Investigation to Failure Analysis of Rolling Element Bearing With Various Defects

7/30/2019 Investigation to Failure Analysis of Rolling Element Bearing With Various Defects

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International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 6340(Print), ISSN 0976 6359(Online) Volume 3, Issue 2, May-August (2012), IAEME

138

INVESTIGATION TO FAILURE ANALYSIS OF ROLLING

ELEMENT BEARING WITH VARIOUS DEFECTS

PROF. AMIT AHERWAR

DEPARTMENT OF MECHANICAL ENGINEERING,

ANAND ENGINEERING COLLEGE (SGI), AGRA

EMAIL: [email protected]

PROF. RAHUL BAJPAI

DEPARTMENT OF AUTOMOBILE ENGINEERING

HINUSTAN COLLEGE OF SCIENCE & TECHNOLOGY

MATHURA

PROF. MD. SAIFULLAH KHALID

DEPARTMENT OF MECHANICAL ENGINEERING,

ANAND ENGINEERING COLLEGE (SGI), AGRA

ABSTRACT

In this present work, highlights the various modes of failure and their respective causes with visual effect of

appearance. The damaged bearing samples were investigated and visual inspection is done to find out the

mode of failure. The component failure list to highlight the most affected bearing part and its root cause

failure analysis is done. This paper described the cause and effect diagram to evaluate the most serious

mode & its cause of failure. This series of articles is intended to serve as an aid in identifying the causes of

bearing failures and to provide guidance on how to avoid future problems. If the machinery has been

plagued by repeated bearing problems, the illustrations that complement the text can provide invaluable

assistance in identifying the root cause of a bearing failure. When bearing failure occurs, consider cleaning

and inspecting it and comparing the observations to the result in this series on bearing failure analysis. The

first thing to look for is an illustration that depicts similar damage to the failed bearing. Read the text

associated with the picture, so as to get a better understanding of why the bearing failed. Rolling element

bearing life expectancy is directly related to the number of revolutions performed by the bearing, the

magnitude of the load and the lubrication and cleanliness of the lubricant. Various fault detection

techniques mainly infrared thermography, envelop analysis etc.; to find the different mode of failure in the

component are discussed in this paper.

Keywords: Condition monitoring, fault diagnosis, rolling element bearing, fault detection

1. INTRODUCTION

A bearing is a mechanical element that permits relative motion between two parts, such as the shaft and the

housing, with minimum friction. The functions of the bearing is to ensure free rotation of the shaft or the

INTERNATIONAL JOURNAL OF MECHANICAL

ENGINEERING AND TECHNOLOGY (IJMET)

ISSN 0976 6340 (Print)

ISSN 0976 6359 (Online)

Volume 3, Issue 2, May-August (2012), pp. 138-149

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axle with minimum friction, supports the shaft or the axle and holds it in correct position, takes up the

forces that act on the shaft or the axle and transmits them to the frame or the foundation. The term rolling

bearing includes all forms of roller and ball bearing which permit rotary motion of a shaft. The rolling

contact bearing has a low starting friction and thus it offers low friction hence also called antifriction

bearings. A complete unit of ball bearing includes inner ring, outer ring, rolling element (balls or rollers)

and the cage which separates the rolling element from each other. Rolling bearings are high precision, low

cost but commonly used in all kinds of rotary machine. Sriram Pattabhiraman, George Levesque, Nam H.

Kim, Nagaraj K. Arakere [1], presents Uncertainity analysis and parametric studies for estimating the

fatigue failure probability of surface cracks in silicon nitride ball bearings subjected to rolling contact

fatigue. Wouter Ost, Patrick De Baets and Wim De Waele [2], investigated the failure of ball bearing of a

dockside crane, which had been in service for 22 years, was replaced, noise emanating from the bearing

was observed. Gradually the play of the newly installed bearing increased and after 5 years this had to be

replaced. Upon visual inspection a large deformation of one of the bearing rings was observed, and when

the bearing was opened 5 fractured balls were found and some parts of the raceways showed extensive

pitting. Analysis of the bearing showed that faulty hardening of the bearing caused pitting of the raceways,

which led to failure of the bearing.

