Page 1 CFM Proprietary Data Unauthorized Disclosure Prohibited CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure 1- Background On June, 21, 2002, SWA CFM56-7B ESN 874265 experienced a commanded IFSD after the oil filter bypass light illuminated in flight. Ground investigation revealed metal debris in the AGB/TGB MCD. During further removal of the AGB, it was found : liberation of key locks coming from the 3 studs that secure the roller bearing outer race to AGB housing, wear-ovalization of the AGB housing at the 3 threaded holes receiving the 3 studs, good condition of the 3 studs remained attached with the roller bearing outer race, excessive radial play on all five AGB mounts links, residual AGB alignment condition (dim. « A » - dim. « B ») checked at 0.051’ (1,29mm) vs. .002’ (0,05mm) required, good condition of horizontal drive shaft splines (no visual wear). 2- Engine and AGB history CFM56-7B22 ESN 874265 delivered in July 1998 installed on #2 on Boeing 737-700 N7183W. One maintenance action reported on AGB since EIS related to HMU replacement (line 6) made in july 1999 without any connection with failed line 3 roller bearing. Engine & AGB TSN/CSN = 14804/9478 and 14268/9112 since HMU replacement. AGB quality inquiry revealed one minor deviation : 6 tooth dim. of line 3 gearshaft check -4μm under mini. limit (42,765 vs. 42,769 to 42,823 required) ; accepted thru departure record DN 15H06030A. Page 2 CFM Proprietary Data Unauthorized Disclosure Prohibited CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure 3- Part identification (see charts 9 & 20) AGB P/N 340-046-503-0 S/N WQ 1193 Damaged control alternator made of : Stator P/N 9387M17P09 S/N HTL 10296 Rotor P/N 9387M16P02 S/N HTLR 4329 Gearshaft line 3 P/N 340-051-801-0 S/N UN 00225 equipped with : Failed roller bearing P/N 301-480-926-0 S/N UR 29717 Ball bearing P/N 305-115-306-0 S/N UR 29633 Ball bearing housing P/N 335-301-000-0 Starter pad assy P/N 340-047-802-0 equipped with : gearshaft line 4 P/N 340-051-901-0 S/N UN 07643 Fuel pump – HMU pad assy equipped with : Gearshaft line 5 P/N 340-055-202-0 S/N UR 00454 Gearshaft line 6 P/N 335-302-902-0 S/N UN 21379 Gearshaft line 7 P/N 335-303-002-0 S/N U 28596 AGB links returned for wear on spherical bearings : Adjustable turnbuckle link P/N 340-029-501-0 equipped with 2 links P/N 340-103-701 / 801 Rear links (x2) P/N 340-029-401-0 Upper link P/N 340-032-801-0 Page 3 CFM Proprietary Data Unauthorized Disclosure Prohibited CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure 4- Findings 4-1 Parts as received (see chart 9) All the 5 gearshafts from lines 3 to 7 and associated pads were reinstalled on AGB housing. Control alternator stator & rotor were received removed and badly worn by rotor sectorial interference (90°). On the alternator rotor the wear is limited to one sector compare to the stator that is affected on 360°. 4-2 After AGB disassy (see charts 10 & 11) Line 3 (control alternator) roller bearing outer race found totally loose due to hole elongation of the 3 securing studs that machined the AGB housing over 10mm long in gearshaft rotation opposite direction. As a consequence of the roller bearing outer race looseness, respective centering diameters of both outer race and AGB housing hole were affected by superficial fretting – wear. Examination of all other studs installed in the AGB housing did not reveal any unusual shaking or unlocked condition especially related to the similar studs. 4-3 Gearshaft line 3 (control alternator) Inspection of gearshaft input splines, matching with horizontal drive shaft, as well as gear teeth showed good condition. Bearing journals : good condition (no wear readable). 4-3-1 Line 3 ball bearing Good condition (no spalling, no corrosion, no shaking evidence except local fretting marks on 1 out of the 3 outer race securing lugs. Page 4 CFM Proprietary Data Unauthorized Disclosure Prohibited CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure 4-3-2 Line 3 roller bearing Outer race : general quite good condition except : (see chart 12) dents caused by particles related to roller and inner raceway spalling. presence on outer raceway of double superficial wear lines (shiny appearance) formed by the roller ends passing through the inner raceway sectorial spalling demonstrates that the outer race stud breakaway and subsequent axial displacement of the outer race (~1,5mm) likely occurred as a consequence of vibrations induced by inner ring spalling. fretting wear on outer diameter (already mentioned), good condition of shoulders with no roller contact indication . Rollers : all of