T.O. 33B-1-13-483.3.14.4.1While the rubber cures, the surface inspected must stay in the required magnetized state. This can be accomplishedusing a permanent magnet, a direct current yoke, an electromagnet, or some other suitable means. Whatever method ofmagnetization is used, the leakage fields at any discontinuities on the surfaces inspected must be maintained longenough to attract and hold in position the magnetic particles until a partial cure takes place. A two-step magnetizingprocedure has been developed. The first magnetization is accomplished for a short time in one direction, followed by asecond at 90° to the first for the same length of time. This procedure must be repeated for whatever period of time isneeded until the cure prevents particle mobility. Magnetization in two directions 90° apart assures formation ofindications at discontinuities in all directions.3.3.14.4.2After curing, the rubber plugs, which are exact replicas of the surfaces, are removed and visually examined forindications, which will appear as black lines against the gray or yellow background of the silicone rubber. Location ofany discontinuities or other surface imperfections can be determined from the location of the indications on the plugs.The magnetic rubber inspection method is covered in detail in Section 9.
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