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Old 12-04-2008, 01:13 AM   #1 (permalink)
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Best way to remove mill scale?

Now that I've got my Torchmate plasma table up and running I've obviously been going through a lot of flat plate. I've also been practicing a lot with the TIG, and to get good welds you have to take that black coating off of the plate first. I've always loved my 36 grit sanding disks for shaping and smoothing parts, and they work great to remove the scale when they are new, but they quickly get polished smooth and stop working. My wire wheel doesn't do any better. What are you guys using to get your steel clean?
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Old 12-04-2008, 05:12 AM   #2 (permalink)
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I have a friend who makes water tanks for livestock, and uses one of two methods: he either sandblasts the plate, or drags them around the lower part of his yard, which is blowsand, cleans the rust and scale off quickly.
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Old 12-04-2008, 05:35 AM   #3 (permalink)
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a roloc sandpaper disc on a die grinder works great, but I wouldn't want to do a big piece of plate with it, that's for sure.

if you find yourself needing to do this on a large scale, woulnd't it be easier just to buy cold rolled?
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Old 12-04-2008, 05:57 AM   #4 (permalink)
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Use different steel. When I have an important project (mine ) I order P&O steel. I think it stands for pickled and oiled and it looks clean and bare. There is no millscale. Thats what I use on my Plasmacam adn the place that cuts some stuff for me with a laser uses it too. Ask your supplier about the steel used for water, laser, plasma cutting.
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Old 12-04-2008, 06:00 AM   #5 (permalink)
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go to Home Depot and get a gallon of Behr concrete and rust remover. its in a black jug with white and purple label. essentially, its phosphoric acid with some detergent.

edit: i just looked at the Behr website and don't see it. i'll get the product # off the jug i have tonight and post it up...they may have changed packaging.

i mix it 1 part Acid to 2 parts water in a 5 gallon bucket. soak the parts for 30 minutes and it will take off all the mill scale and slag. you might have to lightly rub over them with a scotchbrite or rag to get it completely off.

next, dunk into a bucket of water mixed with baking soda to neutralize the acid and rinse them off.

wipe them dry.

i usually hit the parts with a light coat of WD-40 and wipe with a rag to keep them from flash rusting. the WD-40 is so light it doesn't really affect welding.

you are essentially Pickleing and Oiling the parts...

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Old 12-04-2008, 10:15 AM   #6 (permalink)
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So far it sounds like my options are either buy different steel, or do what I'm already doing, cause all of those solutions would take even longer.

The down side of getting different steel is that my local, super friendly, cheap supplier is very limited on what they actually stock. I'd probably have to order from a place like Industrial Metal Supply, which is a hell of a lot more expensive, and about 30 miles farther away.

EDIT. Damn, just called all the suppliers I know of locally and apparently 3/16 cold rolled is just about impossible to find without a special order. Sucks too, cause I like workin with CR a lot more anyways.
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Old 12-04-2008, 01:12 PM   #7 (permalink)
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this the the Behr stuff:

http://www.behr.com/behrx/act/view/p...ioners&catId=3

its in a new package.

this takes about 20-30 minutes of soaking, but if you leave the parts in longer they still come out fine.

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Old 12-04-2008, 01:42 PM   #8 (permalink)
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I've just used a Dotco with a sanding disk. The good disks will last quite awhile.
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Old 12-04-2008, 08:31 PM   #9 (permalink)
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WTF is a Dotco? I just googled it and came up with about 50 different tools. Everything from Buffers, to die grinders, to drills.
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Old 12-04-2008, 09:56 PM   #10 (permalink)
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I've always used just a regular grinding wheel/disc for mill scale and a 36 grit pad for everything else. Just ease over it with the grinding disc and if it has too much base metal reduction or grind marks take the 36 grit pad and smooth it out grinding in the same direction until all the marks are gone.
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Old 12-06-2008, 12:03 AM   #11 (permalink)
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What I've recently found to work great are the 3M Clean & Strip wheels, they're kinda spendy but they work great. If you need to remove a really large area it might get a bit tedious, but they do work fairly quick.

I don't think that I could go back to anything else now for just cleaning around weld joints. I just use a right angle air die grinder, just make sure to spin the wheel off the material, not into it. Otherwise it'll shoot big chunks of the wheel off and they hurt. You can get them as a normal wheel or as a roloc style wheel. I haven't tried the roloc, but I'd like to.

