Duralumin, Its Properties and Uses Page: 7 of 22
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J. A.C.A. Technical M emorandum No. 284
uce any noticeable effect. If tempering is desired, the metal must
o e given, while hot, a thorough preliminary forging, rolling, or
pressing. The more thoroughly this is done, the greater will be
the gain in strength from the final heating and cooling.
Many forgings, swaged pieces and hot-pressed sections require
no supplementary cold treatment. On the other hand, sheets and
strips, which often need to be thin, and tubing and wires must be
rolled or'drawn cold, after being worked hot. These products can
therefore be previously tempered, if they have the proper thick-
ness. Since an increase in strength and hardness is possible at
the cost of ductility, the metal sheets, strips, wires and tubes
are subjected to moderate compression or tension after tempering,
if a greater strength and hardness is desired than can be obtained
by tempering alone.
In referring to the patent description, I stated that the ma-
terial could either be cooled rapidly, by plunging it into a liquid,
or allowed to cool slowly in the air. The first method yields a
stronger metal and should be employed, unless the metal is very
thin, so that it cools quickly in the air and would be greatly dis-
torted by plunging into a liquid. It should be remembered that the
breaking strength of the air-cooled metal is from 3 to 4 kg (6.6
to 8.8 lb.) less per square millimeter than that of the liquid-
cooled metal.
Heating for the purpose of tempering is best accomplished in
a salt bath. It may, however, be done in a muffle furnace, but the6
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Beck, R. Duralumin, Its Properties and Uses, report, October 1924; (https://digital.library.unt.edu/ark:/67531/metadc58745/m1/7/: accessed March 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.