Stainless Steel Thread Galling

[Dave K]

Does anyone know if thread galling on Stainless Steel is permanant? I would be looking to do this on 303 stainless, and does anyone know if there is a way to purposely gall two parts together. Is there a chemical weld process to maybe weld 2 parts together?

[Joe Michaels]

Galling on stainless steel threads usually occurs when you do not want it to. I have seen it happen with new pipe fittings and with new stainless bolts, just running them together by hand with dry threads. Usually, the fittings or fasteners gall so hard together, we throw them out and get new ones. The few we tried to get apart had the threads messed up badly and we had to then spend time with needle files, dressing galls off the male threads.

I would think galling is a function of how close a fit the threads are, and making sure the same alloy of stainless steel is used for both parts.
Also make sure the parts are absolutely free of any oil or other lubricating substance when making them up. If the threads are a close fit, you will be lucky to get the parts fully made up before the galling occurs.

"Permanent" is a matter of interpretation. Galled threads on stainless parts can sometimes be gotten apart if you use a big wrench and sometimes put a cheater on it. IOW, "Permanent" depends on how much effort is considered "yeah, it's a PITA, it took a big cheater, but I got it apart" vs. "the heck with it. Sucker won't come apart...." face it: ANYTHING made by one guy can be taken apart by another. It is just a question of what "taking apart" consists of. To some people, if they can't get stuff apart with normal hand tools, it's "permanent". To others, such as those of us who work in the powerplants, if something won;t come apart, we put heat on it, use bigger wrenches or take a torch or grinder & cutoff wheel to whatever has to come apart. As I tell my own son: "What one man designed and put together, another man can figure out and get apart."

Like I said, "Permanent" is relative. How "permanent" do you want those stainless parts put together ? Galled parts may give way to a big enough wrench. You ask about "chemical welding". I do not know of anything which would cause a galvanic action between two stainless parts to "chemically weld them". The heaviest duty grades of Loctite will do a great job of locking things together so that wrenches and cheaters probably won;t work. We use enough of the green, permanent Loctite on turbine and locomotive parts and I can say the stuff produces a very strong bond. However, with the application of heat, the Loctite will lose it's bond. A plus to Loctite is it acts as a lubricant when the stainless parts are being assembled, then cures to lock them.

You want "permanent" ? IMO, for most people, "permanent" can be achieved by welding.
If you put the stainless parts together and want to be sure they do not come apart, consider putting some TIG stitch or tack welds on things to lock them for keeps. Nothing short of a die grinder or plasma cutter will get things apart once that is done.

Joe Michaels

[Dave K]

Well, without giving too much away, it's for a friend of mine who is designing a type of lock. He wants this shaft to have a head on it, that is permanent. It is being machined solid right now, but he's looking to save some money on material because of the soaring stainless prices. Welding is out of the question for cosmetic reasons.

[dsergison]

silver solder in the threads. put silver bearing paste flux on parts, assemble, gently heat.

[Dave K]

I'm not sure we can heat it either. It needs to look "pretty" while sitting on a store shelf.

[dsergison]

I doubt silver soldering it will discolor it.

-much.

cheap to try.

[Mike72]

Clean both parts in a solvent that will strip all traced of any lubricant. Toluene is one.Screw together and torque down.

[Dualkit]

What about assembling them with a bonding agent
like JB Weld or something similar?

[Dave K]

Not sure about JB weld. If you hit these parts with a hammer, would they pop apart? Its for a trailer toungue hitch. Needs to be secure. I'll suggest the silver solder, but I think he's looking for something that can be assembled quickly also. He will be making these by the thousands.

[dsergison]

swage a collar over a grove on the end of the rod.


brazing is easily scaled up to a "by the thousands" process. you prepare them, and run them through an oven large batches at a time.

[dsergison]

use left handed threads. this will only foil %75 of total thieves.

those who didn't know righty tighty lefty loosey have a 1/2 luck chance.

the other 1/2 have 1/2 a chance of galling them up themselves trying the wrong way.

[img]smile.gif[/img]

[Dave K]

swage a coller over a grove on the end.

You mean like a snap ring? Something that will collaps when slipping the head onto the shaft and then expand when it hits the i.d. groove inside the head? We kinda thought of that idea and it's a strong option, but we're trying to get other ideas.

If you meant something different, please explain.

[Dave K]

I ran the brazing option past him and he's afraid of it being too easy for someone to heat up the head and pull it off, thus unlocking the locked reciever.

[dsergison]

no, like have a groove in the rod, over which you put a collar having a little ring of raised material to match the grove inside. then you smash the hell out if it in hopes of displacing some metal into the grove.

common process but requires a hell of a smasher.

[Dave K]

Once again, makes it not very appealing on the store shelf.

[dsergison]

take shaft and turn shallow groove.

split the end of the shaft 2 ways and put a hole in it axially.

make collar to fit grove which can be pressed onto shaft.

press a dowel pin, plug etc, flush into end of hole in rod preventing collapse and removal.

I dub this the "expanding arbor" type option.

[fizzissist]

Stainless threads WILL gall!!! (and yes, it's permanent)

Danger, Will Robinson, Danger!

We make 304SS hardware for ultra-high vacuum systems, and the stuff has to be uber-CLEAN before assembly and installation. Threaded SS parts are coated lightly with a vacuum-safe powder, paste, or in the case of the big boys, a very thin plating of silver to prevent galling.

In your case, you want it to gall, so like Mike72 says, clean the parts and assemble.

We pre-clean with a detergent, then ultrasonic 'em with Alconox, then a final hit with pure alcohol or acetone.

I'd consider freezing the bolt, and warming the female side to help in assembly maybe (test it first). No promises it won't gall during assembly.

[Dave K]

Ok, now I got ya. I'll run it by him and see what he says. Thanks

[dsergison]

spiralock threadform would just about guarantee good galling action.

[Dualkit]

With out a picture guessing a solution is tough,
I assume you are dealing with a male thread
and a female thread and assembling them?
If one end has a bolt type head, can you run
the tolerances on each close enough that it
takes 200 foot pounds of torque to assemble
them, then I am sure they won't rattle apart.
What type of stainless?, you can hold tight
tolerance on 303 and 416 all day, others
would be more difficult.