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alexnees
Jan 4, 2007, 2:26 PM
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Hey all,
I'm hoping someone can explain to me the REASON that biners are weaker when the gate is open. Bear with me as I try to explain the reasoning behind this seemingly ridiculous question.
Obviously, an oval loop (closed biner) is going to be stronger than a C-shaped loop (open biner) since the force applied can't lever open a closed biner. But....I've looked at lots of different designs (keylock, regular, wiregate, lockers) and it doesn't seem to me that, even when the gate is "closed," a biner actually forms a closed loop. There's still a gap, usually a couple millimeters, between the notch and the gate. If there wasn't a gap, it would be hard to open and close the biners because the gate would stick. So my question: If a biner is rated at 8kn open and 24 kn closed, and that biner is loaded with, say, 9 kn while closed, why doesn't it deform, stretching open a couple millimeters until the gate prevents it from stretching any more? In other words, it seems as though any biner that catches a big fall should get slightly deformed in the process. Apparently this isn't the case, but can anyone show me where I'm wrong in this?
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areyoumydude
Jan 4, 2007, 2:38 PM
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A 'biner does stretch and the gate engages when enough force is applied. If the gate is open at that point, all the force goes to the top of the spine of the 'biner making it much weaker.
(This post was edited by areyoumydude on Jan 4, 2007, 2:40 PM)
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chug1
Jan 4, 2007, 2:41 PM
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One afternoon I was swinging around underneath the veranda, being held up by a Trango classic screwlock. Loaded with my weight, which would have only been about 0.8 kN, it stretched slightly. It was not a visible deformation, but the gate would no longer open freely. The hook in the nose of the carabiner was starting to engage the bar in the gate.
I assume that if I had loaded it to, say, 10kN, the carabiner body would have stretched so that the hook and bar were loading on each other, and I wouldn't have been able to get the gate open at all.
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moof
Jan 4, 2007, 2:43 PM
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The biners do deflect with load, and witha few hundred pounds the gate starts taking some of the load. The point to the small clearance is to allow biner to be opened under body weight, for example to clip in a rope while aid climbing. For that amount of flexure there is no permanent bending going on, all elastic deformation.
Typically a closed gate biner fails under load at the nose first, breaking off the little catch.
Obviously the gate is much weaker than the spine of the biner, but in the case of a D shaped biner it does not take the majority of the load, as the rope is way over by the spine. This is also why ovals are typically weaker, or are built heavier to compensate for the worse mechanical advantage.
Put body weight on a biner and you should be able to see significant deflection at the nose/gate interface.
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devils_advocate
Jan 4, 2007, 2:44 PM
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alexnees wrote: ... why doesn't it deform, stretching open a couple millimeters until the gate prevents it from stretching any more? In other words, it seems as though any biner that catches a big fall should get slightly deformed in the process. Apparently this isn't the case, but can anyone show me where I'm wrong in this?
Did it ever occur to you that metal can be bent and yet bend back? Look up "elastic deformation" and compare to "plastic deformation".
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climbaddic
Jan 4, 2007, 2:45 PM
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I always wonder that myself. Wire gates for example uses steel. Does this wire really takes the weight? I certainly would be scared to hang on that let along fall on it. Some carabiners use what appears to be sheet metal. I highly doubt those will take any weight either. I guess I need to talk to carabiner designer :)
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bues0022
Jan 4, 2007, 2:56 PM
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You are correct in regards to assuming deformation of the biner when loaded, but the amount is off. The gate helps immensely under load because the deformation is not into the plastic deformation region of the material. Think of this...take a paperclip and bend it so one leg is sticking out. That's plastic deformation. On the atomic scale the particles have shifted around and moved to reach the lowest energy state. Now, take that same leg and push it down slightly, see how it springs back? All materials have a limit to the amount of stress applied before plastic deformation, and in the second case this hasn't been exceeded. Back to the biner question now...When the gate is open, the C shape can deform sooner due to the non symmetric loading about the support. The stress created in the long axis includes a bending moment instead of pure tension. When the gate is closed, the biner will deform slightly when loaded, but not into the plastic deformation regiem (think of a spring). Therefore the gate side can help carry the load. The bending moment is also reduced on the long axis. This is why the closed rating is more than just double the open rating.
