Proceedings Of ASME Turbo Expo 2019: Turbomachinery .

Proceedings of ASME Turbo Expo 2019: Turbomachinery TechnicalConference and Exposition, June 17-21, 2019, Phoenix, USAGT2019-90231EFFECT OF PAD AND LINER MATERIALPROPERTIES ON THE STATIC LOADPERFORMANCE OF A TILTING PADTHRUST BEARINGRasool KooshaLuis San AndrésGraduate Research AssistantMast-Childs Chair ProfessorFellow ASMEJ. Mike Walker ’66 Department of Mechanical Engineering,Texas A&M UniversityFunded by Turbomachinery Research Consortium

Introduction: Tilting Pad Thrust Bearings (TPTBs) Control rotor axial placement in rotating machinery. Advantages: low power loss, simple installation, and lowcost maintenance. As lubricant is sheared, fluid filmand pad temperatures increase. Load capacity of bearingdepends on lubricant viscosity,a function of temperature. Pad thermally and mechanicallyinduced deformations shape theoperating fluid film thickness anddetermine the bearing loadcapacity.2

TPTB current computational analysis 2D hydrodynamic pressure on pad surface. Cross-film viscosity variation. turbulent flow effects. 3D temperature distribution in fluid film. Heat conduction to the pads. turbulent flow effects. 3D temperature distribution in pad and liner. Heat transfer on all sides of a pad.Pressure & temperature gradient in a pad produce elastic deformations.3

Elastic deformations in a pad & linerFluid film model couples to anin-house Finite Element modelwith pad elasticity and pivotstiffness.Peak deformationPressure and temperature 3Ddeformation field in a pad as wellas pad rigid body motion aboutpivot.Babbittor LinerBoth pad deformations changethe film thickness bearingperformancePivotlocationPaper GT2019-90231 includes validation of predictive model for1) Pad deformations vs ANSYS analysis results.2) Pad temperature vs measurements in [1] for a mid-size TPTB.Includes operation spanning laminar to turbulent flow conditions.[1] Mikula. 1986, J. Trib., 29.4

ObjectiveTo quantify theinfluence of both padand liner materialproperties on theperformance of anexamplethrust bearing.GT2019-90231Steel base materialwith Babbitt layer or aPolyether etherketone (PEEK ) liner.

JustificationHigh power density, low viscosity fluids,and extreme operating conditionsenable polymer based materials asalternatives to white metal alloys(Babbitt). Compared to Babbitt, PEEK and PTFE )(Poly-tetra-fluoro-ethylene) low wear rate, corrosion proof and chemical resistance tolerance against particle contaminantsSteel-Polymer TPTB Solid PEEK pads eliminate need forpolymer/steel bonding.PEEK hard-polymerPTFE soft-polymerWhole Polymer TPTB6

Physical Properties: Babbit vs Hard PolymerUnitsSteelBabbittHard-Polymer(White Metal) (PEEK )Thermal ConductivityW/(m.k)51550.87Thermal Expansion10-6 /⁰C122347Young ModulusGPa2105212.5Poisson Ratio[-]0.30.30.35Max. Temperature Limit ⁰C[-]120160Refs.[1][1,2][2,3,4] Low thermal conductivity:Pros: reduces pad temperature rise minimizes pad thermal deformation.Cons: isolates film from t pad increases film temperature rise. Low elastic modulus:Cons: increases pad mechanical deformation large demand for supply flow.May cause oil cavitation at a pad trailing edge.[1] Glavatskih, S., and Fillon, M., 2006[3] Markin et al., Tribol. Int., 2003[2] Yuki et al., GT2014-26798, 2014[4] Zhou et al. J. Lubricants, 20157

Prior Work on Liner Materials for TPTBs2004, ASME/STLE Joint Conf. :Glavatskih and Fillon account foreffects of pad face liner. OD 0.28 m, Ω 3 krpm, 2.0 MPa/padAs the thickness of soft-polymer liner increases: Pad temperature lessens, Film temperature raises at the pad trailing edge, Film thickness decreases at the pad leading edge.Sumi et al. comparemeasured pad temperatures of a hard-polymer liner TPTBagainst those in a Babbitted TPTB. OD 0.73 m, Ω 3.6 krpm.2014, ASMEGT2014-26798: The Babbitted pads bearing fail to carry specific loads larger than 6MPa as the white-metal reached its melting temperature. The hard-polymer liner bearing, however, carried up to 12 Mpa.Compared to Babbitted pad bearings, literature onpolymer lined pad bearings is limited.8

