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STATUS OF THRUST FOIL BEARINGS

RESEARCH FOR OIL-FREE MACHINERY

Travis CableResearch Engineer, PXG

Luis San AndrésMast-Childs Chair Professor

May

2018

BEST PAPER AWARDS 2003,2005, 2008, 2010, 2012 IGTI S&D – Microturbomachinery

High speed gas bearings for oil-free machinery

2002 2018: Multiple sponsors:

NSF, NASA GRC, Capstone MT,

Honeywell, Borg-warner, US NAVY,

TRC

FY 02-18 total: +$ 2M +Test rigs: $250 k+ Software license: $ 120k

Tested multiple foil & metal mesh bearings

4 PHDs + 4 MS + 2UGs/year.

35+ journal papers & many invited lectures

Max surface speed (130 m/s: 70 krpm). Max

dyn. load 100 lbf @ 500 HZ

Status of Thrust Foil Bearing Research

• TRC sponsored effort to

bring metal mesh thrust

foil bearings (MMTFB) to

a commercialization level (Fall of 2015 -Summer 2017).

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• Rayleigh-step MMTFB proved unsuccessful, while another

design worked: a tapered TFB supported a moderate load

W/A~ 3.75 psi.

• TRC & PI funds produced a fully operational test rig for thrust

foil bearings.

• Research with MMTFB continued (unfunded) until the end of

2017.

Existing Test Rig for Thrust Foil Bearings

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A Test Rig for Thrust Foil Bearings

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Shaft Speed, RPOΩ 40 krpm, 212 m/s

Drive Motor Torque 1.1 N.m

Bearing OD Limit 102 mm

Static Load 0 - 580 N

Dynamic Load 0 – 100 N

Cooling Flow 0 – 500 SLPM

Specifications Capabilities:

For specified applied load, shaft

speed, and cooling flow

• Static break-away torque and lift-

off drag torque

• Bearing static stiffness (load vs

deflection)

• Dynamic axial force coefficients

• Pad Temperatures

A RAYLEIGH-STEP METAL MESH

THRUST FOIL BEARING (MMTFB) AND

ITS FAILURE

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Assembled Metal Mesh Thrust Foil Bearing

Dimensions Support Mesh

Material 316 S-Steel Copper

Inner Diameter 45.72 mm 50.8 mm

Outer Diameter 120.65 mm 120.65 mm

Thickness 9.53 mm ~0.40 mm

Rayleigh Step Top Foil

Material 316 Stainless Steel

Coating Parylene® N

Coating Thickness 3 μm

Number of Pads, NPAD 6 [-]

Outer Pad Diameter, DPO 101.6 mm

Inner Pad Diameter, DPI 50.8 mm

Pad Arc Extent, θP 45 °

Step Depth, hS 19 μm

Top Foil Thickness, ttf 0.127 mm

6-Pad Metal Mesh Foil Thrust Bearing

6-Pad Bump Type Foil Thrust Bearing [1]

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.

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Tests with Rotor Speed (Summer 2017)

Rotor brought to 40 krpm and MMTFB pushed against thrust collar

(applied load W/A=7 kPa).

Drag torque increased quickly with

time and pad #3 showed a

temperature rise of ~30 C in 15 s

solid contact & burnt!

.

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Failure of Three Prototype MMFTBs

• Tests with three Rayleigh-step top foils and three sheets of 40

OPI mesh produced solid contact between top foil and rotor

collar.

• Rubbing burned top foils and removed steps.

• Failure due to waviness of mesh and lack of anchor on

leading edge of top foils (windage effect).

Back to Basics

TAPERED PAD

METAL MESH THRUST FOIL BEARING

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Single pad (55 arc)

coated with MOS2

Three 40 OPI metal mesh creates a taper

height of ~0.12 mm.

Thermocouple locates just before the transition

from taper to land section.

.

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Test with Tapered MMFTB (six pad)

• At rotor speed 40 krpm, load in steps applied

to target 5 psi (35 kPa). (300 SLPM cooling)

• A load maintained for 60 s; torque increases

in steps but temperature increases steadily.

• Contact for W/A > 3.6 psi (26 kPA)

contact

kPa

New Proposal

MEASUREMENT OF LOAD

CAPACITY, DRAG TORQUE

AND TEMPERATURE IN A

THRUST FOIL GAS BEARING

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New Proposed Work 2018-2019

1. Revamp test rig with intermediate shaft between the

router motor and thrust collar improve alignment.

2. Test a Trust Foil Bearing from Oil-Free Turbomachinery.

3. Measure TFB load capacity and drag torque and top

foil temperature vs. rotor speed vs. cooling flow.

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Budget

Support for graduate student (20 h/week) x $ 2,200 x 12 months $ 26,400

Fringe benefits (2.4%) and medical insurance ($422) x 12 months $ 5,698

Tuition & fees three semesters (24 ch) $ 13,275

Conference travel and registration $ 1,800

Supplies: bearing parts and rig ancillary parts $ 2,827

Total BUDGET $ 50,000

MEASUREMENT OF LOAD CAPACITY, DRAG TORQUE AND TEMPERATURE IN A THRUST FOIL GAS

BEARING

Test program will continue to show commitment of TAMU-TL, supported

by TRC, to develop sustainable and energy efficient oil-free

turbomachinery.

Questions (?)

Thanks to TRC for past support

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