I really recommend at least trying one of these. You can pick them up at any hardware store or even walmart. Here's a link to what I'm talking about.

http://www.amazon.com/gp/product/B000BQURDI

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Old 12-06-2008, 09:03 AM   #12 (permalink)
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This is what one of the guys at the station used when they made a new griddle out of 1/2" plate. Basically soak it in vinegar.
http://www.armourarchive.org/essays/...and_rust.shtml
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Old 12-06-2008, 09:27 AM   #13 (permalink)
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A torch works pretty damn well...
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Old 12-06-2008, 12:13 PM   #14 (permalink)
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just get some sheet metal, that shouldnt have the hot rolled black finish. that black junk is a B&tch to get off even on square tube it takes forever with a 36 grit flap disc. hitting it with a flap disc will probaly leave a a unflat surface also.
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Old 12-06-2008, 01:42 PM   #15 (permalink)
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just get some sheet metal, that shouldnt have the hot rolled black finish. that black junk is a B&tch to get off even on square tube it takes forever with a 36 grit flap disc. hitting it with a flap disc will probaly leave a a unflat surface also.
I'm not sure what your definition of "sheet metal" is, but I've always known it as that thin stuff your cars body is made out of that crumples up if you lean on it to hard. Not the stuff you'd use for mounting your suspension. I've already searched a number of local suppliers for cold rolled plate, or P&O, and none of them stock 3/16 or 1/8" plate. I could have them special order it, but I'd need to buy about 5X the amount I need, which would cost me an extra $1k or so. Not exactly pocket change.
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Old 12-06-2008, 02:04 PM   #16 (permalink)
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i use 120 grit flap disks
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Old 12-06-2008, 04:28 PM   #17 (permalink)
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Old 12-06-2008, 04:49 PM   #18 (permalink)
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Quote:
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I'm not sure what your definition of "sheet metal" is, but I've always known it as that thin stuff your cars body is made out of that crumples up if you lean on it to hard. Not the stuff you'd use for mounting your suspension. I've already searched a number of local suppliers for cold rolled plate, or P&O, and none of them stock 3/16 or 1/8" plate. I could have them special order it, but I'd need to buy about 5X the amount I need, which would cost me an extra $1k or so. Not exactly pocket change.
o 1/8th i was thinking you where useing some thinner metal. you might check an online steel place for small ammounts.
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Old 12-06-2008, 05:45 PM   #19 (permalink)
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sandblast it, or use a torch. I don't have any experience with any of the chemicals these guys are talking about, but it sounds like something worth trying. sanding disks wear down pretty fast on mil-scale, that shit is hard!
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Old 12-06-2008, 08:04 PM   #20 (permalink)
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I've never tried this, but a zirconia-alumina belt on a 6" hand-held belt sander should make pretty fast work of cleaning a full-size sheet...
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Old 12-06-2008, 09:30 PM   #21 (permalink)
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Muratic acid. You can get it from Home Depot.
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Old 12-06-2008, 11:52 PM   #22 (permalink)
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I use those 80 grit quick change sanding discs for my angle die grinder, they seem to work much better than the flap discs but you will need a good supply they seem to wear out pretty quick. these may be what others are refering to as rolock I'm not sure
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Old 12-07-2008, 08:51 AM   #23 (permalink)
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Muratic acid. You can get it from Home Depot.
do NOT use Muriatic Acid, it causes hydrogen embrittlement on the surface of the material.

Use Phosphoric Acid.

also, there is a difference between "Sheet" steel and "Plate" steel. sheet is primarly measured in "gauge" and plate in decimal or fractional inches.

7ga sheet is nearly the same as 3/16" plate
11ga sheet is about 1/8"
i don't know the thicker guages off the top of my head...

i think plate is a little cheaper than sheet because plate is typically hot rolled and sheet is cold rolled.

give the phosphoric acid a try...its easy and quick unlike standing at a blasting cabinet or running a grinder over the sheet.
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Old 12-07-2008, 11:22 AM   #24 (permalink)
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Dotco is what we call an angle sander with Roloc disks on it. The 3M ones are better than the cheaper ones but they are the only two brands I've used.
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Old 12-07-2008, 12:50 PM   #25 (permalink)
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do NOT use Muriatic Acid, it causes hydrogen embrittlement on the surface of the material.

Use Phosphoric Acid.
Maybe if you leave it in there for a long time....

Phosphoric acid also cause hydrogen embrittlement, its just a weaker acid.
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