the 14 rollers are affected by dents and spalling craters only distributed on track fwd edge and consistent with dents observed on fwd edge of outer raceway (see chart 13). Cage : good condition. Note the unusual roller contact mark characterized by a conical shape with larger contact area on fwd side of cage separator. Inner race : (see charts 14 & 15) sectorial spalling (~90°) initiated from the forward edge of the track and more developed on the fwd edge, maximum spalling depth measured about 0,1mm, after reinstallation of the alternator rotor as it was initially, the inner raceway sectorial spalling appears to be located in the quite same angular position as the alternator rotor sectorial wear. good condition of the remaining portion only affected by dents and a blue discoloration of the track on fwd edge. Control alternator damage is the result of rotor interfering with stator , due to rotor offset motion consecutive to sectorial spalling of the roller bearing inner race and subsequent outer race looseness. Page 5 CFM Proprietary Data Unauthorized Disclosure Prohibited CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure 4-4 Other gearshafts & associated bearings Inspection of all other received gearshafts and associated bearings did not revealed significant findings especially regarding : tooth pattern : no significant wear, exposed roller bearings : good condition of rollers and outer raceway, ball bearings : no hard point or defect detectable by hand rotation. 4-5 Additional exam 4-5-1 Dimensional (see chart 16) Except the dimension related to alternator rotor for which we don’t have the B/P limits, all the other checked dimensions meet specifications. 4-5-2 Metallurgical examination of Line 3 roller bearing inner race and rollers (see charts 17 to 19) Inner race : examination of the 2 cross sections made through the spalling sector revealed : (see charts 17 & 18) some white spots characterized by butterfly appearance corresponding to material ferrite transformation indicative of material fatigue damaging. general correct M50 microstructure : normal carbide distribution, fine martensitic needles, correct hardness (63 HRC vs 61 to 64), microstructure hammered condition as secondary damage. Rollers : correct hardness (63,5 HRC) and M50 microstructure except usual hammering condition of spalling cracks (chart 19). Metallurgical exam of inner raceway showed presence of butterflies facing sectorial spalling typical of fatigue material damaging Page 6 CFM Proprietary Data Unauthorized Disclosure Prohibited CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure 5- AGB links examination (see chart 20 to 23) Quite good condition of upper link exhibiting only few axial and radial gap (0,15mm & 0,05mm respectively) at spherical bearing matching with AGB upper mount. Bad condition of all 3 other received links affected by heavy wear (1,7mm axial max, 0,55 radial max) at each spherical bearing consistent with wrong AGB adjustment measured by customer prior AGB removal (see table of chart 20). On condition : (see charts 21 & 22) spherical bearings mainly worn on one side locally dug on 1 sector by interference with one of the 2 shoulders designed to keep in place the anti friction liner bonded to the outer ring, mount to interference marks. Good condition of ball bearing bores receiving the pins (no wear noticable). After cutting of the bearing exhibiting the maximum play : (see chart 23) anti-friction liner partially missing on one side, heavy wear of bearing outer journal at anti-friction missing location and adjacent shoulder that totally disappeared by rubbing with spherical inner journal, hammered condition of spherical journal only noticeable at remaining–missing transition of anti-friction liner. The above findings, similar to those already done on Southwest –7B ESN 875402, confirm the spherical bearing wear mechanism induced by relative movement of the bearing elements under vibrations. Except upper link found in quite good condition, spherical bearing of all other 3 links exhibited heavy wear as a consequence of vibrations as already identified on Southwest –7B ESN 875402 engine. Page 7 CFM Proprietary Data Unauthorized Disclosure Prohibited CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure 6- AGB spherical bearing wear During removal of this AGB for the above bearing failure, spherical bearing of AGB links were found worn. 4 out of the 5 links were returned for investigation. Except quite good condition of upper link, all spherical bearings of the 3 rear links exhibited heavy wear (until 1,7mm in axial direction and 0,55mm