1. Bearing construction and components

LSKD rolling bearing basically consists of two rings, rolling elements and a cage, which keeps the rolling elements at equal intervals. Seals and shields are applied to prevent the bearing from outside affect such as dust or oil invasion. The main purpose of lubricants in rolling bearing is to reduce friction and wear of each element.

Inner ring

1) Inner ring V-groove type are usually applied for small and medium size LSKD deep groove ball bearings with seals or shieds.

2) Inner ring L-groove type are usually applied for miniature size LSKD deep groove ball bearings with seals or shieds.

3) Inner ring Plain type are usually applied for LSKD open type deep groove ball bearings.

Cage

Cages are mechanically stressed by frictional, strain and inertia forces and they may also be subjected to the chemical action of certain lubricants, lubricant additives or products of their ageing, organic solvents or coolants. Therefore the design and material are of paramount importance for the performance of the cage as well as for the operational reliability of the bearing itself.

Following three types of cage are widely applied in LSKD deep groove ball bearings.

1) Rivet-type cage

Made from high precision strip steel, pressed and formed with spherical ball pockets. The retainer halves are fixed together with rivets. LSKD small size deep groove ball bearings widely use steel Rivet-type cages.

2) Tongue-type cage

Made from high precision strip steel, pressed and formed with spherical ball pocket and tongue shape. The  male  and female retainer halves are caulked together for LSKD miniature ball bearings applicatioin.

Internal sealing arrangements

The performance of sealing is vital to the cleanliness of the lubricant and the overall service life of the bearing arrangement. Integral bearing seals must be able to keep contaminants out and lubricant in the bearing cavity. Sealed bearings are generally used for arrangements where a sufficiently effective external seal cannot be provided because there is inadequate space.

When selecting a seal, the following factors need to be taken into consideration: the type of lubricant (oil or grease), seal peripheral speed, shaft fitting errors, space limitations, seal friction, resultant heat increase, as well as the cost.

Shields and seals

2) Rubber seals (2RS)

2. Bearing materials

The materials from which the bearing components are made determine to a large extent the performance and reliability of rolling bearings.

For the bearing rings and rolling elements, typical considerations include hardness for load carrying capacity, fatigue resistance under rolling contact conditions, under clean or contaminated lubrication conditions, and the dimensional stability of the bearing components.

For the cage, considerations include friction, strain, inertia forces, and in some cases, the chemical action of certain lubricants, solvents, coolants and refrigerants.

Contact seals integrated in rolling bearings can also have a considerable impact on the performance and reliability of the bearings. The materials they are made of have to offer excellent oxidation, thermal or chemical resistance.

The relative importance of these considerations can be affected by other operational parameters such as corrosion, elevated temperatures, shock loads or combinations of these and other conditions.

Rings & rolling elements

Because of high, repetitive stress to the rolling contact areas, fatigue phenomenon will occur to the bearing material after a duration of operation. Loading stress ultimately dislodges a surface section and the bearing fails. To delay the advent of material fatigue, bearing ring and rolling element materials should have the following properties:

1) High level of hardness

2) High rolling contact fatigue resistance

3) Good wear resistance

4) Dimensional stability

5) Good mechanical strength

Today, carbon chromium steel is one of the oldest and most intensively investigated steels; due to the continuously increasing demands for extended bearing service life. The composition of this rolling bearing steel provides an optimum balance between manufacturing and application performance. This steel is normally given a martensitic or bainitic heat treatment during which it is hardened to the range of 60 to 66 HRC. Vacuum degassed, chromium-bearing steel GCr15 is the standard material for precision bearing rings and rolling elements. The material has uniform specification as SAE52100 (America), DIN100 Cr6 (German), JISSUJ2 (Japan).

Chemical composition of representative carbon chrome bearing steels

Cage material

Material for cages is required to have properties of good wear resistance, dimensional stability and good mechanical strength for perfect bearing running purpose. Therefore, for selection of cage material, it is important to consider the operation conditions.

Sheet steel cages

These light weight cages have relatively high strength and can be surface treated to further reduce friction and wear. Cold-rolled steel is used for pressed cages.(Specification see the below table)

Shields & seals material

Shields material

LSKD bearings employ carbon steel as standard, and the option of AISI-300 stainless steel is available when needed.

Seals material

LSKD bearings use a variety of sealing materials to meet the requirements of high temperature operation and compatibility with greases. Buna Nitrile is the standard material used, while fluorocarbon, silicone, and teflon seals are commonly specified for high temperatures.

WARNING!

Safety precautions for fluoro rubber is very stable and harmless in normal operating conditions up to +200 . However, if exposed to extreme temperatures above 300 , e.g. fire or the flame of a cutting torch, fluoro rubber seals give off hazardous fumes. These fumes can be harmful if inhaled, as well as to the eyes. In addition, should not be in contact with the skin either.

3. Bearing tolerances

Tolerance

Bearing tolerances include dimensional tolerance and rotary tolerance or dimensional accuracy and running accuracy, are regulated by ISO or JIS standards (rolling bearing tolerances) etc. For dimensional accuracy, these standards prescribe the tolerances necessary when installing bearings on shafts or in housings. Running accuracy is defined as the allowable limits for bearing run-out during operation.

According to dimension tolerances and rotary accuracy, LSKD deep groove ball bearings are ranged from ABEC-1 to ABEC-7. ABEC-1 is standard grade, while ABEC-3 is higher, ABEC-5 is much higher and ABEC-7 is the highest.

Comparison of tolerance classifications of national standards

4. Bearing fitting

The necessity of a proper fit

Generally speaking, satisfactory radial location and adequate support can only be obtained when the rings are mounted with an appropriate degree of interference. Inadequately or incorrectly secured bearing rings generally cause damage to the bearings and associated components. Therefore it is necessary to make a careful investigation in selecting a proper fit. Some of the bearing failure caused by improper fit is listed below:

Raceway cracking, early flaking and displacement of raceway

Raceway and shaft or housing abrasion caused by creeping

Seizing caused by negative internal clearances

Increased noise and deteriorated rotational accuracy due to raceway groove deformation.

Conditions of rotation and fit

Conditions of rotation refer to the bearing ring being considered in relation to the direction of the load. Essentially, there are "rotating load" and "static load". For bearings parts that under rotating loads, interference fit is usually used to prevent bearing from slipping or “creep”. Meanwhile, clearance fit may be used in “static load” condition to accommodate certain operating conditions or to facilitate bearing mounting and dismounting.

Required running accuracy and fit

Bearing fits are also related to the required operating accuracy and easiness of mounting and dismounting. For example, to reduce resilience and vibration, clearance fits should generally not be used for bearings where high demands are placed on running accuracy. Bearings seating on the shaft and in the housing should be made to narrow dimensional tolerances, corresponding at least to grade 5 for the shaft and at least to grade 6 for the housing.