TT-P-28H
TABLE V. Heat schedule of nominal temperatures.
Heating schedule |
oc |
oF |
8 hours (first day) |
204 |
400 |
16 hours (overnight) |
260 |
500 |
8 hours |
316 |
600 |
16 hours |
372 |
700 |
8 hours |
428 |
800 |
16 hours |
484 |
900 |
8 hours |
538 |
1000 |
16 hours |
590 |
1100 |
8 hours |
650 |
1200 |
Remove the panels from the oven for as short a period of time as possible and inspect (except for the knife test) for compliance with 3.4.5 at the end of each heating period. Remove two panels at the end of the 260 °C (500 °F),
316 °C (600 °F) and 484 °C (900 °F) (see 4.5.12.4) heating periods for use in the salt spray test (see 4.5.12). At the conclusion of the heating schedule, remove the remaining two panels, allow to cool in air, inspect the films of paint
for cracking, blistering, flaking, or peeling and cut with a knife blade in accordance with method 6304.2 of FED- STD-141 to determine adhesion. Test panels shall be in accordance with the requirements of 3.4.5.
4.5.11.1.3 Heat resistance. Panels coated with Type II powder coating materials shall be tested for heat resistance as specified for Table V, but only up to 372 °C (700 °F). Panels coated with Type II materials shall be removed from the heat resistance test at the end of the 260 °C (500 °F), 316 °C (600 °F), and 372 °C (700 °F) heating periods for subsequent testing.
4.5.11.1.4 Recoat properties. To verify the recoat properties of the Type II powder, conduct the following evaluation:
a. The Type II coating applied in 4.5.10.1 and conforming to 3.4.4.1 shall be used.
b. Following removal from the heat test after the 204 °C (400 °F), 260 °C (500 °F), 316 °C (600 °F), and 372
°C (700 °F) exposure, abrade a single spot equal to about 25 percent of the Type II coating applied. c. Apply a 50-micron to 75-micron (2-mils to 3-mils) wet film of Type I paint.
Check for compliance with 3.4.10.
4.5.11.2 Cold-rolled steel. This applies to Type I coatings and does not apply to Type II powder coatings.
4.5.11.2.1 Test panel preparation. Test paints require two 8- by 15-cm (3- by 6-inch) test panels. Panels shall be ASTM A1008/A1008M free of mill scale (see 4.5.11.1.1) and solvent degreased. One side of each test panel shall be flat polished as described in ASTM D609. Spray apply two coats of the test paint to the side of the panel that has been flat polished. Air dry 30 minutes after each coat. After air drying the second coat, bake the test panels at 204
°C (400 °F) (nominal) for 1 hour. Cool to room temperature.
4.5.11.2.2 Heat test. After the bake-cured panels have returned to room temperature, place the panels on a rack as in 4.5.11.1.2 and heat for 24 hours in an oven that has been previously raised to a temperature of 650 °C (1200 °F). Remove from the oven and cool. Inspect the films of paint for cracking, blistering, flaking, or peeling and perform the knife test in accordance with Method 6304.2 of FED-STD-141. Test panel shall be in accordance with the requirements of 3.4.5.
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