T.O. 33B-1-13-117(3) Prepare a dam around the surface or hole to be inspected. Examples are shown in Figure 3-75.Use tape, aluminum foil, special sealing putty and specially made dams (singly or incombination) to form a reservoir to hold the magnetic rubber.Figure 3-75. Preparation for Magnetic Rubber InspectionNOTEPermanent bar magnets usually are made of ALNICO 8 material, are 1 inch indiameter and are either 4 or 8 inches long. The field strength of a permanent barmagnet is notrelated to its length. Usually field strength of over 1000 gauss isadequate for most magnetic rubber inspections and most new permanent magnetswill be much stronger than that. Bar magnets should be tested periodically using agaussmeter to assure the field strength is adequate.It is acceptable to put two or more shorter magnets together to make a longermagnet for those few inspections where the magnet is placed with its side againstthe part being magnetized and the specified magnet length is not available.Step c through h are for the premagnetizaion set-up and adjustment. Magnetizationwill be conducted after addition of the magnetic rubber.
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