The bearings and its rings and rolling elements are primarily made of high carbon chrome steel. Most of the bearings are made of SUJ2, which is equivalent to AISI52100 in the U.S.A. and DIN 100Cr6 in Germany.

For some request, we will use stainless steel or brass with fine anti-corrosive performance.

Mostly, the pressed cages of bearings are made of carbon steel. It also can be request to be made of stainless steel and brass.

Deep groove ball bearings are the most common type of rolling bearings and very widely used. A deep groove is formed on each inner and outer ring of the bearing enabling them to sustain radial and axial loads in either direction as well as the complex loads which result from the combination for high speed applications.

Table 1 Sealed Ball Bearings: Construction and Characteristics

Pressed cages are usually used in deep groove ball bearings and high-speed bearings. As shown on Table 2

Table 2 Standard cage for deep groove ball bearings

Rolling bearings is commonly composed of ring, roller, and cage. It is divided into ball bearings and roller bearing according to the rolling category. The characteristics are as below:

1. It is equipped with high standard and ample specifications with fine interchangeability.

2. Commonly it can simultaneously bear radial load and axial load.

3. it is applicable for use in high and low temperature.

4. it is fit for use in high speed conditions.

Single-row deep groove ball bearing is the structure with the widest application in rolling bearings. The bearings can simultaneously bear radial and zxial load. It is fit for use in the occasions such as high-speed rotation, low noise, and etc.

Bearing Internal Clearance

Bearing internal clearance is the amount of internal free movement before mounting.

As shown in Fig.1, when either the inner ring or the outer ring is fixed and the other ring is free to move, displacement can take place in either an axial or radial direction. This amount clearance and, depending on the direction, is called the radial internal clearance or the axial internal clearance.

Fig. 1 Internal Clearance

Internal Clearance Selection

The internal clearance of a bearing under operating conditions (effective clearance) is usually smaller than the same bearing's initial clearance before being installed and operated. This is due to several factors including bearing fit, the difference in temperature between the inner and outer rings, etc. As a bearing's operating clearance has an effect on bearing life, heat generation, vibration, noise, etc; care must be taken in selecting the most suitable operating clearance.

Table 1 Examples of applications where bearing clearances other than CN (nomal) clearance are used (Unit: µm)

Table 2 Radial Internal Clearance of Deep Groove Ball Bearings

Table 3 Classification of Extra Small and Miniature Ball Bearings

Table 4 Radial Internal Clearance in Extra Small and Miniature Ball Bearings

Remark: 1) The standard clearance is MC3

             2) To obtain the measured value, add correction amount in the table below.

Table 5 Radial Internal Clearance of Bearings for Electric Motor

Note 1. Suffix CM is added to bearing numbers.

             Example: 6205ZZCM

       2. Clearance not interchangeable for cylindrical roller bearings. 

Structure and Classification

Roller bearing is commonly composed of ring, roller, cage. It is devided into ball bearing and roller bearing according to the rolling category. Apart from open type, it also has the bearing with steel shield, e.g. 608ZZ, and bearing with rubber seal ring, e.g. 608-2RS. Below diagram shows structure of roller bearing.

Features

The rolling bearing has features as below:

1) It is equipped with high standard and ample specifications with fine interchangeability.

2) Commonly it can simultaneouslybear radial load and axial load.

3) it is applicable for use in high and low temperature.

4) It is fit for use in high speed conditions.

Single-row deep groove ball bearing is the structure with the widest applciation in rolling bearings.

1. Tolerance Standards

    The tolerances for the external dimensions and running accuracy of rolling bearings are specified by ISO 492/199/582. The applicable accuracy classes for each bearing type and the correspondence of these classes are listed in below table.

Tolerances for dimensions that are critical to mount bearings on shaft or in housing are:

1) Tolerances for bore and outside diameters, ring width and bearing width.

2) Tolerances for inscribed and circumscribed circle diameters of rollers.

3) Tolerances for chamfer dimensions.

4) Tolerances for width variation.

5) Tolerances for tapered bore diameter.

The running accuracy of rolling bearings should be specified with below items:

1) Permissible radial runout of inner and outer rings.

2) Permissible face runout with raceway and outer rings.

3) Permissible inner face runout with bore.

4) Permissible outer ring variation of outside surface generatrix inclination with face.

Tolerance Classes

JIS: Japanese Industrial Standards

DIN: Deutsch Industrie Norm

AFBMA: Anti-Friction Bearing Manufacturers Association

2. Symbols for External Dimensions and Running Accuracy Symbols Description

    d  Bearing bore diameter, nominal

    ds  Deviation of a single bore diameter

    dmp  Single plane mean bore diameter deviation

    Vdp  Bore diameter variation in a single radial plane

    Vdmp  Mean bore diameter variation

    B  Inner ring width, nominal

    Bs  Deviation of a single inner ring width

    VBs  Inner ring width variation

    Kia Radial Runout of assembled bearings inner ring

    Sd  Inner ring reference face (backface, where applicable) runout with bore

    Sia  Assembled bearing inner ring face (backface) runout with raceway

    Ts  Deviation of the actual bearing width

    D  Bearing outside diameter, nominal

    Ds  Deviation of a single outside diameter

    Dmp  Single plane mean outside diameter deviation

    VDp  Outside diameter variation in a single radial plane

    VDmp  Mean outside diameter variation

    C  Outer ring width, nominal

    Cs  Deviation of a single outer ring width

    Vcs  Outer ring width variation

    Kea  Radial runout of assembled bearing outer ring

    SD  Variation of bearing outside surface generatrix inclination with outer ring reference face

           (backface) 

    Sea  Assembled bearing outer ring face (backface) runout with raceway

Tolerances of Radial Ball Bearings