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Navy Rod Seal Testing

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 Several seal configurations were evaluated at elevated temperatures against chrome plated rods (8-12 Ra)

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Navy Rod Seal Testing

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  1. Navy Rod Seal Testing Project Status as of 1 Sept 2002 Results from Rod Seal Testing Under Severe Conditions

  2. Testing Strategy Phase One – Seal Material Selection • Several seal configurations were evaluated at elevated temperatures against chrome plated rods (8-12 Ra) • Resulting materials should be good candidates for updating seals in actuators with chrome plated actuator rods Phase Two – HVOF Rod Coatings • Several HVOF surface coated rods will be evaluated against seals selected from Phase One under the same test conditions • Result is wear resistant surface coating with equivalent or better than chrome for seal service life

  3. Test Conditions Testing Details • Testing was performed in blocks of 16 hours • Temperature was 300°F (149°C) for first testing block and was reduced 25°F (14°C) for each subsequent block • Seals were cold soaked to 0°F (-17.8°C) between testing blocks to evaluate startup leakage • Internal pressure of the stand was connected to the drive actuator and varied constantly from 500 psi to 2500 psi (3 to 17 MPa) • Each hour consisted of 20 minutes of full strokes, 20 minutes of superimposed dither and 20 minutes of dither in place

  4. Test Conditions Full strokes- 3 ½ inches, 1 ½ second period

  5. Test Conditions Seal cavity was plumbed to drive actuator.

  6. Test Conditions Dither in place – ¼ inch, 4 Hz

  7. Seal Material Selection

  8. Seal Material Selection Seal Material Results • One vendor’s seals leaked early on and continued to leak suggesting a material or seal dimension problem • Nitrile and Improved Nitrile baseline seals have proven unacceptable in this test and in the field • Engineered elastomer configurations showed steady leakage with increased leakage during low temperature startup and some produced tar like sludge at the rod seal interface. • Several PTFE spring energized seals showed no measurable leakage throughout testing

  9. HVOF Rod Test Plan HVOF Test Strategy • PTFE spring energized seals showed none of the elastomer related degradation (high temperature damage or low temperature startup leakage) • 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 • Seals selected for HVOF testing were damage resistant coil spring energized PTFE seals from two vendors

  10. HVOF Test Rods Test Rods for HVOF Coating Endurance Test • 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 • Rods as received were much coarser than desired • Rods were installed with PTFE seals from two vendors and tested to Phase One stroking profile to evaluate rod surface wear and seal abrasion • Several of the rod/seal combinations completed the 100 hour test with no measurable leakage

  11. Rod #1 WC/17Co Coarse Finish 20X Surface Finish Ra 9 13 12 Rz 63 79 87 Ry 67 94 181 100X

  12. Rod #1 WC/17Co Fine Finish 20X Surface Finish Ra 5 4 7 Rz 35 31 55 Ry 43 47 67 100X

  13. Rod #2 WC/10Co4Cr Coarse Finish 20X Surface Finish Ra 6 6 6 Rz 43 51 43 Ry 51 67 51 100X

  14. Rod #2 WC/10Co4Cr Fine Finish 20X Surface Finish Ra 5 5 4 Rz 28 35 35 Ry 31 59 59 100X

  15. Rod #3 WC/17Co 0.010” Coarse Finish 20X Surface Finish Ra 7 9 7 Rz 79 59 51 Ry 94 98 59 100X

  16. Rod #3 WC/17Co 0.010” Fine Finish 20X Surface Finish Ra 6 6 6 Rz 51 43 51 Ry 71 67 71 100X

  17. Rod #4 Tribaloy T-400 Coarse Finish 20X Surface Finish Ra 17 18 18 Rz 276 228 220 Ry 299 287 264 100X

  18. Rod #4 Tribaloy T-400 Fine Finish 20X Surface Finish Ra 13 16 12 Rz 205 220 189 Ry 287 350 248 100X

  19. HVOF Results

  20. Seal Material Selection

  21. 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 testing • Conclusion • Fine finish seems easier on seal and produced less leakage through testing

  22. 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 leakage • Conclusions • Vendor 1 appears to work better on the coarse finish • Vendor 2 appears to work better on the fine finish

  23. 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 testing • Conclusions • While both seals show acceptable performance, Vendor 2 seems more prone to leakage

  24. 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 testing • Conclusions • Fine finish seems easier on seal and produced less leakage through testing

  25. 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

  26. 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 testing • Conclusions • Fine finish seems less damaging to seals and produced less leakage during testing

  27. 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 testing • Conclusions • Vendor 1 seal seems to perform better against a coarse surface finish

  28. 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 surface • Conclusions • Vendor 2 seals are prone to initial leakage and appeared to perform better against a fine surface finish

  29. Leakage Summary Seal Performance Conclusions • Except for 2 installations, all seals performed significantly better than baseline Nitrile seals against chrome rod • Fine surface finish seems easier on seal and produced less leakage through testing • Vendor 1 appears to work better on the coarse finish • Vendor 2 appears to work better on the fine finish • Seals from vendor 2 developed early leakage that tended to correct later in testing • Leakage growth on HVOF rods was equivalent to leakage growth on chrome plated rods under these test conditions

  30. Typical Chrome Rod 20X Pre-Test Post-Test 100X Damage accumulated on chrome plated rod during 100 hour endurance test

  31. HVOF Rod 1 20X Pre-Test Post-Test 100X After 100 hour endurance test, there is no visible surface damage on HVOF rod

  32. HVOF Rod 2 20X Pre-Test Post-Test 100X No visible damage to HVOF coated rod during 100 hour endurance test

  33. HVOF Rod 3 20X Pre-Test Post-Test 100X HVOF rod surface was comparable to pre-test conditions

  34. 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

  35. Summary Post-Test Observations • Chrome plated rods under these conditions developed longitudinal scratches resulting in external leakage • This is a common problem on chrome plated rods removed from aircraft actuators • Inspection of HVOF rods showed wear marks and polishing but the accumulated surface damage was much less severe than with chrome plated test rods • Rod 4 with Tribaloy 400 coating showed severe wear but this is believed due to galling on pre-test surface and continued material shedding • Initial surface finish is critical because wear resistant HVOF rods will not polish up in service

  36. 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: • Viton GLT AMS-R-83485 high temperature upgraded seals to replace current Nitrile static seals • Spring energized PTFE seals in primary and secondary positions to replace dynamic rod seals • We are also working with NADEP Jacksonville to qualify HVOF as a repair process for existing chrome plated actuator rods • Air Force has expressed interest in testing direct contact elastomer seals against HVOF rods

  37. Reported Problem Problem Details • One commercial carrier in Europe has reported problems with premature seal wear and external leakage • Aircraft operated by same carrier with exclusive flights inside North America do not have this problem • Inspection of failed actuators identified selective leaching of the cobalt in the HVOF matrix leaving an abrasive spongy surface producing aggressive seal wear • Actuator vendor is actively investigating this problem but mechanism is not yet well understood • Believe de-icing fluid or some other solvent is the source of problems • Expect an update during the next SAE A-6 Fluid Power Committee meeting

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