Wouter Ost, Patrick De Baets [3], described the failure analysis of deep groove ball bearings of an electric

motor, driving an oil-injected compressor, were periodically monitored for vibrations. Tuncay Karacay,

Nizami Akturk [4], presented the Vibration measurements and signal analysis for condition monitoring ofball bearings as their vibration signature reveals important information about the defect development within

them. The Time domain analysis of vibration signature such as peak-to-peak amplitude, root mean square,

Crest factor and kurtosis indicates defects in ball bearings. A. Tauqir, I. Salam, A. ul Haq, A. Q. Khan [5],

discuss the fatigue failure in the central main bearing (CMB) of the compressor shaft of an aero-engine

resulted in an air-crash. The cage of the CMB broke due to fatigue, got stuck between the bearing balls and

the outer race, misaligned them resulting in severe wear of the components and damaged the function of the

engine. R. S. Dwyer-Joyce [6], investigated the solid debris particles in a lubricant can become entrained

into the contacts of ball bearings. The particles damage the bearing surfaces. This can lead to rolling

contact fatigue failure or material loss by three body abrasion. This work concentrates on modelling the

later process for brittle debris materials. B. Liu, S. F. Ling, R. Gribonval [7], identifies a new approach to

the detection of localized defects of rolling element bearings is proposed. It employs matching pursuit with

timefrequency atoms to analyze bearing vibration and extract vibration signatures. In particular, this

approach utilizes not only the temporal and spectral but also the scale characteristics of the vibrationgenerated due to the presence of a defect for the detectionN. Tandon, A. Choudhury [8], presents a reviewof vibration and acoustic measurement methods for the detection of defects in rolling element bearings. It

also considered the detection of both localized and distributed categories of defect. H. Ahmadi and K.

Mollazade [9], presents bearing fault diagnosis to maintain an efficient operating unit and avoid failure of

mineral critical equipment, it is necessary to maintain the critical parts of that equipment. V. Sugumaran, V.

Muralidharan, K.I. Ramachandran [10], has presented fault diagnostics of roller bearing through proximal

support vector machine to reveals its condition and the features that show the nature, through some indirect

means. Statistical parameters like kurtosis, standard deviation, maximum value, etc. form a set of features,

which are widely used in fault diagnostics. Dong Wang, Qiang Miao, Xianfeng Fan and Hong-Zhong

Huang [11], explain the bearing fault detection benefits decision-making of maintenance and avoids

undesired downtime cost. Alan Friedman [12], describe a methodology for automatically detecting and

diagnosing rolling element bearing wear.

2. Rolling Contact Bearing Failure

The rolling element or antifriction bearings have long service life when they are maintained properly. The

most widely used rolling element bearing are ball, cylindrical roller, spherical roller and tapered roller. The

bearings will exhibit no signs of failure unless contaminants such as dirt, abrasive foreign particles, etc.

misalignment, overloading and improper lubrication. Each of the different causes of bearing failure

produces its own characteristic damage. Such damage, known as primary failure, gives rise to secondary

failure. Even the primary failure may necessitate scrapping the bearings on account of excessive internal

clearance, vibration, noise, and so on. A failed bearing frequently displays a combination of primary and


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secondary failure. The types of bearing failure may be classified as follows: (1) Primary Failure- It

comprises of: Wear, Indentations, Smearing, Surface Distress, Corrosion and Electric Current Damage, (2)

Secondary Failure- It comprises of: Flaking (spalling), Cracks, Cage damage.

2.1 Bearing Wear and its Causes.

All bearings normally go through a wear period of several hours after initial operation, after which the

rolling elements and raceways are broken in and perceptible wear starts. In normal cases there is no

appreciable wear in rolling bearings. Wear may, however, occur as a result of the ingress of foreign

particles into the bearing or when, the lubrication is unsatisfactory.

2.1.1 Wear caused by abrasive particles

Small, abrasive particles, such as grit or swarf that have entered the bearing by some means or other, cause

wear of raceways, rolling elements and cage. The surfaces become dull to a degree that varies according to

the coarseness and nature of the abrasive particles. Sometimes worn particles from brass cages become

verdigrises and then give light-colored grease a greenish hue. The quantity of abrasive particles gradually

increases as material is worn away from the running surfaces and cage. Therefore the wear becomes an

accelerating process and in the end the surfaces become worn to such an extent as to render the bearingunserviceable. However, it is not necessary to scrap bearings that are only slightly worn. They can be used

again after cleaning. The abrasive particles may have entered the bearing because the sealing arrangement

was not sufficiently effective for the operating conditions involved. They may also have entered with

contaminated lubricant or during the mounting operation.

