S TRUCTURAL FORCE COEFFICIENTS FROM METAL MESH PADS FOR A FOIL - PowerPoint PPT Presentation

TRC-B&C-02-2016 May TRC Project 2016 400124-00078 Year II S TRUCTURAL FORCE COEFFICIENTS FROM METAL MESH PADS FOR A FOIL BEARING Luis San Andrés Travis Cable Graduate Research Assistant Mast-Childs Chair Professor

Justification • Foil bearings are low maintenance mechanical elements that dispense of expensive lubrication systems, saving on footprint, weight, and cost. • Experiments with metal mesh dampers and small metal mesh foil bearings show promising damping capabilities. • OEMs/TM Users wish to extend metal mesh foil bearings to large turbomachinery applications.

Objective and Tasks Bring metal mesh foil bearings (radial & thrust) to a commercialization level 1. Construct jigs to manufacture metal mesh pads of various lengths: top foil and bearing cartridge, along with a means to verify the pads and (assembled in) bearing static structural stiffness and material damping (loss factor). 2. Document manufacturing procedure and detail steps for verification . 3. Build two low cost test rigs using commercial router motors (25 krpm) to evaluate the static load performance and drag torque of radial and thrust MMFBs . 4. Measure rotor lift-off speed and break away torque, touchdown speed and stall torque, load versus minimum film thickness, and drag power losses, over a range of shaft speeds to 25 krpm.

Components of an Assembled Metal Mesh Bearing t MM Top foil Metal mesh pad 105.4 mm 90.17 mm Journal Bearing cartridge Bearing clearance t MM Components: • Bearing cartridge • Stainless steel top foil • Metal mesh underspring structure (pads)

Metal Mesh Pad Dimensions & Compactness Ratio Five pads constructed (dimensions in mm) CR = 30% • 7.36 mm thick pad gives a null clearance for the assembled bearing m  MM CR Compactness ratio for a metal mesh pad:  V copper MM CR ~ 30% is desirable

Industrial Metal Mesh Overlapping mesh makes for inconsistent thickness when compressed [a] Inconsistent wire mesh Copper mesh from TWP Inc. Parameter Magnitude Mesh Size 16 per in Wire Diameter 0.011 in [b] Wire mesh from TWP Inc. [5] Opening 0.051 in Weight/square foot 0.14 lb/ft 2 557 lb/ft 3 Density of copper

Pad Forming 1 1. A length of copper mesh is cut and weighed until achieving the desired mass (91.8 g) Digital Scale (+/- 0.05 g) 2. The strip of mesh is then folded end over end in a wooden jig to maintain the pads parallelism 2

Pad Compression After 10 s., pad removed from the compression jig and its thickness measured. A hydraulic press applies a load of 3,000 psi for a If pad is thicker than desired, pad short time (10 sec.) to recompressed under a load of 500 psi compress the metal mesh until the desired thickness is obtained. pad.

A Test Rig for Metal Mesh Pads [a] Isometric view [b] Cross-section view Test rig provides the ability to measure pad thickness, as well as perform static load vs deflection and dynamic load measurements.

Sliding Assembly Load cell location Eddy current sensors Dowel pin locations Accelerometer location [a] Isometric view [b] Side view Static load tests: Sliding assembly connects to vertical mill chuck via a strain gauge load cell, moved up and down by mill lever. Dynamic load tests: Sliding assembly connects to an electromagnetic shaker via a dynamic load cell, moved up and down by the e-shaker permanent magnet.

Thickness Measurements Thickness measurements with calipers or micrometers are inaccurate MM test rig installed in a vertical mill. First touch thickness 2.22 N (0.5 lbf). Design = 7.36 mm First touch thickness measurements provide a repeatable and accurate metric for comparing metal mesh pads. Metal Mesh Thickness [mm] Trial 1 Trial 2 Trial 3 Trial 4 Trial 5 Average Pad #1 7.59 7.59 7.59 7.59 7.59 7.59 Pad #2 7.54 7.54 7.54 7.54 7.54 7.54 Pad #3 7.61 7.61 7.61 7.61 7.61 7.61 Pad #4 7.29 7.29 7.29 7.29 7.29 7.29 Pad #5 7.60 7.60 7.60 7.60 7.60 7.60

Load vs. Deflection for MM Pads [a] Load vs. deflection [b] Structural stiffness versus deflection 1. Large initial displacements up to 100 N [ W / A pad ~ 17 kPa)] 2. Pads demonstrate similar, but not identical structural stiffness. Pad #4 is noticeably different. 3. Max structural stiffness of ~ 2.9 MN/m for the largest applied load of 900 N ( W/A pad = 200 kPa)

A Test Rig for Metal Mesh Pads         2 Mx C x K K x F t MM MM S   F     2 Re   M K eq   X   F   Im   C MM   X [a] Isometric view [b] SDOF Model Measured dynamic force, sliding assembly acceleration and sliding assembly displacements. Modeled as a simple single degree of freedom (SDOF) system with a mass, linear spring and damper.

