[DILYSI Dave]

Long time TIG welder, relatively new MIG welder. I was welding some 1/4" plate to the floorpan of a car (.030" maybe?) for some seat mounts, using .030" wire, and a few places, when I would stop the weld, I would get these nasty stalactites that would grow as the weld cooled. Grind them off, and they are hollow. Try to weld again, sometimes cool, sometimes more growths. Eventually I was able to grind all the crap out of there, and get good welds, but I'm wondering what the issue was that started it. Everything was clean - no rust, no paint, etc. Turned the 75/25 gas gas up from 20 CFH to 30 CFH to try and make sure that it's shielded better, but no dice. Not sure what was up, but it's the first time I've ever dealt with it in MIG, and it sucked. I've had similar problems in TIG when I try to weld dirty material, but like I said - all of this was freshly wire brushed.

EDIT - It was my first time welding stuff I had plasma cut. Does the plasma process leave contamination in the cut? Give that it's melting the steel without a shielding gas, I could see the potential for that.

 

[NotAPoser]

Is the nozzle clean?

 

[DILYSI Dave]

Is the nozzle clean?

Good question. I'll check. I suspect it's fine since 90% of the bead was great. But it's worth double checking regardless.

Interesting article on welding plasma cut parts - http://www.thefabricator.com/article/plasmacutting/you-can-plasma-cut-it-but-can-you-weld-itr

 

[jamscal]

It's the plasma edge.

 

[hardline04]

Its the plasma cut. Clean it up first and you should be good to go. Plasma can leave slag that will contaminate the weld.

 

[DILYSI Dave]

How much needs to be cleaned from the plasma edge? Are we just talking wire brushing it, or do I need to remove material with a grinder/belt sander/whatever?

 

[guidolyons]

Its the plasma cut. Clean it up first and you should be good to go. Plasma can leave slag that will contaminate the weld.

Yep.

How much needs to be cleaned from the plasma edge? Are we just talking wire brushing it, or do I need to remove material with a grinder/belt sander/whatever?

Hit it with a flap disc or grinding wheel to knock off the contaminated dross left by the plasma cutter. Clean both sides of the floor pan dirt/rust/grease on the back side can contaminate the weld, too.

 

[DILYSI Dave]

Cool. Thanks.

 

[jettscott]

Clean the gas nozzle, always. Especially if you're making long welds with a good bit of slag. X2 on the plasma cut and using a flap wheel to clean it. What's your gas set on?

 

[Wyoming9]

Dirt paint undercoating slag will all cause that from the gas being released as it is heated

Why does it bother you?

I could see if it was the whole seem

 

[DILYSI Dave]

Can I run the plasma with a different gas to avoid this? I've got Argon, CO2, and 75/25.

Cleaning it isn't a huge deal, but since the purpose of the plasma is to speed up cutting stuff that is going to be welded, adding an operation kinda blows.

 

[Harold Phipps]

will not take much with a flap wheel to get the edge clean.
Even if you used a Beverly shear, you would probably want to spiff u p the edge before welding it.

 

[Slowzuki]

Even the plate oil will cause this with mig. Galvanizing or plating too. Undercoating is the worst. I've found higher wire speeds and hotter can help reduce it but you have to move fast and you'll always get it on the end of the weld unless you're back to a clean spot. I use a wire wheel on the grinder to clean all weld areas when I'm not being lazy. Solves it.

 

[guidolyons]

Can I run the plasma with a different gas to avoid this? I've got Argon, CO2, and 75/25.

Cleaning it isn't a huge deal, but since the purpose of the plasma is to speed up cutting stuff that is going to be welded, adding an operation kinda blows.

You can use nitrogen, but anything other than clean dry air is a waste of money IMHO.

Good prep is just part of getting good welds.

 

[DILYSI Dave]

Nozzle was pretty dirty, so cleaned that, and also did the flapper wheel treatment to the plasma edges. Seemed to cure it -

Thanks!

 

[cdansan]

Just to make sure we don't forget this is still Pirate;
Stalactites grow from the top down. :flipoff2:
Stalagmites grow from the bottom up.

 

[J P]

This might seem like a stupid question but here it goes , i just bought a miller 211 ( welds great ) and on my old welder a weld pack 100 i used flux wire. well today using the miller my welds looked the same as you describe , looking around i found that i forgot to turn on the gas . did ya check ?

 

[DILYSI Dave]

This might seem like a stupid question but here it goes , i just bought a miller 211 ( welds great ) and on my old welder a weld pack 100 i used flux wire. well today using the miller my welds looked the same as you describe , looking around i found that i forgot to turn on the gas . did ya check ?

I leave the gas on. Otherwise, every first weld of the day would be fubar...

 

[Wyoming9]

leaving the gas on one day your going to have a empty cylinder most often when you need it most.

you did turn your gas flow back down??

 

[DILYSI Dave]

leaving the gas on one day your going to have a empty cylinder most often when you need it most.

you did turn your gas flow back down??

I did not. Thanks for the reminder.