Anti-galling coatings. Can plating solve our galling problem?

A. I do not have numbers, but adding electroless nickel to ONE of the two parts will virtually eliminate the galling you are experiencing. It has excellent lubricity, can stand the temp you mentioned, and is a very uniform coating that if put on by someone really good, you probably would not have to grind or hone after plate if the parts are properly sized to start (allowing for the plate).

A. Michael,

In the vacuum industry plating silver on threads, etc. is commonly used to prevent seizing and galling between metal parts. This might work for your application.

A. In plating I think the resistance to compressive forces is generally referred to as hardness. Most plating is rated on Rockwell C (HRC) or Vickers hardness (HV)scales. However, you also have to look at adhesion when talking about resistance to compressive forces.

The coefficient of friction on a plated surface will depend largely on prior surface preparation. Generally, if you have a rough surface prior to plating -- you will have a rough surface after plating.

Silver plating gives you a surface that provides lubricative and anti-galling properties. It can withstand temperatures up to 1200 °F. However, it may not be adherent enough to withstand the compressive forces you write about.

Nodular thin dense chrome plating is also a good anti-galling/anti-spalling coating that can withstand temperatures above 700 °F. It is harder (~ 1000-1200 HV or >300 ksi) than silver plating and may suit your application. It is strongly adherent to basis metals such as 4340 and is extremely resistant to wear and abrasion. However, this a proprietary process owned by Armoloy Inc.

You may also check out nickel plating.

In parting: A good test is better that a thousand opinions.

A. Teer Coatings in England has a graphite-based PVD coating that might fit the bill. I think they market it in the U.S. through Multi-Arc.

A. One of your best options is Electroless Nickel. It prevents galling, you could also use ENi with Teflon so that assembly/disassembly will be easier to perform.

A. Silver is the standard non-galling coating for the vacuum technology business. Silver coated bolts are standard items.

A. I used to use a chromium plating called ARMOLOY NTDC where I worked previously. Armoloy is an American company (Philadelphia I think). The coating is extremely hard, (about 70HRC / 1100HV), satin in appearance, and works wonders. In our experience it adhered and lasted much better than either Nickel or Silver. We used it for Nuclear applications mainly, where exfoliation of Nickel had been a problem.

A. Carpenter Steel makes an austenitic stainless steel called 'Gall Tough' which works well. There is a competitors product called 'Nitronic 60'

A. If silver plating is not used, there are lots of different dry film lubricants, which are affordable solutions, particularly the ones that come in a spray can and do not have to be baked. They are not as good as baked, but would work fine for a touch up.

A. Mike - Another anti-gall coating is manganese phosphate. It also holds an RP [rust preventative] oil very well for corrosion protection. The production process is similar to zinc phosphate. Ask your chemical vendor for info.

A. We provide and train customers for Anti-galling copper plating on all types of premium and non-premium box or pin connections on tree-tops, tubing hangers, top/bottom subs, cross-overs, blast-jints test caps, drill collars, etc.

Major licensors uses this process for Anti-galling reasons.

A. RIE Coatings supplies coating #1713, often topcoated with #4606 for SS fasteners

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A. Hi Laszlo. I can tell you that PWA stands for Pratt & Whitney Aircraft division, but not much more.

Regards,

A. Go to the Everlube Products website and they produce a product that conforms to PWA 36545. It is either Everlube 620C or Esnalube 382, I don't remember which one it is. The site also has information on application of product and MSDS.

Thanks Jed. We try to not recommend one proprietary over another in this forum. But please explain why you feel that hard chrome plating might be a good or better alternative to silver plating. Thanks again.

A. Hi Jan. It is a commonplace to silver plate threads of stainless fasteners to minimize galling issues, although it is not the only potential solution to the problem. To know whether you might have a corrosion problem would require knowing the severity of exposure conditions plus the other materials of construction in electrical contact with the silver plated stainless fasteners though. Good luck.

Regards,