Heat treating and inspection of metals Page: 51
57 p: ill., diagrs., tables. Enclosed at end: Change 1 (4 pages)View a full description of this book.
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TM 1-423
HEAT TREATING AND INSPECTION OF METALS 47
(2) In the continuous method, the magnetism is induced during the
time the inspection medium is being applied, and continues for a suf-
ficient period to allow the particles to orient themselves. As the flux
leakage at any break in the magnetic field is proportional to the in-
tensity of the magnetism, it may readily be seen that the results will
be more pronounced than in the case of the residual method.Q
/
cj /1. Spider being inspected. 3. Special contact blocks.
2. Contact heads.
FIGURH 114--Circular method of magnetization applied to a propeller hub spider.
c. Regardless of whether the continuous or residual method is used,
magnetism may be imparted in either of the following ways:
(1) When the part to be magnetized is placed between the contact
heads of the machine and the magnetizing current is passed directly
through it (figs. 11 and 12), a circular magnetic field is set up in and
about the part and the operation is referred to as circular magnetiza-
tion. This method is particularly advantageous as it will indicate
practically any defect discoverable by magnaflux inspection; however,
this should not be taken to mean that it is the only method to be used.
Inasmuch as circular magnetization requires a current of low voltage
but relatively high amperage, great care must be exercised to prevent
burning, which may result from poor contact, dirty headplates, or too
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United States. War Department. Heat treating and inspection of metals, book, September 10, 1941; Washington D.C.. (https://digital.library.unt.edu/ark:/67531/metadc96657/m1/53/?rotate=270: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.