Best way to remove mill scale from steel?

[Nimonic]

I know THE best way is media blasting, but short of that, what's the best way? Need to prep some fresh new steel for enamel paint. The metal pieces are 4X4"X12' posts

I've used an industrial degreaser and scotchbrite followed by a palm sander with 60 grit paper. That's not getting it done. No way the paint will stick to this surface. Thinking about some coarse flapper wheels or maybe wire wheels, but I doubt that will be that much better than what I've done so far.

Suggestions?

Thanks.

 

[rbgearz]

How big are the pieces? Used to throw my smaller pieces in a cement mixer and let them go for awhile. Noisy but they cleaned up nice.

 

[rockwithjason]

there is a wheel for the 4 in grinder that looks like a scouring pad but more coarse. I can't think of the name of it this second but it really works well. I have heard of people using needle scalers also

 

[Trucky]

Muriatic acid. But BE. CAREFUL. times 100! edit: apparently you'll need a giant tank for that too! LOL.

Short of that, the coarsest wheels you can find.. 16, etc.

HF sells a scaler that's about 50 or 60 bucks IIRC, but I've never used one so I won't offer advice on those.

Can you mention the application?

EDIT: Thanks rbgearz, I thought it said 12" at first! Woops!

 

[rbgearz]

Didn't see that they were 12' long. Flap wheel would probably work.

 

[mountainman72]

I've had success with a course wire wheel on a grinder, but 4x4x12', wow. You'll be there a while.

Brett

 

[Jack Olsen]

Is there different mill scale in different parts of the country? I remove it where I weld, but I have never had to remove it to get paint to stick. Seems like a huge amount of work.

 

[Nimonic]

Is there different mill scale in different parts of the country? I remove it where I weld, but I have never had to remove it to get paint to stick. Seems like a huge amount of work.

I doubt mill scale is much different here vs there. I've always been of the opinion that you need to be down to "white metal" for paint to really stick. I have a pot style blaster that I would normally use for something like this. I probably should have bought some coal slag and gone at it, but then I would have to find cartridges for my ancient respirator and laid out a bunch of plastic.

Yeah, this is going to take a while with hand tools.


These are posts for a wrought iron gate.

Thanks.

 

[Letzgoracin301]

Shoot it with self etch. Respirators are cheap at home depot.

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[Letzgoracin301]

Double post

 

[GYPSY400]

The only other effective alternative to sandblasting is abrasive wheels ( sanding discs) ive used 24, 36 and 50 grit with good results.

The metal doesn't really need to be cleaned of scale to get paint to stick, but it does need to be degreased ( xylene works well) and the welds need to be cleaned throughly

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[Troutsqueezer]

I've used the scouring pad with success (the one that fits on your angle grinder). It's quick but you may have to buy two of them. Xylene is off the retail market here in CA. There are substitutes sold in the Big a Box stores.

 

[Bigplum]

Perhaps dig a trench , line it with plastic sheets and soak the lot in molasses ,
you will go thru a lot of grinding discs and it's going to murder your ears and grinder to clean up that amount of steel

 

[blinn]

Isn't POR15 Metal Prep good enough to paint? I've degreased and coated with Metal Prep for 20 minutes and just scoured it with scotchbright pad before rinsing. No problems.

 

[rodm1]

I would get the 8" grinder out for that. Probably the easiest way is leave it outside and let it rust then grind of the rust. You should post at a welding board they have talked about this before.

 

[rodm1]

Is there different mill scale in different parts of the country? I remove it where I weld, but I have never had to remove it to get paint to stick. Seems like a huge amount of work.

I think different grades of steel are different and probably the mills will very to. Hot role plate seems to have very very tough mile scale to remove. A cores grit grinding wheel seems to be to only way for me. Flapper and wire wheels don't work.

 

[J Persons]

I used a belt sander with an 80 grit belt, it cleaned up a piece of angle iron quickly.

 

[A**holes Garage]

I use a sanding disc on a 4 1/2", but wouldn't want to do that much steel with it.



Sandblast it?

 

[OkRider]

In my experience, sandblasting is the quickest and most efficient method to remove mill scale. You may have a business locally that does that kind of thing for not too much money.

 

[racer1]

I'm in the sand blasting bus. Get them blasted. Its a super simple job. I'd only charge 10-15 bucks each... AND when your done you have the best possible surface to put paint on.. Call a powder coating co, to find a local blaster...do it right, the first time.

 

[Trucky]

I'm in the sand blasting bus. Get them blasted. Its a super simple job. I'd only charge 10-15 bucks each... AND when your done you have the best possible surface to put paint on.. Call a powder coating co, to find a local blaster...do it right, the first time.

That cheap? for 12 foot posts? If you're doing it, I'm assuming you're doing that outside of a booth, resulting in losing media, plus the cost of running a compressor for a while (unless you have a decent one), plus your time and handling of the posts themselves.. not like they fit in a short bed truck very well. I was expecting a bit more $ than that. And I would think a competent business would probably be busy doing more important work (The stuff that makes them their $, and probably a lot more of it for a given time period than your posts would), resulting in you paying more to get into the queue.

