Arc blow on Stainless Steel???

[matt1978]

Hey guys,

We are trying to Pulse mig weld 304L CrNi with 1.2mm 308L wire, 98%Ar 2%Co2 gas. When we weld the 20cm samples, everything is perfect, but when we go to weld the real job, I am getting an interferance in the arc, seems like magnetism. I have tried welding with 2 earth points on the job, I have welded, Left to right, Right to left and even changed the orientation of the job, but nothing is helping to solve the problem. I even changed from Pulse mig too Standard mig and I still got a problem. The joint is a I Beam, with 4 T-Fillets (8mm to 4mm) about 1.2 meter long (2 top, 2 bottom), sometimes you can weld 1 side without problems, next time we can only weld for 30cm and then we get problems. I can't think what else we can do too overcome this. Any ideas?? BTW the pieces which make up the I beam are Plasma cut and are tack welded using MMA, so out of desperation I even insisted that all sides that were to be welded were grinded first (bear in mind this is CrNi) and the job be tacked with Mig. The first two sides I welded were perfect, so I assumed that the problems were down too surface contamination and I had solved the issue, but when I turned the job over and started the 3rd joint, I got the same problems again!! I have changed, wire, Liners, Gas etc and still no joy. I am almost certain that its a build up of magnetism which is causing this problem, but was wondering if there was any tricks to overcome or minimise it. BTW where I am is very hard to get access to even the most basic consumables, so don't be telling me fixes which are gonna require any items out of the ordinary...... Any ideas??

Cheers,

Matt.

 

[tmkankaa]

About the interference

pretty much what it is about
http://www.weldreality.com/arcblowarticle.htm
BR
Mika

 

[fingers99]

Wow!

 

[matt1978]

Thanks Mika,

Some interesting points there I wasn't aware off.

Although the job is Stainless Steel its a Ferretic grade, so I guess what he says about Steel applies, however I am already using Pulse, I can't swap to a lower size wire (Indians have never heard of 1.0mm for some reason) I can't use a higher percentage Co2 as its Stainless I am welding and I had already changed welding directions and earth positions. I will have to try lowering the current and welding slower and also play about with adding even more earth points onto the job aswell as changing sequence of runs (Although it has happend on the first run)

Its very frustrating!

 

[tmkankaa]

It ain't the pulse - it is lack of short circuits I think

I have noticed this same issue when welding with hot arc - In the past i was only doing old rotten cars in every possible position and no worries about this. As you can imagine that kind of welding is done with short arc and there you can not at least loose the game so easily since wire actually contacts the material - not just the arc. I've played with my Fronius a little and noticed that shortening the arc helps as well as reducing droplet-detachment force. Pulsed arc seems to be V_E_R_Y critical to the settings but when it does the job it should give less heat input and some even say that better penetration. Maybe you could use a magnet in your other hand and place it on other side of the blow
BR
Mika

 

[Paul.]

Matt
Years ago i used to make dipper arms for hymac diggers, using 1.2 wire, and occasionally we would suffer from arc blow, particularly on fillet welds, we used to wrap the welding return cable round the beam in a coil, as close as possible to the weld area, it takes some trial and error and can make it worse before finding the right position and number of turns, but it does work.

 

[Drains]

Matt - I was going to suggest wrapping the material with as many coils from the power source as you can - feed or return - similar to Paul's suggestion. Also trying on spray if poss- you didn't specify, but I assume you were on dip.

That lot failing - could you not get the folk you're with to knock up some highly electrically dodgy but otherwise effective de-gaussing coil to energise around the beams. Electrical safety regulations need not apply...

 

[snowcat]

Interesting stuff, I was well aware of hot arc applications on DC suffering it, but less aware of MIG work, my solution has always been to swap to A/C now thats gonna be some issue with MIG....

Getting the coils correct sounds emmm intresting...

 

[matt1978]

Thanks for the input,

I havnt tried wrapping a coil around, will do that today, but I had already tried Multiple earth points and weld direction.

I was thinking about striking up a few times on AC tig on the Job prior too welding. Not sure if that would have the same effect.

As I said, these jobs are already tack welded at another station with MMA, I aint seen the machine used, but I would of assumed its a Transformer MMA, so again, just assuming..... it should already be tacked with AC arc, but I will have too find out for sure.

Simon, I don't know if I'd trust the Indians to nake anything electrical and put it right next too me!! no being stereotypical, but the H and E in the factory is pretty non existant as it is.....