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

T.O. 33B-1-1 3.5.7.3.4. 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. 3.5.7.4. 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 3.5.6.6). 3.5.7.4.1. 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. 3.5.7.5. Suspension Maintenance. The rules are identical with those described in paragraph 3.5.6.6 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. 3.5.7.5.1. 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 3.5.7.5.2 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