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Re: [TowerTalk] Stainless Steel Galling

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Stainless Steel Galling
From: Larry McDavid <lmcdavid@lmceng.com>
Date: Thu, 24 Jun 2010 23:36:22 -0700
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
Stainless steel turnbuckles not secured with jam nuts are not heavily 
loaded, at least not loaded like a structural fastener. Grease may be 
adequate in that case to reduce galling.

Hard disk drives do sometimes use stainless fasteners. But, these are 
almost always single-use products; seldom is a hard drive ever 
disassembled so galling would not be an issue. And, those stainless 
fasteners are often screwed into die cast aluminum, avoiding the 
stainless-on-stainless galling problem.

"18-8" stainless steel is steel with about 18% chromium and 8% nickel 
but is not a specific alloy designation. Stainless steel alloys 302, 
303, 304, 305 and others all have nominal "18-8" composition. These are 
the most common stainless alloys and all will gall under stress, 
especially if clean and certainly if subjected to cyclic loading that 
varies the stress within the threaded joint. Cyclic motion of stainless 
against stainless is a sure cause of galling.

Back "in the day," even tallow was used as a thread lubricant in 
maritime applications. My father was a boilermaker working on WWII ships 
and he always had a coffee can of tallow at hand. Frankly, it smelled. 
Lanolin would work about the same.

In fact, there is a recent product, "Fluid Film," by Eureka Chemical 
Company that is an excellent rust and corrosion inhibitor; its primary 
component is lanolin. Sprayed on, this provides mild lubrication but 
excellent corrosion resistance and is eco-friendly. What better to smear 
on with your hands than lanolin? But, it would not be effective as an 
anti-galling agent for stainless steel.

Loctite 37229 C5-A Copper Anti-Seize and Loctite 37230 Silver Grade 
Anti-Seize are modern anti-seize or anti-galling materials and will 
outperform grease or lanolin in threaded joints. These are the 
"Quickstix" put-ups I mentioned earlier. The Copper Anti-Seize is more 
often used on coarse, large fasteners and the Silver Grade Anti-Seize on 
small screws with fine threads and close slip fits.

Tallow and lanolin have been used historically but engineered materials 
will outperform them. Time has moved on!

Larry W6FUB


Grant Saviers wrote:
> We agree that a fraction of an ounce of prevention is worth more than 
> what it takes to get a galled 1/2-13 SS bolt apart.
> 
> However, Lanacote etc. (anhydrous lanolin) has been used on SS sailboat 
> rigging, particularly on SS turnbuckles that get adjusted frequently for 
> racing, and less often on cruising sailboats, for 50+ years to prevent 
> galling.  It works well enough that anti-rotation safety wires are a 
> must.  It is not a "grease" - i.e. oil added to a carrier base.
> Having used SS fasteners extensively, why is it that (typically18-8) 
> machine screw sizes rarely, or never gall?  From the 60's to now, 
> computer & disk drive manufacturers used billions of such SS sizes 
> without anti-galling materials.
> I always use never-seize for 5/16 and larger.
...
-- 
Best wishes,

Larry McDavid W6FUB
Anaheim, CA  (20 miles southeast of Los Angeles, near Disneyland)
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