2.1.2 Wear caused by inadequate lubrication

If there is not sufficient lubricant, or if the lubricant has lost its lubricating properties, it is not possible for

an oil film with sufficient carrying capacity to form. Metal to metal contact occurs between rolling

elements and raceways. In its initial phase, the resultant wear has roughly the same effect as lapping. The

peaks of the microscopic asperities that remain after the production processes are torn off and, at the same

time, a certain rolling-out effect are obtained. This gives the surfaces concerned a varying degree of mirror-

like finish. At this stage surface distress can also arise. If the lubricant is completely used up, the

temperature will rise rapidly. The hardened material then softens and the surfaces take on blue to brown

hues. The temperature may even become as high as to cause the bearing to seize.

2.1.3 Wear caused by vibration.

When a bearing is not running, there is no lubricant film between the rolling elements and the raceways.

The absence of lubricant film gives metal to metal contact and the vibrations produce small relative

movements of rolling elements and rings. As a result of these movements, small particles break away from

the surfaces and this leads to the formation of depressions in the raceways. This damage is known as false

brinelling, sometimes also referred to as wash boarding. Balls produce sphered cavities while rollers

produce fluting. In many cases, it is possible to discern red rust at the bottom of the depressions. This is

caused by oxidation of the detached particles, which have a large area in relation to their volume, as a resultof their exposure to air. There is never any visible damage to the rolling elements. The greater the energy of

vibration, the more severe the damage. The period of time and the magnitude of the bearing internal

clearance also influence developments, but the frequency of the vibrations does not appear to have any

significant effect. Roller bearings have proved to be more susceptible to this type of damage than ball

bearings. This is considered to be because the balls can roll in every direction. Rollers, on the other hand,

only roll in one direction; movement in the remaining directions takes the form of sliding. Cylindrical roller

bearings are the most susceptible. The fluting resulting from vibrations sometimes closely resembles the

fluting produced by the passage of electric current. However, in the latter case the bottom of the depression

is dark in color, not bright or corroded. The damage caused by electric current is also distinguishable by the


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fact that the rolling elements are marked as well as the raceways. Bearings with vibration damage are

usually found in machines that are not in operation and are situated close to machinery producing

vibrations. Examples that can be cited are transformer fans, stand-by generators and ships' auxiliary

machinery. Bearings in machines transported by rail, road or sea may be subject to vibration damage too.

Where machines subject to constant vibration are concerned, it is essential that the risk of damage to the

bearings be taken into consideration at the design stage. Consequently, where possible, ball bearings should

be selected instead of roller bearings. The ability of ball bearings to withstand vibrations without being

damaged can also be considerably improved by applying axial preloading with the aid of springs. An oil

bath, in which all rolling elements in the load zone are immersed in the oil, has also proved to provide

satisfactory protection. A vibration-damping base helps to prevent damage too. The bearings in machines

that are to be transported can be protected by locking the shaft, thus preventing the small movements that

have such a damaging effect on the bearings.

2.2 Bearing Indentation and Their Causes

Raceways and rolling elements may become dented if the mounting pressure is applied to the wrong ring,

so that it passes through the rolling elements, or if the bearing is subjected to abnormal loading while not

running. Foreign particles in the bearing also cause indentations. The distance between the dents is the

same as the rolling element spacing. Ball bearings are prone to indentations if the pressure is applied in

such a way that it passes through the balls during the mounting or dismounting operations. Self-aligning

ball bearings are particularly susceptible to damage in such circumstances. In spherical roller bearings the

damage originates as smearing and subsequently, if the pressure increases, develops into a dent. Bearings

that are mounted with excessively heavy interference fits, and bearings with tapered bore that are driven too

far up the shaft seating or sleeve, also become dented.

2.3 Bearing Smearing and its Causes

When two inadequately lubricated surfaces slide against each other under load, material is transferred from

one surface to the other. This is known as smearing and the surfaces concerned become scored, with a

"torn" appearance. When smearing occurs, the material is generally heated to such temperatures that

rehardening takes place. This produces localized stress concentrations that may cause cracking or flaking.

