jeff moorman hydraulic systems and flight control actuators (301) 342-9373 navy rod seal testing...
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Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
Navy Rod Seal Testing
Project Status as of 1 Sept 2002
Results from Rod Seal Testing Under Severe Conditions
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
Testing Strategy
Phase One – Seal Material Selection
1. Several seal configurations were evaluated at elevated temperatures against chrome plated rods (8-12 Ra)
2. Resulting materials should be good candidates for updating seals in actuators with chrome plated actuator rods
Phase Two – HVOF Rod Coatings
1. Several HVOF surface coated rods will be evaluated against seals selected from Phase One under the same test conditions
2. Result is wear resistant surface coating with equivalent or better than chrome for seal service life
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
Test Conditions
Testing Details
1. Testing was performed in blocks of 16 hours
2. Temperature was 300°F (149°C) for first testing block and was reduced 25°F (14°C) for each subsequent block
3. Seals were cold soaked to 0°F (-17.8°C) between testing blocks to evaluate startup leakage
4. Internal pressure of the stand was connected to the drive actuator and varied constantly from 500 psi to 2500 psi (3 to 17 MPa)
5. Each hour consisted of 20 minutes of full strokes, 20 minutes of superimposed dither and 20 minutes of dither in place
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
Test Conditions
Full strokes- 3 ½ inches, 1 ½ second period
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
Test Conditions
Seal cavity was plumbed to drive actuator.
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
Test Conditions
Dither in place – ¼ inch, 4 Hz
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
Seal Material Selection
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
Seal Material Selection
Seal Material Results
1. One vendor’s seals leaked early on and continued to leak suggesting a material or seal dimension problem
2. Nitrile and Improved Nitrile baseline seals have proven unacceptable in this test and in the field
3. Engineered elastomer configurations showed steady leakage with increased leakage during low temperature startup and some produced tar like sludge at the rod seal interface.
4. Several PTFE spring energized seals showed no measurable leakage throughout testing
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
HVOF Rod Test Plan
HVOF Test Strategy
1. PTFE spring energized seals showed none of the elastomer related degradation (high temperature damage or low temperature startup leakage)
2. These seals are currently used in F/A-18 E/F, F-22, V-22 and JSF flight control actuators with excellent performance in dynamic applications
3. Seals selected for HVOF testing were damage resistant coil spring energized PTFE seals from two vendors
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
HVOF Test Rods
Test Rods for HVOF Coating Endurance Test
1. Test rods were ordered using HVOF with Tungsten Carbide, Tungsten Carbide Chrome and Triballoy 400 finished to a coarse (8-12 Ra) and a fine (4-6 Ra) surface finish
2. Rods as received were much coarser than desired
3. Rods were installed with PTFE seals from two vendors and tested to Phase One stroking profile to evaluate rod surface wear and seal abrasion
4. Several of the rod/seal combinations completed the 100 hour test with no measurable leakage
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
Rod #1 WC/17CoCoarse Finish
20X
100X
Surface FinishRa 9 13 12Rz 637987Ry 6794181
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
Rod #1 WC/17CoFine Finish
20X
100X
Surface FinishRa 5 4 7Rz 353155Ry 434767
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
Rod #2 WC/10Co4CrCoarse Finish
20X
100X
Surface FinishRa 6 6 6Rz 435143Ry 516751
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
Rod #2 WC/10Co4CrFine Finish
20X
100X
Surface FinishRa 5 5 4Rz 283535Ry 315959
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
Rod #3 WC/17Co 0.010”
Coarse Finish
20X
100X
Surface FinishRa 7 9 7Rz 795951Ry 949859
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
Rod #3 WC/17Co 0.010”Fine Finish
20X
100X
Surface FinishRa 6 6 6Rz 514351Ry 716771
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
Rod #4 Tribaloy T-400Coarse Finish
20X
100X
Surface FinishRa 17 18 18Rz 276 228 220Ry 299 287 264
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
Rod #4 Tribaloy T-400Fine Finish
20X
100X
Surface FinishRa 13 16 12Rz 205 220 189Ry 287 350 248
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
HVOF Results
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
Seal Material Selection
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
Rod 1 Details
Rod 1 Coarse Finish• Both seals vendors
developed early leakage against this surface
• Vendor 1 continued to leak at high rate
• Vendor 2 leakage corrected after 50 hours
Rod 1 Fine Finish• Neither seal showed significant leakage, but Vendor 1
seal showed steady minor leakage through testingConclusion• Fine finish seems easier on seal and produced less
leakage through testing
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
Rod 2 Details
Rod 2 Coarse Finish• Vendor 2 produced
minimal yet steady leakage running against the coarse surface
• Vendor 1 produced no measurable leakage
Rod 2 Fine Finish• Vendor 1 produced minimal yet steady leakage and
vendor 2 produced no measurable leakageConclusions• Vendor 1 appears to work better on the coarse finish • Vendor 2 appears to work better on the fine finish
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
Rod 3 Details
Rod 3 Coarse Finish• Vendor 2 seal
produced minor but steady leakage against this surface
