Thread lubricant (preferably dry...)

[chopper75]

I have an application using an 8-32 Stainless screw into a stainless PEM insert. I'm getting a lot seized screws that I think are gauling from too much friction and pressure.

I'd like to try reducing the friction with a lubricant.

1. The screw is inside a chassis with a lot of electronics, so the lubricant would have to be non-conductive.
2. I'd prefer some sort of dry lubricant just to avoid the mess of grease.
3. The screw is going into a heatsink so the lubricant must have a fairly high temp rating (working on the temp value...)

Any recommendations?

Thanks

 

[dgallup]

What stainless steel? There are many types and some gall much worse than others. Nitronics alloys are particularly gall resistant. Another approach is electroless nickel plating. You could try a Teflon based lubricant but I expect the results will be hit or miss.

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[TugboatEng]

Silver plate the screw.

Otherwise, as dgallup said, Nitronic 60 seems to resist galling with just about every type of stainless. Helicoil inserts are available in Nitronic 60, I can share a vendor that stocks them if interested.

https://www.nickelinstitute.org/med...lingcharacteristicsofstainlesssteel_9006_.pdf

 

[electricpete]

I was looking for a non-conducting dry lubricant for my anti-rotation pins (just in case any powder happened to drop into the 4kv stator) and I came up with this

https://www.crcindustries.com/products/dry-moly-lube-11-wt-oz-03084.html

http://api.crcindustries.com/auto-services/get-pds/03084

Lowers friction, prevents galling and helps to reduce torque and energy consumption. High anti-friction and anti-seizure properties. Fast drying film resists dirt and dust build-up.

So it's non-conducting, dry lubricant intended to prevent galling... that's the extent of my knowledge. I don't know much about susceptibility to thread galling for various materials as the others here.



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(2B)+(2B)' ?

 

[electricpete]

When I was looking for a non-conducting dry lubricant for my vertical motor motor anti-rotation pins (didn't want anything conducting like graphite, just in case powder drifted down into the 4kv stator winding)...

I landed on this: CRC pn 03084 Dry Moly Lube (spray, fast-drying)

So it's non-conducting, dry lubricant, data sheet says it prevents galling... that's the extent of my knowledge. I don't know as much about susceptibility to thread galling for various materials as the others here.

EDIT - The data sheet doesn't specifically say it's non-conducting, but my understanding is after it dries all that's left is molydenum disulfide, which has relatively low electrically conductivity, although you might want to double check all that if you go with this product.

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(2B)+(2B)' ?

 

[EdStainless]

Look at switching insert materials, any Nitronic alloy (30, 40, 50, 60) will be a big improvement. As would any hardened SS such as a PH grade.
I have used boron nitride as a thread lube. It is inert, non-conductive, and white.
You can buy aerosol

https://www.zypcoatings.com/product/bn-glass-release-spray/

https://miller-stephenson.com/boron-nitride-mold-release-spray/

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P.E. Metallurgy, consulting work welcomed

 

[sameer21101970]

Use talcum powder directly. Cheap and easily available. Talcum powder plus molydiumdisulphide is perfect combination.

 

[drawoh]

chopper75,

I have inserted many stainless steel screws into stainless steel PEM[ ]nuts, and I personally have not had problems. I generally used lubricating threadlockers as per MIL[‑]S[‑]46163, like blue Loctite.

A company I worked for recently has a history of problems with stainless steel screws. Stainless steel on stainless steel does gall. They switched to plated steel screws. They stopped having problems, and they made it clear to me they were not switching back.

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JHG

 

[chopper75]

Thanks all for the recommendations. We may look into the Nitronic inserts

 

[btrueblood]

Like drawoh, we install stainless into PEM stainless inserts all day long, with one caveat: the installers must drive the screws by hand, which means they are inserted slowly. Installation with power tools makes it more likely to gall.

 

[TugboatEng]

Installing them all day long is one thing but wait until you have to remove one.

 

[drawoh]

TugboatEng,

I have had no problems removing them. The company I just worked for used power tools.

--
JHG

 

[EdStainless]

One cravat for unlubed SS, if the fasteners have rolled threads then the risk of galling is much lower. With cut threads the risk is very high.

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P.E. Metallurgy, consulting work welcomed

 

[TugboatEng]

I was taking apart a new battery charger recently that has failed. Two out of three screws gallled and seized solid after being half-way unthreaded while using a hand driver. It was an A2-80 screw in a tapped stainless flat bar (unknown grade but I assume 316). The newer charger they replaced it with has a gold coating on all of the stainless hardware. I'm thinking they had similar issues.

At a pump manufacturer I worked at, we used anti-seize only on the multi-stage pump line because the guy building them developed his own technique for setting impeller heights and regularly had to disassemble pumps that didn't perform. His line was the only that was allowed to use anti-seize because the bolts and nuts would regularly seize on disassembly. They were typical F593C fasteners.

The best systems I have seen use silver plated nuts. Swagelok and clones do this on their compression fittings.