Millscale

[200mphbusa]

Here's a method I have found a bit easier if you hove lots of mill scale to remove and about the cost of a disk.

http://weldingweb.com/vbb/showthread.php?t=32280

[MoonRise]

Proving once again ..

That you weld metal.

Attempting to weld 'non-metal' (rust, mill scale, paint, other oxide forms, grease, oil, the neighbors cat, etc) may or may not result in 'acceptable' welds, depending on the welding process used, the base metal trying to be welded, the specific 'non-metal' in the way, and so on.

GTAW aka TIG welding 'tolerates' the least amount of non-metal in a weld of most common arc welding processes.

Mill scale is not metal.

[Gamble]

What if you put the metal into a bucket filled with water and baking soda and ran current through it.
Details here:
http://www.thepontiactransampage.com/rust.html

I had someone try this on their gun barrel after the house was on fire and he was trying to rebuild it. It came out nice after it. But I'm sure you have to wash it with hot water so it doesn't flash rust.

[papaharley03]

What if you put the metal into a bucket filled with water and baking soda and ran current through it

I think Sodium Carbonate (washing powder) works better than Sodium Bicarbonate (baking soda).

Papa

[lotechman]

Something I didn't know was that welding material with oxide on will produce more fumes than welding metal that has the oxide removed.
Many shops I have worked in would consider showing you the door if you removed the scale. They have not allocated the time and discourage it. In one shop after being told not to remove scale next to the weld I just removed the scale when the foreman was not around. When he was watching for maximum production I left it and welded. This is for GMAW.
In the end, removing scale cannot hurt and often will help getting that last little bit of perfection whether is it is neededor not.

[37ford4dr]

will paint adhere to mill scale and be a durable finish if you use a self etching primer?

[lotechman]

There are several levels of paint finishing. Sandblasting of course Is the best. Usually a good power wire brushing will remove any loose scale. Wipe down with thinner to remove any dust or physical dirt then primer. At that point the scale will not come off under normal circumstances.
One structural painter told me that the better paints are ones heavy with oil that take extra long to dry are best. He had no respect for fast drying paints on exterior structural.

[SuedePflow]

There must not be much of any mill scale on 4130 tubing. I've never bothered to gring away at the finish and it welds up beautifully. HR plate is a different story though. I always grind a clean surface on it prior to welding.

I assume acetone alone cannot remove mill scale?

[ZTFab]

There must not be much of any mill scale on 4130 tubing. I've never bothered to gring away at the finish and it welds up beautifully. HR plate is a different story though. I always grind a clean surface on it prior to welding.

I assume acetone alone cannot remove mill scale?

Yes there is.

I prep all of my tubing by sanding off the coating in any area(s) that will be welded. If you think that it welds just fine without taking it off, clean it and you'll be amazed at the difference.

[dstevens]

Yes there is.

I prep all of my tubing by sanding off the coating in any area(s) that will be welded. If you think that it welds just fine without taking it off, clean it and you'll be amazed at the difference.

What are you using? I'm using Scotchbrite purple and acetone.

[ZTFab]

What are you using? I'm using Scotchbrite purple and acetone.

Either one of my Burr Kings or a DA sander with an 80 grit disc and then a wipe down with acetone after either process.

[mechanic416]

ZTFab, That is very nice fitup. It sure makes it easy to weld when its clean and fitted like that.

Again very nice work

[Tool Maker]

My electrical operated spooge tank will take it off. However the other day I bought some hot rolled sheet stock and made some covers for a band saw and then I ran them in my spooge tank and before treating them they were covered with very slick blue scale. after cleaning them to shiny metal there were many small hollows and indentations that the scale had been hiding. I've never noticed this before. Mac

[dstevens]

Either one of my Burr Kings or a DA sander with an 80 grit disc and then a wipe down with acetone after either process.

I've got a DA and some 80. I'll give it a shot. Scotchbrite by hand is time consuming and takes a few sheets to do a whole cage. I've been washing with acetone for a while, works great.

Thanks for the tip.

[SuedePflow]

Yes there is.

