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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. |
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