QC Lab: Worn AnchorsWednesday, September 7, 2016
Whether it's at the local gym or a dreamy vacation cliff in the Mediterranean, we've all been there: You finish a sport climb and are ready to clip your rope through the anchors (e.g., cold shuts, leaver biners, chain links, etc.) when you notice that countless lowerings and top roping have left gnarly rope grooves in the anchors. Will these grooved-out anchors hold? Will the sharp edges trash my rope?
Recently a friend of mine was doing his part at a local sport crag by replacing old bolts and rope-grooved anchors. He pulled these off and wanted me to test them to see how weak they were. (I'm not going to get into the technicalities, pluses or minuses of different kinds of anchors and am not condoning anything in anyway—I'm just looking at only one style of cold shut, one test, two data points, just out of curiosity more than anything.)
The used cold shuts with rope grooves
I've tested (wellâ€¦ I don't actually test anything, but I have a crack team of engineers that perform the testing) many rope-grooved carabiners before and had a sneaky suspicion what I'd see. (I even did a bit of a write-up a while back: qc_kp_archive.php#040606.) I had never actually tested cold shuts, however, so I thought I'd have the QA engineers here at BD test these old ones and compare them to a new one.
Measuring the rope groove of the test samples, the reduction in thickness was about 25%. Thereforeâ€¦ the used cold shuts would be 25% weaker, right? Wrong.
- The two rope-grooved samples tested to 2330 lbf and 2522 lbf, before they deformed and slipped open.
- The new cold shut stretched all the way open at a load of only 1466 lbf.
The cold shuts after testing (the new one is on the left).
So how and why did the rope-grooved cold shuts withstand a higher load than a brand new one? Take a look at these testing photos (the new cold shut is on the left):
The rope groove forces the rope to stay in line with the main axis and direction of load of the cold shut, whereas with a new cold shut, as the load increases, the rope is able to slide out and cantilevers it open at a reduced load. So rather than reduce the tensile strength of the shut due to removal of material, the groove seats the rope onto the spine so that the shut holds more weight before it starts to deform.
- Rope-grooved cold shuts keep the load in line with the strongest axis and therefore can withstand a higher load before deformation.
Just because a rope-grooved anchor may be stronger, however, doesn't make it better. The sharp edges of rope-grooved anchors and biners can potentially damage the rope's sheath. If you see anchors or biners out in the field that look beat up, do your part and replace them. You can also use your own quickdraws or biners at anchors in order to save on wear and tear of the fixed anchors.
Be safe out there,
Kolin Powick (KP) is a Mechanical Engineer hailing from Calgary, Canada. He has nearly 20 years of experience in the engineering field and has been Black Diamond's Director of Global Quality since 2002. Kolin oversees the testing of all of Black Diamond's gear from the prototype phase through continual final production random sample testing. If you have a technical question for KP, please email him at email@example.com and he will TRY to respond.