAMIC or CHROME

METRIC Radial Ball Bearings MAX
(Series M6200, M6300)
Loading slot for MAX # Balls

Deep Groove Ball Bearings
INCH

STAINLESS, CERAMIC or CHROME

INCH Semi-Precision Bearings
(Series 3000)
STAINLESS, CERAMIC or CHROME

Thin Section Ball Bearings
(X, C and A Types)
STAINLESS, CERAMIC or CHROME
Spherical Roller Thrust Bearings
STAINLESS, CERAMIC or CHROME
Self-Aligning Ball Bearings
STAINLESS, CERAMIC or CHROME
Cylindrical Roller Bearings (NEW)
STAINLESS, CERAMIC or CHROME
Spherical Roller Bearings
STAINLESS, CERAMIC or CHROME
Tapered Roller Bearings - METRIC
STAINLESS, CERAMIC or CHROME
Needle Bearings
STAINLESS, CERAMIC or CHROME
Deep Groove Ball Bearings
METRIC

STAINLESS, CERAMIC or CHROME
THRUST Bearings (Ball/Roller)
STAINLESS, CERAMIC or CHROME

Rounded O.D. Bearings
(used for Track Rollers)

Agricultural Bearings

Mounted Units (Pillow Blocks)
2 Bolt, 3 Bolt, and 4 Bolt Units

Drawn Cup Needle Roller Bearings
Rod Ends
Aircraft Bearings
bearings_icon Engineering Data
bearings_icon Glossary of Bearings

Engineering Data

1. Classification and Characteristics of Rolling Bearings

1.1 Rolling bearing construction
Most rolling bearings consist of rings with raceways (an inner ring and an outer ring), rolling elements (either balls or rollers) and a rolling element retainer. The retainer separates the rolling elements at regular intervals, holds them in place within the inner and outer raceways, and allows them to rotate freely. See figures 1.1-1.8.

Rolling elements come in two general shapes: ball or rollers. Rollers come in four basic styles: cylindrical, needle, tapered, and spherical. Balls geometrically contact the raceway surfaces of the inner and outer rings at “points”, while the contact surface of rollers is a “line” contact. Theoretically, rolling bearings are so constructed as to allow the rollling elements to rotate orbitally while also rotating on their own axes at the same time. While the rolling elements and the bearing rings take any load applied to the bearings (at the contact point between the rolling elements and raceway surfaces), the retainer takes no direct load. The retainer only serves to hold the rollling elements at equal distances from each other and prevent them from falling out.

1.2 Classification of rolling bearings
Rolling element bearings fall into two main classifications: ball bearings and roller bearings. Ball bearings are classified according to their bearing ring configurations: deep groove, angular contact and thrust types. Roller bearings on the other hand are classified according to the shape of the rollers: cylindrical, needle, taper and spherical. Rolling element bearings can be further classified according to the direction in which the load is applied; radial bearings carry radial loads and thrust bearings carry axial loads. Other classification methods include: 1) number of rolling rows (single, multiple, or 4-row), 2) separable and nonseparable, in which either the inner ring or the outer ring can be detached, 3) thrust bearings which can carry axial loads in only one direction, and double direction thrust bearings which can carry loads in both directions. There are also bearings designed for special applications, such as: railway car journal roller bearings (RCT bearings), ball screw support bearings, turntable bearings, as well as rectilinear motion bearings (linear ball bearings, linear roller bearings and linear flat roller bearings).

1.3 Characteristics of rolling bearings
1.3.1. Characteristics of rolling bearings
Rolling bearings come in many shapes and varieties, each with its own distinctive features.

However, when compared with sliding bearings, rolling bearings all have the followings advantages:

  1. The starting friction coefficient is lower and only a little difference between this and the dynamic friction coefficient is produced.
  2. They are internationally standardized, interchangeable and readily obtainable.
  3. Ease of lubrication and low lubricant consumption.
  4. As a general rule, one bearing can carry both radial and axial loads at the same time.
  5. May be used in either high or low temperature applications.
  6. Bearing rigidity can be improved by preloading. Construction, classes, and special features of rolling bearings are fully described in the boundary dimensions and bearing numbering system section.

1.3.2. Ball bearings and roller bearings
Generally speaking, when comparing ball and roller bearings of the same dimensions, ball bearings exhibit a lower frictional resistance and lower face run-out in rotation than roller bearings. This makes them more suitable for use in applications which require high speed, high precision, low torque and low vibration. Conversely, roller bearings have a larger load carrying capacity which makes them more suitable for applications requiring long life and endurance for heavy loads and shock loads.

