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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.
2
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
4
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
5
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)
6
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
7
Exploded view of Thrust Bearing Test Rig
8
2013 Test Rig Lubricated with Air
Test rig modified to operate with air.
Designed and manufactured flexure
pivot, 4 pad hybrid bearings ($7,500).
9
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.
10
Test Rig Failure with Air Bearings
Waterfall: DFT amplitude vs rotor speed.
Ps=6.89 bar Ps=5.52 bar
11
Test Rig Failure with Air Bearings
27,000 RPM
Waterfall: DFT amplitude vs rotor speed.
Ps=4.14 bar
…… an instant later failure!
12
Flexible Coupling Failure and RepairRuptured Diaphragm
New Diaphragm
$67802.5 months
13
Rotor Damage and Repair
• Grinded and Chromeplated($958)
• Balanced ($787)
14
Journal Bearings Failure and Replacement
Tilting Pad
Welded
Orifice Land Pocket
$ 7,500 lost
Original (water lubricated)
15
Air Buffer Seals Damage and Repair
16
Slave Thrust Bearing Damage and Repair
EpoxyOrifice
Pocket LandOrifice
17
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
18
Not budgeted
Rotor natural frequency and free-free mode shape
1760 Hz (test)1830 Hz (XLTRC2)
19
Coupling natural frequencies and free-free mode shapes
496 Hz (test)487 Hz (XLTRC2)
1504 Hz (test)1524 Hz (XLTRC2)
20
Current Status of Test Rig
21
• 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)
22
Flexure Pivot Tilting Pad Hybrid Bearings
water lubrication
23
Hybrid Thrust Bearings
water lubrication
24
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
25
Questions (?)
TRC-B&C-03-14A Destructive Failure Incident and Revamping of the Thrust Bearing Test RigMichael Rohmer and Luis San Andrés
26
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.
27
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
28
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