What kind of steel do you have there? Nice work by the way. Mill scale? as in "flakey"? I process thousands of sq ft of sheet steel every day for powder coating. Are you truly dealing with a flakey scale like you would get on a laser cut edge or on the surface of a fresh weld or?
its not flaky just a blue color, thanks for the compliment, it only took 4 patterns and this is the secound firewall, had to use some welding clamps and a piece of angle for a metal brake......
What is it like 18-20 gauge? I wouldn't sweat that blue color if it isn't flaking. Take a close look at the outsides of your bends where you had to brake the sheetmetal. If it's going to crack and flake it will do it on the outside of a bend right on the crown where the metal is stretched. A lot of the steel I process for powder coating has that blue surface. As long as the surface is tight, not flaking/delaminating you should be good to go. We do everything automated with a 5 stage washer that cleans mill oil & soils from the steel, rinses then applies an iron phosphate conversion coating followed by 2 more rinses. The phosphate gives the surface a little "tooth" and it's also a corrosion prevention sort of thing. You can prep steel in this same way at home with some of the water based metal prep products out on the market. Or you can hit the whole piece with a DA and some 320 grit, or just hand scuff it with a fresh piece of maroon or green scotch brite pad, wax & grease remover, epoxy prime and follow through with what ever your paint plan is for the project.
Sheet metal don't get mill scale protection, it gets sprayed or something. Go ahead and paint. The box tube and strapping will have that **** on it and it you want cleaner stuff tell the metal supply place you are tig welding and they'll give you cleaner metal.
you can let it rust lightly. sometimes it's easier to wire brush the rust away than to remove the scale.
Sounds like hot rolled to me, use a DA sander with a course grit. I wouldn't let it on, but that's me. Sandblasting might warp it, nice work.
Don't paint over it, the paint will peel. My shop replaced a panel on a school bus with hot rolled steel. the tech DA sanded the panel with 80 and epoxied it but the black **** was still on there. Six months later it came back with the paint falling off. Best and fastest way to remove it is by sandblasting.
Had the same problem on the tube frame of my lakester. KBS Rust Blaster will take it off. Soak a shop rag or towel in rust blaster and apply to surface. Let is sit for 1/2 hr then remove rag. Mill scale will the come off with a wire brush or co**** 3M nonwoven scrubber. Rust blaster will also etch metal for better paint adhesion.
I knew a guy who would put his fresh steel outside and let it "cure". In other words he let it get a light coat of rust, then sanded it off. Not sayin' this is what you should do.....just sayin...
thanks guys, i cant take any credit for the tunnel, its from howells sheetmetal, about 30 bucks, kinda hard to make that firewall without a sheetmetal break but it can be done....
work with raw steel like that everyday, ot stuff, after all welding, grinding, sanding is done, we just wipe down with solvent and prime, paint....never have any problems....besides it is a firewall, not like a fender or somthing.....wipe it down with acetone and paint, it`ll be fine.....
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