TIG welding stainless Q's?

[Wriggler]

As I understand it for TIG welding stainless you need to use lower amps and make sure the reverse side of the weld is purged, other than that it is basically the same as welding mild.

Is this correct?

I can get by welding mild, it's part of my job, I've had a go at ali which doesn't seem too bad, I just need more practice but I've only ever migged stainless.

Cheers

 

[Mad Mick]

Hi Wriggler,
It all depends what you are working on.In some instances it can be no more difficult than mild steel,but in other cases it can prove to be a complete minefield to the uninitiated.The main problems are distortion due to lack of heat conductivity,oxidisation on the back of the workpiece and the risk of burning thro'.If the material is 3mm or above you should not experience oxidisation on lap and T fillet joints.On V prep and thin material you will need to back purge or tape or clamp aluminium to the back.On thin material you will need a lot more tacks than ms.Lap joints are another one to watch.because if there are insufficient tacks the two pieces are likely to move apart forming a gap,and the more you try to fill it the bigger the gap is likely to become. In short,the job is not as forgiving as ms.Hope this helps,regards,Mick

 

[Freshfabrications]

Well we have all been there the daunting task os welding a new material, but it's like any thing once you gt good at it you can't understand what the problem even was.

Stainless as staited above is a poor conductor of heat, meaning that:

1 the heat melts in the local area more quickly than with mild/cromo/HSLA steels, so yes your right about needing a few less amps, I run 70 - 80 amps on 2 - 3mm stainless but that's just me , do some test pieces!!

2 as the heat does not conduct well the area most medial to the linear weld will have expanded, in most cases, alot more than the most distal material, essentaly cold setting the cold stuff and then shrinking the hot stuff to ad more warpage and confound the whole thing!

Some good tips for stainless are:

As above use a lot more tacks than usual, even on the thick stuff, to help keep things from moving, I would always tack every inch or so when welding stainless 22 guage some times more.

Always clean clean clean, purge thin stuff where ever possible or use Solar Flux B.

Pre heat will get everything expanded before you weld and lessen distortion, as will chills and clamping/retraining the joint untill cool.

Use sequence welding ie, skip or back step welding, short bursts so as not to over heat any one area.

Use a gas lense if you can or slightly more gas coverage than when welding normal steel and make sure you keep the hot work in the gas when cooling so longer post gas is wise (ie to avoid grey scaily welds) wire brush between passes and stop starts. Always clip contamination of the end of filler rods!!!

Stainless wire can be stickey when hot so keep it in the gas sheald and dip in and out in posetive fashion, try not to let the wire get snagged up on the job or you could find it sticks at an inopertune moment!

Once you gt used to it stainless is as fun to weld as Aluminium.

PM if you'd like more tips.

 

[asg fabrications]

solar flux B is that any good???

 

[Freshfabrications]

Solar Flux B is good, though if you can't access the back of the joint after welding you can't remove the glass like flux, have not really seen the benefits in thin stuff though, but this could be my fault with the mix and I can't sorce methil-alcohol so I'm using IP1.

Thick stuff However seems to work well as there is more heat to make the flux react with, it's so much cheaper than purging and purge setup/tools,
just think you'd need to do a few test peices to get a good idea for concistency.

It is about £60 for a tin, 1Lb ,that will last for years if you do Stainless that requires purge but can handle some flux in inaceasible areas then this will save money.

If your in London I'll even give you a tablespoon full to try!

 

[TechnicAl]

Doesnt this mean that Stainless is a better conductor than mild steel?
http://www.engineeringtoolbox.com/linear-expansion-coefficients-d_95.html

 

[Drains]

Doesnt this mean that Stainless is a better conductor than mild steel?
http://www.engineeringtoolbox.com/linear-expansion-coefficients-d_95.html

It says it has a greater linear temperature expansion coefficient. That's not the same thing Al, as you know.

Perhaps you meant to put in this link
http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html

 

[TechnicAl]

Thats better
I couldnt find that one

 

[asg fabrications]

no but how about you post me some to try :-P, been looking at buying some but am jst trying to find some small pouches to try out instead of buying a big tins worth and then find out its no good for me....

 

[Freshfabrications]

Hi ASG Fabrications,

not sure I want to post mistery powder in an envelope, might end up in the knick!!

As your not local to me have you thought about asking the supplier in the UK for a small sample?

Think http://www.solarflux.com/ is a good starting point for contact info!!

If all else fails PM me....