Aluminum Sign Welding/Brazing Newbie

[Stevealex]

Hello, I am trying to repair an aluminum back-lit sign for a customer and have tried to braze certain parts of the sign but with no success. I have never brazed Aluminum before and when I try, the "weld" from the rod does not want to adhere to the aluminum. When it cools, I can just pull the weld right out. The aluminum rods say no flux required so I dont think its that. I also tried using an aluminum welding rod with flux but no luck either. I tried heating the aluminum to several different temperatures, Ive made sure the surface was clean and im not sure why the weld wont stick. Am I missing something? Any help would be appriciated. Thank You!

 

[Rick]

I'm not a welder, but have welded aluminum signs when I was a shop grunt.
What popped in my head was...
What type of welder?
What were your settings?
How did you clean the aluminum?
Any contamination on the welder?

 

[MikePro]

http://www.youtube.com/watch?v=CJ42scaWFnw

 

[Stevealex]

Oxy Acetylene, Soft blue Flame....I Cleaned the Aluminum with rubbing alcohol and wire brush, then wiped clean with cloth. It looks to flow in the crack but when it cools the Aluminum fill just pulls right out. No adhesion at all

 

[Kottwitz-Graphics]

Oxy Acetylene, Soft blue Flame....I Cleaned the Aluminum with rubbing alcohol and wire brush, then wiped clean with cloth. It looks to flow in the crack but when it cools the Aluminum fill just pulls right out. No adhesion at all

To me it sounds like the filler is just melting, and your not heating up the alum.

I'd take it to an aluminum welder. It won't be cheap, but i'd pass the cost on to the customer.

Better to have a customer upset about the cost, than getting it back and have the "weld" fail.

 

[d fleming]

muggyweld.com

 

[MikePro]

If you're filling that crack as a structural fix, you should actually WELD it... either mig, tig, or high voltage stick welding would be ideal, but if you're trying to go the "soldering-stick" route, you'll need to get that 1/8" aluminum red-hot for it to bond properly.

the youtube video I posted made it look easy... since they were "welding" <.050 aluminum. 1/8"+ aluminum takes a LOT more heat to make it work, which is why I love the highvoltage welding.... point n' shoot!

 

[letterman7]

Yep, those "welding rods" you use a torch with are not welding rods. They are simply a surface filler that, with luck, you might get to stick two pieces of thin stock together with. I've never been able to use that stuff as advertised. Use a proper welder - a spool gun with an argon gas shield.

I'm not sure about Mike's comment about getting the aluminum "red hot" for a "brazing" rod... at that temp the aluminum would simply melt.

 

[MikePro]

idk, i've never used "aluminum solder before"...and "Red-hot" wasn't the proper term, i guess... since, at 1200degrees, Aluminum liquifies before ever getting "red hot" like steel would. Also, these rods liquify at less than half (even a quarter of) the temperature, which means they harden almost immediately when exposed to surfaces of lesser temperatures. The aluminum you're attempting to "braze" should be hot enough to melt the material on its own just by dragging the rod across its surface, if you are to stand a chance at all:
"not-so Red Hot" aluminum allows your solder to penetrate the "tooth" of your materials attempting to bond before it cools/hardens.

i'll stick with my coil-fed mig welders, anyday. Just plug em in, point, shoot, and blind/burn yourself.

 

[MikePatterson]

take it to someone who TIG welds. That bismuth solder is crap, the guy at the flea market can stick to cans together but it is not welding.

 

[signage]

TIG or MIG is only way to correctly repair a sign!

 

[qmr55]

Pay someone who can TIG it, to MIG aluminum you need to have a really powerful machine including pure argon for a shielding gas.

Best bet is to TIG it and you will have a lot less problems.

 

[signage]

Some MIG machines accept daul bottles and a spool gun for the aluminum welding!

 

[qmr55]

Some MIG machines accept daul bottles and a spool gun for the aluminum welding!

Yup exactly! 1. You need a shield. 2. Needs to be a powerful machine.

 

[UFB Fabrication]

Also not mentioned was the crack caused from damage or poor design/initial weld. Take it to someone who is qualified to repair it properly. If it falls or fails now you own the problem.