Plasma and Ethercat?

RDA wrote:

The ”whole” idea is to stabileze the molten hafnium, tungsten or whatever the electrode material is.

Hafnium does not melt, it erodes.
Would not be much use molten, and to get it to melt, the surrounding copper electrode would have melted loooooong before hafnium.
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PCW is trying to explain the induction phenomena that happens when applying voltage to a coil and then cutting it, the coil will induce current on it's own.
Find an electromagnet, apply some voltage to it and cut the voltage while watching the scope, it is amazing what voltages can be produced by it, way beyond what has been applied.

While the current and arc voltage can be controlled accurately during cutting,
you have large transients at arc start and stop (which happens in a fraction
of a nanosecond) V=L di/dt  is not your friend here...

Thanks! I will check this out.

During cutting the hafnium is in molten state. Thats why you do controlled current ramps, to try and keep the hafnium steady.
HT link

”Most of this wear occurs at the start and stop of a cut when the molten hafnium material quickly heats up and cools down, melting then re-solidifying.”

Still seems to far fetched, if it melts if will blow out the nozzle, very quickly, but might be just at the surface ...
Hypertherm, so lends to a lot of trust, although i am leaning to marketing.
I have read everything on Hypertherm, Kjellberg Finsterwalde, Thermal Dynamics, Cebora, Victor (now owner of most of these), etc, and never ever bumped into melting Hafnium, all say eroding, although technically that is melting small parts.
As for "controlled current ramps", it does help longevity, but older stuff never had that, just a relay switching on and off a huge transformer.
Some have another transformer to cut the cutting current for a short period while the pilot arc is on till it detects current flowing, then turns on the relay, Thermal Dynamic Pak90 has such a system, and uses high voltage pilot at 50Hz or 60Hz, not HF.
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We should move this discussion somewhere else, any ideas welcome.

Yeah quite out of the original topic. Maybe there could be a generic consumable thread?

Might sound far fetched but it is true. You will have a molten puddle, bead or what ever you want to call it, in the “root” of the arc. You try to constrain and keep it as steady as you can. The copper ( or silver) around the hafnium/tungsten gives means to conduct heat and electricity.

Of course in the old stuff you didn’t have anything “fancy”. You had plasma with electrodes made of tig rods. When the electrode wore, you could pull more from the torch.

I think it was in the -90’s where hypertherm came out with venting. So you don’t only ramp down the current but you match it to the flow rate of the plasma gas at the end of the cut. So you have a separate valve (close to the torch) that lets out the plasma gas. You then see how fast it gets rid of the plasma gas and you ramp down at the same time and rate. This improves the consumable life significantly.

There is quite a lot of cool stuff behind the “scenes” the more complex the systems get.