Fretting in Wind Power Pitch Bearings: Micro-Slip Experiments and Bearing Test Rig Design Román de la Presilla Master of Science Thesis TRITA-ITM-EX.2020:186 KTH Industrial Engineering and Management Machine Design SE-100 44 STOCKHOLM Examensarbete TRITA-ITM-EX.2020:186 Fretting i lager till vindturbinsblad: mikroglidningsexperiment och konstruktion av en lagerprovningsrigg Román de la Presilla [email protected] Godkänt Examinator Handledare 2020 – 05 – 27 Ulf Sellgren Sergei Glavatskih [email protected] [email protected] Uppdragsgivare Kontaktperson Axel Christiernsson Johan Leckner International AB [email protected] Sammanfattning Vindkraft är idag det snabbast växande området för grön elproduktion i Europa och står med 100 000 installerade turbiner för 15% av den totala elförsörjningen. Denna otroliga utvecklingen har berott på en massiv teknologisk insats som måste fortsätta. För att nå Europakommissionens miljömål för 2050 måste expansionen av grön elproduktion och vindkraft till och med trappas upp. Nyligen har en mer aktiv individuell reglering av rotorbladen, vilket möjliggör att bladen kan styras in- och ut ur vinden, visat sig kunna reducera lasterna på blad och andra komponenter avsevärt, vilket därmed möjliggör stora kostnadsreduceringar. Dessa justeringar möjliggörs genom att rotorbladen ansluter hubben via ett rotorbladslager. Dessa nya lastreducerande reglerstrategier tvingar dock lagren att arbeta under högre belastning jämfört med traditionell reglering av rotorbladens lutningsvinkel. Det här sker genom mer frekvent positionering och ofta som små oscillerande rörelser, vilket leder till en högre risk för slitage på rotorbladslagren, som i sin tur kan leda till förlust av rotorbladsregleringen. När så sker kan inte längre en säker reglering av turbinen garanteras och katastrofala fel är möjliga, så som förlust av rotorblad. Det här projektet avser att utarbeta en design för en lagerprovningsrigg som kan användas för att testa rullager med kontaktvillkor som efterliknar de som återfinns i rotorbladslagren. Ett nytt koncept,m som är baserat på en ramlös motor, presenteras. Konceptet avser att förhindra onödigt slitage hos testriggens motorlager och förbättra de dynamiska egenskaperna för en given motorkapacitet. Projektet innefattar även en studie av friktionsbeteendet hos olika smörjmedel under små upprepande tangentiella rörelser, som utförts med en befintlig testrigg på KTH. Sökord: Fretting, Rotorbladslager, Smörjning 1 2 Master of Science Thesis TRITA-ITM-EX.2020:186 Fretting in Wind Power Pitch Bearings: Micro-Slip Experiments and Bearing Test Rig Design Román de la Presilla [email protected] Approved Examiner Supervisor 2020 – 05 – 27 Ulf Sellgren Sergei Glavatskih [email protected] [email protected] Commissioner Contact person Axel Christiernsson Johan Leckner International AB [email protected] Abstract Wind power is the fastest-growing form of green energy production in Europe, today accounting for 15% of the total power demand with 100.000 turbines installed. This tremendous development relied on a massive technological undertaking that must be continued, and even accelerated in order to meet the European Commission’s environmental goals for 2050. Currently, more active individual control of the rotor blades, turning the blade into and out of the wind, has proven its ability to reduce structural loads on the blades and other components significantly, therefore paving the road towards strong cost reductions. To allow for such adjustment, the rotor blades are connected to the rotor hub via pitch bearings. However, these new structural load reduction control strategies force the pitch bearings into a much more demanding operation condition. More frequent positioning activity and often in the form of smaller oscillating motions, when compared to traditional pitch control. This leading to an increased risk of wear damage of the pitch bearing that could fully incapacitate the blade control. At which point the safe regulation of the turbine can no longer be guaranteed and catastrophic failure, such as the loss of a rotor blade, is possible. This project pertains to the design a bearing test rig that can be used to test rolling element bearings with contact conditions that emulate those found in pitch bearings. A novel frameless motor-driven concept is proposed. The concept is aimed towards preventing unnecessary damage of non-test bearings and improving the dynamic performance of the test rig for a given motor capacity. One further objective of the project involved using an existing KTH single contact test rig to study the friction behavior of different lubricants when minute reciprocal tangential displacements are imposed. Keywords: Fretting, Pitch Bearing, Lubrication. 3 4 FOREWORD I extend my most sincere gratitude to both my academic supervisor Professor Sergei Glavatskih and my industrial supervisor Dr. Johan Leckner. The advice, feedback, perspective and passion you shared with me before and during the project were priceless. I also want to express tremendous gratitude towards the professors at Machine Design Department, for diligently sharing your knowledge and experience during these last two years. I am also grateful to Professor Stefan Bjorklund and Staffan Qvarnström for generously taking the time to think out loud with me. Additionally, I would like to thank Tomas Östberg for his support in constructing components used in the experimental set up and to Fabian Schwack for lending his uniquely relevant experience whenever it was needed. To my family, for their unrelenting support and guidance, I express profound gratitude. Finally, Sasha. Thank you for being my center. Román de la Presilla Stockholm, May and 2020 5 6 NOMENCLATURE Notations Symbol Description A Peak to peak amplitude of imposed displacement. Ad Imposed displacement amplitude As Sliding amplitude D Hertzian contact diameter r’ Radius of slip region r Hertzian contact radius s Slip Ratio Sc Test rig and contact stiffness Q Tangential Load W Normal Load δ Slip Index μ Friction Coefficient Abbreviations CAD Computer Aided Design IPC Individual Pitch Control RCFM Running Condition Fretting Map MRFM Material Response Fretting Map PSR Partial Slip Regime MR Mixed Regime GSR Gross Sliding Regime 7 TABLE OF CONTENTS FOREWORD ............................................................................................................................................................... 5 NOMENCLATURE .................................................................................................................................................... 7 TABLE OF CONTENTS ............................................................................................................................................ 8 1 INTRODUCTION ................................................................................................................................................. 10 1.1 BACKGROUND AND PROBLEM DEFINITION ........................................................................................................ 10 1.2 PURPOSE AND RESEARCH QUESTIONS ............................................................................................................... 13 1.3 DELIMITATIONS ................................................................................................................................................. 13 1.4 METHODS .......................................................................................................................................................... 14 2 FRAME OF REFERENCE .................................................................................................................................. 15 2.1 AN INTRODUCTION TO FRETTING DAMAGE ....................................................................................................... 15 2.2 FRETTING IN HERTZIAN CONTACTS ................................................................................................................... 18 Micro-Slip in a Hertzian contact subjected to a tangential load ....................................................................... 18 Other mechanisms that result in Micro-slip ...................................................................................................... 20 2.3 FRETTING MAPS AND FRETTING REGIMES .......................................................................................................... 21 2.4 FRETTING WEAR ............................................................................................................................................... 23 2.5 FRETTING IN LUBRICATED CONDITIONS ............................................................................................................ 29 Oil Lubrication .................................................................................................................................................. 29 Grease Lubrication ............................................................................................................................................ 31 2.6 FRETTING EXPERIMENTS: TEST RIGS ................................................................................................................ 33 2.7 PITCH BEARINGS IN WIND POWER: THE PERSPECTIVE OF FRETTING DAMAGE TESTING ................................... 40 3 IMPLEMENTATION .......................................................................................................................................... 43 DESIGN PROCESS: BEARING FRETTING