Unidentified Metal coating removal?

[Chipm]

These are old no-name fan clutch tools that have a thin silver coating of some sort that is flaking off. How can I safely chemically remove it? No luck with either lye or vinegar so far.

Thanks!

 

[VR6ix]

Clear zinc would be my first guess. Do the edges of the part have the exact same coating? How long was it soaking in vinegar?

 

[Beerhippie]

Clear zinc would be my first guess. Do the edges of the part have the exact same coating? How long was it soaking in vinegar?

If it's zinc of any kind, it should visibly react with an acid. Vinegar might not be strong enough to see the bubbles, but a phos acid or Muriatic (hydrochloric) acid solution will show bubbles immediately. I use one of the two to clean galvanizing off before welding. Muriatic is much faster, but can cause serious rust problems down the line (like within the next hour) if not immediately and thoroughly cleaned with a lot of really hot water. I also use Muriatic acid to induce rust for that "weathered" look on outdoor ironwork.

 

[Chipm]

Thanks for the help! I switched the vinegar to a new jug and now it is working. Maybe the stuff I had in the pantry was too old - it wasn't doing much after 36 hours.

 

[mark-NJ]

Glad it's working for you.....but if it helps: Vinegar (acetic acid) that you buy in the grocery store is usually 5%. If you go to the big-box stores, you can buy 30%. It makes a huge difference.

 

[Chipm]

I removed the zinc and finished it with a rust-blue. Thanks for the help!

 

[ching0n]

I've found muriatric strips pretty much any electroplating I've used it on.

 

[Chris_Hamilton]

Why fool with vinegar when there are much better options. Muriatic acid being one. Phosphoric acid being another. Phos. acid will strip zinc coatings in minutes.

 

[Beerhippie]

Why fool with vinegar when there are much better options. Muriatic acid being one. Phosphoric acid being another. Phos. acid will strip zinc coatings in minutes.

And, unlike Muriatic, leaves a rust-resistant coating. I use Muriatic (hydrochloric) acid to make metal rust.

 

[ching0n]

And, unlike Muriatic, leaves a rust-resistant coating. I use Muriatic (hydrochloric) acid to make metal rust.

good to know about phosphoric. I keep some in gel form as rust reformer but didn't know about stripping galvanized.

I'm still unsure about phosphoric. Should I wait for a rust layer to form to apply or will applying to bare steel also form an iron phosphate layer?

 

[Beerhippie]

good to know about phosphoric. I keep some in gel form as rust reformer but didn't know about stripping galvanized.

I'm still unsure about phosphoric. Should I wait for a rust layer to form to apply or will applying to bare steel also form an iron phosphate layer?

Yes, letting bare steel soak in phos acid solution and then air-dry--no rinse--will result in some level of phosphatization. Different steels react differently.

Here's an Estwing axe I phosphatized:

 

[Firebrick43]

You only want to use a conversion coating/acid if you are painting. I personally use ospho and it is amazing how much better paint sticks with it.

You dont want to use if if you are rust bluing like the OP and its extremely lousy coating compared to a real zinc/manganese phosphate coating such as parkerizing

 

[whateg01]

Why fool with vinegar when there are much better options. Muriatic acid being one. Phosphoric acid being another. Phos. acid will strip zinc coatings in minutes.

Some would say muriatic isn't a better option. Without a way to store it away from tools and machinery it can cause more trouble than it solves.

 

[Beerhippie]

Some would say muriatic isn't a better option. Without a way to store it away from tools and machinery it can cause more trouble than it solves.

I had a sealed jug of Muriatic acid stored next to a box of ****-weld pipe fittings for about a month. I had to toss the fittings as they rusted so badly just sitting a foot away from the sealed jug.

 

[mark-NJ]

What % strength phosphoric acid do you all use? Where do you buy it?

 

[Chris_Hamilton]

What % strength phosphoric acid do you all use? Where do you buy it?

Ospho by Skyco. I get it at Ace Hardware. Klean Strip makes a similar product. Marketed as concrete cleaner at the home box stores. Lowes HD etc.

 

[Chris_Hamilton]

Some would say muriatic isn't a better option. Without a way to store it away from tools and machinery it can cause more trouble than it solves.

I've never used it actually. I meant better as in working faster. When I need to use an acid product I stick with phos. acid.

