T9074-AS-GIB-010/271 Rev 1
4.3.2.5.5 Circular Magnetization; Magnetizing Current. The magnetizing current required for an item depends on its shape, configuration, and size. The optimum current setting shall be determined by means of a segmented magnetic particle field indicator tested as specified in 4.3.1.8. 4.3.2.5.6 Longitudinal Magnetization. When a solenoid is used to magnetize items, the solenoid shall be no larger than necessary to accommodate the item, and items shall be orientated within the solenoid to ensure adequate field strength. 4.3.2.5.7 Longitudinal Magnetizing Current. For longitudinal magnetization using a solenoid, the magnetizing force in ampere-turns should be determined in the following manner for general applications: The ampere-turns used shall be 45,000/(L/D) (±10 percent), where L is the length and D is the diameter of the part. The L/D ratio for parts being magnetized shall be two or more. Coils are usually effective in magnetizing the part for about 8 to 12 inches from each end of the coil. If longer parts are to be inspected, several magnetizing shots will be required. Either the inside or the outside diameter may be used depending on which surface is being inspected. When both surfaces are to be inspected, the larger diameter shall be used. A magnetic particle field indicator shall be used as specified in 4.3.1.8. For those parts whose L/D ratio is less than two, the required magnetizing current shall be calculated using a value of two for L/D and adequacy of magnetization shall be verified by use of a magnetic particle field indicator as specified in 4.3.1.8. 4.3.2.6 Maintenance of suspension. The suspension in use shall be tested for content of magnetic particles at intervals depending upon frequency of use, discoloration and contamination, but in any event not less than once each day. When the suspension becomes discolored by oil or contaminated with lint or other foreign material to the extent that proper distribution and concentration of the suspension or the intensity, character, or definition of the deposit of the magnetic particles are interfered with, the container shall be drained, thoroughly cleaned, and refilled with clean suspension. 4.3.2.6.1 Concentration of Suspension Test. The test method shall be determined by the organization. If for any reason the Government inspector doubts the adequacy of the method employed, he shall request the concentration to be checked by the following tests: a. Fill a standard 100-milliliter (mL) graduate to the 100 mL mark with the suspension directly from the hose or other device used for pouring it over the piece in making a test, or from an immersion tank after the suspension has been thoroughly agitated. Let the suspension stand for 30 minutes to precipitate or until the solid matter is apparently all down. b. Decant the clean liquid as far as practicable without loss of magnetic substance. c. Refill graduate above magnetic substance with Type II Stoddard Solvent in accordance with MIL-PRF-680 or acetone for water-base suspension. Shake well and let stand for 30 minutes to precipitate a second time. d. Read the height or volume of the precipitate in the graduate. The readings shall be as follows:
(1) The nonfluorescent magnetic particles: 1.2 to 2.4 mL. (2) The fluorescent magnetic particles: 0.1 to 0.7 mL. e. If the concentration was checked daily, steps (b) and (c) may be omitted.
f. For manufacturer-supplied aerosol cans, a certification statement from the manufacturer identifying the material by batch, and stating that it meets the concentration requirements of this specification, is an acceptable alternative to the above process.
4-5
Made with FlippingBook - Share PDF online