Innovation in Motion EWEA Conference Brussels 2011 Wednesday 16 th March Novel Attempts for Plain Bearing Solutions in Wind Turbine Drivetrains Presenter: Alexander Kari Authors: Alexander Kari, Christian Forstner, Dr. Johannes Hölzl Miba Gleitlager GmbH, Dr.-Mitterbauer-Str.5, 4663 Laakirchen, Austria

Innovation in Motion Outline 1. Bearing Failure (Overview & Summary)  Failure Cause WTG  Failure Mode REB 2. Analysis of Plain Bearings  Potential Failure Modes 3. Development Activity  HD Simulations  Material Testing  Product Concepts 4. Summary & Outlook

Innovation in Motion Bearing Failures  Results of 2 large European Surveys (source: Durham University, presented at EWEC 2010) - GBX break downs causing highest down time cost in WTG - Root cause is bearing failure in most cases - Most critical locations: planet bearings, HSS and IMS (Timken, EWEC 2010)

Innovation in Motion Bearing Failures  Failure Mode of REB - Shock and peak loads  Hertzian stress increases disproportionate with load - Consequence: bearings oversized  underload – roller sliding – micro pitting & smearing - Down-time, micro movements and vibrations  false-brinelling on race ways  surface damages agglomerate and propagate under high loads/cycles and leading to a bearing failure long before achieving calculated fatigue life !!  Failure Mode of Plain Bearings? - REB failure modes not relevant for plain bearings - HD plain bearings are resistant to shocks and excessive load, down-time, micro movements and vibrations - But: what other failure modes could occur?

Innovation in Motion Analysis of Plain Bearings  Low sliding speed - Oil film creates even under overload and speeds < 0.5 m/s - Verification by: -applying advanced HD oil film simulation tools -performing specific bearing material test rig testing moderate oil film peak pressure in main loaded area clearance gap increases after loaded area oil gap refilled again main loaded area with 100% filled oil gap

Innovation in Motion Analysis of Plain Bearings  Enormous number of start-stops - Engine bearings have to cope with dry friction as well – no hydrostatic support during start - Specific material testing to understand the mechanism and develop specific solutions  Synthetic layers substantially influencing the wear rate !! Miba Synthec® with 7.7 µm wear out 25 µm layer thickness after 1800 cycles

Innovation in Motion Analysis of Plain Bearings  Specific unit load of planet stages too high - Unit load >>10 MPa and up to 50 MPa at 2-3 x nominal load - Not feasible with bearing materials like Babbitt or Al based alloys - Engine bearings have to cope with MPa at nominal load in large diesels and even with MPa in smaller bore engines  High stationary load - Soft elements like Sn in cast alloys will simply be squeezed out - Alloys with soft phases might creep under load/temperature/time - Specific material testing accomplished to confirm feasibility of selected materials embedded Sn in cast AlSn alloy homogenous AlSn Sputter (PVD coating) tough CuZn alloy without soft phases

Innovation in Motion Analysis of Plain Bearings  Life time requirement too high - 200’000 vs ’000 hours for engines sounds not feasible - same with 20 years vs. 5 years life time expectation - but a closer look at both applications delivers the following picture:  comparison of sliding path over time (wear): Wind turbine rotor (bearing 2200 mm): 0.99 mill km Wind GBX 1 st planet (bearing 220 mm): 0.34 mill km Diesel bore 450 (bearing 420 mm): 1.43 mill km  comparison of load cycles (fatigue and wear): Wind turbine rotor (12 rpm, 200’000h) : 144 mill revs./cycles Wind GBX 1 st planet (40 rpm, 200’000h): 480 mill revs./cycles Diesel bore 450 mm (600 rpm, 30’000h): 1008 mill revs./ 2016 mill load cycles  maybe a simple comparison …  but putting WTG life time requirements into perspective

Innovation in Motion Development Activity  Hydrodynamic Simulation (1) - Creation of HD oil film and results shown previously - Beyond that simulations performed to learn more on the characteristics of plain bearings vs. roller bearings:  Oil film pressure almost linear with load increase  Oil film thickness decreases non-linear with load !!

Innovation in Motion Development Activity  Hydrodynamic Simulation (2) - Elasto hydrodynamic (EHD) simulations to analyse edge loading  no big difference in oil film peak pressure  but minimum film thickness remarkable higher  smoothened pressure profile reduces dry friction substantially! asperity contact pressure = degree of dry friction

Innovation in Motion Development Activity  Material Testing  CuZn+: good properties as base material but substantial wear  AlSn20Cu Sputter (PVD lining): wear rate +++ | adapability --  Synthec® (synthetic layer): wear rate ++ | adapability +++

Innovation in Motion Development Activity  GBX Bearings - Concepts for all gear stages for prototype (and serial use) developed but are matter to confidentiality  Rotor Bearing - Direct substitution to double row tapered bearing - Exchangeable bearing pads as a major features - Simulation is focusing on contact pressure distribution - FEM of bearing, rotor and stator - load distribution on bearing and each single pad

Innovation in Motion Summary & Outlook  Simulations - Valuabe information achieved as one part of feasibility for plain bearings as well as for design work - Anyhow simulation tools for wind specific applications will be developed further in particular for the rotor bearing  Material Testing - Feasibility can be confirmed for continuous operation and overload and to a certain extend for start-stop and idling - Start-stop as well as low idling testing under higher loads will be performed during this year (modified test rig)  Test Rig Testing & Field Experience - GBX bearings: rig testing to be continued, first field experience around mid of Rotor bearing: prototype testing on ground level mid of 2012, field experience for 2012/2013

Innovation in Motion Contact Miba Gleitlager GmbH Dr.-Mitterbauer-Str Laakirchen, Austria Alexander Kari T M