Metals are extremely resilient materials which allow for this cyclical loading for a large number of cycles (aluminum is notoriously much weaker than steel however, one reason why in gyms the biners are many times steel). Even in a big fall, the metal usually is far below its yield strength so it won't plasticaly deform.
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alexnees
Jan 4, 2007, 3:21 PM
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Thanks all for the helpful replies, especially bues0022. Obviously I never got far enough in physics to learn about plastic vs. elastic deformation, but it makes a lot of sense. Cool stuff.
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alpinismo_flujo
Jan 4, 2007, 3:57 PM
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This site is so civil now! Last year - you would have been flamed for asking that question.
Kudos!
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petsfed
Jan 4, 2007, 4:20 PM
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climbaddic wrote: I always wonder that myself. Wire gates for example uses steel. Does this wire really takes the weight? I certainly would be scared to hang on that let along fall on it. Some carabiners use what appears to be sheet metal. I highly doubt those will take any weight either. I guess I need to talk to carabiner designer :)
Oddly enough, the wire is just as strong as the rest of the carabiner, for that exact reason. Having looked at a lot of failed wiregates, the wires never failed, it was the aluminum that failed. Crazy, huh?
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gunkiemike
Jan 4, 2007, 4:26 PM
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Back in the Dark Ages (1970's to you youngin's), it was not uncommon to find oval biners that wouldn't open up under a load of 200 lb (less than 1 kN). I still have a couple SMC biners from that era, and you can see noticeable biner flexion, on the order of a few tenths of a mm at the gate pin, just by pulling it lengthwise IN YOUR HANDS. So yea, biners "stretch" until the gate is under tension. New biner bodies are stiffer, due to forged shaping, and (I imagine) stiffer alloys.
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vegastradguy
Jan 4, 2007, 4:26 PM
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petsfed wrote: climbaddic wrote: I always wonder that myself. Wire gates for example uses steel. Does this wire really takes the weight? I certainly would be scared to hang on that let along fall on it. Some carabiners use what appears to be sheet metal. I highly doubt those will take any weight either. I guess I need to talk to carabiner designer :) Oddly enough, the wire is just as strong as the rest of the carabiner, for that exact reason. Having looked at a lot of failed wiregates, the wires never failed, it was the aluminum that failed. Crazy, huh?
even more oddly, a wire gate biner, more often than not, is stronger than a regular one.....
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petsfed
Jan 4, 2007, 9:11 PM
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vegastradguy wrote: petsfed wrote: climbaddic wrote: I always wonder that myself. Wire gates for example uses steel. Does this wire really takes the weight? I certainly would be scared to hang on that let along fall on it. Some carabiners use what appears to be sheet metal. I highly doubt those will take any weight either. I guess I need to talk to carabiner designer :) Oddly enough, the wire is just as strong as the rest of the carabiner, for that exact reason. Having looked at a lot of failed wiregates, the wires never failed, it was the aluminum that failed. Crazy, huh? even more oddly, a wire gate biner, more often than not, is stronger than a regular one.....
They are VASTLY over engineered to deal with the fear that comes with seeing a wire keep you from death. Its only recently that wiregates have started to approximate how light they could be, and still be full strength.
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jeremy11
Jan 5, 2007, 11:44 AM
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http://www.rockclimbing.com/...kes_again_83057.html
here is a biner that I broke while testing. read the description for info.
two major lessons - the force a short static fall applies, and what a bit of whiplash can do - imagine taking a hard fall and looking up to see your rope through a biner popped open like this?? 
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basilisk
Jan 5, 2007, 10:09 PM
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http://www.psychovertical.com/?wiregates
an excellent article on wiregates
if you're lazy, here's a summary: a regular biner has an aluminum body with an aluminum gate. a wiregate has an aluminum body with a steel gate. it should go without saying that steel is stronger than aluminum. therefore, wiregates are ultimately stronger than normal biners
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jt512
Jan 5, 2007, 10:17 PM
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vegastradguy wrote: petsfed wrote: climbaddic wrote: I always wonder that myself. Wire gates for example uses steel. Does this wire really takes the weight? I certainly would be scared to hang on that let along fall on it. Some carabiners use what appears to be sheet metal. I highly doubt those will take any weight either. I guess I need to talk to carabiner designer :) Oddly enough, the wire is just as strong as the rest of the carabiner, for that exact reason. Having looked at a lot of failed wiregates, the wires never failed, it was the aluminum that failed. Crazy, huh? even more oddly, a wire gate biner, more often than not, is stronger than a regular one.....
