a test rig for evaluation of thrust bearings and face...

A Test Rig For Evaluation of Thrust Bearings and Face Seals

Luis San AndrésMichael Rohmer

May 2014

TRC Project 32513/1519F2 TRC-B&C-03-2014

Justification

• Compressors, turbochargers, turbo expanders, blowers, etc., rely on thrust bearings

• as they are the primary means of axial load support and rotor position.

• Axial loads in turbomachinery are speed and pressure dependent,

• their prediction is largely empirical.

• Thrust bearing design relies on validated models, • experimental results will benchmark predictive

tools for thrust bearings.

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0 6 12inch

USET Thrust Bearing Test Rig

0 2 4 in

Radial Bearings

Test Thrust Bearing

Rotor

Slave ThrustBearings

USET Research Program (2005-2008): $787,300Test Rig: $288,500

3

Objective and Tasks (2005-2008)

• Design and construction of thrust bearing test rig.• Measurements of minimum film thickness, pocket

pressures, and flow rates in a water hybrid thrust bearing at various speeds and loads.

• Comparison of test data to prediction of performance from XLHYDROTHRUST.

Test rig funded by USET (AF) program

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Cross Section of Thrust Bearing Test Rig

Rotor Assembly

0 2 in 4 in

Air Buffer Seals

Slave Thrust Bearing

Radial Hydrostatic Bearings

Aerostatic Bearings

Shaker

Thrust Load Mechanism

Test Thrust Bearing

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Schematic Thrust Bearing Test Rig

TB load shaft + housing (3.4 lb)

Rotor (8.7 lb)

Thrust Bearings (Test & Slave): Kz, Cz

Radial (water) Bearings: Kxx, Kxy, Kyx, Kyy, Cxx, Cyy, Cxy, CyxRadial (air) Bearings: Kxx, Kyy, Cxx, Cyy

Test Thrust

Bearing

Axial Force

(8.5 lb)

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Test Results and Predictions

TB clearance vs. load at rotor speeds of 7.5 krpm, 12.5 krpm, and 17.5 krpm.

San Andres, 2008, JANAFF paper

250 psi

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Exploded view of Thrust Bearing Test Rig

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2013 Test Rig Lubricated with Air

Test rig modified to operate with air.

Designed and manufactured flexure

pivot, 4 pad hybrid bearings ($7,500).

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Test Rig Failure with Air Bearings

With supply pressure at 4.14 bar, rotor stable to 27 kRPM.

At 28 kRPM, the test rig made a loud noise: the shaft

banged the bearings. An emergency stop caused the

coupling to break.

The rotor, journal bearings, slave thrust bearing,

experienced extensive damage.

(467 Hz)

(100 Hz)

Amplitude of radial rotor motion vs. rotor speed for operation at various supply pressures. Rotor supported on air lubricated bearings.

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Waterfall: DFT amplitude vs rotor speed.

Ps=6.89 bar Ps=5.52 bar

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27,000 RPM

Waterfall: DFT amplitude vs rotor speed.

Ps=4.14 bar

…… an instant later failure!

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Flexible Coupling Failure and RepairRuptured Diaphragm

New Diaphragm

$67802.5 months

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Rotor Damage and Repair

• Grinded and Chromeplated($958)

• Balanced ($787)

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Journal Bearings Failure and Replacement

Tilting Pad

Welded

Orifice Land Pocket

$ 7,500 lost

Original (water lubricated)

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Air Buffer Seals Damage and Repair

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Slave Thrust Bearing Damage and Repair

EpoxyOrifice

Pocket LandOrifice

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2013-14 Revamp TEST RIG

Repair flexible coupling $6,780Grind and chromeplaterotor $958

Balance rotor $787Replace journal bearings Available

Lapp slave bearing AEROshop

Repair air buffer seals In houseBuild water manifold $944Adjacent piping $501Hardware and tools $253Total $10,271

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Not budgeted

Rotor natural frequency and free-free mode shape

1760 Hz (test)1830 Hz (XLTRC2)

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Coupling natural frequencies and free-free mode shapes



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Current Status of Test Rig

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• Rotor, journal bearings, slave thrust bearing, and air buffer seals installed

• Water supply and exhaust lines completed.

• Future Work:• Install the coupling• Align the rotor• Install instrumentation• Install the thrust

bearing and loading assembly

Proposed Work 2014-2015• Complete revamping of test rig: alignment of rotor,

installation of instrumentation• Measurements of minimum film thickness vs. thrust

load (max. 20 krpm) and supply pressure to 6 bar for a water lubricated hybrid thrust bearing

• Compare measurements to predictions from thrust bearing code

• If time allows: test oil lubricated thrust bearing.

Max speed: 20 krpmBearing OD: 3 inch (76 mm)

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Flexure Pivot Tilting Pad Hybrid Bearings

water lubrication

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Hybrid Thrust Bearings

water lubrication

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TRC Budget 2014-2015Support for graduate student (20 h/week) x $2,200 x 12 months

$ 25,200

Fringe benefits (2.4%) and medical insurance ($118/month) $ 2,368Tuition three semesters ($362 credit hour X 24 h/year) $ 8,686PC with DAQ system $ 3,500Travel to US Conference $ 1,200Supplies: piping, cables, etc. $ 800Total $ 42,662

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Questions (?)

TRC-B&C-03-14A Destructive Failure Incident and Revamping of the Thrust Bearing Test RigMichael Rohmer and Luis San Andrés

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Test Rig Operation (Static Load Tests)

• Supply pressure to air buffer seals (75 psia)• Open water lines and supply pressure into radial bearings

(75 psia).• Supply pressure to gas bearings supporting axial load arm

(75 psia).

• Set supply pressure to thrust bearings (75 psia)• set thrust bearings at nominal clearance (3 mil)• set rotor speed (max 20 kRPM).• Shaker applies axial load: increasing and decreasing• Measure rotor axial displacements at test and slave

bearings.Record flow rates, pocket pressures, and supply and discharge temperatures and pressures.

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Test Rig Instrumentation

• 4 eddy current sensors: rotor lateral motions at each thrust collar, 2 x 2 (X,Y)

• 6 eddy current sensors: rotor axial and tilt motions at each thrust collar; 2 x 3 (120 deg)

• 1 strain gauge load cell: axial load applied by shaker• 2 turbine flow meters: flow into test thrust bearing and flow

out of inner diameter of test thrust bearing • 1 tachometer: rotor speed• 3 strain gauge pressure sensors: pressure in pockets (2)

and on land (1) of test thrust bearing• 8 pressure transducers: supply pressure of each bearing

and air buffer seals, and discharge pressure of test thrust bearing

• 4 thermocouples: inlet temperature of each bearing and discharge temperature of test thrust bearing

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Components of Motor Drive System

SKF Precision/Gilman TechnologiesSpindle Motor Drive (D45985)22KW (30 HP) @ 30,000 RPMConstant torque 0 – 30,000 RPM (62 lb-in

torque)Digital closed-loop speed control with

LabView interfaceWater chillerAll subsequent required hardware and

software

Coupling Corp. of America (CCA), Custom Coupling

- FLEXXOR Twin-diaphragm or Quill shaft design with Anderson Locking hub(s)

30,000 RPM Maximum speed rating825 lb-in max. continuous torque+/- 0.024-0.048 inch Axial Travel allowance (> 8X req’d.)Low axial spring rate (0.01 - 0.02 lb/0.001 inches)Weight: 2.1 – 3.5 lbs.Inertia (Ip): 2.6 – 5.3 lb-in 2̂ 29

a test rig for evaluation of thrust bearings and face...

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