Phosphoric acid and rust removal

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Model T Ford Forum: Forum 2010: Phosphoric acid and rust removal
Top of pagePrevious messageNext messageBottom of page Link to this message  By Dennis Brown on Friday, February 05, 2010 - 03:21 am:

Does anyone use diluted phosphoric acid as a rust removal agent. I was reading about it in an older VF. The reason I was wondering is I was looking at Transmission drums in an engine that had water standing in the pan when I got it and there is some surface rust on the drums so there will be more inside. The article mentioned it left a residue which inhibited rust .
I have some drums I got with a batch of parts several years ago and they look like they were cleaned someway and then coated with a clear coat of some type. Not sure what is on them but they have not started to rust at all.I will figure out how to clean them when I am ready for them.
I have tried the soda and water with a battery charger and it works but I am not overly impressed with it.
Thanks, Dennis


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Jelf on Friday, February 05, 2010 - 07:04 am:

A phosphoric acid product like DuPont 5717S metal prep will remove light rust and prevent its return for awhile, but I would emphasize the LIGHT. I've read that a product available at Ace Hardware stores removes rust well. Maybe somebody who's used it will come up with the name. I've used Blue Lightning rust remover. It's excellent, but expensive.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jeff Humble on Friday, February 05, 2010 - 08:53 am:

I have used MetalPrep 579 duluted in a tub and soaked heavily rusted parts for weeks with excellent results, all rust removed and the steel is left with a golden color coating that protects the metal for a couple of days until it can be painted. Will not work for cast iron and spring steel. The spring steel will be gone in a couple of days.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Alan Woolf on Friday, February 05, 2010 - 09:29 am:

It works fine but it is slow. The one thing you must remember is not to use phophoric acid on high strength/heat treated parts. It can cause hydrdogen embrittlement and ruin the part.

Some hardware stores sell a product called Ospho that is dilute phosphoric acid. I use it for cleaning small parts.

Alan


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Schwab on Friday, February 05, 2010 - 11:48 am:

I've used muratic acid to clean up rust....probably same process as phosphoric acid. The muratic acid is usually stocked at hardware stores, I get mine at Home Depot, I think it's in the garden center. Alan, I've heard about acid making parts brittle, does this apply to sheet metal pieces or just treated parts?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Thunder on Friday, February 05, 2010 - 12:18 pm:

I have used a product called "Ultra One" ultraone.com I only have a small sample kit, so I've not had the opportunity to use is on anything larger than a small bracket. But my experience has been GREAT. I plan on buying some as my project develops.

Standard disclaimer. I am in no way affiliated with this product, nor do I receive any compensation for its endorsment.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Alex Alongi on Friday, February 05, 2010 - 12:35 pm:

I've used Evapo-Rust on several occasions. I like because it's non-caustic & reusable.

http://www.evaporust.com/


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jason Given on Friday, February 05, 2010 - 02:06 pm:

I picked up some phosphoric acid at HD (paint department) a few weeks ago to try removing some rust. I have no clue about its strength. I poured a small amount in a plastic cup and stood an old really rusty T bolt in it. Purposely leaving part of the bolt out of the solution, it took about three days and almost all the rust that was in the solution was gone. I did no prep to remove any rust like the bottle recommended. When I took it out I dragged the bolt through a snow pile to remove any excess acid and then brought it into the house and rinsed it off. I dried it and tossed it on my work bench in the house and it has not rusted at all. It has been over a week since I did this. When I rub my fingers over the bolt, it feels like a porous ceramic. I do not know if that is because of the metal and how it rusted or if it was due to hydrogen embrittlement.

My original thought was to use phosphoric acid to clean the inside of a lightly rusted fuel tank.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Wayne Sheldon on Saturday, February 06, 2010 - 04:16 am:

