Just got caught up on reading for the first time since last night. There's been a lot of activity today. First off, let me say that I'm a newbie at this. I've only made a couple test runs. I've gotten side-tracked with some major garage cleaning and remodeling, but I'll be back at this soon. Here are my thoughts on what's currently being discussed.
First off, I'll repost this link:
http://myweb.tiscali.co.uk/andyspatch/rust.htm
If you haven't checked it out yet, do so. The guy apparently has a lot of experience with the process and has tuned it to get the best quality results, NOT THE FASTEST RESULTS. Those of you getting lots of buildup on the electrodes because of inadequate electrode surface area or high amperage are excellent case studies in what he says.
He's restoring artifacts, so he's concerned about reclaiming as much of the surface as possible. He makes the statement that if the process moves too fast, the resulting surface is more porous. That may not be an issue for what we're doing, but I wonder if our parts will re-rust faster as a result of the increased porosity.
If what he says is true about low current resulting in essentially no build-up on the electrodes, then I'm all for giving the process time to work slowly. During my test runs I was anxious to see something happen, but letting it run slowly and forgetting about it for a while might be a good way to avoid a lot of electrode maintenance. According to what he says, the voltage should be low enough through most of the process that you don't even get bubbling.
I understand the thought process that whatever comes off the part will end up on the electrodes, but maybe that doesn't have to be true. If current density on the part is low, anything that flake off--paint or rust--will have a lower electrical charge. There's bound to be some minimum threshold of charge required to carry any particle to the electrode, such that below that threshold the particle will settle to the bottom of the tank. Following that same thought process, more distance between the part and electrode should allow more particles to settle out.
On line of sight, I think there may be two issues at play here. Line of sight is a problem, but that could be overcome in most cases by suspending another electrode inside or over or under the part. The other issue is charge repulsion on adjacent surfaces.
In '95, the company I worked for supplied center blanks and spun rims to aftermarket wheel manufacturers. We had just added some new steel wire manufacturing capabilities for a DOD contract and were looking for additional markets. About 2 weeks before the SEMA show, someone got the idea to make a custom tailgate for the then relatively new and radically different Dodge Ram to send to the show. I designed it and a couple of our maintenance guys built it. It had a minimal sheet metal frame that matched the adjoining contours of the truck and the center of the tailgate was relatively open to allow air to pass through. The opening housed a grid of 5/16" steel wire that provided enough strength hold a couple hundred pounds. Instead of a plain square grid, it had assymetrical sweeping curves similar to the lines of the bedside. We decided to chrome plate the whole thing before sending it to Vegas to be installed on a truck in the Weld Wheel booth. We had a shop in Indianapolis do the chrome plating. The results looked great from a few feet away, but where the wires passed into the sheetmetal frame the chrome had a yellow tint. The chromer told us we would have been better off to plate the grid separately and then bolt it into the frame because the similar charges have a tendency to repel each other in the sharp corners. The result was poor plating in those areas.
In our case, I'd expect poor rust removal in similar areas. I'd also expect that lower current, and therefore lower overall charge density, would lessen the problem.
Sorry for rambling,
Jerry
