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 Post subject: Dyneema Rope Shrinkage...
PostPosted: Fri Aug 23, 2013 5:18 pm 
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Joined: Mon Sep 12, 2005 7:45 pm
Posts: 766
Location: United Kingdom
This post is blatantly stolen from the Merlin Rocket Forum at
http://www.merlinrocket.co.uk/forum/mai ... =1&search=

I thought it sufficiently interesting and relevant that it was worth reproducing here, I trust the poster will not object...

Quote:
Hi, First a disclosure, I'm the technical manager at Marlow so I have a vested interest.

We produce hundreds of thousands of metres of D12 type rope each year and the feedback for 99% of it is good. However we have have had rare reports like this one spanning perhaps 10 years, only 2-3 per year though. With such few reports it's difficult to pin down exactly what's happening. These reports cover several different industry areas and applications, D12 and D12 MAX, covered and uncovered ropes. We've never found a fault in the material or the construction suggesting that this shrinkage is due to the environment in which the rope is used/stored. The common factor appears to be that the ropes reduce in length while in an unloaded condition rather than when in use or even when new. What we can definitly say is:
-All the ropes are made from DSM Dyneema fibre, either SK75 or SK78.
-This phenomenon has been reported on both D12 and D12 MAX which undergo different stretching conditions.
-Dyneema does not shrink in water like some other fibres.
-Dyneema will shrink if it gets hot when under no tension.

As this can affect both D12 and D12 MAX I don't think the stretching process we put the rope through here at the factory is the cause. Some of the ropes have not been used until months after stretching so residual 'shrink back' is unlikely. We've also not seen this occur with rope in our factory.

DSM Dyneema (the fibre producer) have been informed of this in the past and heat is the only explanation they've been able to offer.

Therefore the most likely cause and the only one we've been able to re-produce in the factory here is that the ropes have been exposed to elevated temperatures while they are stored, the sort of temperatures required would be possible if they were in a mast in the sun for instance. Unfortunately this can only really be proved or disproved by feedback from people who have seen this issue and can report on the conditions the rope was under when it happened. Until then it just remains the leading theory. I also see from the previous post that it's happened to the Chinese UHPME fibre as well So it's not just us!

BTW: For the record: EB's Dynamic range is made from exactly the same fibres and has very similar construction and stretching process as the D12 so is unlikely to behave any differently in this respect :-)


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