The best way to remove rust from cast Iron?

Besides sandblasting, what is the best way to remove rust from cast Iron?

Kinda depends on how big a part.

For small to medium parts, it's hard to beat electrolysis. For larger parts, if you don't want to blast, you can use oven cleaner to get off any heavy paint that remains, and then proceed with a twisted wire cup brush on an angle grinder to get the heavy rust and any residual paint off. From there, any sort of good rust treatment will convert any light rust remaining that the brush will never get to something more stable and paintable. Some are aerosols that leave a paintable base, but I always worried that the base won't be compatible with the primers or paint I plan on using. I like Ospho or Jasco, which are just thin solutions of phosphoric acid and convert the whole surface from plain iron or steel or rust to iron phosphate, kind of the same idea as bluing a gun.

Ditto on the electrolysis. I have used it for years redoing old tools and such. Its the easiest method I have found.I use a beefed up dc power supply to do mine and it really cuts the time down. One warning though if the part has any plating on it don't use this method to clean it. It will remove the plating,it works the opposite of plating. Some of the guys here where I live that look for old Civil War relics use this method as well.

As far as oven cleaner I have not used it on iron but I do use it to clean aluminum. If the part is small enough to put in a plastic bucket I sometimes use water and lye. Be careful to check it often because it can eat away the aluminum iif you leave it for a while. After I wash it I will sometimes polish the aluminum with the finest steel wool I have,then sand lightly with at least a 800 grit sandpaper then polish it off with some siver polish wadding pad I get in a tin at walmart. It gets aluminum to a mirror like finish. I used this when I polished my trim on my old truck. They put a adonizing coating on the aluminum to preserve the shine. But after 30 years or so that coating turns to a milky color. So after you clean it you need to wax it or clear coat it.

ZEP makes a rust remover that works like nobodies business. It comes in liquid form so you can spray it on with a squirt bottle, let it set for a few minutes and then rinse it off. I had an old stove that had been outside for years and was covered in rust and loose scale. It took a couple of times spraying it down with the remover and a wire brush to get the scale off but when I weas done it was back to bare metal and actually looked like it had been sand blasted it was so clean.

Wire brush on a 412 in disc grinder. Hoss

interested in dc power supply set=up

Do a google search on electrolysis rust removal for more info on how to do it. Stovebolt site has a good page and pdf download on it.

As far as the power supply I use its a industrial type , I bought it secondhand. It produces up to about 180 volts and is varible. I don't think it has any name on it of who made it,probably was made in house. I usually clean at around 100 to 150. I can clean stuff in minutes or an hour compared to many hours or overnight if I used a charger. As far as getting one just keep an eye open on industrial sales or other places that sell manufacturing items.

Most folks just use a battery charger, low amps 2 or 10. There's some discussion about advantages to hooking the stuff in the tank to a battery and then hooking the charger to the battery.

Battery chargers do work good. I have a industrial power supply I use that supplies a higher current and voltage. It seems to work really fast compared to a charger. You can look up electrolytic rust removal on a search engine. The website called stovebolt has a good article on it.

Electrolysis is a really good way to strip anything without being abrasive and possibly abusive to the part but be careful. If you have never done it before this process can release gases (most notely hydrogen) which can be poisonious or explosive. Do this in a well ventilated area.