MIL-DTL-15606J
3.7 Grade AA, 65 to 90 percent alumina.
3.7.1 Modulus of rupture. The modulus of rupture shall average not less than 600 pounds per square
3.7.2 Dimensional stability. The stability value shall not exceed 0.75 percent. Expansion, if any, in the length
dimension shall not exceed 1 percent. Shrinkage, if any, in the length dimension shall not exceed 0.75 percent
(see 4.6.5).
3.8 Grade A, alumina.
3.8.1 Alumina. The alumina content shall be not less than 57.5 percent (see 4.6.1).
3.8.2 Pyrometric cone equivalent (PCE). The PCE shall be not less than cone number 35 (3245 °F) (see 4.6.2).
Grade A PCE testing is only required for the initial first article testing of a manufacturer's brand performed in
accordance with MIL-DTL-15606.
3.8.3 Permanent volume change. The permanent volume change after reheating at 2910±10 °F for 5 hours
shall be not greater than +3 nor less than -1 percent after the first reheat. The brick shall not expand nor shrink more
than an additional 1 percent by volume between the first and third reheat (see 4.6.3).
3.8.4 Modulus of rupture. The modulus of rupture shall average not less than 500 lb/in2 for bricks only and no
3.9 Grade B, super duty.
3.9.1 Pyrometric cone equivalent. The PCE shall not be less than cone number 33 (3170 °F) (see 4.6.2).
3.9.2 Permanent volume change. The permanent volume change after reheating at 2910±10 °F for 5 hours
shall be not greater than +3 nor less than -1 percent (see 4.6.3).
3.9.3 Modulus of rupture. The modulus of rupture shall average not less than 600 lb/in2 and no single specimen
3.10 Burner tile. Burner tile shall be of the same quality material and processing as Grade A brick.
3.10.1 Permanent linear change. The permanent linear change after reheating at 2910±10 °F for 5 hours shall
be not more than 1 percent after the first reheat. The sample shall not shrink more than an additional 1 percent in
linear dimension between the first and third reheat (see 4.6.6).
3.11 Workmanship.
3.11.1 Brick. The bricks shall be compact, homogenous in structure, and free from voids, soft centers, and
cracks greater than 1 inch or 10 percent of the brick length (whichever is greater) and that are greater than 0.01 inch
in width. No crack depth shall exceed ¼ inch. Crack-like defects that appear to jeopardize the structural integrity of
the brick are not acceptable. Cracks shall not extend beyond one brick surface (extend around corners). The
following are not considered cracks: crazing (surface cracking), blemishes less than 3/8 inch length that do not meet
crack depth of ¼ inch, discontinuous grain boundaries, and any feature so small (less than 3/32 inch deep) or indistinct
to the naked eye that it cannot clearly meet crack criteria. Crumbling or chipping at corners and edges shall not
exceed 3/8 inch (see figure 2). Corners and edges shall be sufficiently solid and strong to prevent more than 3/8 inch
crumbling or chipping when thumb pressure is applied (see 4.5.3). Defects on the working surface itself shall not
exceed 1/32 inch in depth by 1 inch in length. Buried surfaces of brick shall have the same criteria for crumbling or
chipping at corners as shown for the working surface. Defects on the buried surfaces shall not exceed ¼ inch in
depth by 1 inch in length.
3.11.2 Burner tile. The burner tiles shall be compact, homogenous in structure, and free from voids, soft
centers, and cracks as described in 3.11.1.
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