Mikrostruktur leistungsbestimmend für Makro-Bauteile

Transcription

1 Mikrostruktur leistungsbestimmend für Makro-Bauteile Microstructure the Performance Determining Factor in Macro-Components Metallurgie-Kolloquium TU Clausthal, Dr. Martin Göbel, SKF Group Technology Services Manager Global Testing

2 Die SKF Gruppe 2015 SKF Produkte reduzieren die Reibung und machen Produkte und Prozesse schneller, sauberer und sicherer. Indem wir diese Aufgabe mit größtmöglicher Effizienz, Produktivität und Nachhaltigkeit angehen, ist die SKF Gruppe zu einem der führenden Global Player bei Produkten, Lösungen und Leistungen in den Bereichen Lager und Lagereinheiten, Dichtungen, Mechatronik, Dienstleistungen und Schmiersysteme geworden. Weitere Serviceangebote der SKF Gruppe sind: Technische Beratung, Zustandsüberwachung, Steigerung der Anlageneffizienz und Schulungen.

3 2 - Fatigue testing of rolling bearing steel 1 - Operating conditions of rolling bearings 4 The new challenges of large components 3 - Microstructural alterations under rolling contact fatigue 0 - Bearing steel

4 Bearing steel

5 Bearing steel microstructures Martensite S0 stabilised Bainite Normal transformation temp. Slide

6 Bearing steel microstructures Carburised Components Surface Structure High Ret. Austenite Induction Hardened Components Hardened and annealed Slide

7 Special bearing steel microstructure (very fine and uniform) High hardness High toughness High cleanliness High thermal and mechanical stability High corrosion resistance Slide

8 Bearing steel requirements Impact toughness Hardness and toughness need to be optimized according to the bearing type requirements Hardness Slide

9 Bearing steel requirements - evolution of material cleanliness Reduction of Oxygen, Sulphur and Inclusions à Longer Fatigue Life Oxygen content [ppm] Relative bearing life Relative L10 Brg. Life wt% Sulphur wt% Sulphur wt% Sulphur Oxygen content Content [ppm] (ppm) October 30, 2007 Slide 9

10 Operating conditions of rolling bearings

11 Operating conditions of gears vs rolling bearings Gears - large radius (small volume) one stress cycle per revolution typical N f stress cycles 10 7 typical contact stress MPa Bearings - reduced radius of curvature ~10 ~20 stress cycle per revolution ~ 50 for LSB much large volume at risk required N f of stress cycles about 10 9 typical contact stress MPa

12 Rolling bearings operate under very high cycle fatigue à N f = stress cycles 1.E+12 Number of stress cycles 1.E+11 1.E+10 1.E+09 1.E+08 1.E+07 1.E+06 Very High Cycle Fatigue (GCF) High Cycle Fatigue (HCF) Low Cycle Fatigue (LCF) Range of high N f load cycles of bearing applications Dynamic loading 1.E+05 1.E+04 1.E+03 Car Engines H.S. Trains Turbine Engines Compressors Quasi-static Loading (in relation to rolling bearing operations) Slide

13 Rolling bearing Rolling bearings are the most stressed (Ph ~ 1-3 GPa) and the most dynamically loaded components (up to cycles) in a mechanical system! Slide

14 Orthogonal shear stress Rolling Contact Fatigue (RCF)

15 Fatigue testing of rolling bearing steel

16 The best machine to measure the fatigue strength of bearing material microstructure is... the rolling bearing Bearing material fatigue testing needs to reproduce the shear stress status as found in Hertzian contacts. Dimensional precision and finishing of the bearing components provide an important component of the Hertzian stresses The material microstructure resulting from the manufacturing process and heat treatment is reproduced well in a bearing

17 The fatigue strength of a bearing material microstructure is measured using bearing population samples L 10 The fatigue life L 10 of the bearing is the 90% reliability of the bearing population under test

18 Example of fatigue failure (spalling) of 6309 inner ring used in material fatigue testing Endurance test machine R2

19 Rolling Contact Fatigue is affected by the material volume at risk àbearing size matters Test rigs: Bearing size: R0 rigs diam. 20 mm R2 R1 rigs diam mm R2 rigs diam mm R3 rigs diam mm R4 rigs diam mm R5 rigs diam. up to ~ 500 mm R3

20 Large bearings à the larger the volume at risk à the shorter the life Relative Bearing life Fatigue life Bearing size Slide

21 Bearing RCF life size matters

22 Large size life testing - d m ~ 500

23 and for larger bearings...

