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8/8/2019 Helical Gear Presentation
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A SEMINAR REPORT ON
FATIGUE GAILURE OF HELICAL GEARS
BY
MR. JAMADAR IMRAN M.
ROLL NO. -102090005
UNDER THE GUIDANCE OF
Prof. RATHOD
DEPARTMENT OF MECHANICAL ENGINEERING
2010-11
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ContentsContents
1. Introduction
2. Case study
3.Experimental procedure
4. Results and discussion
5. Conclusion
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Introduction
Failure analysis of helical gear used in aFailure analysis of helical gear used in a bus gearbox bus gearbox
History History--Gear has been in use for 3 yearsGear has been in use for 3 years MaterialMaterial--AISI 8620 Steel AISI 8620 Steel
Evaluation methodsEvaluation methods--Visual inspection, Visual inspection,
photo documentation, chemical analysis,photo documentation, chemical analysis,micro hardness measurement,micro hardness measurement,metallographic examinationmetallographic examination
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TYPES OF GEAR FAILURESTYPES OF GEAR FAILURES
FatigueFatigue
ImpactImpact
FractureFracture Wear Wear
Stress RuptureStress Rupture
Surface contact fatigueSurface contact fatigue-- pitting,pitting, spallingspalling
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CAUSESCAUSES
Poor design of gear setPoor design of gear set
Misalignment of gearsMisalignment of gears
OverloadsOverloads Subsurface defects in internal areasSubsurface defects in internal areas
Use of incorrect materials and heatUse of incorrect materials and heat
treatmenttreatment
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CASE STUD Y CASE STUD Y
Bus with problem with its transmissionBus with problem with its transmissiongearboxgearbox
Gearbox running hot with excessiveGearbox running hot with excessive vibrations vibrations
Problem was with the fourth speed driveProblem was with the fourth speed drivegeargear
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General appearance of General appearance of
failed helical gearfailed helical gear
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Parameters Value
Number of teeth
helical gear
36
Helix angle 150
Module, normal (mm) 4
Pitch circle diameter
(mm)
150
Outer diameter (mm) 158
Face width (mm) 42
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Spectrum analysis and microSpectrum analysis and micro
hardness measurementhardness measurement
Result revealed that material wasResult revealed that material was
AISI8620 carburized steel AISI8620 carburized steel Core hardness =439HV Core hardness =439HV
Surface hardness=550Hv Surface hardness=550Hv
Case depth=0.63mmCase depth=0.63mm Microstructure consist of Microstructure consist of martensitemartensite andand
retained austeniteretained austenite
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MicrostructureMicrostructure
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V isual inspection V isual inspection
No. of adjacent teeth failed due to fatigueNo. of adjacent teeth failed due to fatigue
A triangular piece of the teeth had broken A triangular piece of the teeth had broken
off off Crack initiation and bench marks can beCrack initiation and bench marks can be
seen by necked eyesseen by necked eyes
Origin of crack was at the pitch lineOrigin of crack was at the pitch line No corrosion media were found onNo corrosion media were found on
fractured surfacefractured surface
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Photograph of failed gearPhotograph of failed gear
toothtooth
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PittingPitting
Destructive pitting and spalling were alsoDestructive pitting and spalling were alsonoted on loaded side of each toothnoted on loaded side of each tooth
D
estructive pitting appears as much largerD
estructive pitting appears as much largerpits than initial pittingpits than initial pitting
In spalling pits are large in diameter andIn spalling pits are large in diameter andquite shallow quite shallow
Spalling is caused by excessively highSpalling is caused by excessively highcontact stresscontact stress
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Photograph of Pitted gearPhotograph of Pitted gearteethteeth
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SEM and EDX ExaminationSEM and EDX Examination
SEM inspection to identify cause of fatigueSEM inspection to identify cause of fatiguecrack initiation and propagationcrack initiation and propagation
RiverRiver--like pattern could be seen inlike pattern could be seen inpropagation zonepropagation zone
EDX attached to fractured surface toEDX attached to fractured surface todetermine gear chemistry determine gear chemistry
To verify presence of any other associatedTo verify presence of any other associatedcomponentscomponents
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Crack initiation andCrack initiation and
propagationpropagation
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ConclusionConclusion
Composition, microstructure, hardnessComposition, microstructure, hardnessand case depth found satisfactory and case depth found satisfactory
Fractographic features indicated thatFractographic features indicated thatfatigue was the main failure causefatigue was the main failure cause
Misalignment was observed which hasMisalignment was observed which hascaused failurecaused failure
Formation of destructive pitting andFormation of destructive pitting andspalling at one end was due to loadspalling at one end was due to loadconcentration at that areaconcentration at that area