Pictures showing the joint(s) and the metal backing would be helpful.

Are you good at gas welding sheet steel of a comparable thickness, getting a good bead but not overheating it too much so it sags in places? Are you using a neutral or slightly reducing flame and getting the cone up to the work area, and it still doesn't melt? Are you adjusting the gas properly so the tip is working with the correct flow? I don't know Victor tip sizes, but with Harris, I think #2 would be big enough for 0.040" thick copper.
Something you might consider is using silver solder; if the work is all copper, the Sil-Fos alloy (used extensively with refrigeration tubing) is self-fluxing, melts at a reasonably lower temperature and if used sparingly ( no big globs left unmelted) on tight joints, won't be that noticeable.

I wouldn't think you would have melted the end of the cutting tip; perhaps some spatter or carbon buildup has plugged some of the 'preheat' holes, Even if slightly melted, the end could probably be turned or carefully filed back a bit and the holes cleaned (or carefully 'reamed" as a last resort).

 

What kind of flux are you using? As mentioned above, some brazing and soldering rods are self fluxing. If you over heat it, it will burn the flux and the filler won’t flow and bond to the copper. Start over and shine things up. Most HVAC people that braze copper would use an acetylene-air turbo torch. OA may be too hot, so be careful with the heat. If I was welding steel that thick with a Victor torch, I would use a 0 tip.

 

One suggestion from an artist friend was that the 1/4" steel plate that I set it on may have sucked away the heat. Interesting suggestion to put the part on a heater.....

I am using an esab flux, white powder, I add water to make it brushable. The label is unreadable. I have brass brushes to polish it up.

I am using silicon bronze rod. As I said, I do not do a lot of brazing. I did get the rod to flow along the joint when I applied enough heat to a small test piece. I have done enough soldering to know how that is supposed to work, including silver soldering. Silver soldering is technically brazing, due to the temperature. I am trying to use silicon bronze for the color match, as it is an art piece. The silflo is shiny silver color, in my experience, and would be too obvious after it was cleaned up and buffed.

Tomorrow I will try again, without a 1/4" plate backing, and plan to try my oxy-propane rosebud.

Thanks for the tips.

Richard

 

Have you compared temps of base metal and filler? You call it brazing probably welding. Are you expecting it to flow without melting the base metal?

 

I agree with the Sil-Fos recommendations,, PLUS,,,,

add a source of heat other than the torch.
You would be amazed at the change if you tried brazing while the hat is sitting on a large propane cooking grill, with all burners set to high.

Or possibly use a weed burner propane torch.
Load up the heat from the "other side" so that you can get on to doing the brazing with your torch.

There is no law in the welding books that says heat must come from one source,,,

 

#2 tip should be more than adequate. I've Sil-Phos brazed 2" buried copper pipe with less while water was held 8"-10" away by a Dutch finger. I think your project would require less heat so something must be going wrong with your method. Try directing flame so that as much stays on work as possible instead of burning up in surrounding air.

 

Were you Tig welding it with Copper and didn't like the results? I feel like copper Tigs pretty well... (I haven't done a whole Lot of it, maybe like so many other metals, there's a larger variety of copper alloys than I realize)

 

What filler rod did you use when you tried TIG brazing it?

 

Try using helium as a shielding has it gives a much hotter arc. Copper is a heat sink for sure and if your machine is maxed out and your not able to get a puddle going without cooking the hell out of the part helium is the answer.

 

I used solid copper wire with pennies and TIG. Short welds, let cool and repeat.

 

Just an update: I tried to use my oxy-propane rosebud, but could not melt a piece of rod on the test piece, so not enough focused heat...... That was after I got rid of the 1/4" steel plate, in favor of a lot less thermal mass used in clamping.

I am going to think some more about how I could preheat the piece; given how thin it is, heat would probably need to be continuous to be effective. I am thinking about buying some larger oxy-acetylene tips.

Personal note: This has been a very frustrating project, which seems to have come down to my inability to consistently produce good small weld beads. So far I have thrown away three brims; I keep trying to save the dome. I put the project down for several months, and then I try again. I even got a welding instructor to come to my studio and give me some tips...... I was hoping that brazing would offer a way out,

 

Go back and reread Post 2, then answer the questions, and perhaps I/we might have some other suggestions. Any chance you could make & provide a video of your torch work, in addition to posting a few pictures? Maybe some of the equipment too, from tanks to torch tips?

 

So you are using oxy propane? Oxy acetylene works better for directing heat to a specific area. Propane heat a larger area. If you use just the inner cone, then you compromise heat input. The max heat input is not
Pinpoint at the cone but on the outer area of the flame

 

This is my favorite tip for silver soldering copper. I use 15% silver solder, and no Flux unless I'm soldering copper to steel. It is a uniweld type 17-15. I use a slight carburizing flame. 15% solder comes out more of a bronze color. I've only used oxygen propane once many years ago and hope to never use it again unless I have to.

Sent from my SM-N975U using Tapatalk

 

I have read that oxidizing flame work for copper, bronze and zinc.

