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View Full Version : unable to braze aluminum. what am i doing wrong



rkovvur
02-26-2010, 12:47 AM
I never welded before, so please be easy on me :)

I bought the $50 welder from home depot today (the speciality welder from bernzomatic that has the mapp and oxygencylinder).

I also bought an aluminum brazing rod. However even after using up the entire oxygen cylinder, i was unable to braze the aluminum....

I sandpapered the aluminum pieces. However the melted brazing rod just melted and rolled off the aluminum piece. The flame is hot enough to melt an aluminum piece.

help !!!

pofo
02-26-2010, 12:58 AM
YouTube- Brazing Aluminum

SoSauty
01-15-2011, 11:54 PM
I would like to know also. Can't help but would like to see this varied responses to this thread. The video shows the rod spreading nicely after only 2 seconds of heat. What's going on when the rod melts but just balls up and rolls off?

KyleH2
01-18-2011, 08:38 AM
Ive never brazed, only TIG welded before but pay attention to the angle he is holding the torch and rod relative to the work. Are you holding it similarly? Also I found that the SS brush works better to clean the oxide layer than sand paper.

awemawson
01-19-2011, 07:45 AM
Aluminium is a highly reactive metal that forms an invisable oxide layer in air just as soon as you clean it. The chap in the video was using an aluminium alloy brazing rod that has an active flux core. This flux melts in the heat of the oxy-acetylene flame and spreads over the area being brazed. The active ingredient in the flux disolves the oxide layer, and the rest of the flux acts as a shield from the atmosphere. Note how he was careful to clean off the flux before sanding 'as he didn't want it all over the shop' - it's agressive stuff.

The aluminium part to be brazed needs to be heated just below it's melting point. Too hot and it sags, too cold and it won't braze. The old way was to rub a bar of soap on the part and apply heat. When the soap chars it's ready. If the part is too cool, or there is an oxide layer, the rod will just ball up as you describe. The flame should heat the part and the part should heat the rod - if you just heat the rod directly again it will ball up.

AWEM

SoSauty
01-20-2011, 12:44 PM
Awemawson,

Great BIG thanks, sometimes I get so frustrated at the months, even years it takes to find out a piece of info. Knowing that the object is to be heated first, then that melts the rod, saves a bunch of trail and error. Nice tip that the flux is messy.

(Last year I took an electricity class, then installed a pump in a deep well. Ultimately burned up 1 pump, had to return a 2nd, return a generator, the result of incomplete info. The boxes on pumps do not state their required 'start up' amps, nor was motor 'start up' amp concept covered in beginning electricity. What a needless waste of labor and money.)

low_48
01-20-2011, 01:08 PM
There are several good videos on Youtube. One discusses pushing the heat towards the area to be brazed instead of directly heating the braze area. It has to do with heat transfer in the aluminum.

marbien
03-16-2011, 04:36 PM
Did you clean with alcohol after sanding? Also did you keep the flame at minumum ..... melt move away, melt move away etc

SoSauty
03-23-2011, 12:15 AM
Funny, couldn't get the aluminum rods I bought for practice to braze for anything, even using low temp rods. But then tried 2 steel bushings, used solder, brushed, fluxed, brief propane flame, touched solder and it drew over half-way round the 5/8 bushings in an instant.

After cooling, I tried to break 'em apart with thumb and fingers but couldn't! Somethimes the material tops technique:)

Thanks all

Fastest1
03-28-2011, 07:42 AM
Aluminum and steel react totally different to heat. Steel keeps the heat localized and doesnt dissispate it very fast whereas the aluminum is moving the heat very quickly. This is why the aluminum was balling up because the parent metal was too cold.
Funny, couldn't get the aluminum rods I bought for practice to braze for anything, even using low temp rods. But then tried 2 steel bushings, used solder, brushed, fluxed, brief propane flame, touched solder and it drew over half-way round the 5/8 bushings in an instant.

After cooling, I tried to break 'em apart with thumb and fingers but couldn't! Somethimes the material tops technique:)

Thanks all

diecutter
03-28-2011, 10:05 AM
Check out this video which explains the whole process in detail and in plain terms. A big part of doing this right is heating both pieces to full temperature before adding the rod. That was my biggest problem before I was successful.

Good luck. YouTube - aluminum brazing soldering using alumiweld welding rods