MIL-PRF-81904C(AS)
3.6.3 Hardness. The cured coating compound, when tested in accordance with
4.6.4.3, shall have a minimum hardness of Shore D 55.
3.6.4 Adhesion. The cured coating compound, when tested in accordance with
4.6.4.4, shall be well bonded to the surface, and shall come off in chips less than 1 inch in
diameter.
3.6.5 Pull-off adhesion. The cured coating compound, when tested in accordance
with 4.6.4.5, shall exhibit an average pull-off adhesion strength of 500 psi minimum.
3.6.6 Paint adhesion. Enamel applied to the cured coating compound, when
tested in accordance with 4.6.4.6, shall exhibit an adhesion rating of 2B or better in
accordance with ASTM D3359, indicating less than 35 percent enamel removal.
3.7 Resistance properties.
3.7.1 Lubricating oil resistance. The coating compound, when tested in
accordance with 4.6.5.1, shall withstand immersion in oil for one minute at 250 ±4° F
(121 ±2° C). Eight hours after removal, the film shall exhibit no blistering, film
softening, or other film defects. Discoloration shall not be a cause for rejection.
3.7.2 Ethanol resistance. The coating compound, when tested in accordance with
4.6.5.2, shall withstand immersion in ethanol for one minute at room temperature. Eight
hours after removal, the film shall exhibit no blistering, film softening, or other film
defects. Discoloration shall not be a cause for rejection.
3.7.3 Aviation fuel resistance. The coating compound, when tested in accordance
with 4.6.5.3, shall withstand immersion in aviation fuel for one minute at room
temperature. Eight hours after removal, the film shall exhibit no blistering, film
softening, or other film defects. Discoloration shall not be a cause for rejection.
3.7.4 Impact resistance. The coating compound, when tested in accordance with
4.6.6, shall require more than 40 inch-pounds (in-lbs) (3.4 Newton-meters (N-m))
average on direct (coated surface) impact and 4 in-lbs (0.5 N-m) average on reverse
impact before cracking or flaking is evident.
3.7.5 Humidity resistance. The coating compound shall be tested for resistance
to humidity, in accordance with 4.6.7. Upon removal from the humidity cabinet, the
coating shall have a minimum Shore D hardness of 50. Pull-off adhesion strength shall
not be reduced by more than 30 percent. Thermal efficiency shall not be reduced by
more than 30 percent.
3.7.6 Resistance to temperature shock. The coating compound shall exhibit no
evidence of cracking, loss of adhesion, or film deterioration when tested in accordance
with 4.6.8. Upon completion of the test, the coating shall have a minimum Shore D
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