Metal Preparation & Cleaning

[outraged]

I understand that when MIG welding, the metal needs to be clean of rust, paint, scale, etc... but why exactly is this? at least when it comes to the scale that comes on hot rolled steel?

the process of cleaning the scale off angle iron [or any other steel] is rather time consuming...does every MIG weldor clean their metal to bare shiny steel before welding?

does Stick Arc welding need to have clean metal, as far as the black scale, before welding.

just curious, as i always do clean my steel, it just takes a while and gets very monotonous. i sometimes dont, where heavy structural support is not needed.

please......enlighten me!!!

[Guest]

Re: Metal Preparation & Cleaning

Originally posted by outraged
I understand that when MIG welding, the metal needs to be clean of rust, paint, scale, etc... but why exactly is this? at least when it comes to the scale that comes on hot rolled steel?

the process of cleaning the scale off angle iron [or any other steel] is rather time consuming...does every MIG weldor clean their metal to bare shiny steel before welding?

does Stick Arc welding need to have clean metal, as far as the black scale, before welding.

just curious, as i always do clean my steel, it just takes a while and gets very monotonous. i sometimes dont, where heavy structural support is not needed.

please......enlighten me!!!

No you don't *have* to remove the scale, it is just easier to weld clean metal. Mill scale is an oxide, and usually floats to the top of your puddle, (the bright spot) and will chip off when cool. When I spray arc, I always remove the mill scale, but regular stick, or MIG, I don't. There must not be any oil or grease, and some paints, will give you fits.

There is a metalurgical answer to this question also, which I refrain for mentioning, so as not to confuse the issue.
As always...IMHO.

[Dan]

As Rocky stated mill scale is an oxide which is a potential contaminant to your weld bead. The other thing about this oxide layer is that it melts at a higher temperature then the steel, because of this, this oxide layer acts somewhat like a barrier against your weld bead achieving its maximum penetration possible.

Now, do I remove this layer when MIG welding? The answer is yes. To me it doesn t matter if its short arc, globular, or spray transfer.

Now, for stick welding I would remove it for: 6013, 7014, and 7018. 6010 and 6011 are rods that will burn thru this barrier with out any trouble, so I generally would just weld on the metal without removing the mill scale.