Treating corroded alloy surfaces

[WX]

I recently aquired a manual anchor windlass, the body is cast Aluminium originally painted white. The paint has since peeled away and the alloy suface is pitted.
Anyone any ideas on how best to recondition the surface and what would be a good product to repaint it with?

[PeterSibley]

There are a few products on the market that will clean the aluminium back to shiny and new,the kind of stuff truckies use to clean their shiny bullbars etc .That might be a good start,next comes the question of an anticorrosive finish.....that might be worth a quick call to a paint manufacturer or someone in the yellow pages under metal polishing/electroplating or probably best.....powder coating .Let you fingers do the walking.
cheers,
Peter

[Graham Knight]

I'd have it sandblasted, by someone who knows what they are doing, it's easy to remove too much material when blasting soft alloys.
Then I'd prime it with zinc chromate primer, fill any pitting with epoxy filler, then paint with 2-pack epoxy paint or have it powder coated as Peter suggests.

I've restored quite a few alloy parts for boats and cars and this is how I've always done it, they are all holding up well.

[Ric_Bergstrom]

If your is like mine it is white paint flaking off with lots of powdery corrosion underneath.

This is one of my winter projects so I am anxioulsy waiting on all the great WB suggestions.

Probably last forever as bare aluminum though.

Ric

[merlinron]

take it apert and take to a automotive machine shop and have them peen clean it, like they do to all aluminum motor parts. it will come back smooth and clean as a whistle and ready to be primed and painted. there are special primers for aluminum that etch the surface for better adheasion. one trick i always use when painting from a can is to set the can in a pot of hot tap water for about 15 minutes, it raises the pressure in the can and improves the spray pattern immensly. having the part to be sprayed warm also helps, the surface poors are bigger and the paint has better tooth to hold onto.the warm part cures the paint better, too.

[John Turpin]

I'd be concerned at filling pits/depressions with epoxy then powder coating. I'd be worried that the 'baking' stage of the powder coating process would melt the epoxy. Most epoxies don't like going north of about 150 degrees.

[WX]

Thank you all, much appreciated.

[pipefitter]

If you do get it blasted/powder coated,there is a difference in coatings for marine use. Most common reason that powder coatings fail is failure to isolate stainless fasteners or letting the fasteners breech the coating. Whatever size hardware it is fastened with,it is best to drill the holes a size bigger or else the fasteners wont fit the holes due to the thickness of the coating and you will have to break the powder coat to get the fasteners to fit again, thus starting the corrosion once again. If you isolate the fasteners with teflon washers, it will last much longer.

[ 10-19-2005, 01:04 AM: Message edited by: pipefitter ]

[formerlyknownasprince]

Let us know how you get on. I've got a surplus anchor winch here that I should get going before I get rid of it. It has some pitting too.

Ian

[JimJ]

Me too.

I have a spare o/b propeller that came with Sea Lark. It was wrapped in a cloth and then in a plastic bag. i opened it last weekend to fins a lot of large salt crystals on the now pitted surface of the blade tips extending in for about 25mm.

I have had it soaking in clean water for a few days.

[Wild Wassa]

Originally posted by Peter S:
"... stuff truckies use to clean their shiny bullbars etc."

Restorer's Medium as in, car restorer's medium. It is what the dudes bring their mags back to life with.

Put it on a cloth or or a buffing pad. The car guys then spray on a few coats of clear poly ... but that's them.

Warren.

[ 10-19-2005, 04:55 AM: Message edited by: Wild Wassa ]

[WX]

I will keep you all posted, I'm planning to open it up on friday as it also needs two new oil seals.

[TimothyB]

I've wondered if you can use the electrolytic method to clean rust from aluminum, since you can use it for other metals. Might be an interesting test with some aluminum scrap.

[WX]

I now have a different problem in that I can't get the damn thing apart.
Access to the insides is via a circular plate on one side, this is held in place with countersunk hexhead screws..stainless I think and they are stuck fast.
I think I will have to take it to someone else to open up for me.

[Graham Knight]

I'd be concerned at filling pits/depressions with epoxy then powder coating. I'd be worried that the 'baking' stage of the powder coating process would melt the epoxy Good point. I was thinking more of epoxy painting which would be OK, I don't have much stuff powder coated and I'm not sure what filler you could use in that case, maybe you couldn't.

[Graham Knight]

hexhead screws..stainless I think and they are stuck fast.
I've had this problem with old outboards, heat usually does the trick but you have to be careful not to damage the alloy castings.
The way I do it is to place a piece of steel rod (an old screwdriver will do) in the screwhead, then heat the rod with a blowtorch. The heat is conducted through the screw, you usually need to get it pretty hot as the heat is quickly dissipated by the casting.

[WX]

Thanks Graham, I'll try that. I got an old kero powered blowtorch that works very well..it's about time I fired it up again.

[ 10-23-2005, 03:42 AM: Message edited by: WX ]

[PeterSibley]

By the way...I think that windlass is a "Royal",there's an advert in an old WB by Sven Masden,Vancouver...showing a windlass that looks identical...250 kg pull,9 kg weight. smile.gif

[WX]

I do believe you are right Peter...and it's not meant to have oil in it, that's for the electric version they use the same casting.