MIL-PRF-2819H
3.2 Material. The insulation block shall be composed of asbestos-free, heat-resisting compounds suitable for
3.2.1 Prohibited fibers. Neither asbestos nor ceramic (refractory) fibers nor materials containing any of these
fibers shall be used in the insulation.
3.3 Dimensions and tolerances.
3.3.1 Dimensions. Insulation shall be furnished in block form in 18-inch length by 3-inch width or 36-inch
length by 6- or 12-inch width, as specified (see 4.4.2 and 6.2). Blocks shall be furnished in thicknesses of 1, 1½, 2,
3.3.2 Tolerances. A tolerance of ±⅛ inch in length and ±1/16 inch in width and thicknesses shall be permitted
(see 4.4.2).
3.4 Physical requirements. The insulation block shall conform to the physical requirements specified in table I.
TABLE I. Physical requirements.
Properties
Class 2
Class 3
Density, lb/ft3, maximum
15.0
22.0
Compressive strength, at not more than 5%
60.0
60.0
deformation, minimum lb/in2
Weight loss by tumbling, loss in weight, percent maximum:
After first 10 minutes
20.0
20.0
After second 10 minutes
40.0
40.0
Flexural strength, lb/in2
1/
1/
Change under soaking heat (24 hours at
2.0 (see 4.4.8)
2.0 (see 4.4.8)
1,200 °F for Class 2 and 1,700 °F for
Class 3) linear shrinkage, percent
maximum
Thermal conductivity, BTU-in/hr ft2 °F maximum, at a mean temperature of:
200 °F
0.42
0.54
300 °F
0.45
0.58
400 °F
0.50
0.61
500 °F
0.60
0.64
600 °F
0.65
0.67
700 °F
0.70
0.70
800 °F
----
0.73
900 °F
----
0.75
1,000 °F
----
0.77
NOTE:
1/
Three times density [pounds per cubic foot (lb/ft3)] of the sample tested.
3.5 Simulative performance. Thermal block insulation shall not warp, crack, or show other visible changes
upon completion of the test specified in 4.4.10. Minor surface cracks that do not propagate more than 0.25 inch
internally from the hot face surface of the insulation shall be disregarded.
3
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