Wiktionary
vb. (context intransitive English) to come apart, from the process of rusting.
Usage examples of "rust off".
She dipped the copper bristles in solvent and resumed brushing the rust off the sear.
His voice was getting back to normal, like a door that doesn't squeal as loudly after use knocks the rust off its hinges.
I've seen him take a rusty old wrench he found in a vacant field and scrub the rust off of it until it shone like new.
He had worn all his rust off long ago, but nothing would file his spiky head down.
You'll have to scrape the rust off the handle first, so the connection will be good.
And once you start, you'll find you know almost all of the stuff anyway - it is, as I said, mostly a matter of cleaning the rust off the drillbits and sharpening the blade of your saw.
While Sevri shook it in a sandbag to get the rust off, Paks worked at the stiff lacings of the bridle.