Predictions forthe Effect of PadLiner Materialon Thrust BearingPerformance9

Eight-pad TPTBBased onMax surface speed 13.5 - 278 m/s𝜌 𝑅𝑚 Ω ℎ𝑚𝑖𝑛Reynolds No. 𝑅𝑒 𝜇Lower critical ReL 580Upper critical ReU 800 for turbulence flow[1] Abramovitz, S., J. Franklin Ins.,1955[2] Gregory, R., J. Lub. Tech., 1974.Four pads with same thickness (25 mm)Mikula. 1986, J. Trib., 29.Shaft rotational speed4-13 krpmMax surface speed ΩRo13.5-278 m/sSpecific load per padW/(Ap Np)0.69-3.44 MPaNumber of pads, Np8Outer/Inner diameters267/133 mmPad arc length [ ]39oPivot offset [%]50%LubricantISO VG32 Bare steel pad (with no liner or Babbitt): Solid hard-polymer pad Babbitted-steel pad: 23 mm thick steel 2 mm thick Babbitt Steel pad with hard-polymer liner 23 mm thick steel 2 mm thick liner10

Oil Temp 46 ⁰CLoad 3 MPaFilm Thickness vs. SpeedMin. Film Thickness [μm]Laminar Flow50Solid Hard-PolymerBare Steel40BabbittedSteelBabbitted-Steel3020Polymer on SteelBareSteelSolid Hard-Polymer10Polymer on Steel00 Turbulent Flow5Superlaminar Flow1015Rotor Speed [krpm]20Flow transits to turbulent flow for shaft speed 9 krpm. Solid hard-polymer pad shows a large 13 µm jump in minimum filmthickness due to a significant drop in film temperature (onset ofturbulence) Minimum film thickness at highest speed (20 krpm): Hard-polymer pad 43 µm. Bare steel pad 28 µm.11

20 C lesser than that inthe hard-polymer paddue to an early transitionto superlaminar flow.The solid hard-polymerpad produces largest filmtemperature 136C 46C 182 C, near oil flash point at196 C for ISO VG32 oil.1451301151008570554025Oil Temp 46 ⁰CLoad 3 MPaSolid Hard-PolymerPolymeron SteelBareSteelBabbitted-SteelSuperlaminar Flow2500Reynolds NumberThe Babbitted-steel pad hasthe lowest film maximumtemperature rise:Max. Film TemperatureRise [ C]Film Temperature Rise vs. SpeedBabbitted-Steel2000Polymer on Steel1500Bare Steel1000Superlaminar Flow500800 ReU580 ReLSolid Hard-Polymer0051015Rotor Speed [krpm]2012

Oil Temp 46 ⁰CLoad 3 MPaDrag Power Loss [kW]Drag Power Loss vs SpeedPolymer on Steel20Bare Steel1510Solid HardPolymer5BabbittedSteel005101520Rotor Speed [krpm] Under laminar flow (shaft speed 10 krpm)Solid hard-polymer pad produces the largest drag power loss, 25% more thanthose for other pad types. Under turbulent flow (shaft speed 12 krpm)Due to its higher film thickness, solid hard-polymer pad produces the smallestdrag power loss: 22% and 35% lesser than those for a Babbitted-steel pad andthe polymer liner-steel pad, respectively.13

Oil Temp 46 ⁰CLoad 3 MPaFlow Rate [LPM]Supply Flow Rate vs Speed30BabbittedSteel2520Solid Hard-Polymer1510Polymer on Steel5Bare Steel005101520Rotor Speed [krpm]Due to large mechanical deformation at the pad leading edge Flow forthe hard-polymer pad is significantly higher than those for the other padtypes.Due to a larger thermal rise, the polymer liner-steel pad requires a lowflow rate, 2/3 of the one for the Babbitted-steel pad.14

Hard-Polymer vs Babbitted Pad: Pressure FieldSpeed 10 krpm, Load/Pad 3.0 MPa, Oil Temp 46 ⁰C,Babbitted Steel Pad[MPa]Leading EdgeHard-Polymer PadBabbited-Steel pad: Pressure extends over whole pad. Low peak pressure 50% of one in hardpolymer pad.[MPa]AmbientPressureZoneSolid hard-polymer pad: Areas denuded of oil near trailing edge. Large peak pressure 4 x specific pressure.Leading Edge15

Hard-Polymer Vs Babbitted Pad: Film Thickness[µm]Speed 10 krpm, Load/Pad 3.0 MPa, Oil Temp 46 ⁰C,Minimum FilmThicknessPivotLeading Edge[µm]Minimum FilmThicknessSolid hard polymer pad vs common-useBabbitted-steel pad produces: Smaller minimum film thickness. Diverging gap near pad trailing edge Larger maximum film thickness.DivergingGapPivotLeading Edge16

