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

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



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



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



Test Conditions

Full strokes- 3 ½ inches, 1 ½ second period



Test Conditions

Seal cavity was plumbed to drive actuator.



Test Conditions

Dither in place – ¼ inch, 4 Hz



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



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



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



Rod #1 WC/17CoCoarse Finish

20X

100X

Surface FinishRa 9 13 12Rz 637987Ry 6794181



Rod #1 WC/17CoFine Finish

20X

100X




Rod #2 WC/10Co4CrCoarse Finish

20X

100X




Rod #2 WC/10Co4CrFine Finish

20X

100X




Rod #3 WC/17Co 0.010”

Coarse Finish

20X

100X




Rod #3 WC/17Co 0.010”Fine Finish

20X

100X




Rod #4 Tribaloy T-400Coarse Finish

20X

100X

Surface FinishRa 17 18 18Rz 276 228 220Ry 299 287 264



Rod #4 Tribaloy T-400Fine Finish

20X

100X

Surface FinishRa 13 16 12Rz 205 220 189Ry 287 350 248



HVOF Results






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



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



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



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



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



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



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



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



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



20X

Pre-Test Post-Test

100X

Damage accumulated on chrome plated rod during 100 hour endurance test

Typical Chrome Rod



20X

Pre-Test Post-Test

100X

After 100 hour endurance test, there is no visible surface damage on HVOF rod

HVOF Rod 1



20X

Pre-Test Post-Test

100X

No visible damage to HVOF coated rod during 100 hour endurance test

HVOF Rod 2



20X

Pre-Test Post-Test

100X

HVOF rod surface was comparable to pre-test conditions

HVOF Rod 3



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



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



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



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

Documents

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