Helicoflex Seals

Stephen Haywood Rutherford Appleton Lab& Martin Gibson

With input from Jason, Ian and Garlock

Helicoflex Seals 2Stephen Haywood 4 Apr 2006

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 “” Seal – in order to

make easier to compress.

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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 4Stephen Haywood 4 Apr 2006

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 5Stephen Haywood 4 Apr 2006

Seals in Housings

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PPF0

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Housing

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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. “” Seal is not quite as we expected:

Martin and Stephen trying to progress while Jason and Ian saturated with HEX work.

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Cu Seal

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Dissected Seals

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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 12Stephen Haywood 4 Apr 2006

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 13Stephen Haywood 4 Apr 2006

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 14Stephen Haywood 4 Apr 2006

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 15Stephen Haywood 4 Apr 2006

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 16Stephen Haywood 4 Apr 2006

… 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