1.3.3. Radial and thrust bearings
Almost all types of rollling bearings can carry both radial and axial loads at the same time. Generally, bearings with a contact angle of less than 45° have a much greater radial load capacity and are classed as radial bearings; whereas bearings which have a contact angle over 45° have a greater axial load capacity and are classed as thrust bearings. There are also bearings classed as complex bearings which combine the loading characteristics of both radial and thrust bearings.
1.3.4. Standard bearings and special bearings
Bearings which are internationally standardized for shape and size are much more economical to use, as they are interchangeable and available on a worldwide basis. However, depending on the type of machine they are to be used in, and the expected application and function, a nonstandard or specially designed bearing may be best to use. Bearings that are adapted to specific applications, and “unit bearings” which are integrated (built-in) into a machine’s components, and other specially designed bearings are also available.

2. Bearing Selection
2.1 Operating conditions and environment
When selecting a bearing, having an accurate and comprehensive knowledge of which part of the machine or equipment it is to be installed in and the operating requirements and environment in which it will function, is the basis for selecting just the right bearing for the job. In the selection process, the following data is needed.

(1) The equipment’s function and construction.
(2) Bearing mounting location (point).
(3) Bearing load (direction and magnitude).
(4) Bearing speed.
(5) Vibration and shock load.
(6) Bearing temperature (ambient and friction generated).
(7) Environment (corrosion, lubrication, cleanliness of the environment, etc.).

2.2 Demand factors
The required performance capacity and function demands are defined in accordance with the bearing application conditions and operating conditions. A list of general demand factors to be considered is shown in Table 2.1. Rolling bearings come in a wide variety of types, shapes and dimensions. The most important factor to consider in bearing selection is a bearing that will enable the machine or part in which it is installed to satisfactorily perform as expected. To facilitate the selection process and to be able to select the most suitable bearing for the job, it is necessary to analyze the prerequisites and examine them from various standpoints. While there are no hard-and-fast rules in selecting a bearing, the following list of evaluation steps is offered as a general guideline in selecting the most appropriate bearing.

(1) Thoroughly understand the type of machine the bearing is to be used in and the operating conditions under which it will function.
(2) Clearly define all demand factors.
(3) Select bearing shape.
(4) Select bearing arrangement.
(5) Select bearing dimensions.
(6) Select bearing specifications.
(7) Select mounting method, etc.


Radial & Axial Play, Raceway Curvature & Contact Angle

Radial and Axial Play | Raceway Curvature | Contact Angle | Key Formulas

When a ball bearing is running under a load, force is transmitted from one bearing ring to the other through the balls. Since the contact area between each ball and the rings is relatively small, moderate loads can produce stresses of tens, even hundreds of thousands of pounds per square inch. These internal stresses have a significant impact on bearing life and performance. Thus the internal geometry of a bearing—its radial play, raceway curvature and contact angle—must be carefully chosen so loads can be distributed for optimal performance.

Radial and Axial Play

Most ball bearings are assembled in such a way that a slight amount of looseness exists between the balls and the raceways. This looseness is referred to as radial play and axial play. Radial play is the maximum distance that one bearing ring can be displaced with respect to the other, in a direction perpendicular to the bearing axis when the bearing is in an unmounted state. Axial play, or end play, is the maximum relative displacement, in a direction parallel to the bearing axis, between the two rings of an unmounted ball bearing.

Since radial play and axial play are both consequences of the same degree of looseness between the components, they bear a mutual dependence. Yet their values are usually quite different in magnitude. Radial play can often vary between .0002 and .0020, while axial play may range from .001 to .010. The suggested radial play ranges for typical applications should always be consulted when a device is in the initial design phase.

Suggested Radial Play

Typical Application
Suggested
Radial Play
(inches)
Small Precision High Speed Electric Motors
.0005 to .0008
Tape Guides, Belt Guides, Low Speed
.0002 to .0005
Tape Guides, Belt Guides, High Speed
.0005 to .0008
Gyro Gimbals, Horizontal Axis
.0002 to .0005
Gyro Gimbals, Vertical Axis
.0005 to .0008
Precision Gear Trains, Low Speed Electric Motors, Synchros and Servos
.0002 to .0005
Gyro Spin Bearings, Ultra-High Speed Turbines and Spindles
Consult factory

In most ball bearing applications, radial play is functionally more critical than axial play. While radial play has become the standard purchasing specification, you may also specify axial play requirements. Keep in mind, however, the values of radial play and axial play for any given bearing design are mathematically interdependent, and that radial play is affected by any interference fit between the shaft and bearing I.D. or between the housing and bearing O.D., as shown in the Table of Recommended Fits. Since the important condition is the actual radial play remaining after assembly of the complete device, the radial play specification for the bearing must be modified in accordance with the discussion in the mounting and coding section.