 

I was bending metal last night on this rare occasion using heat with acetylene tank connected. Decided to try some copper /silicon bronze. Used MECO weldmaster torch . I had .025 copper and 1/16 sb. Used acetylene/oxygen. #1 tip. The melted bronze seems to add mass and no melting occurs where sibr is added.

Issue I had was tip too large it would overheat shortly after flow. I will try a 0 or 00 tip. I think the proximity or the melting point. The copper melt everywhere else after the sibr flows.

I think propane is the issue for you, not allowing heat concentration.

Interesting in hearing your result.

 

Correction I had #2 tip on last night. Tried a 1. Much better control. Nothing pretty, though. Seem like it start to flow then overheat and piles up? I am just speculating. Oh, I guess I should try flux.

 

View attachment 51262F2F-F556-4A3D-A5E6-6E64720000E2.jpeg

Hope this photo works. Added flux. However the part where it began to stick there was a large mass of flux. Again, speculating the first part there was not enough flux and it kept balling and would not adhere at all to the lower plate, like not enough heat, but I think it is oxidation.. Notice the color difference.

I used Esab brazo flux added water but it did not make a very good paste. Thus it distributed unevenly.

 

View attachment image.jpg

 

View attachment image.jpg

Here is another photo. Inner cone almost touching added filler. Caked on a large volume of wetted esab flux.!dried it in place with the torch before brazing.

I also, tried Harris staysil silver solder white paste and oxidizing flame. No conclusion on how it works since there are too many other variable for me to correct.

I brazed on top of a piece of square tube. I think heat wicking ,due to a mass ,was not a huge issue compared to wicking due to proximity of directing heat to where I wanted the filler applied. If the cone is too far away, then the filler balls or only adhered yo the vertical plate. It often will not move/flow.

 

View attachment image.jpg Alright, alright alright. Last one, maybe. Photo does not represent well. Close
Cone and small tip, oxidizing flame. Flowed well. I was not comfortable, hesitated and burned hole the end.

All joint are fillets. All are curved so they stand freely. The last one is straight.

 

An oxidizing flame produces a slightly higher flame temperature, but whereas flux is there to dissolve oxides and improve wetting, while an oxidizing flame promotes oxides, I see little reason to use one under normal circumstances. A neutral or slightly reducing flame, with copper or most brasses, will lead to less problems including zinc vaporization on the surface of brass.

Here's a site a quick search found that gives basic information about flame characteristics:

https://mewelding.com/oxyfuel-flame-adjustment-and-flame-type/

 

Yeah, however the difference in flame temperature is remarkable. I tried reducing flame with out flux it worked, but input so much heat due slow build up of heat it burned holes later in the process. With neutral flame and flux i could direct the flame cone into the joint and begin brazing almost immediately. I suspect an oxidizing Flame and flux would be useful on heavier material. In production application I suspect it would be cheaper, use oxidizing flame rather than waiting for reducing flame to heat up and all the heat transfer that occurs in materials like copper. I think a reducing Flame would be better for sweating pipe, since it is broader and will wrap.

Also, read reducing flame is a safety setting since neutral is balanced and will drift. It is less likely to become oxidizing.

Anyway to OP. My suggestions

Acetylene would likely work better for directing heat where you want it to go.
Smaller tip neutral or oxidizing flame.
Lots of flux

 

The late Mr. Tig on copper welding. I cast quite a bit of copper but in the foundry you throw your failures back into the furnace and they disappear so I never had the need to weld it.
https://www.youtube.com/watch?v=cYpYGbC2Drg

Another source:https://www.brazing.com/Support/Procedures_and_techniques/CopperWeldingProcedures.aspx

 

More nonsense from "MrTig" (this clown names himself despite not being much of a Tig welder )

Welding Copper at .45 sec "Pretty difficult", at 3.25 suddenly "isn't that hard"...

I don't know what Helium costs were in 2014, but today his advice is even sillier than it was back then. Use the right size machine, and copper welds just Fine. You can do fun stuff with it too, weld SS and Copper with Romex wire filler!

 

He passed away a few months ago...kind of poor form to call the guy names, even if you disagree with him.

 

Last one.

Cleaned metal with grinder. Used Harris 600 flux is wet slurry/”paste” . Baked flux on to rod. Stopped multiple times to recoat rod. Used neutral flame. I switch flux only because I was out of esab flux.

The coated rod flowed betted and eliminated the trash atop the previous welds. The photo was taken with immediately after welding with zero post weld cleaning.

I did a previous weld with uncoated rod and reducing flame. The metal flowed the same as the fluxed rod, but still has trash in the bead.

Coupon is sitting on 3/8” thick steel table.

Next question… have you ever grinded silicon bronze? It is a bear.

 

Yea, I gotta say, "death" gives everybody a get-out-of-Jail card?

Once dead, you can't be criticized? Any misinformation you leave behind has to stand unchallenged? And this is because of some Child Like Fantasy that the dead might be "looking down" on us and unable to respond in defence?

I called him a clown when he was alive (and I must say I was unaware of his current status when I wrote it this time) and his passing hasn't changed my opinion one bit!