Brown soot whilst MIG welding

hi peter, Ive read a few of your posts lately, and... I may be wrong, but it seems to me that you could benefit a *lot* from an hour sepnt with someone who really knows their welding. Im a relative newcomer to the industry with 5 years experience (in australia) as a welder/boilermaker but have had a pretty wide experience during that time with work in areas as wide as mining, pressure vessels, marine aluminum, prototyping and jig making. Im certified to weld pressure vessels as well as structural steel in downhand and vertical up in several processes.

If i were in your position, what i would do is seek out someone who is clued up about welding and get them to show you a few things. you'll learn a lot more in 10 minutes with someone who's in the know than you will in weeks of tinkering and reading about it on the web. talking about welding is like dancing about singing. Trade qualifications mean surprisingly little in this area - ive met so many tradesmen in my time who have 20+ years in the industry but still dont actually know how to set a welder. they often rely on pencil marks on the welder itself for the settings, and they get crazy mad if you adjust it!

There are no hard and fast fules about welding.... every material is different, as is every weldment. a butt joint will require a different setting from a mitre. as a general rule though, an outside mitre requires about 30% less current than a butt joint while an inside mitre requires about 30% more. vertical up requires a lot less heat than welding on the flat or vertical down. All this talk is really pretty useless though except in terms of a general understanding of more or less is required.

starting with gas coverage, about 15lpm is a good start. keep your nozzle clean of spatter, aim your gun towards the direction of travel, and make sure that you dont have any wind/fans blowing your shielding away. shielding in itself is an art, but the basic points mean consistency.... a consistent gun angle, avoiding jerky movements of the gun.

removing the mill scale is nice, but most people rarely bother unless the weld is to be certified. Im not familiar with your machine, but im assuming that it has a few settings on the front for voltage, maybe A through E? If so, your going to want to go with 'E' for anything 1/4" and over. 185 amps really isnt much to work with, but with chamfering you could realistically weld 1/2" material in a few passes.

so, start with your highest voltage setting. now, get close to the feeder. hold the gun in which ever hand you normally use, and put the other hand on the wire feed control. If your feeder has a '4 touch' setting or 'latch' setting whereby once you press the trigger it keeps welding until you press the trigger a second time, then use it. This is one of the secrets to accurate consitent welding in all positions. start welding, and adjust the wire while you are moving. turn it up to the point that the gun is kicking back in your hand, making a machine gun sound..... this is too much wire. now turn it down until it feels and sounds 'smooth', this is the earliest point where it feels and sounds good to you. This setting will be a slightly 'cold' or 'proud' bead. weld for a while, stop and have a look at the bead.

now keep welding, and adjust it down further... keep going until it seems to 'stall' and drip off the end of the wire... this is too low. but do a weld anyway... look at the finished bead. notice the browning? see how the spatter is really hard to remove? now weld again and turn it up, turn it down... you dont want that dripping, but you dont want it kicking back. while everything is a personal preference, and gun technique changes many things, you will probably want a setting just above the 'drip' setting, rather than just below the 'kick' setting.

as a general rule... more voltage = a flatter wider bead with more penetration, while more wire *reduces* the amount of heat. in general, set voltage for the penetration you want, and then adjust wire to suit. too cold? turn voltage up then adjust wire again. too hot? turn voltage down and adjust wire to suit. browning would usually indicate too high a voltage, or too little wire, or not enough shielding gas. the overall verdict is too much heat. when you have excessive spatter, or the spatter is really hard to scrape off but you have a good looking bead, its a sign that you could probably tweak your wire a little bit.

every welder (machine) is a little bit different, even the same model. every weldor (person) is also different. gun technique does make a huge difference in the way the heat is applied, with gun angle, stickout and weave being the main components. many weldors are really bad at setting their welder, but very advanced at using gun techniques to increase or reduce heat. My personal technique is very adaptable, but a signature of my style is using a short forward step with a longer backstep for tha roll of dimes effect. at higher currents (300amps+) i tend to avoid direct arc at the edge of the bead, instead 'washing' the pool to the edge of the bead on the backstep to avoid undercut.

Shaun

Very well said ! Thank you , from a backyard project weldor . Some of this I had figured out , you've explained a lot of what I've experienced . When you know "why" it's easier .

FWIW, and after the thought, I have noticed that FCAW has more "soot" than other wirefeed processes.

Steve

I haven't seen any soot , but do from time to time have small glassy brown bits of slag . Always on top of the bead , and it comes off fairly easily . I learned here that this is probably contaminants from my base metal , and if I want it to go away I need to brush/grind/file my metal cleaner . If y'all will wxcuse me , I'm gonna sit back and play sponge some more ...

I get that too with this process. The little bit of searching I did indicated - I thought - that this was not a problem as long as it was scrubbed away before laying another bead on top of it. I'm wondering now if that's correct. Of course I get less of it since I cleaned the mill scale off the pieces on which I'm practicing.

Peter

I think it's the MIG version of slag . I make sure to clean it off if I need more than one pass , just as I would with stick welding .

The glassy deposits are indeed slag. It comes from excess silicon and manganese in the steel welding electrode consuming the oxygen in the weld puddle. One would think the shielding gas is perfect, but it's not. Atmosphere does impinge somewhat on the welding arc and surface of the weld puddle, but the composition of the wire compensates for that.

And yes, it needs to be cleaned from the surface before welding subsequent beads or layers.