A systemic approach for enhancing applications reliability through advanced analysis and technical solutions for various bearing damage modes

Transcription

1 A systemic approach for enhancing applications reliability through advanced analysis and technical solutions for various bearing damage modes Relatore Badard Guillaume, Chief Engineer Europe Azienda: Timken Europe

2 Outline Bearings are key components, critical to the application s reliability and its economic success: Main validation process for bearings uses classical rolling contact fatigue analysis (either factor-based theory or stress-based analysis). It is a continually evolving technology (tribology, material science) that has various challenges to overcome. Several failure modes cannot be addressed by classical fatigue analysis and require advanced modeling such as dynamic analysis or structural analysis. Bearing performance can be significantly different from one application to another. It is critical to have the appropriate input data, along with fundamental knowledge and calculation tools, to validate bearings performance and select proper arrangements.

3 Classical Fatigue Analysis: Definition Pitting, spalling / repeated cyclic loading ASTM defines fatigue life as the number of stress cycles of a specified character that a specimen sustains before failure of a specified nature occurs (fatigue spall size: 6mm²) Fatigue life calculations Catalog life analysis per ISO 281:2009 Advanced life analysis per ISO/TS Proprietary bearing life analysis Timken SYBER life Example GSC spall Slice order L FB = a material.a osc.a lube. a load_zone.a misal. a low_load. a debris *90*10 6 *(C 90 /P eq ) 10/3 Revs Stress-based calculations: life per slice based on stress only Testing correlation with calculations Timken performs 1 st in 4 standardized life testing (75mm 600mm OD) to develop advanced life prediction models

4 L10 A (Hours) Classical Fatigue Analysis: Calculations Requires accurate input data: load cycles, temperatures, speeds, assumptions Several parameters influence lifetime calculations: bearing internal geometry (profile, finishes), lubrication, setting influence Mounted Setting (mm) Thermal analysis for true operating temperature consideration (solving heat transfer equation) 1 T r r r r OR 1 2 r 2 T OR 2 2 T z OR 2 OR C k p, OR OR T OR Structural analysis (FEA, compliance matrix ) for accurate bearing loading conditions Roller load comparison between FEA analysis, bearing model using FEA, and bearing model without FEA

5 Classical Fatigue Analysis: Development and Prevention Subsurface stress-initiated fatigue lifetime Timken is engaged in the ongoing development of methods to quantify material inclusion on fatigue life based on type, size, density for more advanced stress-based model Race subsurface stress profile 100 Bearing Life (m Rev) 10 Exper. Life VBLT median Typical inclusion distribution Stress alteration due to inclusion Prevention: Improved performance achieved through optimized internal geometry, cleaner steels, special heat treatments, improved manufacturing methods and forging processes, leading to higher capacity level 1 Normalized Total Number inclusion of Inclusions index

6 Other Failure Modes According to ISO Standard classical rolling contact fatigue analysis or stress-based analysis cannot address several modes of damage including: Surface-originated fatigue (micropitting, peeling) Indentations from debris or from handling Overload (brinelling, heavy spalling) Subcomponent failure (cage, seal, bolts) Corrosion (false brinelling, fretting corrosion, moisture) Adhesive wear (smearing, scuffing, skidding, scoring) Additional means of detection and prevention of such damage modes can be achieved through theoretical calculation tools or bearing application know-how and experience.

7 Surface-Initiated Fatigue / Micropitting Interaction of the raceway and roller asperities leading to high stresses in contact [Low speed operations insufficient lubricant film thickness] + [high amount of sliding between rollers and races high shear stresses] No industry standard calculation for predicting onset of micropitting, but control of particular design parameters (kappa or lambda ratios) can be performed Guidelines: High film thickness proper lubricant selection Lower asperity peak heights improved finishes and surface texture parameter/honing/if Avoid sliding conditions preloaded bearing with true rolling motion Dissimilar materials engineered surfaces, Timken Wear-Resistant Coatings More likely to occur with slow speed bearings SRB inner ring mixed mode, micropitting and PSO P 0 P f s L Surface P, P,, ) s( 0 ress s v f v ( P 0, resv, v ) L Volume TRB outer ring micropitting

8 Plastic Deformation / Indentations from Debris or Wrong Handling Debris indentations Debris from external or internal contamination causing indentations and leading to premature fatigue failures Wear from other components (bearing, gear) or improper lubricant filtration Prevention means: Forced oil lubrication with proper filtration Proper drains for oil sumps Case carburized bearings microstructure, retained austenite Timken Wear-Resistant Coatings Timken debris calculation can help predict the bearing life impact Similar to debris analysis, indentations due to improper handling can be modeled. Φ D K

