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Carbon Arc Brazing

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Chris

Sat Feb 25 2006, 06:46AM

Registered Member #8 Joined: Thu Feb 02 2006, 04:34AM
Location: Harlowton, MT, United States
Posts: 214

I need to braze some thin steel (heating elements) onto heavy steel plate for my downs cell, such as with flux coated brazing rod. I don't have an acetylene torch; the only torch-like apparatus I can come up with that can reach appropriate temperature is a carbon arc running from relatively high voltage/medium current. A higher current arc is far too intense and will simply burn through like a cutting torch with a carbon electrode (in fact that's exactly how I cut out all the 1/8" metal panels). I have been attempting to use the arc similar to a torch flame or TIG arc to heat the metal and melt the rod which is added seperately.

Awhile ago I tried stepping up my welder's low current tap (75V no-load, 100A max) 1:5 and 1:10 with my 10kVA pig (so 375/750V no-load and 20/10A) to use that. It's a little scary working with such potentially lethal voltages and currents that close up, but with heavily insulated gloves it is really no different from the voltages portable plasma cutters and such work at. I haven't tried DC yet, but working right off the AC with a carbon electrode I found the arc very unstable, hard to strike and hard to control, and yet still too hot (pitted the steel rather than heating nicely like a torch flame). A rectifier and some series inductance might make the arc more stable, but I'm still not sure if I will be able to find a voltage/current that will heat the metal or even form a puddle, but not burn or pit, and still have enough heat to work. I could try blowing some argon on there but I doubt it would help too much as the rod already has its own flux.

Perhaps someone here has some ideas or things I can try with what I have to braze successfully. I doubt any other means of attaching the heaters will be successful other than brazing; welding burns through the thin metal too easily, even at the lowest currents. Any ideas are welcome but getting a gas torch such as oxy-acetylene just for this one little project is probably not an option.

Chris

Hazmatt_(The Underdog)

Sat Feb 25 2006, 07:43AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Trouble is carbon arc is for cutting, not brazing. And when you're doing this you're creating slag after the electrode hits the steel, which does not weld.

What I would do, if you can, is heat the thick steel to cherry and let the conducted heat, heat the thin steel. I would do this with my prop oxy setup, but like you're saying, that just isn't an option.

Other ideas are wire fed welding, but too high a current will blast through the thin sheet.

TIG or MIG, but I would assume that takes a lot of practice.

I would say when you don't have the equipment to do something, find someone who does.

I got a 55cu ft. cylinder from swapmeet for $90
oxy regulator for $75
another cylinder 155cu ft from swapmeet $165
cutting torch full kit $99 harbor freight special
propane tank $35
gas fittings and valve hardware and hose $140

with what you're doing, it may be worth it too, to go to a welding supply and ask to RENT a cylinder. I have heard that people do that, course you would still need regulators, but that comes with the harbor freight package deal, which is a super freggin deal!! you get a kit that costs over $400 retail namebrand for $99! And she's a beaut.

Sun Feb 26 2006, 12:13PM

Registered Member #256 Joined:
Location:
Posts: 124

yup actually if you can make a rig to arc between 2 carbons (i have) you can braze. tig is a little bit of practice to perfect. but it is quite easy, mig is wire feed so that isnt too much to do, i too have the harber freight torch set, is a excellent buy, i got it for 85 on special, and all together, a torch set is very handy to have, also, if you get a propane or MAPP gas soldering torch, you should be able to braze easily, specially wit MAPP gas well hope that helps and im assumin u makin potassium or sodiom be carefull

johnf

Sun Feb 26 2006, 07:44PM

Registered Member #230 Joined: Tue Feb 21 2006, 08:01PM
Location: Gracefield lower Hutt
Posts: 284

I would try spot welding your heaters ro the plate. Both iron and heating elements are good candidates for spot welding. A simple mod to your arc welder will make it into a spot welder. all you need is a timer to turn the welder on for a preset time and two copper electrodes pushed hard against each bit to be welded

IamSmooth

Sun Feb 26 2006, 09:19PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

AS TESLAS SON said, MAPP gas should work. You can get a torch cheaply at Home Depot or Lowe's. It will burn over 5800-6000F.

Mon Feb 27 2006, 05:24AM

Registered Member #256 Joined:
Location:
Posts: 124

yes exactly. the Mapp torches can be had for cheap like under 20 dollars so that can be an option, spot welding i cant say anything on having never done it, but it sounds like it can be good.

Hazmatt_(The Underdog)

Mon Feb 27 2006, 09:31AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

to get anywhere near 6000*F you need oxygen. Oh and if you consider using the bottles of oxygen from Home Depot, they only last 12 min. Its more econimical to try to rent a 55 cu ft. oxy cylinder (which may last 2 hours) and rig up your propane as the fuel, and use the harbor freight torch set. You will need to keep the propane tank stem and screw it into the acetlyene regulator of the harbor freight torch set.

Chris

Mon Feb 27 2006, 07:12PM

Registered Member #8 Joined: Thu Feb 02 2006, 04:34AM
Location: Harlowton, MT, United States
Posts: 214

Thanks for the replies guys. Heating the entire panel to a red heat and letting that heat the thin metal and melt the rod sounds like the best option here. This brazing needs done on the bottom of the cell body which is just a steel box, so I should be able to heat it enough by putting it over a simple forge which I could rig up, or maybe just a propane or natural gas burner. It shouldn't take too much heat really especially if I put ceramic fiber insulation around it. Rigging up a carbon arc brazing setup like teslas son described would be difficult (it would need some sort of auto-feed system), but could be another option.

MIG welding would easily burn through even with thin wire at the lowest setting, plus I don't have my own wirefeed welder. I have no experience with TIG welding but have heard it's challenging. It definately needs brazed if I hope to achieve the best thermal conductivity and semi-permanent attachment. Also even the cheapest oxy-acetylene or oxy-MAPP setup with cylinders costs way more than I want to be spending on this. Spot welding something like this would likely require a few kA too - even my big alternator set is only good for about 520A.

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