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?

... 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?

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.....

even more oddly, a wire gate biner, more often than not, is stronger than a regular one.....

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

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

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).

Thats only true for keylock biners
standard biners have two "steel rivets" in the gate which are nearly the same diameter than a wiregate

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.

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...

It does. That's why the biner is stronger when closed; it can only "stretch" so much before its own shape stops the process. When open, there's nothing to stop it from deforming until it snaps.

What does this mean exactly? And what "engineering standards" are you referring to?

I wouldn't say that from an engineering standpoint, climbing equipment is poorly designed.

I don't quite see how the gate is taking any weight or adding any strength (obviously it does, or there wouldn't be a separate 'open-gate strength'). Take a keylock biner for example. The gate has no notch that fits into the nose when closed. So clearly that does not contribute to the open gate strength.

So how does the gate limit the bending (stretching) motion of the biner when loaded? does it prevent the bending outward and snapping off?

this is why you shouldn't tighten your locking biner too much during your rappel. You may feel it and it's loose - don't crank it tight. It will be hard to open again unless loaded.

As mentioned upthread (and 4 years ago—good revival!) you won't be able to deform the biner by hand. It takes more force, such as that generated in a fall, to bring the surfaces in contact with each other.

I happen to have a Camp biner here so I did some quick calculations. The open gate rating is 9kn and closed is 22kn. So the difference is 13kn or about 2900 lbf.

I measured the wire gate, and it is 0.0875" diameter. Calculating the cross section you get .006in^2. Multiply by 2 (for 2 wires) and you get .012in^2. Assume a really strong steel, with a yield strength of 100k psi. That gives you 1200 lb breaking force for the wire gate. That's only about 5.3kn. So clearly, the wire itself does NOT take most of the additional 13kn load of closed vs. open gate. I assume, ahem, that the difference is that the closed gate keeps the biner from deforming too far and allows the strongest part, the spine, to do its job and absorb most of the load?