 

[ching0n]

I had a sealed jug of Muriatic acid stored next to a box of ****-weld pipe fittings for about a month. I had to toss the fittings as they rusted so badly just sitting a foot away from the sealed jug.

I have a vintage drill press that's 3/4 of the way through restoration. I had 4 gallons of muriatic nearby......I'll have to derust it again.

 

[Beerhippie]

What % strength phosphoric acid do you all use? Where do you buy it?

I use a glug or two from the jug per gallon. Phos is so innocuous that it doesn't seem to much matter--unless it's the cost. Those who measure seem to go around 10-20%.

Google it. You can get 85% for around $40/gallon online. Auto body supply shops should also carry it.

I think Ospho is the same stuff but pre-diluted. SDS says it's H3PO4, which is phos acid.

 

[ching0n]

I use a glug or two from the jug per gallon. Phos is so innocuous that it doesn't seem to much matter--unless it's the cost. Those who measure seem to go around 10-20%.

Google it. You can get 85% for around $40/gallon online. Auto body supply shops should also carry it.

I think Ospho is the same stuff but pre-diluted. SDS says it's H3PO4, which is phos acid.

This stuff is reasonably priced:

https://production-s3.wmbarrhub.com/assets/sds/401_Klean_Strip_Concrete_and_Metal_Prep_EN.pdf

Klean-Strip 1 Gal. Concrete Etch, Metal Prep and Rust Inhibitor Outdoor Cleaner GKPA30220 - The Home Depot

Remove rust from iron and steel surfaces with this Klean-Strip Phosphoric Prep and Etch. Features galvanized and aluminum finish.

www.homedepot.com

 

[whateg01]

This stuff is reasonably priced:

https://production-s3.wmbarrhub.com/assets/sds/401_Klean_Strip_Concrete_and_Metal_Prep_EN.pdf

Klean-Strip 1 Gal. Concrete Etch, Metal Prep and Rust Inhibitor Outdoor Cleaner GKPA30220 - The Home Depot

Remove rust from iron and steel surfaces with this Klean-Strip Phosphoric Prep and Etch. Features galvanized and aluminum finish.

www.homedepot.com

That's HCl, hydrochloric acid, in 10-30% concentration, aka muriatic acid.

 

[Beerhippie]

That's HCl, hydrochloric acid, in 10-30% concentration, aka muriatic acid.

CPID

Mostly Phos acid--and other ****--but not HCl.

 

[whateg01]

CPID

Mostly Phos acid--and other ****--but not HCl.

Sorry. Looked up concrete etch from the description.

 

[ching0n]

That's HCl, hydrochloric acid, in 10-30% concentration, aka muriatic acid.

not according to MSDS I linked. hcl goes for <10$/gal and has no rust inhibition.

 

[whateg01]

not according to MSDS I linked. hcl goes for <10$/gal and has no rust inhibition.

Yeah I looked up the etch not prep

 

[mark-NJ]

Slightly off-topic question: Will H3PO4 'burn' millscale off of hot-rolled steel?

I know HCl will (I use it for that all the time), but it would be nice to be able to do so with something that's not an oxidizer.

Anyone know?

 

[ching0n]

Slightly off-topic question: Will H3PO4 'burn' millscale off of hot-rolled steel?

I know HCl will (I use it for that all the time), but it would be nice to be able to do so with something that's not an oxidizer.

Anyone know?

No idea but if it strips galvanizing as stated above....maybe? I've got some forged iron....let me run a test w/my gel phosphoric....

 

[Beerhippie]

Slightly off-topic question: Will H3PO4 'burn' millscale off of hot-rolled steel?

I know HCl will (I use it for that all the time), but it would be nice to be able to do so with something that's not an oxidizer.

Anyone know?

Not in my experience. Sorry.

It'll remove rust and galvanizing just fine, but doesn't do much to much of anything else (it's in your cola and beer).

 

[hans109h]

What % strength phosphoric acid do you all use? Where do you buy it?

When I was in the market the best source I found was https://alliancechemical.com/.

Hans

 

[LopezBart]

You dont want to use if if you are rust bluing like the OP and its extremely lousy coating compared to a real zinc/manganese phosphate coating such as parkerizing

Manganese dioxide from a flashlight battery and phosphoric acid (Ospho) in a boiling solution will do "parkerizing" at home; this is best done outside. Lots of videos on youtube; no need to buy kits.