I just found out about this newsgroup. It's a great source of
Here's my question. I have a PowCon 300ST tig machine. I just
finished welding a new bottom on a Honda generator gas tank. I used
18g mild steel as the replacement metal, which was a little thicker
than the tank metal. Sheilding gas was 75/25 mix set to 10-15 CFH. I
also used 2% thoriated tungsten electrodes, .040". Both tank and new
metal were clean of paint and rust in the area surrounding the weld.
I didn't need any filler metal. As I welded, I would regularly get
spots with porosity problems. I don't think the metal was
contaminated. Are there any poor welding techniques that would lead
to this porosity? I learned to weld last year by taking a class at
the community college which was all SMAW. I'm kind of teaching myself
to tig and mig.
Anyway, the welds look ok, maybe a little brittle. I only had two
small leaks the first time I tested the tank, so I must be close to
doing things right. Any input is appreciated.
Use straight Argon....Mild Steel needs the filler metal too otherwise you
will get porosity, you cannot just fuse the two together like with S.S. or
Alum. There are too many impurities in steel to do this. A Silicon-Bronze
filler works great for this kind of stuff.
Everybody is jumping to some conclusions about your gas but I didn't see
anything about CO2 or other MIG gases in your post. Is this 75/25
A/He? If so, this is the same as I use and I have also frequently
encountered similar difficulties with some steel. It appears to be
caused by impurities in the steel. The best solution I have found when
this arises is to use some stainless filler - 309 SS filler is fairly
inexpensive and readily available.
Overheating can make the problem worse.
Absolute beginner-to-TIG's input: -- it is very easy to overheat your
welds when first trying TIG "just improvising". Having used other
welding processes is almost a disadvantage when you try TIG. You see
these unbelievably incinerated looking welds from people who are trying
their best when used to stick/MIG/oxy-acet.
The TIG heat source is so localised and intense that learning to use it
to get small cool welds -- well, most people with prior welding
experience need to be shown what to do in order to get the idea.
With eg. oxy-acet, the flame temperature is so matched to welding that
overdoing the heat gives a very different consequence of an overly large
weld melt pool(?). TIG is so localised that you really need to know how
to ride at at the correct temperature, because that heat source can go
way way way beyond the useable temperature. Imagine trying to drive a
car which can do 1200miles-per-hour without any idea of how you should
drive it and that in general you are looking to the 25mph to 70mph range.
You might be doing much better, but for many new starters to TIG, this
might be helpful.
Generally in this "oh my gawd what am I supposed to be doing?" scenario,
anyone looking on can see spitting sparks, then when the weld is
finished you can see dusting of orange boiled-off-and-oxidised iron
around the weld - plus the weld looks like a mixture of dirty metal and
coke (the porous black stuff used as a smokeless fuel and in blast
furnaces where coal is roasted without air at red-heat).
Generally a beginner is helped by a rule that "you do TIG welding at the
minimum heat at which you can just weld". To a beginner, this concept
will serve you well.
My immense apologies to Jason if you are much further down the road than
this and the problem is something else.
That's some great information for us new guys.I'm also new to tig.Done
some stick gobbing in the past.How do you tell if the puddle is
becoming over heated?More pointers are greatly appreciated such as
torch movement,straight line or circular movement etc.
Hi Jason, all
By now with the help of other contributors it has been established
that you were using a MIG gas mix when you need pure Argon for TIG.
However, I will press-on and try to do my best with the "temperature"
How can you tell by looking that the weld pools is at the right
temperature? Hmmm... how does one do this indeed? You do do it for
sure, but what is it that we are looking for that we can describe to
Well, the weld pool at the correct temperature is small and it seems
smooth, "quiet" (not swirling, bubbling or doing anything wild) and
grey-metallic viewed through the welding filter. Something I seem to
see is that when you dip the rod into the melt pool the metal climbs
up the rod as if it were viscous, although I would expect that this is
really surface tension. Presumably this only happens when you are
down near the melting point of the steel. But these things are so
vague, I don't think you are going to get anywhere looking for these.
There's something I can tell you which is not vague. For a beginner,
if your machine has a foot-pedal, turn down the current setting on the
machine until foot-flat-to-the-floor you just form a weld pool. You
can even hold the torch stationary in one place above the sheet metal
with the arc running and turn the amperage control knob until you have
a melt pool about 3mm / 1/8th inch diameter (well, if you are
practicing on sheet metal about half that in thickness). Then start
to try to weld. You will soon get to recognise what a cool weld looks
like, compared to the gross fuming things you first had when you tried
TIG without guidance. As you get moving along and supplying filler
rod, you might have to tweak up the amps a little bit, but you will
then know what you are looking for and will keep control with a nice
small cool weld pool. When you've seen it, when "freestyle"
controlling on the foot-pedal you will know what you are after.
'nother thing to warn you of. As a beginner what really confuses you,
particularly when trying fillet welds, is that if you roast the oxide
on the weld surface without melting the metal, the oxide will start to
spit and contaminate the tungsten electrode, just as happens when the
weld pool is grossly too hot. When you are confused and in dispair,
this really does intensify how lost you can get. With the
foot-to-the-floor thing, as a beginner you know that to start a weld
you floor the pedal and you will get a melt pool quickly, so avoiding
this confusing risk to the hopelessly lost novice.
Anyway, I have documented some of my trials and tribulations at
which has some photos of welds. On
you can see a succession of welds which was my effort and progression
towards reasonable TIG welds
Thanks for the info. I chose 75/25 (Argon/CO2) because I was told it
was good for everything except Aluminum. I have a 140 cu. ft. bottle
and a small 40 cu. ft. bottle. If I get straight argon, will that
work for Mig as well? I'd like one gas that will work with both my
mig and tig machines (unless someone wants to send me another bottle
for Christmas!). I mainly work with mild steel but want to try some
aluminum projects. Any suggestions for gas mixes and tig electrodes?
(or is 2% thoriated tungsten good for most metals?)
I think I had the heat low enough as I had a very small puddle about
2mm in diameter.
I really do appreciate all the help. I think I'm a decent welder, but
I'm definately still a beginner and am open to any suggestions.
While you can use Argon with a mig, there aren't many here that will
reccommend it. Might as well use fluxcore wire and no gas..about the
I broke down and bought a second bottle from a guy on ebay that has
hundreds of bottles...I think I paid $20 plus $10 shipping. Took it
to my local gas supplier and they traded me no questions asked for one
of their bottles.
I switched to Lanthanated tungstens at Ernie's suggestion and haven't
looked back. They work really well for all tig
processes....again..check ebay for the deals...I bought mine from
Aglevtech on ebay...his prices are about 1/10th of what the locals
Less is more in tig welding, especially for a beginner (like me) I
have found that I get a consistantly better weld if I use just enough
amps to get a puddle and play with the pedal from there.
On 22 Dec 2003 19:42:25 -0800, email@example.com (Jason Pratt)
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