Is this mill scale?

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1/4" plate I planned on grinding clean and welding up. Covered in some rust and blue coating. I tried grinding disk/ sand paper disk and flap wheel.... I cannot get bare metal for the life of me without grinding this stuff to 1/8" plate.Is this mill scale or some other coating? Can I weld on it?
Reply:Before and after:
Reply:"blue coating" sounds like mill scale. In some plates it can be quite heavy. I have a piece of 3/4" plate that just laughs at sanding disks trying to remove the mill scale. I'd need to use a hard wheel to grind it off.Picts would help us make sure it's not some other coating though.Edit: yes that's mill scale..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:Use a 3m paint removal wheel . That works the best of anything I have found. Here is what they look like.http://cgi.ebay.com/ebaymotors/3M-31...4AAOSwq7JT4ndi.   You can get them at lowes or home depot and most good hardware stores. There are other brands that are cheaper. They all look basically the same. The slang name for the hot rolled high carbon crust is blue blush. The other thing that works well is to use an A/O torch and put the blue cone of the flame right on the blue blush and slowly move it around as the crust pops off. The rest we remove with the paint removal wheels.Last edited by thegary; 04-02-2016 at 10:32 PM.
Reply:OK.. now that you have cleaned it ....weld it. Yes mill scale does interfere with with the weld tie in a little but get past it. Do you know how to weld?Miller TrailBlazer 251Miller HF-250-1Miller MaxStar 150 STLHyperTherm PowerMax 380 plasmaLincoln PowerMig 180Millermatic 252Miller Diversion 180
Reply:Yes you had rust on top of mill scale. Grinding rock is great for removing it flap wheels just glaze over.Ranger 250 thick stuffHobart Handler 140 not thick stuffthe pane and oxy setup
Reply:Thx gents. I assumed it was but wanted to be sure, as I've only ever worked with cold rolled stuff. I put a new grinding wheel on it and seemed to take it off better, the old must have been filled with material.Sounds like welding through it isn't a big deal so maybe I'll just try that first.Thanks
Reply:If you are making an xray weld you want to remove it . For generl purpose you can weld through it.
Reply:Hey by the way that's not 1/4" think maybe 3/16".  By the way it looks in the picture unless you have super large hands.Klutch 220si mig , stick, and dc tigHobart 140 AHP ALPHA 200X 2016Lotos LTP5000DSmith O/P
Reply:I've been experimenting with chemical methods for removing mill scale - phosphoric acid works well - a 20 minute soak, then brush off, rinse with water.  I was using muriatic acid but found a real pain, in fact dangerous - bad news.  I left a small amount in a 5 gal bucket overnight in my shop...it rusted EVERYTHING !  tools, steel - arrrgh.  If using muriatic, do it outside with full face protection, chemical gloves and full clothing - dispose properly.
Reply:Looks like 1/8" sheet/plate, hehe.  Get yourself a 24 or 36 grit flap disk.  It's about the only thing that will effectively remove millscale without using too much pressure/effort, aside from a hard grinding disk.Show a picture of your grinding/disk flap wheel on your angle grinder.  Chances are your grit was way too fine. 1st on WeldingWeb to have a scrolling sig! HTP Invertig 400HTP Invertig 221HTP ProPulse 300HTP ProPulse 200 x2HTP ProPulse 220MTSHTP Inverarc 200TLP HTP Microcut 875SC
Reply:You can stick weld right over that mill scale with no issues at allJasonLincoln Idealarc 250 stick/tigThermal Dynamics Cutmaster 52Miller Bobcat 250Torchmate CNC tableThermal Arc Hefty 2Ironworkers Local 720
Reply:Flap or wire wheel the rust off and gtsm the edges to be welded, and done like dinner
Reply:If you are stick welding, E6011 is best for digging under rust, mill scale, paint, coatings, etc., whereas E6013, 7014, and 7018 are not so good at getting all the junk to float to the top with the slag. If wirefeed welding, see if your local welding supply carries a wire that has deep penetrating characteristics similar to 6011. And straight CO2 gets under the crud better than C25 for this sort of thing.