Standard Radial Play Ranges

Description
Radial Play Range*
NHBB Code

Tight

Normal

Loose

Extra Loose

.0001 to .0003

.0002 to .0005

.0005 to .0008

.0008 to .0011

P13

P25

P58

P811

*Measurement in inches.
Non-standard ranges may be specified.



Raceway Curvature

Raceway curvature is the ratio of the raceway radius to ball diameter. Raceway curvature values typically are either 52 to 54 percent or 57 percent. The lower 52 to 54 percent curvature implies close ball-to-raceway conformity and is useful in applications where heavy loads are encountered. The higher 57 percent curvature is more suitable for torque sensitive applications.

 


Contact Angle

Contact angle is the angle between a plane perpendicular to the ball bearing axis and a line joining the two points where the ball makes contact with the inner and outer raceways. The initial contact angle of the bearing is directly related to radial play—the higher the radial play, the higher the contact angle. The Table of Contact Angles as shown gives nominal values under no load.

For support of pure radial loads, a low contact angle is desirable; where thrust loading is predominant, a higher contact angle is recommended.

The contact angle of thrust-loaded bearings provides an indication of ball position inside the raceways. When a thrust load is applied to a ball bearing, the balls will move away from the median planes of the raceways and assume positions somewhere between the deepest portions of the raceways and their edges.

Table of Contact Angles

Ball Size
Db
Radial Play Code
P25 P58 P811

.025

1/32 & 0.8mm

1mm

3/64

1/16

18°

16 1/2°

14 1/2°

14°

12°

24 1/2°

22°

20°

18°

16°

30°

27°

24°

21°

19°

3/32

1/8

9/64

5/32

3/16

9 1/2°

12 1/2°

12°

11°

10°

13°

17°

16°

15°

14°

15 1/2°

20°

19 1/2°

18 1/2°

16 1/2°

The contact angle is given for the mean radial play of the range shown i.e., for P25 (.0002 to .0005)—contact angle is given for .00035. Contact angle is affected by raceway curvature. For your specific application consult with factory.


Key Formulas


Ball bearings are preloaded for a variety of reasons:
  • To eliminate radial and axial looseness
  • To reduce operating noise
  • To improve positioning accuracy
  • To reduce repetitive runout
  • To reduce the possibility of damage from vibratory loading
  • To increase life and axial capacity
  • To increase stiffness

There are essentially two ways to preload a ball bearing, either by using a spring or through a solid stack of parts.

Spring preloading can consist of a coil spring or a wavy washer, which applies a force against the inner or outer ring of the non-interference fitted bearing in the assembly.

Since in a spring the load is fairly consistent over a wide range of compressed length, the use of a spring for preloading eliminates the need for holding tight location tolerances on machined parts. For example, retaining rings can be used in the spindle assembly, thus saving the cost of a locating shoulder, shims or threaded members. Normally a spring would not be used where the assembly must withstand reversing thrust loads.

A solid stack method may be used when precise location control is required. For example, in a precision motor, the use of built-in preload is suggested. Ball bearings with built-in preload are often referred to as duplex ball bearings. When the set of bearings is assembled, the thrust load needed to make the adjacent faces of the rings contact becomes the desired preload. Built-in preload helps satisfy the requirements of increased axial and radial stiffness and deflection control.

There are three methods of mounting preloaded duplex bearings: back-to-back, face-to-face and tandem.

Back-to-Back (DB)

When a back-to-back (DB) duplex pair is mounted, the outer rings abut and the inner rings are drawn together, providing maximum stiffness.

Face-to-Face (DF)

When face-to-face (DF) duplex pairs are mounted, the inner rings abut and the outer rings are drawn together, providing a higher radial and axial stiffness and accommodation of misalignment.

Tandem (DT)

With tandem (DT) pairs, both inner and outer rings abut and are capable of sharing a thrust load, providing increased thrust capacity.


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