Recommended Aluminum Brazing Rod?
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EschewObfuscation
Mar 10, 2015, 6:18:39 PM3/10/15
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I have a repair task that could benefit from some aluminum brazing. There are lots of brands of brazing rod made for aluminum work, generally aluminum/zinc alloys, some with purported Secret Sauce that makes them Vastly Better Than The Other Guy's Brazing Rod.
Does anyone here have experience with products in this class and recommendations based on that? The key requirement is ease of use and versatility, as I have no control of (or even data regarding) the exact alloy that's to be mended; maximum strength or high melt are not important factors. If brazing isn't feasible, drilled holes and bolts would work, at the cost of being a bit more ugly, wobbly and clunky. But it'd work.
Thanks!
Does anyone here have experience with products in this class and recommendations based on that? The key requirement is ease of use and versatility, as I have no control of (or even data regarding) the exact alloy that's to be mended; maximum strength or high melt are not important factors. If brazing isn't feasible, drilled holes and bolts would work, at the cost of being a bit more ugly, wobbly and clunky. But it'd work.
Thanks!
Keith Rogers
Mar 10, 2015, 6:31:52 PM3/10/15
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I picked up some aluminum welding rods from Harbor Freight and tried them out with a tig welder on pot metal... sort of worked. But this guy (vid below) is able to do something with a torch. I think success will depend on how big your aluminum part is. Aluminum conducts heat away so rapidly that it might be difficult to get thicker parts hot enough to react.
https://www.youtube.com/watch?v=Cvfsoy0Fmy8
https://www.youtube.com/watch?v=Cvfsoy0Fmy8
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EschewObfuscation
Mar 10, 2015, 6:52:22 PM3/10/15
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Yes, sufficient heat is definitely part of the equation. There are also variables of flux composition (that vid showed him not using any flux), as well as rod composition.
I like HF for clunky, low stress tools, cheap ceramic magnets, generic household epoxy etc, don't trust them for anything too chemistry or alloy sensitive. As there are companies that specialize in this stuff, I'm sure there's art to it the chinese lowest bidder supplier won't be replicating, but I haven't the hands on in this area to know what's the shortest path to acceptable results. I'm pretty sure the space doesn't have an acetylene/air torch, so I'd be using propane or propylene. Unless there is such a torch on hand?
On Tuesday, March 10, 2015 at 5:31:52 PM UTC-5, phoglite wrote:
I like HF for clunky, low stress tools, cheap ceramic magnets, generic household epoxy etc, don't trust them for anything too chemistry or alloy sensitive. As there are companies that specialize in this stuff, I'm sure there's art to it the chinese lowest bidder supplier won't be replicating, but I haven't the hands on in this area to know what's the shortest path to acceptable results. I'm pretty sure the space doesn't have an acetylene/air torch, so I'd be using propane or propylene. Unless there is such a torch on hand?
On Tuesday, March 10, 2015 at 5:31:52 PM UTC-5, phoglite wrote:
I picked up some aluminum welding rods from Harbor Freight and tried them out with a tig welder on pot metal... sort of worked...
Michael Kuba
Mar 10, 2015, 9:19:14 PM3/10/15
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Carroll Smith has a few recommendations (no idea if the brands are still around these days...) I'll look when I get home.
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Michael Kuba
Mar 11, 2015, 9:22:46 AM3/11/15
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I misremembered slightly - this is under the section for "nickel bronze welding" (conventional brazing), but the companies produce items considered under "silver soldering" (which is what I think you are looking for). Anyway, in Prepare to Win, he mentions "In this country welding alloys, flux and descriptive literature are available from Eutectic, Allstate, Amaco and Weldco. Your local welding supply house can supply information and descriptive literature. Eutectic's handbooks are particularly good."
Eutectic has some brazing compounds specifically for aluminum, e.g. http://www.castolin.com/en-US/product/eutecrod-190 and http://www.castolin.com/en-US/product/eutecrod-21-fc-e .
My general thoughts are if it's good enough for racecars, it's good enough for almost everything. If it's good enough for airplanes, it's good enough for everything. Carroll Smith tends to use airplane parts to build his racecars, so I find he has generally good fabricating advice.
Eutectic has some brazing compounds specifically for aluminum, e.g. http://www.castolin.com/en-US/product/eutecrod-190 and http://www.castolin.com/en-US/product/eutecrod-21-fc-e .
My general thoughts are if it's good enough for racecars, it's good enough for almost everything. If it's good enough for airplanes, it's good enough for everything. Carroll Smith tends to use airplane parts to build his racecars, so I find he has generally good fabricating advice.
EschewObfuscation
Mar 11, 2015, 12:02:51 PM3/11/15
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Lol, yes, I can credit that line of thought. OTOH, the racing crowd is less concerned about budget, more concerned about weld strength, and willing to require a skill level in excess of mine in this area. Still, those are useful directions for me to go for information, and I appreciate the tip and will go find out what I can. Thanks!
