T.O. 33B-1-1
3-18
3.1.9.12.4
Hand-Held Coil.
For longitudinal magnetization of shafts, spindles, rear axles, and similar small parts, the hand-held AC coil offers a
simple and convenient method of inspecting for transverse cracks. Parts are magnetized and demagnetized with the
same coil.
3.1.9.12.5
Demagnetizing Equipment.
The most common type of demagnetizing equipment consists of an open, tunnel-like coil through which AC is passed
at the line frequency, usually 60-Hertz. The larger type equipment is frequently placed on its own stand, incorporating
a track or carriage to facilitate moving large and heavy parts through the demagnetizing equipment. The
demagnetizing equipment can also include tabletop units, yokes, or plug-in coils that are more suited for the
demagnetization of small parts. However, the large stationary type equipment is preferable when geometrically
complex parts are involved. The use of demagnetization and demagnetization equipment s discussed in detail in
Section 6.
SECTION II
PRE- AND POST-MPI CLEANING & PRE-MPI DISASSEMBLY
3.2
PRE- AND P0ST-MPI CLEANING & PRE-MPI DISASSEMBLY.
3.2.1
Pre-Inspection Cleaning.
3.2.1.1
Definition.
Pre-cleaning is the removal of all foreign material (paint, grease, oil, corrosion, layout dye, wax crayon markings, etc.)
which may interfere with magnetic particle testing that has accumulated since the general cleaning operation but prior
to inspection.
3.2.1.2
Necessity for Pre-Inspection Cleaning.
Parts or surfaces should be clean and dry before they are subjected to any magnetic particle inspection process. The
cleaning process used must not reduce the effectiveness of the inspection process that follows. The cleaning process is
required to remove all contaminants, foreign matter, and debris that might interfere with the application of current or
the movement of the magnetic particles on the test surface. Note, however, that thin coatings such as cadmium,
chromium or paint, if in good condition, will not interfere with the inspection process and do not necessarily have to be
removed.
3.2.2
Considerations when selecting A Cleaning Process.
No single cleaning method can assure removal of all types of contaminants. Most methods are limited to the removal
of only a few types of contaminants. Further, some cleaning methods require equipment that may not be adaptable to
the specific job conditions, i.e., such as cleaning large parts or cleaning in place on an aircraft. Finally, some processes
may cause corrosion of the part to be inspected. The cleaning process must then be chosen with knowledge of the
contaminant, the alloy and the accessibility of the part to be inspected.
3.2.3
Typical Cleaning Methods.
CAUTION
Improper cleaning procedures/materials can cause severe damage. Cleaning should
be accomplished by trained and qualified personnel. For Air Force personnel, T.O.
1-1-691 applies. For Navy personnel, use NA 0l-lA-509. For Army personnel, use
TM1-1500-344-23.
