Galling of stainless steel components

vyv_cox

vyv_cox

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The phenomenon of galling comes up from time to time. It is a form of adhesive wear, i.e. localised welding of peaks and troughs on a micro scale, that affects stainless steel in particular, and a few other metals. I have experienced it on a bottle screw, where the threads were welded together, rendering it completely useless and forcing me to buy a new babystay.

The best palliative in a form that can be applied as a grease or spray is known to be molybdenum disulphide, although claims are made for other products such as PTFE. While reading Professional Engineering I came across an advertisement for a company specialising in the application of tungsten disulphide for the same purpose. It seems to be a coating that they apply but they offer a 'while you wait' service. No idea how much it costs but it could prove useful. The company is called WS2 (the clue is in the name!), website http://www.ws2.co.uk
 
An excellent find.


hmm, the site is very much Work In Progress, as the Case Studies page is just printer's filler.

It's intriguing that cutter wear seems to be reduced by 200 - 500%, mainly by reducing the friction in the swarf removal area. Could be good for routers.

I'm not quite sure from the site whether they also sell the stuff in tubes for on-site application, or whether they just offer a "send us your parts, and we coat them" service.

WS2 seems to be available from other companies, offering very similar services, e.g.

http://www.dynacron.com/
http://www.carterbearings.co.uk/material_td_coating.htm
http://www.indestructible.co.uk/IP3016/


The last company seems to give some idea of how the product should be applied, though.

http://indestructiblepaint.com/PDF/Products/PL270.pdf


I think it won't take off in the marine sector until it's available in DIY tins.
 
A better engineering solution is to not use ss screws in ss bodies. Therefore, for example, use turnbuckles with phosphor-bronze screws into the stainless bodies. Probably works out less costly than the proposed solution which is likely to be temporary.

That said, as a design engineer in the nuclear industry, I have never known of any galling when using 304 ss screws to fasten into 304 ss. However, we don't have sea water present (usually) and in highly corrosive environments, components are welded together..
 
Jaguar 25 said:
A better engineering solution is to not use ss screws in ss bodies. Therefore, for example, use turnbuckles with phosphor-bronze screws into the stainless bodies. Probably works out less costly than the proposed solution which is likely to be temporary.

That said, as a design engineer in the nuclear industry, I have never known of any galling when using 304 ss screws to fasten into 304 ss. However, we don't have sea water present (usually) and in highly corrosive environments, components are welded together..
Click to expand...

I agree with what you say as regards turnbuckles, although this is not always practicable. Mine seized in the south of France, where sourcing a replacement in bronze would have been far from easy, especially in the time frame.

There are hundreds of case histories for galling of every grade of stainless steel, and other metals such as titanium, in almost every industry imaginable. The problem has no connection with corrosion, it is due to adhesive wear.
 
I use either a copper grease, used in the drilling industry, for use with stainless steel and monel drill collars, or a stuff I "found" used in the nuclear industry for stainless bolts nuts etc, which I belive is Zinc based, we also use a zinc based "dope" grease in the drilling industry. I have also had great success with a green stuff called aqualube and have never had a stainless nut bolt or bottle screw sieze. I was well aware of the problem, so sought to eliminate it aboard.
I also use the copper grease on all components I strip and rebuild on my engines, etc etc.
 
The best solution to stainless galling is to put a PVD coating such as titanium nitride on one of the mating parts. (same stuff as on coated drills) We do this on surgical instruments with sliding or threaded parts which are frequently made very clean and therefore more subject to galling. It also adds a real bling factor if done in gold colour. Only trouble is it is an expensive process.
 
vyv_cox said:
The phenomenon of galling comes up from time to time. It is a form of adhesive wear, i.e. localised welding of peaks and troughs on a micro scale, that affects stainless steel in particular, and a few other metals. I have experienced it on a bottle screw, where the threads were welded together, rendering it completely useless and forcing me to buy a new babystay.

The best palliative in a form that can be applied as a grease or spray is known to be molybdenum disulphide, although claims are made for other products such as PTFE. While reading Professional Engineering I came across an advertisement for a company specialising in the application of tungsten disulphide for the same purpose. It seems to be a coating that they apply but they offer a 'while you wait' service. No idea how much it costs but it could prove useful. The company is called WS2 (the clue is in the name!), website http://www.ws2.co.uk
Click to expand...

I once worked at a steelworks where we cold drew stainless steel wire for everything from dental tools and wire ropes to fasteners, and as you can imagine pulling steel through either carbide or diamond dies to cold form it squeeze it thinner does exert as high a surface load as you ever will be able to do. For the really high load applications where we had to avoid galling / cold welding of stainless, we used to copper plate the stainless wire. For slightly less arduous applications or where the user did not want the PITA of stripping copper coat, it was moly disulphide soap. So I would suggest either moly dispulphide grease or copper heavy greases for yacht kit - the loading on the metal in bottle screws isnt anything like as great as in cold forming so unless the threads are cr*p, copperease or similar should be entirely adequate.
 
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http://www.bestolife.com/prod.asp

Shell used to manufacture their own premium casing thread dope for HPHT (High Pressure High Temperature) casing strings. I believe that they released the formulation (or the patent ran out) to the market some time ago. It is now known as API HPHT Modified (IIRC, could be wrong on that). Anyway, Best O Life used to be the licensed manufacturer. I believe that the zinc based dopes had particularly good anti galling properties.

However, you may be thinking of Never-Seize, which is a product used to prevent galling amongst other things.
http://www.bostik-us.com/our-brands/never-seez

In particular: http://www.bostik-us.com/market-products/product-assembly/mro/products/#marinerschoice
Technical Specification For mariners Choice http://www.bostik-us.com/sites/default/files/NSMarinersChoice.pdf

MARINER'S CHOICE
Never-Seez® Mariner’s Choice is a heavy duty anti-seize and extreme pressure lubricant formulated to assure absolute parts protection against seizure, galling and corrosion in fresh and salt water environments.

Mariner’s Choice offers unparalleled resistance to water washout and the best protection in continuous high moisture environments both above and below water lines.
Click to expand...
 
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Offshore on the drilling rigs we use zinc based grease for stainless components. Molykote or Neverseeze are the norm. Auto Clave High Pressure Stainless Fittings recommend Zinc Based Lubes for their stainless connections. Aqua Lube as mentioned above is brilliant but be aware it will not be a clean or tidy job. Its like string cheese and gets everywhere !!!!!

We tend to avoid Copper Coat or equivalent where salt water contamination will occur as over time it sets the grease like cement. Several production equipment companies have banned copper based lubes from their assembly procedures for this reason.

Niall
 
Very long time since I had anything to do with it but there is something in the back of my mind about problems with molly in water, does it get abrasive or something?
 
vyv_cox said:
I agree with what you say as regards turnbuckles, although this is not always practicable. Mine seized in the south of France, where sourcing a replacement in bronze would have been far from easy, especially in the time frame.

There are hundreds of case histories for galling of every grade of stainless steel, and other metals such as titanium, in almost every industry imaginable. The problem has no connection with corrosion, it is due to adhesive wear.
Click to expand...

Vyv,
Z Diffusion supply chromed bronze as standard, rather than stainless steel. They're in Perigny just outside la Rochelle.
 
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