In rolling bearings, sliding primarily occurs at the roller end-guide flange interfaces. Smearing may also

arise when the rollers are subjected to severe acceleration on their entry into the load zone. If the bearingrings rotate relative to the shaft or housing, this may also cause smearing in the bore and on the outside

surface and ring faces. In thrust ball bearings, smearing may occur if the load is too light in relation to the

speed of rotation.

2.4 Fretting corrosion

If the thin oxide film is penetrated, oxidation will proceed deeper into the material. An instance of this is

the corrosion that occurs when there is relative movement between bearing ring and shaft or housing, on

account of the fit being too loose. This type of damage is called fretting corrosion and may be relatively

deep in places. The relative movement may also cause small particles of material to become detached from

the surface. These particles oxidize quickly when exposed to the oxygen in the atmosphere. As a result of

the fretting corrosion, the bearing rings may not be evenly supported and this has a detrimental effect on the

load distribution in the bearings. Rusted areas also act as fracture notches.

2.5 Damage caused by the passage of electric current.

When an electric current passes through a bearing, i.e. proceeds from one ring to the other via the rolling

elements, damage will occur. At the contact surfaces the process is similar to electric arc welding. The

material is heated to temperatures ranging from tempering to melting levels. This leads to the appearance of

discolored areas, varying in size, where the material has been tempered, re-hardened or melted. Small

craters also form where the metal has melted. The passage of electric current frequently leads to the


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formation of fluting (corrugation) in bearing raceways. Rollers are also subject to fluting, while there is

only dark discolouration of balls. It can be difficult to distinguish between electric current damage and

vibration damage. A feature of the fluting caused by electric current is the dark bottom of the corrugations,

as opposed to the bright or rusty appearance at the bottom of the vibration induced fluting. Another

distinguishing feature is the lack of damage to the rolling elements of bearings with raceway fluting caused

by vibrations. Both alternating and direct currents cause damage to bearings. Even low amperage currents

are dangerous. Non-rotating bearings are much more resistant to electric current damage than bearings in

rotation. The extent of the damage depends on a number of factors: current intensity, duration, bearing

load, speed and lubricant. The only way of avoiding damage of this nature is to prevent any electric current

from passing through the bearing.

2.6 Bearing Flaking and its Causes

Flaking (Spawling) occurs as a result of normal fatigue, i.e. the bearing has reached the end of its normal

life span. However, this is not the commonest cause of bearing failure. The flaking detected in bearings can

generally be attributed to other factors. If the flaking is discovered at an early stage, when the damage is not

too extensive, it is frequently possible to diagnose its cause and take the requisite action to prevent a

recurrence of the trouble. The path pattern of the bearing may prove to be useful, see path pattern and their

interpretation. When flaking has proceeded to a certain stage, it makes its presence known in the form ofnoise and vibrations, which serve as a warning that it is time to change the bearing. The causes of

premature flaking may be heavier external loading than had been anticipated, preloading on account of

incorrect fits or excessive drive-up on a tapered seating, oval distortion owing to shaft or housing seating

out-of-roundness, axial compression, for instance as a result of thermal expansion. Flaking may also be

caused by other types of damage, such as indentations, deep seated rust, electric current damage or

smearing.

International Journal of Rotating Machinery Cracks may form in bearing rings for various reasons. The

most common cause is rough treatment when the bearings are being mounted or dismounted. Hammer

blows, applied direct against the ring or via a hardened chisel, may cause fine cracks to form, with the

result that pieces of the ring break off when the bearing is put into service. Excessive drive up on a tapered

seating or sleeve is another cause of ring cracking. The tensile stresses, arising in the rings as a result of the

excessive drive-up, produce cracks when the bearing is put into operation. The same result may be obtained

when bearings are heated and then mounted on shafts manufactured to the wrong tolerances.

The smearing described in an earlier section may also produce cracks at right angles to the direction ofslide. Cracks of this kind produce fractures right across the rings. Flaking, that has occurred for some

reason or other, acts as a fracture notch and may lead to cracking of the bearing ring. The same applies to

fretting corrosion.

2.7 Bearing Cage Damage and Its Causes.If, on examination of a failed bearing, the cage is found to be damaged, it may in many cases prove difficult

to ascertain the cause. Usually other components of the bearing are damaged too and this makes it even

more difficult to discover the reason for the trouble. However, there are certain main causes of cage failure,

viz. vibration, excessive speed, wear and blockage.

