Bonding Tungsten and/or Iridium?

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Jerry Biehler
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Re: Bonding Tungsten and/or Iridium?

Post by Jerry Biehler »

Mine is an old hughes, I think max 40J. It uses a mercury contactor to dump the cap into the transformer.
ian_krase
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Real name: Ian Krase

Re: Bonding Tungsten and/or Iridium?

Post by ian_krase »

While my inadequate resistance brazing transformer was working pretty well for soldering tungsten filaments to SS conductors, I decided I wanted something more. .

But... The whole machine was rather dangerous and clumsy (exposed line current wiring attached to variac by screw terminals, disconnect only on the hot line, no momentary switch, etc), ugly, and the pincers I made were never very good to start with and didn't get much better after I set them on fire trying to solder the power cables to them. To make things worse, the cables were very stiff when cold, but the insulation would quickly become melty and soft after a few seconds of welding.

So... I built this using the same transformer.

Box contains transformer along with a momentary DPDT toggle switch that switches the primary and a fuse holder for safety. Timing is by hand, in typical messy-and-simple Krase Laboratories style. Hold-pressure is also by hand -- for a while I thought this thing wasn't working (was barely getting workpieces red hot) but turns out I was using far too much pressure.

The tongs are very simple and a vast improvement. Two beefy terminal blocks (called "distribution blocks" are used to bond the hefty but flexible silicone insulated #6 (?) cables to the 1/4 inch copper tongs. Each has a brass section brazed to the end to accommodate the set screw to attach the pincer tips which are made of 8 AWG copper electrical wire. Note that brazing will make the copper DEAD SOFT and you need to hammer it a little to re-harden it up enough for further machining.

The terminal blocks also serve as mechanical structure; with a few extra holes drilled they are both epoxied and screwed to a leaf spring "hinge" made of thin stainless. I think a real hinge might be a good upgrade.

I broke both a drill and a tap trying to tap the copper, hence the brass.

Last picture is closeup of 19 gauge SS wire welded with this spot welder. The upper right weld shows molten squeeze-out, and it's easily possible to melt the wire in half with this system (usually when applying too little hand pressure)
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Richard Hull
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Re: Bonding Tungsten and/or Iridium?

Post by Richard Hull »

Resistance welding is made very easy if capacitive discharge is used, as you just dial a voltage to get a rather precise joule energy in every weld.
Professional machines for the vacuum tube industry usually had a selector switch to choose joule energy.

My first resistance welder was a 10 volt 60 amp transformer feeding professional spot welder electrodes (welder supply). The electrodes helped, (no sticking), but it was still an art to judge pressure and on-time.

The Raytheon tube welder made small spot welds a snap.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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