Posted by Sherman in Idaho [72.47.153.61] on Wednesday, April 15, 2015 at 23:24:35 :
In Reply to: Re: Pool liner works great posted by 1361161878356MwMVgh [97.123.56.91] on Wednesday, April 15, 2015 at 19:24:26 :
When I've had parts that it didn't remove the rust from, or didn't remove the rust from some parts of, it has always been due to a bad connection. I hang the parts from hooks of copper wire and sometimes they don't make good contact with a really rusty or painted part. The solution there is to scrape off whatever the hook is touching. The more subtle problem is parts that have several pieces to them, which appear to be connected via rivets or screws, but sometimes there isn't an electrical connection. One solution is to wiggle it around and try again. Another is to hang the part with a hook through whatever portion was not getting de-rusted.
Since I have a power supply that I can dial up as high as 100 volts, sometimes cranking it all the way up will break through a bad connection and get the process started. Then I'll back off to 10 amps and let it percolate for as long as needed. There are probably a lot of cases where a simple 12 volt battery charger doesn't have enough juice to bite through the initial layer of rust, paint, or dirt.
No matter what you do, you want to see bubbles coming up from the whole part when it's in the tank. If the solution is really grungy, it helps to let it clarify overnight first. But if there are bubbles coming up, it will definitely take all the rust off. If it's heavily rusted, it helps to remove it after a while and brush/scrape the loose flaky rust off and then put it back in again. Some well-adhered rust will be chemically converted from red rust to black oxide, which is the same thing the "rust converter" products do, and is similar to gun bluing. That makes a perfectly good base to paint over.
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