My $.02:
Bill Babcock wrote:
>I clean the parts well after (bead blaster with plastic media) and dye
>penetrant test. Sometimes I magnaflux as well, though I can do the
>penetrant testing here. I should set up a magnaflux system--it's not that
>tough.
Years ago, when I worked at Fairchild, I found a small ding in an A-10
aluminum alloy skin. It had to be dye-penetrant inspected for cracks.
Instead of waiting for someone from the paint shop to remove the primer in
the area of the dent with paint stripper, I used a Scotchbrite pad soaked in
MEK. The penetrant inspector then said, "Now it's got to be acid etched." I
learned from that.
Scotchbrite or other abrasive cleaning methods, such as abrasive blast, can
either fill the crack with material or burnish material over the crack,
possibly preventing the penetrant from seeping into it. Since dye-penetrant
inspection can only find irregularities that reach the surface (unlike
Magnetic-particle inspection, which can detect flaws under the surface),
such a crack would not show up. Unless the part was acid-etched after
cleaning.
Maybe plastic media won't do this, I don't know. Maybe steel is different
from aluminum in this regard, I don't know. But then you could use
magnaflux.
Nowadays, we always teach our students to use a non-abrasive cleaning method
if the part is to be dye-penetrant inspected. The inspection kit comes with
a good cleaner, Trichlorethylene, I think.
I think there is a question on the FAA mechanic written test about this
subject.
Anyone else out there ever hear of this? Or was the penetrant inspector just
pulling my leg?
John Herrera
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