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

Understood

to be a simple change of coating Cu – therefore similar mechanical properties.

from Al to Qualify surface effects – crushing of Cu into Cu-Ni Housing.

Garlock quoted and supplied a “ D ” Seal make easier to compress.

– in order to Helicoflex Seals 2 Stephen Haywood 4 Apr 2006

First Assessment

   Martin Gibson arrived.

was ready to test Seals when they Immediately realised they were difficult to tighten:  Not able to completely compress.

 Broke Ti bolt.

Should bottom out Seal: Stephen Haywood Helicoflex Seals 3 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 4 Stephen Haywood 4 Apr 2006

Seals in Housings

Stephen Haywood Helicoflex Seals 5 4 Apr 2006

PPF0

Stephen Haywood Helicoflex Seals 6 4 Apr 2006

Housing

Stephen Haywood Helicoflex Seals 7 4 Apr 2006

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.

Stephen Haywood Helicoflex Seals 8 4 Apr 2006

Cu Seal

Stephen Haywood Helicoflex Seals 9 4 Apr 2006

Dissected Seals

Stephen Haywood Helicoflex Seals 10 4 Apr 2006

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 Stephen Haywood 4 Apr 2006

Qualification

     Pursued 1 st half work.

of Qualification to see if the Seals could Tightened Seals to nominal torque (100 or 170 cN.m).

Qualification :  He Vac leak check   25 bar N 2 proof test 7 bar He leak check at 0 o C  1 bar He leak check at -35 o C  (Thermal Cycle)  (Pressure Cycle) Takes much longer than originally suggested.

8/9 OK so far; one fails investigated.

on 25 bar test – not yet Helicoflex Seals 12 Stephen 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 13 Stephen 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.

Stephen Haywood Helicoflex Seals 14 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 15 Stephen Haywood 4 Apr 2006

… And

 If pre-squashing fails, consider washers .

Thin and hard to locate.

0.6 mm 0.8 mm  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 .

Stephen Haywood Helicoflex Seals 16 4 Apr 2006