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 in
combination) to form a reservoir to hold the magnetic rubber.
Figure 3-75. Preparation for Magnetic Rubber Inspection
Permanent bar magnets usually are made of ALNICO 8 material, are 1 inch in
diameter and are either 4 or 8 inches long. The field strength of a permanent bar
magnet is not related to its length. Usually field strength of over 1000 gauss is
adequate for most magnetic rubber inspections and most new permanent magnets
will be much stronger than that. Bar magnets should be tested periodically using a
gaussmeter to assure the field strength is adequate.
It is acceptable to put two or more shorter magnets together to make a longer
magnet for those few inspections where the magnet is placed with its side against
the part being magnetized and the specified magnet length is not available.
Step c through h are for the premagnetizaion set-up and adjustment. Magnetization
will be conducted after addition of the magnetic rubber.