Nylocs backing out?

Has anyone ever had any experience with or heard of a Nyloc nylon lined nut backing off a bolt?

Here is the situation: I import a very good anchor called a Spade from Tunisia. They come in two pieces a shank and a fluke which mate together in a tapered socket that locks the shank in position when any load is placed on it. When there is no load the two pieces are held together with a 1/2" stainless bolt and stainless Nyloc nut tightened snug to the sides of the socket. About 1" of bolt extends beyond the nut. The nut is not torqued down because the shank must be loose enough to slip forward into the taper to lock. All the load on the bolt is in shear. There is no force in tension or torque. Overall it is a very solid arangement.

Now the problem. A New Zealand sailor is claiming that his anchor (which thankfully I did not sell) failed because the nut backed completely off the bolt which allowed the bolt to fall out. There is very little vibration and no torque on the bolt. The nut was in good condition, new when installed and had never been removed. Is there any way that a Nyloc nut in good condition could possibly make more than 20 turns on a loose bolt on its own?

Reply to
Glenn Ashmore
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I would think so. But I can't give you the details. My experience has been with screws that are used to hold down and attach sheet metal[steel] roofing. Every once in a while you get a screw or two that will not stay in [yes they are into the substrate]. Over a period of weeks or months they unscrew. You can put them in and they just come back out. I am sure it has to do with the thermal different coefficients of expansion of the various materials. If anyone knows the answer please let us know.

Chuck Pilgrim

Reply to
Pilgrim

Glenn Ashmore wrote in news:Wx6Bc.1474$Pa4.1342 @lakeread04:

with the conditions you describe, i cannot see this happening with one exception. Either the bolt was undersized, or the nut was oversized, or a combination of the two.

Reply to
Anthony

Or the NZ sailor cut a corner or two when installing, putting the Nyloc in his pocket to save it for another job and swapping in a regular nut. I had a stainless Nyloc nut sieze on me recently. I installed it to only finger-tight, left it for a day, and when I went to disassemble it, it was super-tight. I put a real wrench on it, and broke the bolt clean off. Half-inch bolt at that. That was some tough Nyloc.

Grant Erwin

Reply to
Grant Erwin

I've purchase bolts and nuts in bulk and occasionally find one that wasn't threaded or tapped. Perhaps the nut wasn't tapped (or stripped) from the manufacturer and thus installed with only the nylon holding on to the bolt. Now, the part that blows a hole in my hypothesis is that if the nut were not tapped, the hole would be too small to fit over the nut. ...but if it were stripped...

I know you said there is no tension load on the nut, but if the anchor is banging on a rock or something at the bottom, it could (conceivably) hammer the nut off. Or rather, hammer the 1" of extended bolt to the edge of the nut which would then fall off since the threads in the nylon have been beaten/stripped away.

Anyhow, just a possiblity

Reply to
skuke

Perhaps the Nyloc was defective. Although not often, I have found Nylocs without the nylon insert, which leaves you with a regular nut.

Shawn

Reply to
Shawn

I believe the Nyloc's work when the nylon is compressed. If just screwed on, there isn't a locking force down the screw as if against a bulkhead.

What I'd do is double nut - plain nut against the Nyloc. That should do it.

Martin

Reply to
Martin H. Eastburn

We had a nyloc nut come off a taper dirve pin on a rotating shaft driving the tap changer on one of our transmission transformers, it caused about $100,000 damage to the transformer. It was an 'engineered' replacement for the original locking mechanism, but it appears to have been defeated by some oil that leaked onto it. Your NZ friend didn't happen to oil part of the anchor did he, perhaps to stop the stainless galling?

regards,

John

Reply to
john johnson

Yes. That's why critical fasteners should be safety wired.

Gary

Reply to
Gary Coffman

Yep, same here except it was a 100# capacity commerical laundry machine where all 8 nyloc nuts worked loose enough on the front bearing housing to cause one hell of a vibration when the drum spun up to extract speed. Third time in 6 months. Ask the guys from another office who does all the bearing jobs to remove the darn things and go to lock washers and nuts. Made an inquiry a few days later at main office and found they went back with nylocks again but used thread lock this time. I don't know but suspect I'll be back on that job in a few months for the same vibration problems. I tend to go with the idea of oil on the threads or even cheap nyloc material in nuts, perhaps just not correct torque applied to nuts.

Rusty Bates

Reply to
Rusty Bates

Perhaps a stover type locknut should be considered.

Reply to
Shawn

One of my products uses 2 ea. 1/4-20 Nylocs and we ship 300 a day. I have yet to see a nut failure in the 4 years of making these. However, we have seen about .5% of the nuts defective out of the box. The guys in that work center have good eyes and seem to catch them during assembly. ( I put their names on the box labels) The usual defects are: no insert, cocked insert, undersized insert, broken or cracked insert, malformed insert pocket. So, take your pick. I don't think that Nylocs are meant to be security nuts, and I wouldn't trust them in that type of situation. Castle nut and pin please!

Reply to
Tom Gardner

I've seen nylock nuts back off bolts before. But it was on an application that had vibration constantly while in use.(Mid 60's eras snowmobiles that used flat stock tempered spring steel for motor mounts)

While not ever having seen the anchor or application you describe, since there is 1" of threaded bolt still sticking past the nut, why not drill this bolt end and install a cotter pin in it for safety sake. It may still get loose but you would not loose anything, as the nut would stop when it untreaded and hit the cotter pin. The hole in the bolt at the end would not alter strength of bolt. Visit my website:

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expressed are those of my wifes, I had no input whatsoever. Remove "nospam" from email addy.

Reply to
Roy

Stainless on stainless galls up pretty easy. I use a lot of stainless fasteners on motorcycles (because they get driven in the road salt seasons in NY) and unless I use a good grade of moly anti-sieze on them, it's asking for trouble.

You've never seen fun until somebody bakes a vacuum system and locks all the conflat fasteners into the flanges, because they put it together dry.

Jim

================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ==================================================

Reply to
jim rozen

I've seen the nylon wear to the point of no longer holding from repeatedly threading it onto/off of the bolt.

Reply to
bridger

Yes. Especially when not torqued tight. I would seriously consider a drilled bolt, castellated nut and cotter pin.

Ted

Reply to
Ted Edwards

None of the other interesting replies mentioned that most nylons absorb water much more readily than other plastics. One could argue that the accompanying swelling should make the locking effect stronger, but I suspect the softening of the material does even more to defeat the lock. If the anchor is repeatedly cycled between wet and dry, the nylon may end up significantly deformed. I also wonder about the effects of salt in the water...

Loren

Reply to
Loren Amelang

There is a reason why things get safety wired or cotter pinned. And of course a reason why most of us never get around to doing it. You can always interupt the threads by giving them a smack or a squeeze so that the nuts cant back off.

Reply to
Beecrofter

And here's a link to all you ever wanted to know about safety wiring.

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In particular note this paragraph near the bottom of the web page, and I quote;

"Putting Holes in Your Nuts"

"This need not be as painful as it sounds. You just need a drill with a very sharp bit, a vise to hold your nuts, a center punch, and a steady hand."

(No really, thats what the man says. See for yourself.) (-8

Dennis van Dam

Reply to
Dennis van Dam

One of the finest bits of technical writing I've seen in a while.

Shawn

Reply to
Shawn

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