Heat treating and inspection of metals Page: 51
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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.
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.. (digital.library.unt.edu/ark:/67531/metadc96657/m1/53/: accessed March 24, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.