I've done a fair bit of rust removal and treatment of various metals over the years. Most of it involved vehicles and equipment but I also do some painting of other metals so removing rust is part of the process.
I've shied away from the converter products, not so much that they don't work but almost all require another barrier coat of some sort for the surface and removing the rust is just as easy, at a lower price.
One of the better rust treatment products is the Martin-Senour Iron Etch line of steel etching products. They are designed to remove rust and some have a detergent, also. It was the use of the MS products that piqued my interest in how these products worked and if I could find a substitute that was less expensive. The Iron Etch was about $25 a quart and a large project meant more cost. What I determined was that Iron Etch, Ospho, and most of the rust removal products contained phosphoric acid. My search then became a source of phosphoric acid that was cheap, available, and did the job. To date, the best I've found is liquid water softener cleaner. It is available at all the big box stores and sells for a fraction of the commercial rust removers.
The WS cleaner is sprayed on and allowed to etch the rust off the steel. In most cases, this is a matter of hours. A second spray coat is applied and the metal rinsed with water. After this, it is important to apply a primer or sealant quickly as the steel will start to rust quickly.
A user needs to be aware of the hazards of using an etching product like this---IT IS ACID__IT WILL BURN YOUR SKIN AND IRRITATE YOUR LUNGS. If you allow the solution to drip on concrete, it will etch the surface of the concrete, not as bad as muriatic acid but it will clean and discolor the surface.
