Suspension Preparation - TM-1-1500-335-23_270

T.O. 33B-1-1 The  need  to  provide  successful  magnetic  particle  testing  under  varying  conditions  has  resulted  in  the development  of  different  materials  to  accomplish  this  result.    These  f luorescent  materials  are  readily available in a dry concentrate powder form suitable for use in water and/or oil suspensions.  Prepared oil- based baths are also available in aerosol-type cans and bulk quantities. Suspension Preparation. Except as described in the following subparagraphs, the details of suspension preparation are the same as for the wet visible non-f luorescent particles (see paragraph A f luorescent background check shall be accomplished on vehicle material used in the f luorescent magnetic particle inspection method if conformance to DOD-F-87935 is in question.  One procedure for checking the background is as follows: a.  Obtain  a  clean  glass  tube  of  sufficient  length  to  reach  from  the  middle  of  the  bulk vehicle container to at least six (6) inches above the container opening when it is in the vertical position. b.  Insert the tube slowly into the bulk vehicle. c.  Place  thumb  over  protruding  end  of  the  glass  tube  and  remove  the  tube  from  the container. d.  Illuminate vehicle in the glass tube with a black light in a darkened area. e.  If vehicle does not f luoresce, proceed with its use.  If the vehicle f luoresces, determine the f luorescence in accordance with the appropriate section of DOD-F-87935.  Dispose of vehicle not conforming to DOD-F-87935. Suspension Maintenance. The rules are identical with those described in paragraph for the wet visible non-f luorescent particles. However, there are three additional sources of deterioration that can occur in a bath of f luorescent particles, and that require discarding of the bath when the condition becomes excessive. Deterioration of Suspension. a.  The first source of deterioration is the separation of the f luorescent pigment from the magnetic particles.  Such separation causes a reduction of f luorescent brightness of indications and an increase in the overall f luorescence of the background.  When this occurs to a noticeable degree, the bath SHALL be changed.  This condition is difficult to  detect  in  the  settling  test  but  can  be  observed  by  directing  a  blacklight  at  the settling  tube  after  the  normal  settling  period.    Refer  to  paragraph  for additional steps to aid interpretation of observations.  Noticeable f luorescence of the solution with a reduced f luorescence of the particles signifies separation.  Observation by   the   inspector   in   the   way   the   bath   performs   is   another   method   of   detecting separation. b.  A second source of deterioration of the bath of f luorescent particles is the accumula- tion of non-f luorescent magnetic dust or dirt in the bath.  When there is a considerable amount  of  finely  divided  magnetic  material  in  the  dust  carried  by  the  air,  this material will accumulate in the bath along with other dust and dirt.  In a bath of wet visible non-f luorescent particles this does no specific harm until the accumulation of total  dirt  is  excessive.    In  the  case  of  f luorescent  particles,  it  tends  to  decrease  the brightness  of  the  indication.    The  fine  magnetic  material  is  attracted  to  indications along with the f luorescent particles, and it takes very little of such non-f luorescent material to significantly reduce the brightness or visibility of the indication. c.  A third source of deterioration of the f luorescent particle bath is the accumulation of f luorescent oils and greases from the surfaces of tested parts.  This accumulation, in time, builds up the f luorescence of the liquid vehicle to the point where it interferes with the visibility of f luorescent particle indications. Change 1 3-73


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