MIL-PRF-24172B (SH)
4.5.1 Test conditions. Unless otherwise specified (see 6.2), the atmospheric conditions surrounding the
specimen prior to and during the test shall be 73.4 ± 3.6 degrees Fahrenheit (oF) (23 ± 1 degrees Celsius ( oC)) and 50 ± 2
percent relative humidity. The conditioning period prior to the test shall be a minimum of 24 hours.
4.5.2 Preparation of sample block (type II only).
4.5.2.1 Sample mold. Sample test molds shall be constructed in accordance with either 4.5.2.1.1, 4.5.2.1.2 or
4.5.2.1.3 as specified (see 6.2).
4.5.2.1.1 Steel. The mold shall be constructed of 1/8-inch thick steel. It shall consist of a steel box without a top
and having inside dimensions of 13 inches in each direction. The bottom shall be removable and provided with devices for
securing it to the sides. On the outside of each of two opposite sides a steel flange, 13 inches in length and 2 inches in
width, shall be firmly attached at the midpoint of the outside surface with 13-in dimension parallel to the top and bottom
surfaces of the box. The inside surfaces shall be dry and clean. A mold release agent may be used.
4.5.2.1.2 Plywood. The mold shall be constructed identical to that of 4.5.2.1.1, except that 1/2-inch thick
plywood shall be used as the construction material.
4.5.2.1.3 Special test mold. When a special test mold is required for a specific application, thickness and type of
material, dimensions, volume, and special configuration (if any) of the mold, construction for free rise or restraint (using
top cover) and any other requirements which may be necessary for suitable mold shall be as specified (see 6.2).
4.5.2.2 Sample preparation. Foaming characteristics of the material shall be determined during the foaming of the
test sample. Unless otherwise specified (see 6.2), proportions and mixing of the base ingredients and preheating of the
resin, if required, shall be in accordance with the contractor's instructions. Check volume ratio between components for
compliance with 3.7.2. Mechanically stir a sufficient quantity of base ingredients, and pour into the specified mold (see
4.5.2.1 and 6.2). If applicable (see 4.5.2.1.3), a top cover shall be secured. The foam shall be allowed to air cure in the
mold for 48 hours prior to removal. The minimum temperature of the air and mold shall be as specified (see 6.2 and 6.3).
4.5.2.2.1 Precautions. Fumes may be present when these foams are prepared. Adequate ventilation shall be
provided or air masks shall be worn. Goggles, rubber gloves, and protective clothing shall also be worn.
4.5.2.3 Removal from mold. Following the specified cure period, if necessary, a long thin spatula shall be used to
cut the foam free from the mold. After the top, where applicable (see 4.5.2.1.3), and bottom covers are removed, the
flanges on the sides of the mold shall be placed on blocks with the original bottom up and a 12-3/4 by 12-3/4 inch piece of
1-inch plywood shall be placed over the flat surface of the foam. Light, steady pressure shall be applied by hand to the
plywood to force the foam from the mold.
4.5.2.4 Preparation of test specimens. After determining the density as specified in 4.5.3, the required specimens
shall be prepared from the block free from skin in such manner that the possibility of overheating is minimized. Prior to
testing, the density of each specimen shall be calculated by accurately weighing and measuring its dimensions. Any
specimen whose density is not wi thin 10 percent of that of the sample block shall be subject to rejection and replaced with
a suitable new specimen.
4.5.3 Density. The density of the foamed material shall be determined in accordance with ASTM D 1622. The
average density of the five specimens shall be reported.
4.5.4 Compressive strength. The compressive strength of the foamed material shall be determined in accordance
with ASTM D 1621, procedure A, except that three specimens shall be used and the specimen size shall be 1 inch by 4 by 4
inches. The average value of the three specimens shall be reported.
4.5.5 Fire resistance. The fire resistance of the foamed material shall be determined in accordance with ASTM E
84 before and after exposure as specified in 4.5.10.
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