# Low temp aluminum welding

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by ohioflyer, Oct 7, 2006.

1. Oct 7, 2006

### ohioflyer

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I was wondering if anybody here has had any experience with low temp aluminum welding/brazing as it may be more technically called as it relates to gas tanks. My plans call for aluminum tanks, but as I'm on a very restricted budget anything that I can do my self and save money is probably the route I'll take. That being said I do'nt want to compromise safety for price. I was thinking about fiberglass tanks but they seem like they would be heavy. This website:

www.aluminumrepair.com

seems pretty together. They list among the appropriate uses for thier product gas tanks, but as my tanks are not in the wings but behind my panel and seat back respectively any input on this system or a similar products suitability for aircraft is appreciated. The main thing that attracts me to systems like this are usability with Mapp Gas, I'm not a welder, I'm a woodworker, buying tools for the latter will be used for a long time, the former would go to waste.

Thanks,
Ed

2. Oct 8, 2006

### Midniteoyl

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I'm no welder either (well, MIG in an maintenance environment and did use Alumaloy a couple of times), but I think you'll see this rod was really ment for cast materials.
Also, wouldn't the torch actually heat the aluminum over a broader area for a longer period of time? Would this not introduce the chance of warping such thin material?

3. Oct 8, 2006

### ohioflyer

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The company that sells the stuff says that it is suitable for cast or sheet aluminum and lists gas tanks as one of its main uses. Of course I take that with a grain of salt, I'm curios about its drawbacks, warpage may be one of them with thin metal. Has anybody tried this stuff?

Ed

4. Oct 8, 2006

### wally

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It is probably a brazing rod. Some I have seen are very hard to use and do not produce a good joint. You can make small repairs with it but I don't think it will do to build with.

My suggestion would be to save up some  and hire a good TIG weldor to put your tank together. You can form it and bend it to shape yourself per your plans and then take it to a weld shop and have them do it. It will be much stronger than that aluminum repair stuff.

Ask around, you may even find an airplane kinda guy with a TIG machine who will do it for you.

And you will NOT be a happy camper with a completed airplane and a leaky gas tank. They are trouble to remove and trouble to reinstall and big trouble if it starts leaking when you are flying.
Wally

5. Oct 8, 2006

### CAB

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6. Oct 11, 2006

### Ivan

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ohioflyer,

For what it's worth, I haven't used that particular brand, but there's quite a number and they all seem to be the same thing. They're a zinc alloy, and these low-temp brazing rods can come in handy around the shop for non-structural work and repairs.

My experience using them on sheet metal is that it doesn't make a bond that is stronger than either the parent material or the brazing material. Maybe it's just my technique, but I don't think so. Not structural, but I keep it in my repetoire at about the same level as lead/tin solder.

Keep in mind that zinc has poor fatigue and creep resistance. I was also thinking about this material for fuel tanks; I concluded that it might have some use on riveted aluminum tanks in place of Proseal, but I certainly wouldn't recommend it.

Best thing I'd recommend is to get some (any local hardware store carrying Bernz-o-matic products usually has that brand's version of aluminum brazing rods) and try it out. Break some joints apart, and the strengths and weaknesses of the product become pretty evident.

Ivan

7. Oct 12, 2006

### ohioflyer

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Thanks everyone for the advice, I'll probably try some eventully, I can put a few boxes together, pressure test than destroy to see how the stuff holds but a concern of mine that I cannot test is vibration. I don't know much about metal and I may be out in left field but wouldn't vibration of dissimilar metals weaken the joint? They often advertise "stronger than the surrounding metal", might that mean also more brittle? prone to vibration cracks?

Ed

8. Oct 12, 2006

### Peter V

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I've seen demonstrations of those aluminium brazing rods. They get very runny. I think if you tried sealing a corner joint, you'll have a big, runny mess on your hands, especially with the distortion you'll introduce. It might work if you can lap all of your joins?

9. Oct 12, 2006

### Craig

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Welding/brazing/soldering

I've used a lot of the material from Tinmantech for both welding and brazing with the torch - both work well, and develop good strong joints, but the technique is not real easy to learn.

It isn't real difficult, either, but is something you want to practice a lot before you try it on airplane parts.

You will need to use the right rods - and more importantly, the right fluxs. And be sure to use the flux well on the backside also.

Tain't no zinc in that stuff!

10. Oct 12, 2006

### Ivan

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Peter V,

The rods may look runny, but they're actually real easy to manipulate.

Ed,

I don't know if you've seen it or not, but the home site for the Falco plans (Sequoia Aircraft or whatever it's called) had a really interesting page devoted to the testing of their welded aluminum tanks, as well as all the difficulties they had trying to eliminate cracking. They describe their vibration testing apparatus, which apparently was copied from someone's experience at Mooney, IIRC. It was a neat setup, and well worth duplicating if you're 'rolling your own' fuel tank.

Ivan

Edit: But keep in mind that if you're looking to do structural work on an airplane, I think Craig's reference to the Tinman pages is the way to go.

Last edited: Oct 12, 2006
11. Oct 12, 2006

### Midniteoyl

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Just how much heavier would glass tanks be, anyways? If at all? They have always seemed pretty light to me, though I never did a direct comparison between two same size tanks. I do know they are plenty strong, and if you use VinylEster, no ProSeal :ban:

12. Oct 13, 2006

### ohioflyer

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Yeah the Falco ranks right up there with Uma Thurman ( both make my knees weak). Thats an interesting article though, I would not have thought that a makeshift vibration machine would hold together long enough for any meaningful test. I could learn from that lesson and build the tanks all with slightly convex sides to reduce oilcanning, although that would be easier to do with a fiberglass tank. I do not really know how a glass tank would compare wieght wise with a aluminum one of the same size and capacity. I had originally thought of using a Tempo marine tank. The problem is that there are not any that are really the right size, they seem heavy, and would probably need mods. After all that I could built my own for less trouble, but after reading the Sequoia article a simple gas tank does not seem so simple.

Ed

13. Oct 13, 2006

### Peter V

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of course, you could go with the lightest, safest, and highest capacity option... a fuel bladder. Standard equipment for Indy cars and armoured vehicles. Explosion and impact resistant!

http://www.aircraftrubber.com/home.html

:ban: