Arc blow

[ryanjones2150]

A few weeks ago, I posted a video made in 1944 about arc blow. It's called the story of AC welding...or something like that. Anyway, I'm not a school trained welder. The extent of my welding education is trial and error and listening to others. So I found the video fascinating and educational, even though I had no memory of running into the troublesome arc blow in the past.

The other day, I was fabbing up some brackets to hold heavy timber headers for a customer that is expanding the porch on his log cabin. 5" X 5/16" angle with a small brace in the web of the angle and a couple of ears to bolt to the timber header. I tried to post some pictures but my iPhone and this new site still don't get along...starting to irritate me too...anyway, I tacked it all together and migged most of the joints. On the inside of the ears, I finished it off with tig because I need a very low profile weld. On both ends of the weldment I had a terrible time starting and finishing the bead. When I'd get to the end of the run at the edge, it was all I could do to bring the puddle out and finish. Drove me crazy. Not to mention slowing me down, it made the start and end look like dog poop.

So now...you experienced guys...how do you combat that problem? What I ended up doing on the tig joints was getting the puddle as close to the end as I could and crammed rod into it to bring it out flush.

What about mig?

This has been a good learning experience for me. What is your experience with this issue?

[H80N]

Ryan

May sound odd.... BUT you can run AC TIG on ferrous metals.... that will minimize ARC BLOW....

it is magnetic deflection of the arc....

Here is an interesting article on ARC BLOW.... mostly related to stick welding... but the physics are the same for all

http://mewelding.com/welding-arc-blow/

[ryanjones2150]

I have AC tig welded on steel before. Actually I tig brazed with AC on steel, cast steel and cast iron.

I've probably had the issue before, but chalked it up to my lack of skill...ha!

Just a little while ago I was welding a spare tire bracket on to a trailer for a customer. It's been very wet here lately and you have to drive through my back yard to get to my shop. So instead of tearing my yard up, I drug out the long stick leads. Left it on DC, wanted to conduct a little praxticle exercise while earning a few extra bucks. I ran some 1/8th 6011 and some 1/8" 7018. On welds that were surrounded by other metal in the same plane, no problem. Welding into a corner, it was very obvious. Honestly, welding into that corner where three plates met on different planes was really the only place I noticed it, and there was no mistaking it.

Now the other day in my tig welding issue, the metal was clamped in my vise and hanging out in mid air. Maybe if it was sitting down flat on the welding table it wouldn't have been so bad. Probably why I haven't had much of an issue with it in the past.

I'll take a look at that article in a bit. Thanks for the suggestion.

[Sberry]

There may be milder cases of blow, tacking up further can help. In corners scale and dirt can act like it, some rust is super insulating. I think true arc blow is rather rare.

[ja baudin]

Dont think its arc blow, tig welding over a mig weldment is very difficult. Tig welding over a stick weldment is even harder. In reverse, mig over tig is easy, stick over mig----easier. Dont ever forget, tig needs to be clean, and dont mix welding processes unless going from a cleaner process to a dirtier one.

Starting with mig then switching to tig is a bad move.

Tig first, then mig, then stick

[ryanjones2150]

The joint was tigged on the opposite side of the mig weld. The mig was an outside corner, the tig is the t-joint. I prepped the metal for tig welding before assembly.

But you're absolutely right, trying to tig over any other process sucks.

Generally, most of my small jobs I can position the item so it's flat on the welding table, which by all accounts extends the magnetic field from the work piece through the welding table. That article h80n posted talks about this. It's worth a read and not very long. With this particular job, the piece was elevated off the table about six inches. If I get some time this weekend, I'll take my test piece and set it up again and attempt to recreate it. Wish I could get some pictures of it.

Sherry, what makes you say arc blow is rare? I'm honestly asking, not being a smartass.

The best way I can explain the phenomenon I ran into...welding along just fine-minus a crappy start at the other corner-got about 1/4" from the end and it was very clear and obvious the arc was being acted on by a force that would not allow it to track to the edge. It would've been cool if I wasn't trying to get paid.

[snoeproe]

Most inexperienced welders wouldn't know the symptoms of true arc blow. It is rare. Things that can make an arc unstable that are not arc blow would be an unexpected gap or opening that gives an opportunity for your arc to become longer. This will cause arc your to wander slightly and begin to dig into the base metal (arc voltage increase). Contamination like dirt or heavy scale or heavy rust can also cause an unstable arc.
True arc blow can make a weld job impossible sometimes. Don't let inexperience tell you your experiencing arc blow.

[ryanjones2150]

Probably just my imagination then.

[H80N]

Probably just my imagination then.

Did ya get a chance to read that paper..??. it does a pretty good job of explaining the phenomena...

knowing you.... would expect the prep & clean was excellent... so it would not matter which process was used in what order...

[ryanjones2150]

I did. It was good and short and to the point. I like that. I generally chalk my issues up to the lack of ability behind the hood, but in this case, I had the same issue on each piece in exactly the same manner. The fit up was good. The metal was absolutely clean and prepped properly. I didn't even consider arc blow until later on when I was doing some reflection on my issues for the day. If I had thought about it, had I been properly schooled as a welder or had more experience as one feller pointed out, I may have snapped to a bit quicker.

I still don't understand how it can be "rare" since it seems to me to be a simple matter of physics.

[H80N]

+1 on the physics

methinks.....maybe it's more common than some believe......

[theweldor]

If it happens when you are welding out of a corner, try welding into the corner. Makes quite a difference.

[ryanjones2150]

First time I've ever had trouble like that. I'm learning how to combat it in the future should I encounter such lack of experience again. I appreciate the suggestion.

Also reading up on run-off tabs? I wonder if clamping them down to the work piece would be sufficient. And then, would copper work well like when welding stainless as a backer or would it need to be ferrous? The reason I went to copper in my thought process is because I have several pieces at the ready that I use as backing plates already...various sizes and shapes too.

[theweldor]

Something else to think about is where the ground clamp is located or how you have the piece grounded. Try moving it around it may help.

[ryanjones2150]

Another good point. Gracias.