Some words of caution concerning acid cleaning, and bear in mind, I am not an expert. Muriatic acid is not the same as phosphoric. Muriatic acid is in the hydrochloric acid family if I remember correctly, and is MUCH MORE DANGEROUS!
If you choose to use muriatic, or hydrochloric acid to clean rusty parts, BE VERY CAREFUL. The fumes CAN DESTROY YOUR LUNGS and can KILL YOU. The fumes are stirred up when a rusty part is put in, so be prepared. The fumes can also do irreparable damage to valuable parts and possessions that are downwind. Eddies and currents can carry fumes odd directions, so be prepared. (I can hold my breath about 50 seconds, can you?)
Be careful with cast iron. A friend of mine , years ago, left an engine head in for a few days, when he took it out, it was about half gone. On the other hand, I (oops) left a VERY rusty (steel) suspension U bolt in for two weeks and it was fine (and very clean). I have cleaned many very rusty parts over the years with no serious problems. One of the rustiest coil box lids I have ever seen came out very restorable after two days soaking in well used acid. I plan to do the boat-tail's hood in a couple of weeks.
Spring leaves are another problem. It will make them brittle and may de-temper them. best to scrape, file and sand.
Muriatic will take chrome off a plated part and leave the nickel underneath in perfect condition. (For those of us that do not like chrome on our nickel age cars.) It will not harm nickel, BUT, if a part is like a hub cap with plating on the outside, but brass not plated inside, the acid could eat the cap up from the inside out.
Phosphoric acids, like metal etch, also will dissolve rust. it is slower, and the fumes are less dangerous. Note, that is LESS dangerous. Still, be careful. Do not get it on you skin if you have any kind of cut, scratch, split cuticle, etc etc etc. You would find out what pain is. Plus, it could cause serious problems with healing of the cut, etc. It is the phosphorous in a florescent lamp that can cause a cut that takes many months to heal.
Phosphoric acid also changes the surface of steel and iron chemically into something that resists oxidation and adheres well to primer and paint.
The best results I've had acid cleaning really rusty parts has been to soak and/or brush well used muriatic an appropriate amount of time (depending upon how rusty?) until reasonably clean. Take the parts, rinse thoroughly with clean water. Then immediately (before the water can dry) brush a full coat of phosphoric based metal prep and leave it. Usually it can sit for days without rusting. I often leave the metal prep on when I prime the part and have had it bond really well. (Reasonably cleaned first, the primer will not stick if there is too much left on)
Popular wisdom says you should clean with a "basic" solution after acid cleaning. Especially if you used muriatic. Usually baking soda and water is used. I keep baking soda in the box within the double plastic containers I store the muriatic acid in, in case of an accident. But I have found that parts rinsed that way usually rust too quickly and do not bond well with the primer and paint.
Hopefully, this will have answered some questions for some out there. And please, PLEASE, be safe. This stuff can work wonders, or destroy something precious. Like a friendship. Or you.
Sorry this is so long, W2


Top of pagePrevious messageNext messageBottom of page Link to this message  By Brent in 10-uh-C on Saturday, February 06, 2010 - 08:38 am:

Dennis, I use it with frequency. You need an organic-lined tank that can be heated to 170 (+/-). You need to be able to submerge the item and then have a way to aggitate it or the acid. Your solution needs to be between 20%-30% phosphoric. We neutralize with plain water.

Phosphoric will not remove anything organic (paint, grease, etc.) so we used a heated caustic solution to remove that first.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Michael K Mullis on Monday, February 08, 2010 - 12:46 pm:

Of all the rust removal methods that I have tried
like Alex, I prefer Evapo-Rust. Very easy. Very safe (biodegradable)non-caustic. I heard of it on another post. Courious, I bought 1 pint and dropped in a heavily rusted "front engine mount" and left it alone over night. The next day the rust was completely gone. A slight black film (that rinced away with water) was all that was left. It can be reused but it does eventually "fill up" with the rust particles that it takes away from the metal. I am not affiliated with the company that produces Evapo-rust in any way.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Bergmann on Monday, February 08, 2010 - 11:04 pm:

Remember the golden rule. Always add acid to the water, never the other way around.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jason Given on Tuesday, February 09, 2010 - 01:33 am:

I bought evapo-rust Sunday, just to give it a try. I also dropped a few heavily rusted bolts in to it and a cowl light mounting bracket. I did not have much time to pay attention to it. I looked at it this evening and the parts were really clean. I did take an old toothbrush and cleaned the threads. Im sold on it. I have a few parts (fuel tank) that I have been trying to determine the best way to clean.
I want to try an ultrasonic system to clean my oil lamps that I cannot get apart. (any tips??) I really do not want to use a chemical while I cannot get them apart.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Michael K Mullis on Tuesday, February 09, 2010 - 08:15 am:

I used some evaporust in my ultrasonic and it worked very well and very quick. I usually degrease parts in purple power degreaser (soak overnight thru a couple of days) with a real good rense before the evapo-rust that has proven very effective.
They also make a spray that will keep the parts from flash rusting after it has been cleaned. It too works great but I can't remember the name. You can check it out on their web site though.


