Welding up flame cut joints.

[Zeke]

Assuming I can get a really nice, straight cut or bevel on each part to be joined, do I need to do any other prep other than hitting the slag with a grinder? When I say good cuts, I mean a decent fit up using oxy/act cutting process. Of course I understand the mill scale and other impurities are going to affect the weld. I'm talking about the face of the cut. I'm mainly asking about SMAW, but some info about this regarding MIG would also be useful. Has he face of the cut been oxidized or something?

And, for others that might have an interest in this question, let's add in plasma cutting as well. Any special prep there?

Ask these questions on the interwebs and you will get what I did — nothing.

TIA

 

[dr_clyde]

Structural steel code AWS D1.1 says all metal must be clean and free of oxides, coatings and mill scale. Even if you're not doing code work, its good welding advice.

Grind to bright and shiny metal and you're good to go.

If you're good with a torch, should only take a second with a flap wheel to zip off the oxides.

 

[Zeke]

That's what I was looking for. So, the face of the cut is going to be oxidized? I know I won't see that, or will I? The face will be blue? (It's been a long time since I flame cut.) I normally use a cut off wheel, but for this project O/A cutting will be faster.

 

[fordkid88]

That's what I was looking for. So, the face of the cut is going to be oxidized? I know I won't see that, or will I? The face will be blue? (It's been a long time since I flame cut.) I normally use a cut off wheel, but for this project O/A cutting will be faster.

Oxy acetelyne cuts by oxidizing the material. So the entire cut will be oxidized

 

[Bigblue&Goldie]

Buzz it with a grinder and you will be 100% fine; that's protocol.

 

[dr_clyde]

Yes, the cut face will be oxidized. It will be dark grey, and have scale flaking off.

CAN you weld it? Yes, it is possible. SHOULD you? No. You want clean steel.

 

[MoonRise]

Quick once-over with a grinder and your appropriate abrasive of choice until you get to clean BRIGHT shiny steel. Then you can weld it.

Same if you have a plasma cut edge, grind to get to clean bright shiny metal.

(tech note: plasma cut steel edges when air is used as the plasma gas will have nitrided edges usually, which MUST be removed before welding. Usually only have to grind off about 10 thou or so to remove the 'bad' zone.)

 

[sberry]

I have welded hundreds of feet, more like thousands of torch cut joints. Been on lots of ironwork in jobs that had dozens of men, no grinders. Scrape with a chipping hammer, that little fuzz won't mean much to a stick electrode or ever common wire for common work.

 

[bad_idea]

What you building?

Home project at a leisurely pace? Clean cuts up.
Paying structural job? Clean cuts up.
Quick and dirty job of average load on welds? Cut it and weld it.

 

[Zeke]

What are your building?

Rocket stove.

 

[joe49]

If your cuts look like a beaver chewed it out grind it.
If your cut looks like a saw cut, with little dross, scrape with a ******* file to remove scale and dross, then weld it.

 

[bad_idea]

Cut it and weld it. No need to waste time grinding anything. Ugly cuts are fine, stick will fill the gaps just fine.

 

[gearhead1]

If I’m going to put air pressure on it or hold a liquid, I grind it - no impurities.

If it’s non critical, like a bbq grill, or just generic stuff, I cut and go.