As an aside, I wouldn't be the slightest bit surprised to learn that great joins could be made with the cheapest rod, if used with the right flux... the problem is knowing if that's the case, and what that flux might be. This is where I'm most likely to stumble: if I should see poor results, is it bad technique, tools, materials, a little of all three? probably.
On Wednesday, March 11, 2015 at 8:22:46 AM UTC-5, memmek2k wrote:
As an aside, I wouldn't be the slightest bit surprised to learn that great joins could be made with the cheapest rod, if used with the right flux... the problem is knowing if that's the case, and what that flux might be. This is where I'm most likely to stumble: if I should see poor results, is it bad technique, tools, materials, a little of all three? probably.
On Wednesday, March 11, 2015 at 8:22:46 AM UTC-5, memmek2k wrote:
My general thoughts are if it's good enough for racecars, it's good enough for almost everything...
Michael Kuba
Mar 11, 2015, 12:52:27 PM3/11/15
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To be fair, a lot of racecar guys are junk at fabricating, so the popular methods are typically reasonably easy. Wouldn't be a bad idea to practice on some scrap aluminum first though.
Speaking as a metallurgical engineer now - you are 100% correct. The mechanical properties of the joint do not change much with composition for these alloys (so we'd need to be generally looking at e.g a 5% alloy addition vs a 10% alloy, not a 5% versus a 6%). So as long as you've got the right general brazing alloy (like, "for copper," or "for aluminum"), you're good there.
What is significantly more finnicky than composition is the surface condition prior to joining, and this is where flux and technique/preparation come in. The goal for a joint like this is what is called a "metallurgical bond." We're looking to have an aluminum atom next to a copper/silver/nickel/etc. atom. That can't happen if there are oxygen atoms in the way or if the joint doesn't get hot enough. A good flux will break down the oxide layer on the surface (which is always present if the metal has been exposed to air - it's just a question of how thick it is) and allow the metal-to-metal atom contact to occur. But, even the best, most aggressive flux can't break through a millimeter thick layer of oxide with dust and dirt and oil on it. So surface prep is important.
If possible, I would plan on cleaning the parts with soap and water and a brush, then rinsing and blow-drying with a fast-drying solvent (acetone or ethanol) before you start. That will get everything else out of the way so the flux can do what it's meant to do.
You should take pictures - if it goes well, it'd be a great writeup for the site.
Speaking as a metallurgical engineer now - you are 100% correct. The mechanical properties of the joint do not change much with composition for these alloys (so we'd need to be generally looking at e.g a 5% alloy addition vs a 10% alloy, not a 5% versus a 6%). So as long as you've got the right general brazing alloy (like, "for copper," or "for aluminum"), you're good there.
What is significantly more finnicky than composition is the surface condition prior to joining, and this is where flux and technique/preparation come in. The goal for a joint like this is what is called a "metallurgical bond." We're looking to have an aluminum atom next to a copper/silver/nickel/etc. atom. That can't happen if there are oxygen atoms in the way or if the joint doesn't get hot enough. A good flux will break down the oxide layer on the surface (which is always present if the metal has been exposed to air - it's just a question of how thick it is) and allow the metal-to-metal atom contact to occur. But, even the best, most aggressive flux can't break through a millimeter thick layer of oxide with dust and dirt and oil on it. So surface prep is important.
If possible, I would plan on cleaning the parts with soap and water and a brush, then rinsing and blow-drying with a fast-drying solvent (acetone or ethanol) before you start. That will get everything else out of the way so the flux can do what it's meant to do.
You should take pictures - if it goes well, it'd be a great writeup for the site.
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EschewObfuscation
Mar 11, 2015, 4:48:24 PM3/11/15
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Unless someone emits a panicky scream "no, no, for the love of all things good don't do *that*!!", my inclination would be sandpaper, cinch (my favorite window cleaner spray), isopropyl, in that sequence. I wouldn't even bother with a blow drier or heat gun unless so prodded; first touch of a torch, and remaining isopropyl will be gone. Convenient how that works. :)
So I'm off to learn what I can about suitable fluxes. Having heard nothing to the contrary, I'm assuming we have no access to an acetylene/air torch.
On Wednesday, March 11, 2015 at 11:52:27 AM UTC-5, memmek2k wrote:
So I'm off to learn what I can about suitable fluxes. Having heard nothing to the contrary, I'm assuming we have no access to an acetylene/air torch.
On Wednesday, March 11, 2015 at 11:52:27 AM UTC-5, memmek2k wrote:
...
If possible, I would plan on cleaning the parts with soap and water and a brush, then rinsing and blow-drying with a fast-drying solvent (acetone or ethanol) before you start. That will get everything else out of the way so the flux can do what it's meant to do.
...
Michael Kuba
Mar 11, 2015, 4:50:07 PM3/11/15
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That'll probably work fine. Important thing is that you got the dirt and grease/oil off.
Best we have I know of is MAPP gas. Would be a good question for Ryan/Myles/Sam.
Best we have I know of is MAPP gas. Would be a good question for Ryan/Myles/Sam.
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