Rolling Element Bearings - Small Elements Which Are Capable Of Running Large Machines.

Introduction :

Rolling element bearings are very critical components of rotating machines and the presence of defects in the bearing may lead to failure of machines. Hence, early identification of such defects along with the severity of damage under operating conditions of the bearing may avoid malfunctioning and breakdown of machines. Defective bearings are source of vibration and these vibration signals can be used to assess the faulty bearings.

Bearings are classified into two main categories ; rolling element bearings and journal bearings. The terms Antifriction bearings, Rolling bearings and Rolling elements are used for bearings in which the load on rotating component or rotating load is transferred through finite rolling parts in contact with rotating and fixed parts. In sliding contact bearing rotating part is in direct contact of the fixed parts. Rolling bearings exist in a large range of applications across almost all industries and they play very important role in all aspects of modern human life. Rolling element bearings are further classified as Ball bearings and Roller bearings based on the shape and type of contact of rolling element. Both ball and roller bearings are further classified as per their geometrical change in shape for the load requirement as Radial, Angular and Trust bearings.

Bearings are the most widely used components in the rotating machinery. It has a wide range of applications starting from a simple bicycle to complex turbo machineries.Bearings provide relative motion between support bodies and the rotating part and also transmit load. The condition of a machine is directly related to the condition of bearing in that machinery.

To understand the behaviour of a bearing during operation, several techniques have been used. Among them, vibration signals is the most powerful technique used for detecting the condition of a bearing. Bearings generate vibration during operation, and even new, geometrically perfect bearings generate vibrations. The sources of vibrations are defects of rolling bearing, unbalanced loads, misalignment and changing of load zone. Therefore vibrational signal analysis plays an important role in analizing the health of a machine.This method allows inexpensive repair on a prescheduled control basis in comparison with a catastrophic failure, whose repair may cost much more in terms of money and machine running time.

With increasing use of soft technology, mechanization and automation in industries, there has been a steep rise in competition. Industries cannot afford longer break down time for the any machines. For that predictive maintenance a technique is used by industries. Condition monitoring is proven tool of predictive maintenance technique. A reliable condition monitoring can be used for schedule data collection without periodic shutdown.

Bearing Defects :

The bearings defects are usually classified into two types. One of this are the local defects, in which defects such as crack pits, spells, defects generated due to fatigue are categorized and the Second type is Distributed defects. Waviness, surface roughness, off sized rolling element, misaligned races, defect generated during manufacturing and installation are common distributed defects in Distribute defects in rolling element bearing.

Causes of Bearing Failures :

There are many causes for developing defects in different parts of bearing. It is difficult to identify exact cause of bearing defects. Moreover one or more following reasons are responsible to damage the bearings. If it is taken care about all the causes it is improve the operation of bearing, reduce catastrophic failure and increases the life of bearing.

Some of the causes are listed below :
1.Foreign Matter
2.Bearing Fatigue
3.Corrosion
4.High Temperature
5.Improper Installation
6.Electric Damage