It is a good way to remove mill scale & rust, but the acid/metal waste is expensive to get rid of. Don't try it in Your shop, as the acid fumes will CAUSE rust on everything.
Product Name: Phosphoric Acid
Ingestion: Can produce burns on the mouth and lips, severe gastrointestinal irritation, nausea, bloody diarrhea, difficult swallowing, severe abdominal pains, thirst, acidemia, difficult breathing, convulsions, collapse, shock, and death.
Inhalation: Breathing of vapor or mist is possible. Breathing this material may be harmful or fatal. Symptoms may include severe irritation and burns to the nose, throat, and respiratory tract.
Skin: May cause permanent skin burns. Phosphoric acid may not produce an immediate burning sensation upon contact, delaying the awareness of the worker that contact has occurred. Symptoms may include redness, burning, and swelling of skin, burns, and other skin damage.
Eyes: Can cause permanent eye injury. Symptoms include stinging, tearing, redness, and swelling of eyes. Can injure the cornea and cause blindness. Carcinogenicity Lists: No
NTP: No IARC
Monograph: No
OSHA Regulated: Yes
Summary of Chronic Health Hazards: There is no evidence that phosphorus poisoning can result from contact with phosphoric acid. The risk of pulmonary edema resulting from the inhalation of mist or spray is remote. Prolonged inhalation may cause respiratory tract inflammation and lung damage. Medical Conditions Generally Aggravated by Exposure: In persons with impaired pulmonary function, especially those with obstructive airway diseases, the breathing of phosphoric acid dust or mist might cause exacerbation of symptoms due
Sure, but it's also a major ingredient in cola.
Muratic acid's fumes are flammable, don;t ask me know I know, they just are.
I know acid dips are used for galvanizing, I am not familier with it for pre-painting.
Muriatic acid is another name for hydrochloric acid.
HCl itself is technically a gas, and is NOT flammable. It is only acidic in the presence of water, and in aqueous solution, its fumes are also not flammable (but breathing them can be quite harmful).
BUT, when HCl comes into contact with a reactive metal, rather than acting as an acid, it acts as a strong oxidizer (numerous acids can wear several hats), and in that reaction, the metal is dissolved into a chlorate salt, and hydrogen gas is released. Hydrogen is the gas that bubbles when zinc (think galvanizing) is dipped into muriatic acid. Yeah, that fizzing is VERY flammable.
In the USA (and also in Brazil) preparation of steel surfaces for painting is carried out according to the standards of the Steel Structures Painting Council.
www.sspc.org/standards/scopes.html#sp
There are several ways for preparing the surface, according to the service it will be submitted to after painting.
Access SSPC's site, as indicated above, and start reading standard SSPC-SP COM, that gives a general idea on how to select the most indicated standard for your particular service.
Giovanni S. Crisi
Sao Paulo - Brazil
This is mostly for ornemental iron work. When I clean tubing with solvent (laquer thinner) it removes the oil but the surface is still so slick that paint will chip very easy. On angle and plate the scale can only be removed by blasting which leaves the metal too rough. I was thinking the acid dipping would remove these things while not etching the plate, and angle too much. But etch the tubing just enough that the paint and primer would stick better.
Robert,
Since your application isn't an industrial, stringent one, but will be used for, say, househeld items like ornaments, you don't need to follow stringent requirements as those of SSPC. I'll tell you what to do.
You can use muriatic (or hydrochloric acid, which is almost the same) together with an acid inhibitor. What's an acid inhibitor? Is a chemical substance that allows the acid to eat up the oxydes and foreign matter, while leaving the metal untouched. In this manner, you'll get rid of unwanted material and the metal surface will look clean and shiny.
Many years ago I used with full success an inhibitor by the name of "Rodine", that was made by ICI of Great Britain. Now, ICI has been acquired by Akzo Nobel and I don't know whether they still make that product. In any case, the inhibitor doesn't need to be Rodine, it may be any other good quality brand. A reputable chemical products distribuitor in your area can give you a reliable advice.
On the inhibitor package, or attached pamphlet, there should be the instructions on how to use it: acid name and concentration, inhibitor percentage, how to prepare the solution, temperature, safety precautions etc. Follow strictly those instructions.
It wouldn't be a bad idea to appoint the services of a part time chemist to perform the pickling operation.
Giovanni S. Crisi
PS. Muriatic acid is the name for commercial hydrochloric acid, it has a greenish color. Hydrochloric acid is the name of pure HCl, it is transparent, looks like water.
Robert, What your looking for is done almost exclusively by powder coaters, they have a 3 or 4 part wash to clean parts before coating, as far as powder coating goes I, like everyone else like to stay with tried and true processes (blast & paint ) but after a few jobs where they spec'ed p.c. I'm sold. Holds up better than paint and basically same cost!!!!
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