3. Different Modes of FailureBearings are designed for a given number of load cycles on the races. If the fatigue loads and the resulting

stresses exceed the bearing capacity, they will eventually cause cracks and spalling to develop in the races

and leads to bearing failure [13].The various mode of bearing failure are:

(a) Poor Design(b) Misalignment(c) Poor Installation(d) Improper loading(e) Insufficient Lubrication(f) Poor care and maintenance


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4. Method for failure detection in rolling element bearing

4.1 Infrared Thermography

Infrared Thermography is a fast and non-intrusive method to detect the presence of abnormally warm zones

on the surface of the bearing. We propose here to establish a link between the temperature rise and the riseof the vibratory level of a mechanical component in the course of degradation. The method particularly

concerns the detection of the appearance of a defect of spalling on a rolling bearing. The damping of the

vibration has the effect to transform a part of the damping vibratory energy into heat. This heat creation

induces a rise in the ring temperature, more particularly on its external surface.

4.2 Envelope Analysis

Envelope Detection or Amplitude Demodulation is the technique of extracting the modulating signal from

an amplitude-modulated signal. The result is the time history of the modulating signal. The signal may be

studied/ interpreted as it is in the time domain or it may be subjected to a subsequent frequency analysis.

Envelope Analysis is the FFT (Fast Fourier Transform) frequency spectrum of the modulating signal.

Envelope Analysis can be used for diagnostics/investigation of machinery where faults have an amplitude

modulating effect on the characteristic frequencies of the machinery. Examples include faults in gearboxes,turbines and induction motors. Envelope Analysis is also an excellent tool for diagnostics of local faults

like cracks and spallings in Rolling Element Bearings (REB).

4.3 Fatigue Wear Particle Analysis

Surface fatigue wear, also called rolling contact fatigue, predominantly occurs in rolling element bearings.

Fatigue wear in rolling bearings generally starts with micropitting - small areas on the bearings surface

where material has been removed due to repetitive stress. At its terminal point, surface fatigue causes

significant surface spalling - large craters often several hundreds of microns across, which are easily visible

to the naked eye. While the effects of fatigue on bearings are well-documented, wear debris analysis offers

a unique insight into fatigue failure. Because the particles that are removed from the bearing surface are

deposited in the oil and become the mirror image of the surface distress, the onset and progress of rolling

contact fatigue can be detected. Surface fatigue begins with microcracking on the surface or subsurface of arolling contact bearing. The subsurface cracking typically nucleates at material defects or inclusions in

bearing steels. With high stress on the rolling contact surfaces, subsurface microcracking propagates

parallel to the surface, causing the material to eventually dislocate or spall and form fatigue wear particles.

Recently, particulate-indentation induced surface fatigue has attracted greater attention among tribologists.

The risk for particle-induced surface fatigue is greatest when solid particles are roughly the same size as

bearing dynamic clearances (clearance size particles) and are harder than bearing surfaces and not too

friable. This enables them to enter bearing interfaces and dent bearing surfaces that have suffered from this

type of surface fatigue show massive indentations.

4.4 Vibration Condition Monitoring Technique

Condition monitoring is the process of monitoring a parameter of condition in machinery, such that a

significant change is indicative of a developing failure. It is a major component of predictive maintenance.

The use of conditional monitoring allows maintenance to be scheduled, or other actions to be taken to avoid

the consequences of failure, before the failure occurs. Nevertheless, a deviation from a reference value (e.g.

temperature or vibration behavior) must occur to identify impeding damages. Predictive Maintenance does

not predict failure. Machines with defects are more at risk of failure than defect free machines. Once a

defect has been identified, the failure processes has already commenced and measure the deterioration of

the condition. Intervention in the early stages of deterioration is usually much more cost effective than

allowing the machinery to fail. Condition monitoring has a unique benefit in that the actual load, and

subsequent heat dissipation that represents normal service can be seen and conditions that would shorten


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normal lifespan can be addressed before repeated failures occur. Vibration analysis has been used in fault

diagnosis of rotating machines with rolling bearings for decades. Recent evidence shows that vibration

condition monitoring technique provides greater and more reliable information, thereby resulting in a more

effective maintenance program with large cost benefits to industry. Vibration analysis in particular has for

some time been used as a predictive maintenance procedure and as a support for machinery maintenance

decisions. As a general rule, machines do not break down or fail without some form of warning, which is

indicated by an increased vibration level. By measuring and analyzing the vibration of a machine, it is

possible to determine both the nature and severity of the defect, and hence predict the machine's useful life

or failure point. The overall vibration signal from a machine is contributed from many components and

structures to which it may be coupled. However, mechanical defects produce characteristic vibrations at

different frequencies, which can be related to specific machine fault conditions. By analyzing the time and

frequency spectra, and using signal processing techniques, both the defect and natural frequencies of the

various structural components can be identified.

