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What makes ropes stretchy?
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Rudmin


Sep 8, 2010, 1:35 PM
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What makes ropes stretchy?
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What makes a climbing rope different from a static rope? I read on Wikipedia that the core strands are chopped into shorter lengths:
In reply to:
In dynamic climbing line, the core fibres are usually twisted, and chopped into shorter lengths which makes the rope more stretchy.

This sounds vaguely plausible but also kind of made up. Does anybody know what physical mechanism makes a rope dynamic? Is anybody in the rope industry?


kennoyce


Sep 8, 2010, 2:12 PM
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Re: [Rudmin] What makes ropes stretchy? [In reply to]
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[WARNING]I'm not in the rope industry and probably don't have a clue what I'm talking about, so take this for what it's worth[/WARNING]

I highly doubt that any core fiber is chopped to any length within any dynamic or static rope used for climbing/rescue. I am fairly sure that the stretch comes from the twisting of the core strands in the rope. I think I have heard that rope manufacturers twist half the core strands in one direction, and half in the opposite direction to help keep the rope from wanting to twist as much. I would assume that the core strands in a static rope are much straighter and this is what makes them static. Obviously the nylon itself will still stretch which is why static lines do stretch some.


rock_fencer


Sep 8, 2010, 3:02 PM
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Re: [Rudmin] What makes ropes stretchy? [In reply to]
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going to go out on a limb here and say dynamics are made of some variation of Nylon 6,6 while statics are made from polyester which is less stretchy. i'm lazy and dont feel like looking it up, at the end of the day its the material properties. Things like the Kernmantle construction and the twisting of the core strands etc... add additional ability to stretch.


Partner drector


Sep 8, 2010, 3:26 PM
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Re: [kennoyce] What makes ropes stretchy? [In reply to]
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kennoyce wrote:
[WARNING]I'm not in the rope industry and probably don't have a clue what I'm talking about, so take this for what it's worth[/WARNING]

Then why bother to post?


kennoyce


Sep 8, 2010, 3:26 PM
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Re: [rock_fencer] What makes ropes stretchy? [In reply to]
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rock_fencer wrote:
going to go out on a limb here and say dynamics are made of some variation of Nylon 6,6 while statics are made from polyester which is less stretchy. i'm lazy and dont feel like looking it up, at the end of the day its the material properties. Things like the Kernmantle construction and the twisting of the core strands etc... add additional ability to stretch.

This is a good point, some static ropes are polyester (which has a higher modulus than nylonat 423 ksi vs. 400 ksi), but I think the majority of static ropes out there are nylon.


kennoyce


Sep 8, 2010, 3:28 PM
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Re: [drector] What makes ropes stretchy? [In reply to]
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drector wrote:
kennoyce wrote:
[WARNING]I'm not in the rope industry and probably don't have a clue what I'm talking about, so take this for what it's worth[/WARNING]

Then why bother to post?

Obviously because I'm board at work, why else?


rock_fencer


Sep 8, 2010, 3:35 PM
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Re: [kennoyce] What makes ropes stretchy? [In reply to]
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duh, do people come here when they aren't bored???

SterlingJim can chime in with the real reasons.


Partner drector


Sep 8, 2010, 3:38 PM
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Re: [Rudmin] What makes ropes stretchy? [In reply to]
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From azom.com:

Modern Rope Construction
A modern dynamic climbing rope is made from continuous-drawn nylon yarns. A consequence of drawing the nylon is strengthening and stiffening as the molecular chains of this semi-crystalline polymer become orientated. These fibres can be spun to create high strength, low stretch ‘static’ rope, which is widely used in caving and industrial rope access where shock loading is unlikely and percentage elongation is required to be at a minimum.

Producing Desired Properties
To create a yarn with elastic properties suitable for arresting a fall safely, the drawn nylon is heat treated up to 120°C. Loss of chain orientation and strain-induced crystallinity as a result of the annealing process, gives the drawn nylon yarn a reduced Young’s modulus. This process increases the energy absorption properties of the yarn and reduces the impact force on the body during a fall.

From farrropesuk.com:

The Kern (inner core) can be made up of virtually straight parallel strands or a braided construction, more parallel strands reduce elasticity but is slightly stiffer, braided (basically meaning interwoven strands) is more elastic but is more flexible.


kennoyce


Sep 8, 2010, 3:40 PM
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Re: [rock_fencer] What makes ropes stretchy? [In reply to]
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In reply to:
SterlingJim can chime in with the real reasons.

My thoughts exactly.


tower_climber


Sep 8, 2010, 9:42 PM
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Re: [Rudmin] What makes ropes stretchy? [In reply to]
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From one of the premier SSRT manuals:

High-stretch (often referred to as dynamic) kernmantle ropes are composed of a braided sheath over a twisted core strand bundle.

Low-stretch (or static) ropes are constructed of a braided sheath over parallel continuous fibers of the inner core. Because of the core weave, the rope is designed not to spin, and to stretch only minimally when tensioned.

(On Rope, Smith/Padgett 1996)

In dissecting ropes, I have found the preceding description to be accurate. Higher-stretching static ropes (PMI Access Pro, NER KMIII) have a slightly wrinkled set of core fibers. Extremely low-stretch rope (PMI Classic) has smooth and straight core fibers. Dynamic ropes have core fibers that are separated into bundles (8-12 bundles total) and each bundle is twisted. The rope resists twisting while loaded because; a, the kernmantle construction discourages it and, b, the core bundles are not twisted with each other.


wiki


Sep 9, 2010, 7:27 PM
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Re: [tower_climber] What makes ropes stretchy? [In reply to]
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tower_climber wrote:
From one of the premier SSRT manuals:

High-stretch (often referred to as dynamic) kernmantle ropes are composed of a braided sheath over a twisted core strand bundle.

Low-stretch (or static) ropes are constructed of a braided sheath over parallel continuous fibers of the inner core. Because of the core weave, the rope is designed not to spin, and to stretch only minimally when tensioned.

(On Rope, Smith/Padgett 1996)

In dissecting ropes, I have found the preceding description to be accurate. Higher-stretching static ropes (PMI Access Pro, NER KMIII) have a slightly wrinkled set of core fibers. Extremely low-stretch rope (PMI Classic) has smooth and straight core fibers. Dynamic ropes have core fibers that are separated into bundles (8-12 bundles total) and each bundle is twisted. The rope resists twisting while loaded because; a, the kernmantle construction discourages it and, b, the core bundles are not twisted with each other.

Yep.

From my experience, the core in a static (semi-dynamic static??? around 5% stretch anyway...) rope is braided (usually 10 or so braids) but I am guessing that has the same effect as parallel strands (i.e. can't twist).


vegastradguy


Sep 9, 2010, 7:53 PM
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Re: [wiki] What makes ropes stretchy? [In reply to]
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try reading this to get a better idea of how ropes are made.

http://www.rockclimbing.com/...actory_Tour_864.html


wiki


Sep 10, 2010, 12:55 AM
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Re: [vegastradguy] What makes ropes stretchy? [In reply to]
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Cool article... Thanks!
Should have got a rope at the end of it though Tongue


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