T.O. 33B-1-1
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poor surface conditions, and (4) inspection for defects that require magnification for detection and
interpretation. Magnetic rubber inspection involves the use of a material consisting of magnetic
particles dispersed in a room temperature curing silicon rubber. The material is catalyzed, applied to
the test surface, and the area to be inspected is magnetized, causing the particles to migrate through the
rubber and accumulate at discontinuities on the surface. Following cure, the solid replica casting is
removed from the part and examined for indications.
b. The magnetic principles discussed in Section 1 of this chapter apply equally to Magnetic Rubber
Inspection.
3.9.2
Safety Precautions.
a. General safety precautions are applicable to magnetic rubber inspection. The silicon rubber, dibutyltin
dilaurate, stannous octoate, cure stabilizers, cleaners, and release agents are or can be skin and eye
irritants, skin sensitizers (causing allergic reactions), and inhalant and ingestion hazards. For specific
information concerning any of the materials used as magnetic rubber, magnetic rubber catalysts, release
agents, or cleaners consult the Material Safety Data Sheets, or contact the appropriate Safety Officer.
Silicon oil is an ingredient in the material and can result in very slippery surfaces, especially floors, if
not well controlled.
b. When performing magnetic rubber inspection on aircraft using electromagnets to magnetize, the
aircraft SHALL be grounded.
3.9.3
Gel Time, Pot Life and Cure Time.
Gel time is defined as the time from the addition of the catalyst to when the viscosity starts to noticeably increase. Pot
life refers to the time from the addition of the catalyst to when the material can no longer be poured and magnetization
must be completed. Cure time is the time to completely cure.
3.9.4
Magnetic Rubber Inspection Procedure.
WARNING
Cleaning solvent ML-C-38736 contains aromatic naphtha, ethyl acetate, methyl
ethyl ketone, and isopropyl alcohol. Cleaning solvent is flammable. Vapors may be
harmful. Use with adequate ventilation. Avoid contact with skin and eyes.
CAUTION
Areas to be magnetic rubber inspected must be free of grease, oil, dirt and other
foreign matter which could cause false or confusing indications or could prevent the
base material from curing.
NOTE
Prior to the initial inspection remove, as much as possible, corrosion, sealant, loose
paint, and other foreign material from the inspection area.
a. Obtain the required materials and equipment. Refer to Table 3-7 and Table 3-8.
