What's wrong with this weld

[bc30se]

Hello

(I am sorry for the size but I just paste it from the google)

What I mean is the looks of the weld just after welding. It is not my weld by the way but... I must admit I get the same results. I can polish up the joint afterwards, but it doesn't change the fact that I am not able to figure out, how to make the weld look clean without additional scrubbing. I mean, if you compare this one to the one here

I doubt the guy did any clean-up job afterwards.... the same here

and here

The wled looks shiny, there is a bit of bluish tint, but damn.. it looks even sexy with it.

What to remember about?? I have of course used different settings, different flowrates, tried pulsing, my gas is pure argon. As usual, I would feel obliged to hear your input...

 

[wheresmejumper]

you need a gas lense,preferably a large diameter gas lense
then the right amps.too much will darken the weld
also too little amps will cause you to move too slow which also puts too much heat into it and it will go dark.

 

[Tigman]

Too much heat !

 

[Tigman]

Also it looks like the components welded are aged , so maybe contamination from inside the tube !

 

[hotrodder]

The grey look to the top example is what happens after a dark blue heat tint, more detail here... http://www.bssa.org.uk/topics.php?article=140
It's mostly a heat input versus shielding quality thing i.e. too hot and/or too slow and the metal is a higher temperature when the gas shield is lost as the torch is moved. Arc length effects heat input too http://www.mig-welding.co.uk/forum/threads/tig-practice.44645/#post-494271 and the dia of the filler wire also has a role to play... larger dia wire = more heat needed to melt it = need to weld hotter and/or slower to avoid the weldpool freezing everytime you add wire. When it comes to thin wall tube (no gap/prep needed) with a good fit up then 1.6mm wire is on the thick side and changing to some 1mm can make a big difference. While we're talking wire, don't pull it back too far as the hot end will oxidise and those oxides will be added to the weld next dab of the wire. Smaller wire can be more difficult in this regard as it's more prone to melting and balling up if kept too close to the arc

Material thickness effects things too in that it's a lot easier to get 'good colour' on thick stuff than it is with thin. Not the reason why the top example is grey but worth noting it's the only pic of thin wall tube to thin wall tube...
From the surface texture the other tube stuff is thicker wall pipe, all of the other pics are of fillets and the second example was done using pulse with too low of a frequency for the travel speed (not enough overlap of the freeze lines, lots of fisheye defects) which hasn't helped the weld width either although it's exhaust bits so no big deal as the silly punters judge quality the thing by weld colour alone
A gas lens can improve shield quality, moreso with certain weld geometries like outside corners/butts on tube than with fillets which trap argon unless you're welding overhead. Obviously a bigger ceramic shields a larger area than a smaller one, less obviously more argon doesn't improve things. Turning the gas flow down can often yield better results than turning it up. Especially with tube/outside corners where geometry is diverting the gas away which can draw air in if flow rates are excessive

ETA with thinnish stuff and/or full pen butts if you don't purge the weld the back will oxidise LOTS and 'grow' a heavy scale (especially if too hot/slow in which case those oxides get drawn through the puddle as well). This is often refered to as coking or sugaring and it's the result of the chromium being 'burnt' out of the stainless. Without a purge an attempt at a full pen weld is gonna be full of oxide inclusions and almost certainly LOF (lack of fusion) defects too

 

[bc30se]

thank you

I use gas lenses of course, then... what flow rate do you suggest for thin material? I am going to do some more practice...

 

[german8rcoupe]

First pic looks like chrome plate as opposed to a stainless exhaust. Maybe that helps to discolour/contaminate the weld?

 

[overload]

First pic looks like chrome plate as opposed to a stainless exhaust. Maybe that helps to discolour/contaminate the weld?

My thought as well.

 

[langy]

First pic looks like chrome plate as opposed to a stainless exhaust. Maybe that helps to discolour/contaminate the weld?

Thats polished stainless, trying to tig on chrome looks worse !!!

 

[hotrodder]

What Langy said. That looks to me like a used exhaust that got cut (maybe through an existing weld?) to change the end can mount / tweak the fit. I'm wondering if it was maybe welded with mild steel wire? FWIW polished stainless exhaust (mix of 304L and 316L IIRC) being mocked up under a chrome bumper... http://www.mig-welding.co.uk/forum/threads/welding-304.34462/#post-379248

Vast majority of everything i weld is done at around 5 litres/min through a #7 ceramic on a gas lens. Occasionally run a little less or more flow than that depending on joint geometry and/or amount of stick out. If i've got an extra large gas lens on with a #12 cup might run up nearer 10 l/min occasionally but they still work fine without turning the gas up most of the time

 

[Rocketman]

Hotrodder has a point with the mild steel wire. I was getting my exhaust re-fitted with proper bends that actually fitted my car at custom chrome in Coventry. The guy there pointed out how the welds on the exhaust even though it was stainless were all mild steel (he also pis**ed himself at the poor fitting the other so called custom exhaust specialist did).

Anyway the guy at custom chrome said most places making up stainless exhaust use mild steel wire, though they always used stainless wire themselves.

 

[bc30se]

Perhaps they used a mild steel wire, but I do havesimilar results when using stainless wire (308, 316), and the material I use is usually new and clean (tubes or 2 mm sheet)

 

[brokenbiker]

I get that a lot when trying to tig stainless and everyone I have asked about it have all said too much heat either because amps are too high, or speed is too slow

 

[langy]

I get that a lot when trying to tig stainless and everyone I have asked about it have all said too much heat either because amps are too high, or speed is too slow

Yep its too many amps or too slow usually

 

[biffa]

Unless your using a massive gas lense touch angle plays a massive part aswell

 

[brokenbiker]

not wanting to hi-jack but it is completely relevant, what size gas lense would be needed for a t joint with 2 1.75" tubes, one being coped to fit the other.

it is the joint I am trying to get right at the moment using AFAIK 308 S/S and 312 filler. wall thickness is around 2mm and amps are set a bit hot at 90ish amps but I am travelling quite quick. still get that dull grey though. is the travel speed the problem not letting the gas cover for long enough?

 

[wheresmejumper]

Id be moving fast at 60 amps....

 

[brokenbiker]

I thought my amps were a bit high. will try turning them down and see what I get