in radial) caused by relative movement of bearing elements under dynamic loads. These findings are consistent with the wear mechanism already identified on Southwest –7B ESN 875402 after TSN/CSN = 10857/6864. Note ; change in design study in progress to introduce new spherical plain bearing. Page 8 CFM Proprietary Data Unauthorized Disclosure Prohibited CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure 7 – Conclusion : AGB input gearshaft “line 3” roller bearing failure Bearing failure cause : inner raceway spalling Consequences spalling of all the 14 balls looseness of both cage rails shaking - break away of outer race securing 3 studs, machining of AGB housing by rotation of the outer race and associated 3 studs over 10mm long, alternator rotor offset and contamination until interference with alternator stator… Dimensional part inspection did not show any nonconformity. Metallurgical examination of the inner race did not reveal any material anomaly other than material fatigue evidenced by the presence of subsurface fatigue butterflies in raceway . Operating time accumulated by this bearing (14804h/9478cy) and spalling mechanism (initiation at inner raceway fwd edge and subsequent roller spalling on fwd ends) leads to make an hypothesis that bearing failure is consecutive to a constant inner race radial load potentially induced by an alternator rotor unbalance ; however, no analysis on alternator parts to verify this hypothesis could be done, due to their high damage condition Note : ESN874265’s is 1st reported case of failed AGB input gearshaft bearing SEIS in the CFM56-7B 20thSept.02, Southwest ESN 874171, TSN 16160 / CSN 10408 suffered a similar event; CFM has requested hardware of this 2nd event back for investigation . No relation ship between roller bearing failure and AGB link wear has been evidenced ; CFMI experience on CFM56-3 & -7B shows AGB misalignment consequences to be either ball bearing damage or horizontal drive shaft crack-separation without any noticed consequence on roller bearing condition. Page 9 CFM Proprietary Data Unauthorized Disclosure Prohibited CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure Starter pad assy Line 3 gearshaft MFP-HMU pad assy Control alternator 1 & 2- AGB as received 3 & 4- Control alternator stator - rotor wear condition resultant from rotor offset 3- 4- 5- Line 3 ball bearing view : no evidence of damage AGB Wear on 360° Sectorial wear (90°) Page 10 CFM Proprietary Data Unauthorized Disclosure Prohibited CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure Cross section showing line 3 configuration 1- General view of line 3 gearshaft after removal 2- Wear of outer race OD & condition of the 3 studs remained attached with the outer race 3 & 4- Housing wear condition : elongation of the 3 stud holes and bore matching with outer race Roller bearing outer race found break away from AGB housing 3- 4- Failed bearing Page 11 CFM Proprietary Data Unauthorized Disclosure Prohibited CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure Detail views showing AGB housing hole elongation 10mm = stud displacement Thread marks Gearshaft rotation direction Page 12 CFM Proprietary Data Unauthorized Disclosure Prohibited CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure 1- Roller bearing outer raceway : general quite good condition First superficial wear lines formed before studs breakaway 2- Picture 1 detail showing the quite good condition of the roller track except double wear lines caused by roller ends. Second superficial wear lines formed after studs breakaway & 1,5mm outer race axial displacement 1,5mm (outer race rearward displacement) Page 13 CFM Proprietary Data Unauthorized Disclosure Prohibited CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure 1- Roller & cage view : good condition of the cage but all 14 rollers exhibit spalling evidence at fwd edge side 2- Detail of spalling condition at fwd edge side representative of all 14 rollers 3- Complementary views showing roller condition representative of the 14. Spalling Sliding marks Fwd face Page 14 CFM Proprietary Data Unauthorized Disclosure Prohibited CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure 1- 3- 2- 1 to 3- Rotor/gearshaft relative angular positions - matching marks Control alternator rotor Line 3 gearshaft 4- Same angular position of bearing inner raceway spalled sector and alternator rotor wear sector 5- (opposite to 4-) quite good condition of both alternator rotor & roller bearing inner raceway Sectorial spalling (115°) Wear sector (90°) Page 15 CFM Proprietary Data Unauthorized Disclosure