5. Analysis on Failure of REBThe analysis of Rolling Element Bearing (REB) begins with the initial inspection of the failure bearing

samples. For the analysis point of view the various rolling element (ball) bearing samples having different

failure modes are investigated and the most offensive cause is detailed. During the examination the various

components of the bearing are dismantled and visual appearance of the failure mark is point out. The

following are the detailed information of the bearing samples under inspection:

Sample-1

Bearing

specification

Bearing No.: 6212

(a) (b)

Type Single Row Radialball bearing

Inside Diameter 60mm

OutsideDiameter

110mm

Race Width 22mm Failure

mode

Inner Race

Crack

Failure

mode

Smearing of

RacewayLubrication Grease (Shell) Failure

CausesDue tooverload

FailureCauses

Due to Lack ofLubricant

Sample-2

Bearing

specification

Bearing No.: 6208

(a) (b)



OutsideDiameter

80mm

Material Crome Steel

Max.Speed 7000rpm

Race Width 18mm Failuremode

Cage Fracture Failuremode

Due toMisalignment

Lubrication Grease (Shell) FailureCauses

Due toMisalignment

FailureCauses

Due to impropertooling


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Sample-3

Bearing

specification

Bearing No.: 6203

(a) (b)



Outside

Diameter

40mm


Max.Speed 17000rpm


Ball PathWidened

Failuremode

Smearing ofRaceway

Lubrication Grease FailureCauses

Due toMisalignment

FailureCauses

ImproperLubrication

Sample-4

Bearingspecification

Bearing No.: 6304

(a) (b)

Type Radial Deep groove

ball bearingInside Diameter 20mm

OutsideDiameter

52mm


Max.Speed 10,000rpm


FrettingCorrosion

Failuremode

Corrosion Etching

Lubrication Grease Failure

Causes

Due to

loose/tight fits.

Failure

Causes

Due to

contamination

Sample-5


Bearing No.: 6206

(a) (b)

Type Deep groove ballbearing


OutsideDiameter

60mm


Max.Speed 10,000rpm


FrettingCorrosion

Failuremode

Burning tends toscuffing

Lubrication Grease Failure

Causes

Due to passage of

electric current

Failure

Causes

Due to Lack of

Lubricant


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Sample-6


Bearing No.: 6203

(a) (b)

Type Deep groove ballbearing


Outside

Diameter

40mm


Max.Speed 17,000rpm


Wear around theRaceway.

Failuremode

Rusting around theRaceway

Lubrication Grease (Shell)FailureCauses

Lack ofcleanlinessduring mounting.

FailureCauses

Due to Loose fitting

Sample-7


Bearing No.: 6203

(a) (b)

Type Deep groove

ball bearingInside Diameter 17mm

OutsideDiameter

40mm

Max.Speed 17,000rpm


Race Width 12mmFailuremode

FrettingCorrosion onouter surface

Failuremode

Corrosion Etching

Lubrication GreaseFailureCauses

Due to moistureor corrosivesubstance.

FailureCauses

Due tocontamination

Sample-8


Bearing No.: 6205

(a) (b)

Type Deep groove ball

bearing


OutsideDiameter

52mm


Race Width 15mm

Max.Speed 10,000rpm

Race Width 15mm Failuremode Discolorationof Inner Race Failuremode Overheating

Lubrication GreaseFailureCauses

Due toinadequatelubrication.

FailureCauses

Due to overload.


