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TM 5-4210-220-12
4-9. GENERAL MAINTENANCE PROCEDURES - Continued
4-9.3
General Inspection Instructions - Continued
k
Fluorescent Penetrant Inspection - Continued
After applying penetrant, the surfaces will be cleaned with lukewarm water less than 120 deg. F. (Cool water
may be used, but cleaning time will be longer). Pressurized water spray may be used to shorten the washing
cycle. The following methods may be used to develop the parts:
(1) Wet Developer Method
Parts shall be completely covered in developer by spraying or dipping. Parts shall be dried and developed
in a recirculating hot air drier for one half the penetration time.
(2) Dry Developer Method
Parts must first be dried. They dry developer shall be spread on all surfaces by dusting or by dipping the
part. Parts shall be developed for one half the penetration time.
(3) No Developer Method
When no developer is used, drying and developing time shall be at least equal to penetration time to allow
sufficient bleeding of penetrant from defects. If additional clarity is required during inspection dry
developer may be applied by a hand powder bulb.
Following development, the part shall be inspected under black light. Any evidence of cracks is cause for
rejection. After inspection the parts shall be cleaned with dry cleaning solvent (Item 10, Appendix E) and
covered with rust preventive oil.
m.
Lapping Procedures
(1) Clean the part with dry cleaning solvent (item 10, Appendix E) and dry with compressed air. Clean the
lapping blocks with compressed air. Do not use a cloth or any other material for this purpose.
(2) Spread a good quality 600 grit dry lapping powder on one of the lapping blocks. Place the part to be
lapped flat on the block and, using a figure eight motion, move it back and forth across the block. Do not press on the
part, but use just enough pressure to keep the part flat on the block. It is important that the part be kept flat on the block
at all times.
(3) After each four or five passes, clean the lapping powder from the part by drawing it across a clean piece of
tissue placed on a flat surface and inspect the part. DO NOT LAP EXCESSIVELY.
(4) When the part is flat, wash it in dry cleaning solvent (item 10, Appendix E) and dry it with compressed air.
(5) Place the dry part on the second block. After applying lapping powder, move the part lightly across the
block in a figure eight motion several times to give it a smooth finish. DO NOT LAP EXCESSIVELY. Wash the part in
dry cleaning solvent (item 10, Appendix E) again, and dry it with compressed air.
(6) Place the dry part on the third block. Do not use lapping powder on this block. Keep the part flat and
move it across the block several times, using the figure eight motion. Lapping the dry part in this manner gives it the
"mirror" finish required for perfect sealing.
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