Dynamic Load Measurements for MM Pads [a] Real part of complex stiffness [b] Imaginary part of complex stiffness 1. Real part of complex stiffness is representative of a SDOF system with a linear spring 2. Imaginary part shows a general decrease with excitation frequency, not representative of linear viscous damping. 3. Trends and magnitudes are almost identical, despite differences in pad thicknesses.

Structural Stiffness for Metal Mesh Pads Applied mechanical preload W = 60 N, W/A pad = 14 kPa. Motion amplitude of 20 μ m peak-peak Pad #1 Pad #2 Pad #3 Pad #4 Pad #5 Linear stiffness coefficient, K MM [MN/m] 0.96 1.70 1.64 1.96 1.59 Excited Mass, M [kg] 2.91 2.93 2.89 2.92 2.98 K M Natural Frequency, [Hz] 92 122 121 131 117 MM R 2 Value [-] 0.986 0.994 0.995 0.996 0.995 1. Structural stiffness values for Pads 2-5 are similar ~ 1.75 MN/m. 2. Despite similar static load vs deflection results, Pad #1 is displays lower dynamic stiffness K MM .

Material Loss Factor for Metal Mesh Pads Applied mechanical preload W = 60 N, W/A pad = 14 kPa. Motion amplitude of 20 μ m peak-peak   Im F / X   K MM Material loss factors for Pads 1-5 4 5 Pad # 1 2 3 Average loss factor, γ 0.43 (±0.23) 0.22 (±0.05) 0.24 (±0.05) 0.20 (±0.04) 0.24 (±0.05) Material loss factors are similar ( γ ~ 0.22). Uncertainty shows Pad #1 results are likely in error.

Dynamic Load Measurements for Pad #5 [b] Increasing amplitude of motion [a] Increasing mechanical preload Fixed mechanical preload of Fixed amplitude of motion of W = 60 N, W/A pad = 14 kPa 20 μ m peak-peak 1. Dynamic stiffness ( K MM ) for Pad #5 increases linearly with mechanical preload, but decreases (linearly) with amplitude of motion. 2. Dynamic stiffness ( K MM ) for Pad #5 differs from the static stiffness, derived from load vs. deflection tests. More pronounced at larger loads ( W >30 N).

Dynamic Load Measurements for Pad #5 γ avg ~ 0.22 [a] Increasing mechanical preload [b] Increasing amplitude of motion Fixed amplitude of motion of Fixed mechanical preload of 20 μ m peak-peak W = 60 N, W/A pad = 14 kPa 1. Loss factor ( γ ) for Pad #5 is not significantly affected by mechanical preload or amplitude of motion. 2. General decrease of loss factor ( γ ) for Pad #5 with increasing excitation frequency (30-300 Hz).

Schematic of an Envisioned Test Rig Test rig similar to that presented in Refs. [6,7] Non-rotating section E-shaker Static loading plenum Compression Spring Torque measurement Aerostatic guide bearing apparatus Test thrust bearing holding apparatus Router motor (40 krpm) Thrust runner and rotating shaft Rotating section Front View

Loading Mechanism for a Test Rig [a] Front view of a static loading [b] Cross section view of a static mechanism for a foil bearing test rig Loading mechanism for a foil bearing test rig Test rig similar to that presented in Refs. [6,7]

Continuation Proposed Work 2016-2017 1. Refine test rig for the dynamic load characterization of metal mesh pads. 2. Assemble a radial MMFB (5 pads), mount it atop a rotor and measure its lift-off speed and other parameters for shaft speeds up to 40 krpm and an increasing static load (specific loads up to ~180 kPa, W ≤ 300 lbf). 3. Complete design and construct a novel metal mesh foil bearing. 4.Complete the construction and troubleshoot a test rig for evaluation of foil thrust bearings and perform static load tests with the novel thrust bearing.

TRC Budget 2016-2017 Support for GS (20 h/week) x $ 2,400 x 12 months $ 28,800 Fringe benefits (2.7%) and medical insurance ($377/month) $ 5,300 Tuition three semesters ($ 363 credit hour x 24 ch/year) $ 9,090 Travel and registration to a technical conference $ 1,200 Total Cost: $ 44,390

Questions (?) TRC-B&C-02-16 S TRUCTURAL FORCE COEFFICIENTS FROM METAL MESH PADS FOR A FOIL BEARING Travis Cable and Luis San Andrés Thanks to TRC for their support