• Vendor 1 produced no measurable leakage against this surface
Rod 3 Fine Finish• Vendor 2 seal produced minor but steady leakage against
this surface• Vendor 1 produced minimal leakage late in testingConclusions• While both seals show acceptable performance,
Vendor 2 seems more prone to leakage
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
Rod 4 Details
Rod 4 Coarse Finish• Vendor 2 showed
initial leakage against this surface and continued to leak through testing
• Vendor 1 developed steady minor leakage against this surface after 40 hours
Rod 4 Fine Finish• Vendor 1 produced little if any leakage • Vendor 2 showed steady minor leakage through
testingConclusions• Fine finish seems easier on seal and produced less
leakage through testing
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
Coarse Rods
Steady Leakers• Vendor 1 on Rod 1
and Vendor 2 on Rod 4 produced steady leakage through testing
Vendor 1• Except on Rod 1, no
Vendor 1 seals produced measurable leakage Vendor 2
• Seals from vendor 2 developed early leakage that had tendency to correct later in testing
Conclusions• Vendor 2 seals were prone to initial leakage
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
Fine Rods
Steady Leakers• Rod 4 finish was
not a fine finish and both vendors’ seals produced steady leakage
• 2 other seals produced minor leakage during testing
Minimal Leakage• Several seals developed little if any leakage during
testingConclusions• Fine finish seems less damaging to seals and produced
less leakage during testing
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
Vendor 1 Seals
Rod 1 Coarse Finish• Some condition
caused premature failure of this seal
Steady Leakers• Two other seals with
steady leakage were on fine rods
Other Seals• Most seals showed little if any measurable leakage
through testingConclusions• Vendor 1 seal seems to perform better against a coarse
surface finish
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
Vendor 2 Seals
Steady Leakage• Many of the seals
showed initial leakage that was corrected later in testing
• One seal on Rod 4 with very rough finish leaked steady through testing
Fine Finish• Two seals produced little if any measurable leakage
against a fine rod surfaceConclusions• Vendor 2 seals are prone to initial leakage and appeared
to perform better against a fine surface finish
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
Leakage Summary
Seal Performance Conclusions1. Except for 2 installations, all seals performed
significantly better than baseline Nitrile seals against chrome rod
2. Fine surface finish seems easier on seal and produced less leakage through testing
3. Vendor 1 appears to work better on the coarse finish 4. Vendor 2 appears to work better on the fine finish5. Seals from vendor 2 developed early leakage that
tended to correct later in testing6. Leakage growth on HVOF rods was equivalent to
leakage growth on chrome plated rods under these test conditions
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
20X
Pre-Test Post-Test
100X
Damage accumulated on chrome plated rod during 100 hour endurance test
Typical Chrome Rod
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
20X
Pre-Test Post-Test
100X
After 100 hour endurance test, there is no visible surface damage on HVOF rod
HVOF Rod 1
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
20X
Pre-Test Post-Test
100X
No visible damage to HVOF coated rod during 100 hour endurance test
HVOF Rod 2
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
20X
Pre-Test Post-Test
100X
HVOF rod surface was comparable to pre-test conditions
HVOF Rod 3
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
Rod 4 (Tribaloy T-400)
20X
Pre-Test Post-Test
100X
Severe damage to rod 4 appears related to poor pre-test surface finish and shedding of material
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
Summary
Post-Test Observations1. Chrome plated rods under these conditions developed
longitudinal scratches resulting in external leakage2. This is a common problem on chrome plated rods
removed from aircraft actuators3. Inspection of HVOF rods showed wear marks and
polishing but the accumulated surface damage was much less severe than with chrome plated test rods
4. Rod 4 with Tribaloy 400 coating showed severe wear but this is believed due to galling on pre-test surface and continued material shedding
5. Initial surface finish is critical because wear resistant HVOF rods will not polish up in service
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
Plan Ahead
Based on these results, results from Viton GLT testing in 1996 and reports from Canada regarding Viton packed actuators currently in service, NAVAIR is planning to qualify F/A-18 actuators with:
1. Viton GLT AMS-R-83485 high temperature upgraded seals to replace current Nitrile static seals
2. Spring energized PTFE seals in primary and secondary positions to replace dynamic rod seals
3. We are also working with NADEP Jacksonville to qualify HVOF as a repair process for existing chrome plated actuator rods
4. Air Force has expressed interest in testing direct contact elastomer seals against HVOF rods
Jeff Moorman Hydraulic Systems and
Flight Control Actuators(301) 342-9373
Reported Problem
Problem Details1. One commercial carrier in Europe has reported problems
with premature seal wear and external leakage2. Aircraft operated by same carrier with exclusive flights
inside North America do not have this problem3. Inspection of failed actuators identified selective
leaching of the cobalt in the HVOF matrix leaving an abrasive spongy surface producing aggressive seal wear
4. Actuator vendor is actively investigating this problem but mechanism is not yet well understood
5. Believe de-icing fluid or some other solvent is the source of problems
6. Expect an update during the next SAE A-6 Fluid Power Committee meeting