How To Remove Rust

Created: July, 2010
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The removal of rust is a task every model engineer is going to be faced with at some stage and there must be almost as many ways of doing this as there are types of rust. You may hear the term "oxidation" used interchangeably with "rust". This is not quite accurate as while oxidation of iron bearing materials produces the brown stuff we call "rust", oxidation of copper produces a greenish copper oxide, and oxidation of aluminium, under controlled conditions, produces a form of aluminium oxide we call anodizing. So rust is oxidation, but oxidation is not necessarily rust.

But for this How-to tip, we will discuss that redish brown stuff that forms on steel and other ferric materials, often when we least expect it. This is caused by the oxygen, generally dissolved in water, effectively burning the surface with the loss of electrons, which is not really of interest to us. What we want to know is how to remove it, restore the finish, if possible, and perhaps prevent a recurrence.

There are numerous and quite effective "rust converting" liquids you can buy and if you have one stockpiled, good for you. I've used a couple in the past and they work as advertised. Guy Latuard's Third Machinists' Bedside Reader highly recommends a product named Knorrostol, though I've never been able to locate any Downunder. So what to do if you don't have a commercial rust remover on the shelf?

First, let's select a test subject. For a long time, this little Dremel collet chuck wrench sat in a dark, seldom visited corner of my workbench. While the corner was seldom visited by me, Buster the cat did visit and decided he loved that little wrench so much that it needed to be permanently marked as his property. Well let me tell you, there is rust produced by simple oxidation, then there's the capital-R rust produced by cat's pee. Eventually I noticed the smell, and the wrench. The bench corner got an enzyme treatment and the wrench got bagged, not because I especially needed it, more like because I hate to throw things away.

Years later, a restoration page was sent in by Adrian Duncan wherein he described how he brought a Hope B back from the dead. Adrian used "Liquid Wrench", a soft wire brush, and ultrasonic cleaning to clean up and disassemble a cylinder and piston which seemed to be thoroughly rusted solid. Shortly after the piece appeared, an email arrived saying nice things about the site and Adrian's Hope B restoration, but wondering why he had not just used the vinegar trick? This was not one I'd heard of, but a quick web search convinced me that it was well recognized as a rust-remover and I decided I'd give it a try, someday, if I remembered (I don't particularly like the smell of the stuff, actually).

A workshop clean up session a year or more down the track found a little plastic baggie with the extremely rust caked wrench and recalling the tip, I decided to give it a go. One Internet site suggested lightly brushing vinegar on the rust. Not surprisingly, this produced nothing but a smelly, rusted wrench. So the next step was to totally immerse it in 1/4" or so of normal, white, household vinegar in a little ceramic cooking container.

For about three days, nothing happened and I though I'd found yet another piece of disinformation for which the Internet is justly famous. But about day four, I noticed a lump had fallen off the growth. I gave it a bit of a poke with a piece of soft iron and more large lumps fell off. A bit more and all the "growth" had gone, but the surface was still severely rusted. Well this sure was progress, of a sort.

The next day, it was obvious with the "growth" gone, the vinegar was well and truly converting the iron oxide to something else. And after about a week, the wrench was as clean as you could wish with not a sign of rust. The surface is somewhat pitted, as you might expect, this having been a rather extreme case, but the rust was 100% gone. The only downside was how long and how much effort it took to clean away the brown ring left on the inside of the little ceramic container before Ruthie saw it.

So I think it is safe to say that yes, normal, white, household vinegar can be used to remove even the worst cases of rust, provided you are patient and can immerse the part in the stuff long enough (why do I feel like I'm writing a script for Myth Busters?) There are other ways, but this one works so well I'd keep it in mind for when I need a rust removal job done that simple rubbing with steel wool is not up to.



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