Nylon Locknuts Seize on 1/2 inch Stainless Bolts

[DocHeb]

I am installing a piece of horse mat as a bucket edge for snow work. I am using 1/2 inch by 3 inch stainless steel bolts, and am using stainless steel nylon stopnuts. As I tightened several of the nuts onto the bolts with my rachet, they suddenly seized-up, and now I can't tighten or loosen them. I've never had this happen before. I ran a 1/2 - 13 die down the bolt and it seems to be threaded correctly. Of course the kid at the local hardware just shrugged. Are the nuts defective?

 

[ronjhall]

DocHeb
I use a lot of stainless steel bolts and nuts on my boat. Having them seize up is not uncommon. /forums/images/graemlins/shocked.gif

Stainless steel is not a hard steel. Especially the type you would get at a hardware. /forums/images/graemlins/tongue.gif

I'm sure someone that can give a more precise reason why stainless steel seizes up will reply. /forums/images/graemlins/smile.gif

Use anti-seize on the treads to avoid the problem. /forums/images/graemlins/smile.gif

 

[Egon]

Silly question but are the threads the same.

Egon

 

[jmc]

DocHeb,

Don't know if this is the problem here but one of the bad things about SS is it has a tendency to gall with itself, especially if both pieces are the same alloy. Galling is where the surfaces just kind of smear together under stress. Its most likely to happen once they start to draw down hard but you couldn't be tightening them that much with the rubber in there. A defective thread form on either side could get the contact stresses up to where galling might occur. Poor thread finish contributes. Doubt if it is related to the nylon though. Put some penetrating oil on the frozen ones and let them sit for a while. Check the others to see if you can run the nut on by hand. If not. return them. If you want to use them, lube them first.

John

 

[johnbilt]

Hi

I'm familiar with the problem. I don't understand the metallurgy behind it, but yes, stainless will gall very easily and seize. I have found that it will seize even before there is any real torque on it.

I suggest that you buy a tube of anti-seize grease and make sure your threads are clean before you assemble. Just a small nick will create problems. Once they're stuck, I have had to break them or saw them off. They won't thread back off.

I have gone back to using high quality Grade 8 bolts with the yellow gold zinc chromate finish. They are corrosion resistant and they have tough threads. My experiences have been mainly on boats and Jeeps.

Good Luck

John /forums/images/graemlins/cool.gif

 

[SPIKER]

anyhow we build industrial equpiment and lots of it is S.S. and yes it will seize as a small nick is all it takes, those bulk bins are great for having the stuff all piled up and one scratch will end up stopping the nut from bottoming out. one easy fix is to use a tap & die to clean up the threads before you attempt to install them... the other thing is to install them SLOWLY. Oil or anti size don't seem to make much differance if it wants to sieze it will. what seems to help is a good coating of "milk of magnisia" the cheap phillups stuff you take for upset stomach, (works great for header bolts too! best stuff for them made!) the chaulky ness of it forms a slight barrier and will help removal too.


When I was in military it was the ONLY approved thread sealer for after burners on the B1 at the time. It seals and makes removal easier and the stuff wont react. as it dries out the magnisum is left and it will bite into the fastner holding it in-place untill you start to turn it, then as the bolt turns a bit the stuff goes back into a poweder form and acts like a lubercant againe making it come right out the rest of the way.

I have all my exhaust header bolts on with it and have removed them lafterwards with out a bad problem one. last tiem I took them off they were on for almost 5 years. not a one loose or seized...

Mark m /forums/images/graemlins/ooo.gif

 

[keeney]

I doubt that penetrating oil will help get the bolts un-seized. They are likely for all purposes welded together at this point.

When the metal "galls", it basically shreds itself through a friction/abrasion process. The little shards get wedged in tighter and tighter, filling the space between the two parts. The higher the pressure, the more shredding that happens in a quickly-accelerating failure pattern. Eventually, the pressure is so high that the torque required to continue turning exceeds the strength of the bolt. Increased torque will just twist apart the bolt or rip the edges off the nut before it will turn anymore. Once the shards have been wedged in there, pentrating oil will not help.

Sometimes, if you are lucky and notice the galling early enough, you can reverse direction and get the parts unthreaded before the seize up, but even turning in reverse tends to keep the galling process going.

Expanding the nut with heat may help a little.

Its easiest and cheapest to just twist or cut the bolts off.

I also learned about this the hard way. I made the mistake of designing a stainless threaded rod that went through a stainless nut into the height adjustment system of my boat dock. Several of the adjustable legs seized up without hardly any force on them.

I ended up diassembling the frozen legs, and had to cut the nuts off with a saw. I replaced the nut portion of the design with an aluminum part instead. Stainless through hard aluminum, stainless through hard bronze, or even stainless into zinc-plated or galvanized steel will work good.

If you insist on using stainless nuts on stainless bolts, a good anti-sieze compund is a must. Usually, you can tighten them once and get them apart once before needing to re-apply the compound. Look for a water-resistant grease paste with actual metal particles of aluminum, copper, or zinc in it. The brand name "Never-Seze" is suggested. Simple grease or oil will not likely prevent the problem.

On the upside of this, if you never want to worry about the nuts working loose, and you don't care about ever dis-assembling the thing, you can skip the ny-lock nuts and anti-size paste and just tighten regular stainless ones down until they gall!

- Rick

 

[DocHeb]

I'm going to reply to myself rather than each individually, but thank all of you for the good ideas and explainations.

The description of galling and the joints "smearing under stress" is certainly what is happening. I took several of the bolts, held them in a vise, and tightened the nut down. As I tightened, it went easily for a while, and then with one turn I felt a little resistance. The nut was a little warm at that time. If I went one more turn (on or off), the nut got very hot and it was STUCK. There was no further movement to be had in either direction.

Looking at the nut I can see it is a "shinier", more "nickel-colored" metal than the dull, light silver bolts. I think the bolts are a very soft stainless alloy, while the nuts are harder.

I went back and tried to remove the five bolts that installed correctly and two seized trying to remove them. I'll have to cut them off, and will try the Grade 8 bolts.

 

[Tractors4u]

We had a problem at work where we needed fasteners that would not rust because they spent a good deal of time underwater but with stainless galling that was another problem. We used stainless bolts with brass nuts. We never had a problem with galling with that combo.

 

[Junkman]

I use the same combination on the exhaust manifolds on my car. The only problem is that you have to keep going back and retightening them. It is a lot better than having to replace the original iron ones because of rust problems.