MIL-HDBK-660B
4.2.1 Annealing brass waveguide. A commercial brass waveguide is 90 percent copper and 10 percent zinc.
a. To properly anneal this waveguide, it should be heated to a temperature of 427 C (800 F) to 565 C
(1,050 F), depending on the degree of softness desired. Estimated time at temperatures for typical tubes would be 8 minutes for .040-inch gauge wall tubing and 15 minutes for .080-inch wall tubing. The waveguide should then be cooled in air.
NOTE: The higher temperature will result in a softer waveguide but should only be used for making sharp radius bends.
b. A good average temperature for the majority of bends is 482 C (900 F). If temperature control is not possible, 650 C is approximately cherry red on brass.
c. As an emergency, a waveguide can be annealed using two torches. The torch tip should be selected that gives a large soft or spread-out flame to avoid hot spots. Move the flame over both sides of the waveguide continuously until the brass is cherry red.
4.2.2 Filling with gas before annealing (optional). This process applies only to commercial bronze, 90 percent. If the procedure outlined below is followed, it will eliminate oxidation; and the waveguide will remain clean, smooth, and free from discoloration.
a. Provide wooden plugs for the two ends of the waveguide sections. These should fit tightly.
CAUTION: IF THE PLUGS FIT TOO TIGHTLY WHEN COLD, THEY WILL EXPAND AND DISTORT THE WAVEGUIDE WHEN HEATED.
b. In one of the plugs, insert a hose connection and valve.
c. Close the waveguide section with the wooden plugs and attach a carbon dioxide tank to the hose connection.
d. Fill the sections with carbon dioxide until no air remains inside. When the guide is properly filled, a match will go out when placed in front of the escape valve. Never use more than 2 pounds of pressure per square inch.
e. Now anneal the section in the usual way as outlined above.
4.2.3 Annealing aluminum waveguide. The proper annealing temperature for aluminum waveguide is 343 C to
427 C (650 F to 800 F). The amount of time in the furnace should only be long enough to insure that the temperature is the same throughout the metal. Too high a temperature or too much time in the furnace will result in large grain size. The waveguide is then cooled in air at room temperature. Too rapid cooling will result in warping.
4.3 Filling. Unless a bending machine with a mandrel is used, to prevent deformation, the waveguide must be filled with some solid material before bending. Filling may be done with an alloy or rosin; separate procedures for each of these methods as in 4.3.1 and 4.3.2.
4.3.1 Alloy method. When the alloy method is used for filling, the guide should first be thoroughly annealed as outlined in 4.2 and allowed to cool. The guide should then be filled as follows:
a. Tightly plug the guide at one end with a wooden plug.
b. Melt the required quantity of bending alloy in a welded corrosion-resisting steel container suspended in boiling water. (The alloy melts at 71 C to 82 C (160 F to 180 F)).
NOTE: The bending alloy is a type of Wood's metal (a mixture of bismuth, lead, tin, and cadmium). The trade names are Cerrobend, Bendalloy, or equal.
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