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Mill Scale Removal

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Cobra

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#1
So, with the new welder, apparently you have to practice this TIG thing to learn anything! Who knew!
And, as opposed to learning MIG, the metal has to be clean. How big a problem can this be? Right?
Let's just say, I was not impressed with the work to remove mill scale from 3X6 flat bar coupons.
Did this for a couple of days with the trusty flap disk and then decided there had to be a better way.
Enter chemistry. This stuff is a oxide and should be reduced by an acid.
Long and short is - it works! Used swimming pool muriatic (hydrochloric) acid in a 20L (5 gal) pail and the stuff came of a whole selection of cut offs to use for practice.
Having used this stuff before on the floor, advice - do the work outside with all of the garage doors closed. The fumes will rust everything near and far.
Let the pieces soak in the acid for about 20 minutes and then moved them to a second bucket that had water and baking soda to neutralize the acid.
No more flap disk business for my local Princess Auto.
 

dlane

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#2
Might as well make something useful out of them plates and filler rod while your practicing.
 

savarin

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#3
I use vinegar, takes longer but much safer and cheaper (at least here)
 

Cadillac

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#4
You do need to be have clean metal when tig welding. Any deposits on metal will become contaminates in your weld. It is a much more tedious process than mig welding where you can just cut and weld. Hot rolled material has a lot nicer finish than cold rolled. Your gonna need a small arsenal of flap discs either way.
 

GrayTech

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#5
I think you meant cold rolled has better finish, or am I missing something?
 

mrjbinok

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#6
You probably already know this but thought I would throw it out anyway.

DO NOT EVEN STORE A SEALED BOTTLE OF MURATIC ACID IN THE SHOP!! The stuff will still cause metal withing 10 feet of the bottle to oxidize over time. Stuff is flat out bad news around the shop unless you take extra special precautions. (Ask how I know) lol
 

Bob Korves

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#8
You probably already know this but thought I would throw it out anyway.

DO NOT EVEN STORE A SEALED BOTTLE OF MURATIC ACID IN THE SHOP!! The stuff will still cause metal withing 10 feet of the bottle to oxidize over time. Stuff is flat out bad news around the shop unless you take extra special precautions. (Ask how I know) lol
Excellent advice. No acids in the shop. They will eventually leak or fumes will get out, and everything will rust. I actually do keep some acids in the shop, the individual containers are sealed in a heavy polyethylene bag, sealed inside a second PE bag, all inside a 5 gallon plastic paint bucket with a tight fitting lid. I take the bucket out back every year or so, open it up, and make sure none of the individual containers are leaking.

Also, a lot of things are acid that we do not think about, for instance the quart size bottle of soldering flux fluid that was on my shelf is now in the sealed bucket. Look around carefully for acids, read the labels on bottles, make sure they do not rust all your shiny stuff.
 

firestopper

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#9
Invest in a 3M rol-loc and die grinder for quick removal of mill scale (small area). If I had to soak, blast or grind everytime I needed to weld something, nothing would get done. Like others have stated, stay away from acids, they really don't have a place in a welding/machine shop.
For most of my MIG welding, I don't care about the mill scale.

As for TIG welding, not clear why you would be welding material with mill scale. Most TIG applications would be on tubing or cold rolled sheet that is mill scale free. If your simply practicing, just grind off the scale and go. You should wipe the area clean. Lacquer thinner, acetone and alike will work fine. Stay away from brake clean.

Paco
 

Cobra

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#10
You probably already know this but thought I would throw it out anyway.

DO NOT EVEN STORE A SEALED BOTTLE OF MURATIC ACID IN THE SHOP!! The stuff will still cause metal withing 10 feet of the bottle to oxidize over time. Stuff is flat out bad news around the shop unless you take extra special precautions. (Ask how I know) lol

I agree. The jug of it gets stored in sealed plastic bag inside a sealed 20 plastic pail. (same one that gets used with it on the steel)
It is useful stuff, just needs to be treated with serious respect.
 

cjtoombs

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#11
I use phosphoric acid (sold as prep and etch). The problem with HCL is that it leaves behind chlorides on the metal, which promote corosion through chloride complexes with the iron. The phosphoric acid leaves a phospate coating, which tends to prevent corosion. I use the liquid for small parts that I can dip, for larger sections I use the gel stuff, if I don't care about he surface finish (for say, large structural steel with a crappy surface finish to begin with ) I use a needle scaler to break the oxide up before I use the acid. Good luck on your new welding endeavor, I really love TIG, but it can be a bit slower than other methods.
 
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