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How do I remove mill scale?


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#1 jumpinjivinjoe

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Posted 02 February 2011 - 01:32 PM

I ordered some Japanese Brown, a "Vista Patina", and a "Universal Patina". Do I need to remove mill scale from hot rolled steel for these patinas to work? I usually use a wire wheel on an angle grinder, but that takes an unpractical amount of time. An abrasive flap disk wears out too fast. How do you all remove the mill scale?

ps I buy remnant steel which is almost always hot rolled.

Thanks

#2 PTsideshow

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Posted 02 February 2011 - 01:41 PM

Try using the the forum search function, with the term removing mill scale. There are a number of threads on that subject. No point in retyping stuff over and over!


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#3 ShawnM

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Posted 02 February 2011 - 02:09 PM

I ordered some Japanese Brown, a "Vista Patina", and a "Universal Patina". Do I need to remove mill scale from hot rolled steel for these patinas to work? I usually use a wire wheel on an angle grinder, but that takes an unpractical amount of time. An abrasive flap disk wears out too fast. How do you all remove the mill scale?

ps I buy remnant steel which is almost always hot rolled.

Thanks


You do not have to remove all the mill scale. The surface should, however, be cleaned thoroughly. Keep in mind that any underlying color WILL affect the end result. A rusting patina like Japanese Brown or Vista probably will not produce much rust, if any, on top of mill scale. If you have some scale and some bare it will give you a lot of variation in color. I use that to advantage when that's an effect I want.
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#4 jumpinjivinjoe

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Posted 02 February 2011 - 05:04 PM

That modeling effect sounds good ShawnM.

Anyways, I have searched around on this and other forums for mill scale removal, people either say sand blasting, sanding wheel, or muriatic acid.
-I am not set up to do the amount of sandblasting that I would need; plus, sandblasting takes quite awhile.
-Sanding wheel takes to long as well and can be expensive.
-And it is difficult to get a neutral PH metal after muriatic acid.
-A grinding wheel tends to gouge the metal.

I am wondering if there is a chemical or a trick to get it off relatively easily and cheaply.

#5 PTsideshow

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Posted 02 February 2011 - 05:11 PM

Do the search on this forum there a number of methods suggested.The search function works well!
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#6 Rich Waugh

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Posted 02 February 2011 - 08:31 PM

I'll save you the trouble of searching all over - use a 1:4 solution of muriatic acid in water. Soak the work for an hour and check it. Longer if necessary. rinse, neutralize with a solution of bicarbonate of soda in water and rinse again. Dry thoroughly and immediately or it will begin rusting while you watch.

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#7 blboise

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Posted 03 February 2011 - 08:19 AM

"I am wondering if there is a chemical" --- Yes, Muriatic Acid as mentioned with a "soda wash"

"or a trick to get it off relatively easily" -- Yes, Muriatic Acid as mentioned

"and cheaply." -- Yes and no -- if it's me, the answer is no because I usually manage to eat a hole or two in my pants or shirt.

I know of no "easy" way to get the scale off other than blasting, grinding or soaking in acid. There is no abracadabra magical trick. The #%#$ stuff sticks on pretty well. On large projects I try and use cold roll material to avoid the scale. I too try and use remnant steel, but sometimes if you figure in the value of your time on a project, it pays to just buy good, clean, shiny stuff.

If you find that magic solution, let us know.

#8 Naturalsteel

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Posted 03 February 2011 - 09:34 AM

Well, I have posted this before but, you might try a diferent disk. I went through the same thing when I was starting out and had a bunch of hot rolled. I found the striper disks removed mill scale incredably faster and easeier than sanding disks and didn't eat into the metal like ginding disks. I use Norton Bear-tex rapid strip (giving the brand because I don't actualy know if they are all created equal, haven't tried any others). They look like they'd wear out as soon as you touch the metal but they actualy last a good while. I think they run me between $5-7 a disk. The bigest concern with them is catching an edge, that can shred a disk pretty fast. It's cheeper to try one than it is to buy a tub big enough to soak a big piece in acid. I'm with Blboise removing millscale just isn't as cheap and easy as you'd think it should be.
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#9 jumpinjivinjoe

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Posted 03 February 2011 - 12:31 PM

My sculptures have many holes in them so the striping wheel would catch a lot. Though I might use that before I plasma cut the metal.

