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Tomlutz
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Postby Tomlutz » Tue Feb 04, 2020 10:11 pm
Dear metal specialists,
I am using a metal ring to connect my safety system with a wichard. Recently such a ring broke in cold (however not extremely cold, maybe minus 2 degrees Celsius) temperatures (snowkiting). See the ring on the top in the picture. I don't know the properties of this ring and who sold it. I got it along with an old harness I bought for little money.
Now I am a bit concerned: are those rings reliable? On the picture you can see other examples, new. The one to the left I bought from a local sailboat equipment store (expensive - maybe the most reliable, you can hardly see the welding), the other two are from Aliexpress and described as "Welded Precision Polished 316 Stainless Steel Marine Boat Hardware Round O Rings Hammock Yoga Hanging Ring", se e.g.
https://www.aliexpress.com/item/3288802 ... 4c4dcFddNB.
The smaller one from Aliexpress I have already used on water - so far so good.
Anyone else with good or bad experiences?
Thanks, Tom
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edt
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Postby edt » Wed Feb 05, 2020 1:20 am
depends on the type of steel, steel thickness and how it's welded. Could be anywhere from 50 pounds meant as decorative rings for crafting up to a ton. Only way to tell for sure is break it with a stress test. O-Rings usually don't fail catastrophically at their rated strength. When they fail they usually bend into an oval. The one on the left looks like a West Marine Stainless O-ring, those are nice. I don't think I've ever snapped an o-ring like you have. I've bent them before, but never snapped. Welded o-rings can be perfectly ok just depends on how they are made.
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tkaraszewski
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Postby tkaraszewski » Wed Feb 05, 2020 1:34 am
I would never buy this stuff from ali express. I buy stuff like this from reputable chandleries made by sailing supliers.
Yeah, it seems
like a lot to pay $7 for this, but you know it's rated for a 3000kg breaking load, and they've got plenty of hardware on my boat that works great.
Would you sail across on ocean on a boat rigged with aliexpress hardware? I wouldn't.
Save $6, sure, and lose your kite at sea because you relied on the cheapest possible part for a single-point-of-failure connection.
Anyway, this isn't stuff I'll save a few bucks on.
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evan
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Postby evan » Wed Feb 05, 2020 8:31 am
Could be the sloppy, visibly thinner, welding.
The rings I use have no visible welds and always elongate when stressed beyond their intended load.
This is what happens to my 4*25mm rings loaded up to 600DaN, with normal riding forces they stay round:
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foilholio
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Postby foilholio » Wed Feb 05, 2020 2:38 pm
Forged, f*** yer!
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edt
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Postby edt » Wed Feb 05, 2020 5:18 pm
Everything we buy is made in China at one point or another. So it's not like if you buy from a USA shop it's not gonna be made in the USA. Still made in China. Buy it just test a few to destruction to figure out the breaking strength. The real cost in buying from Aliexpress is you have to wait for months for it to ship test it then maybe buy from a different source meanwhile you need to kite today and already spent another $10 for an solid o-ring at the local marine shop. So the opportunity cost is pretty big buying this way.
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foilholio
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Postby foilholio » Thu Feb 06, 2020 3:00 am
$10 is a lot even from a marine shop. You can get rated rings and they are quite expensive. Steel is quite strong, any reasonable thickness say 4mm+ is likely to be far in excess of required. If should deform well before failure too.
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