First of all the wires are stainless steel, which I presume is stronger than aluminum.
But, that said, wire gate and conventional gate biners usually have the same strength rating when their design is otherwise the same. Some wire gate biners have more advanced designs than cheaper conventional gate biners, which is why, I suspect that they have stronger ratings.
Jay
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shockabuku
Jan 5, 2007, 10:29 PM
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basilisk wrote: http://www.psychovertical.com/?wiregates an excellent article on wiregates if you're lazy, here's a summary: a regular biner has an aluminum body with an aluminum gate. a wiregate has an aluminum body with a steel gate. it should go without saying that steel is stronger than aluminum. therefore, wiregates are ultimately stronger than normal biners
I don't understand how that follows. Based on my limited experience breaking biners (on purpose, with a pull testing machine) and the comments from moof, above, it's usually the hook on the nose that breaks, though I saw one solid gate break at the pin. This implies to me that the hook is the weak point, and it remains aluminum even on a wire gate biner. It certainly doesn't make any sense to me that retaining the weak link unchanged, the hook, and changing a part less likely to fail, the gate, to a stronger steel part would do that. I don't understand how the wire gate biner becomes any stonger than the solid gate biner.
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shockabuku
Jan 5, 2007, 10:31 PM
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jt512 wrote: But, that said, wire gate and conventional gate biners usually have the same strength rating when their design is otherwise the same. Some wire gate biners have more advanced designs than cheaper conventional gate biners, which is why, I suspect that they have stronger ratings. Jay
Okay, that sounds better. I can believe the improved design argument.
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gosharks
Jan 5, 2007, 11:28 PM
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shockabuku wrote: This implies to me that the hook is the weak point, and it remains aluminum even on a wire gate biner. It certainly doesn't make any sense to me that retaining the weak link unchanged, the hook, and changing a part less likely to fail, the gate, to a stronger steel part would do that.
The stress (force/area) is higher on the wire gate because the cross sectional area is smaller. Therefore, you need a stronger material there with higher tensile strength (which is measured in stress).
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marde
Jan 6, 2007, 4:48 AM
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In reply to: The stress (force/area) is higher on the wire gate because the cross sectional area is smaller. Therefore, you need a stronger material there with higher tensile strength (which is measured in stress).
standard biners have two "steel rivets" in the gate which are nearly the same diameter than a wiregate
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gosharks
Jan 6, 2007, 11:49 AM
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marde wrote: Thats only true for keylock biners standard biners have two "steel rivets" in the gate which are nearly the same diameter than a wiregate
I dont have a biner around to check this on, but i feel that the cross sectional area of the pin/gate interface(s) is larger than the area of the wiregate wires.
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marde
Jan 6, 2007, 4:34 PM
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after all, it just does not matter.
Biners with closed gates don't brake
(in climbing situations).
The only thing that matters is open gate strength.
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g_i_g_i
Jan 8, 2007, 12:28 PM
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In reply to: They are VASTLY over engineered to deal with the fear that comes with seeing a wire keep you from death. Its only recently that wiregates have started to approximate how light they could be, and still be full strength.
That's not really true: the breaking strength of a carabiner is indeed the force at which it might break, they are not *vastly* over engineered. In fact carabiners do break during normal operation, not even in the worst case scenario, so according exclusively to some engeneering standards (not those used to design climbing equipment, evidently) they are actually not very well designed...
As for the new very light wire carabiners, some of them actually are lighter mainly because of novel design and manufacturing processes (e.g. helium), but the majority are just basically smaller (e.g. neutrino, camp nano, ecc), and climbers nowadays are willing to put up with the smaller size in order to shed grams. In my opinion this has to do with fashion and shifting priorities in the climbing world at least as much as with generally improved designs.
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What does this mean exactly? And what "engineering standards" are you referring to? 
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