Prohibited CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure 1 & 2- Roller bearing inner race sector spalling originating from fwd edge of the raceway 3 & 4- Good condition of race - out of spalled sector - . Note : blue discoloration of fwd edge of roller raceway Initiation area Blue discoloration Roller passing direction Page 16 CFM Proprietary Data Unauthorized Disclosure Prohibited CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure Dia. Dia.OR A Dia. Dia.B IR Dim. checked B/P Values Measured values Prior removal After removal Comments Dia. A 34,992 to 35 --- 34,999 to 35,000 Conform (interference fit = 28μm) Dia. B / outer race 61,991 to 62,000 --- 62,00 Conform Dia. B / AGB housing 61,80 to 62,20 --- 61,98 Conform Dia. IR 40,35 (at spalling location) to 40,475 (90° apart) 40,450 Dia. OR Defined through radial clearance --- 56,475 Roller dia. 8 --- 7,996 to 7,997 Correct values and radial gap 32μm vs. 31 to 50 required IR shoulder width Defined through axial gap --- 8,03 Roller length 8 --- 7,997 to 7,999 Correct axial gap 31 to 33μm vs. 20 to 50 required Dia. C / gearshaft 12,976 to 12,994 --- 12,975 Dia. C / rotor 13,000 to 13.010 --- 12,990 Correct Dia. D / gearshaft 22,199 to 22,221 --- 22,20 Dia. D / rotor 22.238 to 22.250 --- 22,24 Correct Dia. E 35,026 to 35,038 --- 35,028 Conform Dia. F 45,026 to 45,038 --- 45,030 Conform Page 17 CFM Proprietary Data Unauthorized Disclosure Prohibited CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure A B 1- Location of cross sections made through inner race 2- Labeled “A” micrographic view showing axial grain flow. 2- Typical M50 microstructure except hammering condition underneath spalling damage 3- Detail showing correct martensitc microstructure with small carbide networks Good condition of the shoulders free from wear and or overheat Inner race track Roller passing direction Page 18 CFM Proprietary Data Unauthorized Disclosure Prohibited CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure 1 to 3- Cross section labeled “B” on previous chart 6- Hammered condition of the microstructure as a consequence of repetitive roller impact when passing spalling step 4- Spalling cracks and correct microstructure 5- Fatigue butterfly detail 1- End of spalling at roller entry side 2- Spalling sector close to initiation site 3- End of spalling at roller exit side Page 19 CFM Proprietary Data Unauthorized Disclosure Prohibited CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure 1- Illustration showing location of cross section 2- Micrographic view of spalling cracks 3- Spalling cracks detail 4- Typical correct M50 microstructure 5- Spalling crack with flaking partially liberated Roller rotation direction Page 20 CFM Proprietary Data Unauthorized Disclosure Prohibited CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure Upper link Rear link “1” Rear link “2” Adjustable turnbuckle link Upper link Rear link “Characterization 1” Adjustable link Rear link “2” of axial and radial gap Axial Radial Axial Radial Axial Radial Axial Radial Spherical bearing “A” 0,15 mm 0,05 mm 1.20 mm 0,25 mm 0,90 mm 0,25 mm 1,30 mm 0,55 mm Spherical bearing “B” 0 0 0,35 mm 0,13 mm 1,70 mm 0,50 mm 0,95 mm 0,40 mm Spherical bearing “C” 0 0 --- --- --- --- --- --- A C B A B A B A B View of received AGB links randomly repositioned due to the none marking of the parts prior disassembly Axial Radial Page 21 CFM Proprietary Data Unauthorized Disclosure Prohibited CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure Adjustable turnbuckle link 2 & 3- Detail showing wear condition of each ball bearings Wear groove Wear groove Wear Page 22 CFM Proprietary Data Unauthorized Disclosure Prohibited CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure 1 to 3- Supposed rear upper link views showing wear condition of ball bearings 4 to 6- Same as above for supposed rear lower link Interference wear marks Page 23 CFM Proprietary Data Unauthorized Disclosure Prohibited CFM56-7B - Southwest - ESN874265 - AGB input gearshaft roller bearing failure 1 & 2- Complementary views showing the wear condition of both outer journal and anti-friction liner partially missing 3- Wear condition of the ball bearing 4- Detail of fretting wear condition associated with missing anti-friction liner 5- Preferential contact area on 6- Illustration showing missing shoulder at 1 outer ring side Shoulder still present Shoulder totally worn out Anti-friction liner Portion of inner ring surface free from significant wear作者: zippo1983 时间: 2011-5-3 02:24:08
Portion of inner ring surface
free from significant wear作者: 且行 时间: 2011-6-2 11:13:05
