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Helicoflex Seals

Helicoflex Seals. Stephen Haywood Rutherford Appleton Lab & Martin Gibson With input from Jason, Ian and Garlock. The Order. Ordered on Fri 10 Feb. Arrive Mon 27 Mar – 6 weeks later. Cost £23k

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Helicoflex Seals

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  1. Helicoflex Seals Stephen Haywood Rutherford Appleton Lab & Martin Gibson With input from Jason, Ian and Garlock

  2. The Order • Ordered on Fri 10 Feb. • Arrive Mon 27 Mar – 6 weeks later. • Cost £23k • Understood to be a simple change of coating from Al to Cu – therefore similar mechanical properties. • Qualify surface effects – crushing of Cu into Cu-Ni Housing. • Garlock quoted and supplied a “D” Seal – in order to make easier to compress. Helicoflex Seals 2

  3. First Assessment • Martin Gibson was ready to test Seals when they arrived. • Immediately realised they were difficult to tighten: • Not able to completely compress. • Broke Ti bolt. • Should bottom out Seal: Helicoflex Seals 3

  4. Bottoming Out Seal • Bottoming out is important: • Gives correct compression of Seal (good sealing, retain elasticity provided by internal spring). • Requires “groove” in Housing to be correctly designed. • When clamped in position, ensures that joint cannot flex. • Flexing may allow Seal to be compressed and then since elasticity is small (10%?), may not spring back and result in leak. • Seal nominally 1.64 mm (measure 1.68 mm). • Housing groove 1.2 mm • Compressed by ~0.32 mm. • Implies 0.12-0.16 mm to go until bottom out. Helicoflex Seals 4

  5. Seals in Housings Helicoflex Seals 5

  6. PPF0 Helicoflex Seals 6

  7. Housing Helicoflex Seals 7

  8. Investigation • Dissect old Al and new Cu Seals. • Jacket is solid metal. • Cu has larger Young’s Modulus than Al (factor of 2). • Cu supposed to be 0.25 mm thick; Al 0.30 mm – but Cu looks thicker (optical effect ?). • Cu Seal is much harder to twist. • “D” Seal is not quite as we expected: • Martin and Stephen trying to progress while Jason and Ian saturated with HEX work. Helicoflex Seals 8

  9. Cu Seal Helicoflex Seals 9

  10. Dissected Seals Helicoflex Seals 10

  11. Were We Sold Wrong Seal? • We supplied design of Housings and asked for Cu Seal. • Seals are made to order, but not to measure. • The Seal we bought should be compressed by 0.34  0.1 mm. • Our Housing would require this seal to compress 0.44 mm. • No discussions about compression forces. • Should design Housing to suit a Seal. • Flukey (in retrospect) that this Seal does “suit” design. • Appears that compression forces for Al and Cu Seals are same – albeit Al not compressed enough and Cu required to be compressed to upper limit. • Cannot complain that we were sold wrong Seal. Helicoflex Seals 11

  12. Qualification • Pursued 1st half of Qualification to see if the Seals could work. • Tightened Seals to nominal torque (100 or 170 cN.m). • Qualification: • He Vac leak check • 25 bar N2 proof test • 7 bar He leak check at 0oC • 1 bar He leak check at -35oC • (Thermal Cycle) • (Pressure Cycle) • Takes much longer than originally suggested. • 8/9 OK so far; one fails on 25 bar test – not yet investigated. Helicoflex Seals 12

  13. Possibilities • Keep Al Seals – worried about corrosion. • Cu-plate Al Seals – already squashed; need new ones. • Some new type of material for seal ? • Cu Seal: • Increase torque with washers & lubricant – damage Al clamp plates (bend; strip thread) • Leave them not bottomed-out – Jason is not happy • Change Housing – no way ! • Thin washer to force earlier bottoming out – very fiddly • Thin ring to force earlier bottoming out – very fiddly; not room • Pre-squash by 0.2-0.3 mm • Could Garlock supply a better suited Seal or modify existing Seals – I would be very nervous about this Helicoflex Seals 13

  14. Questions • Does it work if only compress by ~0.2-0.3 mm – do surfaces (Seal/Housing) conform ? • How does Seal behave if pre-squash by ~0.2-0.3 mm – will compression forces required still be large ? • Will ask Garlock for advice. Helicoflex Seals 14

  15. Pre-squash • Use washers and lubricate – allows torque to give greater compression (reduces friction). • Pre-squash by ~0.20 mm; ~0.24 mm to b-o; stops with ~0.10 mm to go – but ripped threads. • Use nuts. • Pre-squash by ~0.30 mm; ~0.14 mm to b-o; bottoms out – but badly bend Al compression plates. • Will repeat with new Al plates. • Check Al plates are Dural – as in production. Helicoflex Seals 15

  16. … And • If pre-squashing fails, consider washers.Thin and hard to locate. • When we have found solution which is OK: • Mechanically – bottoms out, doesn’t wreck clamps/bolts • Leak tight will qualify from scratch. • Note: assuming we replace Al Seals, must be very careful not to scratch Housings – use plastic tweezers. 0.6 mm 0.8 mm Helicoflex Seals 16

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