What makes a plasma cutter tick?

By rlitman (***)

Date 03-07-2008 15:48

As I understand it, its very much like a TIG welder, except that the OCV can be over 200V, and there's also usually continuous HF overlay.
With that kind of voltage output, a welding transformer can't be used though.
The real secret to a plasma cutter is in the torch design. You've got crazy metals in the electrode, like hafnium, because while tungsten could take the heat, it can't take the air going past it (although I've heard that some older plasma cutters required separate argon and nitrogen inputs before the modern electrodes were designed), and a special part that ensures that the high speed flow of air is swirling, to keep it in a stable, narrow, jet.

By Plasma-Brain (**)

Date 03-07-2008 16:03

Ok, so its the torch that makes the magic not the machine its self.
Given that would it be possible to convert a plasma cutter into a plasma welder, or would it be easier to try and make a TIG torch that would act as a Plasma welding torch?

thanks for the reply
-Clif

By MDG Custom Weld (***)

Date 03-07-2008 17:32

Again, it's the torch that makes tha magic with plasma welding too, but the power supply helps as well. The basics of PAW are: 1) continus argon for plasma gas. 2) welding sheilding gas of argon, helium, or any mix of them. 3) Continus low voltage arc to produce plasma stream. 4) The plasma gas will continue to flow around the tungsten all the time, welding or not, until the gas or electrical flow is off. 5) The plasma acts as the high freq. in a tig welder and helps the welding current jump from the tungsten to the workpeice on the start of the weld.
Let's see if this picture helps.

By DaveBoyer (*****)

Date 03-08-2008 05:28

Clif, Not trying to be a wiseguy, but it would be easier [read most logical] to buy a state of the art unit that does what You want. They have been messing with this technology for 50 years, and made significant improvements as recently as the last few years, at least with regard to the plasma cutters. Sometimes [older] plasma welding gear shows upon eBay, if You want to play with it keep Your eye out for a cheap setup.

By Plasma-Brain (**)

Date 03-08-2008 18:27

Dave, you are quite correct in that it would be easier and much more logical to go get a plasma welder, but it would also be that much more expensive. Besides, as much as id love to have one i really dont have a use for it at the moment.
As for trying to convert a cutter to a welder, I got the idea from seeing the diagrams for how the plasma welding torch works in the AWS welding handbook, almost the same picture MDG posted.
What im getting at is, If you switched from using compressed air to argon for the main plasma gas, then added a second gas nozel around the cut tip with a manual gas valve like those for converting a DC stick to a DC TIG, wouldent that make a plasma welder? Or am i still missing a peice of the equation here?

Thank you all again
-Clif

By DaveBoyer (*****)

Date 03-09-2008 05:10

Clif, I understand where You are coming from, as I too monkeyed around with different things, many of which were excercises in futility. I am reminded of a joke where a guy in prison says "It took Me 7 months to make this knife out if a spoon I stole from the kitchen" the other inmate says "Why didn't You just steal a knife?" My guess is there must be enough difference in the power suply and controll circuts that using them for other than their intended purpose doesn't work out. I guess this because I have not seen any multi purpose units or conversion kits. This dosn't mean that there are no such items, just I havn't run across any [other than the Pow Con plasma cutter powered by a welder someone mentioned in another post].

By Plasma-Brain (**)

Date 03-10-2008 15:46

LoL, "Why didn't You just steal a knife?" that says it all about this idea, so thank you all for entertaining it.

If i ever get my hands on an old plasma ill let you guys know if it works out...

By rlitman (***)

Date 03-09-2008 07:03

Good question, which I can't answer, but . . .
The plasma cutter head also uses that high flow of air, to cool the electrode, and keep the insides from melting. If you wanted to weld, you would need a much lower flow of argon (or else you would just end up cutting by blowing the puddle all over anyway), which would probably melt your plasma cutter torch head very quickly. :(
That's why my cutter (and probably many others), has a low pressure cutoff. It prevents running the machine into a meltdown.
I don't know enough about the electrical characteristics of the plasma welder, to tell you if a plasma cutter power supply (or maybe even a TIG supply), would work with a plasma welding torch.

By OBEWAN

Date 03-07-2008 19:28 Edited 03-07-2008 19:31

The older plasma units had special electronics too. There was a pilot arc that got the plasma column started. The main welding or cutting arc was delayed until an ionized plasma column was formed. The pilot arcs used to be pure argon. Then the relay kicked in, and boom the main higher powered plasma column jumped across. Then there is the transferred and non-transferred arc stuff. Somtimes the actual arc is only inside the torch, but the plasma column shoots out like a flame through the torch orifice. I went to plasma school at Linde (now ESAB) in 1981. I am sure a lot has changed since then.