A large diameter tubing can be used for aerospace ducting hot or cold air to various places in the aircraft. There are two types of tubing used for this purpose: One is flexible and the other is rigid. On modern aircraft, flexible aluminium tubing is not used as often any more because it is being replaced with specially treated fabric covered ducting. However, the use of rigid tubing still serves a valuable purpose because it can take more abuse than soft flexible ducting.
Aerospace Ducting Of Aluminium Tube.
Either type, heat treated or non-heat-treated aluminium alloy in the annealed condition, is best suited for the making of rigid tubing. The tool used to make tubing or duct pipe is a set of slip rollers. The smallest diameter that can be made using a slip roller is determined by the size of the rolling machine. When a tube diameter larger than the roller is called for, the rollers can be adjusted to make a larger diameter such as those needed for leading edge construction.
The construction of aluminium alloy tubes requires knowing the diameter, length and type of locking joint to be used. Suppose that 3-inch diameter finished aluminium tubes will be made. The circumference of the tubes is the length of metal needed to roll the diameter of the tube. With a diameter of 3 inches times 3.1416, the length of roll out is 9.42 inches, and the finished tube length is 18 inches. To each of the 9.42 inch ends add one inch to make the joggle and locking seam.
Once the joggle and seam are bent, release the slip roller and lock the flat sheet into place in the middle. After the slip roller is locked into place, adjust the rollers to begin the initial curvature of the tube. Crank the rollers back and forth and roll the tube from one end to the other until the tube begins to take shape.
Each time you roll, gradually increase the tightness of the rollers until the tube is completely rolled into shape. Release the slip roller and remove the tube from the roller. Check the diameter and seams for alignment. Once the seam is joined, slip it over a pipe clamped in a bench vice and begin flattening the seam. This action will lock the seam into place.
If more joint security is needed you may want to install soft aluminium rivets (AN470A3-6) along the seam. The holes for the rivets are drilled by slipping the tube over a pre-formed 2 x 4 clamped in a bench vice. The rivets can be bucked using the same pipe you used to lock the seam. If this piece of tubing is going to be fitted into another piece of tubing, the rivets used to secure the seam must be countersunk (AN426A3-4).