Why Keeping Tools Rust-Free is Important
A while back, I lent some tools to a neighbor down the street who was working on a project in his garage but found that he didn't have all the necessary tools he needed. Now, I like to think of myself as a pretty nice guy, so since I had what he needed, I let him borrow them. Imagine my surprise when he returned them a couple of weeks later, they had begun to rust. Now, my neighbor's not a bad guy, and it had been pretty rainy, but this meant I had to replace the tools...or so I thought.
I brought up the issue to a buddy of mine who works for a casting company, and he said that anytime his company works with metals, they have to finish it in such a way that makes the metals practically impermeable to the elements. I wondered if it was possible or too late to do that to my tools, so I got to researching the process, which I found was called passivation. I'll tell you what I did about my rusty tools later, but for now, I'll teach you a bit about rust-proofing metals.
What is Passivation?
I learned that before metal parts are sold to companies, they go through a process called passivation, which basically makes them rust-proof and safe from corrosion. The process refers to making the surface of the metal "passive," or non-reactive to the elements. In simpler terms, that means steel can get wet from the rain like my tools did, but they won't rust. The way it works is by exposing the outer surface of the metal to either nitric or citric acid, which makes the metal's chromium react with oxygen to form a barrier called chromium oxide. That protective layer, kind of like paint on a car, keeps the metal from corroding when it's in contact with humidity, water, etc. Even if a passivated metal gets scratched, all that does is expose more chromium to the air, which automatically renews the passivation coating.
What Benefits Does it Offer?
Aside from making the metal protected against rusting, it can prevent premature metal fatigue. What that means is that with metal parts that have to bend or flex, like springs, if rust takes over, the metal becomes brittle and can snap and break when it does its job. As you can imagine, that's not an ideal situation and can lead to costly repairs. For example, imagine the suspension springs in your car—if those were to break, fixing them would probably cost you a hefty amount of money. A different process, called electropolishing, further protects against premature metal fatigue by stripping off inconsistencies in the surface. If there are any gouges or nicks in the metal, they can lead to the ultimate destruction of the piece. By putting it through electropolishing, you basically resurface it so it's extremely smooth and thus not at risk of turning into a broken part.
What Industries Use It?
Plenty of industries use these methods. Medical device passivation is a big deal, because it covers not only the things used in, say, hospitals and doctor's offices, but also certain things that pharmaceutical companies use. While hospital tools like blades for surgery need passivation or electropolishing to ensure the tool works its best and isn't corroding or harboring bacteria—tetanus can live within rust—other things like asthma inhalers function better if the metal on the inside of the canister is really smooth so that the drug doesn't stick to the metal. Things like dental tools are also prime candidates for these processes, as you might imagine. Aside from medical uses, though, the food and beverage industry and the automotive industry use these processes. For the food and beverage industry, this is good because it means the food processed on their machinery is safe and bacteria free—remember, smooth surfaces mean there's no place for bacteria to flourish. As for automotive purposes, cars rusting can have a tremendous impact on their safety—in addition to the previously mentioned suspension springs, pretty much the entire car is made out of metal. If none of it was rust-proof, we'd be replacing our cars a lot more frequently, and—well, let's not give them any ideas. Further, electropolishing and passivation—electropolishing more so—can help with sizing. Since metal removal with this process can be controlled extremely precisely, you can make a part fit very precisely.
As for my tools, well, I figured it'd probably be cheaper just to replace the few wrenches and saw blades I had lent my neighbor than it would have been to get them passivated or electropolished. Still, it was nice to know that if I wanted to, I had the option of restoring my tools to what they once were.