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Failure Analysis of Bearing Samples

0102030405060708090

100

Inner Ring Outer

Ring

Rolling

Element

Cage

Failure Component

PercentageofFailureMode

Percentage of Failure

Mode

6. Result and Analysis

6.1 Failure Mode and Effected bearing component

Table 6.1 describes the different bearing sample failure and the effected bearing component:-

Bearing Failure Bearing Ring Rolling Element Cage or Retainer

Inner Ring Outer Ring

Wear Fretting Smearing Cracks Corrosion Cage Failure Pitting Discoloration Brinelling Flaking

The major causes of bearing component failure may be overloading, lubrication, mishandling, poor

mounting practices. The failure analysis of bearing samples has been done regarding the failure componentwith their percentage of Failure mode. Results shows the most encounter failure component is inner ring

which depicts 90% of failure mode while rolling element depicts the least one with 30%.

0

10

20

30

40

50

60

70

80

A B C D E F G H I J

Percentage

ofFailureMode

No. of Failure Cause

Failure-Cause Analysis of Bearing Samples

Failure Mode

Fig: 6.1-Variation of Percentage of Failure Fig 6.2 Percentage of Failure modes Vs

Failure Mode Vs Failure Component Causes

(A) Improper mounting; (B) Inadequate lubricant; (C) Electric current; (D) Contamination; (E) Moisture/chemicalaction; (F) High temperation; (G) Poor handling; (H) Misalignment; (I) Improper lubrication; (J) Over loading/ axial

loading

Another analysis has been done based on the number of failure causes with the percentage of failure mode.

Results shows the maximum percentage of failure mode is due to Overloading; Axial Loading while 10%

of the failure mode is due to electric spark which is the least one. The other causes depicts likewise

improper mounting 60%, inadequate lubricant 30%, contamination 50%, moisture/chemical action 30%,

failure cause due to high temperature 40%, poor handling 50%, misalignment 20% , improper lubrication50%.

General Trend of Major Failure Causes

The Failure reasons of a rolling element bearing may be due to overloading/axial loading, Inadequate/Improper

Lubrication, Poor handling & Misalignment. In many cases these faults are caused by incautious operation and

insufficient technical knowledge. These faults can cause major damage in machinery. Design faults include incorrect

shape, dimensional errors, bearing faults, selection of wrong bearing and insufficient technical knowledge. The Fig


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showing that the major trends of failure cause is due to loading either overloading or axial loading while the least

one is due to misalignment. For proper life expectancy of bearing these parameters must be considered.

Fig.6.3: Showing major percentage of bearing failure causes.

Conclusion

The rolling element bearing problems and determining their root cause of failure is often difficult, because many

failure types look very similar. This is because bearing failures are almost always precipitated by spalling or flaking

conditions of the bearing component surfaces. Spalling occurs when a bearing has reached its fatigue life limit, but

also when premature failures occur. For this reason, it is important to be aware of and able to recognize, all of the

common failures of rolling element bearings. This ability to correctly recognize the root cause of bearing problems

will lead the analyst to the right conclusions with regard to the bearing failure. Manufacturing defects in rolling

element bearings make up less than one percent of the millions of bearings in use today around the world and this

small defect percentage is being reduced continually by improvements in manufacturing techniques and bearing

materials. Bearing manufacturers use ultrasonic inspection devices to detect surface and subsurface bearing material

defects, eliminating poor quality products during the production process. Eddy current testing is used to evaluate

surface hardness and detect cracks to ensure 100% product conformance to bearing specifications. Only a small

fraction of all the bearings in use fail because they have reached their material fatigue limit. The vast majority ofbearings outlive the machinery or component in which they are installed. According to many bearing experts, the

following statistics apply to rolling element bearings failures, no matter in what type of rotating equipment they are

installed (electric motors, pumps, fans, gear drives, etc.) Fail prematurely due to mechanical vibration, excessive

temperatures, electrical discharge caused by static electricity or current flow, or by operating conditions which allow

overloading and/or over speeding. These bearing life percentages may vary from industry to industry depending on

operating conditions, maintenance practices and industry operational culture. For example, in the pulp and paper

industry, poor lubrication or contaminated lubricants are the main causes of failure.

Future ScopeThe future scope of this study will be to improve bearing life expectancy ratings, defined as the number of

revolutions or number of operating hours at a given constant speed which a bearing is capable of, before the first

sign of fatigue spalling occurs on one of the rings or rolling elements. This dissertation work can be extended to

employ different optimization technique to find the exact probability of failure so as to improve the service life of

the bearing.

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Documents

Investigation to Failure Analysis of Rolling Element Bearing With Various Defects