Unravel the mysteries of science....

[jimcroisdale]

Hi all,

Ok. Some of you out there must be real techno geeks. You know who you are!

I want to know how welders work (I can't help it, being obsessive/compulsive....). I want to know about voltage, amps, square waves, slopes, anything you can think of! Give me the full science/physics bit, as hard as you like. Don't water it down - I can take it, I'm a Yorkshireman!

Hope that gets you all thinking - lets see how much info we can get on this one thread. I'm off to bed now, but I want this finished by morning. Do you hear?

Remember - plenty of long words!

Cheers as ever,

Jimbob

 

[cobminor]

We can give you as much science and technical stuff as your avatar can take, WELDING, thats that done then.

 

[weldequip]

XYZ = MIG/TIG/MMA x2. That do yer for starters?
Sleep on it!
weldequip

 

[jimcroisdale]

Sheesh! Poor Arnie - what did he ever do to you? Perhaps if I find an Einstein pic you might tell me what I want to know?

Here's hoping....

Jimbob

 

[weldequip]

Err, well it could be x3, I'll have to look it up!
I'll be back!
(I just had to, sorry!)
weldequip

 

[jimcroisdale]

Bloomin' heck!

Well, that didn't tempt anyone at all did it? C'mon guys, someone explain the physics of it to me!

How come a welder has enough voltage to cause an arc, and enough amps to melt steel, but if I hold the end of a welding rod and stand in a puddle I'll only get 'a bit of a jolt'! Shouldn't that kill me?!

I know this doen't affect the way it's all used, but I can't help wanting to know.

Cheers,

Jimbob (new avatar pending after the abuse....)

 

[cobminor]

Not abuse, just a comment on your choice of avatar. I am old enough to have seen him on British TV before he went in to films. He was a thick Austrian weightlifter. I don't think things have changed much.

 

[Drains]

LOL. You're meant to let go when you start to fizz!

 

[Drains]

Briefly, cos I have to go and give the dog his tea - (and this is also good for a thread somewhere else) - the voltage isn't high enough to jump through the air, which is why the arc needs to be struck. Then the amps melt the jesus out of the wire/ electrode, making a sort of molten electrickery carrying wire, that splats onto the job. There you go. Scientific enough for you? Hahaha
Si

 

[malcolm]

I don't know either, but I'll give it a shot.

Simon's point about striking the arc is valid. With MIG welding nothing starts to happen until the wire hits the metal. With arc and scratch TIG it's the same, and HF TIG allows the arc to start at a distance by adding some high voltage.

Once the arc is going what keeps it going? Speculating here. For a start we're not talking about air - we've either got a shielding gas or whatever nasty gas the flux cored stuff gives off. The shielding gasses give improved arc so whatever explanation that might follow here will most likely work better with the shielding gas.

We've started the arc by touching metal against metal, then when we pull it away just a microscopic distance the gap is still small enough for the low voltage to jump in a lightening sort of way. That causes the gas to ionize. The electric energy makes electrons jump off the gas atoms, and once that's happened the gas does conduct. That's how lightening works - once it starts it keeps goining along the same line. Free electrons floating around the place is the way metals conduct electricity, so the gas is probably conducting electricity nearly as well as metal might do. Add a bit more distance and you can get a bit more more gas conducting in the same way. And so on.

That's how I think it works, though you'd need to remove a mad scientist's brain to confirm.

What's happened to Arnie? A bit of photoshop and you should be able to get him welding up that molten terminator.

 

[jimcroisdale]

Cheers Malcolm, I think I'm starting to get it.

Note my new avatar - a nice weldery pic. How dull. I looked for a picture from the movie Aliens - the bit where the woman (Vasquez) with the bandana is welding the door shut to keep the aliens out. Couldn't find it though.

"What ever ya gonna do, do it fast!"

Jimbob

 

[Drains]

Jim, if you want the REAL techno geeks, ask at UKWelder, the home of the pro MMA welder, welding engineer and inpector. If you ask correctly, they may deign to answer your question in every detail, to the umpteenth degree (they may rip you to pieces, it is a lions den). Either that or wait for TechnicAl, who is omnipresent, and if he looks this way, will tell you all.

I thought your Arnie avatar was great. I vote, bring him back!

 

[jimcroisdale]

Cheers Simon, I might look into that. Arnie is back for now too - until I find something I want to stick with.

 

[shenion]

We've started the arc by touching metal against metal, then when we pull it away just a microscopic distance the gap is still small enough for the low voltage to jump in a lightening sort of way. That causes the gas to ionize. The electric energy makes electrons jump off the gas atoms, and once that's happened the gas does conduct. That's how lightening works - once it starts it keeps goining along the same line. Free electrons floating around the place is the way metals conduct electricity, so the gas is probably conducting electricity nearly as well as metal might do. Add a bit more distance and you can get a bit more more gas conducting in the same way. And so on.

That's how I think it works, though you'd need to remove a mad scientist's brain to confirm.

Actually, it works via an inductor. Start with a low-voltage DC. Strike an arc and a short occurs. This builds up current in the inductor. Then the wire melts back. This would cause current to drop suddenly, just like an old car points ignition. If you ever put a scope on the points side of a car ignition, you would see it jump to several hundred volts when the points open.

The field in the inductor collapses and generates a huge voltage that can arc across several mm. The inductor then oscillates.

Once an arc is maintained, the DC pulses (most are DC rectified but unfiltered so the DC is acually hallf sine wave pulses), retrigger the arc. Once started, the plasma is enough to re-arc at a low voltage.

The inductor tries to maintain a constant current. It will resist a sudden change in load and ramp up the current slowly (slow in electronics sense, we're talking microseconds here.) If the output drops suddenly, it will produce a voltage to maintain the current.

 

[jimcroisdale]

I think I need a lie down after reading that....

 

[Drains]

OK Shenion, i'm going to jump in here and ask how the variable inductance on a mig (usually the bigger sets) works? Turn it down, spatter, turn it up, no spatter. Apparently it "wets the weld toe"! Eh?

Oh, and Jim, remember the old maxim, "be careful what you wish for..." ?

 

[shenion]

Small inductance will make the current build up/decay real fast. So you get real short pulses of high current.

Larger inductance will make the current more even. Longer pulses with a lower current.

The power is the same, high-current w/ short pulse, or lower current with longer pulse.

 

[Drains]

Thanks S. I'm gonna go away and think about the implications of that...
Si