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Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714
It turns out that Forming Gas with <= 5.7% H2 is nonflammable in the regulatory sense. Cylinders and regulators (the other kind) use CGA 580 fittings, same as compressed nitrogen or argon.
Ref: (ignore the mistakes) and this MSDS by Praxair:
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714
Here's a picture of the shielding-gas cup I made for wire balling. The general setup is about the same as the unshielded apparatus that I showed earlier in this thread. Argon is flowing at a few cm per second -- any more than that, it carries away heat & it takes a lot more current to melt the wire end. I was surprised to see a cathode glow coating the last couple mm of upper electrode, at atmospheric pressure. I think there's a bit of it on the tip of the screw in today's picture.
The photo shoot brought evidence that argon ionizes more easily than air. Variac was just high enough to start the arc (electrical measurements will follow sooner or later). Soon after an unplanned stoppage of the gas flow, the arc got skinny and orangey and then went out. It came back by itself when gas flow was restored. Macro photos to follow sooner or later.
Here, on the same station, is a fancy projector lamp I picked up at the flea market this morning. No diode, and variac at 100%. I think it's what they call a xenon short-arc lamp. Don't know which terminal is the cathode, or whether they are normally energized with AC. I guess normal current is on the order of 1 ampere.
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Arc polarity for fusing wire?
