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DMM: Viper Size L (2013 model as shown) Padded Adjustable Harness, 5 Gear Loops Fits: Waist 87-104cm Legs: 55-70cm   $89.00
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Chockstone Forum - Gear Lust / Lost & Found

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Author
Breaking a biner

JMK
4/03/2013
10:36:43 AM
This is a question for all u scientist and engineers out there.

On sat I clipped a ringbolt that caused the biner to press against the rock as there was a bulge at that point. I was concerned as I thought this might cause the gate to lever open and the snap the biner in the event of a fall. So I swapped the draw with a small scrwegate, which I flipped upside down - this caused the spine to press against the rock.

Question: does maintaining the close loop with a screwgate change the strength at which the spine might break?
patto
4/03/2013
10:53:58 AM
It says on the side of the biner. Open gate strength is normally ~7kN as opposed to 24kN when the gate is closed. So it is normally about a third of the strength.

Having a close biner pressed against the rock will also reduce the breaking strength. But its hard to guess how much as it depend on the bulge.
One Day Hero
4/03/2013
11:32:16 AM
It all depends on the size of your bulge.

BlankSlab
4/03/2013
11:48:25 AM
On 4/03/2013 patto wrote:
>It says on the side of the biner. Open gate strength is normally ~7kN
>as opposed to 24kN when the gate is closed. So it is normally about a third
>of the strength.

I would have thought loading a biner across its short axis (i think this is what jmk is refering to) it would be reduced (by how much i don't know). Also i was of the opionon that the closed gate strength was when its orientated correctly (long axis).

JMK
4/03/2013
12:29:20 PM
It is orientated along the long axis. It is also not a question of open vs closed as the gate is keeping it closed. The bulge of the rock pushes the Biner against the rock and in a fall the weight would apply to the spine of the biner as it tries to lever the bolt out.

I have seen this 3 times now and always used a screwgate believing that keeping the biner closed can only help. This obviously only happens with poor bolt placement. In the case of the route on sat the bolt shoul be 5cm lower or 30 cm higher.

IronCheff
4/03/2013
2:09:15 PM
Biners are intended to work in tension only. Thats how they are tested and rated. The situation you have described is introducing bending(leverage) to the Biner. This is not good, how much force it will take before failure with depend on many factors only some of which I am aware of. One thing you can be certain of is that it will be less than what it can take purely in tension. I think having a locking screw gate will add little difference for bending forces.
I think a better solution in this case would be passing a sling through the ring and clipping it with a biner.
BBSR
4/03/2013
2:09:30 PM
If I understand correctly, then the situation you are talking is where loading the carabiner, would make it want to bend around the minor axis. Eg both the gate side and the spine, would want to bend in towards the rock (so that the profile of the carabiner would no longer be straight).

In general I would think you want the biner to be in pure tension. When you start to bend things, it places uneven stresses across the cross sections of them ( this is essentially why an open gate biner is much weaker, it has a larger bending component).

In a practical sense, I guess it probably depends on the biner and the bulge as to whether or not it can withstand it. I wouldn't think the biners are tested for this sort of loading, so I'd definitely avoid it where possible. I suppose you could thread a sling around the ringbolt and clip with a carabiner? But that could have it's own issues (bolt not smooth, or narrow radius etc), might end up worse.

I've worried about the same thing, and I'd probably do the same as you (put a locker on it).
dawyndham
4/03/2013
2:20:09 PM
As others have said, this is not the way a biner is engineered to be loaded, so it's impossible to say if any particular biner will hold.

The exception, as there always is one, is K-type biners designed for Via Ferrata. They are designed and tested for a twisting/bending load as it's something that is quite likely in a Via Ferrata fall. That's K as in "CE EN 12275 type K" if you want to read what is involved in the test.
BBSR
4/03/2013
2:21:37 PM
Looks like Iron Cheff beat me to the post button by about 30s. Apologies for the repeat.

JMK
4/03/2013
2:30:19 PM
Would a steel screwgate be better?

A threaded sling is what I have done in the past as well but I notice that the biner tends to fall into cross load position if u do not girth hitch . I would not girth hitch as a fall could burn thru the sling.
egosan
4/03/2013
4:38:23 PM
On 4/03/2013 JMK wrote:
>Would a steel screwgate be better?
>
>A threaded sling is what I have done in the past as well but I notice
>that the biner tends to fall into cross load position if u do not girth
>hitch . I would not girth hitch as a fall could burn thru the sling.

Chopping it and refitting a well placed bolt would be the best option. This is what happens when you fall on rings that are too recessed.

http://www.chockstone.org/Forum/Forum.asp?Action=DisplayTopic&ForumID=5&MessageID=8600&Replies=173&PagePos=80&Sort=LastMessage#NewPost
Mike Bee
4/03/2013
6:37:13 PM
On 4/03/2013 JMK wrote:
>Would a steel screwgate be better?
>
>A threaded sling is what I have done in the past as well but I notice
>that the biner tends to fall into cross load position if u do not girth
>hitch . I would not girth hitch as a fall could burn thru the sling.

Burn through it?
I thought the main reason for discouraging the use of girth hitches was the it introduces a very tight bend into the sling which halves the strength of it.

Where does the heat come from to melt through the sling? I wouldn't have though there'd be enough movement in the sling/biner system to generate enough friction to melt through the sling. I can imagine the sling getting glazed or singed, but not melt through.
Keen to be corrected though :)
egosan
4/03/2013
8:50:21 PM
On 4/03/2013 Mike Bee wrote:

>Where does the heat come from to melt through the sling? I wouldn't have
>though there'd be enough movement in the sling/biner system to generate
>enough friction to melt through the sling. I can imagine the sling getting
>glazed or singed, but not melt through.
>Keen to be corrected though :)

I am not sure where it would be coming from on a ring. However, he may be referring in someway to the work by DMM and BD's QA people. Both of which have videos online of knots in dynama/spectra slings failing at scary loads because of the low melting point of those sorts of fibers and the large amount of friction generated heat in tightening a knot in a factor 2.

One of the videos is just tying knots in slings and the other is girth hitching 2 slings together. That one is good and scary.

shortman
4/03/2013
8:54:30 PM
Define scary.

Miguel75
4/03/2013
10:07:44 PM
Here's a link to a DMM test extending a biner away from an edge using a sling. They discuss which is better, a larks foot (girth hitch) or basket hitch;

http://dmmclimbing.com/knowledge/improvisation-larks-foot-or-basket-hitch-vid/

Here's a Black Diamond QC report on joining slings and what can happen;

http://www.blackdiamondequipment.com/en-us/journal/climb/all/qc-lab-connecting-two-slings-together

JMK
4/03/2013
10:58:16 PM
Thanks - definitely an argument to take a sling / extender draw on a sport route as you do not know the placement of the bolts

There are 16 messages in this topic.

 

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