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Page Title: Fluorescent Penetrant Inspection
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TM 5-4210-233-14&P-1 4-9.  GENERAL MAINTENANCE PROCEDURES-Continued (3) Scattered short sharp bursts are seen. Bursts are caused by metals working at temperatures that weaken and break the material. Bursts are not usually seen until the metal is cut through to the burst area. (4) Separate  short  wavy  lines  in  the  same  general  direction  are  seen.  Flakes  are  caused  by  improper cooling. They are not usually seen until the metal is cut through to the flake area. (5) Fine,  sharp,  tightly  packed  lines  are  seen  (grinding  cracks).  These  are  usually  caused  by  a  glazed grinding wheel. The wheel, instead of cutting the material, rubs and overheats the material. The lines are thermal cracks similar to heat treat and hardening cracks. j.  Fluorescent  Penetrant  Inspection.  This  type  of  inspection  can  be  carried  out  on  any  metal  but  is  usually reserved for non-magnetic material (e.g. aluminum, stainless steel). The parts shall be warm prior to applying penetrant. The penetrant may be applied by dipping, painting or spraying. All surfaces to be examined shall be completely covered. Penetrant time for various metals is as follows: Aluminum Alloy - no less than 20 minutes. Magnesium Alloy - no less than 20 minutes. Brass or Bronze - no less than 30 minutes. Ferrous Alloys - no less than 30 minutes. After applying penetrant, the surfaces will be cleaned with lukewarm water - less than 120 deg. F (49°C). (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. The 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 3, Appendix E) and covered with rust preventive oil. k.  Lapping Procedures. (1) Clean  the  part  with  dry-cleaning  solvent  (item  3,  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. 4-152

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