AGMA 13FTM16-2013 The Anatomy of a Lubrication Erosion Failure - Causation Initiation Progression and Prevention.pdf
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1、13FTM16 AGMA Technical Paper The Anatomy of a Lubrication Erosion Failure - Causation, Initiation, Progression and Prevention By R.J. Drago and R.J. Cunningham, Drive Systems Technology, Inc., and W. Flynn, Chalmers clean with no evidence of corrosion products observed and deep in size. DST also not
2、ed that the erosion was observed in the root area on either side of the pitted surface. No clear evidence of electrical arc type damage or any other type of metallurgical defect was observed on any of the tooth defects metallurgically examined. 15 13FTM16 Figure 14. View of cavitation erosion defect
3、 within tooth contact pattern (Note: The very light contact pattern on the coast flanks is a normal condition due to back driving as the machine is shut down) Hardness, chemistry and microscopic examination of pinion shaft and defects Three (3) cross sections through the teeth defects from Pinion Se
4、gment B were removed for determination of certain metallurgical properties. These samples were cut on a perpendicular to the Pinion axis and were prepared such that the defects could be polished into. This was done in order to determine the microscopic characteristics of the cavitation erosion defec
5、ts. Each sample was then evaluated in the unetched condition for microhardness traverse data. Subsequently, the samples were chemically etched for microstructural features both at the surface and below the surface. This included evaluation for any evidence of reharden and/or retemper burns. The thre
6、e test samples were labeled A-1, A-2 and A-3. The areas removed for evaluation contained three teeth each as shown in Figure 15. Figure 15. View of four (4) areas to be removed from tooth segment B for further metallurgical evaluation 16 13FTM16 Also shown in Figure 15 is a fourth test sample, label
7、ed B-1. This test sample was removed from an area which was defect free as illustrated in the figure. It was prepared by removing a cross section perpendicular to the direction of the helical teeth. This sample was used to determine the actual metallurgical characteristics of the Pinion component. I
8、t included case and core hardness properties, nitride case depth and microstructural features of the Pinion shaft teeth. After removal of the all four (4) areas by EDM machining, each was metallurgically mounted and polished. A polished cross-section through one of the A test samples is illustrated
9、in Figure 13c. All of the A samples looked similar to that shown in the figure. After metallurgical preparation of all four test samples, a small additional area was removed for the purpose of determining the chemical makeup and quality level of the Pinion Shaft material. A brief summary of the test
10、 samples is given in Table 1. a. Hardness evaluation 1. Each of the four (4) tooth segments was carefully removed from Tooth Segment B by electro discharge machining. Subsequent mounting and polishing was accomplished using standard metallurgical techniques. Samples were water cooled during cutting
11、and polishing to assure that properties of the material would not be altered. Each sample was evaluated for microhardness characteristics at the surface as well as the core. All microhardness traverses were accomplished using a Leitz Microhardness Test Machine. Hardness traverse evaluation was accom
12、plished at depths below the surface of 0.003, 0.005, 0.010 inch and then every 0.010 inch up to 0.050 inches. DPHN values obtained were converted to Rockwell C values using standard conversion tables. A polynomial fit to the hardness vs. depth curves was used for all test samples to determine the ni
13、tride case depth. The nitride case depth was determined as the depth where the hardness dropped to 110% of the core hardness. This hardness value was determined as R/C 36. In addition, each sample was evaluated for surface and core hardness and decarburization if present. 2. The microhardness result
14、s for test samples A-1, A-2 and A-3 are illustrated schematically in Figures 16a, 16b and 16c respectively. Data obtained from these curves are illustrated in Table 2. The results for test sample B-1 is also illustrated in Table 2 and shown schematically in Figure 16d. 3. Based on the hardness vs. d
15、epth curves, each tooth surface had been nitrided. Hardness values obtained on each test sample were consistent with each other and typical of heat treated and hardened material. Table 1. Test samples removed from pinion tooth segment B for further metallurgical evaluation Test sample label Area eva
16、luated Sample removed for Evaluation purpose A-1 Cross section through 3 tooth pit defects Erosion/pitting features, other defects and microhardness studies Confirm failure mode A-2 Cross section through 3 tooth pit defects Erosion/pitting features, other defects and microhardness studies Confirm fa
17、ilure mode A-3 Cross section through 3 tooth pit defects Erosion/pitting features, other defects and microhardness studies Confirm failure mode B-1 Cross section through 2 tooth pit defects Hardness, microstructure nitride case depth around the tooth profile Confirm Pinion heat treat properties Unla
18、beled Cross section in core area of pinion tooth segment Chemical analysis major elements + carbon, sulfur and phosphorus Determine material chemistry and quality level of steel used for Pinion 17 13FTM16 a) Schematic representation of hardness data from test sample A-1 b) Schematic representation o
19、f hardness data from test sample A-2 c) Schematic representation of hardness data from test sample A-3 d) Schematic representation of hardness data from test sample B-1 Figure 16. Hardness vs. depth curves for all test samples Table 2. Microhardness vs. depth below surface data (All R/15N and BHN re
20、quirement values converted to R/C values) Coupon sample Coupon test location Surface R/C evaluated at 0.005 inch Nitride case depth at R/C 361), inch Core hardness range, R/C See figureA-1 Damaged flank 48.5 0.030 31 - 33 16a A-1 Undamaged flank 45.5 0.022 16a A-2 Damaged flank 49.0 0.030 31 - 33 16
21、b A-2 Undamaged flank 47.0 0.023 16b A-3 Damaged flank 47.0 0.032 31 - 33 16c A-3 Undamaged flank 47.0 0.024 16c B-1 Left flank 47.0 0.024 31 - 33 16d B-1 Right flank 47.0 0.023 16d B-1 Root 47.0 0.022 16d Requirements 47 - 552)0.018 - 0.023 33 - 37.53)NOTES: 1)Determined at hardness drop to 110% of
22、 core hardness 2)Values converted from R15N 84 88. 3)Converted from BHN 320 - 360 18 13FTM16 4. All nitride case depth values (obtained at R/C 36 depth) met or exceeded the requirements given in Reference G - shown in the Background section of this DST report and listed in Table 2. The nitride case
23、depth values obtained on all of the samples are considered consistent with heat treated nitrided 4340 steel. Surface and core hardness values also met the requirements. 5. Comparison of the data shown schematically for test samples A-1 to A-3 with test sample B-1 shows that the values obtained from
24、the latter sample was more consistent than that of the former. The reason for this is the cut angle of each test sample. Sample B-1 was cut on a perpendicular to the angle of the helical tooth resulting in consistent values on either side of the tooth profile. Samples A-1 to A-3 were cut on a perpen
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