Hold the replica with finger tips and focus by lowering or raising the replica beneath the
microscope lens (rather than raising or lowering the lens itself) This allows the inspector to view
the replica at various angles and to scan the entire area of interest.
Evaluate the magnetism level. Although magnetic rubber responds satisfactorily to a wide range
of magnetism, the reliability is increased if the optimum level is used. Too little magnetism will
result in faint indications that are easily missed. Too much magnetism darkens the background
so that indications might be hidden. The experienced inspector can determine if the magnetism
level is satisfactory. Adequate magnetism on the replica of a hole is indicated by a dark "halo" at
the pouring spout or corner. Adequate magnetism on flat surfaces and areas of gentle contour is
indicated by darkness in the rough areas of the replica. On very smooth surfaces, external
"penetrameter type" indicators such as staples, nickel foil or other magnetic material may be
taped to the part to indicate magnetism.
Evaluate replica quality. Replicas that contain excessive air bubbles, debris, or poorly mixed
rubber are difficult to interpret and should be recast. Examples of poor replica quality and other
false indications (artifacts) are included in Figure 3-78 illustrating typical examples of crack
indications, discontinuities and other surface conditions.
Classify each replica according to the severest indication detected (See Table 3-11):
Surface defects. A replica may show obvious surface defects (tool marks, corrosion pitting, etc.)
that are not attracting magnetic particles. The inspector is not responsible for identifying this
type of defect unless the procedure specifically requires such identification. The inspector may
identify gross surface defects, but replicas will be classified A or B only when there are
visible magnetic indications present. A replica classified as C may show surface defects.
s. Resolve B indications. The following methods will be attempted in order until the B indication is
resolved to either an A or a C:
Reinspect. Correct any technique or procedural errors. Clean the inspection area down to bare
metal if necessary. Vary inspection technique as appropriate.