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Dare on Tuesday, February 09, 2010 - 10:31 am:

YES, l use ortho phosphoric acid to clean the inside of the blck and head, block in particular around the edges where freeze cracks can occur, plug up the return and pour in fron the front, allow to sit overnight and drain, allow to dry, this leaves a nice coating that will protect the inside lining of the block and head........good luck, can use diluted but neat is better.

Cheers David.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Arnie Johansen on Tuesday, February 09, 2010 - 12:19 pm:

From the above posts it seems to imply that muriatic acid may cause hydrogen embrittlement of the metal. What about phosphoric acid dipping of parts. Will phosphoric acid cause hydrogen embrittlement also?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Arnie Johansen on Tuesday, February 09, 2010 - 07:54 pm:

Are there any chemists in the group that can answer the question? Does hydrogen embrittlement of metal happen when it is dipped in phosphoric acid?

thanks,

Arnie


Top of pagePrevious messageNext messageBottom of page Link to this message  By jack daron-Indy. on Tuesday, February 09, 2010 - 11:10 pm:

Arnie,I used to be one ,but I think you need a metalurgist.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Erich Bruckner on Wednesday, February 10, 2010 - 02:46 am:

I don't know enough to feel good about using an acid. I also used Evapo-rust and had very good results. Can't beat the safe and friendly solution. Safe for your hands and the environment too. Works for me.

Erich


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dane Hawley on Friday, February 12, 2010 - 06:28 am:

One part Molasses, eight parts water. Soak the offending metal bits for about a week or until rust-free.
Cheap, effective, safe, but a little slow.

Dane.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jason Given on Monday, February 15, 2010 - 01:12 am:

I spoke with the metallurgist at work Friday, about hydrogen embrittlement. He stated he would get me some more information regarding Phosphoric acid and its effects on metal. I believe he is going to send it to me in an email. (at least I hope so)
He stated basically with hydrochloric acid there is some kind of Hydrogen+ thing that occurs (it kinda sounded like french to me). Everyone seems to be familiar with this issue, so I wont try to explain it now. He stated how we at work cure/stop this from being an issues is to bake the hydrogen out of the metal. The directions he gave me is within 2 hours after the metal is removed from hydrochloric acid the part must be placed in a 350 deg F oven and backed for 2 hours (it might be 3hrs) This process stops the effect, and has little to no effect on hardened steel. If you do not bake especially hardened steel the hydrogen embrittlement becomes an issue only when the hardened metal only during an impact.

He stated he assumed phosphoric acid has a similar effect. As I said above he is going to check into this. When I hear back from him I will forward on the information.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jason Given on Tuesday, March 02, 2010 - 01:11 am:

I spoke with the metallurgist last Friday. He stated that hydrogen embrittlement is not much of an issue when using Phosphoric acid, which is due to the slow reaction time. He stated after the acid bath it should only need a good wash down in plain water to remove the acid.

Hydrogen embtittlement is only an issue in hardened parts and only while the hydrogen is still in the metal. To get rid of the hydrogen he stated that you should bake the hydrogen out of the parts at 350 deg F for a minimum of 2 hours. This low temperature has little to no effect on the tempering process to harden the part. While the hydrogen is in the metal the part could fail if the part is subjected to impact loading.

He stated that muriatic acid is more reactive and for that reason the hydrogen is formed at the molecular bonds more readily. He also stated that with time the hydrogen will work its way out of the parts.


Top of pagePrevious messageNext messageBottom of page Link to this message  By peter kable on Wednesday, March 03, 2010 - 08:13 am:

The actual use of Phosphoric acid has not been exactly pinned down in this discussion.

Phosphoric acid reacts with rust (Iron oxide) and neutralises it. It is part of the normal process in painting ferrous metals as rust under paint is not what one wants when you spend time and money painting.

All car manufacturers use a phosphoric bath to wash the bare steel bodies in before paint is applied. It is done immediately before the primer is applied.

