Stainless steel fasteners 2

It's not the nylock insert that's causing the seizing, it's the s/s, it's galling. A slight bit of anti seizing compound or even oil will prevent it, with the appropriate reduction in torque. You might try using regular nuts with Loctite, strength dependant on the application...Mike

Mike is right on here, the rule is NEVER assemble SS fasteners without some type of lube. Never-Seize will work if dissassembly is often necessary, but WD-40 or such will do OK if the bolt/nut are seldom/never dissasembled. I personally have had some poor results with chem lockers on SS stuff, they don't always come apart easily, but it's worth a try. I like the NyLok's myself for the small stuff, but must rely on conventional lock washers for the big fasteners. Sounds like a short lesson on stainless steel fasteners is in order for your crew.


Rod

Thanks Mike and Rod,

I have done some investigation today. A lot of people i talked to mentioned lubricants and also the problem of galling with stainless steel fasteners. However, no one has yet given me an explanation of why this is a particular problem with stainless steel. I've had inspection measure the fasteners and they are within their tolerance grade. I've checked the standards and it seems that A4-70 grade has similar tensile strength and hardness to metric grade 8.8 steel fasteners. If the fasteners are nearly the same as 8.8's in tolerances, tensile strength and hardness then why do the A4's experience galling and not the 8.8's? I have not experienced these problems with softer/weaker fasteners like brass or aluminium.
Can anyone explain why stainless steel fasteners have this problem? Is it something to do with its composition? Friction co-efficient?
I know this probably seems like a minor problem but i'll be working with stainless steel (and stainless fastening systems) alot more in the coming months and i would like to get a full picture of its problems.

Thanks.

Part of the difference between stainless and hardened carbon steels (used for Gr8.8) is that the stainless easily gets a work-hardened surface. When the surfaces are rubbed together under stress they harden, then bits of the harder metal break off from the slightly softer layer below. The surface roughness increases very rapidly with continued rubbing and you get galling. The metallurgists can probably explain it better.
By the way, aluminium and zinc surfaces can also be very prone to galling.

Here's a good starting point:
A (or other internet) search for "stainless steel fastener galling" will yield a wealth of info...

Use Ani-Seize for stainless steel bolts

"Use Ani-Seize for stainless steel bolts"

NOT a 'Pat A'nswer!!(Pun intended).

Anti seize is NOT a good lubricant for SS fasteners in ALL cases. Quite often its use is restricted in certain applications (electrical, explosives, etc.). However it is acceptable where its use is not restricted (as is just about ANY lube).


Rod

I made a little investigation and found that dry torque for SS M8 could be up to 16,5 Nm. If you use WD40, you must further reduce it by 20%. If you use Anti-Seize you should reduce it by 55%! (Maybe nylock gripping action demands even further decrease!)
Maybe wrong torque recommendations you have?

We have an ongoing galling problem with A4 nuts and bolts and cannot use lubricants etc due to the environment they are used in. I am told that using dissimilar stainless solves the problem i.e A4 bolts with A2 nuts. But I cannot use A2 as it's corrosion resistance is not good enough. Another suggestion in to use a different strength pairing i.e A4-70 bolts with A4-80 nuts.
Anyone any experience of this working?

Once a long time ago we had a BUNCH of large dia SS anchor bolts and nuts that 'could not be lubed'! Atomics International had every engineer that worked for the AEC on that job and NO ONE could get even ONE bolt to come to torque without galling (once this happens the only cure is to cut the nut from the bolt and chase the threads (with lube, of course---typical government circle jerk). It took probably two weeks of this BS before anyone was willing to listen to those of us responsible for installation. They 'allowed' us to WAX the threads---voila---problem cured.
Using dissimilar spec SS has NOT proven benificial in my experience.


Rod

Yup, tried doing both the dissimilar composition and strength routine when trying to solve my above problem. They did not work well enough to be of any benefit. The stainless steel machines I was working on were for waste water processing in the food industry. We could not use conventional lubricants like never-seize etc. We eventually found a solution by using a food safe dry lube from BP combined with a dedicated assembly tool that the torqued the assembly up at approx 30 rpm. Still had some that galled but compared to what was happening it was a big improvement.

