Heat treating and inspection of metals Page: 49
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HEAT TREATING AND INSPECTION OF METALS 46-47
(2) The magnetizing current is supplied to the part to be inspected
by means of the contact heads shown at (12) and (13), figure 9.
The bipolar coil (8) may be used to produce a magnetic field around
parts held between the contact blocks.
(3) The inspection medium is contained in a tank or sump and
applied to the part being inspected by means of the hose and nozzle
shown at (11). The excess fluid drains back to the sump from the
grill top of the machine. Pressure is applied to the medium by
means of a circulating pump contained in the sump. This pump
also serves to, keep the ferromagnetic particles well mixed in the
b. Demagnetizing apparatus.--After parts have been magnetically
inspected, the magnetism must be removed in order to return them to
their original condition. This operation is accomplished by passing
the parts through an alternating current field. Two demagnetizing
units are furnished as standard equipment with each magnaflux ma-
chine, giving a sufficient size range to accommodate practically any
piece used in aircraft construction. These units are mounted side
by side on suitable supports. In either case, the unit consists chiefly
of an insulated coil of wire to which alternating current is connected
through a suitable switch attached to the unit.
(1) The smaller of the two units, shown at (1) in figure 10, has
an opening nine inches square and is particularly adapted for small
engine and propeller parts.
(2) The large unit, shown at (2), has an opening 24 inches square
and will accommodate large pieces of equipment. A set of rollers
and movable platform are provided for moving heavy objects through
c. Rinse tank.-A rinse tank is usually provided for removing the
inspection medium, after completion of the test. Any type of tank
may be used for this purpose, provided it is of a size sufficient to
allow "slushing" of the parts. The rinse bath may consist of clear-
light oil or a mixture of equal parts of naphtha and carbon tetra-
47. Magnetizing methods.-a. The effectiveness of magnaflux
testing is lost unless certain basic principles regarding the direction
of flow of the magnetic flux lines are observed. If the direction of
the flux lines are parallel to the defect, only a small amount of the
magnetic flux will be interrupted, with the result that there will be
insufficient polarity developed to attract the ferromagnetic particles
in sufficient quantities to indicate the defects. When the direction
of the flux is at an angle of 90 to the length of the defect, the flux
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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/m1/51/: accessed March 23, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.