Effect of liner thicknesson TPB performance25 mmFor a drop-in pad change in bearing: keeppad thickness 25 mm.Change in polymer thickness or babbittthickness change in steel backing portionthickness.Bare steelpad0.2 mmthick lineror Babbittlayer1 mmthick3 mmthick5 mmthick17

Babbitt vs Hard-Polymer Liner: Min. Film ThicknessMinimum Film Thickness [μm]Babbitted-steel padHard-polymer Liner Pad60605 mm3 mm1 mm504030301 mmBare Steel0.2 mmBare Steel200.2 mm105 mm3 mm504020Speed 4 krpm,Oil Temp 46 ⁰C,10000.51.52.53.50.51.52.53.5Specific Load per pad [MPa]Under a light load 1 MPa minimum film thickness increases as babbitt orhard-polymer liner thickness increasesUnder a heavy load 2 MPa oppositeeffect.18

Max. Pad Temperature Rise [ºC]Babbitt vs Hard-Polymer Liner: Max Pad TemperatureHard-polymer Liner PadBabbitted-steel pad8080Bare Steel0.2 mm706050505 mm401 mm3 mm30202010101.50.2 mm403 mm0.5Bare Steel7060 1 mm30Speed 4 krpm,OilTemp 46 ⁰C,2.53.55 mm0.51.52.53.5Specific Load per pad [MPa]A Babbitt layer should be sufficiently thick ( 1 mm) to effectively lower the padpeak temperature rise.Even a thin 0.2 mm hard-polymer liner isolates pad from film to lower the padtemperature rise.A thick 5 mm hard-polymer liner reduces a pad temperature rise up to 30 C, ¼of that for bare steel pad.

Babbitt vs Hard-Polymer Liner: Drag Power LossHard-polymer Liner PadBabbitted-steel padDrag Power Loss [kW]330.2 mmBare Steel2.82.81 mm0.2 mm2.62.61 mm5 mm2.4Speed 4 krpm,Oil Temp 46 ⁰C,Bare Steel2.45 mm2.22.23 mm3 mm221.81.80.51.52.53.50.51.52.53.5Specific Load [MPa]Both Babitt thickness and a hard-polymer liner thickness influence thedrag power loss.Under a light specific load 2.0 MPa, due to a larger film thickness, athicker liner produces a lesser power loss,Under a heavy specific load 2.0 MPa, all pads show the same dragpower loss, as their film thicknesses are similar.20

Babbitt vs Hard-Polymer Liner: Flow RateHard-polymer Liner PadFlow Rate [LPM]Babbitted-steel pad5 mm665Speed 4 krpm,Oil Temp 46 ⁰C,5 mm53 mm3 mm441 mm31 mm3Bare Steel220.2 mm10.2 mmBare Steel10.51.52.53.50.51.52.53.5Specific Load per pad [MPa]For both hard-polymer liner-steel pad and Babbitted steel pad, the layer thicknessdoes change the flow rate, due to changes in fluid film thickness.A thick 5 mm babbitted-steel pad requires a flow rate almost twice that of thebaseline steel pad.A thin line of hard-polymer does not affect flow rate, however, a thick layer does.21

GT2019-90231ConclusionEFFECT OF PAD AND LINER MATERIALPROPERTIES ON THE STATIC LOADPERFORMANCE OF A TILTING PAD THRUSTBEARING22

ConclusionGT2019-90231 A solid hard polymer pad can improve bearingperformance for operation at a high rotor speed as it offersa low drag power loss and a large fluid film thickness. Both a solid hard-polymer pad and a hard-polymer liner ona steel pad isolate the fluid film to increase the oiltemperature near its flash point. Due to a large mechanical deformation of the hard-polymerpad, the analysis predicts lubricant cavitation at the padtrailing edge when operating under a heavy load. Compared to a Babbitted-steel pad, a thin liner of hardpolymer on a steel pad lower the pad thermal deformations reduces the fluid film thickness a lesser flow rate butmore drag power losses.23

Planned WorkGT2019-90231A hard-polymer pad improves bearing loadperformance; however, it demands a significantlylarger supply flow rate. Work will focus on modeling the effects of flowstarvation on the static load performance ofpolymer lined TPTBs to minimize the supply flowand the drag power loss.24

Thanks to the Turbomachinery ResearchConsortium for a multiple year support andcontinued interest.Questions (?)Learn more at http://rotorlab.tamu.edu25

Fellow ASME Funded by Turbomachinery Research Consortium Proceedings of ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition, June 17-21, 2019, Phoenix, USA GT2019-90231 J. Mike Walker ’66 Department of Mechanical Engineering, Texas A&M University. Introduction: Tilting Pad Thrust Bearings (TPTBs) Control rotor axial placement in rotating machinery. Advantages: low power .