S9407-AB-HBK-010 Datasheet, PDF (170/276 Pages) Glenair, Inc. – HANDBOOK OF SHIPBOARD ELECTROMAGNETIC SHIELDING PRACTICES

S9407-AB-HBK-010, Rev. 2
b. Completely remove oil, graphite, or other carbon- or sulfur-bearing material from parts
prior to annealing.
c. Support the parts by suitable means to minimize warping or bending during the
annealing process.
d. Separate the laminations by means of a pure calcined aluminum oxide powder or a
suitable equivalent. (Annealing nickel-iron steels at temperatures above 1600° F,
particularly in a hydrogen atmosphere, may cause sticking of the laminations and parts.)
7.3.5.2 Instructions for Heat-Treatment of Mumetal
a. Pack the laminations or parts in a completely welded box that has only two openings
through which the hydrogen enters and leaves the box.
WARNING
As a safety precaution, it is necessary to purge with nitrogen before
and after the annealing cycle.
b. Anneal only in pure dry hydrogen produced by the electrolytic process, passed over a
copper or palladium catalyst, with the moisture removed by activated alumina,
phosphorous pentoxide, or other drying agent so that the dew point of the gas is
reduced to at least -60° F. The dry hydrogen atmosphere should be well circulated with
a minimum flow rate of 10 times the volume of the retort per hour. (A significantly lower
flow rate will not be adequate to completely purify the shielding material.)
c. Heat the charge to 2150° F at any convenient rate. After the charge is uniformly
heated, hold it at 2150° F for 4 hours. Furnace cool at the rate of 200° F per hour to
600° F. Purge with nitrogen, after which the charge can be withdrawn from the furnace.
NOTE
Mumetal which is annealed at 1850° F for 4 hours is approximately
50 percent as effective as that annealed at the normal 2150° F
temperature.
Annealing can be accomplished in atmospheres other than pure dry
hydrogen, but with poorer results. For example, annealing in a
mixture of 80 percent hydrogen and 20 percent nitrogen produces
magnetic properties approximately 80 percent as effective as when
annealing in pure dry hydrogen. Annealing in a vacuum develops
properties between 50 percent and 75 percent as effective as those
attained in a hydrogen atmosphere. Annealing in a pure nitrogen
atmosphere develops magnetic properties approximately 50 percent
as effective as those attained in a hydrogen atmosphere.
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