Table 2-1. Flaw Detection
Appear as a straight line, usually continuous throughout
its length and generally exist singly. These cracks start
at the surface.
Cooling cracks -
In bars of alloy or tool steels, are the result of uneven
cooling after rolling and usually are deep in a longitudinal
direction, but are not straight.
Crack contaminant -
Material which fills a crack and which may prevent
penetrants from entering.
Fatigue cracks -
Progressive cracks which develop in the surface caused
by the repeated loading and unloading of the part or by
what is called reverse bending.
Forging cracks -
Cracks developed in the forging operation due to forging
at too low a temperature, resulting In rupturing of the
Grinding cracks -
Thermal cracks due to local overheating of the surface
being ground, generally caused by lack of coolant,
Improper coolant, dull wheel, too rapid a feed, or too
heavy a cut.
Heat treatment cracks -
Ruptures produced in the tempering of metal due to
uneven cooling and contracting of one portion of a part
Hot cracks -
Same as cold cracks but developing before the casting
has completely cooled.
Machining cracks -
A surface defect generally called machining tear and
caused by too heavy a cut, a dull tool, chatter, or
dragging the tool over the metal when not cutting
Open cracks -
Those flaws which can be detected by contrast penetrant
Cracks caused by the release of internal stresses due to
metal removal by immersion in acid or chemical
Plating cracks -
A crack developed by the plating process, usually occur-
ring In parts having high internal stresses