I was reading on another forum that after you neutralize the muriatic acid with baking soda the metal becomes alkaline, which is not good for coatings. It seems like it would be difficult to get the ph to neutral and not either acidic or alkaline. Would acetone neutralize muriatic acid? With acetone I would not be introducing water to the steel. Muriatic acid does seem to be my best option though.

#10 ShawnM

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Posted 03 February 2011 - 03:27 PM

My sculptures have many holes in them so the striping wheel would catch a lot. Though I might use that before I plasma cut the metal.

I was reading on another forum that after you neutralize the muriatic acid with baking soda the metal becomes alkaline, which is not good for coatings. It seems like it would be difficult to get the ph to neutral and not either acidic or alkaline. Would acetone neutralize muriatic acid? With acetone I would not be introducing water to the steel. Muriatic acid does seem to be my best option though.


Well, if the other forum does not recommend soda, why don't you ask the other forum what to use? I believe the members here have given you their best advice.
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#11 Tony Mertens

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Posted 03 February 2011 - 08:13 PM

I use plain old vinegar. It may take a few days depending on how thick the scale is. I've never had good luck with those stripper wheels on plate for some reason. They work great on angles, tubes, etc. If you are going to patina it why worry about neutralizing it. Wash it, then patina, then spray with acetone, then clear coat. You are probably correct to strip it before cutting. Flat sheet is easier to work with than a sculpture.

#12 sbrown

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Posted 03 February 2011 - 09:29 PM

I have used muriatic acid, but don't like dealing with it. I also prefer vinegar; you can get a gallon at the grocery store for about $4. I cover the metal surface with paper towel and pour on the vinegar to soak. Cover with plastic and let set for 24 hours. The next day spray off the metal and the mill scale will mostly wash off. It is then easy to sand or wire brush down to bare metal, which I think will give you the best results for Japanese Brown patina. Good Luck.

#13 Rich Waugh

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Posted 03 February 2011 - 10:00 PM

Steel cannot be made "alkaline" or "acidic" by dipping it in a solution of either acid or base. Rinse with water afterward and all you have is "neutral" steel. I'm not going to get into the hair-splitting fine points of alkaline and acidic metallic salt residues here because they aren't a factor if you rinse properly.

If using muriatic acid makes you nervous, plain white vinegar is a workable substitute. Slower, but ultimately just as effective for removing scale. You still have to neutralize and rinse, of course. The laws of physics and chemistry aren't suspended just because you're using chemicals from the kitchen instead of from the garage.

Acetone has neutral pH and can't titrate anything to neutrality, sorry - it is a solvent, not a reagent.

If you need to pickle something too big to fit in a bucket or handy tub, simply knock together a "corral" of scrap lumber and drape heavy polyethylene plastic sheeting over it - instant bathtub any size you need up to about 20'x20'. Think outside the box.

I have no issues with anyone on "other" forums who disagree with my positions on things; I've been doing this for forty years or a bit more and have garnered a smidgen or two of information along the way. I'm willing to share that information freely, but not really willing to waste my time debating it with anyone. I do this stuff for a living and could better spend that time making money, thanks. :-)

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#14 crquack

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Posted 03 February 2011 - 10:28 PM

Acetone is great for some things. However, beware if you are going to patinate after using it: It leaves a layer of oily residue. I am not sure why, one explanation is that the commercial acetone is never completely pure. If I am going to patinate I always follow acetone with a second degreasing stage, rinse and *thorough* drying.

#15 jumpinjivinjoe

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Posted 04 February 2011 - 04:54 PM

Since this was posted some new information has come to light
Here is the link
Please read be fore using brake and other aerosol automotive cleaners



I have now made a frame out of 2 x 6 scrap lumber and layed some heavy plastic in it. I filled this up with some phosphoric acid (concrete etcher). I will let my sculptures soak in that for awhile and see how it turns out.

I like the idea of acetic acid (vinegar), since it is cheaper (Vinegar=$4, Muriatic=$10, Phosphoric=$20/gallon) and easier to neutralize.

CRQuack, I didn't know that acetone leaves an oily residue. I will have to use brake cleaner from now on.

Tony, The reason why I need to get the mill scale off is because the patinas need to react with the metal (ie. rust), if it was paint or a non-acid based patina I would not care.

Thank You Everyone!

#16 Tony Mertens

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Posted 04 February 2011 - 09:41 PM

I understand you need to remove the millscale for the patinas. I've used plenty of japanese brown myself. I just wouldn't worry about neutralizing until after the patina, you're only adding more acid with the patina. Don't mean to argue with anyone here either. I just got my information from the "Patina King", Ron Young. Like I said, I just remove the scale, wash with a good cleaner, patina, acetone, and immediately after clear coat. By the way, once you wash it do not touch it with your bare hands, they will leave oil tracks. don't ask me how I know that. [Doh!]

