On Fri, 2 Sep 2005 20:19:01 +0100, Badger wrote
(in article <
[email protected]>):
>
> "Rich" <[email protected]> wrote in message
> news:[email protected]...
>> So you need more current to weld ally ( or make blobs on the floor ) is it
>> very hard and what is the foot pedal I have seen on some big welders?
>
> You need more current initially to "pool" the metal, due to ally dissipating
> the heat through itself quicker than steel, that's why it's so easy to make
> ally puddles on the floor! oops! The foot pedal is an alternative to the
> button on the hand torch, on welders that have this, some cheaper machines
> are what is referred to as "scratch-start", where you have to make contact
> with the tungsten electrode to fire up the arc.
> Badger.
>
>
The foot pedal is (usually) a current control so you can wind the current up
and down as you progress along the weld. IME this is pretty much essential
for welding ali since you need to put a lot of heat in to get the weld going,
and then back off one the material is hot or you'll make a hole. You also
need to be able to back the current off as you finish the weld or you'll end
up with a pit in the bead. Some machines will do this automatically, ramping
the current up when you push the button on the torch and down when you let
go, but the foot control gives you more flexibility.
There's loads of good welding advice on the net. Hang out on
sci.engr,joining.welding for a while and some good advice will come along
soon. Miller Electric and Lincoln Electric both have lots of stuff on their
websites, too, and there is also The Welding Institute.
Unless you are doing very long runs (feet of bead at a time) at currents over
about 150A you won't need a water cooled torch. I have a 200A TIG machine
(Lincoln) which will easily weld 4mm Ali plate and will run off a 13A socket
(although probably not forever at full output). It was quite a lot of money,
though (~2k).
Apart from the oxidisation issue with Ali (which is why you need AC) the big
problem is its heat conductivity. If you start with cold pieces of material,
they just soak the heat away from the weld so it's difficult to make the bead
flow properly. Once the surrounding material is hot enough for the
temperatures to stabilise then laying a pretty bead isn't much more difficult
than for steel, but if I'm only welding a short piece of material, I find
I've usually reached the end of the weld before this happens.
You can use the same shielding gas (pure argon) for TIG welding ali or
steels, but you will need zirconiated (red) electrodes for steels and
thoriated (white) electrodes for Ali. You're supposed to be able to use
ceriated (grey) electrodes for both, but I've not had a lot of success with
these.
I've never played with scratch start (aka 'lift-TIG') but I understand that
for welding Ali, life is a lot easier with HF start. With Ali, you really
want to avoid the contamination of the bead which comes from metal-to-metal
contact between the material and the electrode. AIUI, lift-TIG is the poor
man's option and anyone who has HF start will not use the lift-TIG option
even if they have it available.
The most important thing with TIG welding is to prepare everything carefully
in advance and be scrupulously clean, especially when working with ali. The
books all say this, and it's easy to ignore, but it is absolutely true and it
really makes a difference. I started out with a stick welder, progressed to
MIG and then on to TIG, and as I have moved from one process to the next, I
have learned (the hard way, of course) that each is less forgiving of
dirt/corrosion and poor fit parts than the last.
I'd also recommend Lincoln equipment . It's more expensive than the
Clarke/SIP equivalents, but it's professional gear, and I find the guy who
runs their Sheffield retail outfit very helpful and easy to deal with.
Nick
1990 90 2.5TD
