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
Posts: 826
Joined: Tue Nov 24, 2009 8:08 am
Real name:
Location: Beaverton, OR

Re: Bonding Tungsten and/or Iridium?

Post by Jerry Biehler » Thu Aug 17, 2017 4:48 am

Short cycle is not going to cut it, you need more current. I am making a wild ass guess you are using a microwave oven transformer to build one. You only want about one or two turns around the core and that wire needs to be HEAVY, nothing at a model shop is going to do it. You really need something in the 4 to 2 gauge range. Then it is kept as short as possible to the tongs for spot welding.

A proper weld will leave material on the substrate when you do a pull test.

This guy made a pretty nice one: http://www.5bears.com/welder.htm

ian_krase
Posts: 447
Joined: Mon Nov 28, 2016 7:48 am
Real name: Ian Krase

Re: Bonding Tungsten and/or Iridium?

Post by ian_krase » Thu Aug 17, 2017 6:56 am

The transformer is from a 1950s-era... machine (which also provided the housing for my variac) called a "Microbrazer". (some kind of hybrid between resistance welding and silver brazing?) It had a vacuum tube *and* a large relay.

The transformer has a lot more than 2 turns, and it looks like along the lines of double 12 gauge *solid* wire. I suspect it is indeed better suited to i.e. driving evaporation filaments than welding.

Jerry Biehler
Posts: 826
Joined: Tue Nov 24, 2009 8:08 am
Real name:
Location: Beaverton, OR

Re: Bonding Tungsten and/or Iridium?

Post by Jerry Biehler » Fri Aug 18, 2017 1:57 am

Ok. Hats a resistance soldering unit. It will not work for spit welding. Too high of voltage and too low current. It's even a little small for evap filaments.

ian_krase
Posts: 447
Joined: Mon Nov 28, 2016 7:48 am
Real name: Ian Krase

Re: Bonding Tungsten and/or Iridium?

Post by ian_krase » Fri Aug 18, 2017 6:11 am

I was successfully able to heat a (small) filament from "red hot" to "white hot" to "light bulb" to "bright light bulb" to "AAAAHHHH MY EYES" and even to "OH YIKES" with that thing, so that's what I am sticking to.

Does that mean I need to go down to Halted for some huge capacitors?

User avatar
Dennis P Brown
Posts: 1489
Joined: Sun May 20, 2012 2:46 pm
Real name: Dennis P Brown
Location: Glen Arm, MD

Re: Bonding Tungsten and/or Iridium?

Post by Dennis P Brown » Fri Aug 18, 2017 2:05 pm

Not totally clear what you want but capacitors do not generally like being shorted; a spot welder is a massive short. Not sure it makes economic sense to add a cap bank to make up for low current in a x-former. I'd think buying a better x-former is the easier option. If it is just a power supply, then maybe that would work for a pulse system but not for continuous or long term supply for a filament.

John Futter
Posts: 1291
Joined: Thu Apr 22, 2004 2:29 am
Real name:
Contact:

Re: Bonding Tungsten and/or Iridium?

Post by John Futter » Fri Aug 18, 2017 8:20 pm

I know some spot welders use caps
stud welders being an example where they need quite a few thousand amps to to weld a high tensile 1" dia stud to a RSJ or UB.
All the good scientific welders i have used over the last 40 years have been low voltage timed spot welders
ie timer to xfmer primary a selector switch for a couple of output winding choices (current choice Hi/lo)
The nice little Beckman unit I have was made for welding mass spec and SEM filaments no caps in sight
I use this unit to make K type thermocouples almost on a daily basis

ian_krase
Posts: 447
Joined: Mon Nov 28, 2016 7:48 am
Real name: Ian Krase

Re: Bonding Tungsten and/or Iridium?

Post by ian_krase » Sat Aug 19, 2017 2:04 am

Yeah, i was looking at the potential for capacitative discharge but failed to find the requisite farad of electrolyts at a low price.

Jerry Biehler
Posts: 826
Joined: Tue Nov 24, 2009 8:08 am
Real name:
Location: Beaverton, OR

Re: Bonding Tungsten and/or Iridium?

Post by Jerry Biehler » Sun Aug 20, 2017 10:56 am

These resistance soldering units are only intended for a short duty cycle, run them for long at any major portion of their max current out and you will fry something. Most of smaller filaments/boats I have take about 150amps minimum. Trust me on this, I used to work on welding equipment for a living including spot welders.

You can also use batteries to make a spot welder. Hackaday has had several posts about homemade units: https://hackaday.com/?s=spot+welder

User avatar
Richard Hull
Site Admin
Posts: 10842
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

Re: Bonding Tungsten and/or Iridium?

Post by Richard Hull » Mon Aug 21, 2017 6:06 pm

We have been through this spot welding bit before in these forums.

Professional spot welders of the sort we need all use capacitors but they fire into a special transformer and not the welding lines.

Typical would be 500 volt capacitors of 20-200ufd (paper or plastic film, oil filled.... electrolytics are out) these are charged and a thyratron or SCR is used to place their voltage on a 120 volt transformer primary for a number of micro-seconds. The secondary, (usually a 2.5 volt 50 amp), are the weld lines.

I have used a normal 120 volt transformer with a 2.5 volt 50 amp secondary as noted above to successfully do all manner of spot welds in the early days of my fusor efforts until I obtained a formal Raytheon, vacuum tube, spot welder that has a joule rated selector switch.

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.

ian_krase
Posts: 447
Joined: Mon Nov 28, 2016 7:48 am
Real name: Ian Krase

Re: Bonding Tungsten and/or Iridium?

Post by ian_krase » Tue Aug 29, 2017 5:02 am

I replaced my feed wires with 8 AWG (the largest that can fit into my terminal blocks) and directly soldered them to the jaws. I also silver-brazed copper jaw tips to the jaws.

I think it discernably works better.

Post Reply