Usually the steel bodies have traces of oil and dirt on them when they are finished after pressing and welding together. They have been exposed to the air, they may have been touched by sweaty hands and been splashed with water.

Any moisture in the air or from other sources will start the metal rusting. The best way to guarantee the metal is clean is to bring it in contact with Phosphoric acid.

The car manufacturers dunk the bodies into a phosphate tank and then wash is with water and dry it. It then proceedes into a primer tank and on to painting.

If you have bare steel and intend painting you should always assume it may have rust starting to form. The answer it to clean it with a phosphoric Acid solution that is diluted as per instructions immediately prior to priming the metal.

Once wiped over and washed off or otherwise treated depending on the instruction you should avoid getting it wet, touching it with your skin or leaving it for more than 1/2 hour before the primer is applied. The acid leaves a temporary phosphate coating on the surface. If it dries and leaves any white powder wipe it with a dry clean cloth prior to primer.

This step only takes a few minutes even if you are about to prime a complete car body which has been sanblasted but if skipped and the conditions are right your next many hours of spraying rubbing and polishing will be completely a waste of time if the metal rusts as it can under the paint. You then have to strip off the paint use the PA to kill the rust and do it again.

Usually metal painted properly lasts years, sometimes one finds a small spider shaped rust spot under paint on any car, other times (rarely one sees worse damage even finger prints or whole palms of hands where someone has touched the metal before it was painted.

If you use any other acid it will clean the metal but phosphoric is the only one which guarantees that you have done everything possible to do the paint job correctly.

Some manufacturers have primers that contain phosphoric acid in them and can be applied directly to metals without the need to wash them first with PA. but you would still need to ensure the metal didn't have loose rust on the surfaceand follow their instructions.

As for mechanical parts you can use phosphoric acid, molasses works also and is cheaper and some of the other suggestions ( except muriatic or hydrocloric acid) would be Ok also. but its main use is as described above.

Phosphoric acid is really safe, obviously you don't drink it or splash it in you eyes but unless you have an open wound it won't burn or sting. Thought there is probably someone who has sensitive skin that it would affect.

Even with all the latest OH&S rules its use has not been restricted, Having had teenagers using it for over 30 years I never had one that managed to inflict himself or others with an injury, it always stayed out on the bench in the shop ( still does).


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Patrick - (2) '26's - Bartow, FL on Wednesday, March 03, 2010 - 09:15 am:

I have used full strength Muriatic Acid for 40 years to remove heavy rust from steel and it remains my rust remover of choice. It immediately attacks rust all the way down to the bottom of rust pits and will leave the good metal alone, but will eventually start attacking it after several days, but the rust will be gone way before then and the part will be clean, rust free and ready to prime.

Like any corrosive chemical, it can be dangerous if the directions and cautions are ignored but, if followed, will yield very satisfactory results. Muriatic Acid must be used outside or the fumes will rust any metal they come in contact with. It will destroy aluminum, cast iron and pot metal in quick order and, if spilled on concrete, will attack and disolve it. Always have a bucket of water with a handful of baking soda mixed in to neutralize any that might spill on your skin and to neutralize the acid on the part you are cleaning, once the rust is removed. It is best to use a neutralizing container large enough to fully submerge the part in, especially if there are seams in the part that the acid has seeped into. The soda water must be able to get down to the deepest portions of the part to neutralize the acid, for if it doesn't, the acid will remain and continue attacking your part from the inside out. Keep the part submerged and turn it often, until there are no more bubbles rising from the part. After fully neutralizing the acid, rinse with clean water, dry with a towel and heat the part with a heat gun or hair dryer to rapidly evaporate any remaining water to minimize surface rust.

I have tried "Ospho" and did not like it at all. Instead of removing heavy rust, "Ospho" supposedly converts heavy rust into an inert black crust that is supposed to protect the metal, however, I just don't like leaving crusty rust in place, even if it is inert and it can have an inverse affect. I read several years ago in an earlier Forum posting where one member used used "Ospho" to clean out the heavily rusted water jacket in his block and when he came back to it, the water jacket was completely clogged and overflowing with a thick, hard, black residue. I don't know if he was able to salvage the block, but that is one thing to watch out for. Jim Patrick


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