24 Large size testing - R5 test rig

25 Nautilus bearing life testing SW1 2.5 m

26 Microstructural alterations under rolling contact fatigue

27 Microstructural alterations in RCF Local fatigue damage Matrix wide changes Slide

28 Local microstructural alterations Fraunhofer butterfly mapping after running RCF at 3 GPa Fraunhofer butterfly distribution: 3GPa vs GPa Localized fatigue damage around inclusions (butterfly)

29 Matrix wide microstructural alterations DER (Dark Etching Region) Voskamp A. Microstructural change during rolling contact fatigue, PhD thesis, Delft University of Technology/SKF Engineering & Research Centre; cycles; 3.3 GPa; 70 C Z 0 =184 um 825 MPa 490 MPa 360 MPa Steel microstructure change in the subsurface of a ball bearing after a very long over-rolling. (a) Dark etching region (DER) developed in the subsurface. (b) Longitudinal section showing the high angle band (HAB) and low angle band (LAB) visible in the DER. (c) A cross-section of the ring showing the DER.

30 Microstructure fatigue damage in RCF Microstructural fatigue damage of the material No microstructural alterations (good performance) Transition line ISO 281 Fatigue Limit (dm=100 mm) Slide

31 Localized microstructure fatigue damage (Stress above the fatigue limit) Stress Cracks grow from weak links where local stress exceeds local strength. Crack growth rate increases with stress (σ- σ u ) and crack length. Fatigue limit σ u depends on bearing size Number of stress cycles Slide 31

32 Ultrasonic measure of microstructure fatigue damage of a large size bearing after testing Slide 34 Result of LSB ultrasonic scanning

33 The new challenges of large components...

34 Example: Siemens Wind Power (6MW) Slide

35 Example: Siemens Wind Power (6MW) Rotor blade manufacturing and transportation. Slide

36 Example: Siemens Wind Power (6MW) Slide

37 SKF 2-row taper roller bearing: Nautilus Slide

38 HALT - Highly Accelerated Life Testing of large size bearings Rotor bearing: Nautilus > kg Outer Diameter 4 m 6 MegaWatt Turbine

39 Large Size Bearing Test Center MSTR - dedicated to wind main shaft applications 40 Mio Investment Biggest LSB test center in the world Two new huge LSB test rigs Extremely high loads and dynamics Start of test rig assembly June-2016 Start of operation H DDTR - dedicated to general bearing development Slide 42

40 The building Sven Wingquist Test Center Slide 43

41 The location - SKF Werk 3 in Schweinfurt

42 MSTR Main Shaft Test Rig Slide 45

43 MSTR - purpose Testing of single bearings Testing of shaft arrangements à Dynamic testing, validation and development of single wind main bearings and full wind main shaft arrangements (optionally including customer parts) à Application of relevant load conditions based on field information and simulations Slide 46

44 Main Shaft Test Rig MSTR (dedicated to wind main shaft applications) Dynamic application of high load, especially bending moments Radial load: 8 MN Axial load: 8 MN Bending moment: 40 MNm (typically) Rotational speed: 30 rpm Bearing size: 4 m Dynamic capabilities: 5 Hz Slide 47

45 DDTR Dynamic Development Test Rig

46 DDTR- Purpose à Dynamic testing for development purposes up to high rotation speeds à For large size bearings in wind, pulp & paper, cement, steel industry, marine, etc Slide 49

47 Dynamic Development Test Rig DDTR (dedicated to general bearing development) High speed, dynamic application of medium load, medium sized LSB Radial load: 7 MN Axial load: 3 MN Bending moment: 10 MNm Rotational speed: 250 rpm Bearing size: 2.5 m Dynamic capabilities: 5 Hz Slide 50

48 Start of operation in H1-2017

49 Thank you very much for your attention! Special thanks to Dr. Antonio Gabelli SKF Engineering & Research Center - The Netherlands Slide

50 Abstract The microstructures of heat treated bearing steels are discussed and their main characteristics reviewed. Rolling bearings are machine components operating under very high cycle fatigue, exceeding overrolling cycles in some very demanding applications. Contact pressures found in rolling bearings can be up to the plasticity limit of the material, making rolling bearings the most dynamically loaded components of a mechanical system. Metallurgical development of bearing steels and the determination of overrolling fatigue properties are primarily based on endurance testing of bearing population samples. Fatigue testing by using bearings offers two major advantages: i) Fatigue cycling in a bearing can be 20 times faster than a common rotating bending approach. ii) In bearings the material s microstructure which results from the manufacturing processes and heat treatment is reproducible very well (a prerequisite for mass production). Therefore conclusions how to improve the material s performance by optimizing the metallurgical processes can be derived and verified from bearing fatigue testing directly. Bearing fatigue predictions are based on the probability of failure of the weakest link. Large material volumes at risk, as found in large size bearings, have a strong impact on the fatigue properties of the bearing itself: size matters! The development of advanced material microstructures for large wind turbine main shaft bearings is discussed in terms of the experimental methods that are needed and the gigantic testing infrastructure required to carry out such a task. Slide

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