Womble

This forum seems to be an old one but in case someone else stumbles across it like I have, please allow me to offer the following.

Anti seize is a good product to use in most applications. If you don't have a can of this in your shop, I have been recommending 2 things for years now to customers and have yet to have the problem reappear.

First, don't use power tools. The faster the revolutions, the greater the chance of stainless galling. If you must use power tools, turn the speed down as low as possible.

Second, and more importantly, wax is a basic coating that will help eliminate the galling. Any wax will work, even floor wax. Dip the nut, let it dry, and use it. If you have large quantities to use, have your supplier get the product wax plated. Also, if you need a bio degradable coating, this is available on the market.

Galling is common, especially with stainless nylon lock nuts, but it can be eliminated.

David Long
Marine Fasteners

This problem is referred to as “Thread Galling”. Thread galling is most prevalent with fasteners that are made of Stainless Steel, Titanium and other alloys which self-generate an oxide surface film for corrosion resistance.

Thread galling is also referred to as “Cold Welding” as during fastener tightening, pressure builds between the contacting thread surfaces and protective oxides are broken. The interface metal high points then shear or lock together. This cumulative clogging action causes additional adhesion and increases the severity of the galling.

In extreme cases the galling effect leads to complete thread seizing and if tightening is continued the fastener can be twisted off or its thread stripped.

To help reduce the amount of galling produced, slowing down the RPM of screw tools will frequently reduce and in some cases solve the problem completely. As the screw tool RPM increases, the heat generated during tightening increases. As the speed and inevitably the heat increases so does the tendency for the occurrence of thread galling.

If corrosion resistance is not an issue then changing the alloy grades of stainless or material type of the bolts that you are using could also reduce the problem of galling.

Lubricating the internal and/or external threads frequently eliminates thread galling. The proposed lubricant should contain substantial amounts of Molybdenum disulfide (Moly), graphite, mica or talc. Some proprietary, extreme pressure waxes may also be effective. Lubricants can be applied at the point of assembly or pre-applied as a batch process similar to plating. Several chemical companies offer anti-galling lubricants.

There is an anti-seize for every application. I have used food grade versions, high vacuum versions and many others.
If you can use very hard nuts (17-4PH or 17-7PH) it will help.
For all around use I don't like the compounds that contain metals, you can get into problems. Look for ones based on synthetic lubricants with tungsten disulfide. I have made my own by mixing WS2 with wax, but it isn't worth the hassle.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

Wow. I had forgotten this thread. It IS a bit old but, still speaks to the problem. I wonder why some problems seem to reappear again and again.

AWILD, you appear to know SS fasteners well enough but, there are just too many applications that have "special" lube requirements to generalize, eg --- "The proposed lubricant should contain substantial amounts of Molybdenum disulfide (Moly), graphite, mica or talc."

EdStainless, your experiences seem to be similar to some of mine. Many applications such as the food industry have restrictions on lube types. Indeed, some places (eg Golden West Foods) we were instructed NOT to use lubes of any type. A problem I refer to at another gov't. job in a post above from a couple of years ago. This restriction, using lubricants on SS hardware, is still prevelant in some of todays gov't. jobs, unfortunately.
Biosafe waxes are so common that it makes one wonder what hidden agendas go into the makeup of the specs for some of these jobs.

Oh, yes. There is a flipside to this. At a "rendering" plant on Bandini Blvd. in L.A. back in the early 80's while installing a piece of machinery, the 'lube' problem was that there was so much (all over the floor, walls, tools etc) that it was extremely difficult just handling the SS fasteners...! ;o)

Rod

The galling resistance of Nitronic 60 stainless is FAR higher than that of 304/316. Costs more, what else is new?<g>

If the external threads are still stripping & you use never-seez, you might want to try Strain Hardened bolts [i.e., A-193-B8 Class 2] they have the B8 underlined on the head marking for Identification.