MIL-PRF-26915D
4.8.4 Drying time test. The primer shall be sprayed on the 4.6 test panel to a dry film thickness
of 2.5 to 3.5 mils. The primer shall be air dried in a well-ventilated room or chamber free from
drafts and dust, and in diffused light (not in direct sunlight). An illumination of approximately 25
foot-candles is preferred for drying oil films. The temperature of the air shall be between 70°F to
82°F with relative humidity of 50 ± 5% (see 3.4.5).
4.8.5 Flexibility test. Solvent cleaned 0.022 ± 0.002 inch thick panels coated with primer as
specified in 4.4 and cured as applicable shall be bent 180 degrees over a ½-inch diameter mandrel.
Similar panels shall be conditioned for one hour at -65°F and while still at that temperature, bent
180 degrees over a 4-inch diameter mandrel. The panel shall be visually examined immediately
for evidence of failure, and then after conditioning to room temperature shall be examined again
for compliance. Cracking or loss of adhesion in the bend area shall constitute failure (see 3.4.6).
4.8.6 Lifting properties examination. Test panels primed IAW 4.6.3.1 shall be individually
topcoated with the following materials IAW 4.6.3.2:
a. a second coat of primer.
b. semi-gloss alkyd enamel.
c. high-solids polyurethane.
The panels shall be visually examined to verify conformance (see 3.4.7).
4.8.7 Adhesion (wet tape) test. Test panels cleaned by each method in 4.6.2 shall be coated with
the following:
a. primer only 2.5 to 3.5 mils thick.
b. primer 2.5 to 3.5 mils thick plus enamel 2.0 to 3.0 mils thick.
c. primer, 2.5 to 3.5 mils thick plus polyurethane 2.0 to 3.0 mils thick.
The panels shall be tested IAW FED-STD-141, Method 6301.2 (see 3.4.8).
4.8.8 Adhesion to weathered finishes test. Test panels coated with primer plus polyurethane
topcoat which have been through the accelerated weathering test shall be scuffed with 400 grit
sand paper, solvent-wiped and recoated with primer and primer plus polyurethane topcoat. The
coating shall be allowed to dry for 24 hours. The coating shall then be visually examined for
adherence (see 3.4.9).
4.9 Environmental conditions tests.
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