9 Plastic Deformation: Overload Overload will typically results in permanent plastic deformation or true brinelling, which leads to spalling High transient impact loads result in stresses that exceed the material maximum tensile strength Systematic prevention: ISO 76 calculations, proper safety factors Stress-based static analysis Include actual deflections, roller load sharing Proper input data Appropriate mounted clearance and/or preload Accurate FEA

10 Subcomponent Failures: Cage Damage R Results from excessive loads on cage bridges What can reduce the risk of cage damage? Proper cage selection and design optimization (bridge thickness, shape) Proper roller loading, good load zones, avoid roller skewing FEA example cage stress R Fimpactright Fimpactleft Roller/cage bridge impact force versus roller location Qo 2.00E E E E E E E E E E E E E E E E+00 Roller revs. Example of roller-cage load impact force vs. roller location Outer race load Qo (N) CAGEDYN (SYBER) / limited DOF analyses: based on transient roller kinematics, analysis of cage impact loads DBM higher DOF: more complex analysis Vibration signal analysis (aditionnal input for CAGEDYN) I r Impact Forces in N Cage/bearing FEA analysis Cage dynamic calculations (DBM, CAGEDYN) F r

11 Corrosion: Fretting, Microvement or Moisture False brinnelling caused by small amplitude vibration or relative axial movement between rollers and races Mitigation: Preloaded bearing design, proper packaging/transportation /operation procedures and appropriate lubrication selection Fretting corrosion: micro-movement between two surfaces, which generates red or black iron oxides and leads to increased body wear, increased looseness, spinning races, and potentially fretting fatigue of component. Mitigation: ring creeping risk calculations, improved fitting practice or component integration Moisture corrosion and water ingress assessment: rust, oxidization, degradation of metal over time when exposed to water, humidity Mitigation: proper sealing system or corrosion-resistant material

12 Temperature C Adhesive Wear: Sliding/Smearing/Scuffing Adhesive Wear is the result of inadequately lubricated surfaces sliding against each other under load, leading to material transfer between surfaces Sliding can result from: Roller acceleration/deceleration on entry/exit into the loaded zone High speed, light load and narrow load zone Light load, high speed conditions Sudden load variation change in load vector Loss of roller traction Dynamic analysis performed using CAGEDYN or multibody simulations: - Roller rotational speed in one bearing revolution: sliding calculations - Local contact temperature - Smearing criteria assessment. : P. V 250 Final mean temperature Dynamic bearing model predicted smearing criteria 50 0 orbital roller location

13 Wear Prevention: Timken Wear-Resistant Technology What is ES302? Permanent thin (1-2 m) film layer Lower modulus, higher hardness than bearing steel Dispersed carbides cubic b-wc1-x (~2 nm) Hard amorphous hydrocarbon matrix nanocomposite structure Timken experience: Originally developed in 2007 Full-scale production on rollers since 2008 Benefits: Reduced friction In sliding or boundary/mixed lubrication Reduced wear Improved micropitting, smearing/scuffing resistance Improved rolling contact fatigue life Poor lubrication conditions Debris contaminated environments

14 Adhesive Wear: CRB Smearing Test Parameters Load (kn) Torque (N*m) Tested full-size CRB 160mm ID x 290mm OD 1800 RPM SAE20 oil without EP/AW additives ~1.5% C1 Rating reversing load directions Ground Honed/IF Radial Load Time (min) Torque Black Oxide Wear Resistant 100 minutes 4 test treatments; 3 bearings per treatment Treatment ID Treatment Description Ground Standard Ground Rings and Rollers Honed / IF Honed Raceways, IF Roller Texturing Only Timken Wear-Resistant Bearings did not develop any smearing pattern on the raceway before test completion Honed / IF / Black Oxide Wear-Resistant Honed Raceways, IF Roller Texturing, Black Oxide Treatment on both Rings and Rollers Honed Raceways, IF Texture and Coating on Rollers

15 Conclusions - Bearing applications are increasingly moving toward the edge of standard technlogy limits, and it is therefore critical for a customer to work with the right bearing manufacturer partner to properly analyze bearing performance for all kinds of operating conditions in order to improve application overall reliability. - As bearings are always part of a system, their behavior has a direct influence on other components. It is therefore important to model them as precisely as possible to allow the accurate understanding of the application as a whole, and to make documented design decisions for all system components. - Several failure modes are not addressed by classical rolling contact fatigue analysis and special tools must be used to assess the risks associated with their occurence. - There are technology solutions adapted for each damage mode that should be carefully considered when selecting bearings.

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