Heat treating and inspection of metals Page: 54
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48 AIR CORPS
(2) Plug all oil holes and small internal passages with paraffin or
hard grease to prevent the ferromagnetic particles $rom entering
internal lubrication, passages.
(3) Adjust the amperage according to the size and shape of the
piece. This is done by means of the rheostat shown at (5) in figure 9.
It is advisable to begin with a relatively low setting and raise it if
necessary, as this procedure will reduce the danger of burning.
(4) Install the piece in the magnetizer by adjusting the movable
contact head and engage the magnetizing current switch.
(5) Apply the inspection medium freely to the entire surface and
inspect carefully for indications of flaws. (If serious defects are
shown to be present at this time, the part should be rejected, and no
further test is necessary.)
(6) Demagnetize the part in demagnetizing unit.
(7) Install bipolar coil and adjust movable contact head to form
the necessary electrical contact (fig. 13).
(8) Engage magnetizing current switch.
(9) Remove bipolar coil, and apply inspection medium, making a
final inspection for defects.
(10) Demagnetize part in demagnetizing unit.
(11) Remove inspection medium in rinse tank, completing the test.
b. The following is a detailed description of the various operations
that follow magnetization:
(1) Application of inspection medium.-As previously mentioned,
the inspection medium consists of finely divided ferromagnetic parti-
cles, and may be applied in several forms. The method used by the Air
Corps, consists of flushing the part thoroughly with a mixture, con-
sisting of magnaflux No. 7 paste dissolved in a light oil. The paste
is obtainable from the Magnaflux Corporation. The oil can vary
considerably in character, but preferably should be some type of light
oil, or a dry cleaning solvent conforming to Federal Specification
PS661a. Kerosene mixed with a light grade of engine oil makes a
satisfactory substitute. Other products that can be used are varsol
manufactured by the Standard Oil Company or ultrasine manufac-
tured by the Atlantic Refining Company.
(2) Evaluation of defects.-Proficiency in the recognition of the
various types of magnaflux indications, and ability to evaluate their
significance by making a reliable estimate of the character, depth,
and extent of the underlying discontinuities that cause them, can only
be gained from practical experience. A fair knowledge of metallurgy,
heat treatment of ferromagnetic materials, a conception of grain flow
in the part, and of the location, direction, intensity, and character of
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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/m1/56/: accessed July 24, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.