Preventing rust on bare steel before painting

I make small parts out of galvanized steel fence that is welded. Before I can paint them I clean the parts in an acid bath to clean the galvanized coating off and to remove the rust that is almost always present in the weld where the two pieces of wire connect. I make 1000's of these parts ahead of time and paint them all at once. After the parts are clean I rinse the parts off and dry them in a shop made tumbler that blows hot air on them while they tumble to dry them. The parts look great until the next day when I get ready to paint them and find that half of them are rusted already.

I need to find a way to prevent these from rusting over night so they can be painted, or even better, for a week or longer so I can make even more ahead of time. I can't oil them or use anything will will interfere with the adhesion of the paint or I'm right back to cleaning them again. I need to be able to paint them without spending a lot of time getting them ready since it already takes all day to paint them in the quantities I need to get done.

I've left them in buckets of water overnight and that works but then I need to spend hours I don't have drying them. I tried putting them in the shop's refrigerator thinking the lower humidity would help and that worked great until I took them out. The warmer air in my air conditioned shop caused condensation that need to be dried, again taking a lot of time.

I haven't been able to find any answers on this forum or on line but I thought somebody might have an answer for me. Everything I've found about preventing rust on line basically talks about different coatings that cover the metal.

Thanks,

Steve

I have the same problem. I soak a part in phosphoric acid and just let the part dry on cardboard. The acid will dissolve the galvanized coating and clean any
rust. The residual coating that dries on the metal will inhibit future rust and will take paint. The stuff I'm referring to is the solution that comes in many products.
One is the solution that you brush on nail heads that are rusty before painting a house.

I'm guessing the paint is not super glossy lacquer or similar, so how about a paint preparation that improves paint adhesion as well as prevent rust? Something like Ospho, or Pickel-X or Metal Prep? Most leave a phosphate coating on the bare steel.

I'm a fan of phosphoric acid too, I de-rust with electrolysis but that leaves a fresh, raw metal surface that flash rusts in minutes unless treated - phosphoric does the job, if it's something that'll remain bare metal (mill table, lathe boring table etc.) it gets furniture wax (*silicone free* if you might ever want to paint it or nearby) heat up with a hot air gun until it melts and wipe off the excess - mill table f'rinstance hasn't rusted in 2 years with soggy English winters

Dave H. (the other one)

Thank you for the replies. The phosphoric acid sounds like exactly what I need. I'm guessing I can just dip the parts in and let them air dry and I'll still be able to paint right over top of it when I'm ready? Will that discolor the steel when it dries? I clean the parts now with diluted muriatic acid I buy at Home Depot and rinse them off. If I leave that acid on the parts then they turn almost black and leaves a film on the parts that needs to be cleaned off. From what I'm reading I'm afraid this will do the same thing if it's not rinsed off and then the parts are uncoated again and open to rust.

can you buy the parts un-galvanized ?

What doo they look like ?

I buy the 16 ft lengths of field fence and cut that up to make my parts so I can't get it not galvanized. I found the Ospho hopefully in stock at Ace hardware, I'll go buy a gallon and try it out. It sounds like what I'm looking for. It'll probably be cheaper to keep cleaning with the muriatic acid and then just dip the parts in the Ospho if it works. I'll let you know what happens. Off to the store!

After you are done with cleaning them, just submerge them in Lacquer thinner and leave them there until you need to paint them. They will be dry within minutes of removing them from the container you have them stored in. Maybe a little smelly for a short time while drying but very effective. They can be in there for a long time and never rust. Just look inside a thinner can and it is like new even sitting on your shelf for years. When it is empty and left open it will eventually rust. We had a vacuum chamber for drying small parts after washing before paint. The chamber was very effective and even the parts that sat in there over the weekend never rusted. They were cast iron parts. Ours had a heater on it also. Google vacuum parts dryer.

Could you just drop them in a sealed container of 90% isopropyl alcohol? It'll evaporate off your parts pretty durn quick when it's time to paint. Not positive the effect it'd have on paint adhesion.

Here is a link to a description of the phosphating process. It is more than just dunking the parts. You can also look up the process in Metals Handbook. Mine is the ninth edition, volume 5, surface cleaning, finishing and coating.

Phosphate coating [SubsTech]

Tom

steveonmars said:

Thank you for the replies. The phosphoric acid sounds like exactly what I need. I'm guessing I can just dip the parts in and let them air dry and I'll still be able to paint right over top of it when I'm ready? Will that discolor the steel when it dries? I clean the parts now with diluted muriatic acid I buy at Home Depot and rinse them off. If I leave that acid on the parts then they turn almost black and leaves a film on the parts that needs to be cleaned off. From what I'm reading I'm afraid this will do the same thing if it's not rinsed off and then the parts are uncoated again and open to rust.

Click to expand...

When dry you can paint.

The color changes to a dull gray.

I am doing what you are doing with the muriatic acid, as a first stage rust remover. The phosphoric acid is applied only to coat the part.
I have found no other way to protect steel from rust before painting. I know I could use oil but then it has to be cleaned off.

zinc phosphate is the standard choice for steel coating in preparation for paint. It is a reasonably hot bath, 90*C ~200*F that parts have to stay in for about 5 minutes or more, depending on thickness of the layer you want.

HCl leaves chlorine on the surface that should be cleaned off in NaOH bath. I recommend staying away from HCl for cleaning unless you follow with NaOH bath. Phosphoric acid can be used for cleaning as well as a separate bath of phosphoric acid with zinc added to it for zinc phosphate coating.

Yes i have done the acid cleaning thing, and yes they rust really easy after that.
I thought it may have been acid fumes in the area doing damage to adjacent parts.
i found its best to get them dry really dry, could be some residual acid left on the part.
The material was a magnetic stainless tool steel which should be fairly resistant to rusting as it was to be used in food service processing.
had to rework quite a few parts to get them looking good to go.

This process works:

5717S™ METAL CONDITIONER

5718S™ CONVERSION COATING

painting over ospho is not a good choice unless the ospho is neutralized/removed. i used to use a ppg metal prep, don't remember the number but it will google.

I used flood penetrol for a project...not sure how well it would work as an undercoat.

Hydrochloric is disasterous for causing rust,and should be dumped on a concrete waste to neutralize it......even a sealed of container of the acid will rust any steel around....get rid of it....Chloride ion quickly penetrates steel to cause catastrophic failure in the long term.

I have done a fair amount of KG and Cerakote on firearms. KG has a product called K Phos that is a pre coat prep that is supposed increase resistance to rust and increase the durability of the coating. I’m guessing it’s just phosphoric acid. These types of coatings are sensitive to the prep of the bare metal so obviously the Phosphorus doesn’t affect the adhesion.

Dip the parts in Evaporust, then let them dry. They won't rust before painting.

metalmagpie

Thanks for all the info.

Penatrol isn't available any more, I used it before for coating unpainted steel for a clear finish and it did work nice. A little expensive for what I'm making to use before painting.

The Evaporust is basically the same as the Ospho from what I've been reading. I'll try the Ospho first since I just bought some.

It sounds like my biggest problem is using the HCL to clean the parts in the first place. It's cheap and easy to find which is why I'm using it. I'm going to try the Ospho, which is basically phosphoric acid with some additives. I'll see how that works using it both instead of the HCL and after the HCL and let everyone know what I find.

One of my main issues is cost. I'm disabled and make these parts to sell on eBay and a couple other sites for extra money. My profit margin is low enough to sell a lot and still make some money. If my costs go up too much I have to raise my prices and then I don't get the sales to offset the time and money I spend making them. Just raising prices a year ago to offset the Post Office price increase costs me a lot of sales.