Can't say as I've encountered a residue after the acetone but I suppose it's possible.

Edited by Tony Mertens, 04 February 2011 - 09:45 PM.


#17 crquack

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Posted 04 February 2011 - 10:08 PM

I understand you need to remove the millscale for the patinas. I've used plenty of japanese brown myself. I just wouldn't worry about neutralizing until after the patina, you're only adding more acid with the patina. Don't mean to argue with anyone here either. I just got my information from the "Patina King", Ron Young. Like I said, I just remove the scale, wash with a good cleaner, patina, acetone, and immediately after clear coat. By the way, once you wash it do not touch it with your bare hands, they will leave oil tracks. don't ask me how I know that. [Doh!]

Can't say as I've encountered a residue after the acetone but I suppose it's possible.


The quick way to show it is to take a flat plate of metal and clean it thoroughly with acetone. Then do the waterbreak test. Then clean the plate with a cleaner (I use Zep Heavy Duty from Home Depot containing 2-butoxyethanol and sodium metasilicate), rinse and repeat the waterbreak test.

Chalk and cheese...

BTW, just in case, the waterbreak test is clip 5 here:

https://www.caswellp...vies/index.html

#18 Rich Waugh

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Posted 05 February 2011 - 02:12 PM

JumpinJoe,

You said, "I like the idea of acetic acid (vinegar), since it is cheaper (Vinegar=$4, Muriatic=$10, Phosphoric=$20/gallon) and easier to neutralize. "

Your figures are correct, but a bit misleading. Vinegar is 5% Acetic acid by volume. Muriatic acid is Hydrochloric acid (HCl) generally about 34% by volume, and Phosphoric acid (P2O5) can be any concentration from about 10% by volume to pure, depending on what you buy and where. At $20/gal I'd guess you're probably getting something like 10-30% strength.

If you dilute the muriatic to the same concentration as vinegar you would end up with about nine gallons for a net cost of $1.10/gallon - considerably cheaper than vinegar. The phosphoric is still going to be more expensive as it costs so much for an already diluted solution. Now, if you can get full-strength phosphoric for $20/gal that would end up pretty cheap since it will do the job fine at 8-10% concentration.

The degree of difficulty of neutralizing is a function of molar strength and concentration and also what you use to neutralize with. For muriatic acid, the ideal neutralizer would be lye, also sometimes called caustic soda. The chemical name is sodium hydroxide (NaOH). When you titrate to neutrality with lye the end result is HCL+NaOH= NaCl+H2O, or plain old salt water. Plus, of course, whatever you have dissolved in it, typically iron. Environmentally pretty benign. Something to consider.

Just putting things in perspective here, hope it helps.

Rich
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#19 Rich Waugh

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Posted 05 February 2011 - 02:18 PM

I understand you need to remove the millscale for the patinas. I've used plenty of japanese brown myself. I just wouldn't worry about neutralizing until after the patina, you're only adding more acid with the patina. Don't mean to argue with anyone here either. I just got my information from the "Patina King", Ron Young. Like I said, I just remove the scale, wash with a good cleaner, patina, acetone, and immediately after clear coat. By the way, once you wash it do not touch it with your bare hands, they will leave oil tracks. don't ask me how I know that. [Doh!]

Can't say as I've encountered a residue after the acetone but I suppose it's possible.



You're quite correct; if you rinse thoroughly after the pickling and then use an acidic patina chemical like Japanese Brown there is no great benefit to neutralizing. Other finishes like dye patinas or paints, however, may be seriously compromised later if you don't neutralize and rinse. And, of course, if you let the piece sit around after pickling and just rinsing it will rust almost immediately. If you neutralize it will rust more slowly. :-)

Rich
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#20 jumpinjivinjoe

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Posted 06 February 2011 - 04:16 PM

The phosphoric acid I buy is 30-40%, if I remember right. I dilute this by half. Anyways, after a 24 hour phosphoric acid bath, the mill scale brushes right off! However my 6 mil polyethylene seems to be also dissolving so I will need to find/make a metal tank.

The water break test is a useful tip, thank you.

I still find it peculiar that the Japanese Brown instructions says that there is "no need to rinse" before putting on the clear coat.




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