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I made a smoke oil tank for a North American F-86, this may held answer some questions, here is a link. http://allmetalshaping.com/showthread.php?t=18066 To control distortion from welding in a flat section of the tank can be done with some pre-planing. A flat sheet of material has relative low stress from the cold rolling process. The stress is uniform and that is why the panel stays flat. Welding of the edges or rosette welds to hold in bulkheads causes higher stress concentrations from several factors including, material shrinkage from the weld, re-crystallization from exceeding the anneal temp and internal material changes to crystallized structure from the high heat of welding. It is important to isolate the high stress area of the weld, from the low stress area of the flat panel. This is done by tipping all edges several degrees 3/16" - 1/4" in from the edge. Dimple all holes that is the same size or slightly larger than your weld. The broke edge creates a mechanical lock and defines the edge from high stress to low stress. The weld is large enough that it covers the broke edge so it is not seen once welded. Because a steel weld is smaller than an aluminum weld, plan the broke edge accordingly. Flange welded tanks have been around for many years with millions o flight hours flown on this seam design. With that being said, it is possible to have them fail due, more times than not due to bad welding. Lack of penetration, oxide development and filler rod selection all play a roll in the failure. Pressure testing should always done, once the tank is made. I fill all of my tanks with water, then use compressed air to 5 psi. I'm welding up a tank right now, will see i I can post some pictures in the next few days. Bill
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Bill Tromblay "A sign of a good machinist, is one who can fix his F$@& Ups" My mentor and friend, Gil Zietz Micro Metric Machine. |
#12
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I recall kne of the tanks on an old classic sports car had a lot of detail embossed on the flatter section to stiffen it. Sounds similar to what you are talking about although this tank was riveted and soldered. It was steel. But large flat sections are probably not desirable.
https://www.tinmantech.com/assets/im...rdFuelTank.JPG
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Scott in Montreal Last edited by sblack; 12-30-2019 at 02:26 PM. |
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I suspect it wasn't the flanges, but the welding that resulted in the problem. There doesn't seem to be enough load on the seams to result in failure when running up on the ground.
John Thorp was the Lockheed connection I mentioned previously. His tank designs were butt welded. Another friend, a top level auto engineer with extensive tank design experience felt flange welds were fine. all else being equal. FWIW
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Marc |
#14
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Hi Scott, The problem with that tank is not the design. That design is proven by the tens of thousands of airplanes carrying fuel inside it, for decades, in rough environments. Had there been an issue with that design it would have been subject to an Airworthiness Directive, and the entire industry would have changed that design. The problem is in the execution of that design, by the craftsman building that tank. Example from real world aviation: I have two wing tanks here that were made by a "pro fab/welder" shop. .040 5052 with flanged ends that were fusion welded with a tig/TIG. Made to "copy" an original 1940's existing pair of tanks. The cracks in these end seams are not longer than 14 inches, and the fuel also splashed all over a hot engine and pilot, as he got down as fast as possible, and got it all shut off in time to exit safely and the plane was saved. Problem: no baffles to support the long distances between end plates, so under positive and negative G's the seams failed, opposite each other and at the same end panel. P1030144 copy.jpg P1030145 copy.jpg It does help to have some familiarity with the various aviation tank designs so as to make clear and accurate conclusions.
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Kent http://www.tinmantech.com "All it takes is a little practical experience to blow the he!! out of a perfectly good theory." --- Lloyd Rosenquist, charter member AWS, 1919. |
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Hi Sean, Here's one proven baffle install design, no distortion, no big heat sinks, no fancy clamping .... : IMG_0111.jpg 70_brazing the rivet heads.jpg The olde bead roller makes twin beads parallel to each other, downwards, trapping the baffles in place, allowing for easy riveting, and then distortion-free brazing of the rivet heads. (pssst - brazing does not melt the parent metals to join them together - so there is zero "solidus" or "shrinking" as the molten metal cools back down). Brazing the aluminum rivet heads onto aluminum tanks is very common in aviation tank methodology, and has been since about 1939, according to ALCOA.
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Kent http://www.tinmantech.com "All it takes is a little practical experience to blow the he!! out of a perfectly good theory." --- Lloyd Rosenquist, charter member AWS, 1919. |
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Wow Kent. Thanks! Have to make a supercharger coolant tank for under the hood. I’ll definitely copy that design.
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Sean |
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Here's a table of weld properties based on the two base alloys and the weld properties you most value. It's best to print it out and tape it together. You pick your base alloys off the edges and the intersection of the base metals provide codes for weld properties for most common fillers. For a tank I'd usually pick 5356 for 6061/6061 due to the high ductility of the weld. I would expect 1100 to be very ductile too but not sure about the rest of the weld properties.
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Jeff |
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Global selection, from a global supplier.
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Kent http://www.tinmantech.com "All it takes is a little practical experience to blow the he!! out of a perfectly good theory." --- Lloyd Rosenquist, charter member AWS, 1919. |
#19
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Scott in Montreal |
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So.....i wasnt happy with my 6061 0.060" tank. Kept getting little cracks > rewelded = shrinkage......scrapped it
Bought some 3003 0.125" Cut it up with table saw. Got the fits really nice, including baffles. Welded it up in no time, no cracks, no leaks. Its a little overweight i supposed, but hey, i could lose a few lbs too. cdbd7NCu7l10WVu9KJEwxl5FwQYNh3YoIGFktWc542qeAgvqi3BKbLB_5nXOG-5RoTFfvxBtRDlPn41kF3wS0bYLalACHfIW.jpg
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Sean Last edited by galooph; 02-18-2020 at 09:42 AM. |
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