What are kevlar ropes
Polyamide, Dyneema or Kevlar? Material and knot science
In mountaineering and climbing, three types of “soft materials” - that is, slings and cords, climbing harnesses and ropes - are used in particular: polyamide, polyethylene (better known under the brand name Dyneema) and aramid (known as Kevlar). These materials have different properties that every mountaineer should be aware of in the interests of their own safety.
Polyamide (nylon) - the rubber material in climbing
Polyamide - also known under the brand name nylon - is the classic among climbing materials. The first climbing ropes made of polyamide enabled a completely new level of reliability. Without them, climbing would be inconceivable in its current form. Depending on how they are manufactured, there are dynamic ropes (which may stretch up to 40 percent in the event of a standard fall) or semi-static ropes. But also climbing harnesses or via ferrata sets are now often made of polyamide.
One advantage of the material has already been mentioned: polyamide is very elastic. It can stretch significantly more before it breaks. However, in comparison, the material is also somewhat thicker and heavier than aramid and polyethylene.
Polyethylene (Dyneema) - flyweight on the rock
Polyethylene - better known under the brand name Dyneema from the Dutch manufacturer Royal DSM N.V - is very light and has a high cut resistance. That's why there was initially a lot of hype about this new miracle material.
That has since settled: Although Dyneema has a significantly higher tensile strength than polyamide, which is why the loops are significantly narrower, when it comes to elongation, polyethylene lags behind polyamide with around 3.5 percent elongation. In addition, the knotability is much worse due to the smooth surface, which also harbors potential hazards.
Aramid (Kevlar) - when things get hot
Kevlar is similar to Dyneema in many ways. However, the material feels stiffer and is significantly more heat-resistant. It is often used in combination with polyamide - for example for tape slings with a polyamide sheath, or auxiliary lines such as the rapline, where Kevlar is woven with polyamide fibers.
Hybrid forms between Dyneema, Kevlar and polyamide
For tape slings, there is often a mixture of polyamide and Dyneema. They appear either as mixed fabric tape slings or as core-sheath rope pieces (Dyneema core, polyamide sheath) for construction of stands, such as the Dyna Dyneema polyamide cord from AustriAlpin.
Belt slings made of Kevlar also have a sheath made of polyamide. This construction is particularly important here because Kevlar is quite UV sensitive.
Table: Advantages & Disadvantages of Polyamide, Dyneema & Kevlar
|material||Moisture sensitivity||UV resistance||Cut resistance||advantages||disadvantage||operation area|
|polyamide (Nylon, perlon)||medium||sensitive||low||Easy to knot; certain elasticity||heavy weight, more sensitive to moisture||Sling for self-belaying, as a stand sling|
|Polyethylene (Dyneema)||low||medium||Well||Low weight, high edge cut resistance||difficult to knot; poor energy intake||Rope extension, head loops, hourglasses and threading hooks|
|Aramid (Kevlar)||low||sensitive||Well||High edge cut resistance||poor energy intake||Hourglasses, construction of a stand (especially with dubious safety points)|
|Hybrid (polyamide + dyneema)||medium / low||medium / sensitive||medium||Compromise made of polyamide and polyethylene material||Stand sling, body slings|
Durability of tape slings made of polyamide, Dyneema & Kevlar
Manufacturers give the lifespan of tape slings - if they are not used - with a maximum ten years at. However, if a webbing sling is used regularly, its service life is significantly reduced due to abrasion, UV radiation and other factors. Mammut specifies a period of use of seven years for infrequent use (once or twice a week), and up to three years for heavy use, i.e. several times a month.
However, the issue of durability is a bit more complex with slings and cords. In principle, a distinction must be made here between the types of construction - core-jacket construction vs. tubular tape:
- UV radiation: A tubular band, for example, ages much faster when exposed to strong UV radiation than a core-sheath construction. This means that although polyamide is UV-sensitive, this is hardly of any consequence in the case of climbing ropes, for example, because the core is protected by a sheath. However, if you find a sling left outside, you should always exercise caution. The various susceptibilities of the materials can be found roughly classified in the table above. This also applies to fixed quickdraws in climbing gardens!
- material: In the case of polyamide, you can tell how old it is by the splicing, i.e. the furry surface of the material. This is more insidious with Dyneema, because you cannot tell that this material is aging. After three to five years, they often only hold 13-15 kN, as tests by the DAV have shown.
- Be careful with chemicals: Like all parts of personal protective equipment for climbing - such as ropes or climbing harness - slings and accessory cords do not get along with acids, solvents or other chemicals. Even if they cannot be seen from the outside, they can tear after contact with these substances even with the slightest exposure.
- Melt burn: As with all ropes, it is essential to pay attention to the risk of melt burns. You really should never (never, never!) Abseil directly in a sling or hang a sling from a running rope in a carabiner. It is essential to watch out for ropes that could damage the sling through friction!
- Be careful with fixed loop material: You should be just as skeptical about threaded hourglasses or old loafers as you would with fixed quickdraws, because moisture, sun and mechanical stress cause the material to age and reduce its strength. It is worth taking a look at BergundSteigen 2014.
So it's important: Sling material must be replaced regularly. A "still possible" endangers your own life and that of your rope partner!
Knotability of Dyneema & Co.
The knot thing is important and every climber or mountaineer needs to master a certain repertoire and know the impact these knots have on his or her safety.
Knots weaken the material: how much depends on the material on the one hand, but also on the knot itself. A knot in the sling can significantly reduce the load limit. With polyamide tape slings, this can be up to 60 percent, with Dyneema and Kevlar even up to 75 percent!
There is another problem with Dyneema: A normal blind stitch begins to wander due to the smooth surface from a load of two kN.
The general rule is: Use sewn tape slings if possible! Because if you use accessory cords and non-sewn tape material, for example to build a standing octopus, you have to find out exactly what the material is about and what knots you should use!
The loop knot often used in the past falls into the category of “To be handled with care”, as Pit Schubert explained in detail in his book Security and Risk in Rock and Ice or Walter Siebert.
Elongation: Dyneema & Kevlar vs. Polyamide
As already mentioned: Dyneema and Kevlar are more sensitive than polyamide when it comes to rope stretching. If you want to see the effect before your eyes, watch the test scenario from DMM in this video - based on factor 1 and factor 2 falls, also with and without knots.
Here is once again shown why one ...
- ... should never fall directly into a sling (e.g. in a stand),
- ... should never, never fall into a Dyneema sling and
- ... should never, never, never fall directly into a ribbon sling with a knot - not even a 60 centimeter sling.
Incidentally, this problem is alleviated if you “stand” with rope and a mast throw.
Auxiliary lines made of Kevlar
Auxiliary lines made of an aramid-polyamide mixture are used in particular for material transport or abseiling. They are very light and have little rope stretch. Edelrid has developed a mixture here with Rap Line 2 (for the detailed Rap Line 2 test report).
But even here there are some pitfalls, as Chris Semmel described in his 2009 article in Bergundstieg. Conclusion: caution should be exercised both when untying the end of the rope and when lowering it. And aramid-polyamide ropes are also problematic for high-speed tours, because the impact force increases due to the significantly lower rope elongation and thus the risk of being carried away!
You can find ribbon slings and cords made of all materials here:
More on the subject of slings, climbing ropes & Co. in the Bergzeit magazine
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