I prep all of my tubing by sanding off the coating in any area(s) that will be welded. If you think that it welds just fine without taking it off, clean it and you'll be amazed at the difference.

I'll give it a shot next time we weld up some 4130. I just picked up a DA yesterday.

For reference, here's some pics that show the surface and minimal prep prior to welding. We may have lightly hit it with a wire brush prior to welding, but it came out pretty good anyway. I look forward to gauging the difference after hitting it with a DA.

[ZTFab]

I'll give it a shot next time we weld up some 4130. I just picked up a DA yesterday.

For reference, here's some pics that show the surface and minimal prep prior to welding. We may have lightly hit it with a wire brush prior to welding, but it came out pretty good anyway. I look forward to gauging the difference after hitting it with a DA.

It looks like you're using SMW or a similar filler which helps with the mill scale but I think you'll like the result after cleaning the scale off.

Here is a set of link bars I made from 1.5" and 2" DOM mild steel. Before cutting and notching I sand the entire tube on my Burr King, then fit and weld.

It's easier to just sand the entire tube in one shot then handle a bunch of smaller parts. Added benefit is that they are ready for paint or powdercoat with a simple wipe down of acetone.

Sorry for the crappy cell phone pics.

[SuedePflow]

I'm not familiar with what SMW is. I know we use regular ER70S-2 filler on 4130 tube.

Beautiful welds, btw.

[Warpspeed]

I think the clue here, is that anything that looks distinctly different (bright and shiny) after sanding or grinding, must have had some kind of scale or oxide layer on the surface. We all know what "black pipe" or "structural steel" looks like, it sure ain't shiny. It is the mill scale that makes it that darker color.

[mafiacustomz]

i have some 1/8" or i think its also 11 gauge steel i dont know if its hot or cold rolled but i think its hot and it takes forever to get to clean metal with a DA flap or the 90 sander. I dont want to use a grinder disk it cuts to deep i want as much metal as i can. What is a faster way i looked and muriatic acid seems to do the job and great for the price $3 a gallon anything better.

I would also like to know do you clean the metal shiny thin use weld primer and does it penetrate and ground good thur this primer like clean metal.

[SuedePflow]

As a bit of a follow-up; we hit some 4130 tubing with a DA and welded it up. It makes for a more colorful weld, but it otherwise welded up the same with or without scale. Maybe this tubing I buy is just cleaner than most others? It seems that this is the only material that I don't have to spend time cleaning up before welding...

[MetalMan23]

Nice work ZT, those r some some nice lookin welds

all I know is HRS welds 10x better when you take the millscale off. However you want to take it off, just make sure its gone

[Alan Murfee]

You can wash it by leaving it in water containing washing soda or detergent, it would remove rust to some extent.

[LawsonWeldingLLC]

will paint adhere to mill scale and be a durable finish if you use a self etching primer?

The issue is, Mill scale (Fe 3 O4) will absorb moisture, it is not adhered the same way lets say ( to dummy it down ) steel to steel is. ( I am talking about the atomic structure ) and remember paint may be porous depending upon how it is applied. ( how many mils, proper procedure etc.etc.etc ) I have seen more than once in a corner, on a edge, even a flat sheet, where paint has been applied over mill scale, not long after exposure to the elements you see a small oxidization, over time u see more, and more and more, it just needs a entry point. Realize it may look "bonded" but for ultimate finishes a blasting is required, finished with a etching primer, and proper painting.

Lets think about it another way, What is the self etching primer etching itself into if it is applied to mill scale.

The U.S. is a 5 billion dollar corrosion industry, its my job to try and replace as much of this a year as possible, so im okay with people painting over mill scale.

[Raul]

HA~!!!
I'm so tough I remove millscale with my TEETH~!!

[Stick-man]

A good example of mill scale. These are the gussets for the fork lift carriage project.
http://weldingweb.com/vbb/showthread.php?t=280591 This was really heavy mill scale and very tough to cut through. Once you're through the mill scale, the steel was easy to bevel.

BTW, I beveled these with a tiger paw. I really need to start using these more often. The good ones work fantastic. I couldn't believe how fast I could cut this bevel.