The Home Machinist!

Thanx for the replies. I was told that there is something that is called "rust converter", I guess its some sort of acid that "corrods" the rust and turns it into a blackish layer. but as I've been told it must be coated with primer paint, so, its not for use on machine tools.

That, too, is a phosphoric acid product, with which I've had less than acceptable results. I painted the 1,000 gallon oil tank behind my shop---and wish I hadn't. Anywhere there was heavy rust it continued rusting. Never again!

The doors on my shop are commercial steel doors, made by Curries. It took a few years to get the shop finished, so doors that came primed rusted slightly. One has yet to be painted. I used phosphoric acid to clean the rust, as well as Naval jelly. There's considerable difference between the Naval jelly (buffered and made thick so it adheres), but both of them eliminate rust down to clean metal. It does require a little attention---one can't apply, walk away, returning later and expect a perfect job, but a perfect job can be accomplished with just a little effort. Once killed, the rust does not return in the short term. I've allowed cleaned surfaces to sit more than a couple days and found them just as rust free as they were when I had finished the stripping process. That's significant in that we have moderate humidity where we live, so things rust readily.

Phosphoric acid tends to build a phosphate coating, which manifests itself as a somewhat iridescent finish.

Harold

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Wise people talk because they have something to say. Fools talk because they have to say something.

I frequently use Phosphoric acid in liquid form. Much cheaper than products marketed for rust removal. And I've never seen it attack ferrous metals at all. Usually I just fill a tub and soak parts, gets them nice and clean as long as you get all oil off before putting them in the acid. If it's too big, you can soak a rag. Very mild stuff, I've gotten it on my skin a few times with no problems, though I always wear gloves and eye protection.

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Russ
Master Floor Sweeper

This is good information. The way the post was presented was not to place a 150# table into a tub but to remove rust while still intact.

The black surface that results from a phosphating process on steel is iron phosphate and this film has properties somewhat like blotting paper. The rust protection is derived from the type of oil that is caused to soak into this fine layer. A phosphate layer devoid of any subsequent oil sealant will not afford any rust protection to the steel. A phosphate layer is an excellent base upon which paint can be applied and be caused to efficiently adhere.
Regards,
Bill.

Your description pretty well covers my experience, the only difference being that the black layer didn't appear to absorb paint worth a damn. The oil tank in question continued rusting, in spite of using a high quality primer and paint after the application of the rust converter.

By sharp contrast, where I used both Naval jelly and phosphoric acid directly, once rust had been dissolved, the remaining surface was bright metal with a trace of iridescence. It was clear that the acid had done something to the surface of the steel---as it resisted rusting. May not have been effective had I left water on the surface, but it was dried with a rag immediately after rinsing. Not a hint of surface rusting by this process.

My conclusion is that using phosphoric acid, by any means, is an excellent way to kill rust. I have had no difficulties in any way with surfaces that were treated accordingly, but the notion of converting it and allowing it to remain leaves a great deal to be desired.

Harold

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Wise people talk because they have something to say. Fools talk because they have to say something.

Harold,
I should have mentioned that my comments on the phosphating process related to a manufacturing situation where the steel surface being treated is invariably not rusted. I was not wanting to imply that any phosphating process has the ability to restore and rust proof a steel surface that is already substantially rusted; it does not.
My comment was just a technical aside.
Regards,
Bill.

That pretty much parallels my experience, although it is contrary to claims made by the suppliers of the product. They really want you to believe that rust is inert once treated.

I don't think so.

Thanks for your comments. They bolster my thoughts.

Harold

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Wise people talk because they have something to say. Fools talk because they have to say something.

Hi
reading your comments based on your experience using the phosphoric acid, I've learnt that there is a black layer on the table after using the stuff. I would like to know if there is a way to remove that layer in order to "restore" the grey metallic look of the table?
Thanx.

As I understand it, the black layer is iron phosphate, the result of the phosphoric acid reacting with the rust. I expect it would be removed by abrasion, but it's doubtful you'll ever restore the surface to the condition before rusting. The damage has been done. It's entirely possible you'd have to remove several thousandths of material to get down to sound metal, where you'd have a uniform color.

Harold

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Wise people talk because they have something to say. Fools talk because they have to say something.

Today was office day for me.
Washed both vans, made some phone calls, and did an experiment.
It took a bit to find some "washing soda" as it not sold at either of our local grocery stores. I did stop by the local paint and body place and pick up a pint of "Rust-Mort" for 20 something dollars, it is 75% Phosphoric Acid, before I found Arm and Hammer "Super Washing Soda" at the local Ace Hardware for 4 something.
As anyone who has read my posts knows, I have lot of rust to get rid of. =:0

Here is the before picture of a swivel base for a 6" vise.



In the 5 gallon bucket. Added soda and water. Took a piece of flat bar, and used a c clamp to hold it to the side of the bucket. Connected battery charger. Left is set for a couple of hours. Pulled it out to have a look and things were going well. Blasted it with a hose, couple of quick hits with a SS wire brush and back it it went. Let run for about 5 more hours. Dried it off, add some oil, took some paper towels and a T-nut cleaner to the inside of the track. And this is what I have now.



I did not flip it around during the process, so that the anode was on the back side. I think it was in good shape to begin with.
I will take picture of the set up while doing the next parts.
I have not tried the Phosphoric Acid yet. This is working so well it is like magic.
I will take a wire brush to the degree ring where the numbers are, to make it easier to read. Then I need to find it a home, out of the way, in the shop.

Thanks for having this discussion, it is going to save me a lot of time, money, less paper towels/rags, less time around solvents, no air born rust from brushing. It's just a win win in my book. Should have done it sooner.

Now to rig up a multi-part setup, and do a small vise. Who knows what else may hit the soda bath soon.

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Pat P in the Great NW.

I recently tried out some stuff called "Evapo-Rust", which I found at Horror Fright (and also at Tractor Supply) to remove surface rust (I want to emphasize SURFACE) from a small tilt-table I'd gotten.

I did NOT do any kind of dimensional measurement (and I doubt that I could have, in any meaningful way) to see if the stuff changed the actual metal. But it certainly removed the rust, leaving a surface that looked like aged iron. Not bright, but not black either; kind of greyish. There were a few marks on the surface where the toothpicks I'd used to keep the surface off the bottom of the tub rested, but nothing that couldn't be lapped out, or just let be.

Now, I don't have a clue how this would work on heavy rust. But it might be worth a try. The hype claims that it "reconverts" rust to metal, but I don't buy that. For superficial rust, though, it seems to do the trick.

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Pete in NJ