T.O. 33B-1-1
3-122
l. Using the mixing container or a syringe, fill only the number of holes or other test areas that can be
magnetized within the pot life. Following fill, all vent holes should be sealed with putty to prevent the
continual flow of rubber.
NOTE
Holes in steel having high retentivity may be magnetized by a "residual" method.
Using this method, the hole is filled with magnetic rubber and is magnetized with
an electromagnet at the maximum field obtainable for a period of about one-second.
This should establish a residual field of 25-100 gauss. This field must stay
undisturbed for 30 to 60 seconds (depending on the level of residual magnetism).
Do not magnetize the hole in a second direction nor magnetize any other hole on
the same test part until the 30 to 60 seconds have elapsed.
m. Magnetize each test area according to the pre-magnetization setup established in steps c through h.
n. Identify each replica by recording the following data on an identification tag, or on an individual bag
(for storing replica after cure).
(1)
Aircraft serial number and/or part number.
(2)
Hole number or other inspection area identification.
(3)
Date.
NOTE
Care must be exercised to avoid excessive disturbance of the magnetic rubber when
inserting the tag.
o. Allow magnetic rubber to cure for the time specified. Avoid movement of the part and contamination
of the magnetic rubber by foreign matter.
p. Determine that the magnetic rubber is cured (tack-free) by lightly touching the replica or the material
remaining in the mixing container.
q. Remove each replica as follows:
(1)
Remove the magnets if applicable.
(2)
Remove tape, aluminum dam, duct sealer putty, and/or central conductor and dam assembly.
(3) Gently remove replica from test area.
r. Visually examine replicas for overall condition and proper identification. A 7X to 10X stereo
microscope and illuminator SHALL be used for microscopic examination as follows:
(1)
Adjust the illuminator so that the light does not produce a glare on the surface of the replica. A
good stereo microscope with excellent light gathering characteristics and a strong light projected
at a shallow angle is generally sufficient for this work. Experience has proven that an improper
microscope or lighting may result in small cracks going undetected. The inspector may check
the adjustment of the illuminator periodically on a replica that is known to display a faint crack
indication.
