Is dyneema rope without a sheath safe for climbing?
I recently was given some old Chouinard hexes my uncle used back in the 70s. They look great, and I see no reason why I can't re-sling them and use them as perfectly safe protection.
I've found some 5mm Dyneema rated for over 5000lbs, but I can't find any as good rope with a sheath.
I know that with Kevlar, this isn't really a problem because its abrasion resistance is so high, but what about Dyneema? Am I mistaken about Kevlar? Can I use this rope without a sheath for building anchors?
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PPE or ALL climbing gear in general should only be used if there is ZERO question in your mind about the safety of the equipment (ropes, slings, anchors, prussiks, carabiners etc). Your life depends on this stuff. Don't short cut or try to save a few bucks. Do it right or don't do it at all.
This post was sourced from https://outdoors.stackexchange.com/a/8435. It is licensed under CC BY-SA 3.0.
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Do not use this cordelette for your protections: Knots will slip so the connection of the cordelette ends to form a ring will fail under load. Only use sewed Dyneema slings.
Still Dyneema cordelettes are often used for climbing as they are much lighter for the same strength than nylon based ones. To know how this is possible despite the problem mentioned we look at the materials used to construct ropes:
Dyneema, a trademark name for high-density polyethylene (PE), Nylon (polyamid PA) and Kevlar (aramid Ar). Dyneema and Kevlar have both about 4 times more strength per diameter than Nylon. Nylon is highly elastic and breaks at ca. 37% elongation, Dyneema and Kevlar are almost static (break at 2-4% elongation). The resistance against abrasion is only given qualitatively in my source: Nylon small, Kevlar medium and Dyneema high. The melting points are 250degC for Nylon, 130degC for Dyneema and 550degC (actually it decomposes) for Kevlar.
From the image provided in your link it really looks like the Dyneema cordelette in question has no sheath. The abrasion is not a problem as it has a very high resistance, but another characteristics is: Dyneema has very low friction on itself. Never ever form a ring of Dyneema webbing or cordelette using a knot, the knot will open under tension. Only sewed Dyneema slings can be used.
For this reason dyneema cordelettes for climbing come with a sheath made from nylon or polyamid. These are perfectly suited for your case but more expensive than plain nylon cordelettes. Dyneema webbing which does not have a sheath is always sold as sewed sling.
My source is the alpine security journal bergundsteigen 3/12 "FAQs-Dyneema". It may be accessible online, but is maybe behind a paywall: http://www.bergundsteigen.at/file.php/archiv/2012/3/62-67%20%28faqs-dyneema%29.pdf
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