Alternate inorganic and/or organic coating for lead alloy [ballast plate]???

[WKTaylor]

Need your help with a very odd problem...

I have a ballast plate made from [gagggg... me] lead alloy [AMS7721 or AMS-L-18331]. Lead corrodes and obviously needs a corrosion protective finish.

The 'standard finish' [for decades] has been cadmium plate [AMS-QQ-P-416 Type II Class 2] or zinc-plate [ASTM B633] + post-plating chromate surface treatment + zinc-chromate primer + orange enamel topcoat.

Alternate finish was recently designated as zinc-nickel plate [AMS2417 Type 2] + post-plating chromate surface treatment + epoxy primer + orange epoxy topcoat.

Shop is 'balking' at all platings because: (a) cadmium is prohibited; (b) zinc is not available [on base] and zinc-nickel [bath] process is sensitive to contaminates that would 'spoil bath' for all other critical plating needs.

My first inclination is to enforce original cadmium or zinc plating + post plating chromate treatments by an 'outside' vendor...

However there is a 'side' of me trying to find 'work-around' base-platings, thus...

Apply...

(a) zinc or manganese phosphate treatment directly onto the etch, or grit-blast, cleaned lead surface + zinc-rich epoxy primer + colored topcoat...

or

(b) zinc-rich epoxy primer treatment directly onto the etch, or grit-blast, cleaned lead surface + colored epoxy topcoat...

or

(c) ???????????????

Please advise any unique and/or tried/true ideas for application of protective coatings to lead alloy.



Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[Compositepro]

I assume this is for an aircraft application. Lead is very soft so I do not think any of the standard treatments would hold-up well in service. Scuba weights are often coated with PVC plastisol coating about 1/8" thick. It is applied by heating the weight and dipping in liquid plastisol, which congeals with heat.

 

[moltenmetal]

Ditto on the plastisol- it's what I've seen used on lead weights which are frequently handled.

 

[berkshire]

Will,
Is this a mass balance weight? In the past I have had success with a fine coat of epoxy resin and fiberglass cloth, where plating services were not available then polyurethane paint over the epoxy while the epoxy is still " Green" . Since most of your work is Military you may not have that option . But I will mention it for what it is worth.
B.E.

You are judged not by what you know, but by what you can do.

 

[WKTaylor]

Berkshire... Yes this is a large/heavy flight control balance weight.

I decided on a course of action based on several comments... including a company that makes lead ballasts for boats/ships... and several coating experts who where also head scratching.

NOTE. Thick coatings described above are not usable on this ballast plate since it hast to fight tightly on a balance panel.

I am reluctant to 'cough-up' the actual process... right now... since I am unsure my shop can do the process... regardless I'll let everyone know what I 'finally dispositioned' AFTER the wet-tape tests.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]