Am I totally off base here? That figure seems rather low to me.

 

[Zeke]

I used a belt sander with an 80 grit belt, it cleaned up a piece of angle iron quickly.

Bingo. Nice, big ol' belt sander. Like a 4 x 24, the only way to fly.

 

[A_Pmech]

Unless these parts are going outside in a fairly harsh location, there's no need to remove the scale before paint.

 

[racer1]

trucky... With my industrial blaster, those posts would take me about 5 min per pc. Maybe..If not less.... x4 = 20 min. 15 bucks each makes me, 3 bucks per min, or 180 bucks an hour. I'd have less than 10 bucks in materials in those posts, for the $60 charge. Don't feel sorry for me, I make a killing on small parts........And still make every body happy... Take a nasty rusty steel wheel for example. I charge $15 each. 15 min for set of 4. $60....think how long you could sand and grind and scrape to do 1 wheel and try make it perfect.....Hours and hours, and they still won't be perfect. For $60, I make them perfect, save you 2 days work, customer is crazy happy, and I make $240 bucks an hour to do it. And everybody is happy..............Just like any task, the right equipment makes all the difference.

 

[A**holes Garage]

Just like any task, the right equipment makes all the difference.

this/

 

[Zeke]

That cheap? for 12 foot posts? If you're doing it, I'm assuming you're doing that outside of a booth, resulting in losing media, plus the cost of running a compressor for a while (unless you have a decent one), plus your time and handling of the posts themselves.. not like they fit in a short bed truck very well. I was expecting a bit more $ than that. And I would think a competent business would probably be busy doing more important work (The stuff that makes them their $, and probably a lot more of it for a given time period than your posts would), resulting in you paying more to get into the queue.

Am I totally off base here? That figure seems rather low to me.

The local blaster charges $100/hr for sand. He can do a lot in an hour. His compressor died a hundred years ago and he bought a portable rotary. That was a good business until the EPA stepped in.

 

[NOZZLEMAN]

Dustless blasting is picking up here around San Antonio... guy was just in my complex blasting a car. Uses crushed glass, air & water. Things are built in Houston and can hook you up with a guy in Weird Town. Good Luck !!

 

[csp]

there is a wheel for the 4 in grinder that looks like a scouring pad but more coarse. I can't think of the name of it this second but it really works well. I have heard of people using needle scalers also

These paint removal discs work really well at removing mill scale.

 

[Nimonic]

I bought some black diamond and fired up the pressure blaster. It's been ~10 years since I used it.

I forgot how much of a fun mess this is!

 

[Deadbooks]

i have the same issue, roughly, 60 pieces of 2x2/4/6 x 12'. first error was not just buying them pre-primed.

and then they came and were completely greased up. everything I tried failed to remove it bc it was so thick - until I used a pressure washer. best used on a warm sunny day.

i'll skip how I've had to store them - but let's just say the grease came in handy minimizing the rust.

now I'm going to run them through an edge sander.

I thought about sandblasting and wondered if it would give me 2 for 1 in ripping the grease and the scale off.

 

[HMCFab9]

Sandblasting if you can get it done cheap enough.
I've heard or people using Vinegar.
I have used Muriatic acid, but it's Real Nasty stuff, gives off some real bad odors & you have to rinse it with water / neutralize it with baking soda & dry it real fast or it will flash rust.

 

[jim1987]

Roloc disc

 

[DenisG]

www.ksdot.org/burdesign/bridge/constructionmanual/painting.pdf

 

[rockwithjason]

These paint removal discs work really well at removing mill scale.

yup, this is what i was thinking of. power block did a test of several methods and they had the best results with these

 

[Nimonic]

yup, this is what i was thinking of. power block did a test of several methods and they had the best results with these

Actually ended up using a combo of both strip discs and blasting. I'd use the discs for a first pass to loosen and remove about 1/2 the scale and then finish with the blaster using black diamond ultra fine. That way I didn't cook my right angle grinder and it also cut down on the blast time. The blasted surface will hold paint better too.

The wet blasting seems like a great idea but at $5900 for the entry level unit they are crazy expensive. I've got ~$100 in a HF setup and then I ditched their **** hose and dead man valve/nozzle and used a Clemco hose and 1/8" nozzle. I've got almost as much in the Clemco hose and nozzle as I do in the whole HF unit.

Thanks all for the suggestions.

 

[theoldwizard1]

Degrease it. Scuff it. Wipe down with alcohol/acetone. Use an etching metal prep or self etching primer. I have not used this stuff, but it has gotten good reviews, Kleen Strip Phosphoric Prep and Etch

Use an "industrial" alkyd enamel (Valspar or Rustoleum) with a hardener.