Bonding Tungsten and/or Iridium?

This forum is for specialized infomation important to the construction and safe operation of the high voltage electrical supplies and related circuitry needed for fusor operation.
Jerry Biehler
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Re: Bonding Tungsten and/or Iridium?

Post by Jerry Biehler » Wed Aug 30, 2017 8:59 am

Based off of what? When you pull the wire off does the wire break and leave material behind? Is it slightly embedded in the base material?

ian_krase
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Re: Bonding Tungsten and/or Iridium?

Post by ian_krase » Wed Aug 30, 2017 10:33 am

Yes and yes.

Bruce Meagher
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Re: Bonding Tungsten and/or Iridium?

Post by Bruce Meagher » Wed Aug 30, 2017 8:44 pm

Ian,

As Jerry and others have mentioned, ideally you want a transformer whose secondary has one or two turns to make proper spot welds. You’re after gobs of current for a very short interval (with pressure). Check out the attached two documents for a great primer on the subject. Of course you can weld two pieces together by pumping power in like you are doing, but a proper spot weld requires lots of current for a short duration to create an ideal nugget. Dissimilar metals and different thickness material require special attention to the electrode design to make the nugget form properly.

Last year I was struggling with spot welding a tungsten filament to an NPS support for a vacuum tube. George clued me in to the proper surface preparation requirements for the material being welded so don't forgot about that aspect too.

Bruce
Resistance welding.pdf
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Fundamentals of Resistance Welding.pdf
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Justin Fozzard
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Re: Bonding Tungsten and/or Iridium?

Post by Justin Fozzard » Wed Sep 27, 2017 9:03 pm

Here are some photos of the innards of a Hughes 250 Watt-Seconds impulse welder that I use for electrode welding.
The capacitors are charged to a maximum of about 450V and are discharged into the output transformer using surprisingly small thyristors.

Front Panel:
Hughes Welder 1.jpg
The supply and output transformers:
Hughes Welder 2.jpg
The 450V capacitor bank and thyristor pcb. The large green wirewound resistor at bottom right is in series between the capacitor bank and thyristors.
Hughes Welder 3.jpg
Underside of thyristor pcb with the thyristors at top left.
Hughes Welder 4.jpg
The output transformer and primary winding selector switch for altering the pulse shape.
The five turn secondary winding is made from several layers of thin copper tape about 1 inch wide:
Hughes Welder 5.jpg
Justin Fozzard.

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Richard Hull
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Re: Bonding Tungsten and/or Iridium?

Post by Richard Hull » Wed Sep 27, 2017 11:10 pm

My 1950's Raytheon vacuum tube spot welder, (got it for free), also charges its oil capacitor bank to about 500 volts and is an adjustable 40 to 200 joule unit. Like your system, it has a monster transformer with 1/8" thick strap copper output windings. and the switching is done with large vacuum tube thyratrons. It gives a nice "thump" sound as the weld is made.

Small, capacitive discharge, spot welding systems give a consistent power delivery to what is welded each time.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

Jerry Biehler
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Re: Bonding Tungsten and/or Iridium?

Post by Jerry Biehler » Thu Sep 28, 2017 11:08 pm

Mine is an old hughes, I think max 40J. It uses a mercury contactor to dump the cap into the transformer.

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